Transfer molding
Encyclopedia
Transfer molding, like compression molding
, is a process where the amount of molding material (usually a thermoset plastic
) is measured and inserted before the molding takes place. The molding material is preheated and loaded into a chamber known as the pot. A plunger
is then used to force the material from the pot through channels known as a sprue and runner system into the mold cavities. The mold remains closed as the material is inserted and is opened to release the part from the sprue and runner. The mold walls are heated to a temperature above the melting point
of the mold material; this allows a faster flow of material through the cavities.
Transfer Molding. This is an automated operation that combines compression-, molding, and transfer-molding processes. This combination has the good surface finish, dimensional stability, and mechanical properties obtained in compression molding and the high-automation capability and low cost of injection molding and transfer molding. Transfer Molding is having a "piston and cylinder"-like device built into the mold so that the rubber is squirted into the cavity through small holes. A piece of uncured rubber is placed into a portion of the transfer mold called the "pot." The mold is closed and under hydraulic pressure the rubber or plastic is forced through a small hole (the "gate") into the cavity. The mold is held closed while the plastic or rubber cures. The plunger is raised up and the "transfer pad" material may be removed and thrown away. The transfer mold is opened and the part can be removed. The flash and the gate may need to be trimmed. Another key point is that a premeasured amount of thermosetting plastic in powder, preform, and even granular form can be placed into the heating chamber.
The molds in both compression and transfer molding remain closed until the curing
reaction within the material is complete. Ejector pins are usually incorporated into the design of the molding tool and are used to push the part from the mold once it has hardened. These types of molding are ideal for high production runs as they have short production cycles. Transfer molding, unlike compression molding uses a closed mold, so smaller tolerances and more intricate parts can be achieved. The fixed cost of the tooling in transfer molding is greater than in compression molding and as both methods produce waste
material, whether it be flash or the material remaining in the sprue and runners, transfer molding is the more expensive process.
Transfer molding (TM) (or resin transfer molding, RTM) differs from compression molding in that in TM the resin is inserted into the mold (or tool) which contains the layers of fibres or a preform, whereas in compression molding prepregs or molding compounds are in the mold which is then heated and pressure is applied. No further pressure is applied in TM.
In RTM the resin is injected or drawn into a mold, which contains the fibres, from a homogeniser under low pressure.
The mold can be made from composites for low production cycles or with aluminium or steel for larger production. The differences between the two types being that metal has better heat transfer, hence quicker cycle times; metal lasts longer and deforms less, but at a higher cost. The main problem with this production route is that air can be trapped in mold and hence a method must be incorporated for allowing this air to escape. A number of solutions to the problem exist including extending one level of reinforcement beyond the cavity (with a 25% resin loss), appropriate vents and creating a vacuum in the mold (which also improves quality). Larger structures, better properties (less movement of fibres), increased flexibility of design and lower cost are some of the advantage this process has over compression molding due mainly to the low pressure injection. Other benefits include rapid manufacture, not labour intensive, ability to vary reinforcements easily or include cores such as foam and produce low and high quality products.
In the semiconductor
industry, package encapsulation is usually done with transfer molding due to the high accuracy of transfer molding tooling and low cycle time of the process.
However, the drive to introduce "Green" manufacturing is becoming a mandatory process in most semicon assembly operations. New transfer mold designs integrated with suitable surface treatments like CrN, MiCC and H Cr plating are becoming more popular in the industry.
Some common products are utensil handles, electric appliance parts, electronic component, and connectors. Transfer molding is widely used to enclose or encapsulate items such as coils, integrated circuits, plugs, connectors, and other components.
Compression molding
Compression molding is a method of molding in which the molding material, generally preheated, is first placed in an open, heated mold cavity. The mold is closed with a top force or plug member, pressure is applied to force the material into contact with all mold areas, while heat and pressure are...
, is a process where the amount of molding material (usually a thermoset plastic
Plastic
A plastic material is any of a wide range of synthetic or semi-synthetic organic solids used in the manufacture of industrial products. Plastics are typically polymers of high molecular mass, and may contain other substances to improve performance and/or reduce production costs...
