Iscar’s Machining Tips for Composites I
scar offers these tips for successful machining of composite materials. The harder the matrix and higher the reinforcing fiber content, the more PCD coatings/inserts will be needed at the cutting edge. When hole size allows, orbital drilling with a solid- carbide end mill or helical interpolation using the Multi-Master with PCD-coated tips is preferable to straight twist drilling. For shallower holes, use stubby, straight-shank drills. For deeper holes, design the process for absolutely reliable ejection of all types of chip. Consider “peck drilling” and even coolant flushing, if possible. Match speeds and feed to the layers in the laminate. Be ready to change parameters for each layer as the drill progresses. Select the tool geometry based on the last material in the stack. If the last material is a plastic, use a tapered drill with a long point angle. If the last layer is aluminum or titanium, a high-shear drill with a sharp point angle will exit more cleanly and leave less burr. The tapered drill would just smear aluminum. In thicker composite structures, beware of heat buildup as well as chip jamming. Select drills with narrow flutes, wide gullets and tighter spirals that complete the hole before things get too hot and in addition consider coolant. When titanium is in the stack, the preferred practice is everything that composites hate. To avert work hardening and overheating and to keep chips controllable, select tools with low reliefs and rake angles and a low spindle speed. Although coolant or mist is not generally used, it may be unavoidable for titanium because of heat and/or chip flushing. In short, take everything into account in tool selection, including the relative thicknesses and location of the metal and plastic layers. It is a balancing act. A stack heavy towards the metal favors solid-carbide tools with internal coolant. If CFRP is the main part, PCD carbide tools would be preferable. Be sure the process reliably breaks up the titanium chips into small, easily ejected pieces. You especially don’t want to risk a titanium chip jamming the hole in a composite. Again, the most effective remedies are slower speeds and pecking cycles.
materials. PCD tools tend to outperform diamond-coated drills in materials with high plastic content because they can maintain a sharper cutting edge.”
“Common challenges in machining composites are excessive tool wear, delamination of layers, uncut fibers, fiber pullout, and scrapped parts in both milling and drilling.”
RobbJack has developed cutting tool solutions like its solid PCD-tipped W-Point drills for drilling carbon fiber-rein- forced polymer (CFRP) parts like wing spars to eliminate poor quality cuts and expensive scrap. “The W-point geometry supports the materials as it pierces through and its sharp outer edge shears the material without delamination, uncut fibers, or fiber pullout. The solid polycrystalline diamond tip outperforms diamond-coated carbide drills for tool life up to 25 times longer than uncoated carbide,” said MacArthur. He recounted how one manufacturer was going through 25 carbide drills to make one ship set of wing spars, scrapping many very expensive parts in a costly and unstable process. “RobbJack’s solid PCD-tipped W-point was the only tool that
could meet the manufacturer’s exacting design and perfor- mance standards, cutting over 4000 clean holes in tolerance; other tools struggled to get 160 holes. Cutting tool savings totaled $548,290.08 per year,” said MacArthur. Another tool that RobbJack has developed for composites is a solid diamond-tipped drill with multifaceted geometry. “The compound 135° and 20° tip geometry has tested to be the best drilling solution across the most diverse range of carbon fiber composites,” said MacArthur. “The new multifaceted solid-dia- mond tipped drill produces the cleanest holes I’ve ever seen in carbon fiber materials. There is no delamination or uncut fibers in almost every material we have tested in our machining lab. “ RobbJack has been able to grow wear-resistant diamond on the cutting edges of carbide tools. “One solution we have developed is a combination tool that trims and bevels composites in one operation. This tool eliminated three other tools and eliminated the operation of trimming the part to match the CAD model. The tool bevels the mating surfaces and trims the part in one operation, reducing cycle time by five days,” MacArthur said.
Software Simulates Programming, Materials Choices The sheer volume of composites being used in the aircraft industry seems to dwarf all other applications and
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