机械类专业英语教学课件作者韩林烨关雄飞Unit8课件.pptVIP

Unit 8 Feed Directions for Milling Operations Text Basically, there are two directions in which a milling cutter can be fed into the work-one with the feed in the direction of cutter rotation or climb milling and the other with the feed opposite the direction of cutter rotation or conventional milling. Climb Milling Climb or down milling causes the tool to make a chip of maximum thickness at the start of the cut at and near the part surface and maximum thickness at the end of the cut inside the material. The work is pushed down and into the cutter. Thus, less clamping and machining horsepower are required. The extra force on the table, however, means that the milling machine must have a backlash eliminator for eliminating play between the nut and the table screw. Most modern CNC machines come equipped with backlash eliminators. More accurate roughing cuts with a minimum of machining marks or surface breakouts are attainable with this method of milling. Chips are pushed behind and away from the cutter and do not tend to dull the tool by remaining on its front cutting edges. Climb milling is also recommended for machining thin parts or parts that are hard to hold down. Manufacturers of carbide tipped tools suggest climb milling especially when cutting work-hardened materials. Conventional Milling When conventional milling is practiced the chip has no thickness at the start of the cut inside the material and attains maximum thickness at the end of the cut near and at the surface of the part. The chip is pushed up from the Inside of the part and in front of the cutter. Conventional or up milling requires more fixture hold-down force and is recommended for materials with hard outer scales such as castings, forgings and hot rolled steel and for finishing CNC operations.3 Recall climb milling causes the cutter to cut the outer scale first which can create high tool impact loads and excessive tool wear on hard-scale materials. Conventional milling is also recommend