With the development of new generation of carbon fiber reinforced plastics (CFRP) and laminates to be lighter and stronger, their performance continues to improve, and their status in various fields such as skis, tennis rackets, military aircraft and automobiles has become increasingly prominent. Someone predicted in the December 2010 issue of “Composite Materials Technology” that “no other technology can surpass carbon fiber reinforced plastics and help automakers achieve the goal of lightweighting faster.” As a workpiece material, it has been the mainstay for a long time. The challenge is how to improve the manufacturing process, especially machining. Although it is applied to airframe or ship frame with excellent performance, all kinds of fiber-reinforced epoxy resin, polyester and vinyl plastics have high hardness and are difficult to cut, and cannot tolerate a little abnormal deviation in the processing process, and the pre-processing added value High, and no waste is allowed.
Fortunately, a new generation of special tools have emerged to solve the most common processing needs of various composite materials. For example, ISCAR’s PCD LINE series drills and milling cutters have a wide machining coverage and are proven composite materials machining tools. There are drill bits suitable for processing thicker materials with aluminum alloy as the bottom layer, and drill bits suitable for processing thinner materials with carbon fiber reinforced plastic as the bottom layer. It also provides a series of combination tools, such as countersunk screw hole combination drills, drill reamers, slot milling cutters and combination drill milling cutters. It can be said that since the first appearance of reinforced composite materials, for the first time, an out-and-out high-performance tool can be found at any time to deal with any imaginable composite material processing task.
At present, the preferred tool solution for cutting composite materials is: using solid carbide as the matrix, thin PVD diamond (PCD) coating, brazing PCD inserts or sintering PCD at the cutting edge. In actual applications for thousands of advanced composite materials, Iscar’s above-mentioned tools are superior to most other similar products (including CVD diamond-coated carbide tools). The harder the material, the higher the density of the reinforcing fiber, and the greater the room for process improvement.
The reason is obvious. From the perspective of the tool, the solid carbide tool has the necessary rigidity and dimensional accuracy to ensure the precision of the workpiece size tolerance, position tolerance and surface finish. The solid carbide also makes it possible to optimize the cutting geometry, which can reduce the cutting force, cutting heat, uncut fibers, cupping, wire drawing, fuzzing and other problems, as well as better control of chips.
The thin PVD diamond (PCD) coating (applied to solid carbide tools or PCD inserts) makes the cutting edge more wear-resistant, thus ensuring that the tool maintains the original geometric structure during a longer machining cycle. The secret lies in the realization of the PVD diamond (PCD) thin coating. They not only provide the wear resistance of diamond, but also help maintain the ideal cutting geometry for carbide tooling. In contrast, the CVD (chemical vapor deposition) coating method inevitably forms a thicker diamond coating, which is not conducive to geometric structure optimization.
Mainstream composite material processing tools
As mentioned earlier, solid carbide matrix diamond-enhanced drills have proven very successful. They can keep the sharpness longer than ordinary solid carbide tools when processing composite materials.
There are currently four diamond-enhanced tools on the market suitable for processing composite materials:
⑴ CVD diamond-coated cemented carbide-has the advantages of high wear resistance of diamond and dimensional accuracy of cemented carbide tools. The disadvantage is that the coating is thicker, which may reduce the sharpness of the cutting edge or even make the cutting edge deviate from the correct Geometry.
⑵ PVD diamond-coated cemented carbide-both the high wear resistance of diamond and the dimensional accuracy of cemented carbide tools, the cutting edge is sharper, and the control of the cutting edge geometry is better.
⑶Brazed diamond blades on the solid carbide substrate-suitable for situations where only the front edge of the tool has diamond wear resistance requirements.
⑷High-pressure solid sintered diamond (PCD) solid carbide drill bit-its characteristic is sintered diamond (PCD) in the cutting edge of solid carbide tool.
Iscar recently proposed an innovative solution to solve the problem of drilling composite and laminated materials, that is, the use of transformer end mills (MULTI-MASTER) series cutter head. Transformers series can realize quick-change tool heads, fast loading and unloading, and easy to operate. One tool bar can hold a variety of exchangeable tool heads. This new tool head combines a diamond cutting edge with a tool geometry optimized for composite materials. With this cutter head, rough machining, semi-finishing and finishing operations can be performed successively. Its geometry is suitable for machining open cavities, slot milling and shoulder milling.
Another promising new product is ISCAR solid carbide drill reamer (SOLIDRILL-REAM). Combining a drill bit and a reamer can realize more precise hole processing in one step. This technology uses brazing different PCD blades on the same cutter body to perform drilling and reaming step by step.
Early hole processing in composite materials
Hole processing mainly refers to processing rivet holes, which is an inevitable main process in composite material processing. Due to the inherent hardness and dimensional stability, fiber reinforced plastics cannot decompose the misalignment stress caused by center eccentricity during rivet hole processing.
Early solutions mainly relied on the use of solid carbide tools to machine centering holes on CNC machine tools with offset and interpolation programming functions. Because a tool smaller than the hole diameter is used, this is actually an orbital milling process, not a real drilling. Compared with drilling, the use of this process route can indeed reduce the cutting heat and reduce the feed resistance, which also makes it possible to use one tool to process holes of different diameters and irregular cavities, and reduce the inventory cost of the tool .
The problem of tool wear prompts people to adopt a common “workaround”: programming to compensate for tool wear. Although this strategy can guarantee the processing size, it is not conducive to the surface finish and cutting heat control.