Drilling processing of the hottest high manganese

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Drilling processing of high manganese steel ZGMn13

Abstract: high manganese steel ZGMn13, as a typical difficult to machine material, is widely used in parts with large impact because of its excellent wear resistance and low price. Based on the introduction of the basic properties and drilling processing of high manganese steel ZGMn13, this paper expounds the tool structure and materials that can be used in ZGMn13 drilling processing in practice

Keywords: ZGMn13; Drilling; Work hardening; Cemented carbide; Drill bit

1. Introduction

since the British Hadfield invented high manganese steel in 1882, it has been used for more than 100 years. It has become a traditional wear-resistant material and has been widely used. Such as excavator bucket, crusher jaw plate and lining plate, tank track shoe, driving wheel, driven wheel and track support roller, railway frog, etc. The wear resistance of ZGMn13 steel is incomparable to any other steel. However, it has good working performance and shows the difficult machinability when cutting it. It is a typical difficult to machine material, especially in hole processing. Because drilling itself belongs to semi closed processing, it makes the drilling of ZGMn13 steel more difficult

2. Basic properties of ZGMn13 steel

the main components of ZGMn13 steel are: 1.30% C, 0.30% ~ 0.80% Si, 11.0% ~ 14.0% Mn (Mn/c=10 ~ 12). ZGMn13 steel castings are hard and brittle in nature. It is difficult to machine and cannot be applied in practice. The reason is that there are carbides in the as cast structure. Practice has proved that ZGMn13 steel shows the best toughness and resistance only when all austenite structures are obtained. (7) tensile force and zigzag sample billet grindability should be cut from the end rolling direction of flat steel at a distance of 1/3 of the width from the edge. In order to obtain good pure austenite structure of ZGMn13 steel, water toughening treatment must be carried out. Water toughening treatment is the operation of quenching treatment. Its method is to heat the steel to a temperature above the critical point (about 1000-1100 ℃) and hold it for a period of time, so that the carbides in the steel can be completely dissolved into austenite, and then quickly quenched in water for cooling. Because the cooling rate is very fast, the carbide has no time to precipitate from austenite, so it maintains a uniform austenite state. The original hardness of ZGMn13 is similar to that of 45 steel (normalized), about hb180 ~ 220. When ZGMn13 steel is subjected to strong impact, the hardness of the surface layer rapidly increases to hb450 ~ 550, and this kind of work hardening layer can reach 0.3mm. Therefore, it has high wear resistance, while its core still retains its original toughness. When the hardened layer is worn off by external force, a new hardened layer can also be produced

3.zgmn13 steel has serious work hardening. ZGMn13 after the hardened layer is formed on the machined surface. It is difficult to process again. Therefore, it is strictly forbidden to stop halfway in the actual drilling process, and it is also required to use one-time tool walking as much as possible in the process setting. In the middle of drilling, if the drill bit is damaged and cannot continue cutting, you can hear the harsh scream when changing the drill bit to cut again, which is the effect of cutting in the work hardening layer. Because the horizontal edge of the drill has a large negative rake angle, it belongs to a wedge-shaped scraping in the drilling process, and the work hardening process increases the axial force, which is easy to wear or collapse the horizontal edge

3.2 low thermal conductivity. The thermal conductivity of ZGMn13 is 13W · M-1 · k-1, which is 1/4 of that of 45 steel. The heat cannot be transmitted rapidly during the cutting process, resulting in high cutting temperature and aggravating the wear of the drill bit. During the drilling of the middle 31.5 hole of ZGMn13 railway frog, the drill bit became red, which seriously reduced the durability of the drill bit

3.3 high toughness and plasticity. The impact toughness of ZGMn13 is 2.9 ~ 4.9j · cm2, which is 6 ~ 10 times that of 45 steel, and the elongation (plasticity) is 50 ~ 80%, which is 3 ~ 5 times that of 45 steel

this not only makes the cutting easy to deform and increase the cutting force, but also makes the chips strong and tough and not easy to break. The chips are mostly wrinkled and long banded. It is very easy to wind on the tool bar during drilling

