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Stainless steel is one of the most commonly used metal in different industries, especially in construction and building. Stainless steel products and parts also play an significant role in mechanical devices and machine tools. To manufacture high volume of stainless steel parts in high speed, CNC machining is a good choice. Based on the techniques performed on CNC machines, how to mill stainless steel parts? Here we are going to learn about Stainless steel CNC milling, involves the challenges, characteristics, solutions, tool selection, and more processing tips.
Challenges of Stainless Steel Milling
The main feature of stainless steel milling is intermittent cutting, and the impact and vibration in the cutting process are relatively stable, which is not as stable as that in CNC turning. Due to the characteristics of stainless steel material, such as large toughness, difficult chip separation and strong trend of work hardening, the disadvantage factors in the milling process are increased.
1. The material has high toughness, high temperature strength and hardness, difficult cutting deformation, and high cutting force in chip cutting process.
2. The adhesion and fusibility of stainless steel are strong, and the chip is easy to adhere to the edge of milling cutter, which worsens the cutting conditions.
3. Due to intermittent cutting, large impact and vibration, and the characteristics of stainless steel, the cutter teeth are easy to crack and wear.
4. The trend of work hardening of stainless steel is strong, intermittent cutting will increase the trend of hardening and make the cutting conditions worse.
5. Due to the comprehensive influence of the above factors, it is not easy to carry out high-speed cutting of stainless steel.
Therefore, the following measures should be taken for stainless steel milling
1) The milling machine with higher power and less vibration is selected.
2) The tool material with good impact toughness and wear resistance is adopted.
3) Suitable tool structure and geometry are adopted.
4) Select appropriate cutting parameters.
5) Select suitable cooling and lubricating fluid.
6) Operate correctly.
Cutters and Processing Tips of Stainless Steel Milling
1. Material of milling cutter
When milling stainless steel, due to intermittent cutting, the impact load is large and the cutting condition is bad. Therefore, the material toughness of the cutting part of the tool is required to be better, and it can bear a larger impact load. When milling stainless steel, the cutting materials of milling cutter mainly include high speed steel and cemented carbide. Generally, high-speed steel tools are mostly used in low-speed cutting, especially for shape milling cutter and rod milling cutter with small diameter. Due to the difficulties in manufacturing, it is more suitable to use high-speed steel tools. For stainless steel, the wear resistance of high speed steel is still not ideal. Therefore, if the conditions permit, it is better to use super hard high speed steel containing cobalt and aluminum to make cutting tools, so as to improve the durability of cutting tools. In medium and high speed milling, especially in face milling, yw2 or YG8 is more suitable, sometimes YT15 can be used. The milling cutter made of yw2 has higher wear resistance than YG8.
2. The influence of geometric parameters of milling cutter on stainless steel milling
1) Anterior horn gamma
The size of the rake angle has a great influence on the stainless steel milling process: increasing the rake angle, the chip deformation is easy in the cutting process, the cutting resistance is small, and the chip is relatively separated. If the rake angle of the milling cutter is equal to zero, the resultant force r generated during milling tends to push the milling cutter away from the workpiece, so that the cutter teeth are more difficult to cut into the workpiece. This kind of tool is not generally used when machining stainless steel. For the milling cutter with positive rake angle, the resultant force generated during milling only tends to pull the milling cutter like the workpiece, which makes it easier for the milling cutter to cut into the workpiece. Therefore, when milling stainless steel, the rake angle of milling cutter is generally 10 ° to 20 ° and 15 ° is more. When machining stainless steel with carbide bit, different rake angle can be used according to different conditions. Generally, the milling cutter with negative rake angle is not suitable for milling stainless steel. When using the assembled high-speed cutter head, the large rake angle of 25 ° to 30 ° of the edge part instead of the round chip curling groove can be ground out as the Turner does. In order to improve the durability of the cutter, a 0.05-0.2 edge band should be left on the edge of the cutter, and the fully fast cutter will soon curl when milling stainless steel.
2) Posterior horn
The larger the back angle of the milling cutter, the smaller the wear caused by friction. However, the larger the back angle, which will weaken the strength of the cutter teeth, the main back angle of the cutter head can generally reach 20 ° when milling stainless steel with high-speed cutter head.
3) Main deflection angle and secondary deflection angle
The main deflection angle is one of the main angles of the end milling cutter, which can determine the chip shape and section. Generally, 60 ° to 80 ° is selected. The width of the polished edge is generally about 1-1.5, and the minor angle of the rod milling cutter is generally between 1 ° and 2 °
4) Helix angle
It is a very important angle for cylindrical milling cutter, end milling cutter and rod milling cutter. As soon as the angle changes, the rake angle on the vertical section also changes, and the number of working teeth also changes.
When milling stainless steel, the cutting edge should be sharp and able to withstand impact, and the chip groove should be large. Large helix angle milling cutter (cylindrical milling cutter, end milling cutter) can be used. The helix angle B increases from 20 °to 45 °(n=5 °), and the tool life can be increased by more than 2 times, because the working rake angle G0e of milling cutter increases from 11 °to more than 27 °at this time, so milling is light and fast. But the value of B should not be larger, especially when B≤35 °is suitable for end milling cutter, so as not to weaken the cutter teeth.
