Principles of Design for Laminated Tooling

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Principles of design for laminated tooling

P. M. DICK ENS

Th e emergence of ra pid pr ot otyping over the last 7 8 years ha s ha d a revolu-tiona ry eect in man y companies undert aking new product design. Curr ently, t heemphasis ha s moved from rapid pr ototyping to rapid tooling. U se of laminated

to oling for sheet met al wor kin g ha s already been pr oved and som e wor k ha s alsobeen undertaken to build laminated tooling for moulding plastics. Laminated

to oling is relat ively ra re at th e mo men t and as more tools are built usin g thistechnique th e ben ets and limit at ions will beco me more clear .

1. Background

Th e emergence of rap id pro to typing over the last 78 years has had a revolu-

tionary eect in many companies undertaking new product design (Hinzmann 1995).

All these techniques manufactur e models by adding th in layers of materia l on top ofeach other, rather than using traditional techniques of material removal or material

forming (Dickens 1995). Companies are now investigating how this additive layer

technique can be used furth er do wn the develop men t rou te for the produ ction of

to olin g or even produ ction parts (Tromans and Wimpenn y 1995).Curr ently, the emphasis has moved from rapid protot yping to rapid tooling. It hasbeen recognized that there are even greater potential cost and time savings in the

to olin g area. A pro totype may cost a few tho usa nd poun ds an d take a few weeks to

manufacture. However, a tool will often cost ten or a hundred times as much and may

ta ke ten times as long to make. F or an y new prod uct, the manu factur e of prototype or

produ ction tooling is denitely on the critical pa th. If companies can make similar

cost and savings for tooling as they have already made for prototypes, then the eectwill be enormous.

2. Horizontal and vertical clamping

To ols has been manu factured for some time by adding layers of sheet steel an d

th en xing them to gether (Yokoi et al. 1984, Vouzelaud and Bagchi 1992). ProfessorNak agawa at the University of Tok yo ha s made sheet metal stamping and forming

to ols by stacking th e sheet pro les hor izontally (F ig. 1). One Japan ese company

regularly manufactures meta l forming too ls this way and so far has made 10 000 tools

(Naka gawa 1995). The laminations can be bolted together or clamped within a frame.

This technique works well for blanking tools (Schreiber and Clyens 1993) but can belimiting for forming tools. It can be very dicult to x islands within a tool cavity

without producing witness marks on products (Fig. 2). In this situation it is more

no rmal to x sheets with rivets.

Other workers (Glozer and Brevick 1992, Walczyk and Hardt 1994) have stacked

sheets vertically. It is often much easier to then clamp them together, particularly for

00207543/97 $12.00 1997 Taylor & Francis Ltd.

INT. J. PROD. RES., 1997, VOL. 35, N O. 5, 13491357

R eceived January 1996.Department of Manufacturing Engineering & Operations Management, University of

Nottingham, University Park, Nottingham NG7 2RD, UK. Tel. (0115) 9514063; Fax (0115)9514000.


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cavities (Fig. 3). The clamping arrangement may be internal as shown in Fig. 3 orexternal with a frame.

Th e distance between tie rods depends o n the size of the tool, but for mediu m size

to ols of abou t 1 m squ are a typical distance is 50 mm. This distan ce will depend also

on the geometry of the t ool. The clamping arrangements shown in F igs 2 and 3 areclassed as Level 1. It may be necessary to use a second-level clamping system where a

1350 P. M . Dickens

F igur e 1. La minated tooling for sheet met al blanking.

F igur e 2. F ixing of sheets with rivets around the per iph ery and on islands.

F igur e 3. Cla mping of vertical sheets.


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group of sheets need assembling as a un it. This may be required where design changes

are anticipated and would allow a replacement section without separating all the

sheets. A third-level clampin g system may be required for clamping sheets that have ata ll prot rusion (F ig. 4) or where shu t-o faces are poorly supported.

3. Cavity size versus sheet thickness

One main problem of designing a laminated tool is choosing the sheet thickness.Generally, thin sheets are required for small cavities. This is because the stair stepping

eect of layered sheets is much more obvious o n surfaces with small radii and thick

sheets (Fig. 5). It is possible to use ve-axis prole cutting to eliminate some stair

stepping, but there is a limit to the angle of cut possible (Fig. 6). It is not alwaysnecessar y to remove th e stair steps. F or example, vacuum forming of sheet does no t

1351Principles of design for laminated tooling

F igur e 4. Third-level clampin g for tall pr ot rusions.

