sheet metal design doc

176
PMA DESIGN GUIDELINES FOR METAL STAMPINGS AND F ABRICATIONS Publishers: Precision Metalforming Association 6363 Oak Tree Blvd. Independence, Ohio 44131 Phone: 216-901-8800 Fax: 216-901-9190 www.metalforming.com

Upload: ashuadbnel

Post on 24-Nov-2015

172 views

Category:

Documents


15 download

DESCRIPTION

Sheet Metal Design Doc

TRANSCRIPT

  • PMA DESIGN GUIDELINESFOR METAL STAMPINGS AND FABRICATIONS

    Publishers:

    Precision Metalforming Association

    6363 Oak Tree Blvd.

    Independence, Ohio 44131

    Phone: 216-901-8800

    Fax: 216-901-9190

    www.metalforming.com

  • ii DESIGN GUIDELINES

    Copyright 2004

    By Precision Metalforming Association

    All rights reserved.

    Publication in whole or in part

    without permission is prohibited.

  • DESIGN GUIDELINES iii

    This publication is for designers, specifiersand buyers of precision sheet metal com-ponents. It is intended to assist in effectivelydesigning and specifying the products of themetalforming industry, so that the versatility,properties and economies of sheet metal maybe fully realized.

    It is not a guide to manufacturing. Nor is itexhaustive in covering metalforming design.Rather, it seeks to selectively provide guide-lines in key areas of design and specificationwhere general information is lackingareaswhich experience has shown to be frequentsources of misunderstanding between customerand supplier.

    Manufacturing processes are described onlybriefly to provide a basis for better un-derstanding the advantages and limitations ofmetalforming. The emphasis is on design con-siderations and values which can lead to realis-tic product expectations.

    The guidelines are not standards. Instead,

    they are suggestions and recommendationsbased on extensive observationswhich arebelieved to represent good design practices,using current technology, which can providecost-effective products appropriate for generalusage.

    In many cases higher levels of precision areachievable, but almost always at additionalcost. Special requirements for products withunusual properties or extraordinary precisionare typically the subject of negotiations withyour supplier.

    In todays JIT manufacturing environment, itis possible to design a precision product startingwith a nominal tooling expenditure and veryshort prototype lead time. Continuous develop-ment of the product, through early productioninto high volume product maturity, can occursmoothly with progressive changes in metal-forming processes, and without altering productquality.

    Careful planning is required to achieve this

    INTRODUCTION

  • iv DESIGN GUIDELINES

    scenario. The following checklist covers someof the important considerations. It is vital, notonly that a designer attempt to answer thesequestions prior to design development, but alsothat the designer share as much of this informa-tion as product security will permit withprospective suppliers.

    A. What is the estimated annual productquantity requirement during peakdemand?

    B. What is the estimated total programquantity?

    C. Will tooling, gauging and fixturing beamortized or capitalized?

    D. At what volume will tooling expendi-tures be evaluated?

    E. Which are the critical dimensional tol-erances?

    F. Are assembly tolerances actuallydimensioned from point of assembly?Assembly dimensions should alwaysbe taken from actual attachmentpoints.

    G. Does the drawing tolerance block listthe greatest tolerance allowable oneach dimensional parameter? Aretighter requirements individually tol-eranced?

    H. Are cosmetic surfaces adequatelyidentified?

    I. Does the print designate viewing andtest specifications for all finishrequirements?

    J. Are all gauging points clearly speci-fied?

    K. Does a general or specific packagingspecification apply?

    L. Must the product conform to specificgovernment regulations or meet certi-fication requirements?

    M. What is the product function?Early attention to considerations such as

    these, and early communication with prospec-tive suppliers, can help clarify key parametersinvolving function, economics and appear-anceand avoid misunderstandings, disap-pointments, costly redesign and retooling.

    This publication represents the collectiveefforts of Precision Metalforming AssociationsDesign Guidelines Project Committee over aperiod of several months.

    It is hoped that this effort will assist designersto achieve product function and appearanceeconomically, and avoid design induced defects,through effective design practices. The Commit-tee welcomes comments and suggestions.

  • DESIGN GUIDELINES v

    ACKNOWLEDGEMENTSPrecision Metalforming Association and the Design Guidelines Committee acknowledge withgrateful appreciation the contributions made by the following:

    ASM InternationalAmerican Society for Testing & MaterialsThe American Society of Mechanical

    EngineersAmerican Welding SocietyAnchor Tool & Die CompanyBihler of AmericaCincinnati IncorporatedDayton Rogers Manufacturing Co.Edison Welding InstituteEuclid Heat Treating CompanyHerr-Voss CorporationHewlett PackardIBM

    Lindberg Heat Treating Co.MC Machinery Systems, Inc.Mazak Nissho Iwai CorporationNiagara Machine & Tool WorksPenn Engineering & Manufacturing

    CorporationPrecision Steel Warehouse, Inc.Q-Processes Inc.U.S. Amada, Ltd.U.S. Baird CorporationUlbrich of Illinois, Inc.Wysong & Miles Co.Yoder Manufacturing

    Mark Anderson, Mayville Metal ProductsJack Brown, Alpha Precision, Inc.John J. Caschette, Genesee Metal Stampings, Inc.Leonard Coraci, Jr., Dayton T. Brown, Inc.Larry Crainich, Design Standards CorporationBrian L. Deakins, Deakins Metal Spinning, Inc.Walt Dieckmann, The Binkley CompanyJohn Dosek, Keats Manufacturing CompanyTony Fisichella, MSM Industries, Inc.Michael Grant Service Stampings Illinois, Inc.Sherwood Griffing, U.S. Baird CorporationAlan Hall, Gem City Metal SpinningDaniel J. Hickle, Mayville Metal ProductsThomas Johnston, Acme Metal Spinning, Inc.

    Peter K. Mercer, PackProWilliam Merg, Schulze ManufacturingGlenn Nelson, Roll Forming CorporationDavid B. Peters, Corry Contract Inc.L. Wayne Ridgley, Wayne Metal Products Co., Inc.Herman G. Schmitz, Sausedo Metal Products, Inc.Michael Schons, Radar Industries, Inc.Joe Sokol, North Star CompanyTim Synk, Superior Roll FormingCharles C. Vicary, Ervite CorporationDavid Windsor, Winco Stamping, Inc.Clarence Wrentmore, Miami Manufacturing Co.Robert G. Zeller, Natter Manufacturing Co., Inc.

    PAST CONTRIBUTORS

    Karla Aaron, Hialeah Metal Spinning, Inc.Philip Bryans, Ware Manufacturing Co., Inc.Robert Byrne, Superior Metal ProductsLarry S. Field, Elray Manufacturing CompanyNorbert Markl, ITW/CIP Stampings

    Kent Mishler, Thomas Engineering CompanyMarko Swan, Cygnet Stamping & Fabricating, Inc.John Wagner, Hamond Industries, Ltd.Ken White, Eskay Metal Fabricaring

    PMA DESIGN GUIDELINES COMMITTEEMichael Grant, Chair, Service Stampings Illinois, Inc.

  • DESIGN GUIDELINES vii

    CONTENTSIntroduction...................................................................................................................iii

    1 Part Drawings; A Communication Tool .........................................................................1

    2 CAD Design...................................................................................................................5

    3 Material Selection .......................................................................................................19

    4 The Shearing Process .................................................................................................39

    5 Designing For CNC Turret And Laser Fabrication.......................................................43

    6 Press Brake Forming...................................................................................................53

    7 Stamping.....................................................................................................................61

    8 Roll Forming................................................................................................................79

    9 Metal Spinning ............................................................................................................87

    10 Designing For Drill Press Work....................................................................................93

    11 Deburring ..................................................................................................................103

    12 Abrasive Surface Preparation ...................................................................................107

    13 Spot Welding.............................................................................................................111

    14 Welding .....................................................................................................................119

    15 Inserted Fasteners ....................................................................................................129

    16 Heat Treating .............................................................................................................137

    17 Plating .......................................................................................................................143

    18 Painted Parts.............................................................................................................149

    19 Packaging .................................................................................................................157

    Glossary ....................................................................................................................161

  • Part Drawings

    DESIGN GUIDELINES 1

    1PART DRAWINGS; A

    COMMUNICATION TOOLH ow your prints influence the quality and costof your sheet metal parts and stampings.

    The ease of interpretation of the designersdrawing sets the tone of manufacturingsuccess for the project. The drawing is the onlylink to your thought processes which createdthe product. The importance of the drawing as acommunication tool cannot be over empha-sized because it is an instrument, used by manypeople in the complicated processes of manu-facturing.

    Some of the most important thoughts shouldbe applied BEFORE the drawing is begun. Theposition in which the part is portrayed willoften determine the ease of interpretation.International Standard Organization (ISO)drafting standards, for instance, stipulate thatthe part to be shown the same way as it wouldbe held in the machine during fabrication. Thisis not always possible, but lathe parts, for exam-ple, are always shown as they would be clampedin the chuck or collet. The operator thereforedoes not have to reverse the image in his mind,

    one less chance for error.The following are intended to improve com-

    munication excellence. It is imperative to makethe part features most prominent. The partmust jump out at you from the drawing. Toachieve this, use the heaviest lines for the out-line and all visible lines. These should be heav-i e r by a factor of three, compared to dimen-sional lines. Invisible edges should be shown athalf the full line strength and then only, if theyclarify the picture.

    Cross-cut sections are one of the most infor-mative views you can give to the interpreter ofyour drawing. D o n t be handicapped by the n o r m a l projection of a cut view. If showingthe view in the opposite direction from n o r-mal would make interpretation easier, then doso with directional arrows and an identifyingl e t t e r. C u t-view lines and arrows should beslightly heavier than the outline for properdirection of the view.

    Avoid boobytrapping your drawing. A typ-ical example are tightly spaced dimensionallines going to different features. To eliminate

  • Part Drawings

    2 DESIGN GUIDELINES

    this problem, offset one line to space themapart, show one dimension on a different viewor add an exploded view. Centerlines which arealmost in line with each other should be termi-nated with a short cross-line behind the last fea-ture to which they belong. This eliminates avery common cause for error. See Figure 1.

    One more ISO drafting standard whichwould be prudent to adopt, is to show the

    Figure 1. Illustration of good drafting practice anddimensional call-outs.

    overall dimension for each view as the farthestdimension from the outline. If the total length,width or depth is given elsewhere in conjunc-tion with other dimensions, list it as a referencedimension.

    When developing a design, dont hestitate touse plain English explanatory notes to aidinterpretation, make a point or further developa detail. Avoid the use of unusual languagewhich can be misinterpreted.

    For critical features in your design, use func-tional dimensions and tolerances which aredirectly interlinked with the related feature. Fori n s t a n c e, if a bracket is to be used to mount apart and spacing is critical to the front and topsurface, dimension the bracket directly from thefront and top of the part, not from some otherfeature.

