Stainless steel material processing difficulties mainly have the following aspects:
1.High cutting force and high cutting temperature
This kind of material has high strength, cutting stress and plastic deformation, so the cutting force is large. In addition, the poor thermal conductivity of the material causes the cutting temperature to rise, and the high temperature is often concentrated in the narrow and long area near the cutting edge, which speeds up the tool wear.
2.Severe Work Hardening
The Austenitic stainless steel and some high temperature alloy stainless steels are all AUSTENITIC, which tend to work hard when cutting, usually several times as common carbon steels. The tool life is shortened when cutting in the work hardening zone.
3.It sticks to the knife
Both Austenitic stainless steel and Martensitic stainless steel are characterized by high chip strength and toughness during machining and high cutting temperature. When the strong and tough chips flow through the front face, there will be bond, fusion welding and other bond tool phenomenon, affecting the processing of parts Surface roughness.
4.Tool wear is accelerated
These materials generally contain high melting point elements, high plasticity, high cutting temperature, so that tool wear accelerated, sharpening, tool change frequently, thus affecting the production efficiency, increased tool use costs.
Mainly to reduce the cutting line speed, feed. Using special processing stainless steel or high-temperature alloy cutting tools, drilling and tapping the best internal cooling.
Processing Technology of stainless steel parts
According to the analysis of the above-mentioned processing difficulties, the processing technology of stainless steel and the design of relative cutting tool parameters should be quite different from that of common structural steel:
1.Hole drilling
In the drilling process, due to the poor thermal conductivity of stainless steel materials, small modulus of elasticity, hole processing is also more difficult. In order to solve the problem of hole machining, the suitable cutting tool material is selected, and the reasonable cutting parameters and cutting parameters of the cutting tool are determined. When drilling the above materials, the bit should generally choose W6Mo5Cr4V2Al, W2Mo9Cr4Co8 and other materials bit, these materials bit is expensive, and difficult to purchase. But when the common W18CR4V standard high speed steel bit is used to drill holes, it has some disadvantages such as small vertex angle, too wide chip to discharge out of the hole in time, cutting fluid can’t cool the bit in time, and the poor thermal conductivity of stainless steel material, as a result, the cutting temperature focused on the cutting edge is increased, which is easy to cause two back surfaces and the main edge to be burned and broken, which reduces the service life of the drill bit.
1) when using W18CR4V high speed steel bit to drill, the cutting force and cutting temperature are concentrated on the drill point. In order to improve the durability of the bit, the top angle can be increased by 135 ~ 140. The increase of the top angle will also reduce the leading angle of the outer edge and narrow the chip, which is beneficial to the chip removal. However, when the top angle is increased, the cutting edge of the bit becomes wider and the cutting resistance is increased, so the cutting edge of the bit must be ground. After being ground, the bevel angle of the cutting edge is 47 ~ 55 and the front angle of the cutting edge is 3 ~ 5. When the cutting edge is ground, the corner of the cutting edge and the cylinder surface should be rounded to increase the strength of the cutting edge. Because the elastic modulus of stainless steel is small, the elasticity of the metal under the chip layer is large, and the work hardening is serious during the processing, too small back angle will accelerate the wear of the back surface of the bit, and increase the cutting temperature and reduce the life of the bit. Therefore, it is necessary to increase the back angle properly, but if the back angle is too large, the main edge of the drill will become thin and the rigidity of the main edge will be reduced. In order to narrow the cuttings and facilitate the removal of cuttings, it is necessary to open the cross-distributed cuttings slots on the two back surfaces of the bit.
2) the choice of cutting parameters, when drilling, the choice of cutting parameters should start from the basic point of reducing the cutting temperature, because high speed cutting will make the cutting temperature rise, and high cutting temperature will increase tool wear, so the most important thing in cutting parameters is to choose cutting speed. In general, the cutting speed of 12 ~ 15 m / min is suitable. The feed rate has little effect on the tool life, but too small a feed rate will cause the tool to cut in the hardened layer and increase the wear, while too large a feed rate will make the Surface roughness worse. Considering the above two factors, the feed rate should be 0.32 ~ 0.50 mm / R.
3) selecting cutting fluid, in order to reduce the cutting temperature, the emulsion can be used as the cooling medium.
2.Reaming
1) the geometric parameter design of the cutter, the carbide reamers are mostly used in reaming of stainless steel materials. The structure and geometric parameters of reamers are different from those of ordinary reamers. In order to enhance the strength of reamer teeth and prevent the phenomenon of chip clogging during reaming, the number of reamer teeth is usually less. Sentence is too long, please supply a shorter sentence.
2) when reaming, the feed rate is 0.08ー0.4 mm / R, the cutting speed is 10ー20 m / Min, the coarse reaming allowance is 0.2ー0.3 mm, and the fine reaming allowance is 0.1ー0.2 mm. Hard alloy cutting tools should be used for coarse reaming and high speed steel cutting tools for fine reaming.
3) cutting fluid selection, stainless steel material reaming hole, can use the total loss system with oil or molybdenum disulfide as a cooling medium.
