sheetmetal hints creo2

8/20/2019 Sheetmetal Hints Creo2

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1B Integrated Design Project

Hints on the use of Creo for

Sheet Metal Design

1 PhilosophyAs was demonstrated in the final CAD sessions of part 1A, Creo has an application

dedicated to sheet metal components, with the ability to flip between the folded componentand the flat pattern (usually referred to as the development) as cut out prior to bending. Mostmodern cutting machines, whether using punches, laser beams or water ets, can accept D!"files, as produced by many CAD pac#ages, as the main instruction input, thus ma#ing savingsof time and effort while decreasing opportunities for error.

$he following notes are a guide to the use of Creo in the %D&. 'hilst modelling yourdesign does reuire some investment of time, it will more than repay this when cutting out andmodifying your chassis and other components as well as providing the power to chec# forinterferences and to animate mechanisms.

As designers, it is important to remember that the primary purpose of producing a drawingor a model is to provide a statement of your reuirement. 'hilst a good designer will designfor a method of manufacture, the role of a drawing as a set of manufacturing instructions issecondary, in that manufacturing processes evolve and s#illed technicians will have their owntechniues. 'hen modelling a folded sheet metal component, your reuirement is for the fullyfolded item and so this is what should be modelled. $he power of Creo can then be employed

to derive the flat development for cutting out and subseuent bending.

Example - Production of a simple bracket.aunch Creo in the normal way, start a new model and immediately change the *+ub

$ype-to Sheetmetal. ote that the ribbon at the top of the screen has different icons to thesolid modeller. /ntil a first wall is present the only icons highlighted as available are labelled

“Extrude” and “Planar”. &lanar allows the modelling of a flat panel, of any shape, whichmay be subseuently bent up. $his would, however, be contrary to the stated principle of*draw the reuirement- as it would not afford control of the final dimensions of the foldedcomponent. Any changes to the material thic#ness or bend allowance would cause variations tooverall dimensions.

/sing the option of “Extrude” allows the bent component to be drawn and final, overalldimensions to be fi0ed. +elect this icon and remember that it is the edge view of thecomponent being drawn, complete with bends of suitable radii. $he following diagram showsthe creation of a *- brac#et. ote that the use of *internal- s#etches is recommended 2 ust

press 3M4 and select from the menu that appears. 5r simply select a s#etch plane.

+.&.$ebboth August 6716


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ote that the s#etch consists of a single line which is “Thickened” on the dashboardafter leaving the s#etcher. Direction of thic#ening and material thic#ness and bend radiican be selected on the dashboard. ote that bend radii do not, now, need to be s#etched but

can be specified under the *Options” menu.$he s#etch can now be accepted by clic#ing on the tic# icon and with a blind e0trusion

depth specified the folded brac#et produced as shown below.

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2 Starting the Chassis

'hilst comple0 parts can be built up by creating an unattached wall and subseuentlyattaching e0tra features to it, it is usually uic#er and simpler to start off with a solide0trusion when designing something li#e a chassis with multiple bends.$he recommended procedure is described below, using an e0ample to illustrate the variousstages.

2.1 Shelling from solid model

Draw your chassis design in the standard Creo modeller as a solid *bric#- 2 see "igure 1.3emember to ma#e sensible choices of datum plane positions 2 you will be pleased you

did later. +elect, under *5&83A$%5+-, the convert to sheet metal option and from the

menu that appears choose shell.

%t is now necessary to select which faces of the solid will be removed, bearing in

mind that one piece of material from the flat pattern cannot be in two places at once. 5ncesurface choices are complete you will be as#ed for the material thic#ness. $he sheet steelused for %D& construction is 7.9mm. "igure 6 shows the resulting shell.

"igure 1

"igure 6

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2.2.( !elief %n "igure < a typical flat pattern is shown. ote that as no corner relief was selected

then sharp darts are cut into the start of the bend, resulting in a high rate of material

deformation in this corner. Although, for the thin material being used, this is acceptable,the ease of bending will be improved by removing some material from this area.

Choose the Smt 'onversion from the family tree and, on the 3M4 menu select

“Edit $efinition” to redisplay the dialogue bo0 shown above in "igure :. ?ighlight the

righthand icon and see the effect of choosing one of the options shown in "igure =.3ecommended dimensions are shown.