    To avoid tolerance accumulation from succes-sive bends, always attempt to dimension fea-tures and flanges from co-planar interiord a t u m s. Indicate the critical dimensions throughnotes or tolerance additions and indicate thenoncritical dimensions in the same manner.

    Use drawing block tolerances where possibleto indicate non-critical dimensions. F u l l-m i l-

    limeter metric or single-digit decimal inchdimensions should be used with appropriatetolerances to locate operator-placed featuressuch as spot welds, tack welds and self-piercingrivets.

    Computer Aided Design (CAD) creates awhole new set of challenges. See the next chap-ter for further details.

    The craftspeople working on your projecthave spent years to hone their print readingskills. They have to rely on standards to be con-sistently correct in their interpretation.Changing these standards is guaranteed tocause problemssomething you, the designerwill want to avoid.

    Making your design easy to quote and manu-facture requires good communication betweenthe designer and supplier.

    Even the most clearly detailed prints toooften fall victim to the reduction, scanning andfaxing process. Convenient and expedient asthese methods are, details can get skewed in theprocess. Numerals, especially, get distorted, as isevident when an eight becomes a three and thefives turn into sixes, etc.

    Binding documentation, for this reason,should never be faxed or scanned unless it isimmediately followed up with originals sent bymail. The exception may be an original A size(812 x 11 in.) print which should come throughthe faxing process without distortion. B i n d i n gdrawings for actual production must be submit-ted in their original size.

    Table I is a guideline and explanation for thequantity of drawing sets required depending onthe number of processes involved.

    The lack of binding documentation for eachuser on each project has resulted in countlesserrors, delays and expenses in the past. Alwayssupply sufficient original document sets.

    An available sample part, or even a cardboard mock-u p, is of tremendous help in thequoting process and should be supplied when-ever possible. Even the best print is not as easi-ly interpreted as a sample part, especially acomplicated one.

  • Part Drawings

    DESIGN GUIDELINES 3

    Giving options on design features which maybe fabricated in various ways will let the metal-forming supplier use the best processes for eco-nomical production. Table II is a partial listingof interchangeable processes which could begiven as options.

    As part of a complete drawing, an itemizedlist of all components is a must. C o m p o n e n t ssolely identified at their locations lead to frus-trating searches and double checks, with a goodchance of missed items.

    The designer and/or buyer should also checkthe availability and lead times of specified com-p o n e n t s, as they are beyond the influence ofyour metalforming supplier. It is not uncom-mon to encounter lead times of up to 12 weeksfor relatively minor items essential to the pro-j e c t . If a drawing has undergone revisions, a nEngineering Change Order (ECO) listing thesechanges is of great help to the estimator whenrequoting a project.

    setsrequired listing of processes involved

    1 initial quoting only for basic fabrication

    2 for quoting involving secondary outside servicessuch as painting, silkscreening, etc.

    3 for all basic production jobs1 set for quality control (controlling documents)1 set for programming1 set for production routing

    4 for production requiring dedicated tooling3 sets as above1 set for tool design and building

    5 to 6 for production requiring dedicated tooling withoutside tooling services

    4 sets as above1 set for outside tooling services, minimum

    call-out alternative

    inserted threaded nut - extruded and taped

    inserted stand off - formed feature

    spot welded joint - riveted joint- adhesive bonding (tape)- mechanical inter-locks (several)- formed-in-place rivet- other welding processes- combination of above

    fixtured assembly - self-aligning features

    closed hem - open hem or plastic edge protector

    multiple part assembly - one-piece construction

    one-piece construction - multiple part assembly

    plastic grommet - n/c formed and flattened hem

    spot welded screeni n s e r t - selective perforation

    plastic card guides - pierced and formed card guides

    Table I.Guideline for quantity of drawing sets required.

    Table II.A partial listing of interchangeable processes.

  • ForFeatures

    or Datumsof Size

    Feature Control Frame.008 A B C

    Geometric CharacteristicZone Shape Symbol

    ToleranceModifier

    Primary DatumSecondary Datum

    Tertiary Datum

    Datum Ident. Symbol-A-

    .4 0A 1

    Target Area Size A/A

    Plane & Target No.

    Datum Target Symbol

    CombinedFrame

    .0005-A-

    Basic

    TheoreticallyExact

    .750

    Composite PositionalTolerance

    -C-

    -B-

    .0 3 0.00 8

    AA

    B C.03 0.0 0 8

    AA

    B C

    -A-

    4H 0/ .262-.268

    Datum Reference Frame/ 3 Plane System

    Converting Numbered Screw to a DiameterMax Screw O.D. = .013 x Screw No. + .060Conversion Customary to Metric & BackInches x 25.4 = Millimeters (Exactly)Millimeters x .0393700787 = Inches

    Positional Tolerance FormulasH = MMC 0/ Hole SizeT= MMC 0/ Positional ToleranceF = Fastener 0/ Virtual Condition

    Floating Fastener SystemEqual Tolerance Distribution1. T = H - F2. H = F + T

    Floating Fastener SystemUnequal Tolerance DistributionT1 = MMC 0/ Positional Tolerancepart #1T2 = MMC 0/ Positional Tolerancepart #2H1 = MMC 0/ Hole Size-part #1H2 = MMC 0/ Hole Size-part #23. T1 = (H1 + H2) - (2F + T2)4. H1 = (T1 + T2) - (2F - H2)

    Fixed Fastener SystemEqual Tolerance Distribution5. T = (H - F)/26. H = F + 2T

    Fixed Fastener SystemUnequal Tolerance Distribution7. T1= H1 - (T2 + F)8. H1 = T1 + T2 + F

    Straightness on a Unit Basis

    FEATURE TOLERANCETYPE SYMBOL CHARACTERISTICDATUMREQD

    ALLOWABLEMODIFIERS

    S

    R

    SR

    ()

    Individual(Single)

    Form(Shape)

    Individualor Related

    Profile(Contour)

    Orientation(Attitude)

    Location

    Runout

    Modifying Symbols

    AdditionalSymbols

    Related

    Straightness

    Flatness

    Circularity

    Cylindricity

    Profile of a Line

    Profile of a Surface

    Angularity

    Perpendicularity

    Parallelism

    Position

    Concentricity

    Circular Runout

    Total Runout

    NotAllowed-Related

    to aperfectcounter

    part

    Allow-able

    Required

    Preferred

    Required

    Required

    Required

    Maximum Material Condition

    Regardless of Feature Size

    Least Material Condition

    Projected Tolerance Zone

    Diameter (Face of Dwg.)

    Spherical Diameter

    Radius

    Spherical Radius

    Reference

    Arc Length

    On Axis

    None

    AllowedOnly OnDatum

    , orRecored

    None

    Geometric Dimensioning & Tolerance Summary Fact Data Sheet

    Exclusions to Rule #1 Perfect form at MMC1. Stock Specification2. *Flatness Note3. *Exclusion by Note

    4. Free State Variation5. Straightness-Axis*1 Perfect Form at MMC not Reqd

    Ch

    r

    r = C h+28h

    h = r - r - C4

    Form at MCC

  • DESIGN GUIDELINES 5

    Computer Aided Design, CA D, was intro-duced as a tool to aid designers in devel-oping part drawings as well as decreasing thetime necessary to draw the development onp a p e r. Over time it has become a much morepowerful tool enabling engineers to check form,fit, function and tolerancing of details or entireassemblies prior to actual parts being built. Inthe time it takes to input data, the designer canhave a 3D visual model. As this process devel-oped, Computer Aided Manufacturing, CA M ,was introduced to the manufacturing environ-ment. This allowed for data to be input into aCAM system to create machine tool programs,thus automating many of the processing stepsthat were traditionally done manually.

    OverviewAs CAD and CAM were developed, the

    metalforming industry welcomed them withopen arms. Virtually all metalforming compa-nies today have some sort of CAM system with-in their engineering departments, drasticallyreducing the time required to produce a part.

    The industry is demanding that this process betaken further by exchanging CAD files. Th i sallows for the customer to design parts on theirCAD system and exchange them with theirmetalforming suppliers. The goal for manycompanies is to create a part/assembly on acomputer screen and then to have it manufac-tured without any paper drawings being creat-ed, reducing the overall time required fromdesign concept to completion of parts.

    Traditionally, the process from concept to themanufacturing of parts was very time consum-ing. When a CAD model was completed, it wasturned over to a drafting department to createa typical orthographic drawing. The drawingwould be given to a metalforming companywho would recreate the part as a flat patterndevelopment in their CAD system. From thereit would be downloaded into a CAM systemto create a machine tool program. This processallowed for numerous opportunities for errors.Today there are many CAM systems on themarket that will actually take a CAD file andautomate the unfolding for you, creating a flat

    CAD DESIGN2

  • pattern development, with little opportunity forerror.

    One advantage of exchanging CAD files isthe ability to get your product design into thehands of the supplier prior to the design beingformally completed. Early supplier involve-ment in design reviews for manufacturability,tooling and manufacturing methods can bereviewed before changes are costly.

    It should be noted that there are certain limi-tations to CAD file exchange. CAD files mustbe drawn to full scale. All objects within a filemust be put exactly where you want them. Thisis imperative for the simple reason that whenthe CAD file is imported into your supplierssystem and goes through the unfolding processit will place all of your geometry exactly as youhave drawn it. If you have misplaced a hole,your final product will have that same hole mis-placed. Simply put, what you CAD is what youget. As CAD file exchange becomes fullyimplemented within the manufacturing envi-ronment and paper documents become obso-lete, the CAD file will become the master docu-ment for inspecting finished products.

    Fi n a l l y, CAD files must be clean. There can-not be overlapping lines or lines that do notintersect. If these types of problems are con-tained within the CAD file upon file exchange,then your supplier must take valuable time incleaning up your file. Lines that dont intersectcannot cleanly go through the unfolding process.

    Overlapping lines that exist within the filecan create major problems in the machine toolp r o g r a m s. For example, if the part happens tobe run on a laser cutting machine, you will getholes or edges that are double burned thusdestroying the parts edge, causing a closely tol-eranced feature to be out of specification.These and many other problems can occurwhen a CAD file is not clean.

    Within the metalforming community thereare many different types of CAD programs thatare available. Because of the variety ofCAD/CAM systems in use today, there are cer-tain guidelines that must be closely adhered to

    when exchanging CAD files.

    Guidelines for Designing in CADThis chapter is intended to help avoid diffi-

    culties in exchanging files. Information willinclude proper part geometry, what should beand what should not be contained within thefile, different methods of file transfer, and mini-mum hardware requirements for CAD filee x c h a n g e. If these guidelines are followed youwill be able to exchange files, while avoidingmany of the major problems that have beenexperienced in the past, with virtually any com-pany with a CAD system.

    In transferring the design of a sheet metal partor assembly via CA D, it is important that all nec-essary information be communicated to assurethat the intended functionality will exist. Th i sinformation includes the CAD model, critical-to-function dimensions and non-geometrical infor-mation, such as metal type, and surface finish.

