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When using drilling, refining, and bonding processes to process some austenitic and martensitic stainless steel materials such as 1Cr18Ni9Ti and 2Cr13 holes, common problems such as accelerated tool wear, poor surface integrity, and diversity in chip removal may arise during the processing, seriously affecting the processing quality, production cycle, and processing cost of such matches Material parts Analyze the above essential material processing differences based on themes such as metal technology and metal cutting principles, and explore an effective process for drilling, refining, and boring stainless steel materials

Analysis of Differences in Stainless Steel Material Processing

The main differences in processing stainless steel materials include the following aspects:

1. High cutting force and high cutting temperature

This type of material has high strength, substantial stress, and plastic deformation during cutting, resulting in high cutting force In addition, the material has extremely poor thermal conductivity, causing an increase in cutting temperature, and the high temperature is often concentrated in the arrow area around the tool edge, there accelerating tool wear

2. Separate work hardening

Austenitic stainless steel and some high performance alloy stainless steel are all Austenitic structures, with a strong margin for work hardening during cutting, usually several times that of order carbon steel Cutting tools in the work hardening area shorts tool life

3. Easy to stick knit

Both austenitic stainless steel and martensitic stainless steel have the characteristics of strong and rough cutting chips and high cutting temperature during processing When strong and tough chips flow through the front cutting surface, adhesive phenomena such as bonding and welding will occur, affecting the surface roughness of the processed parts

4. Accelerated tool wear

The above materials generally contain high melting point elements, high plasticity, and high cutting temperature, which accelerate tool wear and frequent tool grinding and replacement, there affecting production efficiency and improving tool usage costs

Processing Technology of Stainless Steel Parts

Based on the above analysis of machining differences, the machining process and related tool parameter design of stainless steel should have significant differences from ordinal structural steel materials The detailed machining process is as follows:

1. Drilling processing

When drilling, due to the poor thermal conductivity and small elastic modulus of stainless steel materials, hole processing is also quite complicated The main solution to the back in hole processing of such materials is to choose appropriate tool materials, determine rational geometric parameters of the tool, and determine the cutting amount of the tool When drilling the above materials, the drill bit should generally be made of materials such as W6Mo5Cr4V2Al and W2Mo9Cr4Co8 The advantage of these materials is that they are relatively expensive and difficult to purchase When using the commonly used W18Cr4V ordinal scale high speed steel drill bit for drilling, there are drawbacks such as small top angles, too wide chips that cannot be discharged out of the hole in a Timely Manner, and cutting fluid that cannot cool the drill bit in a Timely Manner In addition, the poor thermal conductivity of stainless steel material causes an increase in the cutting temperature concentrated on the cutting edge, which can easily lead to burns and chipping of the two real cutting surfaces and main cutting edges, reducing the service life of the drill bit

(1) Geometric parameter design of cutting tools

When using the W18Cr4V ordinary high speed steel drill bit for drilling, the cutting force and cutting temperature are concentrated on the drill tip To improve the cost resistance of the cutting part of the drill bit, the top angle can be applied incrementally The top angle is generally selected from 135 ° to 140 ° Increasing the top angle will also reduce the outer edge front angle and arrow the drilling chips, which is conductive to chip removal How, after increasing the top angle, the reverse edge of the drill benefits wizard, causing an increase in cutting resistance Thereforee, it is necessary to grind the reverse edge of the drill After grinding, the objective angle of the transitional edge is 47 ° to 55 °, and the front angle of the transitional edge is 3 ° to 5 ° When grinding the transitional edge, the cutting edge and the corner of the cyclical surface should be rounded to increase the strength of the transitional edge Due to the small elastic modulus of stainless steel material, the metal under the chip layer has a large elastic recovery, and the severe work hardening during the machining process A too small back angle will accelerate the wear of the real cutting surface of the drill bit, increase the cutting temperature, and reduce the lifespan of the drill bit Therebefore, it is necessary to increase the back angle appropriately, but if the back angle is too large, it will make the main edge of the drill bit thin and reduce the rigidity of the main edge Therebefore, the back angle should be between 12 ° and 15 ° In order to arrow the drilling chips and facilitate chip removal, it is also necessary to create stacked distribution of chip separation grooves on the two real cutting surfaces of the drill bit