3.4 large linear expansion coefficient. The linear expansion coefficient of ZGMn13 steel is about 20 10-6 ℃ - 1, which is similar to that of brass. Under the action of cutting heat and cutting temperature, the workpiece locally expands rapidly and deforms, which affects the machining accuracy

4. Reasonable drilling conditions of ZGMn13 steel

4.1 tool material. With the continuous development and maturity of powder metallurgy technology, cemented carbide tools are widely used in cutting difficult materials. However, the manufacturing level of cemented carbide in China still lags far behind that in foreign countries. We must continue to improve. At present, the commonly used cemented carbide tool materials for ZGMn13 steel drilling are YG8, YG6X, YS2, yw2, y1v767, y1v798, etc. Although YG cemented carbides are commonly used, they are not suitable for high-speed cutting. Because when the rotating speed is high, the wear at the turning point of the outer edge of the drill bit is faster, and the wear of the rear cutter surface is accelerated, and the tool durability is reduced. In the case of high rotating speed and stable cutting process, class VI 'cemented carbide can be considered. Adding an appropriate amount of TAC or NBC (generally 0.5% - 3%) to YG cemented carbide can improve its hardness and wear resistance without reducing its toughness. With the increase of cobalt content in cemented carbide, these advantages are more significant. Therefore, the universal cemented carbide with TAC and NBC as additives is also suitable for the drilling of high manganese steel. The coating technology of cemented carbide has developed from single coating to composite coating technology, which solves the contradiction between hardness and toughness of cemented carbide

4.2 tool structure. Most of the drill bits used in ZGMn13 steel are of welded carbide blade structure, and there are also occasions where indexable shallow drills are used. The welding structure is relatively simple and the manufacturing cost is low. The E2 cemented carbide blade is inserted and welded in the groove. The main welding methods are oxygen acetylene flame brazing and high frequency induction brazing. However, because the coefficient of linear expansion of cemented carbide blade is much smaller than that of tool body steel, there are more residual stresses after welding, especially on the larger brazing surface, it is easy to produce welding cracks. In the drilling process of ZGMn13 steel railway frog, the drill bit failure caused by welding cracks is more than 10%. The bit cutter system with indexable structure is necessary for the users of the expanding ring experimental machine to detect and identify the strength of the pipe body. The experimental equipment is relatively complex. The blade is generally cemented carbide coated, so the cost of the bit is high

5. Several common cemented carbide bits for drilling ZGMn13 steel

5.1 general cemented carbide bits. This kind of drill adopts insert welding. Since about 57% of the drilling force is generated on the horizontal edge during the drilling of the drill bit, the axial force can be reduced by grinding the horizontal edge short, and the rake face of the grinding horizontal edge can be increased to further reduce the axial force and torque and improve the durability of the drill bit. Reduce the spiral angle of the cutter body by 13 to 20., Increase the sharp angle from 2 to 140., To facilitate chip removal. Or grind into double sharp angles to improve the heat dissipation conditions. When drilling shallow holes, straight groove drills can be used, which can not only enhance the drilling strength, but also have simple manufacture and low cost. In order to keep the drill sharp, regrinding should be carried out in time when the wear size of the outer edge corner is less than 1mm. The cooling shall be sufficient during drilling, and intermittent cooling is not allowed. The production practice of dry drilling shows that the durability of the drill bit is low

