Research Status and Development Trend of High Speed ​​Dry Cutting Technology
2022-10-16 14:05:11
Abstract: High-speed dry cutting technology is an advanced manufacturing technology developed on the basis of high-speed machining and dry cutting technology. It is the concrete implementation of green manufacturing in the field of metal cutting. The tools, machine tools and auxiliary processes required for high-speed dry cutting have certain specialities, which are three important aspects that affect the high-speed dry cutting technology.
As an advanced cutting technology, high-speed cutting (HSC) machining has been widely used since the 1980s. High-speed machining uses cutting speeds and feed rates much higher than conventional machining, which not only improves machining efficiency, but also reduces machining man-hours while achieving high machining accuracy. With the development of high-speed spindle technology, new types of tools are constantly appearing, and the optimization research on high-speed machining process parameters is also deepening, which makes the theoretical research and application of high-speed cutting technology have been greatly developed.
The main advantages of high-speed machining are: 1. The cutting force is reduced by about 30%, which is especially suitable for parts with poor rigidity. 2. Due to the cooling and lubrication of the tool and the workpiece during machining, the influence of cutting heat on the workpiece is reduced, which is especially suitable for processing. The workpiece with thermal deformation; 3, the excitation frequency is much higher than the natural frequency of the machine tool and the process system, the processing is stable, the vibration is small, and the surface quality is good; 4. The production efficiency can be greatly improved. However, high-pressure and large-flow cooling methods used in high-speed cutting will increase environmental pollution, increase production costs, reduce tool durability, and increase machine corrosion.
In order to solve the above problems, the current method is to change the use parameters and dosage of the cutting fluid to develop a new type of pollution-free green cutting fluid; the other is to stop using the cutting fluid during the cutting process, using dry cutting, which can Fundamentally solve the problems caused by cutting fluid.
Dry cutting technology is a green cutting processing technology developed in the 1990s to adapt to the world's rising environmental protection requirements and sustainable development strategies. Currently, industrialized countries such as Europe, America and Japan attach great importance to dry cutting research, dry cutting. The technology has been successfully applied to the production field and has achieved good economic benefits.
High-speed cutting has the characteristics of reducing cutting force and small thermal deformation of the workpiece. It provides favorable conditions for dry cutting. The goal of high-speed dry cutting is not only to limit or stop the use of cutting fluid, but also to ensure high processing efficiency and processing quality. However, in high-speed dry cutting, due to the lack of cooling fluid lubrication and chip removal of the cutting fluid, the friction between the tool and the workpiece in the cutting zone is intensified, the cutting force is increased, the cutting temperature is increased, the cutting vibration is enhanced, and the chip removal is not smooth. Will affect the machine tool processing performance and tool life, reduce the processing quality. Therefore, it is necessary to research and optimize from the aspects of tools, machine tools and auxiliary processes, so that high-speed dry cutting technology can be more widely used.
A high speed dry cutting tool technology
High-speed dry-cutting tools are subject to higher temperatures than wet-cutting. The friction coefficient between the tool and the chip and the contact surface of the tool and the workpiece is also as small as possible, and the tool is also required to facilitate chip breaking, chip removal and heat dissipation. It needs to be solved from several aspects such as tool material, tool coating and tool structure optimization.
Tool material
The rapid development of tool materials is the basis for the implementation of high-speed dry cutting. For high-speed dry cutting, the chemical affinity of the tool material and the material to be processed is required to be small, and it must have good heat resistance, high red hardness and thermal toughness. Current tool materials for dry machining include ultrafine grained cemented carbide, PCD (polycrystalline diamond), CBN (cubic nitriding shed), ceramics and cermets. Fine-grained carbides are particularly resistant to high temperatures, high strength and impact toughness, and are suitable for dry-cutting drills and milling cutters. PCD (polycrystalline diamond) and CVD diamond coated inserts have high hardness and thermal conductivity, suitable for high speed dry cutting of non-ferrous metals (such as copper alloys, aluminum alloys) as well as titanium alloys and wear-resistant high-performance composites, but not Processing ferrous metals. CBN (cubic boron nitride) is second only to diamond in hardness and wear resistance. It has excellent red hardness, chemical stability and low friction coefficient. It is ideal for high-speed dry cutting of ferrous metals such as hardened steel and chilled cast iron above HRC50. Tool material. The cermet has good hardness and impact resistance and poor thermosetting properties, so it is mostly used for finishing and semi-finishing. Ceramics have a high hardness. It has the advantages of good chemical stability and anti-adhesion, low friction coefficient, etc. It is a relatively inexpensive dry cutting tool material, but its strength, toughness and impact resistance are poor, and it is suitable for high-speed dry cutting of gray cast iron and steel.
