In summary, whether it is martensitic stainless steel, ferritic stainless steel or austenitic stainless steel, or even austenitic + ferritic stainless steel, the corresponding processing methods should be formulated according to different metallographic structures. In order to achieve the desired processing results, create more economic and social benefits. Metal products consumed by rust in the world account for about 10% of metal production, so it is very important to improve metal corrosion resistance and corrosion resistance. Stainless steel "target=_blank> stainless steel can achieve relatively good corrosion resistance requirements, from the initial military to industrial and civilian fields. Therefore, stainless steel "target=_blank> stainless steel workpieces for a variety of complex curved surfaces require a large amount. However, due to the particularity of the material, the processing technology has become a problem in the production of products.
The speciality of stainless steel "target=_blank> stainless steel itself
Influence on CNC machining
Different types of stainless steel "target=_blank> stainless steel is difficult to CNC cutting due to different mechanical properties and chemical composition. Some stainless steel "target=_blank> stainless steel is difficult to achieve satisfactory surface roughness during cutting. And some stainless steel "target=_blank> stainless steel, although it is easy to achieve the required surface roughness, but the tool is particularly easy to wear during the cutting process. After summary, all kinds of stainless steel "target=_blank> stainless steel is difficult to cut. The main reasons are as follows:
High thermal strength and high toughness are not suitable for high-speed CNC cutting. Austenitic stainless steel "target=_blank> stainless steel and martensitic stainless steel" target=_blank> stainless steel has low hardness and tensile strength, only equivalent to 40 steel However, the elongation, section shrinkage and impact values ​​are relatively high. For example, the elongation of 1Cr18Ni9Ti is 210% of that of No. 40 steel, so that it is not easy to be cut during the numerical control high-speed cutting process, and the work consumed during cutting deformation is quite large. Relatively speaking, stainless steel "target=_blank> stainless steel has less strength reduction at high temperatures. For example, 45 steel has a permanent strength of 7kg/mM2 at 500°, while 1Cr18Ni9Ti maintains its permanent strength at 19° at 550°. 24kg/mM2. It has been proved that stainless steel "target=_blank> stainless steel cutting is more difficult to process than ordinary carbon steel under the same cutting temperature, and its high thermal strength is an extremely important factor.
The trend of work hardening is not good for CNC turning. In the process of CNC high-speed turning, the metal in the cutting zone is deformed due to the extrusion of the tool tip on the workpiece material. The crystal is slipped, the lattice is distorted, the structure is dense, and the mechanical properties are also As the change occurs, the general cutting hardness can also increase by 2 to 3 times. The depth of the hardened layer after CNC cutting can vary from tens of microns to several hundred microns, so the work hardening caused by the previous pass prevents the cutting at the next pass, and the high hardness of the work hardened layer leads to the tool. Particularly easy to wear.
Strong adhesion of the chip and poor thermal conductivity have an effect on the CNC cutting. During the CNC cutting process, the cutting debris is easily adhered or fused to the tip and the blade to form a built-up edge, which causes the surface of the workpiece to be machined. Roughness deteriorates, while increasing vibration during cutting and accelerating tool wear. Moreover, a large amount of cutting heat cannot be transmitted in time, and even the heat generated by the cutting cannot be transmitted to the whole of the chip, resulting in a total heat of the incoming tool being 3 to 5 times higher than that of ordinary carbon steel, so that the cutting edge loses cutting performance at high temperature. . In the CNC cutting process, a large amount of thermal energy generated cannot be quickly discharged, and is inevitably transmitted to the cutter to raise the temperature of the cutting portion. At the same time, due to the difficulty in chip removal, especially the continuous chipping, the chips that are cut are congested, especially the inner holes are processed, and the chip congestion is more serious. In addition, due to the limitation of the shape of the thread cross section, the tool itself is inferior in strength, and vibration is easily generated during processing. The tool tip is easily burned due to excessive local temperature during the cutting process or is cracked due to too much vibration.