5.2 cemented carbide group drill. The structure and manufacture of this kind of cemented carbide bit are the same as that of general cemented carbide bit. The bit body should have good rigidity and strength, generally made of 40Cr, and the length should be as short as possible. The blade material can be YG8 or yw2. If the crown bit is selected, the drilling effect is better. The geometric parameters and angles of the cutting part are basically similar to those of cast iron group drills, except that the tip height is increased to 0.08d (D is the drill diameter), and the arc radius of the arc edge is increased to 0.4d, so as to improve the strength of the tool tip, improve the heat dissipation conditions and play a role in chip separation. At the same time, grind out a double front angle at the outer edge, and grind out a negative front angle, and increase the rear angle at the outer edge to 20.. After the drill is grinded, it should be polished carefully with an oilstone to improve the smoothness of the cutting edge, and the cutting edge should not have sawtooth. During the drilling process, the cooling shall be sufficient. If conditions permit, the whole workpiece can be immersed in cutting fluid for drilling. Proper selection of cutting parameters can control the cutting temperature within the range of about 600 ℃. At this time, the processing conditions are more favorable. At the same time, it can be observed that when the workpiece is thin and drilled to the outlet, the material reaches the degree of dark red

the blunt standard of group drills is equally important, which is the same as that of general cemented carbide drills. However, the structure of the tool tip of the group drill is complex, and the grinding requirements are high, which requires a very high technical level for the staff

5.3 welded carbide shallow hole drill without transverse blade. The significant difference between this kind of drill and the general cemented carbide drill is that it has no horizontal edge. Shang Guiqin, director of the State Key Laboratory of food contact materials testing (Changzhou) of the General Administration of quality supervision, inspection and quarantine, was replaced by a gap with a width of △, and a depth of several millimeters at the core of the drill, thus forming a non cutting area in the core of the drill. In the non cutting area, a small core with a constant diameter of △ will be produced in the cutting process. Due to its low strength, it will be repeatedly generated and broken in the gap, and the broken part will be taken away with the chips. Since the drill bit has no transverse edge, the axial force during drilling is small, which can be reduced by 30 ~ 50%. Controlling △ is the key to manufacturing drill bits, which is generally taken as about 0.8mm. In order to facilitate the self breaking of the small core, the greater the toughness of the processed material, the smaller the width of the gap △ should be

5.4 indexable shallow hole drill. The cutter angle of indexable shallow hole drill is composed of two parts: the cutter slot and the blade, so the machining accuracy of the cutter body is required to be high. Since the cutting edge of the drill is composed of two pieces of 6 overlapping sample blades, the outer edge and the inner edge, they are not symmetrical about the axis of the drill. In order to balance the radial force during drilling, the outer edge and inner edge must be configured according to the principle of mechanical balance. The drill bit has good centering in drilling, stable cutting and high machining accuracy. The convex triangular cemented carbide coated blade is used, and the chip breaking groove on the blade forms 10. Right and left front corners. The rear corner is 7., The cutting edge is sharp, which can reduce the work hardening of ZGMn13 steel. The sharp angle of the bit is 160., The chip deformation is small, and the flow direction is close to the direction of the chip removal groove, which is conducive to chip removal. In the process of use, it should be noted that when the hole is drilled through, a thin sheet will fly out, so it should be protected safely

6. heating process applied to ZGMn13 drilling processing

heating methods mainly include acetylene oxygen flame and plasma heating method. The former is simple and practical, while the latter has been tested in turning ZGMn13. The former is applied in drilling ZGMn13 steel sheet material, and the effect is remarkable. When ZGMn13 after water toughening is reheated above 350 ℃, carbides will precipitate again and form troostite or tempered martensite. The plasticity and toughness of the steel will drop sharply. But the temperature exceeds 600 ℃ "At C, the plasticity and toughness increase rapidly. Therefore, when drilling within this temperature range, it is stable, labor-saving, smooth processing, and will not produce edge collapse. It not only ensures the processing quality, improves the production efficiency, but also prolongs the service life of the tool.

when drilling with this simple heating method, align the acetylene oxygen gas welding gun with the center of the drilling hole and heat it to about 450 ℃, that is After the steel plate is red, it can run in the hole immediately after leaving the heating. High speed and large feed can be adopted. It has been proved that acetylene oxygen heating drilling of high manganese steel is a simple, practical and efficient machining method

7. Conclusion

in the drilling process of ZGMn13 steel, it is mainly to solve the problems of work hardening and cutting heat. Any new type of drill bit

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