2. Optimization of tool structure
The failure mode of the cutting tool is mainly the crater wear, so the larger front angle is generally used to reduce the contact area between the chip and the rake face. In order to make up for the weakening of the edge strength of the large rake angle, it is often equipped with a reinforcing blade or even a rib on the rake face. A large positive rake angle, sharp and powerful cutting edge facilitates chip breaking. In short, the structural design of dry cutting tools must take into account the problems of chip breaking and chip removal. For the processing of ductile materials, chip breaking is very important. At present, the design and manufacturing technology of the three-dimensional curved chipbreaker of the turning tool is relatively mature, and the corresponding chip breaking groove structure can be quickly designed for different workpiece materials and cutting amount. Dimensions and greatly improve chip breaking capacity and control of chip flow direction. In addition, in order to accelerate the cooling of the tool to reduce the cutting temperature, a heat pipe cutter or a liquid nitrogen cooling tool can also be used.
In the method of cooling the tool with liquid nitrogen, a metal cap is flipped on the rake face of the turning tool, and the inner cavity and the surface of the blade together form a closed space. The cap has liquid nitrogen inlets and outlets. During the dry cutting process, liquid nitrogen continuously flows in the closed space, absorbing the cutting heat on the blade, so that the tool does not produce excessive temperature rise, and always maintains good cutting performance and smoothly realizes cutting.
3. Tool coating
With high-speed dry cutting, it is still not possible to achieve good results if only the currently available thermally stable tool materials and optimized tool geometries are used. Therefore, the use of a hard-coating hard coating on the flank and a soft coating with solid lubricating properties allows the tool to withstand higher cutting temperatures. The role of the coating is to provide a low friction layer, which reduces the friction and adhesion between the tool and the surface of the workpiece, which is equivalent to the lubrication of the cutting fluid; the second is to provide insulation between the cutter and the cutting to prevent cutting. The heat propagates to the tool, which is equivalent to the cooling effect of the cutting fluid.
Coating materials can be classified into soft coatings and hard coatings. Soft coatings based on MoS and WL/C are mainly used in applications where the sliding properties of the coating are very high. The hard coating mainly includes TiN, TiCN, TiAlN, etc. TiAlN has good heat resistance and high temperature resistance, hardness up to 3500 HV, working temperature up to 799 ° C, and the addition of Al makes the tool's oxidation resistance greatly improved. It is the most commonly used material for high speed machining and dry cutting. TiN can be used as a “universal coating†for dry cutting, mainly for dry tapping (except for cast iron wire), and TiN coating works well for solid carbide milling cutters.
In high-speed dry cutting tools, a multi-layer composite coating is often used to combine a hard coating and a soft coating, that is, two physical vapor deposition processes are used in one coating process to first produce a hard coating TIALN, and then The WC/C soft coating is formed on the sputtering method to improve the life of the tool. At present, new coating technologies such as high hardness, high thermal stability diamond film coating, CBN film coating, nano-scale coating composed of different combinations of coating materials, etc., have been greatly developed, and they have Its excellent anti-wear and self-lubricating properties make it suitable for high-speed dry cutting of a wide range of materials.
Two high-speed dry cutting machine technology
Since the high-speed dry-cutting machine tool no longer uses the cutting fluid, it will inevitably lead to changes in its overall structure and layout, mainly reflected in the thermal insulation performance of the machine tool, the chip removal speed, the dust washing effect and the three stiffness of the machine tool base member (static stiffness, Higher requirements are proposed in terms of dynamic stiffness and thermal stiffness.
