SHEET METAL WORKING

Sheet metal is simply metal formed into thin and flat pieces. It is one of the fundamental forms used in metalworking, and can be cut and bent into a variety of different shapes.

Countless everyday objects are constructed of the material.

Thicknesses can vary significantly, although extremely thin thicknesses are considered foil or leaf, and pieces thicker than 6 mm (0.25 in) are considered plate.

The thickness of the sheet metal is called its gauge. The gauge of sheet metal ranges from 30 gauge to about 8 gauge. The higher the gauge, the thinner the metal is.

There are many different metals that can be made into sheet metal, such as aluminum, brass, copper, steel, tin, nickel and titanium. For decorative uses, important sheet metals include silver, gold, and platinum.

Sheet metal has applications in car bodies, airplane wings, medical tables, roofs for building and many other things.

Sheet metal of iron and other materiales with high magnetic permeability, also known as laminated steel cores, has applications in transformers and electric machines.

and sheet metal continues to have many decorative uses, including in horse tack.

Introduction

Sheet metal is simply metal formed into thin and flat pieces.

It is one of the fundamental forms used in metalworking, and can be cut and bent into a variety of

different shapes. Countless everyday objects are constructed of the

material. Thicknesses can vary significantly, Although extremely thin thicknesses are

considered foil or leaf, and pieces thicker than 6 mm (0.25 in) are considered plate.

Sheet metal processing The raw material for sheet metal manufacturing

processes is the output of the rolling process. sheets of metal are sold as flat, rectangular

sheets of standard size.

If the sheets are thin and very long, they may be in the form of rolls.

the first step in any sheet metal process is to cut the correct shape and sized ‘blank’ from larger sheet.

Sheet Metal Forming processes

Introduction1. Sheet metal processes involve plane

stress loadings and lower forces than bulk forming

2. Almost all sheet metal forming is considered to be secondary processing

3. The main categories of sheet metal forming are

• Shearing• Bending• Drawing

ShearingShearing is a sheet metal cutting operation

along a straight line between two cut-ting edges by means of a power shear.

Blanking and punching Blanking and punching are similar sheet metal cutting operations that involve cutting the sheet metal along a closed outline. If the part that is cut out is the desired product, the operation is called blanking and the product is called blank. If the remaining stock is the desired part, the operation is called punching. Both operations are illustrated on the example of producing a washer

BendingBending is defined as the straining of the sheet metal around a straight edge

Drawing

Drawing is a sheet-metal operation to make hollow-shaped parts from a sheet blank

Equipments

Mechanical Press –

The ram is actuated using a flywheel. Stroke motion is not uniform.

Hydraulic Press – Longer strokes than mechanical presses, and develop full force throughout the stroke. Stroke motion is of uniform speed, especially adapted to deep drawing operations

Dies and Punches

Simple- single operation with a single stroke

Compound- two operations with a single stroke

Combination- two operations at two stations

Progressive- two or more operations at two or more stations with each press stroke, creates what is called a strip development

Progressive dies & Punches

Tools and Accessories

Marking and measuring tools

Steel Rule : It is used to set out dimensions.

Try Square: Try square is used for making and testing angles of 90degree

Scriber : It used to scribe or mark lines on metal work pieces.

Divider : This is used for marking circles, arcs, laying out perpendicular lines, bisecting lines, etc

Marking and measuring tools

Cutting ToolsStraight snip - They have straight jaws and used for straight line cutting. Curved snip - They have curved blades for making circular cuts.

Straight snip

Curved snip

Striking Tools Mallet - It is wooden-headed hammer of round or rectangular cross section. The striking face is made flat to the work. A mallet is used to give light blows to the Sheet metal in bending and finishing.

Types of Mallets

It Forms useful group and form metal sheet into useful shapes.

Supporting tool as well as forming tool. Fitted on workbench and job worked on

them

BICK IRON HATCHED STAKE FUNNEL STAKE CONVEX STAKE PIPE STAKE Etc.

LAYING OUT OF PATTERN , projective geometry

CUTTING or SHEARING BENDING BY USING STAKES JOINING THE EDGES OF SHEET SEAMING : LAP, SEAM, HEM CAP SOLDERING RIVETING Bolts and Nuts

SolderingSolderingIronIron

Move soldering iron until tip isMove soldering iron until tip istouching wire & solder padtouching wire & solder pad

Move solder to touch edge of tip. Move solder to touch edge of tip.

SolderSolder

Hold until solder melts Hold until solder melts on tip by wireon tip by wire

SolderSolder

Move solder back to touch wire onlyMove solder back to touch wire only

SolderSolder

Move solder in to form a Move solder in to form a small pocketsmall pocket

SolderSolder

Look for Look for shinny filletsshinny fillets

Definition: A process which a filler metal is placed at

or between the faying surfaces, the temperature is raised high enough to melt the filler metal but not the base metal.

The molten metal fills the spaces by capillary attraction.

Torch Brazing Oxy-fuel torch with a carburizing flame First heat the joint then add the filler

metal

Applications•Roofings•Ductings•Vehicles body buildings like 3 wheelers, 4 wheelers, ships, aircrafts etc.•Furnitures, House hold articles and Railway equipment

It forms popular group of permanent Engineering Fasteners.

It replaces this method by welding. It is largely used in today manufacture

of boiler shells, structural steels rail wagons bridges etc.

Elements are TAIL, SHANK AND HEAD Rivetting is done by chipping of the tail

of Rivet.

