外文翻译--数字控制.doc

Numerical Control With China being fast to become global manufacturing center, of our country manufacturing industry in recent years develop swift and violent, numerical control is it become market competition and enterprise development new and on already to process, CAD and manufacture (CAD/CAM ) become a hot issue of the mechanical manufacturing industry. One of the most fundamental concepts in the area of advanced manufacturing technologies is numerical control (NC). Prior to the advent of NC, all machine tools were manually operated and controlled. Among the many limitations associated with manual control machine tools, perhaps none is more prominent than the limitation of operator skills. With manual control, the quality of the product is directly related to and limited to the skills of the operator. Numerical control represents the first major step away from human control of machine tools. Numerical control of machine tools is reported to have been first developed between 1947 and 1952 at the Massachusetts institute of Technology, in conjunction with the Parsons Aircraft Corporation. The development of numerical control techniques is accredited to the need for producing very accurately sized and intricately shaped parts for aircraft, principally space vehicles. Because of the complex shapes, considerable times was being spent in ensuring that the work/tool relationship was correct before machining took place; this led to long manufacturing times and hence high costs .In order to reduce costs, attempts were made to control automatically the work/tool relationship .This resulted in the development of positional control using numerical principles on a Cincinnati Hydrotel vertical mill. Numerical control means the control of machine tools and other manufacturing systems through the use of prerecorded, written symbolic instructions. Rather than operating a machine tool, an NC technician writes a program that issues operational instructions to the machine tool. For