Types Of Transfer Moulding

Type Of Transfer Moulding:

1. Resin Transfer Moulding (RTM)

2. Vacuum-Assisted Resin Transfer Moulding  (VARTM)

1. Resin Transfer Moulding (RTM): 

1. RTM is a low pressure moulding process, where a mixed resin and catalyst are injected into a closed mould containing a fiber pack or preform. When the resin has cured the mould can be opened and the finished component is removed.

2. This is a variation of compression moulding and is particularly valuable when intricate shapes have to be moulded. 

3. It is also useful when metal inserts have to be incorporated (as in electrical component

4. It is used frequently when the mould sections are very delicate, when the moulded parts has thick sections 3.2 mm or more, or when an insert is retained in the cavity for moulding in place.

5. A wide range of resin systems can be used including polyester, vinylester, epoxy, phenolic and methyl methacylates etc, combined with pigments and fillers including aluminum trihydrates and calcium carbonates if required. 6. The fibre pack can be either, glass, carbon, arimid, or a combination of these. 

7. The mould can be made from composites for low production cycles or with aluminum or steel for larger production. 

                                               OR

Resin transfer moulding is commonly reffered to as liquid moulding with this process, a resin is mixed with a catyst and injected into a mould that contains dry fibbers such as fiber glass. A static mixer regulator the ratio of polyester resin to catalyst. Usually a ratio of 100: 1 of resin to catyst is used. The mixture is then injected a flow pressure of approximately SPI in to the mould. The read ion time is usually minutes.

Advantages of RTM

Wide Range of Production Quantity

The process can be tailored to individual application, rendering the technology suitable for a wide range of production quantities. 

Design Flexibility

RTM offers design flexibility of tailoring the materials closely to the applied loading system. One can mould shapes that are difficult, if not impossible, to form by conventional methods. 

Labour Savings

As the resin is pumped in the mould during the RTM process, the moulder can reap the benefit of saving labour spent on impregnating the fibers.  

Lower Start-Up Cost

The initial cost is only a fraction of the high capital cost associated with matched mould operations for equipment and tooling. 

Dimensional Tolerances

RTM allows designers to have close tolerances in the product. 

Surface Finish 

High quality surface finish on both sides of the product is obtained in RTM process.  The parts can be gel coated, pigmented or painted. 

Part Reproducibility

As RTM process is a closed mould technique, the moulded parts are reproducible. 

Faster Production

Faster production means less cycle time for moulding the product.  The moulds will be available for next shot in a short time than the hand lay up process.  If the production requirement is large and one cannot go for investing on costlier compression moulding, RTM is the best bet for such cases. RTM produces parts at a rate that is 5-20 times faster than open moulding technique. 

Lower Material Wastage

Compared to open moulding techniques, very less material wastage is obtained in RTM process. 

Fillers

High filler loading can be achieved with low viscosity resins. Use of filler results in lower exotherm, which in turn increases the life of FRP mould. 

Higher Fiber Volume Fraction

Higher fibred volume fraction is achievable in RTM by selecting proper type of reinforcement. 

Low Void Content

Void content less than 1% can be consistently achieved with RTM. 

Low Operator Skills

During regular production, skill required of the operator is minimal. 

Limitations

The process is more costly than hand lay-up for small production runs. 

The tooling can get complicated for reentrant cavities (projections or undercuts). 

Parts having open cell cores (inside) such as honeycomb cores porous foams, tubular structures are difficult to make by RTM. 

The process may become uneconomical for parts having low thickness/thin and smaller in size. In this case moulding operations are prolonged and productivity will be lower than the hand laid up products. 

The mould fabrication is not a simple extension of a hand lay-up mould. 

Application

In the semiconductor industry, package encapsulation is usually done with transfer moulding due to the high accuracy of transfer moulding tooling and low cycle time of the process.

2. VACUUM ASSISTED RESIN TRANSFER MOULDING (VARTM)

1. This method is also referred to as vacuum infusion process (VIP) moulding.

2. VARTM is single sided moulding process where the dry preform (reinforcement or coring materials) is placed into the mould. 

3. VARTM parts are formed in an open cavity mould. 

4. The opposite side to the tool surface is primarily a vacuum bag surface comprises of transfer media, peel ply fabric, bleeder/breather media and sealant tape.

5. A distribution medium (a mesh) is used and laid on top of the top release fabric to help maintain an even distribution of resin and facilitate the flow of resin through the thickness of the panel.

6. The low viscosity resin typically enters the preform through resin distribution and vacuum distribution lines with the aid of vacuum.

Process

1. Aluminium flat plate is cleaned with acetone and freekote is sprayed 

2. Non-porous teflon, porous teflon are laid up on the Al tool 

3. Dry fabric preforms are laid on the teflons and a distribution mesh is put over the fabric. 

4. Again porous teflon and non-porous teflon are laid up sequentially 

5. Spiral tubes were installed on two side of the distribution mesh. One for resin infusion and another for suction. 

6. Complete lay-up was covered with a thin heat-resistant vacuum bag and debulked for an hour 

7. Once debulking is completed, resin is infused. 

8. As resin flow appears to come out through the ejection line, resin flow is cut off. 

9. The vacuum is kept on while the resin is left for 24 hours to cure.

Materials

Resins: Any resin with low viscosity, e.g. epoxy, polyester, vinyl ester 

Fibers: fabrics made from carbon, Kevlar, Quartz, glass and polyester fiber.

Advantage

1. Cost-effective: VARTM uses vacuum power to pull the resin through the closed mould and to hold the two pieces together. This fact means that the “male” and “female” pieces of the mould can be much lighter, resulting in a significantly reduced price of fabrication. 

2. Vacuum assisted resin transfer moulding (VARTM) is ideal for the manufacture of large-scale composite structures.

3. The advantages of the VARTM process over the RTM process are scalability and affordability for the fabrication of large composite structures

Application

VARTM applications including marine, ground transportation and infrastructure parts.