機(jī)械專業(yè)畢業(yè)設(shè)計(jì)---英文翻譯原文-文庫吧
2024-11-11 17:34 本頁面
【正文】 ationary 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 seconds 。 they may be less than one second for small tools , or up to 30 seconds for tools weighing 110 kg (250 lb) ． The trend in tool changers is to use simpler mechanisms ,resulting in faster toolchanging times ． Machining centers may be equipped with a tooland/or partchecking station that feeds information to the puternumerical control to pensate for any variations in tool settings or tool wear ． Touch probes can be automatically installed into a tool holder to determine reference surfaces of the workpiece , for the selection of tool settings , and for the online inspection of parts being machined． Note in that several surfaces can be contacted , and that their relative positions are determined and stored in the database of the puter software ． The data are then used to program tool paths and to pensate for tool length and diameter , as well as for tool wear in more advanced machine tools ． Types of Machining and Turning Centers Although there are various designs for machining centers , the two basic types are vertical spindle and horizontal spindle 。 many machines are capable of using both axes ． The maximum dimensions that the cutting tools can reach around a workpiece in a machining center is known as the work envelope
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