Rapid Tooling Applications Grow
Rapid tooling, a term which once referred to a costly and/or somewhat crude specialty branch of rapid prototyping, has evolved into a major commercial and research-driven field of its own with a growi...
Rapid tooling, a term which once referred to a costly and/or somewhat crude specialty branch of rapid prototyping, has evolved into a major commercial and research-driven field of its own with a growing impact on almost all sectors of the plastics injection molding industry. Driven by customers’ demands for shorter design cycles, the number and types of new rapid tooling materials, projects and technologies are dramatically on the rise. As this report shows, a number of Canadian companies and institutions are playing a significant part in the development of rapid tooling processes.
RAPID PARADIGM SHIFT
The notion that a “rapidly” made tool is at best useful to make a few prototype parts from urethane or epoxy is no longer valid. While rapid prototyping/tooling methods such as Ciba Specialty Chemical Corp.’s (65) Parts-in Minutes still play a useful role in enabling companies to get their product to markets faster, rapid tooling processes are now being applied just as readily to make production-ready tools from conventional steel or aluminum. By using combinations of traditional and cutting edge technologies, moldmakers, molders and design engineering firms are showing that rapid tooling is more of a mindset than a specific piece of equipment or single method.
A good example of this “cross fertilization” of conventional tooling and rapid tooling methods is demonstrated in a project in which Waltec Engineering (66, Wallaceburg, Ont.) produced a tool for its U.S.-based customer Webster Plastics in just 13 working days. First reported in Canadian Plastics (Jan. 98), the project began when Waltec received a stereolithographic (SLA) model of the part — a handle used in a fire-resistant storage product– and a request from the customer to build the mold using accelerated production procedures.
Waltec enhanced part design in two days using Pro Engineer solid modeling software. While the STL file was sent to an SLA service shop in the U.S., Waltec created preliminary cutter paths using Cimatron CAM software. In three days Waltec received the SLA part and the go-ahead to begin mold production. The production ready mold was produced from P20 steel in eight days, a record at the company.
Windsor-based tool shop and RP service bureau Advantage Engineering (72) has recently developed its own rapid tooling process, Advantage Rapid Tooling (ART). President Steve Hengsperger says ART is a totally cast process that starts with a SLA master and produces a high quality, dimensionally accurate tool within two to four weeks. The tools are made from a metal alloy, a variation of which is used in Europe to make prototype stamping dies. The alloy is not porous and can be grained, says Hengsperger. Advantage has completed a number of tooling projects using the ART process and the company’s long-term goal is to use the in-house rapid tooling process to compete with aluminum in the production of prototype automotive fascia molds.
PUSHING THE RP WINDOW
The National Research Council’s Integrated Manufacturing Technologies Institute (67) has two 3D Systems SLA machines (68), as well as one DTM selective laser sintering (SLS) Sinterstation 2000 system (69) which it is using in partnerships with Canadian companies to develop and improve rapid tooling technology.
One such project, involving Siemens Automotive Division (Tilbury, Ont.) and Regal International Tool & Mould Inc. (70 Windsor, Ont.), studied the feasibility of using the SLS Sinterstation and RapidTool process for making mold inserts for injection molding of a plastic manifold. The project succeeded in making a crack-free metal mold insert with a diameter of 254 mm and a height of 220 mm in about three weeks. The 47 kg insert, which was the largest mold insert ever made DTM’s RapidTool process, required a number of modifications in equipment and methods to produce.
In the SLS rapid tooling process, a “green” core and cavity is built by a layering process of a steel powder and a polymeric binder. The green part is infiltrated with a liquid polymer binder and then dried in the oven. This reinforced green part is then put through a three-stage furnace cycle which, one, debinds the polymer at relatively low temperatures, two, sinters the parts into a compact, porous skeleton and, three, infiltrates copper into the skeleton of the mold above the melting temperature of copper. After copper infiltration the part is fully dense and has the mechanical and physical properties of a steel-copper composite.
According to principal NRC researcher on the project, Dr. Mark Liu, a first attempt to make a mold insert using standard RapidTool procedures, resulted in a part with two large cracks. Liu says the cracks were a result of a number of factors, including stresses caused by unequal heating inside the furnace, gas generation during the polymer debinding stage and oxidation. Liu says the effects of these factors, while minor for small parts, is magnified in larger parts. To minimize oxidation, the polymer-infiltrated part was dried in an oven purged constantly with nitrogen. The flow of the gas also reduced drying time from 20 to 14 days. Also, the furnace was modified to achieve better thermal insulation, which in turn provided a more homogeneous temperature distribution. Finally, ramping rates of the furnace cycle was reduced to minimize temperature gradients inside the part.
These modifications resulted in a crack-free mold insert. The insert was placed in an injection molding press and injection molded with a 33 percent glass-filled nylon. After 17 shots the insert was removed and inspected for wear. No wear was observed on the SLS-made inserts, whereas a similar insert made from aluminum-filled epoxy showed signs of wear after the same number of shots. The project team concludes that time to produce large inserts with the modified version of the RapidTool process could be shortened from three weeks with further improvements in the drying and furnace-cycle stages. The process is viable for prototype up to short-run production, according to the final report.
Liu says that since the project, DTM has introduced different materials that eliminate the debinding step and is supposed to help alleviate cracking problems (see box, p. 26). Even with the new materials, Liu says, some modifications to equipment and process parameters would have to be made in order to make large mold inserts, such as those used to make manifolds. CPL