Achieve ultra-thin protective coatings
Overmould Ltd’s High Pressure Resin Transfer moulding service provides a reliable and cost-effective way to reduce your cycle times and reduce overall project costs. We coat and protect electronics with incredibly thin resin coatings of a high temperature and highly chemically resistant material.
What Is High Pressure Resin Transfer Moulding?
When polyamides and Low Pressure Overmoulding can’t reach the temperature specifications that are required for certain applications, (aerospace electronics for example), the transfer moulding process is the alternative option. Epoxy based resins are loaded into the heated mould tool, as opposed to polyamide hotmelts used in Low Pressure Moulding (LPM). A preformed pellet of the chosen resin is pushed into the mould cavity using a press and the heat and pressure causes it to flow and create incredibly thin coatings of highly temperature and highly chemically resistant material to protect the electronics.
High Pressure Resin Transfer Moulding Techniques
Transfer moulding is a variation of compression moulding using polymers. Our Transfer Moulding service can achieve the ultra-thin coatings (in microns) that are highly temperature resistant as opposed to Low Pressure Moulding, which is limited to 2mm, possibly 1mm coatings with hotmelt polyamides.
Once curing is complete, the mould tool is opened, and the sprue breaks away from the part and is separately removed as well as any residual, cured material.
Another variation of Transfer Moulding technology is known as plunger transfer, and this is where the two-part mould assembly has a plunger in the top plate and a pot in the bottom. Again, the sprue or cull is ejected with the parts. This method offers shorter cycle times than compression moulding because in transfer moulding, considerable work is done on the material during the transfer process, and the heat transfer paths are shorter. This leads to faster heating, curing and cycle times than compression moulding.
Materials for Transfer Moulding
The transfer moulding process commonly uses thermosetting materials, though it is possible to use thermoplastics as well.
Some of the most common materials used in the Transfer Moulding process include:
- Polyester (Unsaturated)
- Phenol-formaldehyde plastic (PF, Phenolic)
- Silicone rubber (SI)
These materials may be combined with additives to encourage free-flowing characteristics.
How the Transfer Moulding Process Works
The transfer moulding process is similar to injection moulding, with a few key differences.
The process is as follows:
- The material (which may or may not be pre-heated) is placed into a holding chamber called the transfer pot.
- A hydraulically powered plunger pushes the material through a channel, called the sprue, into the mould cavity.
- The material remains inside the mould and is either cooled to solidify (thermoplastics) or heated up to cure (thermosets). Any material still within the sprue remains attached to the part as it solidifies.
- When the material is solid, the mould is opened and the part is ejected.
- The extra material from the sprue is trimmed off.
An alternative approach is similar to compression moulding. The polymer material is not placed directly into the die, but is often pre-heated before being loaded into a separate heated pot chamber situated above the die. A hydraulic plunger (ram) forces the polymer into the die cavity via a sprue. When cured, the moulded component is released using ejector pins.
Transfer Moulding Technology Overview
- Integral transfer mould ready for pressure to be applied to a compound in the chamber.
- Mould fully closed. The compound has been plasticised by heat and pressure, and transferred from the chamber through the sprue, runners and gates to the cavity.
- Mould fully open and ready for the operator to remove moulded parts and cull.
Design Of Transfer Moulding Tools
The size of the part that can be transfer moulded is limited by the size of the presses available.
A large part would have a projected area of 650cm2. The tool and the press needs to be capable of producing components with varying wall thicknesses, delicate holes, and the inclusion of inserts (these would not be possible by compression moulding.)
A key advantage in Transfer Moulding is that closer tolerances are possible than with LPM. This is particularly true of dimensions perpendicular to the parting lines because the mould is clamped shut before injection.
Typical transfer moulded parts include: Electronic components, PCB’s, Automotive ECU’s and aerospace components as well as electric connectors (particularly with fragile metallic inserts) and small rubber components.
The downside is that mould-making costs tend to be higher than for comparable LPM mould tools.
Contact Our MD Mr Dave Morris On firstname.lastname@example.org For More Information About Transfer Moulding Services With Overmould
Typical Applications of Transfer Moulding
- Coating semi-conductors.
- Encapsulated ECU’s and ruggedising electronics.
- Encapsulating electronics for the automotive and aerospace industries
- Materials used – e.g. Sumitomo -/ BakerLight – Epoxy based materials.
How Can Transfer Moulding Enhance Your Product?
Transfer moulding design advantages are realised when the simplicity of the machine’s design and process is observed, and it allows for a few unique advantages over injection moulding:
- Allows for inserts: The Transfer Moulding process is ideal for products with metal inserts moulded into the part.
- Fast and relatively low cost to set up: Inexpensive machinery that is easily assembled means transfer moulding is ideal for a quick start-up.
- Lower maintenance costs: The machinery involved in transfer moulding is less costly than that of injection moulding with maintenance being at a lower cost.
- Sharper edges: The transfer moulding process, due to the higher pressures, can achieve sharper edges and cut-offs than injection moulding.