Application of the most popular indexable arc edge

2022-07-28
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Application of indexable arc edge end milling cutter in machining high manganese steel frog

1 High manganese steel is a kind of wear-resistant steel with single-phase austenite structure. The high manganese steel after water toughening treatment (the heat treatment method of heating at 1000 ~ 1100 ℃ and cooling with water) has a significant work hardening effect, that is, under the action of high external force impact, its working surface hardness increases from 170 ~ 220 HBW to more than 450 ~ 550 HBW, and the core still maintains a very high toughness, thus obtaining high impact resistance, wear resistance and crack propagation resistance. High manganese steel frog (hereinafter referred to as high manganese steel frog) for railway turnout is manufactured by using the above characteristics. The utility model has the advantages of good integrity, strong wear resistance, safety and reliability, low cost, convenient maintenance, etc

the use of high manganese steel improves the hardness, strength and service life of parts, which is a favorable side. However, it is precisely because of its physical properties such as severe work hardening, low thermal conductivity, high cutting temperature, high toughness, high elongation, difficult chip breaking, large linear expansion coefficient and large cutting force, especially the work hardening phenomenon, that brings great difficulties to the machining of high manganese steel. High manganese steel is classified as difficult to machine material according to the degree of difficulty in removing material from parts

2. With the development of railway transportation towards high speed and heavy load, the requirements for the quality of transportation equipment are becoming higher and higher. High manganese steel frog is a track passing equipment that enables the wheels of locomotive and vehicle to pass from one rail to another rail. It is a key component of railway turnout equipment. Material: ZGMn13. The workpiece is generally 4 ~ 6m long, 140 ~ 180 mm thick and 350 ~ 500 mm wide

mechanical processing of high manganese steel frog is mainly plane processing. The cutting method is end milling. Generally, carbide indexable end milling cutter is selected as the cutting tool. Because it is a high manganese steel casting, and the workpiece is long and thin, the deformation is large during processing, so it is difficult to process. Our factory has developed high manganese steel frog machining for more than ten years, and has accumulated some experience

over the years, we have used 767 cemented carbide as the cutting tool material for machining high manganese steel frogs

the structure of the tool mainly adopts wedge block clamping and axial positioning ring. This structure has the advantages of convenient and reliable clamping and high positioning accuracy. As long as the geometric dimensions of the positioning element and the blade have high manufacturing accuracy, the tool can be guaranteed to have high positioning accuracy. When the cutting force is too large, the blade and the blade seat are limited to move along the axial direction to prevent damage to the tool body

as the milling process is intermittent cutting, each cutter tooth will have impact when cutting into the workpiece. In order to maximize the contact between the rake face and the workpiece at the place far away from the tool tip and cutting edge when the milling cutter cuts into the workpiece, so as to improve the stress of the cutter tooth during cutting, improve its impact resistance, protect the tool tip and reduce edge collapse, the high manganese steel frog processing end milling cutter adopts the form of double negative rake angles, namely: γ F and γ P is less than zero, γ f=-5°, γ p=-7°。

indexable end milling cutters produced in China and imported from abroad are generally quadrangular blades. For ultra-light and ultra-thin non-woven fabrics that need to provide comfortable wearing, good air permeability and excellent barrier performance, the main deflection angle κ R is mostly 75 °. Our factory has been used for many years in the past. Although the product quality and production efficiency can basically meet the requirements, due to the particularity of high manganese steel processing, the sharp edges and edges of square blades and straight cutting edges are serious in production. The consumption of blades, tool pads and tool bodies is large, and the cost is too high. In recent years, we have changed the square blade to the circular blade and introduced the indexable arc edge milling cutter into the processing of high manganese steel frog. Because the cutting edge is circular arc, there is no weak tip, edge angle and weak area, so there is no tip to collapse in the cutting process. Moreover, in the cutting process, not only the cutting pattern is changed, but also the main deflection angle of the tool is changed κ R also changes with the change of cutting depth, which improves the machining conditions. It has been proved by experiments and applications that changing the straight cutting edge to arc cutting edge to process high manganese steel frog along with the movement of grating has achieved obvious results in avoiding blade collapse, increasing cutting depth and feed, improving production efficiency and reducing cost. It should be pointed out that changing the shape of cutting edge is an effective way to overcome the edge collapse of cemented carbide inserts

the basic structure of the indexable arc edge end milling cutter is shown in Figure 1

