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Taming LSR: Molding liquid silicone rubber with Mike Tranquilli

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And now, here’s our chat with Manufacturing Manager Mike Tranquilli, on the topic of LSM (that’s liquid silicone molding). Enjoy!

Tell us about Apple’s liquid silicone rubber (LSR) capacity.

We have 20 injection molding machines. Seventeen are horizontal. Three are vertical — they range from 14 to 110 tons.  They are set up to accommodate different shot sizes — the smallest one is a quarter of a gram, and they go up to 350 grams (a little over ¾ of a pound). Most of them are electric and servo-controlled for precision and accuracy.

We also have a certified Class 7 cleanroom which has three injection molding machines.  This gives us the ability to meet any medical requirements our customer might have.

Which, of course, includes molding complex shapes.

Yes, LSR [liquid silicone rubber] is hard to control, and flashes easily. The key is to be able to displace or vent air out of the cavity to achieve a complete fill in the tool.

With our higher control, we configure and mold parts that have minimal flash when they come out of the tool — they don’t require any secondary operations to clean them up afterwards.

You also have more control over shot profile. We can fill at different pressures and feeds when we need to weave around complex corners and shapes.

Are these parts always “all rubber, all the time”?

No. With our capacity for control, we can also do over-molding — that is, shoot LSR around various substrates, like metal, fabric, or screen. The resulting seals are flash-free and essentially two parts pre-assembled into one. This cuts down on secondary work for customers. Instead of two components to assemble, you now just drop in one part.

Tell us about your low cycle time and automation. Does that create the opportunity to run high-volume molding?

Yes. Our machines’ capabilities and our set-ups give us the ability to mold a large volume of O-rings or seals. We have O-ring tools from a single cavitations up to 800. Also, because of our standards set-up and mold design, removing the parts from the tool can easily be is automated.

What are the benefits of cold rubber molds?

Well, there is not as much waste. Once you mold LSR, it can’t be recycled. So with the cold runner, as you feed directly onto the part and into the cavity. You eliminate the runner from standard tooling.  Since the material does not go through a runner, you don’t pick up as much of the heat history. Again, that gives you more control over each cavity fill, and control over individual fills.

Cold molding is also beneficial in higher volume situations. Volume becomes the justification for the more expensive tooling and set-up process — you reduce waste and spend less on materials.

With the cold runner set-up, we have standardized they way we shoot groups of parts. We can shoot multiple groups at once, gaining more capacity and control over the fill and production.

Let’s end this with a summary of Apple Rubber’s molding capacity.

With our capabilities and controls, we can produce higher quality, higher standard parts. We can supply a wider range of industries, including medical and aerospace, fulfilling their high-precision requirements.

It’s a win-win for us and our customers. We even have two LSR compound UL listed to UL50 to meet customers’ complex housing seal electrical enclosure designs.

Thanks for your time, Mike!