F igur e 5. Comp arison of pr ole with 4 and 1 thickness sheets.

F igur e 6. F ive-axis cut pr oles with 4 thickness sheets.


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tran sfer all th e detail from the to ol to the part. Similarly, in produ cing hidden pa rts,

such as automot ive under-the-bonnet components, it may n ot be necessary to have a

good nish.

Th e th ickness tolerance of sheets, as stated by rolling mills, is propo rtionally verylarge ( 0.1 mm for 1 mm thick sheet). The cumulative eect of this on a tool with

1000 sheets could obviously be very large. In practice the actual tolerance is verymuch smaller. It is more sensible to measure the sheet thickness variation before the

CAD slicing is undertaken. The easiest solution is to slice the tool with the minimum

sheet thickness. This will then produce slightly more sheets than required. When the

to ol is th en assembled, it is necessary to simply leave ou t some sheets.

4. Sheet prole production

Th e main techniq ue for prod ucing the sheet proles is laser cutting, which can be

used for most materials and is reasonably fast. There may be a problem with edge

quality when using lasers due to o xidation and burring or because of the heat-aectedzone. In this situation it may be necessary to use water jet or abrasive water jet cutting.

These ar e slower tha n using a laser an d usua lly more expensive. Each prole must

ha ve a un ique identication number. Th is can become dicult when large tools with

several thousand sheets are involved. Th e numbering system should be logical so th at

one end of the tool begins with prole 1 and continues sequentially. Usually, eachprole is sent to the laser cutter as a separate dxf. le.

5. Conformable cooling channelsA major benet of using laminated tooling is the possibility of having much more

complicated cooling channels. In conventional tooling, the cooling channels are

usually drilled in a straight line. However, the cavity may be highly complex andcurved. In this situation some parts of t he cooling system may be much further away

from the cavity than other parts. It is possible to have slightly more complicated

cooling systems where cooling pipes are cast into aluminium tools. However, these are

still limited by the minimum bend radius of the pipework and their inability to follow

th e contou rs of the cavity. An example of th is is sho wn in F ig. 7. With conformablecooling channels (Fig. 8) it is possible to have variable cooling in dierent parts of the

to ol. This could give variable mechanical properties and could also be used to contro l

1352 P. M . Dickens

F igure 7. Co nventiona l machined coo ling cha nnels.

F igur e 8. Co nfo rma ble coo ling cha nnels.


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solidication directions. Conventional cooling channels are normally of a round

cross-section. With conformable cooling channels in laminated tooling the channels

can be of any cross-section. It is also possible to change the cross-section along the

length of the channel. However, cooling channels in laminated tooling present aproblem for watertight sealing. It is dicult to clamp sheets together so that no leaks

occur. Therefore, it is necessary to either seal the internal cooling channels or theoutside surfaces of the tool. Internal channels can be sealed with various resins but

th is reduces their therma l con ductivity. The outsid e of steel tools may be sealed with a

solder paste or brazing operation but th is then provides a problem if the tool needs to

be disassembled. It is possible to use high-temperat ure adhesives between each sheet,but again this can cause problems if disassembly of t he tool is required.

6. Avoiding distortion in laminated tooling

Laminated tooling needs to be designed carefully otherwise distortion can be a

serious prob lem. The individual sheets form a block which is very similar to a pack o fcards. They can therefore twist in several directions unless restrained. There are

various forms of distortion as follows:

6.1. V ertical distortion

Vert ical distortion is caused by uneven t ightenin g and lack o f rigidity of clampingrod s. The distortion shown in F ig. 9 is caused by overtightening of th e top set of rods.

6.2. Horizontal distortionHorizontal distortion (shown in Fig. 10) is due to too much play between the tie

rods and the individual sheets and/or alignment during assembly.

6.3. Twist

Twist (shown in F ig. 11) is due to incorrect alignmen t du ring assembly an d uneven

tightening of tie rods.


F igure 9. Vertical dist or tion.

F igure 10. Hor izont al dist or tion.


