China Shenzhen Perfect Precision Product Co., Ltd. company news

When cutting, the force generated by the high-speed operation of the equipment is mainly used for cutting. In this way, high heat will be generated in the processing process, causing harm to the cutting tools and blanks. Therefore, the help of cutting fluid is needed when cutting. Cutting fluid plays a great role in reducing friction and cutting temperature in the cutting process. 1、 Function of cutting fluid 1. Cooling effect: through the heat conduction, convection and vaporization of the cutting fluid, it can effectively improve the heat dissipation conditions and reduce the temperature of the cutting area, so as to improve the service life of the tool and reduce the thermal deformation of the workpiece. 2. Lubrication: after the cutting fluid penetrates into the contact surface between the chip, the tool and the workpiece, it adheres to the metal surface to form a lubricating film, which can reduce the friction coefficient between the chip and the front of the tool and the back of the workpiece and the tool, reduce the bonding phenomenon, inhibit the chip buildup, reduce the surface roughness, and improve the tool life. 3. Washing and chip removal: the cutting fluid can wash away the fine chips generated in the cutting process, so as to achieve the purpose of mechanical cleaning and prevent the machining surface or machine tool damage. In deep hole machining, cutting fluid can also play the role of chip removal. 4. Antirust effect: after adding antirust additives to the cutting fluid, a protective film can be formed on the metal surface, so that the machine tool, workpiece and cutting tool will not be corroded by the surrounding medium and play the role of antirust.  Types and selection methods of cutting fluid 1. Types of cutting fluids: commonly used cutting fluids include aqueous solution and cutting oil. (1) Aqueous solution: aqueous solution is a cutting fluid with water as the main component. Although the cooling and washing effect of natural water is good, it is easy to rust machine tools and workpieces. At present, emulsion is the most commonly used in aqueous solution. Emulsion is a mixture of oil and water, because oil cannot be dissolved in water. In order to mix the two, emulsifiers (fatty acids, sodium soap, potassium soap) must be added. When in use, as long as the prepared emulsified oil is added with water, emulsions with different contents can be obtained. Emulsion with low content has strong cooling and washing effect, which is suitable for rough machining and grinding; The emulsion with high content has strong lubricating effect and is suitable for finishing. (2) Cutting oil: the cooling and washing effect of this kind of cutting fluid is worse than that of aqueous solution, but its lubrication and rust prevention effect are better. Pure mineral oil has poor lubrication, but it is rich in resources. Among them, mineral oils with low viscosity, such as l-an15 and l-an32 oils, light diesel oil, kerosene, etc., are widely used. Vegetable oil and animal oil contain polar molecules, which can form a stronger lubricating film. The lubricating effect is better than that of pure mineral oil, but it is not suitable for general use because of its high price. 2. Selection of cutting fluid: there are many kinds of cutting fluid, which should be selected reasonably according to the cutting conditions and the requirements of cutting fluid. The general principles for selecting cutting fluid mainly include the following aspects: (1) Select cutting fluid according to the material properties of the workpiece: when cutting brittle materials such as cast iron and bronze, in order to avoid the fine crumbs adhering to the machine tool and difficult to remove, generally do not use cutting fluid. However, when finishing cast iron, kerosene with good lubricity and low viscosity can be selected as cutting fluid in order to reduce the surface roughness value. When cutting general steel materials and workpieces with large plasticity, emulsion or vulcanized oil is usually used. (2) Choose cutting fluid according to the processing properties: during rough machining, the surface is rough and generates more heat. Generally, choose emulsion with strong cooling effect; During finish machining, in order to refine the surface roughness, cutting oil mainly used for cooling can be used. (3) Select cutting fluid according to the tool material: when planing with high-speed steel tools, generally cutting fluid can be used; When planing with cemented carbide tools, generally do not use cutting fluid to avoid cracks caused by sudden cooling and heating of the blade.

