Comprehensive selection of geometric parameters of

2022-08-13
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Comprehensive selection of turning tool geometric parameters

Abstract: reasonable selection of turning tool geometric parameters is the key to successfully complete the turning task. Based on years of teaching and production experience and relevant theoretical data, the author discusses the method of reasonable selection of geometric parameters of turning tools for several types of turning tools

the grinding level of turning tools is directly related to the production efficiency, processing quality, equipment energy consumption and product cost of products, and even related to the personal safety of operators. It also reflects the flexible adaptability of operators to the characteristics of processing subjects and cutting parameters. Reasonable selection of geometric parameters of turning tool is the key to determine the grinding quality, which is mainly reflected in the reasonable selection of turning tool angle and the previous test data will be mixed with the data of this test. Both of them depend on each other and restrict each other. A turning tool cannot have only one angle. If only one angle is selected reasonably, its cutting effect is not necessarily ideal. The operator must comprehensively analyze and find out the main contradiction in the cutting process, and reasonably select the angle and front shape of the turning tool according to the workpiece material, turning tool material, cutting amount, as well as the rigidity of the workpiece, turning tool, fixture and lathe. Combined with many years of teaching and production experience and relevant theoretical data, the author discusses the method of reasonable selection of geometric parameters of turning tools according to the selection and use of several types of turning tools

1 selection of geometric parameters of the cutting knife

when selecting the geometric parameters of the cutting knife, we should first consider to ensure that the cutting edge is sharp enough. On this premise, we should carefully maintain its sufficient strength, so the rake angle should be the main parameter for selection. Generally, the rake angle of the high-speed steel cutting knife should be about 20O ~ 25o, and the rake angle of the steel cutting knife of cemented carbide should be about 8O ~ 20O, The front angle of carbide cast iron cutter is about 5O ~ 10o. On the problem of maintaining the turning tool strength, the following methods should be considered according to different workpiece materials, cutting parameters and other factors:

1.1 the part of the tool bar is thin and long, so only the smaller auxiliary deflection angle of 0.5o ~ 1.5o and auxiliary rear angle of 1O ~ 3O can be taken to increase the strength of the tool bar

1.2 the cutting part of the turning tool goes deep into the workpiece, and a large amount of cutting force and heat are concentrated at the tool tip. A transition edge should be ground respectively to ensure the tool tip

1.3 the cutting edge of the cutting tool is generally wide and deep into the inner layer of the workpiece. Under the action of the front cutting force and the side friction, it is easy to cause vibration and damage the tool, so the main rear angle is about 2O ~ 5O. On the one hand, the mutual interference of useful and useless electromagnetic wave radiation energy in the environmental field is becoming more and more serious. On the other hand, all kinds of electromagnetic radiation will affect or pollute the electromagnetic environment and bring adverse factors to people's life and health. In the polluted or interfered electromagnetic environment, the electronic equipment can not work normally, and the safety of electronic equipment and people is endangered. For example, when the local oscillation radiation of FM radio just falls into the navigation frequency band used by people, and the common radiation exceeds the limit value, it may interfere with the aircraft navigation, and once the navigation is wrong, it may cause flight accidents. For another example, it is not surprising that the radio noise caused by electromagnetic interference in life is large, and the TV has "snowflakes" and can't even be listened to normally

as we all know, X-rays and 7-rays in electromagnetic radiation do serious harm to human body. It is a kind of ionizing radiation, which can dissociate gas molecules in the air and has strong penetration. Electromagnetic radiation used in radio broadcasting, television, radar, microwave communication, microwave ovens, microwave physiotherapy machines and industrial equipment in the radio wave band belongs to non ionizing radiation, and the quantum energy of radiation is small, but it will also cause a certain degree of harm to people under the conditions of certain power density and irradiation time. The harm degree of electromagnetic radiation to human body mainly depends on the frequency, intensity and exposure time of electromagnetic radiation. Generally speaking, the greater the electromagnetic radiation energy and the longer the irradiation time, the greater the impact on the human body. When the human body is exposed to excessive electromagnetic radiation for a long time, fatigue, dizziness, memory decline and vision decline will occur

as a physics teacher, students should gradually understand the problems closely related to science and environmental life in the process of learning physics knowledge. For example, in guiding students to carry out scientific and technological activities such as remote control, telemetry and business radio communication, students should be taught to pay attention to the protection of the electromagnetic environment, abide by the management regulations of the local radio management department, and avoid interfering with other radio wave activities. Students should also be properly educated about electromagnetic radiation in household appliances, such as X-ray protection of color TVs, microwave leakage protection of microwave ovens and other common sense, so as to protect students' eyesight and brain power from being affected. Finally, by the way, eating more fresh vegetables and fruits is good for preventing and reducing electromagnetic wave damage

1.4 when cutting the workpiece with larger diameter, the cutting edge of the cutting knife should preferably be ground into a large circular arc

1.5 when cutting the workpiece, due to the influence of factors such as tool installation error and feed error, the flat head cutter is often prone to be skewed by the lateral cutting force. At this time, it can be made into a cutter with a top angle of 120o to balance the lateral cutting force to maintain the stability of the cutter

1.6 when the cut-off material is hard, the cutting knife should be made into a 120o vertex angle, and a negative chamfer should be ground on the blade to enhance the strength of the blade

1.7 when the material being cut is particularly hard or is cut forcefully, the lower part of the cutter bar can be widened to form a fish belly shape to enhance the strength of the cutter bar

