Injection Molding Vs. Transfer Molding: What’s the Difference?

Injection Molding Vs. Transfer Molding: What’s the Difference? makenica.com/injection-molding-vs-transfer-molding-whats-the-difference April 8, 2021

The production of silicone rubber goods necessitates a delicate balancing of performance and consistency. To achieve this balance, various production processes must be considered and compared to decide which process better matches the product's particular needs.

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For several plastic and rubber fabricators, the choice processes are injection molding service and transfer molding, each with its own combination of benefits and drawbacks.

Here is a comparison of the main features and advantages of injection molding service and transfer molding to help you decide which technique is better for your unique product.

What is Injection Molding?

Injection molding service is one of the most popular methods of producing plastic and rubber components. The first injection-molding system, patented in 1872, operated as a big hypodermic needle, with a plunger injecting plastic into a heated cylinder and then into the mold.

As the market grew, so did the need for low-cost, mass-produced goods, which prompted the injection-molding method to grow.

A screw machine replaced the plunger mechanism in 1946, assisting in mixing the aggregate before injecting it into the mold and speeding up the process. Further advancements extended the capabilities of injection molding machines, allowing the process to evolve into what it is today.

APPLICATIONS Plastic Injection molding service creates thin-walled plastic pieces, most commonly in cylindrical, cubic, or complex three-dimensional forms of sizes varying from 0.01 square inches to 80 square feet. The process is most widely used for thermoplastics, but it is often used with composites, elastomers, and thermosets.

Manufacturers of plastic injection molding companies often use injection molding services to produce plastic housings, kitchen products, consumer electronics, power tools, and vehicle interiors. This procedure is also used to make open containers such as buckets, household items such as toothbrushes and plastic toys, and medical equipment such as syringes and valves.

THE PROCESS Here's how the injection molding process works: The material, which is often in the form of pellets or granules, is fed into a heated barrel and heated to a molten state.

As the material is liquid, it is thrust into a channel called a sprue into the mold cavity by a reciprocating screw or ram injector.

The melt is retained within the mold, and either cooled to solidify (thermoplastics) or heated to cure (thermosets).

The mold is opened, and the element is expelled until the material has solidified.

COMMON POLYMERS

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Injection molding is used for both thermoplastic and thermosetting materials. Some of the more commonly used materials by plastic injection molding companies include: Polystyrene (PS) Acrylonitrile Butadiene Styrene (ABS) Polyamide (PA) Polypropylene (PP) Polyethylene (PE) Polyvinyl Chloride (PVC) Other short fiber reinforced plastics ADVANTAGES Injection molding service is a common and cost-effective method of molding plastic and rubber materials. This is largely due to its particular range of benefits, which include the following: Immediately Pre-Heats Material: As the injection screw moves down the injection pump barrel, it heats the material when mixing it. This reduces the material's viscosity and helps it to flow more naturally into the mold cavities. This results in faster cavity filling and faster thermosetting material curing.

Higher Capacity: Since injection molding machines can handle more cavities, they can produce more units per production cycle in injection molding companies.

Minimal Waste: Injection molding service creates far less waste than transfer molding due to a smaller sprue and the absence of overflow channels.

Fast: Injection molding intervals usually last between two seconds and two minutes, not including post-processing.

DISADVANTAGES Though the injection molding process is suitable for huge production runs, it has certain drawbacks, which include: Just Thin, Uniform Walls: Injection molds usually require a uniform, thin walls varying in thickness from 0.015 to 0.5 inches. Thick sections or non-uniform molds usually cause defects.

Rounded Corners: Since injection molds are less capable of manufacturing units with sharp corners, molds with rounded corners are required.

High Setup Costs: Injection mold machines are far more costly than transfer molding machines, and the setup process is much more complex.

POSSIBLE DEFECTS

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All molding methods followed by injection molding companies are susceptible to flaws.

The following are examples of injection molding flaws: Flash: The molten fluid seeping out of the mold cavity and solidifying is referred to as flash. If the injection pressure is too high or the mold has too much clearance, this will happen.

Warping: This is an irreversible bending of the element that can arise if it cools at a variable rate.

Bubbles: Air gaps may occur when the injection temperature is too high, the material contains too much moisture, or the material cools at a non-uniform rate.

Unfilled Sections: This can happen if there is inadequate material or if the material flow rate is too slow.

Sink Marks: These voids in the mold will form if those parts of the mold solidify first.

Ejector Marks: Ejector marks will occur if the cooling time is insufficient to allow the component to set completely or if the ejection force is too high.

What is transfer molding?

Transfer molding is similar to injection molding service and is generally known as a simpler injection molding variation. The procedure is somewhat similar to older versions of injection molding before the invention of the screw injector. The processes are what distinguish the two forms of molding.

Transfer molding, like injection, pushes material into a mold with a sprue, but instead of a screw injector, it uses a plunger.

APPLICATIONS Transfer molding is a common method of encasing electronic components in rubber or plastic. Inserts such as metal prongs, semiconductor chips, or ceramics may be inserted inside the mold before injection, causing them to "float" within the plastic as it cures. This technique can be used to make pins, studs, screws, and molded terminals.

Transfer molding is important in a variety of industries because of this distinct advantage.

It is used in the natural gas industry to produce metal-to-rubber face seals used to create interfaces for gas valves.

Employees in the electrical industries use it to form connector seals around electrical wires, such as spark plug wires. It is also used in the hydraulic industry because of its potential to achieve finer cutoffs and corners, which is advantageous for producing sharper lip seals.

