Transfer Molding
Transfer molding involves injection of a molten polymer or material into a predesigned mold cavity. Pressure is then applied to push the material into the mold cavity, where it takes the desired shape and hardens.
Types Of Transfer Molding
The following are transfer molding processes that you can use:
Resin transfer molding involves placing reinforcing fibers into the mold cavity and then injecting resin into the molded cavity under pressure.
Just as the name suggests, vacuum resin assisted transfer molding works by vacuuming the molten material into the mold cavity.
This is a small transfer molding that is used in making small molded products that cannot be made using large molding platforms.
Benefits Of Transfer Molding
Improved dimensional control – Perfect for parts requiring high tolerance. This is because it can be used to produce products of any given shape, size, and configurations.
Structural integrity – Transfer molding ensures equal material distribution that results in the structural integrity of the products and minimizes breakages and cracks.
Reduced material waste – Compared to other melding processes, transfer molding minimizes material overflow while at the same time maximizing material usage and reducing costs.
Efficiency – The transfer molding manufacturing process is fast and has short curing and cooling periods which result in high production volumes.
Wide range of designs – This manufacturing process can be used to produce a wide range of designs both simple and complicated.
Limitations of Transfer Molding
Some of the limitations of transfer molding include:
- It takes time to produce complex designs using transfer molding because you will have first to make or design a complex mold cavity.
- Another limitation of transfer molding is the limited part size. To make very large parts you will need a very large transfer molding machine and vice versa.
- The materials that can be used for transfer molding are limited.
Transfer Molding Defects
Some of the transfer molding defects may include:
· Pressure Distribution
When pressure is not distributed uniformly it can result in voids, incomplete filling, and parts variations. All these will render the products produced obsolete and unfit for purpose.
· Sharp Defects
When sharp defects occur in the manufactured product, it can result in cracks and delamination of the part or product produced.
Application Of Transfer Molding
You can use transfer molding in making or manufacturing:
- Automotive parts and components such as seals, gaskets, engine mounts, and electrical connectors.
- In the making of aerospace industry parts and components such as seals, gaskets, electrical connectors, and other parts for aircraft structures.
- Electronic components such as electrical connectors, circuit boards, encapsulated components, and sensor housings.
- Manufacturing of consumer goods such as appliance parts, kitchenware, electrical switches, and small electronic devices.
- Used in manufacturing medical components.
- Production of energy systems components such as wind turbine blades.
- Manufacturing of marine components such as boat hulls and fittings.
- Defense and military applications such as manufacturing of protective gear, weapon parts, and communication devices.
Transfer Molding Process
The transfer molding process involves the following easy step. Though you should note that the steps can vary slightly depending on the configuration of the molding machine.
STEP 1 Preparing the mold – The mold is usually made from steel or aluminum. The mold is designed according to the specific product that you want to produce.
STEP 2 Preheating the mold – After the mold is prepared, it is preheated to the desired temperature to ensure that proper curing and flow of the material are achieved.
STEP 3 Measuring and preparing the material – This step involves preparing and measuring the material that will be used in making the product. It can be any polymer or composite material as desired.
STEP 4 Loading the material – The prepared and measured material is put into a transfer pot which is attached to a piston or plunger. The transfer pot is usually adjacent to the mold.
STEP 5 Heating the material – The polymer inside the pot is heated to its melting point to enable smooth flow into the mold cavity.
STEP 6 Transfer and compression – The heated material is transferred from the pot to the mold cavity by applying pressure. the plunger attached to the pot is used to push the material into the mold cavity.
STEP 7 Curing – The material injected inside the mold cavity is compacted to ensure there are no air pockets of voids. It is then left to cure under pressure until it solidifies.
STEP 8 Cooling and solidification – Cooling is carried out after the curing process. The material is cooled down either by air-colling or water-cooling methods.
STEP 9 Mold opening and removal – After the material has solidified, the mold cavity is opened and the molded part is removed. The excess material from the mold is trimmed down.
STEP 10 Post-processing – The molded product can undergo post-processing such as surface finishing, machining, painting, or assembly depending on your specific use of the product.
Transfer Molding Materials
· Thermoset Polymer
Thermoset polymer is preferred because of its rigidity and durability especially when it undergoes curing.
· Polyurethanes
Polyurethanes is a versatile elastomer that offers great chemical resistance, flexibility, and cushioning properties.
· Epoxy Resins
Epoxy resins are preferred in transfer molding because of their thermosetting and adhesiveness which results in excellent mechanical and electrical properties.
· Carbon
Carbon is a high-strength and at the same time lightweight material which is widely used for making aerospace and automotive parts through transfer molding.
· Kevlar Fibers
Kevlar fibers are made from aramid which is a material known for its exceptional strength, heat resistance, and abrasion resistance.
· Organic Fibers
These include cotton, hemp, and flax used in composites for their low cost, lightweight, and environmental benefits and are used in resin fiber molding.
More Resources:
Transfer Plastic Molding Process – Source: Science Direct
Plastic Fabrication Process – Source: Wikipedia