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Polymer Technologies : Moldflow Plastics Insight
Clifton, NJ-based Polymer Technologies, Inc. (PTI) is an injection molding company that provides research development and plastics manufacturing services to government, aerospace, commercial, and medical markets. The 15-year old company utilizes both engineered and commodity-type plastics and metal products. Its services include product design and development, production molding, product assembly, material selection, mold design and construction, engineering support, and metal injection molding (MIM). MIM is a high-volume, high quality, cost-effective process that helps eliminate secondary machining operations for metal part production.
PTI's three labor shifts run 16 injection molding machines, the largest being 650 tons. In addition, the company recently purchased a new injection molding machine with advanced computer controls. They also operate both vertical and horizontal presses. There are two sintering furnaces. One is a hydrogen batch system with high vacuum, nitrogen, argon and hydrogen capabilities. It has an all-metal hot zone made of molybdenum. It allows for hot and very clean processing. The other furnace is a hydrogen pusher furnace that is approximately 60 feet long. It pushes a train of plates along the length of the furnace from the warm zone to the hot zone where the sintering occurs. PTI invested more than $1 million in the two furnace systems.
Metal injection molding
Dr. Jerry LaSalle is PTI's director of MIM operations. He's responsible for the development, manufacturing, and a portion of the marketing of the MIM processes. Metal injection molding is a unique method of fabricating intricate net shape metal, ceramic and metal ceramic components via technologies more commonly associated to the plastics industry. Unlike injection-molded plastics, it requires subsequent sintering to fully consolidate. Typical MIM differs from standard net shape metal processing in that it uses fine 10-20 micron powders, incorporates binders, and is not limited to axial symmetric parts. Based on its superior molding properties in thick-sectioned parts, PTI uses a water based agar binder system developed by Honeywell for many of its applications.
In terms of MIM processing, La Salle says some of the challenges of designing and manufacturing PTI's products include repeatable dimensional targets. "MIM is very analogous to plastic injection molding up to a point. A MIM binder is, in some respects, a very highly loaded polymeric material. Many of the considerations in terms of plastics do apply with metal injection molding feedstocks. The details can be different. The major difference is when the plastic part is molded and tool is debugged, and the dimensions are finalized, you are typically finished with the process. However with MIM, operators must eliminate the binder and sinter the metal powder together. There are some significant chemistry changes and part shrinkage that occur during sintering that need to be monitored. With part shrinkage, dimensional repeatability is dependent upon the same process parameters as for plastic injection molding, but has additional process requirements associated with sintering," La Salle says.
PTI customers expect chemistry and mechanical targets to be achieved, along with dimensional repeatability, and quality control traceability. The company meets these requirements through application of molding and sintering science to the MIM process including stringent process control procedures during the molding and sintering operations. As in plastic injection molding, quality feedstock, proper gate and runner design, and consistent molding cycle, for example, are necessary for a quality component. However, with MIM, stringent operating procedures must also be applied to sintering as they affect the final chemistry, mechanical properties, and dimensional retention.
La Salle adds, "For aerospace customers, for example, mechanical requirements can include some very sophisticated mechanical properties such as high cycle fatigue and high temperature oxidation resistance, as well as tensile properties and hardness. For medical products, very controlled quality procedures must be implemented, as well as documentation and traceability throughout the whole process. These and other aspects are considered part of meeting our customers' specifications."
Meeting those requirements takes a combination of science and skill to mold the part with a larger MIM part. That's where PTI's rich plastics heritage comes into play. The company, founded by its current president J. Melvin Goldenberg, specializes in difficult to mold plastic parts - frequently a lot of long L/D ratio parts, thin walled parts, very thick heavy walled parts, parts comprised of materials that are difficult to mold, or are difficult to mold because of design configurations. "The expertise of our company's founder and his desire to drive the company into new technologies has been applied to the MIM process," explains LaSalle who holds a Ph.D. in material science from Northwestern University. "MIM has some different challenges related to uniform knitting and part integrity during molding and part ejection. Compared with typical plastics they also have very low viscosity and high thermal conductivity, which makes them unique to model by computer simulation.."
Moldflow Plastic Insight software
LaSalle and his colleagues are using Moldflow Plastics Insight (MPI) from Moldflow Corporation (Wayland, MA) for MIM and plastic injection molding processes. They also use Pro/ENGINEER and CADkey for CAD. He and the chief simulation engineer, Boris Chernyavsky, have been using MPI for several years. Prior to working at PTI, they worked at Honeywell International and used MPI there for plastics and in developing the MIM process.
MPI is being employed in both tooling design and simulation of molding. Sintering simulation software, analogous to MPI, is also being developed under a government "Advanced Technology Platform" (ATP) program that is headed by PTI and consists of a team of seven companies and Penn State University. The goal of sintering simulation is similar to that of molding simulation but is not yet developed to the same level.
PTI is using MPI to simulate mold designs before the tool is actually built. The simulations help users determine different gate designs and locations, placement of cooling lines, and melt overflows. "MPI allows us to design the tool for maximum compatibility with the MIM feedstock before incurring the expense of a costly tooling mistake or an unacceptable design," La Salle says.
"We are very fortunate that our company is a very skilled molder and tool designer," La Salle adds. "The software does not replace experience and talent, however, it does allow people who may not have the same level of expertise to become part of the design process. MPI also allows us to do some trouble shooting very easily. Some of the materials we use are very expensive. Therefore, less time on the production floor working through a problem saves labor and material costs. Using MPI, we have been able to run simulations and locate and eliminate unsightly nit lines."
La Salle and his colleagues used MPI on an aerospace flow body part made out of a nickel-based super alloy known as IN 718, known for its strength, durability, oxidation-resistance at elevated temperatures. A flow body directs jet engine exhaust to other parts of the plane, such as heating the passenger cabin.
"Working with Honeywell Engines & Systems (Tempe, AZ), we have been targeting a flow body. Using conventional methodologies, the part is very difficult to machine. By molding this complex, 1.7 kilogram part to a more near-net shape, significant machining costs can be saved. MPI simulation was critical in assisting with gate design and prediction of knit lines," reports La Salle.
Typically, MIM is utilized for parts weighing up to 25 grams. The flow body project entails a much larger part with a three to four-inch diameter. The project is unique for MIM due to the size and shape of the part and the material used. PTI is current working on qualification parts for Honeywell. There has been some beneficial development between the two companies.
La Salle says that he and his colleagues evaluated other software including SigmaSoft and Pimsolver before selecting MPI. "We found that Moldflow has the most experience, technical depth, strong support organization, and widest range of applications," adds La Salle. Goldenberg notes, "When it came down to making a decision, it was an easy choice. MPI offers more user knowledge, so our users did not have to learn a whole new system. Other providers offered us better deals in terms of pricing - unbelievably lowered prices because they wanted to be part of the ATP university program will garner a lot of publicity. They wanted the exposure and were willing to sacrifice the standard pricing of the software. Yet, my engineers opted for Moldflow. That's a powerful statement."
La Salle says MPI is user friendly, however, he advocates taking advantage of Moldflow's training. While the software has only been in place for a short while at PTI, he says it's helped reduce development time by several weeks.
La Salle concludes, "Clearly, more and more manufacturers are using computational and analytical techniques to reduced design time and cost while significantly improving yield and quality. The development and testing of the sintering simulation software using the ATP program led by PTI is one example of this trend."
For more information about Polymer Technologies, visit www.polymertek.com. For more information about Moldflow, MPI, and the company's other software products and services, visit www.moldflow.com.
Author: Laura Carrabine