1. Mechanism of high-speed dry cutting machine
a. Choose high-speed machine tools with high stiffness
Due to the higher cutting force and more cutting heat during the high-speed cutting process, the vibration between the tool and the workpiece and the thermal deformation of the machine tool are significantly increased, so the selected machine tool basic components (such as the column, The three rigidity of the bed, the workbench, etc.) is large, such as the use of new materials such as artificial granite to integrally manufacture the bed body, not only the three stiffness is good, but also the vibration damping effect is obvious. In addition, the combination of a virtual axis machine tool that is considered to be a "new CNC machine tool in the 21st century" and a "major technological revolution in machine tool structure" and high-speed dry machining technology will achieve better results.
b. Adopt fast chip layout
One of the main points of applying high-speed dry machining is to expel most of the heat from the chips before they pass through the machine. To this end, the following chip removal methods can be adopted: 1 High-speed dry-cutting machine tools should use vertical spindles and inclined beds as much as possible, and inclined partitions should be used around the workbench, which helps hot chips to fall into the row quickly. In the flutes. 2 With the help of gravity chip removal. Taking drilling as an example, the conventional layout of the machine can be changed. The workpiece is mounted on the lower part of the spindle, and the tool is drilled from the bottom up. Under the action of gravity, the chips can be smoothly discharged from the hole without using the cutting fluid with pressure to assist Chip removal. 3 use the siphon phenomenon to remove debris. In the drilling process, dry air can be used to suck the chips in the holes by siphoning without using cutting fluid. 4 Use vacuum or jet systems to improve chip evacuation conditions. For example, the "clean recycling system" developed by a Japanese company uses a structure in which the cutter portion is covered, and the compressed air blown from the inside is used to discharge the chips through the spiral duct in the direction of the tool rotation.
c. Use a structure with good thermal stability and appropriate insulation measures. The machine bed is made of heat-stable structure and material to minimize the influence of cutting heat. If the temperature is balanced, the left and right sides, the top and the bottom of the bed are designed into four communicating cavities and the oil is injected to ensure the same temperature of the entire bed. In addition, the basic components such as the machine column and the base adopt a symmetrical structure and select a material with a small heat capacity, and the spindle adopts a constant temperature water cooling device, etc., which can improve the thermal stability of the machine tool.
Appropriate thermal insulation measures are taken. For example, the chip flute is made of heat-insulating material, and the high-speed cutting zone uses an insulating cover to block hot chips, which can reduce the heat transferred from the chips to the machine during the chip removal process.
2. Spindle of high speed dry cutting machine
The main shaft should have high speed and high rigidity, especially dynamic stiffness, to adapt to the increase of cutting force and the increase of cutting vibration during dry cutting. Therefore, the dynamic high-speed and high-power electric spindle technology can effectively Suitable for high-speed cutting requirements, it uses a built-in shellless servo motor direct drive method, eliminating the influence of the intermediate drive chain, can achieve higher spindle speed, and can also improve the stiffness and frequency response of the spindle, suppress or reduce The cutting vibration of the spindle unit during dry cutting, while using ceramic bearings and advanced lubrication technology, reduces the thermal impact of the spindle during processing. The sealing technology of the spindle is also an important factor in achieving high-speed dry cutting. At present, in the design of high-speed spindle, the dynamic optimization of the electric spindle structure is adopted, and the dynamic stiffness and thermal stability of the spindle unit are improved by combining the thermal balance design, the circulating internal cooling technology and the bearing oil and gas lubrication technology. In terms of dust prevention, the labyrinth non-contact structure is combined with the high-pressure gas (O.4MPa) of oil and gas lubrication, which can effectively prevent the intrusion of suspended particles during processing.