Intelligent manufacturing is a major component of the most popular industry 4.0 concept in today's manufacturing industry. So, what is intelligent manufacturing? Literally, intelligent manufacturing is different from those traditional manufacturing concepts in the past, such as lean manufacturing, digital manufacturing, networked manufacturing, agile manufacturing, etc. Although these concepts also appear tall, they are slightly inferior to intelligent manufacturing. However, in essence, intelligent manufacturing is inseparable from the above technologies, because they are important supports of intelligent manufacturing. Next, we will discuss in detail what is intelligent manufacturing, why we should develop intelligent manufacturing, and how to develop intelligent manufacturing. What is intelligent manufacturing? Here, we must realize that "intelligent manufacturing" is not a concept born out of nowhere, but a concept gradually formed by the manufacturing industry through long-term evolution and integration according to its internal development logic. In terms of content, it includes lean manufacturing, digital manufacturing, networked manufacturing, agile manufacturing, etc. mentioned above, and based on these technologies, it forms the general name of advanced manufacturing processes, systems and modes with the functions of deep information self perception, intelligent optimization self decision, precise control and self execution. Why develop intelligent manufacturing? The reason why we want to develop intelligent manufacturing technology is that it is the need of manufacturing transformation and the demand of the market. In recent years, in order to further improve the manufacturing level and increase its international competitiveness, various manufacturing powers have issued a number of manufacturing development strategies and plans, including the development of intelligent manufacturing technology. Once implemented, it will play a significant role in improving product quality, reducing costs and shortening the development cycle. In addition, the maturity of relevant technical conditions has also created essential conditions for the development of intelligent manufacturing. There are network technology and digital technology. Among them, networking not only refers to the Internet, but also includes the deep connection and integration between people and equipment, equipment and equipment, and equipment and materials. In addition to numerical control technology, digitalization also includes virtual scheme design and engineering development through computer iteration. These two technologies are inseparable from intelligent production. How to develop intelligent manufacturing? In order to develop intelligent manufacturing and catch up with or even surpass the world's advanced manufacturing countries, we should take the in-depth implementation of digital engineering as the premise, and start from the five aspects of intelligent design, intelligent process, intelligent production, intelligent service guarantee and intelligent management, so as to finally comprehensively promote the popularization of intelligent manufacturing. Intelligent design needs to establish a huge template library of data, so as to facilitate designers to select references from them, and constantly avoid shackles in human-computer interaction, so as to truly realize the "what you want is what you get" intelligent matching. The intelligent process connects the design department and the production workshops. It is an intelligent bridge between design and manufacturing. Based on intelligent information platform, it can transform design language into manufacturing language, and accurately convey the designer's ideas to production personnel; It also makes the products produced meet the original intention of designers. Intelligent production is a production mode that integrates intelligent equipment, units, production lines, workshops, factories and industrial chains into an organic whole. Several intelligent equipment and units can be combined into intelligent production lines, and several intelligent production lines can be combined into intelligent workshops. Intelligent workshops with several organic connections form intelligent chemical plants. Finally, multiple intelligent chemical plants form an intelligent industrial alliance of the industry. Intelligent service guarantee is a manufacturing service based on industrial big data and network. It is supported by technologies in the information field such as cloud computing, data fusion processing and analysis, remote monitoring and diagnosis, and establishes a guarantee system that is not limited by space distance to provide support for the smooth operation of the whole intelligent manufacturing. Intelligent management is to generate a bi based management cockpit to make decisions based on the accurate and real-time data extracted by the expert system or decision support system, and finally help managers make correct decisions through some interactive way.