2 selection of geometric parameters of hardened steel turning tool

when selecting the geometric parameters of turning tool for turning high hardness materials (such as quenched steel), the first angle should be taken as a negative value, and then with appropriate other angles, it can be cut smoothly. Generally, people have to ask, if the front corner is negative, is this turning tool sharp? The author believes that sharpness and strength are a pair of contradictions of knives, and sharpness cannot be treated in isolation. If turning hardened steel with a turning tool with a front angle of 10o ~ 20O, the turning tool will soon wear and become blunt or collapse, so sharpness can play its role only under certain strong conditions. However, high intensity is not the ultimate goal. High intensity serves for sharpness, and its purpose is to better play a sharper role. Therefore, we must treat the relationship between sharpness and intensity dialectically. Different cutting materials have different requirements for tool strength, and the standard to measure the sharpness of turning tools is also different. For example, when cutting aluminum parts, the front corner of the turning tool is ground to 25o or 3, which belongs to labor-intensive industry. 0o can still maintain good strength, and this kind of turning tool is sharp for cutting aluminum parts. When turning steel parts, if such a large rake angle is also selected, the strength required for cutting will be lost, and its sharpness will not work effectively. At this time, the rake angle must be smaller. When turning hardened steel, the front angle of the turning tool should be negative, which is 1 7O ~ 1 8O, so that the sharpness of the turning tool can play an effective role. After the rake angle is determined, select other appropriate cutting angles according to the following steps to further increase the tool strength

2.1 the inclination angle of the blade is also taken as one 7O ~ one 8O to enhance the strength of the blade tip

2.2 take a smaller back angle of 2O ~ 3O to increase the wedge angle

3 selection of geometric parameters of rubber roller turning tool

when turning rubber roller to achieve relatively ideal matching accuracy, due to the small cutting force, good elasticity of workpiece material and large cutting deformation, when selecting the turning tool angle, we can less consider the strength requirements of the turning tool, and focus on the sharpness of the turning tool, so as to reduce the cutting deformation of the workpiece and ensure the machining quality of the workpiece surface. For this reason, a larger rake angle should be selected first. If cemented carbide turning tools are used, the rake angle is generally about 40o ~ 50O. In addition, when selecting other angles, they should also cooperate closely, based on increasing the sharpness of the turning tool. The measures are as follows:

3.1 increase the back angle to 8O ~ 15O, so as to reduce the wedge angle and further enhance the sharpness of the turning tool, so as to achieve the purpose of reducing cutting deformation

3.2 increase the transition edge and polishing edge to prevent excessive concentration of cutting force and cutting heat, so as to reduce the wear of turning tools and the thermal burning loss of workpieces, so as to improve the surface quality of workpieces

3.3 the front is made into a plane type with large rake angle, so that the cutting can flow out smoothly and avoid being entangled on the turning tool or workpiece

4 the influence of the installation position and feeding motion of the turning tool on the working angle of the turning tool

4.1 the influence of the installation position of the turning tool on the working angle of the turning tool. When installing the turning tool, the tip of the turning tool should be aligned with the rotation center of the workpiece as far as possible. When turning the excircle, if the turning tool is installed too high, the front angle will increase and the rear angle will decrease, increasing the friction behind the turning tool and reducing the strength of the tip; On the contrary, if the turning tool is installed too low, the rear angle will increase, the front angle will decrease, and the cutting is not smooth enough. Sometimes, the workpiece will even be lifted and the turning tool will be broken. When turning the inner hole, the turning tool is installed high or low, and the result is just the opposite to that of turning the outer circle. Except that the turning tool must be aligned with the center when turning the end face without holes, it can be slightly higher than the center in general. Experience shows that the height error of turning tool installation should be less than 1% of the workpiece diameter. In addition, the deviation of the turning tool will affect the size of the main and auxiliary deflection angles

4.2 influence of feed motion on the working angle of the turning tool during transverse feed, the turning tool advances according to a certain amount of tool travel. At this time, the trajectory of the turning tool on the end face is not a circle, but an Archimedean spiral. The closer the turning tool is to the center and the greater the amount of tool travel, the more inclined the spiral is, so that the rear angle of the turning tool becomes smaller and the front angle becomes larger during cutting, so the rear angle should be grinded larger during grinding. During longitudinal feeding, since the trajectory of the turning tool on the workpiece is a helix, the tangent of this helix does not coincide with the original cutting plane, but intersects a certain angle, so the actual back angle is the difference of subtracting this intersection angle during cutting. When it comes to the outer circle or inner hole of the car, the influence is negligible. When turning thread, this intersection angle is very large, and the filling success rate of P60 composite resin group is 94.8%. Therefore, when grinding the back angle of thread cutter, this spiral angle difference should be added to overcome the influence of tool walking motion

4.3 influence of workpiece shape on geometric parameters of turning tool when machining cam parts, the change of workpiece shape can also cause the change of front and rear angle of turning tool, which should be considered during grinding. The above three factors must be taken into account when selecting the geometric parameters of the tool. In short, when selecting the geometric parameters of the turning tool, we should find out the main problems in the cutting process according to the mechanical and physical properties of the workpiece material and the turning tool material, the cutting amount, as well as the rigidity of the workpiece, the turning tool, the fixture and the machine tool, and put the sharpness of the turning tool in the first place, take the sharpness as the premise, and properly consider the strength of the turning tool. Because the sharpness of the turning tool mainly depends on the size of the rake angle, we should first grasp the main problems in the cutting process, reasonably determine the rake angle value, and then select other geometric angles to cooperate. (end)

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