【正文】 spindle speeds are usually in the range of 4,0008,000 rpm 。 detection system was used to test the implementation of machine parts (table, turntable, skateboards, etc.) of the displacement and velocity variation, and the test results back to the input, and input mands to pare the difference adjusted in accordance with its machine tool movements 。 it is the principle behind transfer lines ． Commonly used in highvolume or mass production ． Transfer lines consist of several machine tools arranged in a sequence ． The workpiece , such as an automotive engine block , moves from station to station , with a specific machining operation performed at each station ． The workpiece is then transferred to the next machine for another operation , and so on ． There are products and situations , however , where transfer lines are not feasible or economical , particularly when the types of products to be machined are changed rapidly ． An important concept , developed in the late 1950s , is that of machining centers ． A machining center is a putercontrolled machine tool capable of peerforming a variety of cutting operations on different surfaces and different directions on a workpiece ． In general , the 畢業(yè)設(shè)計(jì)◆英文翻譯原文 第 2 頁(yè) 共 6 頁(yè) workpiece is stationary and the cutting tools rotate , as they do in milling and drilling operations ． The development of machining centers is intimately related to advances in puter control of machine tools , in general , a numerically controlled lathe(turning center) has two turrets carrying several cutting tools for turning , facing , boring , and threading． The workpiece in a machining center is placed on a pallet or module that can be move and swiveled(oriented) in various directions ． After a particular cutting operation has been pleted , the workpiece does not have to be moved to another machine(as has been done traditionally) for additional operations , such as drilling , reaming , or tapping ． In other words , the tools and the machine are brought to the workpiece ． After all the cutting operations have been pleted , the pallet automatically moves away with the finished workpiece , and another pallet containing another workpiece to be machined is brought into position by automatic pallet changers ． All movements are putercontrolled , and palletchanging cycle times are on the order of 10 to 30 seconds ． Pallet stations are available with multiple pallets serving the machining center ． The machines can also be equipped with various automatic parts , such as loading and unloading devices ． The machining center is equipped with a programmable automatic tool changer ． Depending on the design , up to 200 cutting tools can be stored in a magazine , drum , or chain (tool storage) ． Auxiliary tool storage is available on some special machining centers for many more cutting tools ． The cutting tools are automatically selected with random access for the shortest route to the machine spindle ． The toolexchange arm shown in is a mon design ． It swings around to pick up a particular tool (each tool has its own toolholder) and places it in the spindle ． Tools are identified by coded tags , bar codes , or memory chips attached directly to the tool holders ． A toolchanging time is typically between 5 and 10 seco