The process of milling is to process the workpiece into the required shape and size by using the contact between the milling cutter and the workpiece. In this milling process, the milling cutter cuts the metal material on the surface of the workpiece into chips, including the cutting effect of the blade and the role of the tool surface pushing and supporting, so that the chips are separated from the processing surface. Cutting effect of the blade: when the tool contacts the workpiece, the stress in the workpiece gradually increases with the increasing force, and the stress is the largest at the contact with the blade. Where the stress on the workpiece is the largest and most concentrated, the metal material is the first to crack and separate. Therefore, the separation between the metal surface layer material and the metal matrix of the workpiece is always formed at the contact with the blade, which is the cutting effect of the blade. Pushing action in front of the tool: under the action of sufficient mechanical force, with the continuous relative movement of the tool and the workpiece, the cut metal will separate along the direction of the blade movement to form a machined surface. At the same time, the extrusion in front of the tool causes the cutting layer to produce elastic deformation and plastic deformation until finally forming chips, which flow out along the front of the tool, which is the pushing effect in front of the tool. Deformation of the cut metal under the action of the tool: the cut metal forms four deformation areas under the action of the cutting edge, front and back of the tool, namely, the basic deformation area, the friction deformation area in front of the tool, the deformation area in front of the edge and the friction deformation area behind the tool. The internal stress state and deformation in the four deformation zones are interrelated and affect each other. Types of chips and their forming conditions Due to different workpiece materials, different cutting conditions, and different deformation in the cutting process, different chips are produced. According to the different shapes of chips, chips can be divided into banded chips, nodal chips, granular chips and crumbling chips. 1. Banded chip: in the cutting process, if the slip on the final sliding surface has not reached the degree of fracture, a continuous banded chip with hairy outer surface and smooth inner surface will be formed. Strip chip is the most common kind of chip in finish machining. In processing plastic metal materials, such chips are often produced when the cutting speed is high, the thickness of the cutting layer is small, the rake angle of the tool is large and the edge is sharp. 2. Nodal chip: the nodal chip is formed under the condition of fracture due to sufficient sliding on the final sliding surface. The segmented chip has non penetrating cracks, the outer surface is serrated, and the inner surface is smooth. This kind of chip is mostly produced when processing plastic metal materials, with low cutting speed, large cutting layer thickness and small tool rake angle. 3. Granular chip: when the crack penetrates the whole chip layer and separates the chip into a ladder shaped unit body, granular chip (also known as unit chip) is formed. Granular chips are produced when machining metal materials with poor plasticity, low cutting speed, large cutting layer thickness and small tool rake angle. 4. Chipping: when cutting brittle metals (such as cast iron, etc.), because the plasticity of the material is very small, the metal surface layer will produce elastic deformation and very small plastic deformation under the cutting and pushing of the tool, and then it will be brittle and broken to form chipping chips. The harder and brittle the workpiece material, the smaller the rake angle of the tool, and the greater the thickness of the cutting layer, the easier it is to produce such chips.

In the process of metal cutting, the high-speed rotation of the cutting tool will cut the metal into the desired shape. However, in this process, when the high-speed tool is in contact with the metal surface, cutting steel or other plastic materials will cause the adhesion of metal materials on the front near the cutting edge of the tool, forming chip nodules. However, after the metal is cold worked, the strength and hardness are increased and the plasticity is reduced, and the surface hardening will occur. Debris tumor 1. The cause of debris tumor Chip buildup is the product of metal deformation and friction in the friction deformation area in front of the tool under specific conditions. When cutting plastic materials, the chip flows out along the front of the tool from the cutting edge, and the stagnant layer at the bottom of the chip is affected by the friction in front of the tool, and the flow speed slows down. Under the action of high temperature and high pressure, when the friction force is greater than the binding force of the stagnant layer, the metal of the stagnant layer separates from the chips and adheres to the front, forming chip nodules. 2. Influence of chip buildup on cutting process When the metal becomes a chip deposit, it will produce severe deformation, so the chip deposit has a high hardness (about 2-3 times the hardness of the workpiece), which can replace the cutting edge for cutting, and has a certain protective effect on the cutting edge. The existence of chip buildup can also increase the actual rake angle of the tool and reduce the cutting force. This is a favorable aspect of the influence of chip buildup on the cutting process. The adverse effects of chip buildup on the cutting process are as follows: (1) The existence of chip buildup will increase the thickness of the cutting layer, thus affecting the dimensional accuracy of the workpiece. (2) The growth and falling off of chip nodules will increase the surface roughness of the machined surface and reduce the surface quality. (3) When the chip mound breaks and falls off, part of the debris will flow into the tool workpiece contact area and form a "furrow" on the workpiece surface. Debris may also be embedded into the surface of the workpiece, causing hard spots and accelerating tool wear. (4) When the chip buildup breaks, the cutting force also changes, making the cutting process unstable. Based on the above, in general, especially in finishing, chip buildup is unfavorable to the cutting process, and measures should be taken to inhibit or avoid the generation of chip buildup. 