Caulking: Operation of burring down the edges of the plates and heads of the rivets to form a metal to metal joint

Fullering is a better option

SNAP or CUP HEAD

PAN HEAD

CONICAL HEAD

COUNTER SUNK HEAD

SNAP HEAD or Cup Head : Commonly used form and forms a strong joint.

PAN HEAD: Max strength and widely used It is used for heavy steel structures.

CONICAL HEAD:Genrally formed by hand hammering .restricted to use in small work.

COUNTERSUNK HEAD: Provides flush head and it doesnot project from work surface. Commonly used in ship building.

LAP JOINT: The end of the plate to be joined are made to overlap each other and joined by means of rivet.

BUTT JOINT: The end of plates are abutted against erach other and plates are connected by means of rivetts after providing one or two cover plates or cover straps.

Rivets may shear Plates may shear between

rivets. Plates may burst Plates or rivets or both joint

loose.

Self Study: Pulleys and belts Chains and sprockets Seals and Circlip Shaft Couplings

Pitch

The pitch of a thread is the distance from one point on the thread form to the corresponding point of the next thread. Pitch is measured parallel to the thread's axis or centerline. Click to see a sample appear to the right

Pitch

Notice the pitch can be measured

from crest-to-crest OR

Root-to-Root

The lead (pronounced "leed") is the distance that a threaded part (such as a nut) would move or travel in the horizontal direction if the screw thread was rotated 360 degrees.

Threads are always assumed to be right handed threads unless marked with the initials LH (Left Hand) at the end of the thread note.

 Most screws have single threads. Single Thread - The lead is equal to the pitch. Double Thread - The lead is twice the pitch Triple Thread - The lead is three times the

pitch.

Screws of the same diameter are made with different pitches (number of threads per inch) for different uses. The various combinations of diameter and pitch have been grouped into screw-thread series. These series are listed in ANSI B1.1. Each is denoted by letter symbols, as follows:

Coarse-thread Series (UNC or NC) In this series the pitch for each diameter is relatively large. This series is used for screws, bolts, and nuts produced in quantity, and also for fastening in general.

Fine-thread Series (UNF or NF) In this series, the pitch for each diameter is smaller (there are more threads per inch) than in the coarse- thread series. This series is used where a finer thread is needed, as in making automobiles and airplanes.

Extra-fine-thread Series (UNEF or NEF) In this series, the pitch is even smaller than in the fine-thread series. This series is used where the thread depth must be very small, as on aircraft gear or thin-walled tubes.

Screw threads are also divided into screw thread classes based on their tolerances (amount of size different from exact size) and allowances (how loosely or tightly they fit their mating parts). You can get exactly the screw thread you need by choosing both a series and a class. In brief, the classes for Unified threads are:

Class 1 has a large allowance (loose fit). They are used on parts that must be put together or taken apart quickly and easily.

Class 2 is the thread standards most used for general purposes, such as for bolts, screws, nuts, and similar threaded items.

Class 3 has stricter standards for fit and tolerance than the others. They are used where thread size must be more exact. Simply, a tighter fitting thread.

The letter “A” following the fit class number (1,2, or 3) denotes external threads only; the letter “B” following the fit class number denotes internal threads only.

Thread Note Definition of Meaning.750 0.750 diameter (3/4”)10 10 threads per inchUNC Unified National

Coarse thread series  

2 Class 2 (Normal Fit)A External Thread

You specify (call for) a particular screw thread by telling its diameter (nominal or major diameter), number of threads per inch, length of thread, initial letters of the series, and class of fit. Any thread you specify will be assumed to be both single and right hand unless you say otherwise. If you mean the thread to be left hand, include the letters “LH” after the class symbol. If you mean it to be double or triple, include "double" or "triple." Some examples using fractional sizes follow:

1 1/4-7UNC-1A means. ………… 1 ¼” diameter, 7 threads per inch, Unified National Course threads, class 1 fit, external threads.

7/8-14UNF-2B means……….….. 7/8” diameter, 14 threads per inch, Unified National Fine threads, class 2 fit, internal threads.

1 5/8-18UNEF-3B-LH means …. 1 5/8” diameter, 18 threads per inch, Unified National Extra-Fine threads, class 3 fit, internal, left hand threads.

You specify tapped (threaded) holes by a note giving the diameter of the tap drill (21/64"); depth of hole (1 3/8”); thread information (½” diameter, Unified National Course threads, Class 2); and length of thread (1"), as:

A detailed representation approximates the real look of threads (Fig. 10-10). For this kind of drawing, you do not have to draw the pitch exactly to scale. Instead, just make it about the right size for the drawing. Draw the helixes as straight lines. Draw the threads as sharp Vs. In general, you do not usually use the detailed representation in working drawings, except where you need it for clearness. You also do not usually use it if the screw is less than 25 mm (1 in.) in diameter.

A schematic representation shows the threads with symbols rather than as they really look. For this kind of drawing, you leave out the Vs (Fig. 10-11).You also need not draw the pitch to scale. Just make it about the right size for the drawing. Then draw the crest and root lines accordingly. Space them by eye to make them look good. These lines can be at right angles to the axis or slanted to show the helix angle (see Fig. 10-17). The American National Standards calls for crest lines to be thin and root lines to be thick. However, you may make all your lines the same thickness to save time. This is especially so on regular pencil working drawings.

A simplified representation is much like a schematic representation. In this case, however, you draw the crest and root lines as dotted lines, except where either of them would show as a visible solid line (Fig. 10-12 at A, C, F, G, H, I, and J). You save time by using the simplified representation because it leaves out useless details.