Stainless steel material processing difficulties
It mainly includes the following aspects:
1. Large cutting force, high cutting temperature
This type of material strength, cutting tangential stress, 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 area near the cutting edge of the tool, thus accelerating the tool wear.
2. Severe work hardening
Austenitic stainless steel and some high temperature alloy stainless steel are austenitic structure, when cutting work hardening tendency is large, usually several times of ordinary carbon steel, cutting tools in the work hardening area, shorten the tool life.
3. It sticks to knives easily
Both austenitic stainless steel and martensitic stainless steel are characterized by strong chip toughness and high cutting temperature.When the strong and tough chip flows through the front cutting surface, it will produce bonding, fusion welding and other bonding phenomenon, which will affect the surface roughness of processing parts.
4. Tool wear speeds up
The above materials generally contain high melting point elements, large plastic, high cutting temperature, so that the tool wear speed, grinding, frequent tool change, thus affecting the production efficiency, increased the cost of tool use.
The main is to reduce the cutting line speed, feed.Adopt special processing stainless steel or high temperature alloy cutting tools, drilling and tapping the best internal cold.
Stainless steel parts processing technology
Through the analysis of the above processing difficulties, the stainless steel processing technology and related tool parameters design and ordinary structural steel materials should be greatly different, the specific processing technology is as follows:
1. Drilling processing
When drilling, due to the poor thermal conductivity of stainless steel material, small elastic modulus, hole processing is also more difficult.To solve the hole processing problem of this kind of material, it is mainly to choose the right tool material, to determine the reasonable geometric parameters of the tool and the cutting parameters of the tool.When drilling the above materials, the drill bit should generally choose W6Mo5Cr4V2Al, W2Mo9Cr4Co8 and other materials of the drill bit, these material drill is more expensive, and difficult to purchase.And use the commonly used W18Cr4V standard high speed steel drill bit, drilling due to apex Angle smaller, outside the chip are too wide to timely discharge hole, cutting fluid is not cooling bit faults in time, coupled with the stainless steel material thermal conductivity is poor, lead to focus on the blade cutting temperature, easy to cause two plane of blade and the blade after burn and the collapse edge, reduce the service life of drill bit.
1) tool geometric parameter design when drilling with W18Cr4V ordinary high speed steel drill bit, cutting force and cutting temperature are concentrated on the drill tip, in order to improve the durability of the cutting part of the drill bit, can be appropriate to increase the top Angle Angle, the top Angle is generally selected 135° ~ 140°, the top Angle will increase the front Angle of the outer edge will reduce, cuttings narrow, to facilitate chip removal.However, when the top Angle is increased, the transverse edge of the drill becomes wider, resulting in increased cutting resistance. Therefore, the transverse edge of the drill must be polished. The bevel Angle of the transverse edge after polishing is 47° ~ 55°, and the front Angle of the transverse edge is 3° ~ 5°.Because the elastic modulus of stainless steel material is small, the metal under the chip layer elastic recovery is large, in addition to the serious work hardening in the processing process, the back Angle is too small will speed up the wear of the bit after the cutting surface, and increase the cutting temperature, reduce the life of the bit.Therefore, it is necessary to increase the back Angle appropriately, but if the back Angle is too large, the main edge of the drill will become thin and reduce the rigidity of the main edge, so the back Angle should be 12° ~ 15°.In order to narrow the cuttings and facilitate the cuttings removal, it is also necessary to open crisscrossing cuttings slots on the two rear cutting surfaces of the drill.
2) the choice of cutting parameters when drilling, the choice of cutting parameters should be from the basic point of reducing the cutting temperature, because high speed cutting will make the cutting temperature increase, and high cutting temperature will aggravate the tool wear, so the most important cutting parameters is to choose the cutting speed.Generally, the cutting speed of 12 ~ 15m/min is more suitable.The feed has little effect on the tool life, but too little feed will make the tool cut in the hardened layer and aggravate the wear.If the feed is too large, the surface roughness will become worse.Taking the above two factors into consideration, it is appropriate to choose 0.32 ~ 0.50mm/r as the feed quantity.
3) cutting fluid selection drilling, in order to reduce the cutting temperature, can use emulsion as the cooling medium.
2. Reaming processing
1) geometric parameters of the tool design the majority of stainless steel reamer processing using carbide reamer.The structure and geometrical parameters of reamer are different from those of ordinary reamer.In order to enhance the strength of the reamer teeth and prevent the occurrence of chip blocking phenomenon, the number of reamer teeth is generally less.The front Angle of the reamer is generally 8° ~ 12°, but in some specific cases, 0° ~ 5° front Angle can also be used to realize high-speed reamer.The rear Angle is generally 8° ~ 12°;The selection of the main deflection Angle depends on the hole. Generally, the through-hole is 15° ~ 30°, and the through-hole is 45°.When reaming, in order to make the chip discharge forward, the Angle of blade inclination can also be appropriately increased. Generally, the Angle of blade inclination is 10° ~ 20°.The width of the blade belt is 0.1 ~ 0.15mm;The inverted cone on the reamer should be larger than the ordinary reamer. The hard alloy reamer is generally 0.25 ~ 0.5mm/100mm, and the high speed steel reamer is 0.1 ~ 0.25mm/100mm.The length of the correction part of the reamer is generally 65% ~ 80% of that of the ordinary reamer, and the length of the cylinder part is 40% ~ 50% of that of the ordinary reamer.
