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Last month, we discussed a process-modeling technique commonly usedto simulate metalforming opera-

tions; we refer to this technique as theone-step method. One-step methodsare used during product developmentand process planning to assess manu-facturing feasibility.

Other techniques using incrementalsolvers (codes) also are available. Incre-mental solvers are used for detail eval-uation,with the focus primarily on thedevelopment of the tool process. Thesecodes visually display the contact of thepunch with the steel sheet at incre-mental points throughout the manu-facturing process.

Incremental analysis, inherently more sophisticated, requires more pre-processing steps and computing time

than do one-step methods. But theadvantages of incremental codes offsetthe additional time and effort required.Users can conduct a series of virtualdie tryouts using precise blank shapesand specific material properties on pro-duction-intent tooling geometry.Besides formability assessments, trim-line optimization, springback analysisand process sensitivity studies also may be carried out. Depending on process

complexity, this could take as long as aday or two, or only a few hours.

In addition to material propertiesand a defined blank, the forming punch,die cavity, pressure pad and draw beadsalso are modeled for analysis. To simplify modeling, only the surface geometry of the tooling is required. The simula-

tion software sets boundary conditionsfor the tooling surfaces so that the com-puter automatically interprets them asrigid, nondeformable bodies rather thanas thin flexible surfaces. Working withsurfaces greatly reduces preprocessingtime while increasing computationalspeeds.

Incremental solutions will display actual wrinkle shapes, sizes and loca-tion, whereas one-step codes can only identify areas that may potentially wrin-

kle. Incremental solutions also will iden-tify splitting areas while accurately pre-dicting strain, stress and thicknessdistributions.

It is generally ideal to use one-stepand incremental codes as complemen-tary tools in the die-design process.Flat-blank results from a one-step analy-sis can be used as input data for incre-mental analysis. In Fig. 1, the blank output was determined by a one-step

T O O L I N G B Y D E S I G N P E T E R U L I N T Z

Process Design: An Incremental Approach

Tooling Technology

Peter Ulintz is Advanced Product

Engineering Manager for Anchor

Manufacturing Group, Inc., Cleve-

land, OH. Having worked in the

metalforming industry since 1978,

his background includes tool and

die making, tool engineering, engi-

neering management, advanced

process planning and product

development. Ulintz has been

speaking at PMA seminars,

symposiums and roundtables

since 1996, focusing on tool and

die technology, deep-draw stamp-

ing, metalforming simulation and

metalforming problem solving. His

published technical works include

a computer-assisted deep-drawing

method and metalforming-simula-

tion case studies.

Peter Ulintz

pete.ulintz@toolingbydesign.com

www.toolingbydesign.com

Peter Ulintz presents “Com-

puter-Based Metalforming

Simulation” at PMA’s Design-

ing and Building Stamping

Dies seminar on December 5-6

in Nashville, TN.

Check www.metalforming.com

for this and other seminars.

Fig. 1—Blank, punch, die and pressure-pad models.

56 METALFORMING / NOVEMBER 2006 www .m e t a l f o rm i n gm a g a z i n e . c om

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solution; you may recognize this blank (in red) from last month’s column.

In addition to the blank and pro-gressive-die carrier, the forming punch,die cavity and draw pad also are mod-eled. When a draw pad (blankholder) ismodeled, the quantity, location and

pressure profiles of the nitrogen cylin-ders also are specified. Including pres-sure profiles, which describe the rela-tionship between the rises in gaspressure vs. cylinder stroking distance,provides realistic evaluation of theprocess mechanics.

Unlike the one-step codes, incre-mental codes are not restricted to a sin-gle forming operation. It is thereforecommon to model all the forming oper-ations using incremental codes, as Fig.

2 illustrates. Modeling all the processsteps allows strains generated in previ-ous forming operations to be carriedover to subsequent operations. This isparticularly important because strainhistory plays an important role inaccurate formability and springback prediction.

Perhaps the greatest advantage incre-mental codes offer is the ability to seethe blank deform in small incrementalsteps in a “see-through” die. How often

have you encountered a problem with a

tool in the press shop and tried to watchwhat happens as you slowly inch theslide down? Eventually, you lose sight of what’s happening as the die closes.Wouldn’t you have a better opportuni-ty to solve the problem if you couldsee exactly what was happening inside of 

the die? Incremental codes allow us todo just that, making this technology valuable in troubleshooting press-shopproblems as well.

My last four columns have focusedprimarily on process-modeling tech-niques in general, and metalformingsimulation in particular, and for very good reasons. External pressures toreduce lead time and lower die costs,coupled with internal pressures to winmore business and avoid costly mis-

takes, require the use of these science-based engineering methods. To remaincompetitive, science-based die engi-neering is rapidly replacing traditionalexperienced-based engineering in dieshops and press shops around the world.

Are you still relying on experienced-based engineering methods? If so, and your next job requires forming partsfrom an unfamiliar material or devel-oping a complex forming operation, your next experience may be a costly 

one. MF

Fig. 2—Incremental analysis conducted from blank to finished part.

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