    CAD Model DescriptionA CAD model is a collection of geometric

    entities that describe the size and shape of a part.The entities may be 2-dimensional and show sev-eral orthographic views, or 3-dimensional andviewable from any orientation. 3-D, solid modelsare preferred by most manufacturers becausethey are more versatile for programming and forgenerating additional documentation.

    Rules for Designing Part FeaturesA sheet metal parts CAD model should be

    composed of geometry that exactly describesthe intended design of the part or assemblywithout unnecessary complication. See Fi g u r e1. All geometry should be created at full-scaleusing nominal sizes. All edges, transitions andcross-sections that are represented in the modelshould be represented by geometry that is freeof gaps, overlaps and duplication. See Figures 6and 7 for illustrations of common CAD errors.

    CAD Design

    6 DESIGN GUIDELINES

  • CAD Design

    DESIGN GUIDELINES 7

    Design Features E d g e s of the entire periphery of the sheet

    metal should be shown, with consistent sepa-ration equivalent to the metals thickness.Connecting lines whose length is equal to them e t a l s thickness must be drawn along theperiphery at every edge transition that occurs.See Figure 2.

    Bends in the material can be shown with orwithout bend radii. Bend radii, if shown,should be represented by pairs of concentricarcs with mold lines connecting inner andouter radii to show the extent of the bend.For simplicity, models with consistent bendradii can be represented with square cornersas if the bend has no inside or outside radius.The actual radius will need to be allowed forin the design and communicated to the sup-p l i e r. Bend reliefs, if required, should beshown. See Figure 3.

    H o l e s in a part should be detailed asdescribed above for the periphery edges,including lines to connect the two surfaces.For circular holes, at least one line should be

    PJ

    C

    NH

    G

    EM

    D

    FB

    AK

    L

    U

    R

    T

    Q

    S

    Figure 1. This model is a typical wireframe drawing showing various types of corners, bends and other commonly usedsheet metal features. The preferred CAD geometry for each feature shown in the above diagram is detailed in Figures 2-5.Note: One side of diagram is drawn with bend radii and the opposite is drawn without.

    CORNERS

    SHARP

    DETAIL A DETAIL B DETAIL C

    RADIUSED CHAMFERED

    Figure 2. Connecting lines on periphery of corners.

  • used to show that the circles are related.Additional lines that would appear in orthogo-nal views to show the extent of the hole aregenerally desirable. See Figure 4.

    Other Fe a t u re s. Coined, drawn, formed,machined or rolled features as well asinstalled hardware should be represented bygeometry that details the edges, any transi-tions and cross-sections of the features orhardware. See Figure 5.

    Figure 3. Preferred method for showing bends with and without radii.

    8 DESIGN GUIDELINES

    HOLES

    DETAIL K

    DETAIL M DETAIL N

    CIRCULAR OBROUND SLOT

    RECTANGULAR WITHIN BEND

    DETAIL L

    Figure 4. Preferred method of showing somemore common cutouts on drawings.

    BENDS

    DETAIL D DETAIL E

    DETAIL G DETAIL H DETAIL J

    90 180 HEM OFFSET

    DETAIL F

    CAD Design

    FORMED FEATURES

    COUNTERSINK EXTRUSION HALF-SHEAR

    DETAIL P

    DETAIL T

    DIMPLE

    DETAIL R

    ENLARGED FOR CLARITYDETAIL S

    SHORTENED FOR CLARITY DETAIL U

    DETAIL Q

    EMBOSS CARD GUIDE

    Figure 5. Preferred method of showing other common features on drawings.

  • CAD Design

    DESIGN GUIDELINES 9

    Figure 6. Some common CAD model errors illustrated in two views of a sheet metal part with a 90 bend.

    INNER AND OUTERARCS DESCRIBINGBEND ARE NOTCONCENTRIC

    DIMENSIONS THAT AREINACCURATEDO NOTMATCH CAD DATA

    1.500

    1.000

    DUPLICATE ENTITIES ERRANT GEOMETRY

    ENDPOINTS THATDO NOT MEET

    VARYING MATERIALTHICKNESS

    OK

    NOT OK NOT OK

    RADIUS SHOWN ON OUTSIDE OF BENDS BUTNOT ON INSIDECONSISTENTLY SHOW OR

    DO NOT SHOW BOTH RADII

    CONSISTENT APPROACH (NO RADII) BUT NO ALLOWANCE IS MADE FOR

    MINIMUM BEND RADIUSTHISDESIGN IS NOT POSSIBLE AS

    SHOWN WITH TWO 90 BENDS

    OK

    Figure 7. Two CAD model problems in sheet metal parts with offset bends shown both correctly and incorrectly.

  • 10 DESIGN GUIDELINES

    Parts Separated By Layer(all parts in the assembly are in one file)Pros:+ requires only one file transfer+ all information kept in one place, nothing lost+ assembly information is defined with part

    models+ view any combination of parts by choosing

    layers+ file translation only needs to be done once

    Cons: file is larger and slower to manipulate file size may exceed CAD system limitations large file will need to be revised and exchanged

    whenever a single component is revised layer names may change during file translation

    Parts Separated By File(multiple files, one part in each file)

    Pros:+ revision level can be incorporated in file name+ customer only sends files for parts being revised

    Cons: file translation must be performed on each file

    individually if an assembly model is desired, it must be

    pulled together from all of the translated files

    ALL LAYERS OR ALL FILES LAYER 1 OR FILE 1

    LAYER 0 OR FILE 0 LAYER 2 OR FILE 2

    Assemblies: Two MethodsAssemblies of sheet metal parts can be

    described with CAD models using one of thesemethods:

    1) a separate file for each component. SeeFigure 8.

    2) one file which uses a separate layer foreach component.

    There are distinct advantages and disadvan-tages to each of these methods, as detailed inTable 1.

    Figure 8. Views showing an assembly CAD file and separation of components by layer or by file.

    Table 1. Comparison of two methods of communicating assemblies.

  • Critical-to-Function DimensionsIn the past, part designs were typically com-

    municated by hand-drafted drawings, showingvarious views of the part with dimensions forevery detail and with all pertinent informationincluded. With CAD systems, some designershave stopped generating dimensioned drawingsof any kind, since dimensions can be extractedfrom the CAD model instead. Unfortunately, theresult is an incomplete hand-off of information.The designer still needs to communicate to themanufacturer other types of information: thedimensions that are critical to the success of the

    design, tolerances and the other non-geometricalinformation that were included in the drawings.

    Two-dimensional drawings are the best wayto communicate critical-to-function (CTF)d i m e n s i o n s. Figure 9 is an example of a CTFdrawing that includes critical dimensions andmost of the necessary non-geometrical informa-tion. In addition, this drawing contains enoughdimensions to completely form the describedpart. Without this information most manufac-turers would have to create an additional draw-ing to detail the formed part to the shop and forquality assurance records. This CTF drawing is

    CAD Design

    DESIGN GUIDELINES 11

    Figure 9. Features of critical-to-function drawings.

    SECTIONAL VIEW OFFORMED FEATURE

    SECTION AAFORMING DIMENSIONS

    REVISION INFORMATION

    HIDDEN-LINE IMAGEOF ISOMETRIC VIEW

    TITLE BLOCK

    NOTES:

    1. _________________________

    2. _________________________

    3. _________________________

  • CAD Design

    12 DESIGN GUIDELINES

    simpler to produce than a complete fabricationdrawing because it has fewer dimensions.

    A flat pattern view is acceptable and some-times very helpful. The manufacturer will usethese views mainly as a reference for the quot-ing process. If dimensions are included in anyunfolded views they should be for referenceonly, since the manufacturer will need flexibili-ty in order to meet the dimensions and toler-ances of the formed part.

    Non-geometrical informationRequired information other than the wire-

    frame geometry and CTF dimensions areknown as non-geometrical information. It is tex-tual information and most of it can be commu-nicated in the CAD model or CTF drawing, butit can be separately enclosed in an ASCII textfile or on paper. Information regarding whom tocontact and the CAD media should be enclosedin a file elsewhere because that information willbe needed in case there are problems or ques-tions and to extract files from the media.

    Checklist of non-geometrical informationwhich needs to be communicated

    Design Engineer - name, phone #, e-mailaddress and fax #

    Manufacturing Engineer - name, phone #,e-mail address and fax #

    Buyer - name, phone #, e-mail address andfax #

    CAD media information CD/e-mail/d i s k e t t e /tape: commands required toextract the files

    File format and version number:IGES (.igs), STEP (.stp), ACIS (.sat),Parasolid (.x_t), Granite (.g)

    Part number Revision Revision description

    Part title

    Estimated number of parts required peryear and part life time

    Related CAD file name(s) or layername(s)

    Material - thickness, type, hardness (ifapplicable), etc.

    Punch or burr direction, material graindirection

    Deburring instructions Finish - plating instructions, painting

    instructions (i.e. mask, over spray, color),s p e c i f i c a t i o n s, camera ready art or digitalfile, etc.

    Tolerances Part marking informationAllowable bend radiiAllowable bend reliefAllowable corner radii

    Allowable tooling holesHardware list - quantity, description, part

    number

    Assembly instructions - welding, tapping,riveting, etc.

    TolerancesCAD models define the dimensions of a part

    c o m p l e t e l y, but generally do not describe thetolerances that should be maintained for eachdimension. Critical dimensions should be shownexplicitly in the CTF drawing with tolerances,but unless this is a complete fabrication draw-i n g, most of the remaining features are left undi-mensioned and untoleranced. One solution is anote or tolerance block that defines the generalt o l e r a n c e s, not dependent on two- or three-place dimensions, but instead according to whattypes of features are being dimensioned.

  • CAD Design

    Example: Possible Tolerance NoteAs specified by the critical-to-function draw-

    ing, standard tolerances will be the following:

    Single-hit hole size Edge or hole to edge or hole Edge or hole to form Form to form Form angle

    The CAD model will contain all the nominaldimensions for a design, but tolerances need tobe explicitly communicated to the supplier in aCTF drawing or other specification document.Tolerances should be called out as bilateral tol-erances (i.e.: 2mm) so that nominal falls in themiddle of the tolerance band. Do not use uni-lateral tolerances (i.e.: +0.010"/-000"). They willcause the nominal dimension in the CA Dmodel to be at the edge of the tolerance band.

    If the CAD model is used to program a CNCoperation, the computer-driven machine will tar-get the nominal dimension and operate at theedge of limit for acceptable product. The CNCprogrammer can intervene and manually edit theprogram to target the middle of the toleranceband, but then the process is no longer being dri-ven by customer data and errors can be made.

    File Formats CAD Files. CAD software is developed by

    independent companies, competing to be thefirst to market with the best combinations ofcapabilities and cost. CAD systems each usetheir own unique way of organizing and storingthe CAD data. Brand specific file formats areincompatible with each other. Part designs cre-ated by one CAD program are unreadable byothers unless a neutral file format is used whentransferring the CAD data.

