|
Frequently asked questions
Over
- moulding Macromelt®
Moulding
Process Moulding
Machines Mould sets
Frequently asked questions on over -
moulding
1.
Can
you over-mould a PCB with surface mounted components?
Yes, we have over-moulded hundreds
of different PCB’s without damaging boards/components or reflowing solder.
Tests show that material injected at 218°C (425°F) typically will cool down to
less than 150°C (300°F) by the time it reaches the board.
2.
Is
the final component distorted in any way with this process?
No, not if proper design
guidelines are followed. (Uneven encapsulation such as a very thick material
section on one side of a PCB with a thin layer on the other could result in
warping).
3.
Will
the part maintain dimensional stability after moulding?
Shrinkage ranges from 1 to 1.5%
for the different Macromelt materials.
4.
How
can air bubbles be avoided in the final moulded part?
Ensuring that the mould-set is
vented correctly and optimising the injection profile is the key to avoiding air
bubbles. Densely populated circuit boards may require several steps in the
injection profile to avoid any “shadow effects” behind components. We would
typically start by optimising flow with translucent materials to detect where
voids occur and then change to black materials for production.
5.
Can
batteries be over-moulded without reducing their effectiveness?
Many types of batteries have been
successfully over-moulded with Macromelt. However, simple prototype over-moulding
for a particular battery is recommended before starting full-scale production.
6.
Which
wires, cables, circuit boards and solder masks do these materials adhere to?
Macromelt® adheres well to most
substrates including PVC wires and PCB’s. Henkel Corporation offers adhesion
testing of their Macromelt® materials on any specific substrates; this type of
testing will identify the most suitable material for a given application.
7.
When
should this technology be considered for grommets and strain relief moulding?
The adhesive properties of the
Macromelt® material will offer great seal and strain relief to most wire and
cable materials. When true strain relief is needed especially for sensitive
cables/applications such as Cat 6 patch cords and connectors, the Macromelt®
materials are superior.
8.
Are
over-moulded parts water proof?
Over-moulded components will
typically meet or exceed IP 67 rating for the type of environment it is capable
of operating in. This means they are dust tight and protected against the
effects of immersion. The selection of Macromelt® material grade is critical as
there are different degrees of water resistance.
[top]
Frequently
asked questions on Macromelt®
Materials
1.
What is Macromelt®?
Macromelt® is group of high
performance polyamide adhesives. They are essentially reformulated hot melts
with strong adhesive properties designed specifically for insert moulding of
electronics. Macromelt® is a thermoplastic material that cures simply by
cooling. It does not cross-link nor does it release any toxic fumes.
2.
What is the minimum tolerance that the
Macromelt‚ materials can hold?
Tolerances of 0.1mm (+/-
0.004”) can be met on smaller components.
3.
Can material regrind be used?
For applications where adhesive
properties are critical, regrind should not be used. The regrind material will
contain a small amount of mould release agent, which could compromise adhesive
properties. Furthermore, the mechanical properties of the material will degrade
some from repeated re-melting. For non-critical applications the runners can
simply be thrown back into the melt reservoir without any regrinding. It is
strongly recommended to confirm that components moulded from “regrind”
material meet specifications.
4.
How do Macromelt® materials compare to
engineered resins economically?
Macromelt® rarely replaces
traditional plastic materials directly. If a component can be moulded
successfully with PVC, there is no reason to consider Macromelt®. If PVC moulding results in high scrap levels as a result of high injection pressure,
Low-Pressure Moulding may be more economical as a result of reduced scrap.
Typically, the Low- Pressure Moulding operation is an alternative to potting as
it replaces several manufacturing operations. Over-moulding with Macromelt® is
typically a single step process. When a component is over-moulded with Macromelt®
there is normally no need for a separate plastic housing. The over-moulding
material becomes the housing.
5.
Who will provide technical support for the
materials?
Henkel will supply material
support. Application engineering and support such as prototypes and the
development of moulding parameters will be supplied by Engineering Solutions Ltd.
6.
What is the delivery time for materials?
The Macromelt® OM product line
is manufactured in Europe and warehoused in the UK.
Henkel generally keeps about 2 tons of each material above forecasted
volumes. Drop shipments from Henkel or Engineering Solutions customers usually
take 5 business days form the point the order is made with Henkel customer
service. Other Macromelt® materials (used for moulding) are also readily
available.
7.
How are the materials packaged?
Should they be dried prior to
use? Materials are shipped in double walled 20 kg (44 lbs.) bags. The materials
are nylon-like and will absorb some moisture from the air. The materials are
shipped at the recommended level of 0.2% moisture and should be kept in an
air-tight container after the bag has been opened.
