机电技术专业英语 教学课件 作者 徐起贺 张庆良pata b lesson Eleven.pptVIP

* 机电技术专业英语 Lesson Eleven Text The work of the machine shop in building machines is to make each part to the required shape and size. The unique feature of all machine shop operations is that the parts are precisely formed to the desired shape and size by removing metal from the workpiece in the forms of chips. These metal chips may be very large or very small as in the case of grinding operations. Assembling of the finished parts is, of course, the final job. The material to be machined is generally in the forms of hotrolled bars, colddrawn bars, machined bars, castings, or forgings. Tools, dies, machine parts, and engine parts frequently must have very precise dimensions and smooth surface finishes. These characteristics can sometimes be obtained by other manufacturing methods, but they must usually be achieved more economically, and to a higher degree, by machining. Value is added to the raw materials that are processed to become machine parts in the machine shop, by virtue of the work done to change their shape, provide precise dimensions, and create their final smooth surface finishes. Metal Cutting Operation System Lesson Eleven Machine tools Machine tools can be considered to serve four main purpose. (1) They hold the work or the part. (2) They hold the cutting tool or tools. (3) They impart to the cutting tool or work or both whatever motion is required for cutting or forming the part. (4) They are arranged, ordinarily, for regulating the cutting speed and also the feeding movement between the tool and the work. Metal cutting tool The metal cutting tool separates chips from the workpiece in order to cut the part to the desired shape and size. They must meet the following conditions. (1) The tool is harder than the metal to be cut. (2) The tool is so shaped that its cutting edge can penetrate the work. Lesson Eleven (3) The tool is strong and rigid enough to resist the cutting forces.