    Neutral file formates include I G E S ( . i g s,Initial Graphics Exchange Specification) andS T E P ( . s t p, S t a n d a rd for the Exchange ofP r o d u c t model data) are generally supported byall major solid modeling CAD programs.Neutral formats will strip away parmetric data

    that created the original geometry.Industry standards have been developed to

    give CAD programs a universal file format fortranslating CAD information from one compa-nys CAD format to another. Its official name isthe Initial Graphics Exchange Specification and often referred to as IGES. Files savedaccording to the IGES specification are identi-fied by the DOS file extension,.IGS.

    As with most standards, the capabilities ofthe universal IGES format follow the industryit supports. The IGES standard is updated tosupport the new capabilities designed intoCAD systems, but there is a time delay. Today,IGES captures 3-D model information, surfacesand wireframes. It does not include 3-D solids,parametrics or certain complex curve functions.

    CAD software companies take responsibilityfor how their CAD information is translated toand from the IGES format. Some CAD pro-grams allow the designer to save a design direct-ly to an .IGS file. Others require that you savethe design in the CAD systems native file for-mat, and then run a separate program to con-vert it to an .IGS file. In either case, it is impor-tant to use the most current revision of theIGES translator so your .IGS files can be under-stood by CAD systems at other companies.

    A word of caution in using IGES. There areseveral pitfalls that can make it very difficult touse IGES effectively:

    CAD systems (and even IGES) do not sup-port all of the geometric shapes used in theCAD design world. The root of most transla-tion problems lies in the basic differences in theway CAD systems store design information.CAD systems may describe common geometricshapes in incompatible ways.

    While one CAD system may not recognize acircle (but represent it with a 90 ellipse) anoth-er system may not recognize an ellipse (but rep-resent one with polyline arcs). Translating adesign through this combination turns circlesinto polyline arcsthe polyline arcs may not beunderstood when the design is translated back

    DESIGN GUIDELINES 13

  • CAD Design

    14 DESIGN GUIDELINES

    to the CAD system used by the original design-er. And that designer will not understand whythe circles were deleted from the design with-out authorization. Each translation is an oppor-tunity for creating errors.

    The IGES and STEP translator for yourCAD system may be poorly written. They areoften written by third party services who may notunderstand all the hidden incompatibilities. Ifyour CAD system uses a shape, a color, a linewidth, or other feature that is not supported byIGES and STEP, the translator will determinewhether or not the entity gets written to the IGESor STEP file, and what it will be translated as.

    Your IGES or STEP translator may not be acurrent revision. The latest IGES and STEPtranslator will typically convert an old designf i l e. But an old translator will not recognize theformat of a new IGES or STEP file and may dis-card data without telling you or create a file thatis unopenable on the receiving CAD system.

    Pitfalls are common in todays world andmake it very difficult for a good supplier tointerpret a good CAD file. To minimizeproblems, test the compatibility between CADs y s t e m s. Then expect to check all translateddesigns carefully on an ongoing basis.

    Kernal specific file formats include, AC I S(.sat, Spatial Te ch n o l o g y), Parasolid (.x_t,Unigraphics Solutions), and Granite (.g,Parametric Te ch n o l o g i e s). These file formatswill provide a better level of compatibility andare recommended over Neutral file formats, ifavailable. Kernal specific file formats, like neu-tral formats, will strip away parametric datathat created the original geometry.

    Product specific file formats are the nativefile format of the creating CAD software. Thisis always the best option for moving CAD dataif your fabricator supports compatible software.It is recommended to check with your fabrica-tor on software type, file format and transfermedia before sending any CAD file.

    While IGES and STEP are the standard for-mat for CAD geometry, there are other file for-mats that have become defacto standards forexchanging drawings and text. (IGES will han-dle drawings and text, too, however the transla-tors available today do an unreliable job oftranslating them.)

    D r awing Files. Though drawings can beincluded in an .IGS file, this guideline recom-mends two formats for drawings, HPGL(Hewlett Packard Graphics Language) andDXF (Drawing Interchange Fi l e, a formatdeveloped for Au t o CAD and commonly usedby 2-D CAD systems).

    H P G L is a printing format that computersuse for telling a plotter how to plot a drawing. Tosave an HPGL file, one tells the CAD software itshould plot to a plotter, but captures the instruc-tions to a disk file instead. In order to print thefile later, one copies the disk file to an HPGLdevicea plotter or printer. This capability isavailable on most CAD software packages.

    The HPGL formats key strength is that alldrawing information is reliably captured in theelectronic file and can be printed on a widerange of plotters and printers. The file formathas two drawbacks. First, the file will have thedrawings size coded into it when the file is cre-ated. Secondly, the file is a set of plottinginstructions. It is no longer a CAD design andcannot be revised with most CAD software sys-tems. HPGL files do not keep track of attributeinformation or drawing layers. It is essentiallyan electronic version of a plotted drawing.

    Test the compatibility betweenCAD systems.

    Create a test file that includes each of the entitiessupported by your CAD system.

    Translate the file into the target CAD system.

    Compare each entity.

    Do this both ways between customer and supplier.

  • .DXF is another standard CAD design fileformat. It is commonly used by 2-D CAD pro-grams, but is 3-D capable. (Your CAD manualwill explain the process for saving a .DXF file.)The .DXF file can be revised and plotted. It issimpler and 2-D drawings are more reliablyinterpreted than drawings from an IGES file.Drawbacks are that it will be a bigger drawingfile than an HPGL file.

    Text files. Text files are very useful fordescribing non-graphical information. Th e ymay be saved on the same e-mail or disk asCAD files. Text files can be in a variety of for-mates including Microsoft Word and WordPad.

    File ContentsUntil there is greater standardization in the

    i n d u s t r y, transferring design information fromone CAD system to another will be unreliable.

    To simplify matters, we recommend thatcompanies use each of the file types for the par-ticular job they do best:

    Use native CAD files, if supported, first. Use Kernal specific file as a second choice. Use .IGS or .STP as a last resort Use .IGS for design models. Use .DXF or HPGL for drawings. Use .DOC or .TXT files for text informa-

    tion.

    File PreparationWe recommend that all files be compressed

    using a compression utility such a WinZip orStuffit. This reduces e-mail transmission timesand archives all files into a single file. If the filesare coming from a Macintosh, include theDOS 3 character extension to all files to allowfor safe transfer to Windows systems.

    File Transfer E-mail attachments are the simplest way of

    transferring the CAD data and accompanyingf i l e s. This usually has a 2 meg file size limita-tion. Check with your fabricator regardingmailbox size limitations.

    Your fabricator may have an FTP sitewhich allows for peer-to-peer transfers. Usuallylarger fi les can be transmitted using thisapproach and the transfer is more secure.

    Disk Transfer. Files can be saved to a CD,floppy disk or Zip disk and sent via overnightmail. Unless otherwise arranged, the diskshould be a DOS format

    CAD Design

    DESIGN GUIDELINES 15

  • Save design as anIGES wireframe.Strip out solidsand surfaces.

    Verify part numbers andrevision levels

    are correct.

    Flowchart for Exchanging CAD Files

    Complete designand save file.

    Fax a copy of theagreement form

    to the other party.

    Plot drawings toHPGL files.

    Create text filesas desired.

    Follow instructionsfor file transfer.

    Copy file to 1.44MB3-1/2 diskette.

    E-mail or fax a copy ofthe agreement formto the other party.

    Save the design in thenative file format for your

    CAD systemperagreement byboth parties.

    Set communicationssoftware to (9600,N,8,1)

    or faster. Dial andconnect with remote

    host computer.

    Archive the filestogether and create

    a self-extracting.EXE file.

    Isother party

    using the sameCAD software

    ?

    Mail to other partywith a copy of theagreement form.

    Attach file toE-mail message.

    Send E-mailmessage toother party.

    Methodof transfer

    ?

    Yes

    No

    Modem DisketteE-mail

    16 DESIGN GUIDELINES

  • DESIGN GUIDELINES 17

    Floppy Disk Drive

    3-1/2" diskette 1.44MB able to read DOS format

    CAD File Transfers

    Minimum RequirementsHardware & Software

    Preferred File Transfer Methods modem upload/download 3-1/2" DOS diskette

    Optional File Transfer Methods (only when prearranged between customer and supplier) Internet e-mail magnetic tape 5-1/4" diskette

    Format of Transferred File(s) file shall be compressed and archived in a self-extracting .EXE file. .EXE file may include: .IGS 3 dimensional model .DXF drawings .TXT files containing text HPGL plotter files CAD model shall not include solids or surfaces. optional file formats, solids, and surfaces may be used if prearranged between customer and supplier.

    Modem 9600bps (or faster) v.42 bis (or better)

    Computer Software communications software with host capability. file compression software software for creating self-extracting .EXE files.

    File Compatibility able to read: IGS files DXF files HPGL/HPGL2 files

  • 18 DESIGN GUIDELINES

    Date:_________________________

    Customer/Supplier CAD Agreement

    Company Name:_______________________ Contact Name: ______________________Project Name:_______________________ Title: ______________________

    Phone: ______________________Part Number(s):_______________________ Fax: ______________________Revision Level:_______________________ E-mail: ______________________

    Action Requested CAD Media: Quote Disk Prototype Modem Production E-mail

    Other

    Deviations allowed: Material substitutions Others Hardware substitutions Tolerances Redesign for manufacturability

    Other docs required: Types of files included: Customer standards .IGS model Other .DXF model/plots

    HPGL/HPGL2 plotsControlling document is .TXT docs

    CAD model Material/hardware list Plot files Other Hardcopy drawings Other__________________________ CAD software used?______________

    Command required to extract files

    All nominal dimensions for prototypes and production parts will be taken from the

    CAD modelThe customer agrees that the CAD model will be used to program computer

    aided manufacturing (CAM) processes.

    Sample

  • DESIGN GUIDELINES 19

    3MATERIAL SELECTION

    Commercially produced materials suitablefor stamping and fabrication cover a broadr a n g e. Included are not only all types of ferrousand non-ferrous metals but also a large array ofp a p e r, f i b e r, leather and plastic products. Th i schapter deals exclusively with ferrous andn o n-ferrous metals which are most commonlyused in metalforming.

    Typical properties of metal alloys commonlyused in metalforming appear in the tables thatfollow.

    The following is a density chart for the mate-rials covered in this chapter.

    Density ChartMaterial DensitySteels 0.28 lbs./cubic inchSpecial Low Carbon Cold

    Rolled Steel Products 0.28 lbs./cubic inchSpring Steels 0.28 lbs./cubic inchStainless Steels 0.29 lbs./cubic inchAluminums 0.11 lbs./cubic inchCopper & its Alloys 0.32 lbs./cubic inchBrass 0.31 lbs./cubic inchPhosphor Bronze 0.32 lbs./cubic inchBeryllium Copper 0.30 lbs./cubic inch

    SteelsAll steels used in metalforming start out as

    hot rolled. However, the use of hot rolled steelis limited because it is not available in thick-nesses of less than 0.060 in. (1.5 mm). Also, thethickness variation of hot rolled stock preventsits use in high-precision applications.

