Cover story: Focus on Cadcam and simulation Parametric die

The automotive industryshares a common goal toreduce new car develop-

ment cycles from 48 - 60 monthsto only 24 months. To helpachieve such a drastic reductionin “time-to-market”, companieshave focused on cutting toolingdevelopment time, which repre-sents a large share of the totalproduct development cycle.

Draw-die development – the cre-ation of binder and addendum sur-face geometry for sheet-metal parts– has represented a particularlydifficult challenge for automotivemanufacturers and suppliers toreduce lead-time and tooling costs.

Over the past year, 20 automo-tive manufacturers and 20 leadingtooling suppliers in Europe, NorthAmerica and Asia have all imple-mented a new software to addressthis problem (see Figure 1).

TRADITIONAL BINDER AND

ADDENDUM DESIGN PROBLEMS

Once the product design depart-ment finalises the design of a newsheet metal part, for example adeck-lid, fender, bracket or cross-member, it is released to the feasi-bility and tooling departmentswho must then design an appro-priate stamping die to fabricatethe part.

The traditional approach is formethods engineers and die design-ers to create or “build” therequired binder and addendumsurfaces in a CAD system.However, this method has threedisadvantages:

1. Long lead time

Designing die faces in a conven-

Cover story: Focus on Cadcam and simulation

for small parts and structural com-ponents, several days are required.

2. High cost

Design modifications are expensiveto make in a CAD system.

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International Sheet Metal Review September/October 2001 29

Parametric die faces in one hour

tional CAD system is very time-consuming. For typical automotiveskin panels and large inner panels,the average time required to com-plete a draw-die developmentranges between 1-2 weeks. Even

How 20 auto

manufacturers and 20

tooling suppliers are

reducing die design costs

through automated

software tools

Audi

BMW

DaimlerChrysler

Fiat

Ford

General Motors

Honda

Iveco

Mitisubishi

Nisssan

Opel

PSA Peugeot Citroën

Renault

Saab

Scania

Skoda

Subaru

Volvo

VW

Germany

Germany

USA, Germany

Italy

USA Turkey

USA

USA

Italy

Japan

Japan

Germany

France

France

Sweden

Sweden

Czech Republic

Japan

Sweden

Germany

Batz

Comau (UTS)

Christy Industries

EDAG

Gestamp

Karmann

Krupp Drauz

Kuka Werkzeugbau

Laepple

Mayflower

Ogihara

PCI

SAT (Stola)

Schuler

Superior Cam

Swindon Pressings

Tecnisabadell

Thyssen Nothelfer

Tower Meleghy

Troy Design & Mfg

Spain

Italy

USA

Germany

Spain

Germany

Germany

Germany

Germany

UK

USA

France

Italy

Germany

USA

UK

Spain

Germany

Germany

USA

AUTO MANUFACTURERS TOOLING SUPPLIERS

Figure 1: 40

automotive and

tooling companies

engaged in driving

down lead times

and reducing cost

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Successful draw-die developmentsrequire the expertise of die designersand methods engineers with manyyears of practical experience andgood CAD skills. Almost always,they make several iterations of designmodifications before finalising a goodstamping die (e.g. changing radii,adjusting drawbars). However, mak-ing such design modifications in ageneral purpose CAD system is cum-bersome and slow. Mistakes, modifi-cations, and especially the design ofdifferent “what-if” concepts for thebinder and addendum, are costly.

Furthermore, when time runs outdue to production deadlines, compa-nies are forced to carry out toolingtry-outs in the press, which is evenmore costly.

3. Low throughput

With a manual, CAD-basedapproach, the die designer must waituntil the die surfaces are completed –several days or weeks – before carry-ing out virtual try-out simulations tocheck his designs for cracks, wrinklesand other stamping criteria. It is farmore productive and cost-effective ifthe die designer immediately triesout his die concepts, discards unfeasi-ble designs early on, and concen-trates on further developing only hisbest design(s).

As a result of these drawbacks, sev-eral automotive companies partici-pated in a program to develop a faster,more efficient and less costly methodfor die face design.

