【文章內容簡介】 view the graphics model from varying angles, such as a top, front, side, or isometric view. A toolpath that looks correct from a top view, may show from a front view that the depth of the cutting tool is incorrect. Changes can easily be made and seen immediately. When the toolpath and the sequence of operations are satisfactory, machine ready code has to be made. This is as easy as specifying the CNC machine that is to be used to machine the part. The code generator for that specific CNC machine during processing accesses four different files. The JOBPLAN file for the tool information and the GRAPHICE file for the toolpath and cutting sequence. It also uses the MACHINE DEFINE file which defines the CNC code words for that specific machine. This file also supplies data for maximum feed rates, RPM, toolchange times, and so on. The fourth file taking part in the code generating process is the TEMPLATE file. This file acts like a ruler that produces the CNC code with all of its parts in the right place and sequence. When the code generation is plete, a projected machining time is displayed. This time is calculated from values such as feed rates and distances traveled, noncutting movements at maximum feed rates between points, tool change times, and so on. The projected machining time can be revised by changing tooling to allow for higher metal removal rates or creating a more efficient toolpath. This display of total time required can also be used to estimate production costs. If more then one CNC machine tool is available to machine this part, making code and paring the machining time may show that one machine is more efficient than the others. CAD/CAM Another method of creating toolpath is with the use of a Computeraided Drafting (CAD) file. Most machine drawings are created using puters with the description and part geometry stored in the puter database. SmartCAM, though its CAM CONNECTION, will read a CAD file and transfer its geometry represents the part profile, holes, and so on. The programmer still needs to prepare a JOBPLAN with all the necessary tools, but instead of programming a profile line by line, now only a tool has to be assigned to an existing profile. Again, using the SHOWPATH function will display the toolpath for each tool and their sequence. Constant research and developments in CAD/CAM interaction will change how they work with each other. Some CAD and CAM programs, if loaded on the same puter, make it possible to switch between the two with a few keystrokes, designing and programming at the same time. The work area around the machine needs to be kept clean and clear of obstructions to prevent slipping or tripping. Machine surfaces should not be used as worktables. Use proper lifting methods to handle heavy workpieces, fixtures, or heavy cutting tools. Make measurements only when the spindle has e to a plete standstill. Chips should never be handled with bare hands. Before starting the machine make sure that the workholding device and the workpiece are securely fastened. When changing cutting tools, protect the workpiece being machined from damage, and protect your hands from sharp cutting edges. Use only sharp cutting tools. Check that cutting tools are installed correctly and securely. Do not operate any machine controls unless you understand their function and what they will do. The Early Development Of Numerically Controlled Machine Tools The highly sophisticated CNC machine tools of today, in the vast and diverse range found throughout the field of manufacturing processing, started from very humble beginnings in a number of the major industrialized countries. Some of the earliest research and development work in this field was pleted in USA and a mention will be made of the UK39。s contribution to this numerical control development. A major problem occurred just after the Second World War, in that progress in all areas of military and mercial development had been so rapid that the levels of automation and accuracy required by the modern industrialized world could not be attained from the lab our intensive machines in use at that time. The question was how to overe the disadvantages of conventional plant and current manning levels. It is generally ackonwledged that the earliest work into numerical control was the study missioned in 1947 by the US government. The study39。s conclusion was that the metal cutting industry throughout the entire country could not copy with the demands of the American Air Force, let alone the rest of industry! As a direct result of the survey, the US Air Force contracted the Persons Corporation to see if they could develop a flexible, dynamic, manufacturing system which would maximize productivity. The Massachusetts Institute of Technology (MIT) was subcontracted into this research and development by the Parsons Corporation, during the period 19491951,and jointly they developed the first control system which could be adapted to a wide range of machine tools. The Cincinnati Machine Tool Company converted one of their standard 28 inch HydroTel milling machines or a threeaxis automatic milling made use of a servomechanism for the drive system on the axes. This machine made use of a servomechanism for the drive system on the axes, which controlled the table positioning, crossslide and spindle head. The machine cab be classified as the first truly three axis continuous path machine tool and it was able to generate a required shape, or curve, by simultaneous slide way motions, if necessary. At about the same times as these American advances in machine tool control were taking Place, Alfred Herbert Limited in the United Kingdom had their first Mutinous path control system which became available in the next few years in both the USA and Europ