MATERIALS -- OVERVIEW, PLASTICS, AND RESINS
Paul S. Fussell
The aim of rapid prototyping is to rapidly produce a product. At the moment, this product is made, for the most part, of inferior material that permits the user to show notion, or perhaps generate a few other parts suitable for limited testing. This condition has been true since the initial systems were commercialized, while the promise of true engineering products is only slowly being realized through machine and material improvements. Heralding this achievement is a gradual progression up the maps of material properties. Although Fig. 5.1 reduces the complexity of material choice and performance to just the two parameters modulus and strength, it shows a simplified schematic of this progression.
The progression, however, is not sufficiently advanced to speak to the real need of the rapid product developers: this community needs rapid prototype materials that behave, with high fidelity, like engineering materials, and specifically engineering polymers. Rapid prototyping is having a useful effect on product visualization and other limited fields, but the lack of rapid prototyped engineering materials is a significant barrier, perhaps the single most significant barrier, to dramatic growth of this technology and its profound impact on the product development endeavor. For the panel's observations during this review, there is little visible work that will produce this new material.
Given non-engineering material, the viability of any rapid prototype effort hinges upon the integrated success of material, machine, and the information used to drive the device. This strong interdependence manifests itself in every nuance of the equipment's design, performance, and eventual optimization. There are numerous examples of this linkage in extant rapid prototyping technology. One is 3D Systems' ability to successfully commercialize QuickCast. This was made possible by the use in the SLA-250 of the epoxy resin SR 5170, with its properties of accuracy, dimensional stability, and weakening in the presence of high-temperature steam, in conjunction with successful design of the internal lattice structure of the solid object (Jacobs 1995). It is fair to say that the epoxy material has substantially added to the shareholder's value in 3D Systems, Inc., as well as changed the resin market in the United States and Europe.
Improvement and optimization of rapid prototyping approaches is equally dependent upon both material and machine design. For DTM to successfully introduce the nylon material, it had to apply a new level of sophistication in thermal control of the powder column. Similarly, 3D Systems had to make significant control parameter alterations to deal with the difference between the kinetics of epoxy cure and the earlier acrylate systems.
In commercial rapid prototyping, there is also the delicate art of finding a balance between material properties, material cost, equipment cost, ease of use, and overall system performance and throughput. Each vendor of equipment chooses a different price point for its technology and vigorously proceeds to develop its relevance to the marketplace. This is certainly as true in Europe and Japan as it is in North America.
It is therefore germane to study the state of materials development in rapid prototyping, as well as the interweaving of material design and machine design. This chapter explores the state of materials development -- polymers, metals, and ceramics -- in the European and Japanese rapid prototyping environments, with limited comparison to North America.