Customized Plastic Injection Overmolding With TPO And ABS Material

Customized Plastic Overmold Injection Molding With TPO And ABS Material

Description:

Overmold tooling is classified as insert molding.

To help identify the difference in the two types of molding, think of injection molding as discrete components molded within a closed mold and insert molding as molding around an item inserted into the mold. During the insert molding process, the goal is to completely fill the mold cavity so that the cosmetic and functional requirements of the finished part are met, but at the same time not cause any uncontrolled molding material to exit the cavity and cause damage to the connector or cable inserted into the mold. It becomes a race to inject molding material into the cavity fast enough so it does not cool and cause restriction and then stop it before it flashes (escapes) at the connector or cable openings in the mold.

The key to overmold tooling is not just the mold tool that achieves the desired shape, but the integration of proper cable preparation and connector termination to provide a finished part that meets the quality and cost requirements. If the approach to the design is fragmented, in other words designed to satisfy the electrical requirements without regard for the mechanical requirements of the overmolding process, the finished part typically will be a problem.

Two basic types of injection molding machines are used in the overmolding industry : horizontal injection and vertical injection. Each machine type requires a different mold design and may affect the achieved output of the machine.

Specifications:

Overmold Tooling System

What does the overmold tooling system look like and what are its components?

1. The mold base is the mounting unit attached to the molding machine plattens that holds the mold. There are many options in mold base designs. Universal multi-unit dye (MUD) bases provide off-the-shelf solutions to mold makers, including mold inserts for machining cavity and mold sections. Because these MUD bases typically add cost to the overall tooling system, many companies in the industry design their own custom configurations that allow for a wider range of mold sizes that can accommodate a range of molds at a lower cost.

In vertical injection molding machines, the sprue bushing is where the injection unit lines up against the mold and allows the molding material to flow from the injection unit into the cavity. The bushing should be made out of hardened tool steel and should be replaceable because it can be subjected to millions of cycles

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2. The "runner" is how the molding material is "funneled" through the molds to get to the different cavities. The runners connect the cavities together. Cold slugs or "runoffs" are essential to good cosmetics and reduced scrap rates as they allow material to flow without excess restriction caused by material cooling off within a runner and causing restriction which, in turn, causes material to be injected at higher pressures.

3. The loader bar is a section of the mold usually in one end of the cavity that is lifted up either by hand or the machine to allow the operator to insert a connector or terminated leads into it. Then, the bar is retracted back into place and a new part is ready to be molded.

4. The cavity is where the components are molded. Everything in a cavity is important because it affects the way a finished part will look: its shape, surface finish and size. Cavities can be aluminum or steel, and be polished, textured or plated.

5. A wire shut-off, or "pinch-off," is the section of the mold that pinches off on what is exiting the mold (typically wires) so that the molding material does not cause material to flash outside of the cavity. The fit and design of the shut-off are important. It must be tight enough to not allow the material to flow out of the cavity, but not so tight that it damages what it is shutting off. Shut-offs should be removable so that they can be interchanged with various sizes to accommodate varying cable diameters.

6. Knockouts are rods or pins that come up through the cavity or loader bar sections to eject or push out the finished parts after they have been molded. Knockouts usually leave residual impressions in plastic parts and are used only if required.