机电行业基础英语上册冯宜丽Unit4课件教学.pptVIP

proverbs and sayings Conversation Picture The Change of Load From the two pictures, we can see that before the learning load is reduced, students carry a lot of books with them every day, wet with sweat. However, after the learning load is reduced, tuition makes many parents get into debt because their children have to go to college for a good future. At present, many students can’t afford the heavy tuition, for which many of them will have to say good-bye to school or their parents will have a heavy debt load. When we call for reducing the students’ learning load, we should also call on the tuition to be reduced. 馋死 PPT研究院 POWERPOINT ACADEMY * * Text A  The History of CNC and NC Development 2 In 1949, the U.S. Air Force awarded Parsons a contract to develop a new type of machine tool that would be able to speed up production methods. Parsons commissioned the Massachusetts Institute of Technology(M.I.T) to develop a practical implementation of his concept. Scientists and engineers at M.I.T built a control system for a two-axis milling machine that used a perforated paper tape as the input media. In a short period of time, all major machine tool manufacturers were producing some machines with NC, but it was not until the late 1970s that computer-based NC became widely used. NC matured as an automation technology when inexpensive and powerful microprocessors replaced hard-wire logic-making computer-based NC systems. Perforate vt.?穿孔于，刺穿e.g. The nail perforated her coat and left an ugly rip. 钉子穿透她的上衣，留下一块难看的破绽。 This machine can perforate the sheets of stamps. 这台机器能在整版邮票上打孔。 Text A  The History of CNC and NC Development 2 In 1949, the U.S. Air Force awarded Parsons a contract to develop a new type of machine tool that would be able to speed up production methods. Parsons commissioned the Massachusetts Institute of Technology(M.I.T) to develop a practical implementation of his concept. Scientists and engineers at M.I.T built a control syst