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| Insert Molding Basics |
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Insert molding, which is the process of injection molding plastic in or around another object, is easily accomplished
with "Wasp" Mini-Jectors. Items such as cord sets, grommets, slip ring and brush assemblies, fishing lures, and
handles on utensils are being successfully molded using the Mini-Jector. The "V" mold allows the operator to
place the inserted object(s) in the mold halves and then assemble the two halves together before placing them
in the machine. This ensures that the insert remains in its proper place until the mold is filled.
There are several ways to locate an insert placed in the mold. Let's use a knife handle mold as an example. If
the knife blade has a shoulder, this creates a convenient point to line up the insert with features on the mold
to ensure proper location of the insert. Location of the insert could also be accomplished via a small hole in
the blade that could be placed over a corresponding pin in the mold.
Once the insert is properly located, the next issue is sealing the juncture where the molding is to end. The
ability of the mold to seal off at the desired point is highly dependent on the tolerances held in manufacturing
the insert. When dimensions cannot be held to any degree of precision, a high temperature plastic such as Teflon
can be used as a seal at the "kiss" point. This allows some flexibility because the sealing material will conform
to the irregularities of the insert. This also works well sealing around wire, as in a cord set mold.
When molding around wire, you want the machine to squeeze the wire slightly, not only to seal it off, but also
to prevent the pressure of the material in the mold from blowing the wire out of the mold. Remember, however,
that the self-clamping "V" mold must undergo its wedging action before this squeeze is applied. If the wire
insert requires a large degree of compression, the molten material may flow out between the mold halves before
the nozzle force can clamp the mold.
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| Encapsulating Mini-Circuits and Other Delicate Products |
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When an entire object with fragile components (such as a mini-circuit) is to be encapsulated, the encapsulation
can be done in two stages. First, the object is encapsulated with a soft, easy-to-mold material such as
plasticized PVC. This is similar to epoxy potting. Then, the potted part is encapsulated with a harder material
at much higher pressures, producing a sandwiching effect. This is referred to as "overmolding."
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| "C" Model Machines for Cable Splicing Repair |
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The model #45C, #50C and #55C machines are variants of the standard "Wasp" models designed to mold splices
on repaired or joined cables. The mold is at right angles to the normal position, and the injection unit is
mounted on "C" supports to allow the cable to be lifted into the molding area without machine parts interfering
with the cable.
Very large cables or cables with many wires may have to be stretched between the two sides to prevent the hot
plastic from pushing the wire down, creating a void. This stretching can be accomplished by putting two compound
machinist's vises at each side of the mold area. The cable can be clamped in the vises and stretched by moving
the compound slides.
In cable repair or other insert molding around wire, heating the mold or the ends of the wire may assist in
sealing the ends of the molding around the wire. On the "C" model machines, the optional mold heat package heats
the mold by heating the "V" slot (which is insulated from the machine base), which transfers heat to the mold.
On other "Wasp" machines, the mold can be pre-heated in an oven. (Always use proper insulated gloves when handling
hot molds).
Typically, the squeeze of soft insulated wire (such as PVC or elastomer-coated wire) by the mold should be at least
0.010". If you have a wire diameter of 0.375" the hole in the mold surrounding the wire should be no larger than 0.365".
Make the clearance smaller on new molds; they can always be enlarged if the squeeze is too great.
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