Introduction to HP-RTM and Wet Compression Molding of Composite Materials

 

This article mainly introduces two composite material molding processes, namely HP-RTM and wet compression molding process.

 

HP-RTM is the abbreviation of High Pressure Resin Transfer Molding in English. The full name is High Pressure Resin Transfer Molding, referred to as HP-RTM molding process. It refers to the molding process of using high pressure to mix resins and inject them into a vacuum-sealed mold pre-laid with fiber reinforcement materials and pre-set inserts, and then obtain composite products through resin flow filling, impregnation, curing and demolding.

 

Keyword Introduction in the above Introduction:

 

▪ High pressure: The high pressure here is relative to the traditional RTM (Resin Transfer Molding) process. HP-RTM increases the injection pressure to 80bar. The advantage of high-pressure injection is that the resin can reach each corner faster, so it can increase the fiber content of the product, improve product performance, and is more suitable for parts with complex shapes;

▪ Pre-laying: The pre-laid fiber-reinforced material here refers to the fiber material that has been cut and pre-formed;

▪ Pre-set inserts: Inserts refer to parts placed in the mold before molding. The materials are metal and non-metal. In this way, the molded product has the inserts wrapped in its own structure and cannot be removed. Whether the pre-set inserts are needed is determined by the structural design of the product.

 

The above process can be reflected by a simple process flow chart:

 

 

As mentioned above, the HP-RTM molding process is an optimized molding process compared to the traditional RTM process. In different optimization directions, other processes based on the RTM process have also been developed to further improve production efficiency and product performance, such as the HP-CRTM (High Pressure Compression Resin Transfer Molding) molding process currently owned by HRC.

 

The HP-CRTM molding process is to move the mold up 0.5~1mm before the resin injection in the HP-RTM process technology to increase the gap between the sealed mold cavity. The mold can have a wider runner to reduce the resin flow resistance. After the injection is completed, the mold is completely closed under high pressure. The resin system flows with the closing pressure to fill the mold. The molding pressure is relatively low, which ensures that the fiber is not disordered and a higher injection speed is guaranteed.

 

The Process Flow Chart is as Follows:

 

 

HP-RTM Molding Process is one of the composite molding processes widely used in many industries. Its advantage is that it can achieve low-cost, short-cycle, large-volume, high-quality production (good surface of parts) compared with traditional RTM process. It is used in many industries such as automobile manufacturing, shipbuilding, aircraft manufacturing, agricultural machinery, railway transportation, wind power generation, and sporting goods.

 

Below, let’s take a look at some specific products obtained by using HP-RTM molding process and other related processes derived from it:

 

Carbon Fiber Electric Skateboard

Carbon Fiber Hat Beam

BMW i8 Body Side Frame

 

AUDI AG’s carbon fiber floor module,

Ultra-RTM process is applied in the molding process

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 Wet Compression Molding Process

 

The second molding process introduced in this issue is the wet compression molding process, also known as the WCM (short for Wet Compression Molding) process. Let’s first look at the relevant process flow chart:

 

 

The molding steps of the wet molding process can be broken down as follows:

 

1. Use the cut carbon fiber or glass fiber dry cloth to lay it into a plane;

 

2. Transfer the material to the mold;

 

3. Apply glue to cover the fiber with resin;

 

4. Close the mold, vacuum, pressurize, heat and cure;

 

5. Open the mold and take out the product.

 

The main feature of the wet molding process is that dry fiber cloth is used for early cutting, and the resin is sprayed before being placed in the mold for molding and curing. This also makes the process more suitable for processing products with low shape complexity (2D or 2.5D modeling). It is widely used in the industry. Its advantages are fast batch production cycle, simple mold design, and low unit cost.

 

Here are a few groups of products and cases obtained by using the wet molding process:

We string together the above keywords to get the basic process flow, as shown below

 

 

Carbon Fiber Mini Hood

 

 

The above picture shows the application of wet molding process in BMW i3 and i8 models, where 17 “wet pressed parts” are used in BMW i3 (right) and 21 are used in i8 (left).

 

 

 

In the above picture, the wet molding process is used to produce the “Carbon Core” passenger compartment components of the BMW 7 Series, providing shorter production cycles and lower costs for parts with less complex shapes.