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Product and Process Innovation by Means of Rapid Manufacturing

Dimiter Dimitrov, Kristiaan Schreve, Eric Bradfield

Global Competitiveness Centre in Engineering (GCC)

University of Stellenbosch

Private Bag X1, 7602 MatielandStellenbosch, South Africa

[email protected]@sun.ac.za

[email protected]

Abstract

Rapid Manufacturing is a term that embraces rapid prototyping and rapid tooling. Rapid

Prototyping (RP) is an exiting new technology, which enables users directly from CADmodels to create physical prototypes early in the design cycle so that flaws can be detected

and corrected before they mushroom into costly expenditure. Initially conceived for designapproval and part verification, RP now meets the need for a wide range of applications frombuilding of test prototypes with material properties close to those of production parts to

fabricating models for art and medical applications. Furthermore these systems allow

functional performance to be optimised through an iterative process of prototyping, testingand analysis. Rapid Tooling (RT) generally concerns the production of (bridge, soft) tooling

using pattern (inserts) most often produced by RP methods.

This paper reflects on experiences gained at the GCC in the use of 3 Dimensional Printing

(3DP) technology (Z402 RP-System) in conjunction with different secondary processes such

as investment and vacuum casting. As a result several successful process chains were

developed for applications in the automotive, consumer goods and packaging industries.Here a selection of case studies is presented to illustrate the wide application of the 3DP

technology in the metal casting or plastic processing industries.

Keywords: CAD-modelling, rapid prototyping, 3D printing, rapid tooling, vacuum casting.

1. INTRODUCTION

The development of innovative products and their realisation by means of advanced

manufacturing methods and process combinations is becoming more and more a key issue in

international competitiveness. Leading companies worldwide are discovering that rapidproduct development (RPD) is a huge and relatively untapped source of competitive gain,

especially for new products [1]. This is of particular importance for South Africa too. Inorder to get a competitive edge it has to increase development of new products, to become

more and more a product developer rather than being (mainly) a product user.

The industrial production is subsequently increasingly influenced by the possibilities that

Rapid Technologies can offer. Until recently the industrial use of the new technologies was


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focused mostly on the manufacturing of single prototypes or on prototype multiplication

some 10 20 pieces in material similar to the end product. Today the expectations anddemands of industry are changing into the following directions:

- Production of test runs in final-use material in the range of 50 to several 1000 units

- Dimensional accuracy as achieved by established processes.

Consequently the need arises to locally develop Rapid Technology applications integrated or

combined with advanced manufacturing processes, particularly with high speed machining,and to assure their efficient use in the South African industrial environment.

This paper reflects on experiences gained at the GCC in the use of 3D-printing technology(Z402 RP-System) in conjunction with different secondary processes such as investment and

vacuum casting. As a result several successful process chains were developed for

applications in the automotive, consumer goods and packaging industries. Here a selection ofcase studies is presented to illustrate the wide application of the 3DP technology for metal

casting or plastic processing.

2. OVERALL CHARACTERISTIC OF THE 3D PRINTING PROCESS

The Z402 3D printing system from Z Corporation is one of the most basic RP systems

available today. It utilises the principle of ink jet printing, perfected in the 1990s, along withrelatively cheap and readily available standard components and materials. This combination

ensures a stable and robust RP system that delivers relative accuracy at remarkable speed and

low cost. For this reason leading automotive companies such as DaimlerChrysler, Germany,make wide use of the Z402 system concurrently throughout their design life cycle to help

reduce development time and improve quality [2].

The Z402 system uses a specially modified printer cartridge to deposit a two dimensional

profile of resin onto a layer of powder that forms the build surface. Similar to the SelectiveLaser Sintering (SLS) process the base material is rolled onto the build platform to form each

new layer. The prototype is formed as hundreds of layers of powder are built on top of one

another. At present there are mainly two types of powder, namely the ZP100 plaster based

powder, which allows a layer thickness of 0.08 mm to be grown, and a cheaper more robustZP14 starch based powder, which enables a layer thickness of 0.18 mm. The different

materials and post processing possibilities that form part of the system also mean that there is

a vast range of applications. Apart from the characteristics of the base powders, several resinscan be used to harden the prototypes and provide different properties for design verification

and testing. Using the Automated Waxer, parts can easily be infiltrated with surgical wax to

provide strength and to form patterns for investment casting. Recently, a new ZP15 powderwas acquired which allows the manufacturing of elastic parts.

Hand finishing can also be done to produce smooth and painted surfaces for visualisation,marketing and sales purposes. Careful hand polishing in combination with suitable

impregnation materials allows surfaces that meet the requirements of patterns for vacuum


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casting. However, post processing costs as well as possible negative impact on the part

accuracy could be determined limitations.

It has to be pointed out that during the post processing the danger of damaging a part is

serious. Therefore the operator for this last process step has a high responsibility for the

successful realisation. This is of particular importance for the 3D printing process, where thefreshly grown parts, particularly those build with starch based powder, are very brittle.

