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<h1><b>Mold-set design for low-pressure insert molding</b></h1>
<p>Introduction<br>
Any experienced <b>mold maker</b> can manufacture mold-sets for <b>low-pressure
molding</b>. These guidelines will point out some aspects of mold making for
this technology that differs from "<b>high pressure mold</b>-set"
manufacturing.</p>
<p>Materials<br>
Mold-sets for <b>low-pressure molding</b> are normally manufactured from 7075
Aluminum. The <b>polyamide materials</b> are non-abrasive. This combined with
the low injection pressures results in negligible wear on the mold-set. Aluminum
is cost effective to machine. It is excellent at dissipating heat resulting
in shorter cycle times. High wear area where components are inserted should
have inserts from Beryllium Copper or Steel. Mold-sets for very high production
rates can be manufactured from P-20 material or any other convenient tool steel.</p>
<p>Dimensions<br>
Please refer to specific drawings for the different machines. The <a href="a_machines_moldman4000.html">Mold-man
500</a> machine uses two different mold-set sizes. For the <a href="a_machines_moldman8000.html">Mold-man
8000</a> and <a href="a_machines_optimel2002s.html">OptiMel</a> machines the
mold-set size is dependent on the actual application and can vary widely in
size. Typical maximum size is 150mm by 200mm. (6" x 8"). Each mold
half is 48 mm thick. Mold-set guides shall be approximately 35mm long with 6mm
tapered lead. (1.5' long with 1/4" long tapered lead). Two different diameters
shall be used such as 9mm and 10mm respectively.</p>
<p>Cavity Design<br>
The design and surface texturing of the individual mold-set cavities follow
conventional mold making guidelines. It is important to position the parting
line so that the molded components stay in the lower mold half when the mold-set
is opened. This may require a stepped paring line for some application. It is
often possible to avoid the use of locating pins as the low-pressure fill of
the cavity is unlikely to dislocate components. When circuit boards are <b>over-molded</b>,
these can be positioned by locating pins if necessary.</p>
<p>For some applications where holes from locating pins are unacceptable in the
molded parts, a two-step over-mold should be considered. One side of the component
is over-molded first, then the other side. These mold-sets will have two different
cavities and components are moved from the first to the second cavity for completion.
</p>
<p>For pre-molding followed by over-molding of connectors a few guidelines apply:<br>
<b>Macromelt</b> is well suited for pre-molding of connectors with fragile wire
strands or electronic component inside the connectors. It is recommended that
the volume of over-mold material is around 50% of the pre-mold material. The
cavity for the over-mold should be gated to minimize any chance of re-melting
of the pre-mold material. The gate would often be in the <b>strain relief</b>
area furthest from the pre-molded portion.</p>
<p>Venting<br>
The air vents should be 0.05 mm (0.002") deep and up to 2.5 mm (0.1")
wide. Larger parts will require several air vents from each cavity. The vents
should generally be located at the top of the cavity opposite the gate. For
components that protrude more that 1/4" above the parting-line, use inserts
or stepped parting line to allow for venting from top of cavity.</p>
<p>Shut offs<br>
When shutting off around cables and wires, guides are required to facilitate
positioning of the components. Shut offs around wires and cable shall normally
be in the paring line. Shut off around wires is normally 8 mm long and around
cable 8 to 12 mm long. Wire/cable guides are often best made as a trough, which
is two cable diameters deep and positioned "outboards" to the actual
shut off. Use steel inserts for shutting off around steel components, such as
connectors.</p>
<p>Runners and Gates<br>
The polyamide materials contract some 10% when they go from liquid to solid
state. It is critical that the runner/ gate system allows packing of material
during this phase change. The runner shall be slightly oval to release easier.
Typical runner is made with 6 mm (1/4") ball end mill 2.7 (0.106")
deep in each mold half.</p>
<p>Normal gate to be 1.5 to 2.0 mm square by 0.5 mm long (60 to 80 thou square
by 20 thou long). Round gates should be 1.5 to 2.0 mm diameter by 0.5 mm long.
Gates should taper inwards from the runner to the cavity to ensure that gate
material stays on runner after removal.</p>
<p>Ejector Systems<br>
Most production mold-sets utilize ejector systems. The design follows conventional
guidelines: Guide-pins and ejector-pins are sandwiched in between a base plate
and a retainer plate. This sandwiched arrangement slides on shoulder bolts with
return springs. Typical ejector stroke ranges from 3 to 10mm depending on the
application. Refer to mold-set drawings for center of machine ejector system.</p>
<p>Cooling<br>
Mold-sets for <a href="a_machines_moldman8000.html">Mold-man 8000</a> machines
do not require any cross drilling for cooking. The aluminum mold platens are
water-cooled. Mold-sets for <a href="a_machines_optimel2002s.html">OptiMel</a>
machines requires simple cross drilling for direct water cooling. The cooling
channels should normally be 6 mm diameter and equipped with quick connectors
for ease of set-up.</p>
<p>Release Agent<br>
Release agent is required for the mold-sets. A new mold-set may require application
for this release agent several times daily. Extensive research has gone into
selecting the optimum release agent for this technology. We recommend using
MONO-COAT E255 from "Chem-Trend Incorporated". Phone no. (517) 546-4520.</p>
<p> </p>
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