The definition and specific varieties of refractory materials vary with The Times and professional fields. For example, the aerospace industry commonly USES ultra-heat-resistant alloys, titanium alloys and composites containing carbon fiber, etc., all of which are difficult to be processed in this field. Engineers in the space industry have carried out research and development of machining technologies and have developed cutting tools and machining methods suitable for this field. In recent years, the development trend of multi-function and high function of mechanical products is very strong. In order to meet some requirements, the materials used must have high hardness, toughness and abrasion resistance, and the materials with these characteristics are especially difficult to process, so new difficult materials have emerged. Difficult processing materials are emerging with the development of The Times and different professional fields, and their unique processing technology is also developing along with the research and development of The Times and various professional fields.
, on the other hand, with the coming of information society, technical information hard-cutting materials cutting can also communicate with each other through the Internet, therefore, the future of difficult-to-machine materials cutting data and other information will be more full, also is bound to further improve the machining efficiency, based on the hard processing material cutting processing as the core, is introduced in recent years, the development trend of the technology.
Difficult materials in the cutting field
In the process of cutting, the common tool wear includes the following two forms :(1) wear due to mechanical action, such as chipping blade or abrasive wear; (2) wear due to thermal and chemical effects, such as adhesion, diffusion, corrosion and other wear, and fracture, thermal fatigue, and thermal cracking caused by the softening and melting of cutting edge.
When cutting difficult material, the tool wear occurs within a very short time. For example, most difficult materials have low thermal conductivity, the heat generated during cutting is difficult to diffuse, resulting in high blade tip temperature, cutting edge affected by heat is very obvious. The result of this effect will cause the adhesive strength of the cutter materials to decrease at high temperature, and particles like WC(tungsten carbide) are easy to separate out, thus accelerating the tool wear. In addition, the components in the difficult material and some components in the tool material react under the cutting high temperature conditions, resulting in the components falling out, shedding, or other compounds, which will accelerate the formation of tool wear phenomenon such as chisel edge.
When cutting materials with high hardness and toughness, the cutting edge has a high temperature and similar tool wear may occur when cutting difficult materials. Such as high hardness steel cutting, compared with the general steel cutting, cutting force, cutting tool rigidity insufficient will cause the phenomenon such as collapse edge, the tool life is not stable, and can shorten the tool life, especially when processing to generate short chip workpiece materials, can produce crater wear near the cutting edge, often in a short period of time the tool breakage.
When cutting the super-heat resistant alloy, due to the high hardness of the material at high temperature, a lot of stress in cutting is concentrated on the tip, which will lead to plastic deformation of cutting blade. At the same time, the boundary wear caused by working hardening is more serious.
Due to these characteristics, users are required to carefully choose the type of cutter and cutting conditions when cutting difficult materials to obtain ideal machining effect.
Problems that should be paid attention to in machining of difficult materials
The cutting process can be divided into turning, milling and cutting with center teeth (bit, end face cutting of end milling cutter, etc.). Turning is a kind of continuous cutting. The cutting force on the tip has no obvious change. Milling is discontinuous cutting, the cutting force is on the tip of the edge, cutting will occur vibration, the tip of the edge affected by the heat, cutting heating and non-cutting time of cooling alternating, the total heat less than the turning.
The cutting heat during milling is a discontinuous heating phenomenon, and the cutter teeth are cooled during non-cutting, which is beneficial to extend the tool life. Japan's physical and chemical research institute of turning and milling tool life for the contrast test of milling cutter used for ball end mill, turning to general lathe tool, both in the same material and processed cutting condition (due to the different cutting ways, cutting depth, feed, cutting speed and can only be broadly) and cutting test under the same conditions, the results show that the milling processing to prolong tool life.
When cutting with a bit with a center edge (that is, a position with cutting speed of 0m/min) and a ball-head end milling cutter, the tool life near the center edge is often low, but it is still stronger than in turning.
When cutting difficult materials, the cutting edge is greatly affected by heat and often reduces the tool life. If the cutting method is milling, the tool life will be longer. However, difficult materials cannot be processed by milling all the time. There will always be times when turning or drilling is needed. Therefore, corresponding technical measures should be taken for different cutting methods to improve machining efficiency
Cutting tool material for difficult material cutting
The high temperature hardness of CBN is the highest among the existing tool materials, and it is most suitable for machining difficult materials. The new coating cemented carbide is based on superfine grain alloy and is treated with coating material with high temperature hardness. This kind of material has excellent wear resistance and is also one of the excellent cutting tool materials that can be used in difficult machining materials.
Due to the high chemical activity and low thermal conductivity of titanium and titanium alloys in refractory materials, diamond tools can be used for machining. CBN sintered cutters are suitable for cutting materials with high hardness, such as steel and cast iron. It is reported that CBN sintering bodies without binder have been developed.
Diamond sintered tool is suitable for cutting aluminum alloy, pure copper and other materials. With sharp cutting edge, high thermal conductivity and less heat of tip retention, the occurrence of adhesives such as debris tumor can be controlled to a minimum. When cutting pure titanium and titanium alloy, single crystal diamond cutters are selected to be more stable and prolong the tool life.