The problem of CNC cutting stainless steel "target=_blank> stainless steel cutter and its solution
The surface roughness of the thread after CNC cutting is too bad. The scaly corrugation and boring phenomenon are the most common phenomena in stainless steel "target=_blank> stainless steel thread turning. The reasons for these phenomena are: (1) Both sides of the thread cutter The back angle is too small, the friction between the two sides of the blade and the back thread surface deteriorates the machining surface. The effect of the thread rotation angle on the actual back angle of the two sides of the blade must be considered during machining. (2) The front angle of the thread turning tool is too small, the blade The mouth is not sharp enough, the chips can not be cut smoothly, but partially squeezed or torn, which must cause the thread surface to be very rough. When the current angle is too large, the blade strength is weakened and it is easy to wear, crack, and knives, and easier. Causes vibration to cause corrugation on the surface of the thread. Therefore, the appropriate rake angle should be selected according to the different materials of stainless steel "target=_blank> stainless steel. Stainless steel "target=_blank> stainless steel thread for turning resistant concentrated sulfuric acid should be smaller than the turning angle of 2Cr13 stainless steel" target=_blank> stainless steel thread. The cutting edge on both sides of the turning tool should have a narrow cutting edge. Avoid sharp wear of the cutting edge. When cutting 2Cr13, 1Cr17, 4Cr13, the cutting edge should be as sharp as possible, otherwise it will not be easy to achieve the desired good surface roughness. (3) The thread cutter blade is blunt, and the actual front and rear corners are greatly reduced. The chip is severely squeezed during the forming process, which increases the cutting force and increases the vibration during the cutting process, and the machining surface deteriorates severely. Therefore, when turning stainless steel "target=_blank> stainless steel thread, you must keep the sharpness of the blade at any time and replace the cutter head in time. (4) The thread cutter is not fixed firmly, the cutter head extends too long, the cutter bar is not rigid enough, or the machine tool Factors such as poor precision, loose spindles, loose parts of the tool holder, etc. can cause vibration and corrugation on the surface of the thread. Therefore, it is necessary to pay attention to the operation of the machine tool, tools and workpieces during operation to make the system rigid enough. The installation tool is firm and cannot be loosened. The tool nose should be slightly higher than the center of the workpiece by 0.2 to 0.5 mm. It must not be lower than the center to avoid tying. (5) Straight-cut method should be avoided when turning the thread, due to the left and right The side of the chip has a long contact length, which is easy to generate vibration, which increases the load on the tip, causes vibration and increases the resistance during chip removal, and scratches the machined surface. Therefore, the processing of stainless steel "target=_blank> stainless steel thread is the most Good choice of cross-turning thread. This method uses alternating lateral feed, especially for large pitch threads and viscous material cutting, which is the most effective measure to solve the vibration problem. Since the cutting edges are used for the left and right crosses, the wear is even and the tool life can be extended. (6) The matching degree of cutting amount in the process of CNC cutting thread directly affects the processing efficiency. Too small a cut will cause the tool to wear out. If it is too large, it will cause the tool to break. Therefore, the number of feeds and the feed per tool will have a decisive influence on the turning thread. In order to obtain the optimum tool life, the workpiece diameter should not be larger than the thread diameter 0.14 mm, and the feed per knife should be avoided less than 0.05 mm. The total cutting amount of machining should be set at about 0.1mm. The first cutting depth should be 150~200% of the tool nose radius (R), and the maximum can not exceed 0.5mm. For austenitic stainless steel "target=_blank> stainless steel A feed per knife of less than 0.08 mm should be avoided. A normal blade with a small nose radius for internal threads may increase the number of cuts as the depth of the tool decreases.
After the NC machining, the thread size is unstable. After the thread is machined, the threaded ring gauge is used to measure the "open end" of the external thread or the inconsistency of the front and rear tension and the passage of the "stop end". The causes of these ills: (1) the thread shape is wrong. Even if the thread diameter has reached the specified size, the thread ring gauge and plug gauge may still be unscrewed. (2) Threaded teeth. When measuring with a thread gauge, there is often a phenomenon that is limited by directionality, that is, it is tightened from one end and tightened from the other end, and even the "pass end" is passed but the "stop end" is passed. phenomenon. (3) If the internal thread bottom car is too small, or the outer thread bottom diameter is too large, the thread gauge will not be screwed in. This is due to the blunt wear of the turning tool and the squeezing phenomenon during the cutting process. The result of burrs being squeezed out of the diameter or inner diameter. (4) When the internal thread with a small diameter is turned, the rigidity of the turning tool holder is limited due to the size limitation. It is easy to produce a “knife†during the turning process, and the four sizes are large, resulting in local tolerance. (5) When the slender screw is turned, the rigidity of the workpiece is poor, and deformation occurs during the turning process, causing dimensional errors on the thread. (6) When the inner and outer threads of a thin-walled workpiece are turned, the workpiece is locally deformed due to the force and cutting temperature, and a local overshoot of the thread is also generated. Therefore, in order to solve the problem of "thread gauge can not enter", it is necessary to take corresponding measures for the above reasons, mainly from the aspects of correct installation and proper loading of the workpiece.
The subtle effect of cooling lubricant in CNC cutting threads
Proper use of lubricating fluids can improve cutting conditions with less effort. When CNC cutting stainless steel "target=_blank> stainless steel thread should pay attention to:
To understand the special requirements of cooling lubricants (1) Because stainless steel "target=_blank> stainless steel has high toughness and the cutting is not easy to be separated, it is required to have a higher cooling performance of the coolant to take away a lot of heat. (2) Due to its high viscosity and high meltability, it is easy to produce built-up edge during cutting thread, so the coolant should have high lubricating performance. (3) It requires better permeability of the coolant and can penetrate into the cutting. In the micro-gap line of the metal zone, the chip is easily broken off. (4) There must be a certain washing function.
Several suitable coolants (1) vulcanized oils have good cooling performance and lubricating function, and can be divided into direct and indirect according to different preparation methods. The formula of direct fluidized oil is: mineral oil 98%, sulfur 2%. The indirect vulcanized oil formula is: mineral oil 78% to 80%, black motor oil, vegetable oil 18% to 20%, sulfur 1.7%. (2) F43 oil is suitable for stainless steel "target=_blank> stainless steel cutting cooling lubricant, the best for stainless steel "target=_blank> stainless steel thread. Its formula is: No. 5 high-speed motor oil 83.5%, petroleum sulfonate calcium 4%, petroleum bismuth phosphate 4%, oxidized petroleum grease 4 soap 4%, zinc dialkyl thiophosphate 4%, disulfide 0.5%. (3) Vegetable oils such as soybean oil can help to obtain better thread surface roughness and extend the service life of the tool when turning the thread.
In summary, whether it is martensitic stainless steel "target=_blank> stainless steel, ferritic stainless steel" target=_blank>stainless steel or austenitic stainless steel" target=_blank>stainless steel, even austenite + ferrite Body stainless steel "target=_blank> stainless steel, should be based on different metallographic organization to develop the corresponding processing methods to achieve the desired processing results, create more economic and social benefits.
Http://news.chinawj.com.cn Editor: (Hardware Business Network Information Center) http://news.chinawj.com.cn
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