Date Visited:14 December 1995
JTEC/WTEC Attendees:F. Prinz (report author), R. Aubin, E. Sachs, C. Uyehara
Toyota is the largest automobile manufacturer in Japan, third largest in the world. It employs 70,000 people. In 1994, Toyota produced over 3.5 million cars, a decline from the 4.2 million cars produced in 1990. Overseas production increased from over six hundred thousand in 1990 to over one million in 1994.
Toyota has more than 1,300 CAD/CAM systems, mostly 2D units. Portions of its CAD software are commercial. Toyota also has a significant in-house CAD development effort. Features such as automatic creation of fillets are standard in the Toyota CAD environment.
Toyota managers have extensively studied commercially available RP processes. They consider RP to be a potentially important tool to support the design cycle. Several RP systems were investigated in detail: stereolithography, LOM, and SLS (DTM). Comments, benchmarks, and criticisms of the first two are summarized below.
Preprocessing (preparing design data for RP), processing (forming time), and post-processing (removal of support) takes too long using stereolithography (SLA) systems. Parts may curl during post-curing; corrections seem possible. Resins are not transparent enough and their odor is undesirable. SLA parts that could sustain higher temperatures would be preferred for tests in the engine compartment. The accuracy of SLA parts is currently insufficient.
A study of SLA machines was performed by comparing two Japanese and one U.S. vendor. A 500 mm long beam was built in each machine. The total deflection of the resulting beam from its nominal shape was taken as quality measure (curl). The beam made in the machine by the U.S. vendor was off by .3 mm. The Japanese machines produced beams that showed greater deflections (1.5 mm).
A number of other performance criteria were evaluated. Overall, the U.S. vendor performed best. In only two categories (service and build time), the U.S. vendor was considered slightly below Toyota expectations. The rating system had three classifications: satisfactory, not quite satisfactory, and unsatisfactory. In the accuracy category, the U.S. vendor showed a satisfactory mark, while the Japanese competitors were ranked not quite satisfactory. Epoxy resins were used in this study.
Setup time is too long using laminated object manufacturing (LOM) systems. Lifting the paper rolls is beyond Toyota standards: no one at Toyota is supposed to carry objects heavier than 20 kg, and the paper rolls from Helisys weigh 60 kg.
Excavating complex parts from the support structure requires excessive periods of time. The work of excavating parts from the support varies by size and type of parts (bulky or hollow): Very complex parts need more than 30 hours, while smaller, simpler parts need only 1 or 2 hours. Toyota found that the time required for support structure removal of SLA parts is one-fifth to one-sixth of that for LOM parts. The company is trying to shorten LOM excavating time in various ways. Concerns were also expressed regarding the waste of raw material in the form of unused support structures. In comparison, SLA uses less material for support.
Other drawbacks of LOM versus SLA were mentioned: LOM parts exhibit less strength, accuracy is comparatively poor, and production rate is only half of what Toyota expects. For obvious reasons, LOM parts are not transparent, yet transparency is a desirable attribute of RP parts from Toyota's perspective.
According to the JTEC/WTEC team's hosts at Toyota, LOM has an advantage over resin types in making bulky parts like dies in a shorter operating time.
Toyota is at an early stage in evaluating RP for casting applications. Investment casting and sand casting were mentioned. The size of parts that can be built in a DTM machine were considered too small. Toyota intends to evaluate QuickCast in the near future.
Toyota benchmarked CNC versus LOM by producing the same geometry with both techniques. The CNC part was made out of Renwood material. No apparent benefits for LOM could be identified. In fact, CNC came out ahead of LOM in terms of overall cost. The cost figure included the programming efforts for CNC machining. It was mentioned that certain features that are easily possible with the help of LOM may require special skills when using CNC.
The JTEC/WTEC team's hosts listed the desirable properties of RP that would allow RP to make a bigger impact at Toyota: increased accuracy, transparency, elevated temperature resistance, and birefringence for photoelasticity studies. Functional prototypes were mentioned as the ultimate goal for RP. An example given was tooling for vacuum forming for a car seat.