"igure =

Another nicety is illustrated in "igure 9 where part of a sheet is to be bent down and part not. Although &ro8 does offer bend relief for such instances, cutting machines cannot produce slits of @ero width. %t is, therefore, suggested that a cut is inserted which goes ust beyond the bend area, terminating in a full radius, as shown.

"igure 9

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2.! "amily #a$le

%t is vital to define a "amily $able for all folded components as they will be

reuired in both bent and flat forms in drawings, and in the folded form in assemblymodels. $he family table should be started as soon as possible so that the correct instance

can be inserted. "rom the $55+ menu select &amil+ Table and the following bo0

appears

+elect the *Add a Column- iconand the dialogue bo0 shown appears;

?ighlight &eature under *Add %tem-and select the "lat &attern so that the

form loo#s as the one depicted.

Accept selections with 5.

3eturning to the "amily $able window will show it to be partially filled in.

+electing the *Add a row- icon allows a further instance to be added.

+uggest it be called *chassisBfolded-. ote that the generic will have the flat pattern turned on and the folded instance must have it turned off. %t is also useful to have afurther instance of your chassis in the flattened state so adding a further instance will resultin the "amily $able shown below.

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"rom now on, whenever this model is inserted into anassembly or a drawing you will be as#ed which instance

you reuire. (Always choose the generic from the list of

files in the ,orkin" director+ and choose the instancefrom the secondary dialogue bo0 that appears, as shown

opposite). ever put the generic model away with the"lat &attern feature suppressed as this causes trouble with

references in assemblies and drawings.

.#. $o a &amil+ Table before insertin" the model into either an

assembl+ or a dra,in"

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% &oling the Design

+hould the structure of the chassis need modifying, during the design process, then thereare several techniues to choose from.

%.1 Simple Modification of Dimensions

$o modify the overall si@e of the chassis one can return to the original solid e0trusion. $oincrease, for e0ample, the overall length of the chassis is straightforward. +elect the

original e0trusion from the Model $ree and on the 3M4 menu select Edit $efinition. $herelevant dimensions can now be simply altered, although care must be ta#en that other

features such as holes are still in the desired position. +ee below.

?owever the same approach cannot be used if it is reuired to increase the depth of thes#irt. $his cannot be achieved all round the chassis, as the tabs bent down in the central

portion must remain narrower than the slots from which they are cut. $herefore the originale0trusion cannot simply undergo a dimension modification but must be 3edefined toinclude a cut giving a step in depth around the problem area. $his creates more surfacesand so the "irst 'all feature must be redefined to produce the desired shell. $his, in turn,means that the +M$ Conversion feature may need redefinition to reestablish the rips and

bends and to achieve this any corner reliefs must be temporarily removed as theirreferences will go missing in the process. $his is, clearly, too complicated and so it isrecommended that 3edefinition of the original feature is avoided and simpler techniuesapplied.

%.2 Modification of 'alls

The most useful tools are given by the two icons below.

'reate &lat /all

'reate &lan"e /all

*"lat- wall simply means that the shape is defined by s#etching on the flat face, it maystill be attached to the e0isting wall via a single bend of any angle.

*"lange- wall is effectively the same as *e0truded- and means that the s#etch is

edgewise on, therefore comple0 bend profiles may be defined although they must beconstant over the length of attachment. $his command allows attachment to curved edges.4oth of these commands operate with a dashboard type display of parameters to be

defined, with the provisional wall shown in limegreen so that the effect of any alterationscan be seen graphically before being committed to.

4oth have the facility for calling up standard shapes whose dimensions can beedited on a simple graphic menu, or to be userdefined by entering the s#etcher.

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%.% (on)uniform &*tension of 'alls$o e0tend walls by an amount varying over the length of the edge in uestion,

choose the 'reate &lat /all icon. $he following dashboard appears.

&ic# the edge to attach to and set the shape to !ectan"le as well as the angle to &lat./nder the +?A&8 tab a simplified s#etch can be displayed and edited as shown below ;

ote that the effect of changes can be seen *live- in the yellow rendered wall in themain window. $he e0ample shown is a simple rectangular addition over the length of theattachment edge minus 1=mmE observe that the first time the number 1= is entered a minus

sign must be used. 3eadymade shapes available for this feature include *Trape0oid-, *1-

and *T- while any flat shape can be defined by entering the s#etcher with the “Sketch...” button.

