Prototyping technology matures to production

Space Puzzle Molding, the process originally developed for producing prototypes in low quantities, is no longer in its infancy - as illustrated by three automotive examples.

Space Puzzle Molding, the process originally developed for producing prototypes in low quantities (now alternatively termed SPM technology), is no longer in its infancy.

It is a leading rapid process designed to fulfil the requirement for individual sets of plastic parts for prototyping and "alpha build" test, but in recent years it has, in parallel, made major in-roads into small and medium batch production for many markets such as medical, electronic, instrumentation and in particular automotive.

Three such examples of production components for typical automotive applications are given in this article.

Space Puzzle Molding has been elevated in status to a full production process partly on merit as the SPM tooling system has evolved naturally, and partly by changes in the market place, since shorter product life cycles, frequent product modifications, and the trend towards numerous product variants becoming known as 'Mass Customisation' requires ever smaller batch sises of any particular design iteration.

Space Puzzle Molding, therefore, is becoming a significant supplier of production items directly to the vehicle manufacturers and to the tier 1 players of the industry.

Quantities of hundreds or, in specific cases, thousands of parts, are not uncommon.

Unique in the World due to its patented and economic mould system, SPM Technology is the exclusive process created and perfected in Europe by Protoform in Fuerth, Germany.

At the start of a project the CAD department at Protoform uses state-of-the-art software to tailor the customers' component data for injection mould processing.

The same, uniquely designed, SPM injection mould, high-speed CNC machined in aluminium, is used for both prototype and production parts in the in-house injection moulding shop.

The whole production follows the "one-stop" principle for the client, in that project handling is performed under single-source direction, whereby component supply includes such post operations as surface treatment and assembly.

The three practical examples detailed below show how SPM technology is currently enabling efficient and economic part production, even in small batches and short series.

VW Individual, Wolfsburg, needed 3000 pieces of a filigree plastic part for the installation of a printer and a fax machine into the rear centre console of the deluxe Phaeton limousine.

Small batch manufacturing did not justify making a normal injection mould.

For this reason, VW contacted Protoform.

Having consulted several raw material producers, Protoform selected the material (ABS, Novodur, manufactured by Lanxess, Leverkusen) and suggested using an electrolytic chromium plating-technology for the final finish.

The development and production order for small-batch manufacturing of the required parts placed with Protoform specified the delivery of five initial samples to be produced according to the customer-specific VW test protocol.

This required producing a thin-walled component of high quality, without flattened areas, material-dislocations and optical defects, but with a polished high-gloss surface.

It was specified also that these components must be suitable for use in customer cars - if ordered as an optional feature.

The engineers at Protoform designed an injection mould for the component, optimised according to plastic processing requirements.

This mould compensated for the shrinkage parameters of the slender shape.

For the small-batch mould, steel was selected for the tooling material rather than aluminium, in order to guarantee dimensional integrity and surface flatness of the component as well a stainless mirror-finish chromium surface.

It was necessary to introduce minor design changes as the project progressed but this presented no problem.

The SPM process makes tooling modifications a simple and straightforward operation.

After finalising the parameters, Protoform proceeded to manufacture the required 400 or so, chromium-plated parts, delivering them to the subcontractor, a system supplier and car refinement company in Cadolzburg, Bavaria.

The Automobilmanufactur Dresden is the delivery address for a further plastic part for the Phaeton, Volkswagen's premium car, a two-part protective cover for the refrigeration unit.

The component and hence also the mould had to undergo a design change during the manufacturing process.

This is not unusual with new products where, despite careful work in the preceding stages such as simulation of the plastic injection process in virtual mould flow programs, the actuality of the final moulding some times requires slight modifications.

SPM moulds allow this to occur easily and at low cost.

They can support necessary modifications and design revisions at any stage of the project.

In this case the cost to the customer of the necessary alterations of some reinforcement ribs amounted to a mere Eur 250.

In terms of product finishing to complete the component, the cover itself is made of PC+ABS (grade: Bayblend manufactured by Material Science, Leverkusen) with black basic colour.

Subsequent flocking makes the component look like a dark grey carpet.

Nominal batch sise for this production run was 2000 items and approximately 1000 coverings have been manufactured and delivered to date since the project is currently on-going.

The New Chairman is an extended reproduction model of a Mercedes former E-class.

It carries a number of highly technical, production parts made using Protoform's SPM technology.

This South Korean Mercedes copy coasts smoothly along the streets in the Far East as a stretched limousine, fitted with an electropneumatic shock absorption system provided by the Continental Automotive Systems, Hanover, Germany.

In the early stage, when the product was first launched onto the market, the plan was to make it a limited edition of 500 units.

Parts of the shock absorbers in the New Chairman are a piston cover and a piston box, made of robust plastic, with integrated threads.

Since both parts have functional safety implications, they have to fulfil stringent requirements in terms of precision, quality and stability.

They are made of a high-strength polyamide whose glass fibre content is 30% (PA66-GF30, Zytel manufactured by DuPont de Nemours, Bad Homburg).

For this reason Continental Teves, Gifhorn, who received the parts, was a critical customer.

On inspection and evaluation of early mouldings, it was found necessary to modify the SPM moulds to increase roundness in certain areas.

The pre-calculated and detailed filling simulation for this strong engineering plastic had not proved to be representative in practice.

Gating was therefore changed as a result of, unusually high, local wall thickness values required of up to 12mm.

The unit weighs almost half a kilo of weight (496g) and the initial problem moulding characteristics were overcome with a greater number of injection points, a change to mould-flow and a robust extrusion guide.

Each of these 'flight-critical' suspension components had its design changed repeatedly throughout this process.

Having made the necessary changes, to accommodate the high-level of specification, the required quality level was achieved.

The parts were released for installation after a 100% check and complete documentation.

In the meantime, the production volume was extended.

Protoform's SPM technology delivered more than 2000 parts made from the prototype mould (instead of expected 500) to Continental Teves, proving once again that the aluminium moulds have sufficient tool life to provide even greater quantities.

The still widespread belief that prototypes are fundamentally expensive, and suitable for only a few parts manufactured for evaluation, has to be revised as a result of SPM technology's entry into small batch production.

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