3. Feed unit of high speed dry cutting machine
The feed unit should have high stiffness and large thrust, high feed rate and good acceleration and deceleration characteristics. At present, there are mainly "servo motor + high-speed ball screw pair with large lead" and "direct drive of DC linear motor". The maximum feed rate of the precision high-speed ball screw pair can reach 50-80m/min, the feed acceleration can reach 0.5-1.5g; the maximum feed rate of the feed unit directly driven by the linear motor can reach 100-200m/min. The feed acceleration can reach 3~10g. Both feed systems can meet the requirements of high-speed dry machining. Among them, the linear motor feed unit has a strong acceleration and deceleration capability, which is an ideal feed method for high-speed dry cutting. However, the linear motor has a small bearing capacity in use. Problems such as fever and need to be improved.
Three high speed dry cutting technology
Since high-speed cutting conditions, 95% to 98% of the cutting heat will be carried away by the chips, the cutting force can be reduced by 30%. Therefore, machining with a high cutting speed can achieve the same effect as using the cutting fluid. Japan Makino proposed the "Red Crescent" in the cutting process technology. The mechanism is that the cutting speed is very high, and the generated heat is concentrated in the front part of the tool, so that the workpiece material near the cutting area reaches a red hot state, resulting in a significant decrease in yield strength. Material removal rate.
In some machining, pure dry cutting is difficult to achieve. Minimum amount of lubrication (MQL) technology (also known as cutting) can be used. In this method, the compressed air is mixed with a small amount of lubricating fluid, and then injected into the processing area to effectively lubricate the processed portion between the tool and the workpiece. MQL technology can greatly reduce the friction between “tool-to-workpiece†and “tool-to-toolâ€, which can suppress temperature rise, reduce tool wear, prevent sticking and improve workpiece processing quality. The lubricating fluid used is also rare. It is very obvious. MQL technology uses vegetable oils or fats that are harmless to human health, and its amount is very small, generally 0.03 to 0.2 L/h, while in a typical machining center, the amount of cutting fluid is as high as 20 to 100 L/h when wet cutting. It is about 60,000 times of the amount of lubricant used in MQL. The quasi-dry cutting effect of MQL lubrication is quite good and is now very popular. In addition, dry cutting and low-temperature cold air cutting can be performed in some special gas (such as liquid nitrogen) atmosphere.
4 Conclusion
High-speed dry cutting has fundamentally solved the drawbacks caused by cutting fluids, which not only benefits workers' health and environmental protection, but also reduces processing costs. It is undoubtedly a promising green processing technology.
As an advanced cutting technology, high-speed cutting (HSC) machining has been widely used since the 1980s. High-speed machining uses cutting speeds and feed rates much higher than conventional machining, which not only improves machining efficiency, but also reduces machining man-hours while achieving high machining accuracy. With the development of high-speed spindle technology, new types of tools are constantly appearing, and the optimization research on high-speed machining process parameters is also deepening, which makes the theoretical research and application of high-speed cutting technology have been greatly developed.
The main advantages of high-speed machining are: 1. The cutting force is reduced by about 30%, which is especially suitable for parts with poor rigidity. 2. Due to the cooling and lubrication of the tool and the workpiece during machining, the influence of cutting heat on the workpiece is reduced, which is especially suitable for processing. The workpiece with thermal deformation; 3, the excitation frequency is much higher than the natural frequency of the machine tool and the process system, the processing is stable, the vibration is small, and the surface quality is good; 4. The production efficiency can be greatly improved. However, high-pressure and large-flow cooling methods used in high-speed cutting will increase environmental pollution, increase production costs, reduce tool durability, and increase machine corrosion.
In order to solve the above problems, the current method is to change the use parameters and dosage of the cutting fluid to develop a new type of pollution-free green cutting fluid; the other is to stop using the cutting fluid during the cutting process, using dry cutting, which can Fundamentally solve the problems caused by cutting fluid.
Dry cutting technology is a green cutting processing technology developed in the 1990s to adapt to the world's rising environmental protection requirements and sustainable development strategies. Currently, industrialized countries such as Europe, America and Japan attach great importance to dry cutting research, dry cutting. The technology has been successfully applied to the production field and has achieved good economic benefits.