%.( )n )lternative )pproach$o change the shape of a wall the alternative would be to cut a larger than needed

wall down to that reuired. $o effect this, select the “Extrude” icon and choose the id&lane as the +#etch &lane. 3emember that the removed material must be defined by a*closed section- in other words the s#etch must be a oined up shape. 5nce the material to

be removed is defined and the s#etcher e0ited then the e0trusion depth should be definedas *$hrough All- and under the *5ptions- pulldown +ide 6 should also be set to *$hroughAll-.

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%.3 )ddin" /alls ,ith #ends$his command also allows walls to be attached via a bend, by selecting the reuired

angle in the field that had been set to &lat above.%n the e0ample below, a bo0 with > sides bent up has a further return added. As we

reuire to ma#e this addition to all > sides, the shape will be trape@oidal, with >


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%.+ Copying of "eatures

$o repeat the feature on all > walls the *copy and paste- method can be used.

?ighlight the feature to be copied and under the 8D%$ menu select 'op+. $he Paste and

Paste Special commands are now available.

Paste allows an independent copy to becreated on any selected edge. ?owever, in this case

it would be preferable to have dependent copies,i.e. copies which change to match alterations made

to the original feature.

$herefore select Paste Special andin the dialogue bo0 which appears (seeopposite) tic# the bo0 for dependency asshown.

5ing this causes the dashboard toappear and it simply remains to select theattachment edge reuired for the copy.

8nsure that if the e0ternal edge wasselected for the original then the same isselected here and viceversa.

ote that the *clipboard- is nowempty and that further pasting operationsreuire the master feature to behighlighted and copied each time.3epeating the procedure for each wall produces the structure shown below;

%f the dimensions of the original trape@oidal wall are now varied then the copieswill change as well. %f, however, a difference was reuired then any dependent feature can

always be made retrospectively independent by highlighting it and using the ake Sec

4ndep option from the 3M4 menu. ote that, in this case, the new walls all e0tend over the entire length of their

attachment edges despite being of differing lengths. $his is because they are defined asdoing this. %f the original feature had been s#etched and had been defined with all finitedimensions rather than attached to ends of e0isting entities, then some modification ofcopies might have been necessary to achieve the desired result.

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%., #a$s -euiring Bend -elief

%n our e0ample, it is desired to stiffen the chassis by e0tending the side walls intotabs to be bent round and popriveted to the end walls, as below.

$he neatest result is obtained by folding the tabs behind the adacent end wall. $his

can be achieved with the same “'reate &lat /all” command which will ensure correct,flush alignment of surfaces automatically.

8nter the dashboard for this command as before, highlight the attachment edge (itis suggested that a consistent choice of outside edge is chosen) and define the shape. Anice little wrin#le is to use a trape@oid with a very slight angle (e.g. 6 degrees) to provideclearance from the top edge and from the bend at the base, in case the bending is not uite177G accurate.

At the bottom corner of the tab, where its bend meets the bend between base andside wall, there is a region of infinite

deformation. $his must be resolved bysome sort of relief and the default (setunder the dashboard heading 38%8")is asimple rip, giving the effect shown

highlighted opposite.$his is actually undesirable, as it would

be both difficult to bend and would leavea dangerous sharp corner.

%nstead some material would be removed from this area to avoid the situation altogether.Although there are bend reliefs available from the dashboard defining the wall in uestion,these do not wor# very well when adacent to other bends (their purpose is to lie between

bent material and flat material, as shown later).$here are 6 recommended methods to resolve this;

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- 5sin" ori"inal 'orner !elief

3eturn to the +M$ Conversion feature and edit its definition.

+elect 'orner !eliefs from the +M$ Conversion definition and then select

'ircular. Choose Enter 6alue and set diameter to


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relief). $his is because the cuts cannot be computed until the fabrication is flat and, at themoment, the "lat &attern feature is the first time that the sheet has been flat.

$o observe the effect in the foldedup model, it is necessary to insert two featuresinto the model tree.

"irst the 5nbend feature, using the icon shown.

