【正文】 this meant that the motions would be sluggish, and sideways would inevitably suffer from backlash, but more will be said about this topic later in the chapter. The early NC machines were, in the main, based upon a modified milling machine with this concept of control being utilized on turning, punching, grinding and a whole host of other machine tools later. Towards the end of the 1950s,hydrostatic sideways were often incorporated for machine tools of highl y precision, which to sonic extent overcame the section problem associated with conventional sideway response, whiles averagingout sideway inaccuracy brought about a much increased preasion in the machine tool and improved their control characteristics allows concept of the machining center was the product of this early work, as it allowed the machine to manufacture a range of ponents using a wide variety of machining processes at a single setup, without transfer of workpieces to other variety machine tools. A machining center differed conceptually in its design from that of a milling machine, In that the cutting tools could be changed automatically by the transfer machanism, or selector, from the magazine to spindle, or vice this ductively and the automatic tool changing feature enabled the machining center to productively and efficiently machine a range of ponents, by replacing old tools for new, or reselecting the next cutter whilst the current machining process is in cycle. In the mid 1960s,a UK pany, Molins, introduced their unique System 24 which was meant represent the ability of a system to machine for 24 hours per day. It could be thought of as a machining plex which allowed a series of NC single purpose machine tools to be linked by a puterized conveyor system. This conveyor allowed the work pieces to be palletized and then directed to as machine tool as necessary. This was an early, but admirable, attempt at a form of Flexible manufacturing System concept, but was unfortunately doomed to failure. Its principal weakness was that only a small proportion of ponent varieties could be machine at any instant and that even fewer work pieces required the same operations to be performed on them. These factors meant that the utilization level was low, coupled to the fact that the machine tools were expensive and allowed frequent production bottlenecks of workinprogress to arise, which further slowed down the whole operation. The early to mid1970s was a time of revolutionary in the area of machine tool controller development, when the term puterized numerical control (CNC) became a reality. This new breed of controllers gave a pany the ability to change work piece geometries, together with programs, easily with the minimum of development and lead time, allowing it to be economically viable to machine small batches, or even oneoff successfully. The dream of allowing a puterized numerical controller the flexibility and ease of program editing in a production environment became a reality when two ralated factors were:the development of integrated circuits, which reduces electronics circuit size, giving better maintenance and allowing more standardization of desing。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 manni ng levels. It is generally acknowledged that the earliest work into numerical control was the study missioned in 1947 by the US government. The study39。s maximum horsepower for roughing cuts. For a finishing cut, the smallest diameter of the part being machined is selected and then the cutting speed varied until the RPM is equal to the maximum RPM of the machine. This helps in maximizing machining efficiency. Knowing the horsepower requirement for a cut is critical if more than one tool is cutting at the same time. Software for a machining center application would be Ingersoll Tool Company39。 parts can be machined as needs .In conventional production often a great number of parts must be made at the same time to be cost effective. With CNC even one piece can be machined economically .In many instances, a CNC machine can perform in one setup the same operations that would require several conventional machines. With modern CNC machine tools a trained machinist can program and product even a single part economically .CNC machine tools are used in small and large machining facilities and range in size from tabletop models to huge machining centers. In a facility with many CNC tools, programming is usually done by CNC programmers away from the CNC tools. The machine control unit (MCU) on the machine is then used mostly for small program changes or corrections. Manufacturing with CNC tools usually requires three categories of persons. The first is the programmer, who is responsible for developing machineready code. The next person involved is the setup person, who loads the raw stork into the MCU, checks that the correct tools are loaded, and makes the first part. The third person is the machine and unloads the finished parts. In a small pany, one person is expected to perform all three of these tasks. CNC controls are generally divided into two basic categories. One uses a ward address format with coded inputs such as G and M codes. The other users a conversational input。 lasers, plasmaarc, flame cutting, and waterjets for cutting of steel plate。這些年來(lái)，刀具制作者已經(jīng)制作了多種多樣的刀具可用在 CNC 系統(tǒng)上，其中的一部分在第 3 冊(cè)中將被討論。這些現(xiàn)實(shí)是： 集成電路的發(fā)展，它減少了電路的尺寸，使得維護(hù)便利且有利于設(shè)計(jì)的標(biāo)準(zhǔn)化。