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Summary of experience in cutting high manganese steel

high manganese steel is a kind of wear-resistant steel, and high plasticity and impact toughness can be obtained after water toughening treatment. High manganese steel has high wear resistance. Although its hardness is only hb210, its yield point σ S is low, only σ B, so it has high plasticity and toughness. The following is a summary of experience in cutting high manganese steel

1. Category and properties of high manganese steel

steel with manganese content of about 11% - 18% is called high manganese steel. The common chemical composition of cast high manganese steel zmn13 is: Mn content 11% - 14%, C content 1.0% - 1.4%, Si content 0.3% - 1.0%, P content 0.03%, s content 0.05%. It can be divided into high carbon and high manganese wear-resistant steel, medium carbon and high manganese non-magnetic steel, low carbon and high manganese stainless steel and high manganese heat-resistant steel

high manganese steel is a kind of wear-resistant steel. After water toughening treatment, high manganese steel can obtain high plasticity and impact toughness. High manganese steel has high wear resistance. Although its hardness is only hb210, its yield point σ S is low, only σ B, so it has high plasticity and toughness. When high manganese steel is subjected to external pressure and impact load, it will produce great plastic deformation or serious work hardening. The steel is intensively strengthened, and the hardness is significantly improved, up to hb450-550, so it has high wear resistance

2. Machinability of high manganese steel

(1) severe work hardening: during the cutting process of high manganese steel, due to large plastic deformation, austenite structure is transformed into fine grain martensite structure, resulting in serious hardening phenomenon. The hardness before machining is generally hb200-220, and the surface hardness after machining can reach hb450-550. The depth of the hardened layer is 0.1-0.3mm, which is several times higher than that of 45 steel. Severe work hardening increases the cutting force, intensifies tool wear, and is easy to cause tool breakage and damage

(2) high cutting temperature: due to high cutting power, more heat is generated, and the thermal conductivity of high manganese steel is lower than that of stainless steel, only 1/4 of that of medium carbon steel, so the temperature of cutting area is very high. When the cutting speed VC is 50m/min, the cutting temperature of high manganese steel is 200 ℃ - 250 ℃ higher than that of 45 steel. Therefore, the tool wear is serious and the durability is reduced

(3) chip breaking difficulty: the toughness of high manganese steel is 8 times that of No. 45 steel, and the chips are not easy to bend and break during cutting

(4) dimensional accuracy is not easy to control: the linear expansion coefficient of high manganese steel is similar to that of brass. Under high cutting temperature, local thermal deformation occurs, and the dimensional accuracy is not easy to control. When cutting high manganese steel, rough machining should be carried out first, and then finish machining should be carried out after the workpiece is cooled to ensure the dimensional accuracy of the workpiece

3. Characteristics of various tool materials when cutting high manganese steel

high manganese steel is a difficult to machine material and has high requirements for tool materials. Generally speaking, the material is required to have high red hardness, good wear resistance, high strength, toughness and thermal conductivity

1, high speed steel is a kind of high alloy tool steel It can withstand the cutting temperature of 500-600c. At present, it is basically incompetent to process high manganese steel, which is generally used to make non-standard drill bits

2, when machining high manganese steel, cemented carbide tools are generally used for the processing of small parts (CBN tool brand of non-metallic adhesive is more suitable for large high manganese steel parts). According to statistics, when the processing time of a single high manganese steel part is less than 5min, cemented carbide tools can be used, YG series brand with good impact toughness can be used for rough machining, and YW series brand can be used for finish machining

3, characteristics of ceramic materials: high hardness (91-94hra), good wear resistance, high heat resistance (1200), high cutting speed is allowed, but it is brittle, and it is easy to collapse when cutting

4, the characteristics of cubic boron nitride (CBN) material: high hardness (7300-9000hv), high heat resistance (1300-1500 degrees), good wear resistance, chemical stability higher than diamond, low affinity with iron group metals, good cutting performance, generally brittle, at this time, you can choose the CBN tool brand with excellent impact toughness, For example, there are two grades of bn-k1 or bn-s20 for high manganese steel grinding roll and high manganese steel rolling mortar wall (crusher cone) parts processing; Due to the excellent toughness and wear resistance of this kind of non-metallic adhesive CBN tool, it can be competent for rough and finish machining of high manganese steel

4. how to determine the three cutting elements of the tool when machining high manganese steel

no matter what tool material is selected, the cutting amount of the tool is basically carried out according to the following principles: during rough machining, the higher metal removal rate and the necessary tool durability should be guaranteed as far as possible, so generally, the largest cutting depth AP is preferred, followed by the larger feed rate F, and finally according to the requirements of tool durability, Determine the appropriate cutting speed. During finish machining, the machining accuracy and surface quality requirements of the workpiece should be ensured first. Therefore, generally, a small amount of internal and external lubrication is used to achieve the most impractical built-in effect. The amount F and cutting depth AP should be given, and a higher cutting speed should be selected as far as possible υ c。