    Hot rolled steel (HRS) can be purchased inthree qualities:

    1) Hot rolled, with rolling scale on its surfaces.Used for rough and heavy work, often involvingbasic weldments. Least expensive.

    2) Pickled and oiled, referred to as HRPOsteel, where the hot-rolling scale is removed byacidic etching, followed by oil coating for rustprotection. Surface finish can be up to 120 rootmean square (rms). Used on truck chassis andsimilar work.

    3) Skin-passed hot-rolled steel, a HRPOsteel with one skin-pass cold rolling added fora smoother surface, similar to cold rolled steel.All other properties remain the same as regularhot-rolled steel.

  • Material Selection

    20 DESIGN GUIDELINES

    Cold rolled steel (CRS) is a collectivename for all steel which is finish processedthrough a cold rolling reduction mill. Th i sprocess follows the initial hot rolling and thenp i c k l i n g, for scale removal. The cold rollingprocess refines the surface finish and strainhardens the material. The name cold rolledsteel does not, in itself, imply any steel quality,except for the surface finish. See Table 1.

    Sheet and strip CRS sheet and strip aretwo distinct types of steel, both mill producedin coil form. Most mills are dedicated to makingeither sheet or strip quality metal exclusively.U n f o r t u n a t e l y, the terms CRS sheet and stripare very confusing and do not describe a shapeor size.

    Quality American mills produce CRS sheet

    and strip to AISI (American Iron and SteelInstitute) standards having carbon content of0.08 to 0.20%.

    There are different standards for someimported steels with carbon content as low as0.04% which is sold as commercial grade witha lower and sometimes undefined quality.

    The four major differences between coldrolled sheet and strip:

    1) Strip has a much better surface finish.2) Strip is rolled to much tighter thickness

    tolerances.3) Strip is rolled to a maximum width of 24

    in. (0.6 m); sheet steel to 72 in. (1.8 m), but nor-mally 48 in. (1.2 m).

    4) Strip uses a number system for temperdesignations; sheet uses a descriptive system.

    Strips close thickness control and consistent

    Table I. Physical and Mechanical Properties of Selected Cold & Hot Rolled Steel

    Commercial CommercialGeneric Draw Quality Quality 1/4 Hard 1/2 Hard Quality

    Property Cold Roll Cold Roll Cold Roll Cold Roll Cold Roll Hot Roll

    form sheet or strip sheet sheet or strip sheet or strip sheet or strip sheet

    density Ib/in3 (g/cm3) 0.28 (7.87) 0.28 (7.87) 0.28 (7.87) 0.28 (7.87) 0.28 (7.87) 0.28 (7.87)

    mechanical properties

    modulus of elasticity 106 PSl 2.9 2.9 2.9 2.9 2.9 2.9(tension) N/mm2 203000 203000 203000 203000 203000 203000

    tensile strength 1000 PSI 40.6-65.3 39.2-50.8 43.5-58.0 45.0-65.3 55.1 -75.4 45.0-52.2N/mm2 (typical) 280-450 270-350 300-400 310-450 380-520 310-360

    yield strength 1000 PSI 24.6 23.2 24.6 29.7 39.9 24.6N/mm2 (typical) ~ 170 160 170 205 275 170

    elongation %typical range 24-40 35-40 24-40 13-27 4-16 24-40

    hardness HRB 45-75 55 max. 65 max. 60-75 70-85 45-65

    forming, drawing excellent, excellent very good, across grain: 180 bend radius bend radiuswill meet any flat on itself in at bend radius 2T min. 1/2T at 90engineering any direction with grain: 90

    drawing reqt at bend radius

    weldability excellent excellent excellent limited limited excellent

  • tensile strength results in much better formingcharacteristics, possible higher production rates,and superior surface finish.

    Table II is a quick overview of the steel cate-gories with a relative cost comparison.

    Your supplier can make the proper recom-mendation based on the demands your designplaces on the material specification.

    Cold rolled sheet and strip steel is readilyavailable in all standard thicknesses and tem-pers from warehouses specializing in cold rolledp r o d u c t s. Speciality cold rolled sheet and stripof exacting thickness and temper can beordered directly from the mills, but requires aminimum order of at least five tons for sheetand one ton for strip. Delivery leadtimes aregenerally extended.

    Another option utilizes a re-rolling mill withthe ability of re-rolling an off-the-shelf productto exacting thickness, temper and finishrequirements. The advantage of re-rolling millsis the ability to process smaller minimum orderquantities in less time than the hot rolled mills.

    Formability of VariousQualities and Tempers

    Cold rolled sheet in 14 hard and strip #3 tempercan be hemmed with the grain. Drawing quality(sheet) and #5 tempers (strip) because of theirexcellent forming characteristics, are ideally suit-ed for some of the most severe forms and draws.

    Table III illustrates the minimum bend radiusin the various tempers. Caution must be exer-cised when specifying minimum bend radii

    because of the wide range of tensile strengthsand hardness ranges in each temper designation.

    Other ConsiderationsAlmost all rolled stock is produced very

    close to the lowest thickness limit, a conditionto remember during design.

    Two flatness grades are available in sheetform; commercial (roller leveled) and stretcherleveled quality. The latter has the better flatnesscondition. See Table IV.

    Specialty Low CarbonCold Rolled Steel Products

    Shim steel, h a r d-rolled with a bright #2finish available in thicknesses ranging from0.001 in. (0.02 mm) to 0.062 in. (1.57 mm).Width: 6 in. (0.2 m) to 12 in. (0.3 m) only. Coilstock or cut to length.

    Flat wire, h a l f-hard #2 temper, r o u n d e dedges. Thickness starting at 0.032 in. (0.81 mm)and up to 0.187 in. (4.75 mm)

    Width: from 0.250 in. (6.35 mm) to 2 in. (50.8mm) maximum. Consult your supplier for thethickness/width combinations available. C o i lstock or cut to length.

    Coated CRSSeveral metallic coatings are available in two

    coating methods: Hot dip and electrolyticallyd e p o s i t e d . Tin plated steel is available in all tem-p e r s, but the temper designation numbers are

    DESIGN GUIDELINES 21

    Material Selection

    Hot Rolled Cold Rolled

    type sheet sheet strip

    relative cost 1.0 1.5 2.0

    maximum width up to 72 in. 48 in.1 up to 24 in.

    min./max. thickness 0.13/ 0.007-0.0152/0.125 0.005-0.0082/0.1871 special mill orders up to 72 in. wide2

    depending on temper

    Table II. Relative Cost Comparison of Various Steel Categories.

  • the opposite of CRS. All other coated steels arereadily available in soft temper. See Table V.

    For reasons of economy pre-coated coldrolled steel is becoming more widely used insome industries, especially for internal structur-al parts. In manufacturing, the following pointsare to be considered:

    1) The cut edge is not coated.2) Mass deburring via tumbling or vibratory

    methods is not an option. It is best to specify an

    allowable maximum burr height which can becontrolled in production.

    3) TIG & MIG welding require speciale q u i p m e n t , create oxidized areas adjacent tothe welds, and generate hazardous fumes.

    4) Resistance welding generates some blem-ishes in the electrode contact area which areprone to rusting or oxidation.

    5) Mechanical fasteners should be reviewedas an alternate assembly method.

    Material Selection

    22 DESIGN GUIDELINES

    Angle figures show the relationship betweenSheet Description Material the bendline and material grain direction.

    Strip of material thickness 0 45 90

    Tensile condition & Minimum inside form radii required.Hardness capability

    in. mm in. mm in. mm in. mm

    Draw quality Unlimited 0.015 0.4 0 0 0 0 0 0#5 temper forming and 0.030 0.8 0 0 0 0 0 044,000 psi deep drawing 0.060 1.5 0 0 0 0 0 055 RB max. possible. 0.090 2.3 0 0 0 0 0 0

    0.120 3.0 0 0 0 0 0 0

    Soft Very ductile; 0.015 0.4 0 0 0 0 0 0#4 temper can be bent 180 0.030 0.8 0 0 0 0 0 048,000 psi back on itself 0.060 1.5 0 0 0 0 0 065 RB max. (hem). 0.090 2.3 0 0 0 0 0 0

    0.120 3.0 0 0 0 0 0 0

    1/4 hard Medium soft 0.015 0.4 0 0 0 0 0 0#3 temper material with 0.030 0.8 0 0 0 0 0 054,000 psi good to moderate 0.060 1.5 0.050 1.3 0 0 0 075 RB max. forming use. 0.090 2.3 0.090 2.3 0 0 0 0

    0.120 3.0 0.120 3.0 0 0 0 0

    1/2 hard Moderately stiff, 0.015 0.4 0 0 0 0 0 0#2 temper somewhat limited 0.030 0.8 0 0 0 0 0 064,000 psi formability. 0.060 1.5 0.060 1.5 0 0 0 085 RB max. 0.090 2.3 0.120 3.0 0 0 0 0

    0.120 3.0 0.160 4.1 0 0 0 0

    Full hard Very stiff, springy, 0.015 0.4 0.060 1.5 0.03 0.8 0.03 0.8#1 temper recommended for 0.030 0.8 0.190 4.8 0.12 3.0 0.14 3.680,000 psi flat use only, 0.060 1.5 0.220 5.6 0.16 4.1 0.16 4.190 RB max. requires large radius 0.090 2.3 0.250 6.4 0.19 4.8 0.19 4.8

    0.120 3.0 0.310 7.9 0.22 5.6 0.22 5.6

    Table III. Cold Rolled Steel Sheet & Strip Grades Formability Chart

    The required minimum inside bend radius for 90 forms with the burr on the inside.