3. Measures to inhibit or avoid debris accumulation (1) Control the cutting speed and try to use a very low or high cutting speed to avoid the speed range of chip buildup. This is a good way to reduce the surface roughness value. (2) Increase the rake angle of the tool and reduce the cutting deformation. (3) Reduce the thickness of cutting layer and adopt small feed rate or small main deflection angle. (4) Grind the front of the cutter to reduce friction; Use high efficiency cutting fluid. 2、 Cold hardening of machined surface 1. Causes of work hardening In the process of cutting, the surface layer material produces plastic deformation under the action of force, resulting in shear slip between crystals, serious lattice distortion, grain elongation, fragmentation and fibrosis, which hinder the further deformation of the metal and strengthen the metal, and the hardness is significantly improved. The greater the plastic deformation of metal, the more serious the work hardening. 2. Influence of work hardening on the service performance of parts In the process of machining, the cold work hardening of the surface layer of the machined surface is often accompanied by residual stress and fine cracks in the surface layer. The surface layer is the work hardening of residual tensile stress. While the cold hardening increases the microhardness of the surface layer of the part, the residual tensile stress will expand the micro cracks and cause the fatigue strength of the part to decrease, affecting the service life of the part. Therefore, it is hoped that the less the surface layer is the processing hardening degree of tensile stress, the better. The work hardening with residual compressive stress on the surface layer can improve the hardness and strength of the machined surface, delay and prevent the propagation of cracks, and thus improve the fatigue strength and durability of parts.

Milling is one of the common machining methods in machining, and its products are widely used in mechanical production. In the process of milling, the milling cutter will produce milling force because of its high-speed operation. Milling force has a great influence on milling processing. Then, what are the effects of milling force on milling? Now let's talk about hook net in detail.    Milling resistance and milling force 1. Milling resistance: during milling, the resistance of workpiece material to milling cutter cutting is called milling resistance. Milling resistance is mainly: (1) In the process of chip formation before and after the material to be cut becomes chip, the resistance to the tool caused by elastic deformation and plastic deformation, and the friction resistance to the tool when the chip flows out from the front of the milling cutter. (2) The extrusion deformation (elastic deformation and plastic deformation) force and friction resistance of the transition surface of the workpiece and the processed surface layer material on the back of the milling cutter. 2. Milling force: in the process of milling, in order to overcome the resistance of the workpiece to milling by the material of the cutting layer, the tool must have a strong effect on the workpiece. The force of the milling cutter on the workpiece is called milling force. Milling force includes two aspects: (1) The force required to make the workpiece produce elastic deformation and plastic deformation by the cutting layer material, and the force required to overcome the friction resistance between the front of the milling cutter and the chip. (2) The force required to make the transition surface of the workpiece and the processed surface layer material produce extrusion deformation, and the force required to overcome the friction resistance between the back of the milling cutter and the processed surface of the workpiece. Milling cutter is a multi edge tool. During milling, the synthesis of resistance acting on the cutting edge involved in cutting is the total milling resistance; The total milling force is the sum of the forces exerted by all the cutting edges on the workpiece. Obviously, the total milling resistance and the total milling force are a pair of forces and reactions, which are equal in size and opposite in direction. 2、 Factors affecting total milling resistance (1) Influence of workpiece material on total milling resistance: the higher the strength and hardness of workpiece material, the greater the deformation resistance. For materials with similar strength and hardness, the better the plasticity, the greater the plastic deformation generated in the milling process, the larger the friction coefficient between the chip and the front of the milling cutter, and the longer the contact area, so the milling resistance increases. Materials with high toughness have great resistance to deformation and fracture. When milling brittle materials, due to the small plastic deformation, the milling resistance is small. (2) The influence of milling parameters on the total milling resistance: when the milling depth, milling width and feed per tooth increase, the total milling resistance increases due to the increase of the total cutting area. Under the condition of constant total cutting area, reducing the width of cutting layer and increasing the depth of cutting layer can reduce the total milling resistance. The milling speed has no significant effect on the total milling resistance, but when other milling conditions remain unchanged, increasing the milling speed will increase the milling power. (3) The influence of milling cutter on the total milling resistance: the increase of rake angle can reduce the friction of extrusion deformation of the material being cut, smooth chip removal, and reduce the total milling resistance. With the increase of the back angle, the extrusion deformation and friction between the back of the milling cutter and the transition surface of the workpiece and the machined surface are reduced, and the total milling resistance is reduced. The angle of the cutting edge has little effect on the total milling resistance, but changing the size and direction of the angle of the cutting edge can change the direction of the total milling resistance. The magnitude of the main deflection angle can change the direction of the total milling resistance. The diameter of milling cutter has little effect on the total milling resistance, but the wear of milling cutter blade will rapidly increase the total milling resistance. (4) The influence of cutting fluid on the total milling resistance: the water solution dominated by cooling has little effect on the total milling resistance, while the oil cutting fluid with strong lubrication reduces the friction resistance between the front of the milling cutter and the chip, the back and the workpiece surface due to its lubrication, and also reduces the deformation of the chip stagnant layer, thus reducing the total milling resistance.

