PIMT technology is an interesting advancement being put forward by Fused Deposition Modeling (FDM) producers like Stratasys and Stereolithography / Selective Laser Sintering (SLA/SLS) companies like 3D Systems. FDM, SLA and SLS are all different types of 3D printing technology.

What does PIMT stand for?

PIMT stands for Printed Injection Mold Tool (PIMT). It is a novel methodology being introduced as a possible way to replace steel and/or aluminum tooling for injection molding (IM) prototyping processes. The purpose of this article is to discuss PIMT technology and to identify applications where it presently makes sense in comparison to other alternatives for IM tooling. We will also discuss where PIMT technology might make sense in the future depending on technological advances, and where it does not make sense relative to the alternatives presently available.

What is the current standard for Injection Mold Tooling?

Injection molding is typically used for manufacturing large volumes of material (mass-production of parts). For such purposes, injection molding machines use aluminum and/or steel molds (a.k.a. “tooling”).

The steel tooling fits into the injection molding machine and is used repeatedly to produce tens of thousands of parts - typically but not necessarily made from plastic. Steel is useful for this purpose because it has a much higher melting temperature (roughly 1370 degrees Celsius or 2500 degrees Fahrenheit) than the plastic parts being created in the tool cavity (which typically have melting points around several hundred degrees Celsius). The large dichotomy between steel’s melting point and that of common IM plastics means that it holds up very well over time.

Other options for IM tooling include Direct Metal Laser Sintering (DMLS), resin casting, and now Polyjet PIMT technology. DMLS is a type of 3D printing where metal powders are turned into a solid through sintering (heating the material to a point that it fuses without becoming liquid). DMLS holds up fairly well in IM manufacturing relative to resin casting and PIMT because the tool material is metal. It is much less robust than a steel tool produced from conventional steel CNC milling/tooling production, however. This is from the crystalline properties that develop when steel is melted and cured, as opposed to being sintered via a powder. Resin casting is less robust still and holds up depending on the properties of the synthetic resin being cured. Similarly, the effectiveness of PIMT depends much on the plastic being injected during the molding process.

What are the advantages and disadvantages of PIMT tooling relative to the alternatives?

1. Compared to conventional steel tooling: The downside of steel or aluminum tooling made from a CNC machine is that they are expensive and time-consuming to create. The upside is that they are useful for high-volume production. PIMT technology may be useful for very low-volume production because it can be created much more quickly, and at significantly lower expense than conventional steel tooling.

2. In terms of production volume: Aluminum and steel tooling do not warp after 10-100 cycles (the creation of 10-100 parts from the same mold tool) in an injection molding production process. Steel can be used for hundreds of thousands of injection molding (IM) production cycles. The downside of PIMT tooling, by contrast, is that it is only useful for low volume production. The limitation is the durability of the printed tool (i.e. the ability to maintain its shape and not warp during an injection molding cycle). The propensity to warp is contingent on the material the PIMT tooling is made from, the characteristics of the material being used for the final part in injection molding, and the geometry of the part being created. The technology has some serious limitations at present and yet shows a lot of potential down the road. Improvements in PIMT technology could provide serious flexibility and price efficiencies in prototype manufacturing. One of the biggest limitations are the material properties of the printed tooling. Therefore, advances in the ability to print more durable materials will vastly improve the capability of PIMT tools for IM manufacturing. The real benefits of this technology may come with the ability to print materials like aluminum and steel cheaper than they can be machined via CNC.

   3.   Pricing: With regard to price, PIMT technology has a relatively low initial cost. That is, Fused Deposition Modeling (FDM) machines and a PIMT tool are much cheaper to procure and produce than Computer Numerical Control (CNC) machines and an aluminum or steel tool (43% cheaper than aluminum tooling and 72% cheaper than steel tooling according to a Stratasys estimate). The relative cost of PIMT begins to climb with the volume of parts needed during production. That is, the marginal cost (the additional cost associated with producing one additional injection molded part) is much higher with PIMT technology than with conventional metal tooling. The reason is that additional PIMT tools must be repeatedly created as they wear out during IM production. These costs are in addition to the baseline material and manufacturing costs of IM manufacturing. Steel tooling, by contrast, only requires a single tool that can quite often be used throughout the entire IM process. There is NO additional cost (either in time or in money) for tooling once the initial investment is made.

How many parts can be made with different tooling alternatives?

The number of parts that can be created is different based on the material being used for the mold.

(Chart from Stratasys)

Conventional Metal Tooling (via CNC): Steel and aluminum tooling (typically created from machining solid blocks on a CNC machine) can easily create 10,000 parts for any plastic that is used in manufacturing - it doesn’t matter.

