Over Molding/Soft Touch Molding - How can you benefit?

Posted by Al Elger on Aug 25, 2011 10:00:00 AM

blank.pngIt’s a world of hand-held devices we live in today, a world of smartphones and electronic toothbrushes, GPS assistants and specialized power tools for the shop, lab, kitchen, and garden. Nurses check patients with electronic thermometers, contractors align studs with pocket-sized levels, chefs whip cream and eggs with hand-held blenders.

And what, besides electricity, do all of these devices have in common? They’re all made, more or less, from plastic - indeed, in many cases, two kinds of plastic: Inside, a molded plastic frame provides strength and rigidity. On the outside, another type of plastic gives the device a precisely-engineered look and feel: bright colors, a distinctive shape or contour, and perhaps most appealing, a slightly soft, tactile surface that’s pleasant to the touch and just tacky enough to prevent slipping and sliding.

Smiths Medical Over Mold

Plastics, especially as employed in hand-held products, have come a long way in recent years, shedding their, well, plasticky feel while gaining in durability, impact resistance, and ergonomics. Plastic cases can be produced, now, that are much less vulnerable to dropping than their predecessors. Screens are more resistant to scratches. And overall, devices can be shielded much better against extreme heat, water, vapor, and dust.

Making all this possible is a technique called over molding. It involves molding an outside layer of one kind of plastic over, or around, an inner structure molded from a different plastic, thus creating a single item that combines the best qualities of each material. Using this two-stage process, hand-held products can be produced that are highly resilient and also, pleasing to the touch and to the eye. Or, the outer layer of plastic may be chosen because of its special properties as an electrical insulator, its ability to absorb sound or vibration, or its protection against water.

Over molding also offers a means of producing highly intricate pieces that would be too difficult to make in one injection molding process.

Over molding takes special skill and experience, though, to be executed at high volume and with acceptably high manufacturing yields. One major challenge: The two materials involved may have radically different physical properties such as the temperatures at which they melt or how much they expand when heated. If there’s a mismatch, the inner and outer layers of plastic may not fit together properly, or they will adversely affect each other, mechanically or even chemically.

Thus, great care is required at every step of the design and manufacturing processes. First, materials must be chosen for maximum compatibility. Then, great precision is required in designing the pieces to be molded, constructing the two molds, and controlling the two-stage molding process. The aim is to get the two molded plastics to bond together just so and thereby produce what amounts to a single item that has complete and long-lasting structural integrity. No primers or adhesives are used, it’s all a matter of fit.

Kaysun Corporation prides itself in its deep experience in over molding. The company has put its seasoned design, manufacturing, and assembly methods to work for makers of products in a wide range of industries.

Rockwell Collins, for example, chose Kaysun to build the case for its DAGR, or Defense Advanced GPS Receiver, a lightweight, hand-held device designed for use by soldiers in the field. Kaysun was able to build all of the tight-tolerance molds and tools involved in just 6 weeks.

For Smiths Medical, Kaysun helped to design and then built the case for a line of pulse oximetry devices - also hand-held and used to non-invasively measure certain qualities of blood. After analyzing more than two dozen components, Kaysun offered a number of design suggestions, designed the manufacturing and assembly process, and leveraged its deep expertise in polymers to select the right materials for the oximetry product.  The bottom line: Because only one manufacturing platform was involved, Smiths Medical enjoyed additional cost efficiencies. And by giving its end-user customers a product with more options and greater flexibility, the company significantly strengthened its position in the market.

Download our Whitepaper on Complex Injection Molding

Or learn More by reading these case studies:

Smith's Medical Case Study

Rockwell Collins Case Study