During the milling process, the milling cutter itself will be worn and blunt while cutting chips. After the milling cutter is blunt to a certain extent, if it continues to be used, it will lead to a significant increase in milling force and cutting temperature, and the wear of the milling cutter will also increase rapidly, which will affect the machining accuracy, machining surface quality and the utilization rate of the milling cutter. The position of tool wear mainly occurs in the front and back of the blade and its vicinity. The wear of milling cutter is mainly the wear of the back and the edge of the blade. 1、 Causes of milling cutter wear The main causes of milling cutter wear are mechanical wear and thermal wear. 1. Mechanical wear: mechanical wear is also known as abrasive wear. Because there are tiny hard spots on the friction surface of chips or workpieces, such as carbides, oxides, nitrides and debris, grooves of different depths are carved on the tool, causing mechanical wear. The harder the workpiece material is, the stronger the ability of hard particles to scratch the tool surface. This kind of wear has obvious effect on high-speed tool steel tools. Improving the grinding quality of milling cutter and reducing the surface roughness value of front, back and blade can slow down the mechanical wear speed of milling cutter. 2. Thermal wear: during milling, the temperature rises due to the generation of cutting heat. The hardness of the tool material decreases due to the phase change caused by the increase of temperature, and the tool material is adhered to the chip and the workpiece, resulting in adhesive wear; Under the action of high temperature, the alloy elements of the tool material and the workpiece material diffuse and replace each other, which reduces the mechanical properties of the tool and produces diffusion wear under the action of friction. These wear caused by cutting heat and temperature rise are collectively referred to as thermal wear. 2、 Wear process of milling cutter Like other cutting tools, the wear of milling cutters gradually develops with the increase of cutting time, and its wear process can be divided into three stages: 1. Initial wear stage: in this stage, the wear is fast, mainly because after the milling cutter is grinded, the convex peak generated by the grinding mark of the surface grinding wheel and the burr at the blade are quickly ground down in a short time. If the convex peak is large and the burr is serious, the wear is large. Improving the grinding quality of milling cutter, polishing the front and back of the blade with grinding or oilstone can effectively reduce the wear amount in the initial wear stage. 2. Normal wear stage: in this stage, the wear is relatively slow, and the wear amount increases uniformly and stably with the increase of cutting time. 3. Sharp wear stage: after a long time of cutting and use, the cutting edge of the milling cutter becomes blunt, which increases the milling force, the cutting temperature, the milling conditions become worse, the milling cutter wear speed rises sharply, the wear rate increases sharply, and the cutter quickly loses its cutting ability. When using the milling cutter, it should be avoided to make the milling cutter wear into this stage. 3、 Blunt standard of milling cutter In actual work, if one of the following conditions occurs to the milling cutter, it indicates that the milling cutter has been blunt: the surface roughness value of the machined surface is significantly higher than the original, and there are bright spots and scales on the surface; The cutting temperature increases obviously, and the chip color changes; The cutting force increases, and even vibration occurs; The back near the cutting edge is obviously worn, and even abnormal sound appears. At this time, the milling cutter must be removed for grinding, and milling cannot be continued, so as to avoid serious wear and even damage to the milling cutter.