The coated carbide tool is suitable for the cutting of all kinds of difficult materials, but the properties of the coating (single coating and composite coating) are very different. It is reported that carbide coated with Diamond and Diamond Like Carbon coated with cemented carbide have been developed recently, which further expands the application range of coated tools and has been applied in the field of high-speed machining. The shape of a tool for cutting difficult materials
When cutting difficult materials, the optimization of tool shape can give full play to the performance of tool materials. The selection of the geometric shape of the tool such as the front Angle, back Angle and cutting Angle, which are suitable for the characteristics of difficult materials, and the proper treatment of the blade tip have a great impact on improving the cutting accuracy and prolonging the tool life. Therefore, the shape of the tool should not be taken lightly. However, with the popularization and application of high-speed milling technology, small cutting depth has been gradually adopted in recent years to reduce the load of cutter teeth, and reverse milling is adopted to improve the feed speed. Therefore, the design idea of cutting edge shape has also been changed.
It is an effective way to reduce the torque and cutting heat when drilling difficult materials, increasing the Angle of drill and carrying out cruciform grinding. In drilling, the cutting heat is easily trapped near the cutting edge and the chip removal is very difficult. These problems are more prominent in cutting difficult materials, which should be paid enough attention to.
In order to facilitate chip removal, there is usually a cooling liquid injection outlet at the back of the cutting edge of the bit, which can supply sufficient water-soluble cooling liquid or fog-like cooling agent to make chip removal more smooth. This method is also ideal for cooling the cutting edge. In recent years, some coating materials with good lubrication performance have been developed. After being coated on the surface of the drill bit, dry drilling method can be adopted when processing the shallow holes for 3-5d.
The fine machining of holes has always been boring, but recently it has been changed from the traditional continuous cutting method to the discontinuous cutting method of contour line cutting, which is more beneficial to improve chip removal performance and extend tool life. Therefore, this kind of boring cutter for discontinuous cutting was designed and immediately applied to CNC machining of automobile parts. In the aspect of screw hole machining, screw cutting interpolation is also adopted at present.
As mentioned above, the conversion from continuous cutting to discontinuous cutting is carried out with the deepening understanding of CNC cutting, which is a gradual process. When this cutting method is used to cut difficult materials, it can maintain the smoothness of cutting and prolong the tool life.
The cutting conditions of difficult materials
The cutting conditions of difficult machining materials have always been set relatively low. With the improvement of cutter performance, the emergence of high-speed high-precision CNC machine tools and the introduction of high-speed milling methods, etc. At present, the cutting of difficult machining materials has entered the period of high-speed machining and long tool life.
At present, using small cutting depth to reduce the cutting edge load of the cutter, which can improve the cutting speed and feeding speed, has become the best way of cutting difficult materials. Of course, it is also very important to select tool materials and tool geometric shapes that are suitable for the unique properties of difficult materials. For example, when drilling materials such as stainless steel, due to the low thermal conductivity of the materials, it is necessary to prevent the cutting heat from being trapped on the cutting edge. For this reason, discontinuous cutting should be used whenever possible to avoid the friction of cutting edge and cutting surface. When rough machining of difficult material with ball end milling cutter, the tool shape and clamping fixture should be well matched, which can improve the vibration accuracy and clamping rigidity of the cutting part of the cutter, so as to ensure the maximum feed per tooth and extend the tool life at the same time under the condition of high-speed rotation.
As mentioned above, the optimal cutting method of difficult materials is constantly developing, new difficult materials are constantly emerging, and the processing of new materials is always bothering engineers and technicians. Recently, new machining centers, cutting tools, jigs and CNC machining technologies have been developing rapidly. Besides cutting processing, CNC grinding, CNC electromachining and other technologies have also been developing unprecedentedly.
Of course, the collection of information about the processing of difficult materials and the in-depth understanding of the technology are not satisfactory. Because of this, people always feel that the processing technology is somewhat inadequate due to the continuous emergence of difficult materials.
For example, the transition from continuous cutting to discontinuous cutting is conducive to extending tool life, and the use of new coated carbide cutting tools further improves the cutting technology level of difficult materials. In machining of difficult-to-machine materials should pay special attention to the stability of the tool life and workpiece material and cutting tool performance not only proper compatibility, and the machining size, surface roughness, such as the shape accuracy requirement is very strict, therefore, not only should pay special attention to the cutting tool selection, workpiece clamping way and other related technology cannot treat STH lightly.
In the future, the processing of difficult material parts will adopt CAD/CAM, CNC machining and other computer-controlled production methods. Therefore, the construction of database, tool design and production and other tool management systems are of great importance. Difficult-to-machine material machining, applicable tools, jigs, process arrangement, the determination of tool path and other data about the cutting condition, all should be accumulated as the foundation data, along with IT to make the parts production mode in the direction of development, so, hard processing material machining technology to quickly enter a new stage.