2) when the cutting parameters select the reaming, the feed is 0.08 ~ 0.4mm/r, the cutting speed is 10 ~ 20m/min, the rough reaming allowance is generally 0.2 ~ 0.3mm, and the fine reaming allowance is 0.1 ~ 0.2mm.Hard alloy cutting tools should be used for coarse reaming and high speed steel cutting tools for fine reaming.
3) when the cutting fluid chooses the reaming of stainless steel material, the full-loss system oil or molybdenum disulfide can be used as the cooling medium.
3. Boring machining
1) tool material selection due to the processing of stainless steel parts of the cutting force, cutting temperature is high, the tool material should try to choose high strength, good thermal conductivity of YW or YG cemented carbide.YT14 and YT15 carbide blades can also be used for finishing.Batch processing the material parts, ceramic cutting tools can be used, because this kind of material is the main characteristic of the great toughness, work hardening is serious, the chip of cutting the material in the form of unit chip, will make the tool produces vibration, easy to cause the blade to produce micro collapse phenomenon, so choosing ceramic tool cutting such material parts should consider above all is the micro toughness.At present, Sialon is a good choice, especially Sialon material, which is remarkable for its excellent resistance to high temperature deformation and diffusion wear, and has been successfully used in cutting nickel-based alloys, whose life is far longer than Al2O3 based ceramics.In addition, SiC reinforced ceramics are also an effective tool material for cutting stainless steel or nickel-based alloys.
For this kind of material quenching parts processing, can use CBN (cubic boron nitride) blade, CBN hardness is second only to diamond, hardness up to 7000 ~ 8000HV, so high wear resistance, compared with diamond, CBN outstanding advantage is much higher than diamond heat resistance, up to 1200℃, can withstand a very high cutting temperature.In addition, its chemical inert, and iron group metals in 1200 ~ 1300℃ also has no chemical effect, so it is very suitable for processing stainless steel materials.Its tool life is carbide or ceramic tool several times.
2) tool geometry parameters design tool geometry parameters play an important role in its cutting performance, in order to make the cutting light, smooth, carbide tool should be used a larger front Angle, in order to improve tool life.In general roughing, the front Angle is 10° ~ 20°, and the semi-finishing Angle is 15° ~ 20°.When finishing, take 20° ~ 30°.The main deflection Angle is selected based on the fact that 30° ~ 45° is desirable when the rigidity of the process system is good.If the rigidity of the process system is poor, take 60 ~ 75°, when the ratio of length to diameter of the workpiece is more than 10 times, 90°.
When boring stainless steel with ceramic tools, ceramic tools use negative front Angle for cutting in most cases.The size of the front Angle is generally chosen from -5° to -12°.This is conducive to strengthen the edge, give full play to the advantage of high compressive strength ceramic tools.The size of the back Angle directly affects the tool wear, the blade strength also has an impact, generally choose 5° ~ 12°.The variation of main deflection Angle will affect the variation of radial cutting component and axial cutting component as well as the cutting width and cutting thickness.Because the vibration of the process system is very unfavorable to the ceramic tool, so the choice of the main deflection Angle should be conducive to reduce the vibration, generally choose 30° ~ 75°.When CBN is selected as the tool material, the tool geometric parameters are 0° ~ 10° front Angle, 12° ~ 20° rear Angle, and 45° ~ 90° main deflection Angle.
In order to avoid the phenomenon of chip sticking to the knife, the front and rear cutting surfaces of the tool should be carefully grinded to ensure a small roughness value, so as to reduce the chip outflow resistance and avoid chip sticking to the knife.
4) the cutting edge of the tool should be kept sharp, in order to reduce work hardening, feed and back feed of the knife should not be too small, in order to prevent the tool in the hardening layer cutting, affect the service life of the tool.
5) pay attention to the chip cutting groove grinding because of the stainless steel chip has strong and tough characteristics, the chip cutting groove on the cutting tool front surface grinding should be appropriate, so that the cutting process interrupt chip, chip, chip removal convenient.
6) the selection of cutting parameters according to the characteristics of stainless steel materials, processing should choose low speed and large feed for cutting.
When using ceramic tools for boring, the reasonable choice of cutting parameters is one of the keys to give full play to the properties of ceramic tools.The cutting parameters can be selected according to the relationship between the wear durability and the cutting parameters.In intermittent cutting, reasonable cutting parameters should be determined according to the rule of tool damage.Because ceramic knives have superior heat and wear resistance, the impact of cutting parameters on tool wear life is smaller than carbide tools.In general, when machining with ceramic tools, the impact of feed on tool breakage is the most sensitive.Therefore, according to the nature of the workpiece material, in the machine power, process system stiffness and blade strength permit the premise, when boring stainless steel parts, as far as possible to choose the high cutting speed, large back feed and relatively small feed.
7) cutting fluid choose appropriate because the stainless steel has the characteristics of susceptible to bonding and poor heat dissipation, so choose in boring cutting liquid phase bonding and thermal resistance good as important, if choose high chlorine cutting fluid, and has good lubrication and cooling, cleaning and antirust function does not contain mineral oil, do not contain the aqueous solution of salts, such as H1L - 2 synthetic cutting fluid.
The introduction of the technological process, can overcome the processing difficulty of stainless steel, the stainless steel during drilling, reaming, boring tool life been improved greatly, and decrease The Times of operation knife, tool change in improving production efficiency and machining quality, reduce labor intensity and production cost, can obtain a satisfactory result.