High-speed cutting has the characteristics of reducing cutting force and small thermal deformation of the workpiece. It provides favorable conditions for dry cutting. The goal of high-speed dry cutting is not only to limit or stop the use of cutting fluid, but also to ensure high processing efficiency and processing quality. However, in high-speed dry cutting, due to the lack of cooling fluid lubrication and chip removal of the cutting fluid, the friction between the tool and the workpiece in the cutting zone is intensified, the cutting force is increased, the cutting temperature is increased, the cutting vibration is enhanced, and the chip removal is not smooth. Will affect the machine tool processing performance and tool life, reduce the processing quality. Therefore, it is necessary to research and optimize from the aspects of tools, machine tools and auxiliary processes, so that high-speed dry cutting technology can be more widely used.
A high speed dry cutting tool technology
High-speed dry-cutting tools are subject to higher temperatures than wet-cutting. The friction coefficient between the tool and the chip and the contact surface of the tool and the workpiece is also as small as possible, and the tool is also required to facilitate chip breaking, chip removal and heat dissipation. It needs to be solved from several aspects such as tool material, tool coating and tool structure optimization.
Tool material
The rapid development of tool materials is the basis for the implementation of high-speed dry cutting. For high-speed dry cutting, the chemical affinity of the tool material and the material to be processed is required to be small, and it must have good heat resistance, high red hardness and thermal toughness. Current tool materials for dry machining include ultrafine grained cemented carbide, PCD (polycrystalline diamond), CBN (cubic nitriding shed), ceramics and cermets. Fine-grained carbides are particularly resistant to high temperatures, high strength and impact toughness, and are suitable for dry-cutting drills and milling cutters. PCD (polycrystalline diamond) and CVD diamond coated inserts have high hardness and thermal conductivity, suitable for high speed dry cutting of non-ferrous metals (such as copper alloys, aluminum alloys) as well as titanium alloys and wear-resistant high-performance composites, but not Processing ferrous metals. CBN (cubic boron nitride) is second only to diamond in hardness and wear resistance. It has excellent red hardness, chemical stability and low friction coefficient. It is ideal for high-speed dry cutting of ferrous metals such as hardened steel and chilled cast iron above HRC50. Tool material. The cermet has good hardness and impact resistance and poor thermosetting properties, so it is mostly used for finishing and semi-finishing. Ceramics have a high hardness. It has the advantages of good chemical stability and anti-adhesion, low friction coefficient, etc. It is a relatively inexpensive dry cutting tool material, but its strength, toughness and impact resistance are poor, and it is suitable for high-speed dry cutting of gray cast iron and steel.
2. Optimization of tool structure
The failure mode of the cutting tool is mainly the crater wear, so the larger front angle is generally used to reduce the contact area between the chip and the rake face. In order to make up for the weakening of the edge strength of the large rake angle, it is often equipped with a reinforcing blade or even a rib on the rake face. A large positive rake angle, sharp and powerful cutting edge facilitates chip breaking. In short, the structural design of dry cutting tools must take into account the problems of chip breaking and chip removal. For the processing of ductile materials, chip breaking is very important. At present, the design and manufacturing technology of the three-dimensional curved chipbreaker of the turning tool is relatively mature, and the corresponding chip breaking groove structure can be quickly designed for different workpiece materials and cutting amount. Dimensions and greatly improve chip breaking capacity and control of chip flow direction. In addition, in order to accelerate the cooling of the tool to reduce the cutting temperature, a heat pipe cutter or a liquid nitrogen cooling tool can also be used.
In the method of cooling the tool with liquid nitrogen, a metal cap is flipped on the rake face of the turning tool, and the inner cavity and the surface of the blade together form a closed space. The cap has liquid nitrogen inlets and outlets. During the dry cutting process, liquid nitrogen continuously flows in the closed space, absorbing the cutting heat on the blade, so that the tool does not produce excessive temperature rise, and always maintains good cutting performance and smoothly realizes cutting.