DMLS Metal Tooling: Metal tooling that is created through Direct Metal Laser Sintering (DMLS) has considerably different utility depending on the material being used in injection molding. For example, a DMLS produced mold might last for 10,000 parts if the final material is something like PE, PP, PS, ABS or TPE’s (low melting point plastics). By contrast, DMLS tooling may only last for 100 cycles for materials like PC+G, PPO and PPS (higher melting point plastics and/or copolymers).

Tooling from Resin Casting: Cast resin tooling is less effective than conventional metal tooling and DMLS molds but still more effective than PIMT. Cast Resin tooling might last for 1,000 parts with materials like PE, PP, PS, ABS or TPE’s while PIMT tooling might only last for 100 parts. With materials that are more demanding during injection molding (higher temperatures or longer cooling cycles) such as PC+G, PPO and PPS, Cast Resin tooling might only last for 100 cycles.

Polyjet PIMT Tooling: Printed Injection Molded Tool technology is likely to deform after only 10 cycles making it a poor fit for demanding IM materials. The utility of different mold technologies over time really depends on the material the tooling is made out of, the material the final parts are made out of, and how many parts are desired by the client. How close the thermal properties are to one another will dictate tooling life and the number of parts that can be created with a single mold. Tooling with significantly more robust thermal properties (higher melt temperatures) than the part material will last much longer than those with properties closer to the part material.

The Effect of Part Material Used In Injection Molding

Materials identified as class A tend to have lower injection temperatures and pressures than the other classes identified. Materials identified in Class “A” include Polyethylene (PE), Polypropylene (PP), Polystyrene (PS), Acrylonitrile Butadiene Styrene (ABS), and Thermoplastic Elastomers (TPE’s). TPEs are often referred to as thermoplastic rubbers and are generally a combination of a plastic polymer and a rubber. The presence of rubber tends to decrease the necessary injection temperature and therefore results in less wear on PIMT tooling. Materials identified as Class “B” include a mixture of Polypropylene and Glass (PP+G), Polyamide (PA), Polyoxymethylene (POM), and a mixture of Polycarbonate and ABS (PC+ABS). Materials identified as Class “C” include mixtures of Polyamide and Polyoxymethylene respectively with glass (PA+G, POM+G, and Polycarbonate (PC). Materials identified as Class “D” include a mixture of Polycarbonate and Glass (PC+G), Poly(p-phenylene oxide) (PPO) and Poly(p-phenylene sulfide) (PPS). The addition of glass to plastic to create a copolymer tends to increase the necessary injection temperature and therefore results in more wear on PIMT tooling.

An Example of Printed Injection Molded Tooling

Stratasys provides a good demonstration video of PIMT tooling being used to create a plastic propeller part using injection molding. You can view the video here. The example they provide uses ABS plastic as the PIMT tooling material and Polyoxymethylene (POM, a.k.a. “Acetal”) as the injection molding part material. The melting point of POM depends on whether it is a homopolymer (single material) or a copolymer (multiple materials mixed). In either case the melting point falls somewhere between 162 and 175 degrees Celsius. The temperature for the injection molding process was 210 degrees Celsius at 300 bar. Other specifications provided in the video include the following:

Mold Material: digital ABS

Injected Material: POM (acetal)

Temperature: 210 degrees Celsius

Injection Pressure: 300 bar

Holding Pressure: 100 bar

Holding Time: 8 seconds

Clamp Force: 150 kN

Shot Size: 65cc

Cooling Time: 30s

While the part is successfully produced, it is important to recognize that Stratasys’ own data indicates that such a process (in this case using an ABS plastic PIMT tool to create POM, class “B” injection molded parts) would only last between 10 and 100 cycles before the printed tool becomes unuseable. If there was no need to create more than 100 parts then the advertised savings are legitimate and as follows:

Time Savings of 700-1800% and Cost Savings of 43% over aluminum and 72% over steel (based on price proposals from two different metal tool makers and the assumption that a new PIMT tool does not need to be created).

Conclusion

PIMT would be useful for prototype injection molding production where only a smaller number of parts are required (e.g. five to 100) and the material they were created from was not critical. According to Stratasys, PIMT is best fit with thermoplastics that have a molding temperature < 300 °C (570 °F). The best material candidates identified were ABS, PA, PC-ABS, PE, POM, PP, PS, TPEs, and glass filled resins used for the creation of moderately sized parts. PIMT technology is very much limited by the material the printed insert is made from in that it likely will not sustain repeated high temperatures without deformation as is the case with steel tooling. An interesting potential application of PIMT technology would be to retrofit a generic steel tool with 3D printed inserts. The same limitations apply, however, for prototype shops interested in small scale manufacturing of a part in certain materials; it would allow them to create the parts without having to CNC a complicated steel tool.

To learn more, please visit our blog and resources section!

*Charts and feature image from Stratasys