Carbon fiber composite materials have obvious performance advantages. The structural parts produced by them are light in weight, high in strength, impact resistance, small in thermal expansion coefficient, and can be integrally formed. In practical applications, carbon fiber composite products usually need to be processed and then connected with other material components. Since carbon fiber composite materials are anisotropic materials, they are not processed in the same way as general metal materials. What are the characteristics of material processing? Below, by WASTON CUSTOMACHINING to answer for you.
Carbon fiber composite products are usually made of carbon fiber prepreg after heating and curing. The layers are mainly connected by a resin matrix. The bending strength and shear strength are low, and delamination tearing is easy to occur under the action of external force. Therefore, the bending force and shearing moment on the material should be minimized during custom processing. During machining, due to the high hardness, strong rigidity and good fatigue resistance of carbon fiber, it is easy to cause wear to the tool during machining. At the same time, the tool specification and tool wear degree have a great influence on the quality and dimensional accuracy of the machined surface of carbon fiber composite materials. When machining, it is necessary to consider the cutting parameters and the factors of the tool itself. Carbon fiber composites are anisotropic, and their mechanical properties vary greatly in different directions. Therefore, when customizing the machining, it is recommended to make the machining direction parallel to the inner fiber direction of the material as much as possible, which can reduce tool wear and prevent the occurrence of delamination and splitting of the workpiece.
When the carbon fiber composite material is machined, the work done by the shear deformation of the chip and the work done by the front and back friction of the tool are converted into cutting heat, and the heat in the processing area is difficult to diffuse during processing. In order to prevent the temperature from being too high, this phenomenon can be reduced by adding cutting fluid or changing the material and cutting angle of the tool.
Due to the special properties of carbon fiber composite materials, a large amount of debris will be generated during cutting, which will cause harm to the human body and the workplace. During cutting, in addition to improving tools and cutting methods, the use of dust removal equipment is also necessary.
Specific to common processing methods, WASTON CUSTOMACHINING mainly has the following production experience to share with you.
Turning:
It is recommended to use synthetic diamond polycrystalline tools for turning. To ensure the surface processing quality of carbon fiber plates, in addition to selecting appropriate tools and parameters, a reasonable cutting amount should also be selected. The size of the cutting amount is an important factor affecting the cutting force.
Milling:
Milling is a main method of carbon fiber board processing. Generally speaking, when processing a cutting surface extending to the edge of the carbon fiber laminate, the edge of the laminate should be milled first to prevent delamination. It is recommended to use a sharp four-slot end milling. To improve cutting efficiency and reduce cutting force, thereby reducing the possibility of delamination, try to avoid groove feed when milling, and use lateral feed only when there is sufficient support on the back.
Grinding:
In order to avoid the problem of difficult cutting, grinding or special processing is often used, but the grinding efficiency is low, and the feed rate is generally between 0.02 and 0.10 mm. The diamond grinding wheel is suitable for grinding carbon fiber composite materials, but it is easy to stick to the knife. If it is blocked, it is recommended to use a diamond grinding wheel with a particle size of 60-80# as a grinding tool.
drilling:
When drilling carbon fiber composite materials, defects are prone to occur at the entrance and exit. At the entrance, due to the strong bearing capacity of the material, there are relatively few defects, which have little effect on the drilling quality. The exit side is the place where the defects are relatively concentrated due to the less uncut part of the material and the low interlaminar strength.
For example, a carbide twist drill is used to drill carbon fiber composite materials, and the cutting parameters are that the rotational speed n is 6000 r/min, and the feed speed V is 15 mm/min. When the chisel edge of the drill drills out the material, the material around the chisel edge has different degrees of bulge, which is mainly due to the low strength of the outer layers of the material, which is delaminated under the action of the drilling force, and the material retreats to form a bulge. With the further deepening of the drill bit, the fibers are gradually cut by the main cutting edge, and the defect expands around under the action of the drilling force. When the expansion degree of the defect is greater than the diameter of the hole, the final defect is deformed. At this stage, there is an obvious phenomenon. The fibers with an obtuse angle between the fiber direction and the cutting direction of the tool are cut first, and the fibers with an acute angle between the fiber direction and the cutting direction of the tool are not easy to be cut, and the defects also obviously expand outward in this area. When the cutting edge is mostly drilled out, most of the surface fibers are cut off. Due to the reduction of the cutting area, the extent of defect expansion is reduced. At this stage, it can still be seen that when the fiber direction is an acute angle, there are still a large number of fibers that are not cut. When the drill bit is fully drilled, the secondary cutting edge corrects the defects that have been formed, and further cuts the uncut fibers to form the final shape of the hole.
In addition, the axial force is the main factor affecting the generation of defects. The rotating speed of the test drill bit is selected as 6000r/min, and the feed speed is 25, 35, 45, and 55 mm/min, respectively. The test is repeated three times for each group of parameters. Ultrasonic flaw detection was carried out on the specimen after drilling, and the maximum range value of the layered area was determined. When the axial force is less than 65N, there is no delamination phenomenon. When the axial force is greater than 65N, the degree of delamination defects increases with the increase of the axial force.
Composite materials and titanium alloy composite components are the common application forms of composite materials, but the difference in performance between the two materials brings huge difficulties to drilling processing. Polycrystalline diamond (PCD) composite sheet is a kind of cutter blank which is sintered on tungsten carbide (WC) substrate under high pressure and high temperature after uniformly mixing diamond particles with micron size and metal powder such as Co and Ni. new material. PCD composite sheet not only has the superior properties of diamond, such as high hardness, high wear resistance, high thermal conductivity, low friction coefficient, low thermal expansion coefficient, etc., but also has good strength and toughness of cemented carbide. The PCD drill bit thus developed can meet the processing requirements of both composite materials and titanium alloys at the same time. According to the test, when the 5mm PCD drill is used to drill carbon fiber composite materials and titanium alloys, the processing quality of carbon fiber composite materials can meet the requirements, and at the same time, relatively good quality can be obtained when drilling titanium alloys.
The fiber direction has a serious impact on the formation of drilling defects. When the fiber direction and the cutting angle of the tool are at an acute angle, the fiber is not easy to be sheared, and defects are easily generated. Especially when the critical value is around 6.04°, the defects are relatively serious. When the direction and the cutting angle of the tool are obtuse angles, the defects are less and the machining quality is better. The greater the axial force, the more serious the delamination defect, and the greater the axial force, the faster the tearing defect. New PCD cutters and helical face drills have greatly improved the drilling quality of carbon fiber composites.
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