8.
What is the typical shrinkage of the materials?
Shrinkage varies during injection
and can usually be controlled by packing the mould with pressure. The
shrinkage rate 24 hours after injection is 1 to 1.5%, depending on the grade of
material.
9.
Do dyes and pigments added for color change the
material properties?
Generally, there isn’t a
dramatic change in properties (i.e. black versions of the products are similar
to amber). The pigment is extruded into the amber Macromelt material. However,
any colored material, which requires opacity (i.e. white), would need a
significant quantity of inorganic filler, which will affect most of the
properties.
10.
What is the typical viscosity of the material?
Macromelt moulding materials
typically have a viscosity range of 2500-5000 cP at 210°C (410°F).
[top]
Frequently asked questions on the Moulding
Process
1.
How long is a typical injection cycle?
The moulding cycle is dependent on
the size and material section thickness of the component. Typical cycle times
range from 15 to 45 seconds. Multiple cavity mould-sets can be used to reduce the
actual moulding drop rate.
2.
What is a typical injection temperature for these
materials?
Melt reservoir temperature ranges
from 190 to 230°C (370 to 450ºF). Depending on mould-set design, this would
typically correspond to cavity temperatures of 135 to 180∞C (275 to 355ºF).
3.
Do the moulds need to be heated?
No, mould-sets are typically
cooled to approximately 20ºC (68ºF). The Mould-man® series of machines require
no direct mould-set cooling since the mould platens have chilled water circulating
through them.
4.
What is the lowest pressure that parts can be moulded?
2 Bar (30 psig) is typically the
lowest practical pressure. For anything lower the runner and gate design become
very critical. Injection pressures from 4 bar to 20 bar (60 psig to 300 psig)
are typical.
5.
How do you control the filling of the cavity?
The Cavist Mould-man® series of
machines offer programmable injection profiles. A typical profile would consist
of filling 90% of the volume into the cavity at relatively high flow rate and
then packing at low pressure. Packing pressures are typically from 50 to 150
psig and such pressures will not over-pack a cavity. Packing is critical to
prevent sink and voids as the Macromelt® material will shrink when they
transition from liquid phase to a solid.
6.
Are any special de-gating tools required?
No.
7.
How are the moulds cooled?
The Cavist Mould-man® series have
permanent water connections on the side of the machines. This feature allows you
to run chilled water through the mould platens. Mould-sets are then cooled via the
water-cooled mould platens. Typical mould temperature is around 20°C (68°F).
8.
How do you ensure sealing of the component?
Selecting the appropriate
Macromelt® material best suited to the application is the key to sufficient
sealing of the component. Typically the best surface wetting of the component
occurs with lower viscosity material at relatively high temperatures. Higher
packing pressure may also help ensure surface wetting and sealing. The component
design is also crucial. Low-Pressure moulding works best when encapsulating
around a component versus filling into the housing.
9.
Can a conventional heated screw and barrel type
machine be used for moulding?
This has been accomplished a few
times and unsuccessfully a lot of times. Macromelt has very low viscosity at the
correct processing temperatures compared to engineering plastics. This low
viscosity can cause the material to bleed backwards through the screw and
essentially glue it together. Mould-man® machines use positive displacement gear
pumps designed for lower viscosity fluids to inject the molten material into the
cavities.
10.
How much waste do you get with this process?
Typically the material in the
runner and gate is waste. This can represent anything from a few percent to 35%
for very small components. When runners can be recycled for less critical
applications, the waste is zero. With hot runner equipment, most applications
will have zero waste.
[top]
Frequently asked questions on the Moulding
Machine
1.
Does Engineering Solution Ltd provide start-up
training for the Mould-man® machines?
Yes. Start-up and training
typically takes 2 to 4 hours depending on the number of operators.
2.
Who will provide maintenance and user support for
the machines?
Detailed maintenance guidelines
are supplied with the machines and it is strongly recommended to set up
scheduled maintenance. Keeping the melt reservoir clean is the single most
important step towards success with this technology. Engineering Solution Ltd
and Cavist Corporation will also be available for support.
3.
Is the gear pump on the Mould-man® machines
designed for the shot or does it work with a PLC profile?
The gear pump motor is run
through a variable frequency drive with a PLC control. The Mould-man® series
offers programmable/multi-step injection profiles.
4.
What is the delivery time for machines?
Typically 12 weeks.
5.
Are there demo units that can be leased for
prototyping?
Prototyping is typically
performed at Engineering Solution Ltd facilities. Leasing equipment is possible
– please contact Engineering Solution Ltd for details.