"ollow this with the #end #ack feature, using this icon."or both of these features a surface or edge must be selected to stay

fi0ed,(ma#e it the same reference for both features) and the options; 5nbend )ll and #end#ack )ll should be chosen. ow, if the "lat &attern is suppressed, the folded corner loo#sli#e this;

ote that the regions of bent metal are separated by the circular relief.

2 - 5sin" relief added b+ hand in the unbent state

$he method above does result in uite a large hole in the corner but it is possible toremove the minimum amount of material if done manually. Add an 5nbend feature asabove and e0amine the flattened corner detail as e0ample below.

A sheet metal cut can be inserted into the flattened material to remove the line

shown, where two bent regions meet.

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$he first s#etch shown below removes a triangle, whereas the second removes acircle attached to points at the unctions of the bend @ones (diameter comes out at about:.>). ote that in both cases there are no dimensions because e0isting features are used for

all definitions. 7*int8 4n the sketcher9 add % points first.:

$heir effects in the folded state are shown below.

$he cut feature can be mirrored onto the opposite corner by selecting it (either from

the model or the tree) and choose irror .

A mini dashboard appears, on which the only item which must be filled in is the mirror

plane selection.$o mirror onto the bac# corners a datum plane could be inserted halfway down the

chassis. Alternatively either 6 or all > corners could be cut on the same s#etch.

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+elect 'reate &lat /all icon and pic# edge of cut for attachment as shown. Defineshape, angle and bend radius.

$his case is where the inbuilt relief options are particularly useful. 5pen the 38%8"menu from the dashboard;

%t is recommended that the options shownopposite are used

eave both sides the same

Choose Obround.

+elect *Tan to #end- as the length. +elect *Thickness x 2- as the width.

ote that the material removed is from thesurrounding flat area 2 the tab width isunaffected. $herefore the width of the originalcut must be the tab plus two desired reliefs.

$hese choices result in a flat pattern that is both easy to cut and to bend

andwhich produces the result pictured

opposite.$his feature can now be copied to

the other cut using the *Copy H &aste-method previously described. 3emember to

use *Paste Special- to ma#e the copy

dependant. ote that using the mirrorfunction on this feature does not produce the simple result e0pected and is unnecessary if

the tab is, itself, symmetrical.Cuts can be added to these walls, noting that if M%D datum plane is selected as the

s#etching plane then *Throu"h )ll- produces the result below. 3eference the cuts toD$M6 hori@ontally and surface of chassis vertically.

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+hould the model need modifying then the position of the whole feature can becontrolled with the dimension to D$M6 and the width of spacing by the depth of originalcuts. $he width of brac#ets is controlled by the width of original cuts and the height of

brac#ets by the brac#et definition. $he cuts and the holes should always remainsymmetrical to D$M6 as this is how they were originally defined..

4t is al,a+s a "ood idea to spend a little time considerin" ho, to define positions and,hat datums to refer dimensions to in order to simplif+ subse;uent modification.

%. Create "lange 3all

All the above modifications and additions have used the 'reate &lat /all function. ?owever, occasionally, it is useful to be able to create an e0tra wall bys#etching on its edge and then e0truding the profile, as, for e0ample, when multiple bendsare reuired.

$o create an integral sensor brac#et, for e0ample, the dashboard shown below isentered by selecting the icon

+elect the desired attachment edge for Placement9 under Profile go to the 5ser

$efined option and enter the s#etcher (s#etching on the M%D datum plane), specify the

length as symmetrical about the s#etch plane.

5ther possibilities offered by this command include the ability to attach to a curvededge but to manufacture this type of feature would reuire more sophisticated formingeuipment than is available. Also, under the standard profiles are included various types of*safety edge- where material is folded to avoid sharp edges, but these are not consideredrelevant to the %D&.

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Part ! ) 4utput 5 Dra'ings and D6"7s

Drawings must be produced to gain Design Approval. $he reuirements are;1. A general assembly drawing together with enough prints of rendered models to convey

the operating principles of the design.6. Dimensioned drawings for all components to be manufactured. %n the case of the chassis

and other sheet metal parts these should comprise views of both the folded form and theflat pattern.