The geometric parameters of milling cutter have a significant impact on the deformation of metal, milling force, cutting temperature and wear of milling cutter during milling, and thus affect the processing quality, service life and production efficiency of milling cutter. In order to give full play to the cutting performance of the milling cutter, in addition to the correct selection of the material of the milling cutter, the geometric parameters of the milling cutter should also be reasonably selected according to the specific milling conditions. 1. Selection principle of milling cutter diameter and tooth number (1) The selection principle of milling cutter diameter: the diameter of milling cutter is large, the heat dissipation condition is good, the rigidity of milling cutter rod is good, and the allowable milling speed and cutting amount are large. However, when the diameter of the milling cutter is large, the cutting length of the milling cutter increases, the working time is long, the milling torque is large, and the tool material consumption is also large. (2) Selection principle of the number of teeth of milling cutter: milling cutter has coarse teeth and fine teeth. Rough tooth milling cutter has high tooth strength and large chip holding space, but the number of teeth involved in cutting at the same time is small, the working stability is poor, and the vibration is large, which is suitable for rough milling; Fine tooth milling cutter, with a large number of teeth involved in cutting at the same time, small feed per tooth, stable milling, suitable for fine milling. 2. Selection principle of front corner Reasonably increasing the rake angle can reduce the plastic deformation of the cutting layer, the chip deformation is small, the arc radius of the tool tip is easy to reduce, the blade is sharp, and the cutting effect is strong. Therefore, it is beneficial to reduce the milling force, cutting heat and power, improve the machining accuracy and reduce the surface roughness value of the machined surface. However, if the rake angle is too large, the strength and heat dissipation conditions of the blade will be destroyed, which will reduce the durability of the milling cutter. (1) High speed tool steel tools have good bending strength and impact toughness, and larger rake angle can be taken; The bending strength and impact toughness of cemented carbide tools are poor, so smaller rake angle should be taken. (2) During rough machining, in order to ensure better strength and heat dissipation conditions, the front corner should be smaller; When finishing, in order to ensure the quality of the machined surface and make the blade sharp, a larger rake angle should be selected. (3) The strength and hardness of the workpiece material are high, and the front corner should be smaller. When processing plastic materials, choose a larger front angle; Machining brittle materials, select a smaller front angle. 3. Selection principle of rear corner Increasing the back angle can reduce the friction between the back of the tool and the transition surface of the workpiece, and make the edge sharp. However, too large back angle will destroy the strength and heat dissipation conditions of the blade part, reduce the durability of the tool, and even cause blade collapse. The selection principle of the rear corner is as follows: (1) High speed tool steel has high bending strength and impact toughness, and its rear angle can be larger than that of cemented carbide tools. (2) During rough milling, the cutting resistance of the tool is large. In order to ensure the strength of the cutting edge, the back angle should be smaller; During finish milling, in order to reduce friction, make the cutting edge sharp and improve the quality of the machined surface, a larger back angle should be taken. (3) When milling materials with large plasticity and elastic deformation, a larger back angle should be taken to reduce the friction behind; For materials with high milling strength and hardness, a smaller back angle should be taken to ensure the strength of the cutting edge. When the tool has adopted a negative rake angle and the edge strength has been strengthened, a larger rake angle can also be used to improve the sharpness of the tool. 4. Selection principle of principal deflection angle Reduce the main deflection angle, increase the strength of the tool tip, and increase the length of the cutting edge, so as to reduce the thickness of the cutting layer, increase the tool durability, reduce the height of the residual area of the machining surface, flatten the knife grain, and reduce the surface roughness value. Under the condition of the same thickness of the cutting layer, the feed rate can be appropriately increased. However, a small main deflection angle increases the width of the cutting layer and the milling force, especially the axial force acting on the milling cutter and workpiece, which is easy to produce vibration. 5. Selection principle of secondary deflection angle The function of the auxiliary deflection angle is mainly to reduce the friction between the auxiliary cutting edge, the rear of the auxiliary cutting edge and the machined surface of the workpiece. Properly reducing the secondary deflection angle can effectively reduce the height of the machining residual area and improve the machining surface quality. In addition, reducing the secondary deflection angle can increase the strength of the tool tip.