  • DESIGN GUIDELINES 23

    Material Selection

    flatness tolerancesspecified minimum specified width (maximum deviation from a

    thickness inch inches horizontal flat surface), inch

    0.044 and thinner 12 to 36 incl. 3/8 (9.53 mm)(1.12 mm) over 36 to 60 incl. 5/8 (15.88 mm)

    over 60 7/8 (22.23 mm)

    over 0.044 12 to 36 incl. 1/4 (6.35 mm)(1.12 mm) over 36 to 60 incl. 3/8 (9.53 mm)

    over 60 to 72 incl. 5/8 (15.88 mm)over 72 7/8 (22.23 mm)

    flatness tolerancesspecified minimum specified width specified length (maximum deviation from a

    thickness inch inches inches horizontal flat surface), inch

    over 0.015 to 0.028 incl. 12 to 36 incl. to 120 incl. 1/4 (6.35 mm)(0.38 to 0.71 mm) wider or longer 3/8 (9.53 mm)

    over 0.028 12 to 48 incl. to 120 incl. 1/8 (3.18 mm)(0.71 mm) wider or longer 1/4 (6.35 mm)

    Table IV. Cold Rolled Steel Flatness Tolerances

    Stretcher Quality

    Commercial Quality

    Table V.Types of coated CRS and Typical Applications

    Table VI. Tensile Strength andHardness of Selected Spring Steels

    Available Coatings Uses & Comments

    electrolytic tin bright mostly in thin gages for groundingmatte finish purposes and shielding in electronic

    housings

    electro galvanized (zinc) chassis, panels, housings, shelvesplain or bonderized (for and similar products manufacturedpaint adhesion) from material up to .06 (1.5mm)

    thick material are edge protectedby galvanic action

    hot dipped primarily used for building hard-galvanized CRS ware etc., with some applications

    in electronics

    long terne plate used in building hardware,sheet-ing, covers etc., easily solderable,available only in soft tempers

    aluminized CRS heat reflective and corrosionhot dip process resistant in hot environment, auto-

    motive use, electrolytic converters,mufflers etc., soft tempers only

    Spring Steel

    AISI # tensile strength in KSI rockwell C hardness(depending on drawing temperature)

    1050 112-250 22-521075 122-305 26-591095 138-320 30-62

    Aircraft Quality Heat-Treatable Low Alloy

    4130 98-234 25-60

    All above alloys are available in strip quality and width of24" maximum. Check with your supplier for specificmaterial widths in stock.

  • Material Selection

    24 DESIGN GUIDELINES

    Spring SteelsSpring steel is only available in coil or strip

    f o r m , in both annealed and fully tempered springc o n d i t i o n . The latter often is referred to asc l o c k-spring material. In the spring steel designa-tion numbers, the last two digits show the carboncontent in tenths and hundredths of a percent.One other alloying element present in spring steelis manganese (Mn) which improves hardenability.

    Annealed spring steel is easy to stamp andf o r m , but the heat treating to spring temperwhile maintaining shape is a major challenge,requiring straightening, gauging, etc.

    For flat shapes or radiused and open formedparts it is most economical to use the pretem-pered variety of spring steel. High quantity runs

    of prehardened steel parts make carbide diesmandatory.

    Tensile strength and hardness of commonlyavailable spring steels, after heat treat, a r egiven in Table V I . Highest tensile strength,alone, does not necessarily assure the best over-all performance.

    Production From Annealed Spring SteelHigher carbon steels tend to present more

    p r o b l e m s. The more complex crystalline struc-ture is prone to pitting (intercrystalline corro-sion) during pickling, necessary if the product isto be plated. Cosmetic nickel plating is likely tohighlight pickling pits. Plating of spring steelnecessitates a two-hour bake cycle at 325F to

    Angle figures show the relationship betweenType Description of Material the bendline and material grain direction.

    Tensile Material Condition Thickness 0 45 90

    Hardness & Capability Minimum inside form radii required.

    in. mm in. mm in. mm in. mm

    1050 Readily formable 0.015 0.4 0.015 0.4 0.015 0.4 0 064,000 psi into complex shapes. 0.030 0.8 0.030 0.8 0.015 0.4 0 084 RB max. Heat treatable to full 0.060 1.5 0.120 3.0 0.060 1.5 0.060 1.5

    spring temper. 0.090 2.3 0.190 4.8 0.120 3.0 0.090 2.30.120 3.0 0.440 11.2 0.310 7.9 0.190 4.8

    1075 Readily formable 0.015 0.4 0.030 0.8 0.015 0.5 0.015 0.480,000 psi into complex shapes. 0.030 0.8 0.050 1.3 0.030 0.8 0.015 0.486 RB max. Heat treatable to full 0.060 1.5 0.120 3.0 0.060 1.5 0.060 1.5

    spring temper. 0.090 2.3 0.200 5.1 0.120 3.0 0.090 2.30.120 3.0 0.500 12.7 0.190 4.8 0.190 4.8

    1095 Readily formable 0.015 0.4 0.030 0.8 0.015 0.4 0.015 0.490,000 psi into complex shapes. 0.030 0.8 0.050 1.3 0.030 0.8 0.015 0.488 RB max. Heat treatable to full 0.060 1.5 0.140 3.6 0.080 2.0 0.060 1.5

    spring temper. 0.090 2.3 0.220 5.6 0.140 3.6 0.110 2.80.120 3.0 0.500 12.7 0.340 8.6 0.220 5.6

    Table VII. Spring Steel, Soft Annealed Spheroidized Structure Formability Chart

    Shown is the required minimum inside bend radius for 90 forms with the burr on the inside. Recommended minimumbend radii for three grades of annealed spring steel, along with tensile and hardness information. Bends are oriented at0, 45 and 90 to grain direction.

  • DESIGN GUIDELINES 25

    Material Selection

    eliminate hydrogen embrittlement, an inherentresult of plating.

    Table VII illustrates the minimum bendradius in the various grades of spring steel.

    Caution must be exercised when specifyingminimum bend radii because of the wide rangeof tensile strengths and hardness ranges.

    Stainless SteelsOver 100 types of stainless steel are commer-

    cially available. Of these, approximately 25 to30 are readily available in various thicknessesand tempers from warehouses specializing instainless steel.

    Specialty stainless steels of exacting thickness

    Angle figures show the relationship betweenCondition Description of Material the bendline and material grain direction.

    Tensile Material Condition Thickness 0 45 90

    Hardness & Capability Minimum inside form radii required.*

    in. mm in. mm in. mm in. mm

    Annealed Has the best 0.015 0.4 0 0 0 0 0 070,000 psi combined mechanical 0.030 0.8 0 0 0 0 0 087 RB max. and forming qualities 0.060 1.5 0 0 0 0 0 0

    of all stainless steels. 0.090 2.3 0 0 0 0 0 00.120 3.0 0 0 0 0 0 0

    1/4 hard Semi-stiff, 0.015 0.4 0.015 0.4 0.015 0.4 0.015 0.4125,000 psi can be formed 0.030 0.8 0.030 0.8 0.015 0.4 0.015 0.429 RC max. with moderate 0.060 1.5 0.030 0.8 0.015 0.4 0.015 0.4

    spring back. 0.090 2.3 0.050 1.3 0.030 0.8 0.030 0.80.120 3.0 0.060 1.5 0.030 0.8 0.030 0.8

    1/2 hard Stiff, can be 0.015 0.4 0.030 0.8 0.015 0.4 0.015 0.4150,000 psi formed with 0.030 0.8 0.050 1.23 0.030 0.8 0.030 0.834 RC max. severe spring back. 0.060 1.5 0.060 1.5 0.030 0.8 0.030 0.8

    0.090 2.3 0.080 2.0 0.050 1.3 0.050 1.30.120 3.0 0.080 2.0 0.050 1.3 0.050 1.3

    3/4 hard Very stiff. 0.015 0.4 0.030 0.8 0.015 0.4 0.015 0.4175,000 psi Spring back prevents 0.030 0.8 0.060 1.5 0.050 1.3 0.050 1.340 RC max. complicated forms. 0.060 1.5 0.110 2.8 0.060 1.5 0.050 1.3

    0.090 2.3 0.120 3.0 0.090 2.3 0.090 2.30.120 3.0 0.190 4.8 0.090 2.3 0.090 2.3

    Full hard Extra stiff. 0.015 0.4 0.050 1.3 0.030 0.8 0.030 0.8185,000 psi Recommended for 0.030 0.8 0.090 2.3 0.060 1.5 0.060 1.546 RC max. springs and 0.060 1.5 0.120 3.0 0.080 2.0 0.080 2.0

    flat parts only. 0.090 2.3 0.250 6.4 0.120 3.0 0.120 3.00.120 3.0 0.380 9.6 0.190 4.8 0.190 4.8

    Table VIII. Stainless Steel, Type 302 Formability Chart

    Recommended minimum bend radii for five tempers of 302 stainless steel with burrs on the inside, along with tensileand hardness information. Bends are oriented at 0, 45 and 90 to grain direction. Above minimum bend radii incomparison show the great loss of formability brought by increased tensile strength.*Minimum bend radii for Type 304 stainless steel are similar to those Values shown above.

  • Material Selection

    26 DESIGN GUIDELINES26 DESIGN GUIDELINES

    Table IX. Relative Suitability of Stainless Steels for Various Methods of Forming

    Suitability For

    0.29% yieldstrength, Press-6.89 MPa brake Deep Roll

    Steel (1 ksi) Blanking Piercing Forming Drawing Spinning Forming Coining Embossing

    Austenitic Steels

    201. . . . . . . . . . . . 55 b c b a-b c-d b b-c b-c202. . . . . . . . . . . . 55 b b a a b-c a b b301. . . . . . . . . . . . 40 b c b a-b c-d b b-c b-c302. . . . . . . . . . . . 37 b b a a b-c a b b302B . . . . . . . . . . 40 b b b b-c c c b-c303, 303(Se) . . . . 35 b b d(a) d d d c-d c304. . . . . . . . . . . . 35 b b a a b a b b304L . . . . . . . . . . 30 b b a a b a b b305. . . . . . . . . . . . 37 b b a b a a a-b a-b308. . . . . . . . . . . . 35 b b(a) d d d d309, 309S . . . . . . 40 b b a(a) b c b b b310, 310S . . . . . . 40 b b a(a) b b a b b314. . . . . . . . . . . . 50 b b a(a) b-c c b b b-c316. . . . . . . . . . . . 35 b b a(a) b b a b b316L. . . . . . . . . . . 30 b b a(a) b b a b b317. . . . . . . . . . . . 40 b b a(a) b b-c b b b321, 347, 348. . . . 35 b b a b b-c b b b

    Martensitic Steels

    403, 410. . . . . . . . 40 a a-b a a a a a a414. . . . . . . . . . . . 95 a b a(a) b c c b c416, 416(Se) . . . . 40 b a-b c(a) d d d d c420. . . . . . . . . . . . 50 b b-c c(a) c-d d c-d c-d c431. . . . . . . . . . . . 95 c-d c-d c(a) c-d d c-d c-d c-d440A . . . . . . . . . . 60 b-c c(a) c-d d c-d d c440B . . . . . . . . . . 62 d d d440C . . . . . . . . . . 65 d d d

    Ferritic Steels

    405. . . . . . . . . . . . 40 a a-b a(a) a a a a a409. . . . . . . . . . . . 38 a a-b a(b) a a a a a430. . . . . . . . . . . . 45 a a-b a(a) a-b a a a a430F, 430F(Se) . . 55 b a-b b-c(a) d d d c-d c442. . . . . . . . . . . . a a-b a(a) b b-c a b b446. . . . . . . . . . . . 50 a b a(a) b-c c b b b

    (a) severe sharp bends should be avoided. aexcellent; bgood; cfair; dnot generally recommended

    Suitability ratings are based on comparison of the steels within any one class; therefore, it should not be inferred that aferritic steel with an (a) rating is more formable than an austenitic steel with a (c) rating for a particular method.

  • and temper specifications can be ordered direct-ly from mills. H o w e v e r, this requires orders of atleast three tons, with deliveries running up to 36w e e k s, depending on mill backlog.

