In theory, the programming origin can be selected at any position of the workpiece, but as a CNC lathe, most of the machining is a rotary workpiece. In fact, for the convenience of programming and the intuitive size, you should try to make the programming origin as reasonable as possible. The X direction should be taken at the center of rotation of the spindle (), that is, on the spindle line. The Z direction generally takes the intersection of the center of rotation of the spindle and the right (or left) end of the workpiece. In this way, the workpiece coordinate system is also established. 2.1 The choice of the tool point is related to the accuracy, habit, machine coordinate system, programming, etc. When the accuracy of the tool setting is not high, it can be directly selected on the part or some surface on the fixture as the tool point. When the accuracy of the tool setting is high, the tool point should be selected on the design basis of the part. For the part positioned by the hole, the center of the hole is selected as the tool point. 2.2 The knife should be selected in a convenient place for the knife In the numerical control machine with absolute coordinate system, the tool point can be selected at the origin of the machine coordinate system or at the point where the origin is a certain value. When the part is installed, the part coordinate system and the machine coordinate system must have a certain dimensional relationship. . For CNC machines with machine tool origin, the command of the first block is to set the coordinate value command for the tool point to specify the coordinate value of the tool point in the machine coordinate system. 2.3 When setting the knife, the tool position should coincide with the tool point The so-called tool point: refers to the positioning reference point of the tool. For the turning tool: refers to the tip. For the ball knife, it refers to the center of the ball. For end mills: the intersection of the tool centerline and the tool underside. As shown in Figure 1.3, when using the NC machining of the quick positioning command G00, the use of G00 for rapid tool positioning and idle travel can improve efficiency, but note that G00 is not an interpolation command. Its running trajectory is the first two-axis synchronous feed for the oblique movement, after the shorter one axis, and then the longer one axis. Therefore, it is necessary to pay attention to the G00 positioning when it is easy to collide with the workpiece. When the tool is machined to point A, it is ready to return to position B. If the travel path of G00X20Z2.G00 is as shown by the dotted line during programming, the tool will collide with the workpiece. In order to avoid collision between the tool and the workpiece. 3. The influence of the radius of the tool nose on the machining accuracy CNC lathe programming generally uses the tool tip as the tool point and programming point, but in fact the tool tip is not the ideal tool tip and there will be a certain arc. This causes the tool travel trajectory to not match the programmed trajectory, and there is a difference. In particular, when machining a taper or an arc, the tool has a more prominent influence on the machining accuracy. Especially in systems without tool nose radius compensation. Therefore, this factor must be considered when programming. The following is an example of the influence of the radius of the tool nose on the machining accuracy and the corresponding measures when the shape of the workpiece changes. 3.1 When the workpiece machining surface is transitioned from the outer cylinder to the tapered surface When machining from cylinder to cone, the programmed tool should theoretically be in the position of O1, but due to the influence of the radius r of the tool nose, the cutting point of the tool to the cone is actually converted from the original point E. For point A. It can be seen that the cone processed according to this does not conform to the cone of the design pattern, and is larger than the designed cone size, that is, an error occurs in the axial direction and the radial direction, that is, the coordinates of points A and C. It can be obtained from the figure: axial error Δx=r-rcosα radial error Δz=r-rsinα where: r??? tool nose arc radius α??? the angle between the workpiece cone busbar and the center line is to be processed According to the figure, the tool must be in the position of O2, which is equivalent to the movement of the tool tip in front of the Z axis by a ZΔ value. According to the geometric relationship ∠BO2D=α∠CO2D= α/2 Then: CD=rtanα/2ZΔ=r-rαtanα/2 In programming, this error is often ignored. If this error is considered, the processing accuracy of the cone can be guaranteed. Generally, the center programming and the tool nose radius compensation function are used as much as possible. 3.2 When the workpiece machining surface is transitioned from the cylinder to the spherical surface When the radius of the tool tip increases, the AB value increases; otherwise, the AB value decreases. As the radius of the sphere increases, the AB value decreases. To eliminate this error during machining, the cutting point of the tool is changed, that is, the O1 position is moved to the O2 position, that is, a ZΔ value is shifted to the left. According to the geometric relationship: OC = (R + r) cos α Z Δ = CD = OD - OC = (R + r) - (R + r) cos α = (R + r) (1-cos α) Where: R??? workpiece radius r??? tool nose arc radius α??? The angle between the center of the workpiece and the center of the tool tip and the Z-axis coordinate. When programming, the Z-axis coordinate value of the machining cylinder facing the spherical surface plus the ZΔ value is used as the starting point of the cutting sphere to ensure the sphere. Processing quality. Conclusion In summary, I have passed the actual operation of CNC lathe for many years. Fully recognize that CNC machining is a good job in both theory and practice. Especially for manual programming, you must be very familiar with and understand the CNC system. Seriously study and analyze the nature, function, requirements and parameters of each instruction, the influence of the instructions on the processing route, etc., correctly select and use each instruction, and then process a certain knowledge and practical experience of the lathe, it will be very good Use CNC machine tools to avoid errors and major accidents, and to produce qualified products. Automatic Shrink Wrap Machine,High-Speed Automatic Side Sealing Machine,Heat Shrink Wrapping Machine,Semi Automatic Shrink Machine Dongguan Chanfer Intelligent Packing Technology Co., Ltd. , https://www.chanfer.com
Processing of CNC lathe programming problems
1. The choice of programming origin