Injection molding vs SLS polyamide

Posted in Manufacturing , on Monday, September 22

For most of the time developing DURR Beta, we were quite fixed on having the back cover and battery cap in injection molded PE plastics. CNC milled aluminum molds can make this a fairly affordable option that can produce up to around 100.000 parts per mold. However, up until the last phase before production, we looked at alternatives and ended up using SLS polyamide... again.

After, perhaps not the most extensive round of research for low-volume injection molding factories, we kinda settled on a British service called Protomold . They have a great support team, awesome webpages with live calculator tools, and they even sent us samples of the plastics we were considering. Low-volume injection molding really seems like one of their expertise and they also mill their molds at the same factory.

We'd really made an effort in making the geometry moldable, with all kinds of clever (at least in our humble opinion) solutions for difficult problems. However, when comparing the small volume we wanted of injection molded parts to SLS polyamide parts the price couldn't be overlooked; The service Sculpteo Pro offers batch discounts, resulting in almost a third of Protomold's price. Keep in mind that our parts are fairly tiny in size, as well as quite complex. Many many, larger parts with simple geometry might give a completely different picture. The difference for Sculpteo's batch prices also accounts when comparing with other SLS services like Shapeways and Ponoko .

A quick overview of the advantages for the two options:

SLS Polyamide (Sculpteo Pro; batch order):
· Cheaper (for the geometry, size and volume at hand)
· Freedom in geometry; no tools, draft angles, separation lines, etc.
· Allows testing and tuning, with the actual material.
· Flexibility in volume, especially if re-fills are necessary.

Injection molding (Protomold; aluminum mold):
· Large range of materials/ plastics.
· Larger range in color. (You can even get your own plastic from a third party).
· Better finish, accuracy and quality (again we have small parts and really small features)
· Cooler. We're kinda sick of using SLS, and wanted to do like the big dogs. Some other time tho...

Also worth mentioning, we had a some problems with our order at Sculpteo. This might have been bad luck, or because of low staffing during summer. However, a delivery time of about 6 weeks when the order says 5 business days really held us back towards the end. Our shipment was continuously delayed due to machine issues and arrived in a number of smaller batches, which also led to differences in color and dimensions.

Not all parts held up to standards and were weeded out. The final result was acceptable for the finished product, but did leave room for improvements.

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