    Other sources of specialty stainless steels arer e-roll ing mills, which process standardo f f-t h e-shelf material to required thicknesstemper and finish requirements. Delivery fromre-rolling mills is dependent on the mill backlogat time of order placement. Order processingcan take up to 16 weeks. One of the positiveaspects of using re-rolling mills is their ability toprocess minimum orders of 200 lbs.

    Table VIII illustrates the minimum bendradius for the various tempers of 302 stainlesssteel. Stainless steel type 302 is one of the mostductile grades. Caution must be exercised whenspecifying minimum bend radii because of thewide range of tensile strengths and hardness

    range variations in each temper designation.N o t e : Thickness of stainless steel should be

    specified to decimal dimensions and not gauges.

    Basic Types of Stainless Au s t e n i t i c N o n-hardenable chromium

    nickel alloys (non-magnetic in the annealedcondition). This group is also known as 18-8 or s u r g i c a l stainless steel. Ty p e s : 3 0 1-3 0 2-3 0 2 B-3 0 3 - 3 0 4-3 0 5-3 0 8-3 1 0-3 1 4-3 1 6-3 1 7-321 and 347.

    MartensiticHardenable chromium alloys( m a g n e t i c ) . Ty p e s : 4 0 3-4 1 0-4 1 4-4 1 6-4 2 0 - 4 3 1-440A, B and C-501 and 502.

    FerriticNon-hardenable chromium alloys(magnetic) Types: 405-430-430F (F=freemachin-ing) and 446.

    See Table IX for relative suitability of stain-less steel for various methods of forming.

    DESIGN GUIDELINES 27

    Material Selection

    Aluminum Alloys

    Property specular2024-T3 6061-T6 1100-H14 3003-H14 5052-H32 5052-H34 5052-0 sheet

    density (g/cm3) (2.77) (2.70) (2.71) (2.73) (2.68) (2.68) (2.68)

    mechanical properties

    modulus or elasticity 106 PSI 10.6 9.9 10.0 10.2 10.1 10.1 10.1 (not(tension) N/mm2 72400 68300 69000 70000 69300 69300 69300 available)

    tensile strength 1000 PSI 70.0 45.0 18.1 21.7 33.4 37.7 28.3 20.0N/mm2 (typical) 483 310 125 150 230 260 195 138

    yield strength 1000 PSI 50.0 39.9 16.7 21.0 28.3 31.2 13.0 18.0N/mm2 (typical) 345 275 115 145 195 215 90 124

    elongation (typical) % 17 12 9 8 12 10 25 2

    shear strength 1000 PSI 41.3 29.7 11.0 14.1 20.3 21.0 18.1 n/aN/mm2 285 205 76 97 140 145 125 n/a

    fatigue strength 1000 PSI 20.3 14.1 7.0 9.0 16.7 18.1 15.9 n/aN/mm2 140 97 48 62 115 125 110 n/a

    forming, drawing fair fair good good fair fair good fair

    joining characteristics fair excellent excellent excellent excellent excellent excellent (notavailable)

    Table X. Properties of Various Aluminum Alloys

  • Material Selection

    28 DESIGN GUIDELINES

    Angle figures show the relationship betweenTemper Description of Material the bendline and material grain direction.

    Tensile Material Condition Thickness 0 45 90

    Hardness & Capability Minimum inside form radii required.

    in. mm in. mm in. mm in. mm

    0 Soft Exceptional ductility. 0.015 0.4 0 0 0 0 0 013,000 psi max. Good for spinning, 0.030 0.8 0 0 0 0 0 0

    26 RB max. drawing and all 0.060 1.5 0 0 0 0 0 0types of cold 0.090 2.3 0 0 0 0 0 0

    working processes. 0.120 3.0 0 0 0 0 0 0

    H14 1/2 hard Good ductility, 0.015 0.4 0 0 0 0 0 018,000 psi max. still forms 0.030 0.8 0 0 0 0 0 0

    35 RB max. well with small 0.060 1.5 0.030 0.8 0 0 0 0inside radii. 0.090 2.3 0.050 1.2 0.030 0.8 0.030 0.8

    0.120 3.0 0.060 1.5 0.030 0.8 0.050 1.2

    H18 full hard Stiff, but forms 0.015 0.4 0.030 0.8 0.015 0.4 0.015 0.424,000 psi max. well with appropriately 0.030 0.8 0.060 1.5 0.050 1.2 0.050 1.2

    48 RB max. sized radii. 0.060 1.5 0.120 3.0 0.120 3.0 0.120 3.00.090 2.3 0.280 7.1 0.250 6.3 0.250 6.30.120 3.0 0.410 10.4 0.380 9.7 0.380 9.7

    Table XI. Type 1100 Aluminum Formability Chart

    Shown is the required minimum inside bend radius for 90 forms with the burr on the inside. Recommended minimumbend radii for three tempers of 1100 aluminum sheet, along with tensile and hardness information. Bends are oriented at0, 45 and 90 to grain direction. Aluminum, Type 1100 is known for its excellent corrosion resistance and weldability.

    P recipitation hardenab l e A specialtystainless steel alloy. Ty p e s : 1 5-5 PH, 1 7-4 PH,and 17-7 PH, (17-7 PH is most commonly avail-able in sheet or strip).

    Aluminum AlloysAluminum stampings are produced from

    wrought that has been rolled into a thin strip orsheet.

    The cost of aluminum by weight is muchhigher than for steel, but it has the advantage ofa higher strength to weight ratio. Other positive

    properties of aluminum are light weight, g o o delectrical and thermal conductivity and a lastingsilvery appearance, when appropriately treated.A l u m i n u m , among its many available alloysand tempers, offers a wide variety of designapplication choices. See Tables X and XI.

    On the negative side aluminum, unless pro-t e c t e d , tends to scratch and dent through han-dling in use and also during production.Because of the special care required, aluminumis somewhat more costly to handle in produc-tion processing than ferrous metals.

  • DESIGN GUIDELINES 29

    Material Selection

    Aluminum Alloy TemperDesignation System

    The temper designation is always separatedfrom the four-digit alloy designation by a hyphen.

    General Terms-F, as fabricated-O, annealed, re-crystallized-H, strain hardened (work hardened)-T, thermally treated

    Strain-hardened Alloys (1000, 3000, 5000)-H1, plus one or more digits, strain hard-ened only-H2, plus one or more digits, strain hard-ened and then partially annealed

    -H3, plus one or more digits, strain hardenedand then stabilized (low temperature treatmentto improve ductility)

    Heat-treatable Alloys (2000, 6000, 7000)-W, solution heat-treatedan unstabletemper, usually designated by time incre-ment after quench e.g.W + 1/2 hour.-T3, OK-T4, solution heat-treated and naturallyaged to an essentially stable strength level.-T5, OK-T6, OK-T8, OK-T9, OK-T10, OK

    Angle figures show the relationship betweenTemper Description of Material the bendline and material grain direction.

    Tensile Material Condition Thickness 0 45 90

    Hardness & Capability Minimum inside form radii required.

    in. mm in. mm in. mm in mm

    0 Annealed Exceptional ductility. 0.015 0.4 0 0 0 0 0 016,000 psi max. Can be easily 0.030 0.8 0 0 0 0 0 0

    30 RB max. formed and coined 0.060 1.5 0.015 0.4 0 0 0 0to intricate shapes. 0.090 2.3 0.015 0.4 0 0 0 0

    0.120 3.0 0.030 0.8 0 0 0 0

    H14 1/2 hard Good ductility, 0.015 0.4 0.015 0.4 0 0 0 022,000 psi max. still forms 0.030 0.8 0.030 0.8 0 0 0 0

    42 RB max. well with small 0.060 1.5 0.030 0.8 0 0 0 0inside radii. 0.090 2.3 0.050 1.3 0.030 0.8 0.030 0.8

    0.120 3.0 0.060 1.5 0.060 1.5 0.060 1.5

    H18 full hard Stiff, but forms 0.015 0.4 0.050 1.3 0.030 0.8 0.030 0.829,000 psi max. well with properly 0.030 0.8 0.080 2.0 0.050 1.3 0.060 1.5

    56 RB max. sized radii. 0.060 1.5 0.190 4.8 0.190 4.8 0.190 4.80.090 2.3 0.560 14.2 0.500 12.7 0.500 12.70.120 3.0 0.620 15.7 0.530 13.5 0.530 13.5

    Table XII. Type 3003 Aluminum Formability Chart

    Shown is the required minimum inside bend radius for 90 forms with the burr on the inside. Recommended minimumbend radii for three tempers of 3003 aluminum sheet, along with tensile and hardness information. Bends are orientedat 0, 45 and 90 to grain direction.

  • Material Selection

    30 DESIGN GUIDELINES

    -W temper becomes T4 at room tempera-ture after the properties stabilize.

    3000 and 5000 sheet alloys are normally sup-plied for stamping in the O temper.

    -H tempers are more commonly seen in forg-ings or heavy extrusions

    Formability of Aluminum AlloysFormability is directly related to the ductility

    of the material. Alloys in the O and T4 tem-pers have the greatest ductility and are normal-

    ly used for stamping. Stampings are typicallyhardened to full strength, e. g. T 6 , in a subse-quent thermal treatment process. At higherstrength levels, the aluminum alloys have lowerd u c t i l i t y, and are thus more difficult to formwithout cracking.

    Tables XII-XV illustrate the minimum bendradius in the various tempers of 1100, 3 0 0 3 ,5052 and 6061 aluminum sheet. Caution mustbe exercised when specifying minimum bendradii because of the wide range of tensile

    Angle figures show the relationship betweenTemper Description of Material the bendline and material grain direction.

    Tensile Material Condition Thickness 0 45 90

    Hardness & Capability Minimum inside form radii required.

    in. mm in. mm in. mm in. mm

    0 Soft Can be formed, 0.015 0.4 0 0 0 0 0 028,000 psi max. drawn and coined easily; 0.030 0.8 0 0 0 0 0 0

    49 RB max. surface defects, 0.060 1.5 0 0 0 0 0 0scratches etc. must 0.090 2.3 0.030 0.8 0 0 0 0

    be expected. 0.120 3.0 0.030 0.8 0.03 0.8 0.030 0.8

    H32 1/4 hard Readily formed; 0.015 0.4 0 0 0 0 0 033,000 psi max. most often 0.030 0.8 0 0 0.030 0.8 0.030 0.8

    62 RB max. specified for 0.060 1.5 0.030 0.8 0.060 1.5 0.060 1.5general use. 0.090 2.3 0.090 2.3 0.110 2.8 0.090 2.3

    0.120 3.0 0.120 3.0 0.140 3.6 0.120 3.0

    H34 1/2 hard Moderately stiff; 0.015 0.4 0.015 0.4 0 0 0 038,000 psi max. can be formed; 0.030 0.8 0.030 0.8 0.030 0.8 0.030 0.8

    70 RB max. specified when 0.060 1.5 0.080 2.0 0.060 1.5 0.060 1.5higher strength 0.090 2.3 0.190 4.8 0.190 4.8 0.190 4.8

    is required. 0.120 3.0 0.220 5.6 0.190 4.8 0.190 4.8

    H38 full hard Very stiff, but can be 0.015 0.4 0.050 1.3 0.030 0.8 0.030 0.842,000 psi max. formed with restrictions; 0.030 0.8 0.080 2.0 0.060 1.5 0.060 1.5

    80 RB max. used where spring 0.060 1.5 0.200 5.1 0.190 4.8 0.190 4.8action is needed; 0.090 2.3 0.500 12.7 0.500 12.7 0.500 12.7

    not readily available. 0.120 3.0 0.560 14.2 0.500 12.7 0.500 12.7

    Table XIII. Type 5052 Aluminum Formability Chart

    Recommended minimum bend radii for four tempers of 5052 aluminum, along with tensile and hardness information.Bends are oriented at 0, 45 and 90 to grain direction.