In cutting, a variety of materials will be used, and difficult cutting materials are also one of them. It mainly refers to materials with poor machinability. Compared with the widely used high-quality carbon structural steel 45 steel, the difficult to cut material has higher strength and hardness, high work hardening degree, large cutting resistance during cutting, and it is difficult to form and remove chips, thus reducing the durability of the tool and poor surface quality. Common difficult to cut metal materials include: high manganese steel, high strength steel, stainless steel, superalloy, titanium alloy, etc. Difficult to cut materials have the following main milling characteristics: 1. High milling force Difficult to cut materials generally have high strength, especially their high-temperature strength is much greater than that of ordinary steel (45 steel), coupled with large plastic deformation and serious hardening during machining, so the milling force is generally much greater when milling difficult to cut materials than when milling ordinary carbon steel. For example, under the same conditions, the milling force required for milling stainless steel is about 50% greater than that for milling 45 steel. 2. High milling temperature The thermal conductivity of difficult to cut materials is relatively low, and the cutting heat generated during milling is not easy to dissipate, causing a large amount of heat to accumulate in the cutting area (mainly concentrated at the tool tip). 3. Severe work hardening The deformation coefficient of difficult cutting materials is generally large, such as stainless steel, titanium alloy and superalloy. The milling speed starts from 0.5m per minute, and the deformation coefficient increases with the increase of milling speed. When the milling speed is about 6m per minute, the deformation coefficient of chip reaches the maximum. 4. Easy to stick knife Due to the severe work hardening of difficult to cut materials, the chips are strong and tough (that is, the strength and hardness of the chips are high, and the toughness is good). At high milling temperature, when strong and tough chips flow through the front of the milling cutter, it is easy to produce cold welding, fusion welding and other sticking phenomena. Sticking the knife is not conducive to the removal of chips, which is easy to block the chip holding groove, and the knife is easy to collapse or hit the knife, as well as cause bonding wear of the knife. In addition, if the strong chips are serrated, the cutting edge of the tool is easy to be damaged. 5. The wear speed of milling cutter is fast, and the durability is reduced Due to the high strength, high thermal strength, high plasticity, high milling temperature and severe work hardening of difficult to cut materials, some materials have strong chemical affinity and tool sticking phenomenon, so the wear speed of milling cutter is very fast, which reduces the durability of milling cutter. When milling difficult cutting materials, because their properties have their own characteristics, corresponding measures should be taken according to the object when formulating the machining plan. Selecting appropriate tool materials, selecting reasonable geometric parameters of milling cutter, using appropriate cutting fluid, selecting reasonable milling parameters, selecting reasonable milling methods and so on, can be good for milling difficult cutting materials.

In milling processing, milling amount is also an important parameter in processing. Milling amount is the amount of milling that makes full use of the cutting capacity of milling cutter and machine tool performance to obtain high production efficiency and low processing cost on the premise of ensuring processing quality. Then, how to choose the milling quantity? 1、 Selection principle of milling quantity The selection of milling parameters has a close relationship with the machining accuracy of milling, the improvement of machining surface quality and the improvement of productivity. The four parameters are: milling speed, feed rate, milling width and milling depth. Milling speed: the linear speed of the selected point on the cutting edge in the main motion during milling. Feed rate: it includes three aspects: feed rate per revolution, feed rate per tooth and feed rate per minute. Feed per revolution: the displacement of the milling cutter relative to the workpiece in the feed direction every revolution. The feed rate of each tooth is the displacement of each tooth of the milling cutter relative to the workpiece in the feed direction. Feed per minute, the displacement of the milling cutter relative to the workpiece in the feed direction every minute of rotation. Milling width: the dimension of the milling layer measured in the direction perpendicular to the axis of the milling cutter and the feeding direction of the workpiece. Milling depth: the dimension of the milling layer measured in the direction parallel to the axis of the milling cutter. The principle of selecting milling quantity is to maximize the product of milling width (or depth), feed rate and milling speed on the premise of ensuring processing quality, reducing processing cost and improving productivity. At this time, the cutting time of the process is the least. During rough milling, under the condition that the machine tool power and process system rigidity allow and have reasonable milling cutter durability, the milling amount is selected and determined according to the sequence of milling width (or depth), feed rate and milling speed. Among the milling parameters, the milling width (or depth) has the least influence on the durability of the iron knife, followed by the feed rate, and the milling speed has the greatest influence. Therefore, when determining the milling amount, we should choose a larger milling width (or depth) as far as possible, then choose a larger feed per tooth as allowed by the process equipment and technical conditions, and finally choose the allowable milling speed according to the durability of the milling cutter. During finish milling, in order to ensure the requirements of machining accuracy and surface roughness, the width of the cutting layer should be milled out at one time as far as possible; The depth of cutting layer is generally about 0.5mm; Then select the appropriate feed rate per tooth according to the requirements of surface roughness; Finally, the milling speed is determined according to the durability of the milling cutter. In the actual production process of the factory, we can't only superstitious about the choice of these milling methods, but also need to choose according to experience and by looking up tables.

