Stainless steel is a relatively difficult material to process, especially for thread processing. After CNC cutting, the surface roughness of the thread is too poor. The phenomenon of scale-like waves and knife gnawing are the most common phenomena encountered in stainless steel thread turning. The reasons for these phenomena are as follows:
(1) The clearance angles on both sides of the thread turning tool are too small, and the friction between the cutting edges on both sides and the thread surface will deteriorate the processing surface. The influence of the thread rotation angle on the actual clearance angles of the cutting edges on both sides must be considered during processing.
(2) The rake angle of the thread turning tool is too small, the cutting edge is not sharp enough, and the chips cannot be cut smoothly, but are partially squeezed or torn off, which must cause the thread surface to be very rough. When the front angle is too large, the strength of the cutting edge is weakened and it is easy to wear, chip, and pierce the knife, which is more likely to cause vibration and cause ripples on the thread surface. Therefore, the appropriate rake angle should be selected according to the different materials of stainless steel. When turning concentrated sulfuric acid resistant stainless steel threads, a smaller rake angle should be used than turning 2Cr13 stainless steel threads. The cutting edges on both sides of the turning tool should have very narrow cutting edges to avoid rapid wear of the cutting edges. When cutting 2Cr13, 1Cr17, 4Cr13, the cutting edge should be as sharp as possible, otherwise it will not be easy to achieve the required good surface roughness.
(3) The thread cutter blade is blunt, and the actual rake angle and rear angle are changed from large to small. The chips are severely squeezed during the formation process, which increases the cutting force during the cutting process and increases the vibration, and the machined surface deteriorates seriously. Therefore, when turning stainless steel threads, the blade must be kept sharp at all times and the cutter head must be replaced in time.
(4) The thread turning tool is not fixed firmly, the tool head is extended too long, the tool holder is not rigid enough, or the machine tool accuracy is poor, the spindle is loose, the tool holder is partly loose and other factors can cause vibration and cause ripples on the thread surface. Therefore, you must pay attention to the operation of machine tools, tools and workpieces during operation to ensure that the system has sufficient rigidity. When installing a turning tool, in addition to ensuring a firm installation and no looseness, the tip of the turning tool should be slightly higher than the center of the workpiece by 0.2~0.5mm, and never below the center to avoid cutting the tool.
(5) The straight forward method should be avoided when turning the thread. Due to the long chip contact length on the left and right sides, it is easy to produce vibration, which increases the load on the tool tip, causes vibration and increases the resistance during chip removal, and scratches the machined surface. hurt. Therefore, for the processing of stainless steel threads, it is best to choose the method of cross-turning threads. This method adopts alternate lateral feed, especially for the cutting of large-pitch threads and viscous materials. It is the most effective measure to solve the vibration problem. Since the cutting edges are used crosswise, the wear is even and the service life of the tool can be prolonged.
(6) The matching degree of cutting parameters in the process of CNC thread cutting directly affects the processing efficiency. If the cutting amount is too small, the tool wear will be aggravated, and if it is too large, the tool will collapse. Therefore, the number of cuts and the feed per cut will have a decisive influence on the thread turning. In order to obtain the best tool life, the diameter of the workpiece should not be larger than the major thread diameter of 0.14mm, and a feed per tool of less than 0.05mm should be avoided. The total cutting amount of processing should be set at about 0.1mm, the first cut depth should be 150~200 (percent sign) of the nose radius (R), and the maximum should not exceed 0.5mm. For austenitic stainless steel, it should be avoided. If the feed per cut is less than 0.08mm, the common edge insert with a small nose radius for internal threads may increase the number of cuts as the depth of the knife decreases. The thread size is unstable after CNC cutting. After thread processing, use a thread ring gauge to measure the "through end" of the external thread cannot enter or the inconsistency of the front and rear tightness and the "end stop" part pass through.