3. CASE STUDIES

3.1. Conceptual Models

Initially the layered manufacturing processes were conceived for concept modelling. Theidea was to make available to designers a method of quickly producing a prototype of the

part for visualisation purposes. This may be to help sort out problems regarding

manufacturing e.g. it is very difficult to visualise the moulding method of a complexcasting consisting of several cores or the part may be used as an aid to communicate the

design to people, e.g. management or marketing managers, who do not have the ability tovisualise 3D objects on a computer screen. In this regard, the 3D printer used at GCC is ideal

since it is fast and the operational costs are comparatively cheap [3].

In this context, the parts will be produced in any material without significant concerns about

the dimensional accuracy or the surface finish. The most important aspects that must becaptured are the shape and the scale.

Occasionally, when the strength of the component is not a prime requirement, this type ofmodels could also be used for fitment tests. Of course, in this case dimensional accuracy

becomes more important.

This case study is an interesting example of the latter application of the 3DP technology. In

this case a prototype was needed for fitment tests. The part is a rubber boot. In order to testits fitment, it is necessary to have a flexible prototype so that the part can be checked in all

the positions of the boot.

Since printed parts can be infiltrated with several different materials, this part was infiltratedwith a special polyurethane rubber moulding system. This kind of capability is unique

amongst the established layered manufacturing systems. The concertina boot in Fig.1 has a

wall thickness of 1.5 mm. Of course, the material properties of this boot are far from thematerial to be used for the final product, but still, the part is elastic enough to do all the

fitment tests. The big advantage is that the part was ready in a matter of hours about 3

hours for printing and two more for curing and post treatment.


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Fig.1. Rubber Similar Part (normal position left and extended position on the right) Built onthe 3D Printer (courtesy of CAE Stellenbosch Automotive Engineering)

3.2. Lost Pattern for Investment CastingAs opposite of the general view that particularly the Z-Corporation 3D Printer has to be seen

above all as a concept modeller, which brings the designer in the position over a couples ofdays to create a chain of iterations of a new design, each an improvement over the previous

[3], there are other wide application niches. Being dependant on material import it was found

out that this general perception would be to costly for many customers. This is why at GCCan expertise was developed in using the 3D printer primarily as a pattern making device for

both metal and plastic applications, taking great advantage of its building speed and

concentrating on suitable and efficient post treatment techniques. In the same time anextensive research programme was put in place in order to determine the true capability

profile of the process. One of the most successful recent developments in this regard was the

building of a number of patterns for investment casting of the differential housing for a newvehicle model of Ford Motor Company SA. This component is a very robust object overall

dimensions 260 x 240 x 290 mm - exceeding by far the work envelope of the Z402 3DP. Itwas grown in 3 separate platforms within 15 hours, each part being subsequently wax

infiltrated. Thereafter the three parts were assembled and the radii necessary for successfulcasting manually created. In order to assure the required accuracy of the component an

assembly jig was constructed. A standard finish of the pattern was obtained, before dispatch

to the foundry for casting. The pictures below show the 3D wax infiltrated pattern as well asthe final assembly of the axle.

3.3. Prototype Multiplication. Patterns for Vacuum Casting of Plastic Parts

3.3.1. Rubber Components

It was quickly found that application area of the layered manufacturing processes could beextended into producing components in materials similar to these, which will be used for the

end product. This extends the prototyping to functional testing. The need for such parts isobvious. In the automotive industry, this makes it possible to reduce the development cycle

of new models drastically by having fully functional test vehicles ready in much less time.

Clearly, in this instance, there is also a need to have more than one prototype.


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a) 3DP Pattern b) Axle AssemblyFig.2. Differential Housing

When using printed objects as patterns for making silicon rubber moulds, such parts can be

produced in one to two weeks in small batches, typically 10 20 components. The printedparts, although very fragile, can be painted and finished manually to produce patterns,

accurate to within 0.5mm to 1mm (depending on the size), with a very high quality surface

finish. A wide variety of polyurethane is available. Using a vacuum casting system, very highquality parts can be produced.

Figure 3 shows a rubber similar part cast in a silicon rubber mould using a flexiblepolyurethane. Perhaps this example is not the most impressive one for using in this case the

Fig. 3. Sealing Washer (courtesy of CAE Stellenbosch Automotive Engineering)


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process chain 3D printing Silicon rubber moulding Vacuum casting. Since it is a simple

rotational part, a turned mould might be cheaper. The 3D printing indeed excels, whenmaking very complex parts. Overhangs, undercuts, deep holes, etc. can be manufactured

easily through the 3D printing process. Under these circumstances a printer pattern will be

significantly more cost effective than a conventional pattern. The process from receiving a

2D sketch to having available a fully functional rubber similar part for functional test andlayout verification, took 48 hours.

Another example for the same purpose of functional test and layout verification is shown inFigure 4. A core is needed to make the rubber pipe. Two separate silicon moulds were made,

one for the core and one for the pipe. Again, both patterns were produced on the 3D printer.