3. Tool coating
With high-speed dry cutting, it is still not possible to achieve good results if only the currently available thermally stable tool materials and optimized tool geometries are used. Therefore, the use of a hard-coating hard coating on the flank and a soft coating with solid lubricating properties allows the tool to withstand higher cutting temperatures. The role of the coating is to provide a low friction layer, which reduces the friction and adhesion between the tool and the surface of the workpiece, which is equivalent to the lubrication of the cutting fluid; the second is to provide insulation between the cutter and the cutting to prevent cutting. The heat propagates to the tool, which is equivalent to the cooling effect of the cutting fluid.
Coating materials can be classified into soft coatings and hard coatings. Soft coatings based on MoS and WL/C are mainly used in applications where the sliding properties of the coating are very high. The hard coating mainly includes TiN, TiCN, TiAlN, etc. TiAlN has good heat resistance and high temperature resistance, hardness up to 3500 HV, working temperature up to 799 ° C, and the addition of Al makes the tool's oxidation resistance greatly improved. It is the most commonly used material for high speed machining and dry cutting. TiN can be used as a “universal coating†for dry cutting, mainly for dry tapping (except for cast iron wire), and TiN coating works well for solid carbide milling cutters.
In high-speed dry cutting tools, a multi-layer composite coating is often used to combine a hard coating and a soft coating, that is, two physical vapor deposition processes are used in one coating process to first produce a hard coating TIALN, and then The WC/C soft coating is formed on the sputtering method to improve the life of the tool. At present, new coating technologies such as high hardness, high thermal stability diamond film coating, CBN film coating, nano-scale coating composed of different combinations of coating materials, etc., have been greatly developed, and they have Its excellent anti-wear and self-lubricating properties make it suitable for high-speed dry cutting of a wide range of materials.
Two high-speed dry cutting machine technology
Since the high-speed dry-cutting machine tool no longer uses the cutting fluid, it will inevitably lead to changes in its overall structure and layout, mainly reflected in the thermal insulation performance of the machine tool, the chip removal speed, the dust washing effect and the three stiffness of the machine tool base member (static stiffness, Higher requirements are proposed in terms of dynamic stiffness and thermal stiffness.
1. Mechanism of high-speed dry cutting machine
a. Choose high-speed machine tools with high stiffness
Due to the higher cutting force and more cutting heat during the high-speed cutting process, the vibration between the tool and the workpiece and the thermal deformation of the machine tool are significantly increased, so the selected machine tool basic components (such as the column, The three rigidity of the bed, the workbench, etc.) is large, such as the use of new materials such as artificial granite to integrally manufacture the bed body, not only the three stiffness is good, but also the vibration damping effect is obvious. In addition, the combination of a virtual axis machine tool that is considered to be a "new CNC machine tool in the 21st century" and a "major technological revolution in machine tool structure" and high-speed dry machining technology will achieve better results.
b. Adopt fast chip layout
One of the main points of applying high-speed dry machining is to expel most of the heat from the chips before they pass through the machine. To this end, the following chip removal methods can be adopted: 1 High-speed dry-cutting machine tools should use vertical spindles and inclined beds as much as possible, and inclined partitions should be used around the workbench, which helps hot chips to fall into the row quickly. In the flutes. 2 With the help of gravity chip removal. Taking drilling as an example, the conventional layout of the machine can be changed. The workpiece is mounted on the lower part of the spindle, and the tool is drilled from the bottom up. Under the action of gravity, the chips can be smoothly discharged from the hole without using the cutting fluid with pressure to assist Chip removal. 3 use the siphon phenomenon to remove debris. In the drilling process, dry air can be used to suck the chips in the holes by siphoning without using cutting fluid. 4 Use vacuum or jet systems to improve chip evacuation conditions. For example, the "clean recycling system" developed by a Japanese company uses a structure in which the cutter portion is covered, and the compressed air blown from the inside is used to discharge the chips through the spiral duct in the direction of the tool rotation.
c. Use a structure with good thermal stability and appropriate insulation measures. The machine bed is made of heat-stable structure and material to minimize the influence of cutting heat. If the temperature is balanced, the left and right sides, the top and the bottom of the bed are designed into four communicating cavities and the oil is injected to ensure the same temperature of the entire bed. In addition, the basic components such as the machine column and the base adopt a symmetrical structure and select a material with a small heat capacity, and the spindle adopts a constant temperature water cooling device, etc., which can improve the thermal stability of the machine tool.
