Hard machining characteristics of cemented carbide parts
Steel with a work hardness greater than 56 HRC or a strength greater than Rm> 2000 N / mm2 is commonly referred to as hard machining. In most cases, dies or forging dies are carburized or hardened after pre-processing. After pre-processing, you need to reserve a specific finishing allowance. Hard milling is especially important when machining spherical or toroidal shaped workpieces.
Hard milling can cut up to 70 HRC of material, but hand polishing, an expensive process, usually achieves the required surface roughness. To reduce the time required for manual polishing, it is necessary to utilize the cutting edge of the shape defined during milling. For example, with HSC treatment, the surface is close to the roughness of the polished surface, with a maximum surface quality of Rz1.
Carbide milling cutters common on the market are not suitable for cutting in this range. To solve the problem of milling hard materials, some prerequisites must be met.
For example, a milling cutter made of a special cemented carbide material with a unique geometry and corresponding coating is used. In short, the tool needs these three important elements. Particular attention should be paid to the balance between these elements during the manufacture of the tool.
Normally, HSC treatment can cut workpieces with hardness exceeding 56HRC. In this regard, the limitation is the combined effect of cutting speed and temperature. For HSC, the melting point of the work material should be tested at an appropriate cutting speed. Note that the melting point of the work material is usually higher than the maximum permissible temperature of the coating. The best saying here is “keep the tool calm”. This means that, on the one hand, the contact area with the workpiece should be as small as possible, and on the other hand, the cutting should be done at a specific rate so that the cutting does not reach heat above the temperature allowed by the coating. Must be done.
Accurate detection of speed is especially important. For this purpose, it should be based on the actual effective tool diameter. With a lateral feed amount of ap = 0.1 mm, the actual effective diameter of a 6 mm diameter ball end mill is 1.54 mm. To achieve a cutting speed of 200 m / min, the speed must be 41000 r / min.
The chips generated during the process and the heat carried by the chips should be removed as quickly as possible. The best way is to blow compressed air directly from the spindle onto the cutting edge. Compressed air can carry a small amount of lubricant depending on the material of the workpiece. Better surface quality can be achieved with a small amount of lubricant, as chips do not stick to the cutting edge. For hard cuts, do not use emulsions. A mere drop of water can cause a sudden temperature change, splitting the tool into a single component. Cemented carbide microcracks caused by sudden changes in temperature crack the cutting edge. In the case of HSC processing, depending on the diameter and the speed of rotation of the tool, these fragments can have the energy equivalent to the light emitted by a light firearm.
Early HSC milling developed for graphite cutting not only means high speed and high feed rate, but also has a wide range of applications under the combined effect of many factors. The power of hard milling is mainly determined by the machine tool used. Overall, the concept of hard cutting is related to high speed machining.
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