3.Boring and processing
1) tool material selection, because processing stainless steel parts cutting force, cutting temperature is high, tool material should try to choose high strength, good thermal conductivity of YW or YG cemented carbide. YT14 and YT15 carbide inserts can also be used in finish machining. The ceramic tool can be used in batch processing of the above material parts, because the characteristics of this kind of material are high toughness and severe work hardening, and the chip produced in the form of unit chip when cutting these materials will cause vibration of the tool and easy to cause micro-disintegration of the cutting edge. At present, Sialon is a good choice, especially / Sialon material, which is remarkable for its excellent properties of high temperature deformation resistance and diffusion wear, and has been successfully used in cutting nickel-based alloys, the life of which is much longer than that of Al2O3-based ceramics. In addition, SiC whisker reinforced ceramic is also a very effective tool material for cutting stainless steel or nickel-based alloys.
CBN (cubic Boron nitride) blades can be used in the machining of these parts. The hardness of CBN is next to diamond and can reach 7000 ~ 8000HV, so the wear resistance is very high. Compared with diamond, the outstanding advantage of CBN is that its heat resistance is much higher than that of diamond, can Reach 1200 °C, can withstand very high cutting temperature. In addition its chemical inertness is very big, with the iron group metal in 1200 ~ 1300 °C also does not have the chemical action, therefore is suitable for processing the stainless steel material. Its tool life is hard alloy or ceramic tool dozens of times.
2) the geometric parameters of the cutting tool play an important role in the cutting performance. In order to make the cutting light and smooth, large rake angle should be adopted to increase the tool life. Generally, the rake angle is 10 ~ 20 for rough machining, 15 ~ 20 for semi-finish machining, and 20 ~ 30 for finish machining. The main deflection angle is selected on the basis of 30 ~ 45 when the rigidity of the process system is good, 60 ~ 75 when the rigidity of the process system is bad, and 90 when the ratio of the length to the diameter of the workpiece is more than 10 times.
When boring stainless steel materials with ceramic tools, in most cases, ceramic tools are used to cut with negative rake angle. The size of the front corner should be-5 ~-12. This is conducive to strengthening the blade, give full play to the ceramic tool compressive strength of the higher advantages. The size of the back angle has a direct effect on the wear of the tool and the strength of the blade. 5 ~ 12 is generally used. The change of principal deflection angle will affect the radial cutting force and axial cutting force as well as the cutting width and cutting thickness. Because the vibration of the process system is very disadvantageous to the ceramic cutting tool, the choice of the main deflection angle should be helpful to reduce the vibration, generally choose 30 ~ 75. When CBN is used as the tool material, the geometric parameters of the tool are 0 ~ 10,12 ~ 20 and 45 ~ 90.
3) in order to avoid the phenomenon of chip sticking, the front and back surfaces of the cutting tools should be carefully ground to ensure a smaller value of roughness so as to reduce the chip flow resistance and avoid the chip sticking.
4) the cutting edge of the tool should be kept sharp, the cutting edge of the tool should be kept sharp, in order to reduce the work hardening, the feed and the back of the knife should not be too small, in order to prevent the cutting tool in the hardening layer, affect the service life of the tool.
5) pay attention to the grinding of chip-breaking groove, because the stainless steel chip has the strong and tough characteristic, the chip-breaking groove on the tool front surface should be grinded properly, so that the chip-breaking, chip-containing and chip-removing are convenient in the cutting process.
6) the choice of cutting parameters, according to the characteristics of stainless steel materials, processing should choose low speed and large feed for cutting.
When the ceramic tool is used for boring, the rational choice of cutting parameters is one of the keys to give full play to the performance of ceramic tool. In the continuous cutting of ceramic tools, the cutting parameters can be selected according to the relationship between wear resistance and cutting parameters, and the rational cutting parameters should be determined according to the law of tool breakage. Because of the excellent heat resistance and wear resistance of ceramic cutting tools, the influence of cutting parameters on tool wear life is smaller than that of cemented carbide cutting tools. In general, when the ceramic tool is used, the feed rate is most sensitive to the damage of the tool. Therefore, according to the nature of the workpiece material, under the premise that the machine tool power, the technological system rigidity and the blade strength permit, when boring the stainless steel parts, as far as possible to choose high cutting speed, large back to eat knife and smaller feed.
7) the choice of cutting fluid should be suitable, because stainless steel is easy to produce the bond and the heat dissipation is poor, so it is very important to choose the cutting fluid with good anti-bond and heat dissipation in boring, such as choosing the cutting fluid with high chlorine content, and the water solution without mineral oil and without sulphite, such as H1L-2 synthetic cutting fluid, which has good cooling, cleaning, rust prevention and lubricating effects.
By using the above process method, the processing difficulty of stainless steel can be overcome, the tool life of stainless steel can be greatly increased when drilling, reaming and boring, and the times of sharpening and changing the tool in operation can be reduced, satisfactory results can be obtained in improving production efficiency and hole processing quality, reducing Labor intensity and production cost.