Appropriate thermal insulation measures are taken. For example, the chip flute is made of heat-insulating material, and the high-speed cutting zone uses an insulating cover to block hot chips, which can reduce the heat transferred from the chips to the machine during the chip removal process.
2. Spindle of high speed dry cutting machine
The main shaft should have high speed and high rigidity, especially dynamic stiffness, to adapt to the increase of cutting force and the increase of cutting vibration during dry cutting. Therefore, the dynamic high-speed and high-power electric spindle technology can effectively Suitable for high-speed cutting requirements, it uses a built-in shellless servo motor direct drive method, eliminating the influence of the intermediate drive chain, can achieve higher spindle speed, and can also improve the stiffness and frequency response of the spindle, suppress or reduce The cutting vibration of the spindle unit during dry cutting, while using ceramic bearings and advanced lubrication technology, reduces the thermal impact of the spindle during processing. The sealing technology of the spindle is also an important factor in achieving high-speed dry cutting. At present, in the design of high-speed spindle, the dynamic optimization of the electric spindle structure is adopted, and the dynamic stiffness and thermal stability of the spindle unit are improved by combining the thermal balance design, the circulating internal cooling technology and the bearing oil and gas lubrication technology. In terms of dust prevention, the labyrinth non-contact structure is combined with the high-pressure gas (O.4MPa) of oil and gas lubrication, which can effectively prevent the intrusion of suspended particles during processing.
3. Feed unit of high speed dry cutting machine
The feed unit should have high stiffness and large thrust, high feed rate and good acceleration and deceleration characteristics. At present, there are mainly "servo motor + high-speed ball screw pair with large lead" and "direct drive of DC linear motor". The maximum feed rate of the precision high-speed ball screw pair can reach 50-80m/min, the feed acceleration can reach 0.5-1.5g; the maximum feed rate of the feed unit directly driven by the linear motor can reach 100-200m/min. The feed acceleration can reach 3~10g. Both feed systems can meet the requirements of high-speed dry machining. Among them, the linear motor feed unit has a strong acceleration and deceleration capability, which is an ideal feed method for high-speed dry cutting. However, the linear motor has a small bearing capacity in use. Problems such as fever and need to be improved.
Three high speed dry cutting technology
Since high-speed cutting conditions, 95% to 98% of the cutting heat will be carried away by the chips, the cutting force can be reduced by 30%. Therefore, machining with a high cutting speed can achieve the same effect as using the cutting fluid. Japan Makino proposed the "Red Crescent" in the cutting process technology. The mechanism is that the cutting speed is very high, and the generated heat is concentrated in the front part of the tool, so that the workpiece material near the cutting area reaches a red hot state, resulting in a significant decrease in yield strength. Material removal rate.
In some machining, pure dry cutting is difficult to achieve. Minimum amount of lubrication (MQL) technology (also known as cutting) can be used. In this method, the compressed air is mixed with a small amount of lubricating fluid, and then injected into the processing area to effectively lubricate the processed portion between the tool and the workpiece. MQL technology can greatly reduce the friction between “tool-to-workpiece†and “tool-to-toolâ€, which can suppress temperature rise, reduce tool wear, prevent sticking and improve workpiece processing quality. The lubricating fluid used is also rare. It is very obvious. MQL technology uses vegetable oils or fats that are harmless to human health, and its amount is very small, generally 0.03 to 0.2 L/h, while in a typical machining center, the amount of cutting fluid is as high as 20 to 100 L/h when wet cutting. It is about 60,000 times of the amount of lubricant used in MQL. The quasi-dry cutting effect of MQL lubrication is quite good and is now very popular. In addition, dry cutting and low-temperature cold air cutting can be performed in some special gas (such as liquid nitrogen) atmosphere.
4 Conclusion
High-speed dry cutting has fundamentally solved the drawbacks caused by cutting fluids, which not only benefits workers' health and environmental protection, but also reduces processing costs. It is undoubtedly a promising green processing technology.
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