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Th e variou s types of distortion may be reduced or eliminated with registratio n

grooves as shown in Fig. 12. These should run the length of the tool along the slicingdirectio n on three sides and may be dovetailed or simply rectangular .

7. Design of shut-ofaces

Th e shut-ofaces are particularly important in tooling as it is these that constrain

th e par t being produ ced. They are the areas where th e two halves of th e tool to uch . It

is important to design them so that they are not liable to damage or cause other

problems in th e operation of the to ol. A problem that can occur is th e use of sharp-

edged shut-o

faces as in Fig. 13. The outside sheets in this situation can easily be bentand damaged. Ideally the shut-o faces should be at.

1354 P. M . Dickens

F igur e 11. Twist.

F igur e 12. R egistr ation gro oves to eliminate dist or tion.

F igur e 13. Angled and at shut-o faces.


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Another problem that may occur is shown in Fig. 14. This is where shut-o faces

occur above a cooling manifold. In this situation the primary clamping system mayno t rigidly hold the proles t ogether an d vertical movement of the sheets can occur.

This will mea n that th e shut-ofaces are not pressed against each other with sucient

pressure to seal the cavity.

8. General alignment and location features

A substantial baseplate should be used to clamp the tool to the press (Fig. 15). Theto ol sho uld be bo lted to the base plat e with the aid of solid th readed inserts. Helicoil

inserts should be avoided as they will become dislodged more easily if the sheets are

loosened. It is obviously possible to use a base plate with a machined groove for a

registration bar. The pins and bushes to align the two halves of the tool need to be

rigid and there are several methods that can be used to accomplish this. The simplest

technique is to drill holes into th e matin g faces of th e too l to locate the pins an ddowels. An alterna tive is to u se solid inserts which slot into place when t he sheets are


F igure 14. U nsupp orted shu t-o face.

F igur e 15. Basepla te for loca ting to ol.


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being assembled. These solid inserts can then be drilled to accept pins and bushes.More detailed use of inserts is given in the following section.

9. Use of solid inserts

Th ere may be ot her situations where it is vita l to use solid inserts:

(1) When there are tall protrusions it may be dicult to x some sheets together(see Fig. 16).

(2) Some features may be prone to damage and so replaceable inserts could

extend the life of the tool.

(3) Inserts are used in conventional tooling where the same part is made for

dierent customers. In this situation the insert could simply have a dierentlogo or part name.

(4) Inserts are also used where regular design changes are anticipated .

Th e insert sho uld be designed as an integra l pa rt of the to ol an d located accurately

and rigidly.

10. Model slicing techniques

Th e techniques of horizontal and vertical clampin g were discussed earlier and this

largely relates to the direction of slicing. However, it is important to consider the

slicing direction when considering the surface roughness of the cavity. The surface

roughness of the assembled sheets is largely dependent on th e orientation of the cavitysurface to the slicing direction . As the cavity orientation approaches that o f the slicing

direction then the stair stepping eect of building parts by layers becomes more

prono unced.

It may be necessary to design a tool with parts being sliced in dierent directions(Fig. 17). The tool would then resemble a complex wire cut tool where parts are

assembled from dierent directions. However, it may then become more dicult tomatch cooling channels with dierent sections of a tool.

11. Conclusions

U se of laminated toolin g for sheet meta l working ha s alread y been proved an d

some work has also been undertaken to b uild laminated tooling for moulding plastics.

This needs furt her invest igation to determine the economic an d techn ical benets.There is also th e possibility of using laminated to oling in other ap plication s such as

1356 P. M . Dickens

F igur e 16. Solid insert for ta ll pr otru sions.


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die casting and forging. Laminated tooling is relatively rare at the moment and as

more tools are built using this technique, the benets and limitations will become

more clear .

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YOKOI, H., SUZ U K I, T., SU ZU K I, K. and NAKAGAWA, T., 1984, Manufacturing of blanking tooland its die-set by laminating steel sheet. Proceedings of the 12th N orth A mericanM etalwork ing R esearch Conference, Houghton, MI, USA, 30 May1 June 1984, Journalof M anuf acturing Engineering T ransactions. pp. 372378.


F igur e 17. Slicing op tions.

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Principles of Design for Laminated Tooling