(2) Selection of cutting amount

When drilling, the selection of cutting parameters should start from the basic point of reducing the cutting temperature As high speed cutting will increase the cutting temperature, and high cutting temperature will exacerbate tool wear, the most important cutting parameter is the selection of cutting speed In general, a cutting speed of 12-15m/min is more suitable The feed rate has a small impact on the tool life, but choosing a too small feed rate will cause the tool to cut within the hardened layer, exacerbating wear; If the feed rate is too large, it will also cause a decrease in surface roughness. Taking into account the above two factors, it is advisable to choose a feed rate of 0.32~0.50mm/r.

(3) Cutting fluid selection

During drilling, to reduce the cutting temperature, emulsion can be used as the cooling medium.

2. Reaming processing

(1) Geometric parameter design of cutting tools

Most stainless steel materials are reamed using hard alloy reamers. The structure and geometric parameters of a reamer are different from ordinary reamers. To enhance the strength of the cutter teeth and prevent chip blockage during reaming, the number of reamer teeth is generally relatively small. The rake angle of the reamer is generally 8 ° to 12 °, but in certain specific situations, in order to achieve high-speed reaming, a rake angle of 0 ° to 5 ° can also be used; The rear angle is generally 8 ° to 12 °; The selection of the main deviation angle varies depending on the hole, generally ranging from 15 ° to 30 ° for through-holes and 45 ° for through-holes; When reaming, in order to discharge the chips forward, the blade inclination angle can also be increased appropriately. The blade inclination angle is generally 10 °~20 °; The width of the blade is 0.1-0.15mm; The inverted cone on the reamer should be larger than that of a regular reamer, with hard alloy reamers generally ranging from 0.25 to 0.5mm/100mm and high-speed steel reamers ranging from 0.1 to 0.25mm/100mm; The length of the correction section of the reamer is generally 65% to 80% of that of a regular reamer, with the length of the cylindrical section being 40% to 50% of that of a regular reamer.

(2) Selection of cutting amount

When reaming, the feed rate is 0.08-0.4mm/r, the cutting speed is 10-20m/min, and the rough hinge allowance is generally 0.2-0.3mm, while the fine hinge allowance is 0.1-0.2mm. Hard alloy cutting tools should be used for rough reaming, and high-speed steel cutting tools can be used for fine reaming.

(3) Cutting fluid selection

When reaming stainless steel materials, a full loss system using oil or molybdenum disulfide as the cooling medium can be used.

3. Boring processing

(1) Tool material selection

Due to the high cutting force and cutting temperature when processing stainless steel parts, tool materials should be selected as high strength and good thermal conductivity YW or YG hard alloys as much as possible. YT14 and YT15 hard alloy blades can also be used for precision machining. When batch processing the above-mentioned materials and parts, ceramic material cutting tools can be used because the main characteristics of this type of material are high toughness and severe work hardening. The chips used to cut these materials are generated in the form of unit chips, which will cause vibration of the tool and easily cause micro collapse of the blade. Therefore, when selecting ceramic cutting tools to cut such materials and parts, the first consideration should be the micro toughness. Currently, Sialon is a good choice, especially α/β Sialon material is remarkable for its excellent resistance to high-temperature deformation and diffusion wear, and has been successfully applied in cutting nickel based alloys, with a lifespan far exceeding that of Al2O3 based ceramics. In addition, SiC whisker reinforced ceramics are also an effective tool material for cutting stainless steel or nickel based alloys.

For the processing of quenched parts made of this type of material, CBN (cubic boron nitride) blades can be used. The hardness of CBN is second only to diamond, and can reach 7000~8000HV. Therefore, it has high wear resistance. Compared with diamond, the protrusion of CBN has much higher heat resistance, up to 1200 ℃, and can withstand high cutting temperatures. In addition, its chemical inertness is very high, and it does not react with iron group metals at temperatures ranging from 1200 to 1300 ℃, making it very suitable for processing stainless steel materials. Its tool life is dozens of times that of hard alloy or ceramic tools.

