Machining characteristics of three composite materials

First, FRP

FRP is a common name for glass fiber reinforced thermosetting resin-based composite materials and is a difficult-to-cut material. The glass steel has a phenol resin base, an epoxy resin base, an unsaturated polyester resin base, and the like. The main component of the glass fiber filler is SiO2, which is hard and wear resistant, high in strength, heat resistant, and inferior in plasticity than wood powder as filler. The machinability is also different depending on the resin matrix. The epoxy resin base is difficult to cut than the phenolic resin base. Tests have shown that the tool material for cutting FRP is the most severely worn by high-speed steel, and the wear of P-type and M-type cemented carbides is also large, and the K-type wear is minimal. In the K class, K10 with the least amount of cobalt is the most resistant to wear, and the cutting of FRP with diamond or cubic boron nitride tool can greatly improve the production efficiency. When selecting the tool geometry parameters, the glass fiber reinforced plastic sheet, the molding material and the winding material with high glass fiber content are made r0=20~25°; for the fiber winding material, r0=20~30°. Since the resilience of FRP is large, the back angle should be chosen to be large, so that a0=8~14°; the minor declination is smaller, which can reduce the surface roughness, and it is 6~8° when finishing the car. For the processing of easy-delay, raised coiled tubes and fiber-wound FRP, a 6-15° blade inclination should be used. When cutting, v=40~100m/min, f=0.1~0.5mm/r, aP=0.5~3.5mm, aP=0.05~0.2mm when finishing the car.

Second, thermoplastic resin matrix composites

The basic processing characteristics of thermoplastic resin matrix composite machining are:

1) Add coolant to the process to avoid overheating, which will melt the workpiece;

2) using high speed cutting;

3) The cutting tool should have a sufficient capacity of the chip flute;

4) using a small amount of back knife and a small feed;

5) The turning tool should be ground to a certain inclination to minimize the cutting force and thrust of the tool;

6) Drilling of thermoplastic composite materials using twist drills;

7) Tungsten carbide or silicon carbide tools should be used, or high-speed steel tools for special plastics should be used;

8) The workpiece must be properly supported (backed) to avoid delamination caused by cutting pressure;

9) When it comes to precision machining, consider the plastic memory and the room temperature of the processing workshop;

10) The cutter head and the tool are sharp, and the blunt tool increases the cutting force on the workpiece.

Third, metal matrix composites

The most important feature of metal matrix composites (MMC) is that it has good molding properties and can basically meet the requirements of use after one molding. However, with the expansion of composite applications, especially the application of MMC in the industrial and aerospace fields, the processing and finishing of such materials is becoming increasingly important. For example, large SiC/Al plates made in the United States need to be spray-jet cut and fixed on metal-based composite beams with standard steel joints. The volume percentage used on tactical missiles is 25% SiC particle reinforced 2124 aluminum-based composite extrusion. The blank must be processed with a diamond tool before it can be applied, which results in secondary processing such as water cutting, drilling and turning.

Conventional cutting, turning, milling, grinding and other processes are generally available for MMC, but tool wear is more severe and tends to increase with increasing volume fraction and size of the reinforcement. Moreover, the ability of large particles or fibers to resist falling off is strong, and the tool is subjected to strong stress. Therefore, for some single fiber reinforced MMCs, it is often necessary to use diamond tips or diamond-inlaid tools. For short fiber or particle composites, tungsten carbide or high speed steel tools are sometimes used. The strength of the reinforcement also has an effect on the wear of the tool. Generally, the higher the strength of the reinforcement, the more difficult the cutting process is. The study found that silicon-based whisker-reinforced aluminum-based composites are more difficult to process than other aluminum-based composites. For most MMCs, sharp results can be obtained with sharp cutting tools, suitable cutting speeds, large amounts of coolant/lubricant and large feeds. In general, diamond tools are better than hard alloys and ceramic tools, making them more suitable for high-speed turning. Conversely, if a carbide tool is used, the tool life is long if the turning speed is low. Wire saws can also be used to cut MMC, but generally slower and can only cut straight lines.

Because composite materials have different characteristics from traditional materials, the cutting process of composite materials is essentially different from that of metal materials. Therefore, the experience and knowledge obtained from processing traditional materials cannot be directly applied to the processing of composite materials, and new ways must be adopted. Study its processing properties.