1, selection of cutting depth AP

1) the cutting depth should be determined according to the machining allowance of the workpiece. During rough machining, help to solve various difficulties and problems in the project construction in time. In addition to leaving finishing allowance, all the allowance should be cut off as much as possible during one-time cutting. When the machining allowance is too large, the rigidity of the process system is low, the work of the machine tool is insufficient, the tool strength is insufficient, or the impact vibration of intermittent cutting is large, the tool can be moved several times. When cutting castings and forgings with hard skin on the surface, try to make AP greater than the thickness of hard skin to protect the tool tip

2) the machining allowance of semi finishing and finishing is generally small and can be cut off at one time, but sometimes in order to ensure the machining accuracy and surface quality of parts, secondary tool walking can also be used

2, selection of feed rate f

after the cutting depth is selected, the larger feed rate F should be selected as much as possible. During rough machining, due to the large cutting force acting on the process system, the selection of feed rate is limited by the following factors; The rigidity of the machine tool tool workpiece system, the strength of the machine tool feed mechanism, the effective power and torque of the machine tool, and the strength of the blade during intermittent cutting. During semi finishing and finishing, the maximum feed rate is mainly limited by the surface roughness of the workpiece. In the factory, the feed rate is usually selected according to certain tables according to experience (see the relevant tables in chapters such as turning, drilling, milling, etc.). If conditions permit, the cutting database can be retrieved and optimized

3. Cutting speed υ C selection

after the cutting depth AP is selected, the cutting speed can be determined by calculation or table method under the condition of ensuring the reasonable durability of the tool υ The value of C. In the specific determination υ C value, the following principles should be generally followed:

1) when rough turning, the cutting depth and feed rate are both large, so choose a lower cutting speed; When finishing turning, select a higher cutting speed

2) the better the cutting performance of the tool material, the higher the cutting speed can be selected. Therefore, the cutting speed of cemented carbide tool can be several times higher than that of high-speed steel, and the cutting speed of cubic boron oxide tool can be much higher than that of cemented carbide tool. The linear speed applicable to the tool brand can refer to the recommended parameters of the tool manufacturer. The cutting linear speed of Valin bn-s20 CBN tool v=60--85m/min; The linear speed of finishing can reach v=135m/min

5. Tools and precautions for drilling high manganese steel

with the development of tool materials, the processing of high manganese steel has developed from cemented carbide tools in the 1990s to the current non-metallic binder boron nitride tools. For example, bn-s20 and bn-k1 brands, which are widely used at present, are a kind of indexable inserts for machine clamps, which are widely used in the turning and milling of high manganese steel parts. For the drilling of high manganese steel parts, the high-speed steel tool materials with special coating and cemented carbide tool materials are still mostly used at present

2. Several kinds of cemented carbide bits commonly used for drilling ZGMn13 steel

1) general cemented carbide bits. Generally, YG or YW series alloy is used. This kind of drill adopts the form of inlay welding, and the drill has high durability. 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

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 drill bit is generally made of 40Cr, and the blade material can be YG8 or yw2. If the crown bit is selected, the drilling effect is better. 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

3) welded carbide shallow hole drill without transverse blade. The significant difference between this kind of drill and general cemented carbide drill is that it has no transverse edge. Because the drill has no transverse edge, the axial force during drilling is small, which can be reduced by 30-50%

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. The drill bit has good centering in drilling, stable cutting and high machining accuracy. In the process of use, it should be noted that there is generally no problem. When the hole is drilled through, a thin sheet flies out, so it should be protected safely

5) drilling high manganese steel ZGMn13 with heating process: the heating method mainly includes acetylene oxygen flame heating method. When drilling with this simple heating method, align the acetylene oxygen gas welding gun with the center of the drilling hole and heat it, the range is about twice the diameter of the hole, and heat it to about 450 ℃, that is, after the steel plate is red, it will leave the heating and immediately run down, and high speed and large feed can be used. It has been proved that acetylene oxygen heating drilling of high manganese steel is a simple, practical and efficient machining method

2. Pay attention to the following problems when drilling high manganese steel with cemented carbide group drill:

(1) reasonably select the cutting amount: if the cutting speed is too low or the feed rate is too large, the cutting force will increase, which is easy to cause cutting collapse. Generally, vc=30-40m/min, f=0.07-0.1mm/r

(2) make full use of coolant: the linear expansion coefficient of high manganese steel is large, so make full use of coolant when drilling. If possible, immerse the workpiece in the coolant to drill, so as to prevent the drill bit from being bitten and damaged due to the shrinkage of the hole

(3) strictly control the dull standard of the drill bit: if you hear a harsh scream during drilling or find that the rear corner edge of the outer corner of the drill bit is worn by about 1mm, you should regrind the drill bit in time, otherwise continued use will accelerate the wear of the drill bit and cause damage

(4) it is strictly forbidden to stop halfway: when drilling high manganese steel with cemented carbide group drilling, automatic feeding should be adopted, and manual feeding should not be used as far as possible, otherwise the hardening phenomenon will be aggravated, making drilling more difficult. During operation, it is strictly forbidden to stop halfway to prevent "boring" caused by excessive cutting force, which will break the drill bit

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