Types of composite materials for machining centers
Composite materials can be divided into metal to metal composite materials, nonmetal to metal composite materials, and nonmetal to nonmetal composite materials according to their composition. According to its structural characteristics, it can be divided into:
1. Fiber composites. All kinds of fiber reinforcements are compounded in the matrix material. Such as fiber reinforced plastic, fiber reinforced metal, etc.
2. Sandwich composites. It is composed of surface materials and core materials with different properties. Generally, the surface material is of high strength and thin; The core material is light and low in strength, but it has a certain stiffness and thickness. It is divided into solid interlayer and honeycomb interlayer.
3. Fine grained composites. The hard particles are uniformly distributed in the matrix, such as dispersion strengthened alloy, cermet, etc.
4. Hybrid composites. It is composed of two or more reinforcement materials mixed in one matrix material. The impact strength, fatigue strength and fracture toughness of the composite are significantly improved compared with those of ordinary single reinforced phase composites, and it has special thermal expansion properties. It is divided into intralayer hybrid, interlayer hybrid, sandwich hybrid, intralayer/interlayer hybrid and super hybrid composites.
Some problems that should be paid attention to in precision machining of composite materials
1. The interlaminar strength of carbon fiber composite is low, and it is easy to delaminate under the action of cutting force. Therefore, the axial force should be reduced when drilling or trimming. The drilling requires high rotation speed and small feed. The rotation speed of the machining center is generally 3000-6000r/min, and the feed rate reaches 0.01-0.04mm/r. The drill bit should be three sharp two edged or two sharp two edged. The sharp blade can cut off the carbon fiber layer first, and the two edges play a role in repairing the hole wall. The diamond inlaid drill bit has good sharpness and wear resistance. The drilling of composite material and titanium alloy interlayer is a difficult problem. Generally, an integral cemented carbide drill is used to drill according to the cutting parameters of titanium alloy. Drill from the titanium alloy side until the drilling is completed. Lubricant is added during drilling to alleviate the composite material burn. Boeing Company has specially developed PCD combination bits for drilling interlayers.
2. The cutting effect of the three new types of special milling cutters for machining integral cemented carbide composites is better. They all have some common features: high rigidity, small helix angle, even 0 °. The specially designed herringbone blade can effectively reduce the axial cutting force of the machining center and reduce delamination. Their machining efficiency and effect are very good.
3. Composite chips are powdery, which is harmful to human health. High power vacuum cleaners should be used for dust collection. Water cooling can also effectively reduce dust pollution.
4. Carbon fiber composite machining components are generally large in size, complex in shape and structure, high in hardness and strength, and are difficult to machine materials. In the cutting process, the cutting force is large, the cutting heat is not easy to pass out, the resin will be burnt or softened when it is serious, and the tool wear is serious. Therefore, the tool is the key to carbon fiber processing, and its cutting mechanism is closer to grinding rather than milling. Therefore, the cutting line speed of the machining center is usually greater than 500m/min, and the high speed small feed strategy is adopted. The cutting tools are generally solid carbide knurled milling cutter, electroplated diamond grain grinding wheel, diamond inlaid milling cutter and copper based diamond grain saw blade.