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April 1, 2002

7 Min Read
PIM: Technology and folklore

By: Randall German

Many engineers think of injection molding metal and ceramic powders as a new field. That is not true. Various forms of the technology were practiced more than 60 years ago.

Today, in powder injection molding (PIM) we are encountering rules that have no underlying explanation. Folklore is defined as traditional customs, tales, or sayings that are preserved orally—they tend to be widely held yet unsupported notions. It's scary, but we do have plenty of folklore in powder injection molding.

We can attack folklore by broadening our search for information, by asking experts, and by seeking fundamental facts. Here are a few examples of widely held misconceptions about PIM.

  • Special molding machines are required.
    Certain molding machine characteristics are better suited to PIM, especially for higher levels of precision, but many firms are successful with a variety of molding machines. The evidence suggests that there is no single manufacturer or design that is necessarily best.

  • There is easy money to be made in PIM. 
    With its maturation, PIM is a healthy technology that continues to grow by satisfying more and more sophisticated customers. But players with favorable financial positions tend to be more than 10 years old. These leaders have established manufacturing systems that are benchmarks for all net-shape manufacturing. To assume that a late entry will jump into this class is not realistic. Yes, there is success if you work long and hard, but PIM is not a route to quick riches.

  • Only a few firms understand the technology. 
    There are more than 500 firms, several university programs, and a dozen research institutions supporting PIM commercialization. No one has a lock on the technology. The basic concepts are out of the box, so it is unrealistic to think that any participant knows more than another. Yes, there are 25 or so groups that dominate the technical advances, but it is not wise to assume one is smarter or more knowledgeable than another. The field has many successes, failures, and much cross-fertilization, so there is no single pathway or technology that leads to success.

  • A license is required to practice PIM. 
    Some of the first commercial developments in PIM were so long ago (1940s and 1950s) that we have trouble reconstructing the history. In the 1960s, Corning used ceramic PIM to form tableware, a technology that survives in the ceramic casting core business today. In metallic PIM the original patents have expired and the early practitioners have been absorbed by other companies. However, the current supplier network provides an excellent support base for startups. The generic technology really works well and most of the ingredients and equipment can be ordered with a phone call. So, if a company wants to have its hand held during the startup phase, that is fine, but to think there is a proprietary or special technology that requires a license does not reflect reality.

  • You need a materials scientist to succeed. 
    This is a myth that is close to reality in some cases. Several plastic injection molders have successfully entered PIM but struggle with controlling impurity effects on properties, heat treatment specification, and other basic aspects of materials engineering. These can be mastered without full-time staff. One startup called on a skilled metallurgist on an as-needed basis who was staying home with young children. Another plastics firm initially relied on feedstock and furnace vendors for support. A plastics molder in Canada used a network of small contracts to seed critical developments during startup. However, to pass $5 million in annual sales a company needs to master three technologies—materials engineering, manufacturing engineering, and plastic molding—but you can start with only one or two.

  • Powder costs will continue to fall. 
    As PIM growth takes place, some of the powders (especially prealloyed stainless steel) have declined in cost as volume has gone up, but consumption has been increasing faster than the cost reduction. In other words, powder sales (dollars) have increased 20 percent per year while powder shipments (tons) went up 40 percent per year. Along with improved process yields, the increasing tonnage generated a price decrease. For some chemistries this sort of volume growth will not be sustained. For example, with titanium there is much hope for cheaper powder, but if total sales for PIM titanium powder saturate at $15 million, then there is less incentive to invest in improved productivity to lower the price.

  • Component producers that purchase the same feedstock allow for movement of an order between sites. 
    Clearly, a significant trend in PIM is the reliance on purchased feedstock, but that does not cure the need for similar molding practices, equipment, and secondary operations. In general, tool design is highly variable and customized to the shop and molding machine. Hence, moving an order to a second site might produce problems beyond the feedstock, so there is no assurance of success along these lines.

  • Newer binders enable cost-effective production of large components. 
    The binder is not a barrier to large component production by PIM. Large components out of stainless steel (up to 12 kg or 26 lb) were produced in the 1980s using a traditional wax-polymer binder, and today large ceramic components are in production at several sites. There are problems with large components, but more significant are the economic barriers. In metals, as the mass increases, the raw material cost difference (powder vs. casting) leaves plenty of margin for machining the casting. Thus, changing the binder will not solve the critical powder cost issue. Indeed, several economic problems arise with large PIM components. Besides powder cost there are penalties because the molding machines are larger, molding cycles are slower, and debinding times are longer. Accordingly, PIM is less cost-effective as size increases, independent of the binder.

  • Low-pressure molding is less costly. 
    Low-pressure PIM machines are used to reduce machine cost and tool wear. They are used by about 15 percent of the industry, but do not decrease overall manufacturing costs because they lack automation and usually form parts in just a single cavity. So yes, the purchase price is lower (capital cost), but in a comparison across the industry, low-pressure molding shops have lower sales per employee. More important, without high pressure the components formed with a low packing pressure tend to have more internal defects. For surface features (such as in sand blast nozzles and watchcases) there is no problem.

  • Continuous sintering in hydrogen is a PIM evolution. 
    The use of hydrogen sintering in a pusher furnace was first applied to refractory metals and stainless steel in the late 1940s. It was widely used for that application at many sites prior to the first commercial PIM use in San Diego in 1985. Today, continuous furnaces constitute about 20 percent of the installed sintering capacity in PIM and prove most productive for long-running components.

  • Metal powder injection molding is just another form of powder metallurgy.
    Although a few companies practice both PIM and traditional die compaction powder metallurgy, the two have little in common. Metallic component production dominates the PIM industry, leading to the term MIM;for metal powder injection molding. Metallic PIM accounts for two-thirds of the installed production capacity, 60 percent of the employment, and the majority of sales and profits. However, the powders used in PIM are much smaller, the tooling and molding machines are different, the sintering furnace and cycle are different, and the final density and performance are higher via PIM, thus leaving little in common with the traditional die compaction form of powder metallurgy.

    Editor's note: A recognized expert in PIM, Randall German is Brush Chair, professor in materials, at Penn State University in University Park, PA.

    News from Thixomat Inc., Child Hope International, Latitude Mfg. Technology, Honeywell, RTP, BorgWarner Morse TEC, Metal Injection Molding Assn. (MIMA), Metal Powder Industries Federation (MPIF), Complexshap.net, and Husky.

    Contact information
    Center for Innovative Sintered Products,
    Penn State University
    University Park, PA
    Randall M. German; (814) 863-8025
    www.cisp.psu.edu; [email protected]





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