3. Main characteristics and milling test analysis of arc edge end milling cutter

(1) main deflection angle of arc edge end milling cutter κ The characteristic main deflection angle of R is one of the important angles of cutting tools. On the one hand, its size affects the shape of the cutting layer, on the other hand, it directly affects the length of the cutting edge and the load of the unit cutting edge, that is, it directly affects the wear and life of the tool. When the back feed and feed rate are constant, changing the main deflection angle can make the chip thinner or thicker, which will affect the heat dissipation and the change of cutting force. That is, the principal declination angle κ The change of the size of R will directly affect the breaking and striking of the cutting tool

the main deflection angle of general straight edge end milling cutter is a fixed value, and most of them are κ R=75 °, main deflection angle κ For the end milling cutter with a certain R value, the main deflection angle κ R is basically unchanged. The main deflection angle of the arc edge tool κ R is not the case, and its size changes with the change of the back knife amount. Take the 16mm round blade as an example, for example, when the back cutting distance is 4mm, the main deflection angle κ When R is 30 ° and the back cutting distance is 2 mm, the main deflection angle κ When R is 20 ° 42 ′ 17 ″ and the back cutting distance is 1mm, the main deflection angle κ R is 14 ° 28 ′ 39 ″

(2) analysis of cutting force of indexable arc edge end milling cutter cutting force mainly refers to: total cutting force PZ, longitudinal milling component p h, transverse milling component PV and axial milling component P0; With principal declination κ With the change of R, the size of the three cutting forces and the distribution ratio will also change

introduction to relevant technical data, main deflection angle κ When R is 75 °, the theoretical distribution of milling force of straight edge milling cutter is: longitudinal milling force ph= (0.3 ~ 0.4) PZ, transverse milling force P v= (0.85 ~ 0.95) PZ, axial milling force p0= (0.5 ~ 0.55) PZ

according to the actual measurement of milling test, the milling force distribution of indexable arc edge end milling cutter is basically: longitudinal milling force ph= (0.33 ~ 0.37) PZ, transverse milling force pv= (0.45 ~ 0.53) PZ, and axial milling force p0= (0.78 ~ 0.84) PZ (see Figure 2)

test piece material: ZGMn13, milling cutter diameter =160mm, z=10, γ f=-5°, λ P=-7 °, blade brand: 767

cutting parameters: n=140r/min, v=70m/min, fn=168mm, especially uneven/min, fz=0.12mm/z

it can be seen from the above test data that during cutting, the axial force P0 increases, and the main deflection angle κ R changes with the change of back cutting amount, which makes the lateral milling force PV decrease significantly. The horizontal milling force PV is just the main factor affecting the impact of the cutting edge into the workpiece and the wear of the cutting edge. In addition, the chip thickness cut by the arc cutting edge is different, which improves the heat dissipation conditions. In addition, the cutting area of the arc blade is an arc shape without tool tips and edges, and there is no weak area, which makes the mechanical impact and thermal impact in the cutting process smaller than the requirements for lubrication. Therefore, the service life of the arc blade will be greatly improved

4. Selection of cutting parameters

the cutting parameters during milling shall be based on the material of the workpiece to be machined, and shall be comprehensively considered in combination with the power of the machine tool, the rigidity of the fixture and the economic life of the tool, so as to obtain the best economic effect

the machining accuracy of high manganese steel frog is not very high, which belongs to rough machining. In the cutting process, due to the influence of plastic deformation and cutting force, serious hardening will occur in the cutting layer and a certain depth below the surface. In order to avoid the hardened layer caused by the blank surface and the previous cutting, a large back feed and feed are selected in the cutting process. Compared with the straight edge end milling cutter, the cutting speed of arc edge end milling cutter is reduced

high manganese steel frog is processed with arc edge end milling cutter. Generally, the back cutting distance is ap=mm, and the feed distance is fz=0 15mm/z, the cutting speed is v=60 ~ 80m/min. Through production practice, the comprehensive effect is good

5. Conclusion

the carbide arc end milling cutter has simple structure, few accessories, convenient clamping and high precision. It can effectively overcome the shortcomings of low strength, serious wear and edge collapse of the straight edge end milling cutter when used in the processing of high manganese steel frog. Compared with the square blade, the circular blade can be rotated for 2 ~ 3 times, making full use of the tool material, thus reducing the production cost. Practice has proved that it is feasible to use carbide arc edge end milling cutter to process high manganese steel frog. (end)

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