  • DESIGN GUIDELINES 31

    Material Selection

    strengths and hardness range variations in eachtemper designation.

    Hardened alloys are not normally stampeddue to low ductility.

    CopperSeveral types of virtually pure copper are uti-

    lized for its very high electrical and thermalc o n d u c t i v i t y, outstanding ductility for drawingpurposes and its good weathering ability.

    Common Ty p e s. The following commontypes of copper are listed by their CopperDevelopment Association identification number:

    CA 110Also called bus bar copper. M o s tcommonly used for electrical conductor parts.

    Most economical to use, readily available.CA 101 and 102Referred to as O F H C

    copper (oxygen free high conductivity).Specified for the most demanding electronicp a r t s, especially for use in high vacuum envi-ronments. Not susceptible to hydrogen embrit-tlement. More costly with limited availability.

    CA 194Primarily used for lead frames andconnectors.

    Table XV illustrates the minimum bend radiusin the various tempers of copper. Caution must beexercised when specifying minimum bend radiibecause of the wide range of tensile strengths andhardness ranges in each temper designation.

    Angle figures show the relationship betweenTemper Description of Material the bendline and material grain direction.

    Tensile Material Condition Thickness 0 45 90

    Hardness & Capability Minimum inside form radii required.

    in. mm in. mm in. mm in. mm

    0 Soft Soft, almost 0.015 0.4 0.015 0.4 0 0 0 018,000 psi unlimited 0.030 0.8 0.015 0.4 0.015 0.4 0.015 0.4

    Approx. 30 RB formability. 0.060 1.5 0.015 0.4 0.015 0.4 0.015 0.40.090 2.3 0.030 0.8 0.015 0.4 0.015 0.40.120 3.0 0.030 0.8 0.015 0.4 0.015 0.4

    T4 * Moderately stiff, 0.015 0.4 0.015 0.4 0.015 0.4 0.015 0.4(solution heat but can be formed 0.030 0.8 0.030 0.8 0.030 0.8 0.030 0.8treated only) readily, depending 0.060 1.5 0.090 2.3 0.090 2.3 0.090 2.335,000 psi on state of aging. 0.090 2.3 0.250 6.4 0.250 6.4 0.250 6.4

    Approx. 65 RB See note*. 0.120 3.0 0.380 9.7 0.380 9.7 0.380 9.7

    T6 full hard Very stiff, can be 0.015 0.4 0.050 1.3 0.030 0.8 0.030 0.845,000 psi formed by strict 0.030 0.8 0.060 1.5 0.030 0.8 0.030 0.8

    Approx. 75 RB adherence to required 0.060 1.5 0.140 3.6 0.110 2.8 0.110 2.8inside minimum radii. 0.090 2.3 0.250 6.4 0.280 7.1 0.280 7.1

    0.120 3.0 0.380 9.7 0.380 9.7 0.380 9.7

    Table XIV. Type 6061 Aluminum Formability Chart

    *T4 Temper will precipitation harden during ambient temperature storage to 80% of T6 values within 6-9 months aftersolution heat treatment from T0 to T4. Severe reduction in formability is the result. Bends are oriented at 0, 45 and 90to grain direction with the burr on the inside.

  • Material Selection

    32 DESIGN GUIDELINES

    BrassBrass is an alloy of copper and zinc at

    approximately 60-70% Cu and 30-40% Zn con-t e n t , with minor amounts of other elementssuch as lead, depending on the alloy. (Bronze iscopper and tin). See Table XVIII. Brass is awork hardened material only, and is available inannealed through extra spring tempers. Up to1 / 2-h a r d , brass can normally be formed withand against the grain at 0 inside radius and upto 0.040 in. (1.02 mm) thick without cracking.

    Table XVII illustrates the minimum bendradius in the various tempers. Caution must beexercised when specifying minimum bend radiibecause of the wide range of tensile strengthsand hardness ranges in each temper designation.

    Phosphor BronzePhosphor bronze is a copper (Cu), tin (Sn)

    and phosphor (P) alloy, not heat-treat harden-able, but routinely used for its very good springcharacteristics in its as-r o l l e d , strain hardened

    Angle figures show the relationship betweenTemper Description of Material the bendline and material grain direction.

    Tensile Material Condition Thickness 0 45 90

    Hardness & Capability Minimum inside form radii required.*

    in. mm in. mm in. mm in. mm

    Soft Best cold forming 0.015 0.4 0 0 0 0 0 022,000 psi and drawing qualities 0.030 0.8 0 0 0 0 0 022 RB max. of all metals. 0.060 1.5 0 0 0 0 0 0

    0.090 2.3 0 0 0 0 0 00.120 3.0 0 0 0 0 0 0

    1/4 hard Excellent cold forming 0.015 0.4 0 0 0 0 0 025,000 psi qualities with improved 0.030 0.8 0.015 0.4 0 0 0 028 RB max. wear and stiffness. 0.060 1.5 0.015 0.4 0 0 0 0

    0.090 2.3 0.015 0.4 0 0 0 00.120 3.0 0.015 0.4 0 0 0 0

    1/2 hard Good cold forming 0.015 0.4 0.015 0.4 0 0 0 026,000 psi quality with 0.030 0.8 0.015 0.4 0 0 0 042 RB max. moderate springiness. 0.060 1.5 0.030 0.8 0.015 0.4 0.015 0.4

    0.090 2.3 0.030 0.8 0.015 0.4 0.015 0.40.120 3.0 0.050 1.3 0.015 0.4 0.015 0.4

    Full hard Stiff, springy with 0.015 0.4 0.050 1.3 0.030 0.8 0.030 0.828,000 psi moderately reduced 0.030 0.8 0.050 1.3 0.030 0.8 0.030 0.866 RB max. formability. 0.060 1.5 0.080 2.0 0.050 1.3 0.050 1.3

    0.090 2.3 0.080 2.0 0.050 1.3 0.050 1.30.120 3.0 0.090 2.3 0.060 1.5 0.060 1.5

    Table XV. CA-110 Copper Formability Chart

    Recommended minimum bend radii for four tempers of copper, along with tensile and hardness information. Bends areoriented at 0, 45 and 90 to grain direction with the burr inside. *Minimum bend radii for other unalloyed coppers aresimilar to those values shown above.

  • c o n d i t i o n . Conditions available are listed inTable XIX.

    Tensile strengths given in Table XIX are spe-cific to alloy 510, but represent a close approxi-mation for all four alloys listed below. Becauseof the high 10% tolerance in tensile strength,adjacent tempers can overlap in actual materials t r e n g t h . For example, one lot of 12-hard materi-al may be the same tensile strength or evenslightly higher, than the next lot designated34-h a r d .

    Caution is advised when specifying sharplyformed parts and sample bends should be per-formed before specifying the material for pro-d u c t i o n . Inconsistent tempers cause spring-back problems to occur when large radii formsare required. Experimentation is recommendedto confirm manufacturability. Phosphor bronzeis used instead of beryllium copper in manyapplications for economical reasons.

    Table XIX illustrates the minimum bendradius in the various tempers for phosphorbronze. Caution must be exercised when speci-fying minimum bend radii because of the widerange of tensile strengths and hardness rangesin each temper designation.

    Beryllium CopperBeryllium copper (Be-Cu) is the most con-

    d u c t i v e, n o n-s t e e l , spring material available. I tcombines its very high electric conductivity andsuperb elastic limits with fatigue and good heatr e s i s t a n c e. Beryllium copper is a hazardouschemical and skin and eye contact should beprevented. Material cost of beryllium copper isthe highest of the copper alloys.

    Common beryllium copper alloys include:CA 170 1 . 6-1.79% Be .20% min. Co + Ni,

    Rest Cu.CA 172 1 . 8-2.0% Be .20% min. Co + Ni,

    Rest Cu.CA 1750.4-0.7% Be 2.4-2.7% Co, Rest Cu.Material is available in both strip and coil,

    with stamped parts produced from coil beingthe bulk of production. See Table XXI. BeCu isavailable in seven mill hardened tempers fromannealed through extra-hard spring. As with allm a t e r i a l s, formability becomes progressivelymore limited with increasing hardness. Parts tobe heat treated are best made from annealedstock because of unlimited formability.

    Table XXI illustrates the minimum bendradius in the various tempers of beryllium cop-per. Caution must be exercised when specifyingminimum bend radii because of the wide range

    DESIGN GUIDELINES 33

    Material Selection

    Table XVI. Common Alloys of Brass

    Common Alloys

    CA 260 70% Cu 30% Zn Most common, also usedwhen unspecified. called car-tridge brass.

    CA 230 85% Cu 15% Zn Red brass, most often speci-fied for contacts, etc.

    CA 353 62% Cu 36% Zn High leaded brass for stamp-+2% Pb ing use where subsequent

    machining or engraving isrequired.

    CA 360 61.5% Cu 35.5% Zn Free machining brass.+3% Pb

    CA 360 is included here since it is often used to produce hard-ware because of its good machinability. Unannealed it cannotbe riveted or staked without cracking and splitting.

    1/4 hard @ 50 KSI* tensile average 10%1/2 hard @ 65 KSI tensile average 10%3/4 hard @ 73 KSI tensile average 10%hard @ 83 KSI tensile average 10%xtra hard @ 95 KSI tensile average 10%spring @ 102 KSI tensile average 10%xtra spring @ 107 KSI tensile average 10%super spring @ 110 KSI tensile average 10%

    *(KSI = 1000 lbs per in2)

    common alloysCA 505 98% Cu 1.25% Sn 0.1% PCA 510 94% Cu 5.0% Sn 0.1% PCA 511 95.9% Cu 4.0% Sn 0.1% PCA 521 91.9% Cu 8.0% Sn 0.1% P

    Table XVII. Tensile Properties for SeveralTempers of 510 Phosphor Bronze

  • Material Selection

    34 DESIGN GUIDELINES

    of tensile strengths and hardness ranges in eachtemper designation. See Table XXII formechanical and physical pr