Once the moulds were ready, the core was made first. A low melting point (96C) metal alloy

was cast into the mould for the core. The metal core was then placed in the mould for the

pipe and the polyurethane was cast, thereafter the core was melted out.

Fig. 4. Rubber Pipe (courtesy of CAE Stellenbosch Automotive Engineering)

3.3.2. Automotive Grill

Size is often seen as a limiting factor in the layered manufacturing environment. The largestparts, which can be built on RP machines available in South Africa, have build volumes of

500mm x 500mm x 560mm. The build volume of the Z402 3D printer has a working

envelope of 250 x 200 x 200 mm, in reality 230 x 200 x 190 mm. However, on numerousoccasions the CAD models of larger parts were cut accordingly into smaller sections that fit

into the build volume and assembled afterwards. The largest component, used as a

verification model or as a pattern made to date at the GCC consisted of eleven such sections.Still, the final product was within the clients dimensional specifications.

In some cases jigs may be needed in order to assemble the sections. However, recently this

additional link in the chain was removed by adding a support structure to the part in the CADsystem. This is a fast, simple and cheap solution. Depending on the particular part a simple


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egg box structure can suffice. This provides a stable base, on which all the parts can be

assembled. Normally the sections are just glued together.

With aesthetic components it is vital that the joints must be invisible. This is achieved by

post treatment procedures such as sanding, finishing off and painting. Printed objects

infiltrated with an epoxy resin lends themselves ideally to manual finishing. Glued joints arealso much stronger than the very brittle parts produced in the past using cyanoacrylate as an

infiltrant.

The pattern for the grill shown in Figure. 5 was produced in this way. The grill consists of

two parts the grid structure and the grill itself. The most significant portion of the work

went into finishing operations. The dimensional accuracy of the pattern was very satisfactory.All dimensions were within 0.37% of the length (800 mm) of the pattern.

a) The 3D Printed Pattern on b) The Silicon Rubber Mould

its Assembly Jig with the Pattern

c) The Polyurethane Casting

Fig.5. Automotive Grill (prototype)


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3.4. Bridge Tooling. Aluminium Filled Epoxy Moulds

Using aluminium filled epoxy resin rather than silicon rubber makes it possible to produceabout 800 to 2000 injection moulded parts in the final material from the same mould. The

epoxy resin in the mould shown in Figure 6 contains about 80% aluminium powder. A part

built on the 3D printer is used as pattern after manually finishing it. An aluminium bolster is

used to add strength to the epoxy cavity so that the mould can withstand the high injectionpressure and clamping forces. The epoxy is degassed before and after pouring in the mould.

Once the epoxy is cured, it can be machined and finished as any metal. If needed, holes can

be drilled for metal inserts. When very high accuracy is required on the part, using insertsmay be a good option.

The process is more expensive than the silicon rubber moulding due to the higher costs ofmould material - the aluminium filled epoxy. It is also less flexible since the issues such as

draft angles and split planes needs to be more carefully considered. However, due to the

larger number of parts that can be made in such a mould, this tooling goes beyond mereprototyping. If 2000 components can be made from a mould made in 6 working days and

costing about R20 000, than this is a viable option for parts with small expected productionvolumes. It is also anideal option for a pre-production series for marketing research.

Fig. 6. Bridge Tooling an Aluminium Filled Epoxy Mould (courtesy of PowerLogic)

4. Conclusions

The most important conclusion of the presented case studies is that functional prototypes can

be made indeed in a very short time at reasonable cost. The time and cost depend to a largeextend on the objects size and purpose for which it is needed. Hence also the different post-

treatment or secondary processes as required.

The Z Corp. Z402 Rapid Prototyping system in particular is more than capable of producingcost effective and dimensionally satisfactory prototypes in hours. Suitable post processing

procedures and finishing techniques can assure high quality parts for presentation, design

communication and marketing purposes. A lot of work and systematic research still needs to


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be done in order to properly control the dimensional and form accuracy. This is coupled with

the development and availability of new materials more user friendly, consistent and cost-effective. Work towards this goal is already underway.

Acknowledgements

The authors wish to acknowledge CAE Stellenbosch Automotive Engineering and

PowerLogic for permission to use pictures of their products in this paper.

References

[1] Bernard, A., Fischer, A.(2002): New Trends in Rapid Product Development, Keynotepaper, CIRP-Assembly meeting, San Sebastian, August 2002.

[2] Schell, T. (2000): Rapid Prototyping /Rapid Tooling Universelles Werkzeug fuer das

gesamten Produktentwicklung Prozess, Proceedings, 3D Erfahrungsforum Werkzeug- und

Formenbau, 25-26 May, 2000, Dresden, Germany.

[3] Wohlers, T.: (2001), Wohlers Report 2001, Rapid Prototyping & Tooling State of the

Industry, Wohlers Associates, Inc., Fort Collins USA.

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