组合零件加工工艺、程序编制及仿真

AbstractN/C machine tool elements consist of dimensioning system,servomechanismsand open-or closed-loop systems.It is important to understand each element prior toactual programming of a numerically controlled part.The term measuring system in N/C refers to the method a machine tool uses tomove a port from a reference point to a target point.A target point may be a certainlocation for drilling a hole,milling a slot,or other machining operation.The twomeasuring systems used on N/C machines are the absolute and incremental.Theabsolute (also called coordinate)measuring system uses a fixed reference point(origin).It is on this point that all positional information is based.In other words,allthe locations to which a part will de moved must be given dimensions relating to thatoriginal fixed reference point.It shows an absolute measuring system with X and Ydimensions,each based on the origin.The incremental measuring system (also calldelta)has a floating coordinating system.With the incremental system,the machineestablishes a new origin or reference point each time the part is moved.It show X andY values using an incremental measuring system.Notice that with this system,eachnew location bases its values in X and Y from the preceding location.Onedisadvantage to this system is that any errors made will be repeated throughout theentire program,if not detected and corrected.There are two types of control systems commonly used on N/C equipment:point-to-point and continuous path.A point-to-point controlled N/C machine tool,sometimes referred to as a positioning control type,has the capability of moving onlya straight line.However,when two axes are programmed simultaneously with equalvalues (X2.000 in.,Y2.000 in.)a 45 angle will be generated.Point-to-point systemsare generally found on drilling and simple milling machine where hole location andstraight milling jobs are performed.Point-to-point systems can be utilized to generatearcs and angles by programming the machine to move in a series of small steps.Usingthis technique,however,the actual path machined is slightly different from the cuttingpath specified.