!.1 Dra'ings+tart a new drawing and select *Empt+ ,ith &ormat-, browsing for a suitable

C/8D border. 'hen in the drawing, add both *generic- and *foldedinstances of the

model 2 from 3M4 menu choose Properties and then $ra,in" odels. +elect )dd

odel from the D3A'%I M5D8+ menu and insert chassis model twice, once in each

instance. /se Set odel from the D3A'%I M5D8+ menu to determine whichinstance views are added from.

As most features have been defined in the folded state, it is best to dimension these

in the folded views.5verall dimensions and the positions of the main groups of holes should be shown.

%t is necessary to display centrelines by selecting them from the dialogue bo0 accessed viathe icon shown.

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$he dialogue shown now appears and therighthand tab will display centrelines once theview(s) reuired have been highlighted.

5nce the centrelines are displayed manualdimensioning is much simpler as the centrelineitself may be used as a reference. Automaticdimensioning does not really wor# with sheet metal,so it is recommended that dimensions are inserted

manually by selecting the icon shown.

$he bo0 shown is displayed at this point and as a default the option*5n 8ntity- should be selected,although other options allow for thecentre of circles or radii to be usedetc.

%t is not necessary to

dimension every last hole as this information is contained in the D!" file.%t is permissible to use a note about symmetry to minimi@e the number of

dimensions, provided the intention is unambiguous. ote that, with sheetmetal, it is not possible to rely upon the automatic dimensioning provided

by &ro8 and it is recommended to insert dimensions manually.%t is still necessary to produce flat views (from the flat instance of the model) but

the only features which must be dimensioned on these are the bend lines (which must bescribed by hand in the wor#shop later).%t is acceptable to dimension to one side or the other

of bends or even to their centre line, provided that dimensions appear stating therelationship between these. +uch dimensions may be shown once as *$J&%CA- as in thee0ample below.

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3emember to alter any of the properties of a view, ?ighlight that view and on the3M4 menu select *&roperties-.

$his will bring the dialogue bo0 shown up.$he most useful page being *Kiew Display-

which allows the display of a view to be loc#ed intoa line drawing mode, either *?idden- or *o?idden- line display.

!.2 D6"$he cutting machine reuires a D!" file to

be produced. +tart a new drawing file, choosing

Empt+ ,ith &ormat, and select the format * 1bBsteelB>


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3 )ssembl+ odellin"

3. Parts 1ibrar+%t is strongly recommended that the entire assembly is modelled before gaining

design approval and starting manufacture. $o help with this, models of the standardcomponent parts have been placed in the MD& library. $his is accessed, from the *5pen"ile- dialogue bo0, by changing directory to C/8D ibrary and then selecting mdpBlib.$he library structure is shown below and it will be found that each section has adescription of the contents.

/se the &review facility offered by &ro8 to see the file before opening it. ote thatsome of the items have been preassembled to save time. Also note that the gears areshown as smooth drums of the pitchcirclediameter. $o mesh the gears ensure that thesecircles are ust touching. ?owever to chec# the overall space envelope reuired by a gear,

Suppress the final cut and a new outer surface (coloured yellow) will be revealed.

'hen building up a large assembly, it is much easier to use subassemblies, ratherthan bringing loads of individual components into the toplevel model. "or instance;assemble the motor, shaft e0tension and wheel (already done in the library), together with asuitable brac#et of your own devising, into a driveunit assembly before inserting this intothe overall robot, thus saving having to do everything twice and minimising the number ofdatum features that need to be displayed when positioning things.

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8.2 Standard Bracets and other materials%n addition to the chassis, there will, probably, be a reuirement for au0iliary

brac#ets formed from sheet metal. $o save time, a small library of standard brac#ets has been compiled, which can be modified to individual reuirements. ote that fromwherever library files are obtained, they are #ept as readonly. %t will be necessary to save arenamed copy to allow modification. $he types of brac#ets offered are shown below.

$here are also short lengths of the bar and angle materials which may be usedsimilarly.

8.% 0ssem$ly #ips'hen placing parts in an assembly model, remember that when one or two

constraints have been made then the part may be moved by hand (in the remaining degreesof freedom only) by holding Ctrl H Alt while using the MM4 for rotation and the 3M4 fortranslation. $here is nothing wrong with leaving a component partially constrained whileother parts and features are arranged.

