Plastic Micro Molding: The big and small of it

Some things just keep getting smaller and smaller. While you might think we are talking about the amount of product in a box, in this case we are talking about electronics, computer chips and tiny parts of smaller and smaller robots of all kinds.

In a world where we are used to things to getting bigger; sales revenue, population, pot holes and government and our waists, it seems backward to get smaller and smaller.

But high technology seems to continue thriving by making things smaller, more powerful and lighter.  It’s actually been happening for a long time. The first car phones were more like a big heavy brick. They required lots of power, its own antenna and generally poor voice quality. Now we can make a phone so small it would just be keys, and earphone, but we attach powerful computers, cameras, and even heart pulse takers to them even though we still call them smart phones.

The first computers filled large air-conditioned rooms with a vast number of cables under the floor to connect each machine and tape drive. Today that same power is in most smart phones. In 1971, Intel invented a silicon chip that had 2300 tiny transistors on it. By 2015 the number of transistors on a chip is estimated to be over two billion! They are spaced just 14 nanometers apart, not visible to the human eye. Those very small circuits work better when electrons have a shorter distance to travel, so are faster when they are small, and they cost less when there is less material[1].

As silicone chips got smaller the plastic parts used to hold them in place in the computer got smaller too. The auto industry followed some years later.

At the same time another growth area has sprung from computers; robots. While we think of robots as human sized (and looking) machines from old 1950’s movies, today they are built in smaller and smaller packages. The Roomba robot is just over a foot across and just 3.6 inches high. This little floor cleaning robot has a low profile on purpose; to get under chairs and sofas. But other small robots have uses too like defusing bombs in small places, or packing them into expensive space craft, or simply a fun inexpensive toy. Of course, drones are small machines that fly with lots of onboard functions.

While the brains may be from silicone, robots are made mostly of molded plastic. Much of this is very small and precise plastic molding.

Together these two trends mean that micro plastic molding has continued to grow as both the processor and robotic fields grow smaller.

Parts that are needed include very small mechanical arms and cogs for movement, and lots of precision support posts, fittings and snap in connectors. They are used for digital displays and display screens.

Sometimes small parts create big problems. Naturally the tooling can be more difficult just because of the precision necessary to mill very small cavities in block steal. Some tools have molten plastic runners that are larger than the width of the part being produced.

Many plastic parts fit together such as multiple pins being inserted into another piece, requiring very high tolerance limits. To lower manufacturing costs, precision snap joints generally have a protruding part of one component, that has a hook, stud or bead on the end. The shaft is deflected slightly to fit the adjoining piece. The spring in the protrusion catches during the joining operation[2].

These joints can be separable, or inseparable based on the shape and flexibility of the material. It’s a simple concept, but the design of the snap joint can make the difference in success and failure of the product. Several types of joints such as cantilever joints, U-shaped snap joints, torsion joints and annular snap joints. Combinations of these joints can be used based on the complexity of the product. Despite the simple concept, much engineering has been done on the physics of these joints and changed due to temperature, and polymer used.  Much more detail can be seen on this paper, Snap-Fit Joints for Plastics.

So the plastic molding and tooling for micro plastic molding must match the precision of the engineering because the parts must be exact to fit together. But that is only half of the story. The other half is completing the job in a way that is efficient and precise across lots of units in a timely way.

This requires lots of experience in tooling and plastic manufacturing process to get it right consistently. Blending the molding process with the design specifications is a special art that Microdyne has developed over four decades.

The world of small will be more and more interesting as we add processing power and software to very compact and complex robots. They will continually improve our lives as they continue replace mundane tasks for us. At Microdyne we look forward to continuing our “Micro” plastics tradition. We plan to get a lot bigger while molding plastic smaller!

[1]The Guardian, Vanishing Point: The rise of the invisible computer, Time Gross, Jan 26, 2017, https://www.theguardian.com/technology/2017/jan/26/vanishing-point-rise-invisible-computer

[2] Bayer Material Science, Snap-Fit Joints for Plastics, page 3, http://fab.cba.mit.edu/classes/S62.12/people/vernelle.noel/Plastic_Snap_fit_design.pdf