RP, RT help cut tool and part development time in half

When international automotive supplier TRW set to work last year with rapid prototyping (RP) and rapid tooling (RT) specialist Materialise, it had some problems to solve. The TRW operation in Shirley, just outside Birmingham, England, was charged by a client with developing a master cylinder brake fluid reservoir. The client needed a prototype that would accurately represent the final part as it would be used on a new vehicle. It had to be made of the production material and assemble normally to the vehicle for extensive development testing.

Design Issues, Time Pressures, Nerves

The design team faced several knotty problems: the relatively high volume of fluid to be contained, the container's location, association with other components in the engine compartment, and the general limited space available to it. Beyond that, TRW's proposal to go the RP/RT route made the client nervous. They were accustomed to receiving prototypes from manufacturing suppliers. However, the project was on a tight time schedule and RP promised to save weeks compared to the client's traditional methods.

The design team came up with a two-piece solution that is anything but simple. TRW ordered the first evaluation prototypes using the Materialise Next Day program (see April/May 1998 Injection Moulding International). True to its name, when an STL file is received at Materialise in Leuven, Belgium before noon, the sender will have an STL prototype by noon the next day. Located close to the courier service terminals at Brussels Airport, Materialise offers this service anywhere in Europe. It also supplies customers with software to generate and troubleshoot the STL file before transmission. TRW-Shirley's designers had SLA prototypes in hand the day after approving the design files.

Prototype Tooling—Version One
After the initial design models were checked and approved, the go-ahead for prototype tooling was given to Materialise. Tool design was carried out with the same STL files used to produce the approved STL prototypes. Working in its own commercially available Magics Tooling software, Materialise applied the required shrinkage for the polymer to the STL files and designed the two mold halves, slide inserts, and electrodes. (Magics Tooling is an add-in module of Magics RP, a software package for translating and repairing STL files, triangle reduction, and Boolean operations.) 

The mold halves were designed automatically in approximately 3 hours. The nodes on the surfaces representing the parting lines were edited to give the best possible parting planes. A horizontal parting plane was used wherever possible, but a free form was used around the angled tube to optimize parting surface. Both mold halves were saved in STL format. The component was then rotated 90º and the parting planes were recalculated. 

The core from the new tool design was then used to produce the slide by means of the User Coordinate System (UCS) within Magics Tooling. The slide was subtracted from the two cavities using a Boolean operation to create the recesses in which the slides operate. That step was repeated to produce the two inserts required for the undercuts on the housing location ports and the clutch port. An electrode was also generated from the slide with a Boolean operation. It was used to finish the deep cavities on the slide. Including the inserts and electrodes, total tool design time was three days. 

After tool design was completed, the STL files for the tools were exported from Magics into a CAM package and postprocessed for high-speed milling. This ensured continuity from the approved design to the final product. The slides were then sparked and the mold halves were assembled using traditional moldmaking techniques. The tools are manually operated, with the main slide levered out of the tool before it opens. The tools were used to produce 200 components in the undisclosed production material with no quality deterioration in part form.

Version Two—With Changes
After testing of the prototypes, a redesign for a second build was undertaken following the same rapid tooling route. During the redesign the customer modified the installation criteria such that all internal construction was changed, plus some outside profile details. The experience gained in the original design phase enabled the team to take on the revisions and still provide molded components in time to meet the customer's vehicle build in Japan.

Inspection of three samples each of the top and bottom moldings was carried out against the 3-D Catia model in 48 hours by a TRW supplier using a 3-D coordinate measurement machine. Results were welcome: Of 100 inspection hits per sample, mold accuracy per component against the 3-D model was 94 percent correct.

Analysis showed the out-of-specification points were mostly traceable to operator/system errors in targeting on irregular and/or inclined surfaces. Although experience has since shown that complex areas need to be examined in greater detail, the previous manual inspection of assembly reservoirs was not able to achieve this level of accuracy in such a short time.

Dave Innocent, project manager for TRW-Shirley says, "The overall timing of five weeks for this second reservoir was astounding when one takes into account the mass of design changes and the original estimated manufacturing time for the first-phase components, which was already considered extremely quick." Using traditional methods would have meant a 12- to 16-week cycle, rather than the six weeks it took by teaming up with Materialise.

In the end, the TRW/Materialise team provided functional working master cylinder reservoir components that accurately represented the final production piece. Plus, the parts were done on budget and in time to meet the customer's vehicle build plan.

As for the customer's nervousness, the time savings and great performance results in both phases took care of that. TRW-Shirley has ordered another set of reservoir tooling in a completely different design from Materialise. This time the production supplier of the final component will be part of the team to further improve coordination. TRW says taking this route with Materialise has set a new rapid prototype manufacturing standard for all future requirements.