%f it is reuired to add a mounting hole to match a placed component, this can bedone from within the assembly model by using the *Activate- facility. A typical proceduremight be

%nsert a component into the assembly and place #nown constraints upon it. (e.g.;mounting surfaces and orientation of faces and edges).

&osition the component by hand to roughly the right position in remaining plane(s).

Activate the model to be cut (highlight and 3M4 menu). 5bserve little green diamond.

Cut a hole to match that in placed component, possibly using concentric circles.

&lace dimensions on cuts using references in chassis model alone. 3esolve redundantdimensions and constraints as prompted (by deleting coincidences).

$wea# dimensions to round numbers as reuired.

Accept cut feature if satisfactory.

3eActivate assembly model (highlight top level of model tree and use 3M4 menu).

3eturn to definition of placement of partially constrained component and add constraintaligning mounting holes.

*o,ever9 this techni;ue is not suitable for use ,ith instances of famil+ tables.

4f it is used to place holes in the folded instance of a chassis then all sorts of problems

,ill be experienced ,hen the "eneric model is examined9 from suppression of features

to lost references.

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A safer method for folded components is to insert the mounting holes into thegeneric model without worrying about their e0act placement and then editing them in theassembly to bring them to the desired position.

$he procedure is, therefore, amended as follows;

%nsert appro0imate mounting features into chassis model.

%nsert a component into the assembly and place #nown constraints upon it. (e.g.;mounting surfaces and orientation of faces and edges).

&osition the component by hand to roughly the right position in remaining plane(s). 8dit holes to match those in placed component.

$wea# dimensions to round numbers as reuired.

3eturn to definition of placement of partially constrained component and addconstraints aligning mounting holes.

8.! Mechanisms

'hen assembling the elements of a mechanism 'onnections dashboard is used,

rather than the static 'onstraints. $he model can rapidly become overcomplicated unlesssome simple golden rules are observed.

'hen placing an item use either 'onstraints or 'onnections page of dashboard, never both at the same time.

+ee# to minimi@e the number of connections used to describe a mechanism.

Avoid placing individual components into a dynamic assembly. 4uild up subassembliesof components which are statically fi0ed to each other and then combine these withdynamic connections in a higher level assembly which defines the mechanism.

%n the e0ample shown below, a lifting arm is mounted on the chassis and driven bya pneumatic cylinder.

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$he recommended approach is 1. 4uild up the chassis assembly, with relevant mounting brac#ets.6. Create the lifting arm assembly (by attaching component parts with static constraints).:. +tart a new assembly and insert chassis, fi0ed to main assembly frame of reference by

using default location button on right hand side of constraints dialogue bo0.

>. %nsert lifting arm assembly by selecting the dynamic connections dialogue and using a

Pin oint.


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Inde*

"/C$%5 38"838C8 5$8+

2 - =ettin" Started+tarting with +olid Model

6.18ntering sheet metal application

and creating shell

+M$ Conversion 6.6 Defining sheet metal features

3ipping 6.6.1 Deciding which edges arediscontinuous and which bent

4end Definition6.6.6

Kalues of bend radii for materialsused in %D&

"lat &attern6.6.:

Development of model as cutfrom sheet, before being bent

3eliefs6.6.>

Adding corner reliefs and slotsfor ease of manufacture

Adding ?oles and Cutouts 6.: /se of "latL"olded models

"amily $able

6.>

Allowing flat and foldedinstances to be used

independently

% - odification Techni;ues+imple Modification of

Dimensions :.1Modification of original

e0trusion H pitfallsModification of 'alls

:.680tends wall uniformly over

entire length of edge

on/niform e0tension of'alls :.:

Allows e0tension over part ofedge and to varying lengths

Adding 'alls with 4ends :.> Attaching new bent wallAn Alternative Approach

:.<

Cutting away unwanted material

Copying:.=

Adding multiple new features by*copy and paste- method

$abs 3euiring 4end 3elief

:.9

Adding e0tra folded tabs andmanaging relief of material in

corners

4ent $abs from "lat4ac#ground :.

Adding bent walls to flatmaterial, including relief

Create "lange 'all:.

80trusion of wall with severalintegral bends

( - OutputDrawings >.1 Drawings and Dimensioning

D!" >.6 &roducing files for cutting

3 - )ssembl+Component ibrary

sheetmetal hints creo2

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