PARAMETRIC AND FULLY

INTEGRATED SOFTWARE

AutoForm-DieDesigner software isthe result of a development effortled by AutoForm EngineeringGmbH (developers of sheet metalforming software) in cooperationwith tooling departments at BMWand Audi, and with technical feed-back from DaimlerChrysler andGeneral Motors.

The software reduces toolingdevelopment time through rapidparametric design of die faces, andtheir immediate verification andoptimisation with integrated stamp-ing simulation modules.

It is specialised for generatingbinder and addendum surfaces, and

for evaluating the feasibility of draw-die developments and prototypetools. Its three most important inno-vations are:• Fully parametric features,• Complete integration with virtual

try-out software modules, and• An automatic optimiser.

The software’s parametricapproach is based on analytical engi-neering principles. It also conforms tothe die engineering practice of usingsurface profiles (arcs and angles) todesign die faces and is compatiblewith various CAD data formats.

DIE FACES COMPLETE DRAW-DIE

DEVELOPMENTS IN ONE HOUR

Using the software, it takes about onehour to design the complete die facesstarting from only the CAD surfacedata of the part. This includes the fol-lowing steps:

30 September/October 2001 International Sheet Metal Review

• Determination of tip-angle• Filleting of sharp edges

(variable radii)• Filling of holes• Part modifications (morphing)• Design of the fill surface between

double-attached parts• Over-crowning• Binder design• Design of outer (and if required,

inner) addendum• Unfolding of flanges • Generation of the tools

As all the generated die surfacesare parametric, subsequent modifica-tions (die engineering changes) areimplemented in seconds. These diesurfaces and simulation results caneasily be exported using IGES,VDAFS or mesh formats to othersoftware applications, e.g. pattern-making, structural/crash analysismodules, etc.

The software reduces tooling developmenttime through rapid parametric design ofdie faces, and their immediate verificationand optimisation with integrated stampingsimulation modules.

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Dr. Volker Steininger and

Dr. Vallury PrabhakarAUTHORS:


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EASY PART DESIGN

MODIFICATIONS

As almost all part designs are sub-ject to revisions and improve-ments even after they have been“officially released” to the diedesign department, the softwareallows for this.

After the parameterised binderand addendum have been createdfor a specific part, one can thenreplace that part with another (sim-ilar) part designwith a modifieddesign and the software will auto-matically adjust the binder andaddendum accordingly.

This is an important time-sav-ing feature as it allows the originaladdendum and binder geometrythat is created, to be re-used forfuture design revisions of the part.

In addition, automatic filletingand the ability to vary fillet radiion the part geometry, saves con-siderable time and allows virtualtry-outs to be carried out earlier inthe product and tooling develop-ment cycles.

.DIRECT PARAMETRIC LINK TO

STAMPING SIMULATION

SOFTWARE

As a result of the software’s inte-grated system approach and fullparametric linking, all die facedesigns can be immediately evalu-ated with one-step or incrementalsimulation modules.

One-step simulation results areconsiderably more reliable whenbased on the complete die face – asgenerated by the software – ratherthan on the part only. An addedbenefit is that these refined resultsare made possible earlier in thedesign cycle. They are availablewithin a few minutes and includethe required blank outline and var-ious stamping feasibility criteria(see Figure 5).

The incremental module is usedfor high accuracy and virtual try-outsof the complete stamping process.Results include predictions of wrin-kles, cracks, skid and impact lines,surface quality, etc. Incremental try-out results are typically availablewithin 1 hour to 3 hours, dependingon the size and complexity of thepart and the desired accuracy.

Additional try-outs can belaunched at once because of para-metric linking. For example,based on the initial results, theuser can make modifications tothe addendum geometry, and the

various tool geometries requiredfor the next simulations are auto-matically updated. Similarly, ifthe user modifies the punch open-ing line, drawbead positions areautomatically adjusted.


Figure 2-A: The part geometry (CAD surfaces) of an Audi TT rear fender.

Figure 2-B: The initial binder surface (yellow) automatically created in a few seconds, using

only the CAD surface data in Figure 2-A as input. The user can then modify the binder

geometry with surface profiles.