(2) Geometric parameter design of cutting tools

The geometric parameters of the cutting tool play an important role in its cutting performance. In order to make the cutting light and smooth, it is advisable to use a larger rake angle for hard alloy cutting tools to improve tool life. During general rough machining, the front angle is taken as 10 ° -20 °, and during semi precision machining, it is taken as 15 ° -20 °; During precision machining, take 20 ° to 30 °. The basis for selecting the main deviation angle is that when the process system has good rigidity, it can be taken as 30 ° to 45 °; If the rigidity of the process system is poor, it is taken as 60-75 °. When the ratio of workpiece length to diameter exceeds 10 times, it is taken as 90 °.

When using ceramic cutting tools to bore stainless steel materials, in the vast majority of cases, ceramic cutting tools use negative rake angles for cutting. The size of the front corner should generally be between -5 ° and -12 °. This is beneficial for strengthening the blade and fully utilizing the superior compressive strength of ceramic cutting tools. The size of the back angle directly affects tool wear and also has an impact on the strength of the blade, generally choosing 5 ° to 12 °. The change in the main deviation angle will affect the changes in radial and axial cutting forces, as well as the magnitude of cutting width and cutting thickness. Due to the extremely unfavorable vibration of the process system on ceramic cutting tools, the selection of the main deviation angle should be conducive to reducing this vibration, generally selecting 30 ° to 75 °. When using CBN as the tool material, the geometric parameters of the tool are 0 ° -10 ° for the front angle, 12 ° -20 ° for the back angle, and 45 ° -90 ° for the main deviation angle.

(3) When grinding the front blade surface, the roughness value should be small

To avoid the phenomenon of chip sticking, the front and back surfaces of the tool should be carefully sharpened to ensure a small roughness value, thereby reducing chip outflow resistance and avoiding chip sticking.

(4) The cutting edge of the tool should be kept sharp

The cutting edge of the tool should be kept sharp to reduce work hardening, and the feed rate and back feed should not be too small to prevent the tool from cutting in the hardened layer and affecting its service life.

(5) Pay attention to the grinding of the chip breaking groove

Due to the strong and tough nature of stainless steel chips, the grinding of the chip groove on the front face of the cutting tool should be appropriate, so as to facilitate the interruption, holding, and removal of chips during the cutting process.

(6) Selection of cutting parameters

According to the characteristics of stainless steel materials, low speed and large feed rate should be selected for cutting during processing.

When using ceramic cutting tools for boring, the reasonable selection of cutting parameters is one of the key points to fully utilize the functions of ceramic cutting tools. During continuous cutting with ceramic tools, the cutting amount can be selected based on the relationship between wear resistance cost and cutting amount; Intermittent cutting should determine the reasonable cutting amount according to the law of tool damage. Because ceramic tools have superior heat resistance and wear resistance, the impact of cutting amount on tool wear life is smaller than that of hard alloy tools. In general, when machining with ceramic tools, the feed rate is the most sensitive to the impact of tool damage. Therefore, based on the properties of the workpiece material, under the conditions of machine power, process system stiffness, and blade strength, when boring stainless steel parts, it is advisable to choose a high cutting speed, a larger back feed, and a relatively small feed rate as much as possible.

(7) The selection of cutting fluid should be appropriate

Because stainless steel has the characteristics of easy adhesion and poor heat dissipation, it is important to choose cutting fluids with good adhesion resistance and heat dissipation in boring, such as selecting cutting fluids with high chlorine content, and water solutions without mineral oil or sulfite that have good cooling, cleaning, rust prevention, and lubrication effects, such as H1L-2 synthetic cutting fluid.

By adopting the above process methods, the processing difficulties of stainless steel can be overcome, and the tool life of stainless steel during drilling, reaming, and boring can be greatly improved. The number of tool grinding and changing during operation can be reduced, and satisfactory results can be achieved in improving production efficiency and hole processing quality, reducing labor intensity and production cost for workers.

Article source: Stainless steel faucet manufacturer http://www.yishangshijue.cn/