Stratasys PolyJet 3D Printed Injection Molds…A Series

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What if your plastic material requirements for your production parts are more than what rapid prototyping/additive manufacturing technologies can produce? What if you need low volume, say 100 parts in your production material? What alternatives are available?

SolidWorks

One method would be to use injection molding. The injection molding process is very fast and therefore very economical. Yet, every part needs its own costly injection mold making injection molding viable only when mass-production is needed (usually more than 10,000 parts). Injection molding tools take from weeks to months to build. Very often, design mistakes are made and mold changes are needed. In this case time-consuming mold corrections have to be made, usually at your expense, increasing costs and product time to market.

SolidWorks

Another method involves the use of lower-cost, simplified and smaller tools (e.g. one cavity instead of multi-cavity) or using tools of softer and cheaper materials (aluminum). In this case some tooling cost is saved but still tools are expensive and, as with production tools, time is needed to build and make costly mold corrections once again usually at your expense.

SolidWorks

However, there is another method for these low volume runs, Printed Injection Molding Tool (PIMT). Stratasys has developed materials that permit 3D printing of the tool itself, not the parts. The printed injection molding tool (PIMT) is installed on the injection molding machine and the plastic part is injected using the actual production material. PIMTs are relatively inexpensive to build, fast, and ready to inject in a few hours/days. If design changes are needed, the corrected PIMT may be ready and installed in the injection molding machine by the evening shift. PIMTs are suitable for small production series but since tool cost is low, they are commercially viable also when only a few parts are needed. Stratasys PIMTs are not production tools, however they provide a clear advantage, being both cheaper and faster when a limited quantity of production parts is needed.

FAQ's

1. Polymers:

Stratasys PIMTs can be used to inject polyethylene, polypropylene, polystyrene, ABS, and thermoplastic elastomers. However as the polymer's processing temperatures increase, the tool's life will tend to decrease.

2. Part Features:

Stratasys PIMTs are able to produce complex parts including features seen in most injection molding parts such as living hinges, holes, thin and thick walls, bosses, gussets, ribs, press fits, snap fits and logos.

3. Part Size:

Stratasys PIMTs are especially suitable for small parts. Maximum size is limited to the relevant machine normally a 70–80 ton press and no more than a 10" cube.

4. Printed Mold Accuracy:

The overall accuracy for the PIMT, on a well calibrated machine is typically 20-85um for features below 50mm and Up to 200μm for full model size.

(Depending on geometry, build parameters and model orientation)

5. Tool Life:

Depending on polymer and part complexity, PIMTs are suitable for the injection molding of up to 100 parts or more. If multi-cavity molds are used then the number of parts can be multiplied.

In the next posting of this series we will discuss the PIMT mold material, types of molds, mold design, and molding processes (e.g. molding pressures, cooling and ejection).

Resources: Stratasys 3D Printed Injection Molding Tool ("PIMT") Guide

Derek Ellis

Sr. Application Engineer

Computer Aided Technology