6.
How many parameters will need to be set prior to moulding?
6.1. Installation of the mould-set/setting of zero (closed
mould-set parameter)
6.2. The ejector system is activated if applicable
6.3. The injection parameters including temperature,
pressure, injection time and cooling time are set.
Including the installation of the mould-set, the complete
set-up typically takes less than 15 minutes. When a mould-set is run-in for the
first time, extra time must be allowed for optimization of parameters.
7.
Will a special technician need to be trained in
setting up the machine?
All moulding parameter entry is
via the touch screen. The training for this will take no more than 1 hour and is
also fully detailed in the operations manual.
8.
What features are on the PLC controller?
The PLC controls temperature of
reservoir, manifold and hose, clamp operation, injection cycle including
profiles and pump speed (VFD), ejector operation and some safety functions. All
parameters are entered through the simple touch screen menu.
9.
What are the more frequent maintenance items on
the equipment?
Most problems are caused by
insufficient upkeep of the melt reservoir. If the melt reservoir is not cleaned
on a regular basis, charred material will build up on the fins, reducing the
heat transfer to the material. This can lead to “short shots” (incomplete
over-moulds) and various blockages. If the material is left in the reservoir for
days at high temperatures, it will get more viscous and eventually not flow. The
melt filter must be replaced as per the maintenance guidelines. The injection
nozzle and the pump seal will require replacement periodically.
[top]
Frequently asked questions on the Mould
sets
1.
What are the best materials for the construction
of the moulds?
7075 Aluminum is well suited for mould-set manufacturing. Aluminum offers excellent heat transfer (i.e. short
cycle times). Aluminum mould-sets are relatively soft and care must be taken not
to damage the cavity surface. If the component to be over-moulded has steel or
hard glass filled components, it is recommended to have steel inserts in this
area of the cavity. This is generally required when moulding connectors. Mould-set
can also be manufactured from tool steel such as P-20. It may be required to
cross drill steel mould-sets to ensure sufficient cavity cooling.
2.
Can the mould be plated to eliminate mould release?
The Macromelt® materials have
strong adhesive properties and tend to stick to most surfaces. It may be
possible to use some coating for permanent mould release, but we cannot recommend
any specific coating systems at this time.
3.
What kind of mould release is recommended?
After extensive testing of a wide
range of mould release agents, one product has shown superior performance.
Mono-Coat E-255 from Chem-Trend Incorporated. We
do not recommend the use of Silicone based release agents when over-moulding
electronic components. Silicone can migrate over time resulting in partial
electrical insulation and non-functional components.
4.
What type of flow analysis is done prior to mould
design?
None typically. However, existing
software packages for mould flow analysis can be used for this technology as long
as material viscosity is taken into account.
5.
What are the maximum dimensions for a mould-set
for use on the Mould-man® ?
Mould-man® 8000: Maximum 200mm
(8”) wide by 150mm (6”) deep. Mould-man® 8100 / 8200 / 8300: Maximum 250mm
(10”) wide by 200 (8”) deep.
6.
What is the delivery time for mould-sets?
Typically 6 to 8 weeks when
purchased from Engineering Solution Ltd.
7.
Are multi-cavity moulds practical considering the
single station machine only has 1 ton clamping force and the shuttle and rotary
machines only has a maximum of 5 ton clamping force?
Multi cavity moulds are normally
used for all production moulding. 1 ton of clamping force may sound limiting, but
with packing pressures rarely exceeding 10 bar (145 psig) this will normally
allow for cavity cross sectional area of at least 80 square centimeters (12
square inches).
8.
Will a moulding profile be pre-determined for mould-sets provided by Engineering Solution Ltd?
Yes, any mould-set from
Engineering Solution Ltd will be documented so that all moulding parameters can
be entered directly. Some minor fine-tuning may be required as a result of
different ambient conditions.
9.
Are the gates on the mould much different than
those used in traditional engineered plastics?
Typical gates are 2mm (0.080”)
diameter and 0.5 mm (0.020”) long. A tapered design is normally recommended to
ensure the gate brakes consistently from the component without any cutting.
10.
What would be the price range for a typical production mould-set?
Prototype mould-set?
The price range for production mould-sets will vary widely depending on number and type of cavities. Four-cavity
mould-sets for single station machines will typically range from £5,000 to £10,000.
We can offer prototyping services (where the mould-set fixture remains the
property of Eng. Sol) for £750 to £1,500 which would include 10 to 50
completed parts for testing.
[top]
Over
- moulding Macromelt®
Moulding
Process Moulding
Machines Mould sets
| 