With the continuous development of machining industry, people put forward many new requirements for the cutting tools used. These requirements are not only limited to the size, shape and material of the tool, but also in other aspects, such as the coating and dry cutting performance of the tool, which are increasingly becoming important indicators to measure the performance of the tool. Tool coating and surface engineering. The main goal of early coating is to improve the hardness and wear resistance of tools. At that time, the coating material was represented by titanium nitride, which had a large friction coefficient and would produce a lot of friction heat when cutting the workpiece, which was not conducive to the processing. Now, the diversity of cutting tools and their different working conditions determine that the coatings used are very different. For example, the coating used by turning tools and drilling tools is quite different, and the intermittent impact characteristics of milling tools should be considered when selecting the coating. The rapid development of surface engineering technology is inseparable from the rise and maturity of various vapor deposition technologies in recent decades. Vapor deposition technology is a technology that uses the physical and chemical effects in the gas phase to form metal, non-metal or compound coatings with certain functions or as decorations on the surface of workpieces. According to the coating mechanism, this technology can be divided into three types: chemical vapor deposition, physical vapor deposition and plasma vapor deposition. Vapor deposition technology not only realizes the mechanical properties of cutting tools, such as wear resistance, friction reduction and corrosion resistance, but also has the opportunity to show its talents in the fields of electromagnetic, optical, optoelectronic, thermal, superconducting and biological functional materials related to the surface layer. Surface engineering not only enables low-cost ordinary metal materials to show the ability of high-quality metal materials in cutting performance, but also has become an important means to develop various new coatings and film materials, which has great application potential. Clean and environmentally friendly cutting method In addition to cutting performance and service life, people's requirements for cutting tools also include that the machining process should be as clean and environmentally friendly as possible to reduce the pollution caused in the cutting process. As cutting fluid is one of the main pollution sources of machining, it is in line with the purpose of clean and environmental protection that dry cutting gradually replaces the original traditional cutting methods. Dry cutting is a technology of cutting without using cutting fluid and without cold liquid. To adopt dry cutting, we must ensure that we can still complete the processing task with high quality and high quality without using cutting fluid, and do not damage the service life of the tool. To achieve this, it depends on high-quality tool coating. According to the research results of experts, to solve the problem of reducing or eliminating cutting fluid, the tool coating should not only make the tool have a long life, but also have the function of self-lubricating. Previously, diamond coating was used to achieve this purpose. However, diamond coating has three irreparable disadvantages: first, high internal stress, second, poor thermal stability, and third, it is easy to have catalytic effect with ferrous metals, so it can only be used to process non-ferrous metals, and is not an ideal coating material. The appearance of DLC coating solves this problem perfectly. Many research results in recent years have shown that the diamond-like coating with SP2 structure, also known as graphite like coating, has a high hardness, which can reach 20 to 40gpa, without catalytic effect with ferrous metals; Its friction coefficient is very low, and it has good moisture resistance, which can effectively improve the service life of tools, and has been widely used in the field of machining. In most cases at this stage, the use of cutting fluid can not be completely banned. At this time, we should try to make it contain only antirust agents and no organic substances. This can not only reduce environmental pollution, but also greatly reduce the cost of recycling.