THE PROCESS

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With a few main exceptions, the transfer molding process is identical to injection molding. The steps are as follows: The material (which may or may not have been preheated) is loaded into a holding chamber known as the transfer pot.

A hydraulically driven plunger forces the material into the mold cavity through a channel known as the sprue.

The material stays inside the mold and is either cooled to solidify (thermoplastics) or heated to cure (metal alloys) (thermosets). When the part solidifies, any material remaining inside the sprue stays bound to it.

The mold is opened, and the part is expelled until the material has solidified.

The excess material from the sprue is removed.

COMMON POLYMERS The transfer molding process commonly uses thermosetting materials, though it is possible to use thermoplastics as well. Some of the most common materials used in this molding process include: Epoxy Polyester (Unsaturated) Phenol-formaldehyde plastic (PF, Phenolic) Silicone rubber (SI) ADVANTAGES The machine's and process's versatility makes for a few distinct advantages over injection molding: Allows for Metal Inserts: This procedure is suitable for items that have metal inserts.

It is fast and cheap to set up: Transfer molding is suitable for a fast startup due to its cheap machinery and ease of assembly.

Lower Repair Costs: Because the equipment used in transfer molding is less expensive than that used in injection molding, maintenance is less expensive.

Sharper Edges: Because of the higher pressures, the transfer molding process can achieve sharper edges and cutoffs than injection molding.

DISADVANTAGES While transfer molding is less expensive and easier to set up, the machine's simplicity has a few drawbacks: Waste material: Transfer molding usually generates more waste owing to the greater sprue and overflow channels. When thermosetting materials are used, the scraps produced are not reusable.

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Slow: Because of the time taken to preheat the materials before transfer and the lower volume, the production speed is much slower than injection molding.

Smaller Quantity: Since transfer molding machines cannot handle as many cavities as injection molding machines, fewer units are made per cycle.

POSSIBLE DEFECTS A correctly produced transfer mold is just as likely as an injection mold to produce a faulty component, and the two processes will produce identical defects. Among the potential flaws are: Flash: The molten fluid seeping out of the mold cavity and solidifying is referred to as flash. This will arise if the injection pressure is too high or the mold has excessive clearance.

Warping: This is an irreversible bending of the element that can arise if it cools at a variable rate.

Voids: These are often the result of non-uniform pressure distribution, which causes the material to fold in on itself and create voids.

Ejector Marks: Ejector marks will occur if the cooling time is insufficient to allow the component to set completely or if the ejection force is too strong.

WHICH IS BETTER FOR YOUR PRODUCT: INJECTION MOLDING OR TRANSFER MOLDING? While these two methods have certain similarities, the distinctions between them are crucial in deciding which approach is better for producing a particular commodity. The below are the most critical distinctions to remember before choosing which method to use: INVESTMENT These techniques necessitate the use of a toolmaker or machinist to create the molds, which is a costly procedure in and of itself. The cost of the machinery involved, on the other hand, is the most important factor in determining startup costs.

The injection molding machine is considerably more costly than the press used for a transfer mold, owing to the machine's components' size and specialization.

It also takes much longer to set up than a transfer mold machine, which means that a project would take longer to get started. Because of the expense and complexity of injection molding equipment, repair costs are much higher.

SPEED OF PRODUCTION

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Injection molding has a very short operation time, lasting between two seconds and two minutes, depending on the component's size. The total processing period increases through the absence of some excess material, such as flash or the sprue, but it is still much shorter than the production time for transfer molding.

The primary drawback of transfer molding is that the material must be packed before being put in the process, greatly raising the cycle time.

COST OF PRODUCTION The cost of production does not always favor one process over another but rather depends on the commodity's geometry. Materials having a high injection pressure would necessitate a more efficient injection machine, implying that using an injection machine rather than a transfer method would be more costly.

A similar statement may be made with a larger part. Injection machines, on the other hand, will handle more cavities, increasing production per cycle. Injection molding machines are often more automated than transfer molding machines, which means that long-term labor costs are greatly lowered for high-volume projects.

PRODUCT SHAPE AND ACCURACY Both methods are very accurate and provide reasonably consistent outcomes. On the other hand, injection molding can not tolerate rough edges well and can end up rounding off edges that were supposed to be sharp.

Furthermore, although both methods can manufacture units of extremely complex shapes, the cost of doing so with transfer molding is considerably lower than with injection molding. The fact that sophisticated injection molds necessitate more complicated and costly injection systems to produce.

THE AMOUNT OF WASTE While injection molds generate flash and sprue waste, transfer molding generates significantly more waste on average. This is largely due to the inclusion of a larger sprue, air holes, and overflow grooves that injection molds do not have. If the substance is thermosetting, this may result in significant material waste.

SIZE OF THE PRODUCT Both of these techniques work well with small to medium-sized products, but injection molding will produce even larger products, up to 80 square feet in scale. Because of press size restrictions, transfer molding is ideally suited to small and medium part sizes.

PRODUCT VOLUME In terms of component quantity, injection molding greatly outperforms transfer molding.

This approach is much more cost-effective in the long run for large volume projects because of the more automated processes and shorter cycle times.

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Conclusion Both injection molding and transfer molding can manufacture high-quality products in somewhat similar ways. On the other hand, transfer molding is best suited to encasements and small volumes of simpler molds. In contrast, injection molding is better suited to higher quantities of bigger, thin-walled components.

Is your company interested in producing custom-made silicone rubber parts w? Call Makenica – One of the top injection molding companies - to meet with one of our knowledgeable representatives to know our superior manufacturing capabilities.

Read More: 3D Printing in Automobile Industry

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