) is measured and inserted before the molding takes place. The molding material is preheated and loaded into a chamber known as the pot. A plunger
Plunger
A plunger is a common device that is used to release stoppages in plumbing. The tool consists of a rubber cup with an attached stick "shaft", usually made of wood or bronze. Before use, any objects such as hair in the plug grate should be removed and, if possible the overflow hole should be...
is then used to force the material from the pot through channels known as a sprue and runner system into the mold cavities. The mold remains closed as the material is inserted and is opened to release the part from the sprue and runner. The mold walls are heated to a temperature above the melting point
Melting point
The melting point of a solid is the temperature at which it changes state from solid to liquid. At the melting point the solid and liquid phase exist in equilibrium. The melting point of a substance depends on pressure and is usually specified at standard atmospheric pressure...
of the mold material; this allows a faster flow of material through the cavities.
Transfer Molding. This is an automated operation that combines compression-, molding, and transfer-molding processes. This combination has the good surface finish, dimensional stability, and mechanical properties obtained in compression molding and the high-automation capability and low cost of injection molding and transfer molding. Transfer Molding is having a "piston and cylinder"-like device built into the mold so that the rubber is squirted into the cavity through small holes. A piece of uncured rubber is placed into a portion of the transfer mold called the "pot." The mold is closed and under hydraulic pressure the rubber or plastic is forced through a small hole (the "gate") into the cavity. The mold is held closed while the plastic or rubber cures. The plunger is raised up and the "transfer pad" material may be removed and thrown away. The transfer mold is opened and the part can be removed. The flash and the gate may need to be trimmed. Another key point is that a premeasured amount of thermosetting plastic in powder, preform, and even granular form can be placed into the heating chamber.
The molds in both compression and transfer molding remain closed until the curing
Curing (chemistry)
Curing is a term in polymer chemistry and process engineering that refers to the toughening or hardening of a polymer material by cross-linking of polymer chains, brought about by chemical additives, ultraviolet radiation, electron beam or heat...
reaction within the material is complete. Ejector pins are usually incorporated into the design of the molding tool and are used to push the part from the mold once it has hardened. These types of molding are ideal for high production runs as they have short production cycles. Transfer molding, unlike compression molding uses a closed mold, so smaller tolerances and more intricate parts can be achieved. The fixed cost of the tooling in transfer molding is greater than in compression molding and as both methods produce waste
Waste
Waste is unwanted or useless materials. In biology, waste is any of the many unwanted substances or toxins that are expelled from living organisms, metabolic waste; such as urea, sweat or feces. Litter is waste which has been disposed of improperly...
material, whether it be flash or the material remaining in the sprue and runners, transfer molding is the more expensive process.
Transfer molding (TM) (or resin transfer molding, RTM) differs from compression molding in that in TM the resin is inserted into the mold (or tool) which contains the layers of fibres or a preform, whereas in compression molding prepregs or molding compounds are in the mold which is then heated and pressure is applied. No further pressure is applied in TM.
In RTM the resin is injected or drawn into a mold, which contains the fibres, from a homogeniser under low pressure.
The mold can be made from composites for low production cycles or with aluminium or steel for larger production. The differences between the two types being that metal has better heat transfer, hence quicker cycle times; metal lasts longer and deforms less, but at a higher cost. The main problem with this production route is that air can be trapped in mold and hence a method must be incorporated for allowing this air to escape. A number of solutions to the problem exist including extending one level of reinforcement beyond the cavity (with a 25% resin loss), appropriate vents and creating a vacuum in the mold (which also improves quality). Larger structures, better properties (less movement of fibres), increased flexibility of design and lower cost are some of the advantage this process has over compression molding due mainly to the low pressure injection. Other benefits include rapid manufacture, not labour intensive, ability to vary reinforcements easily or include cores such as foam and produce low and high quality products.
In the semiconductor
Semiconductor
A semiconductor is a material with electrical conductivity due to electron flow intermediate in magnitude between that of a conductor and an insulator. This means a conductivity roughly in the range of 103 to 10−8 siemens per centimeter...
industry, package encapsulation is usually done with transfer molding due to the high accuracy of transfer molding tooling and low cycle time of the process.
However, the drive to introduce "Green" manufacturing is becoming a mandatory process in most semicon assembly operations. New transfer mold designs integrated with suitable surface treatments like CrN, MiCC and H Cr plating are becoming more popular in the industry.
Some common products are utensil handles, electric appliance parts, electronic component, and connectors. Transfer molding is widely used to enclose or encapsulate items such as coils, integrated circuits, plugs, connectors, and other components.