DESIGN OF PARAMETRIC DIE FACES FOR AUDI TT

Figure 2-C: View of the automatically generated addendum surface (red), based on default

profiles.

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Dr. Volker Steininger, General Manager, AutoForm Engineering Deutschland GmbH

Tel +49 231 9742 320

Fax +49 231 9742 322

E-mail: [email protected]

CONTACT (EUROPE):

Figure 3-A: A typical addendum profile (red line) and its defining parameters. Within a few

seconds, the user can change these “master” global profile parameters, for example to

increase the die radius.

In addition, the user can also make local surface modifications to the addendum, by

changing local profile parameters or directly manipulating contours such as the punch

opening line, bar height, etc.

Figure 3-B: A drawbar that is created by modifying the parameters

of local addendum profiles (black).

Figure 4: The complete die face for the Audi TT rear fender, created

in about 1 hour using 28 customised surface profiles.

ONE-STEP FORMABILITY

SIMULATION Figure 5: The results of a one-step

simulation taking into account the binder

and addendum from Figure 4.

The stamping feasibility results were

calculated in 2 minutes. The colour plot

shows a summary of various stamping

feasibility criteria. The circled area on the

left shows a risk of wrinkles on the

addendum, very near to the part boundary.

The circled area on the right shows a

crack.

Based on one-step results, the general

die concept can be evaluated early in the

design cycle, and if necessary,

modifications to the part geometry can be

recommended. Furthermore, the resulting

blank outline can be used to design the

initial blank outline for an incremental

virtual try-out.


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AUTOMATIC OPTIMISATION OF

TOOLING AND STAMPING

PROCESS

To further improve the die facedesigns, the software includes anintegrated optimiser module.The user first specifies the allow-able ranges for tool geometry andstamping parameters. The opti-miser then automatically deter-mines the “best” design withinthese ranges through multipleone-step or incremental simula-tions, to achieve the target func-tion: for example, elimination ofcracks and wrinkles, uniform sur-face stretching, no excessivethinning. Tool geometry parame-ters include part, die and drawbarradii, drawbar height, wallangles, over-crown, etc.Stamping parameters includebinder forces, drawbead strength,blank outline, etc.

Benefits

Within the first year of usingAutoForm-DieDesigner, automanufacturers and tooling sup-pliers have already reported thefollowing savings:

• Reduced binder development time by 60%

• Reduction by a factor of 4-5,in the time from CAD partdesign until completed virtualtry-outs

• Reduction of die face development time from one weekdown to one day

• Almost 50% reduction inactual die try-out time andtooling costs

• Two week reduction of toolingdevelopment time, by usingthe generated die faces toorder castings for the dies.

Although it is too early toquantify all benefits, companiesalso expect improved partquality and stamping reliabilitydue to the optimisation oftheir designs. ISMR


Dr. Vallury Prabhakar, General Manager, AutoForm Engineering USA Inc.

Tel: +1 888 428-8636

Fax: +1 888 528-8636

E-mail: [email protected]

www.autoform.de

INCREMENTAL STAMPING TRY-OUT SIMULATION

Figure 6: The results of an accurate incremental try-out simulation of the complete stamping process, using the die

faces from Figure 4.

The colour plot shows the predicted thickness distribution; excessive thinning zones are in red and yellow (two

circled areas on the right). The simulation also shows wrinkles in the circled area on the left. These try-out results

were obtained in about 50 minutes.

The die designer can then make modifications to his original die concept to smooth out the wrinkles and

eliminate the cracks, for example by changing drawbar and wall heights, radii, etc. Furthermore, results such as

wrinkling, splitting, skid mark progression, etc. can be visualised at each step of the drawing process.

OPTIMISATION

Figure 7: The results of optimisation of the initial incremental try-out in Figure 6.

The two crack zones were eliminated and the wrinkling zone was minimised and moved away from the part

boundary.

Automatic optimisation can help the die designer to find the best parameters for his design. It can also help the

process engineer to determine the best stamping conditions.


CONTACT (USA):

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Cover story: Focus on Cadcam and simulation Parametric die