Repair and grinding of the most damaged carbide mi

2022-09-20
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Repair of damaged cemented carbide milling cutter grinding

formed hard oil delivery valve oil return pipe has a large oil output. High quality alloy milling cutter is widely used because of its small shape tolerance. Because it cannot be directly replaced, the tight supply situation will not change the blade soon. Most milling cutters are scrapped after edge collapse, which greatly increases the processing cost

1.1 properties of milling materials

when cutting titanium alloy, due to the poor thermal conductivity of titanium alloy, chips are easy to adhere to the edge of the tool tip or form chip nodules, forming high-temperature areas on the front and rear tool surfaces near the tool tip, resulting in the loss of tool hardness and increased wear. During continuous cutting under high temperature, the binder and weld are impacted by subsequent processing, and some tool materials will be taken away in the process of forced punching, resulting in tool defects and damage. In addition, when the cutting temperature reaches above 600 ℃, a hardened hard layer will be formed on the surface of the part, which will have a strong wear effect on the tool. Titanium alloy has low elastic modulus, large elastic deformation and large springback on the workpiece surface close to the flank, so the contact area between the machined surface and the flank is large and the wear is serious

1.2 normal wear

so as to control the flow into the oil cylinder

in normal production and processing, when the allowance of continuous milling titanium alloy parts reaches 15mm-20mm, serious blade wear will occur. The efficiency of continuous milling is very low, and the surface finish of machined parts is very poor, which can not meet the production and quality requirements

1.3 improper operation

during the production and processing of titanium alloy casting box and box cover, improper clamping, inappropriate cutting depth, too fast spindle speed, insufficient cooling and other improper operations will lead to tool collapse, damage, fracture and other conditions. In addition to being unable to effectively mill, this kind of defective milling cutter will also cause surface defects such as concave machined surface due to "biting" in the milling process, which will not only affect the processing quality of the milled surface, but also lead to the scrapping of machined parts in serious cases

2 improvement method

2.1 micro chipping of cutting edge

micro chipping of cutting edge (i.e. slight damage) is the most common. The tool can be reused by grinding the damaged part of the cutting edge with a grinder. Silicon carbide grinding wheel should be selected for grinding cemented carbide milling cutter, and it is not allowed to dip in water for grinding, otherwise the cemented carbide will be completely scrapped due to sudden cooling and cracking. The grinding process is shown in Figure 1. Figure 2 shows the comparison between the new tool and the scrapped tool after grinding

after grinding with a grinder, the effective length of the sharpened tool is shorter than that of the unused new tool, but this process indirectly enhances the rigidity of the tool, makes the machined surface quality better, and improves the milling efficiency

because the hard and brittle uneven skin will be formed after the blank of titanium alloy casting is formed, it is very easy to cause the phenomenon of edge collapse, so cutting off the hard skin has become the most difficult process in titanium alloy processing. It is suggested to appropriately increase the back cutting amount (2mm-4mm) during the first rough machining, so as to control the tip under the hard skin on the workpiece surface and prevent the tip from directly contacting the hard skin and causing blade collapse

2.2 change the geometric parameters of the tool

in the process of tool grinding, the service life, machining surface quality and cutting efficiency of the tool can be improved by changing the geometric parameters of the tool. Figure 3 is an enlarged view of the cutter head

through the research on the cutting edge of the scrapped carbide milling cutter, it is found that the design of the cutting edge of the new cutter has defects, that is, the lack of transition surface and transition edge. This is the main reason why the strength of the main cutting edge is not enough, resulting in rapid tool wear and prone to "edge collapse"

by grinding the arc transition plane, the arc transition blade is added to the cutting edge to enhance the strength of the tool tip, which not only solves the problem that the cutting edge is easy to wear and collapse, but also improves the surface finish and milling efficiency of the machined parts. At the same time, reduce the cutting thickness at the tip, and form the machined surface under a small cutting thickness, which is conducive to improving the surface roughness of the milling surface. In addition, the polishing blade can be grinded out and made parallel to the machined surface, which plays the role of polishing the surface and improves the quality of the machined surface. Through repeated practice, the radius parameters of the corresponding arc transition edge of end mills with different specifications are shown in Table 1

2.3 reuse of scrapped tool handle

after repeated edge collapse and grinding, the cutting edge will be ground completely and only the tool handle will be left; Or the tool breaks directly from the handle due to improper operation during use. In this case, the remaining effective length of the tool handle can be processed into a formed single tool through wire cutting, grinding, heat treatment and other methods, so that the single tool can be used within the safe and effective clamping range. It can be used not only for milling planes, cutting grooves, chamfering, but also for boring, so as to realize the reuse of discarded tools. Figure 4 shows the single knife processed from the scrapped knife handle

in order to increase the rigidity and strength of the cutting edge of the end milling cutter, the corresponding parts are subject to heat treatment and surface coating, and the cutting edge of the cutter is subject to special treatment. Using this method for reference, in order to make better use of the single tool grinded from the broken end mill shank part (YG cemented carbide), it is necessary to increase the hardness of the tool edge to HRC through heat treatment and quenching, so as to improve the service life of the tool

through the improvement practice and repeated use of a large number of scrapped carbide milling cutters, a complete set of process route for converting scrapped carbide milling cutters into single cutters has been formed: ① cutting the shank squarely by wire cutting; ② Grind out the approximate shape of the cutter head on the grinder; ③ After quenching and heating of the blade, put it into nitrate for cooling to make the hardness reach HRC; ④ The general order of grinding out the cutter head is as follows: grinding the rear cutter face - grinding the auxiliary rear cutter face - grinding the front cutter face - grinding out the transition edge

3 improvement effect

the scrapped carbide milling cutter can be made into a reusable special milling cutter for processing titanium alloy materials by manual grinding. The types can be divided into cylindrical milling cutter, ordinary single cutter, T-type single cutter, etc. According to the operation process of non low temperature groove: complete statistics, about 100 end mills have been successfully ground into shape by using this method, and the service life of the tools after grinding has been increased by times compared with that before regrinding

in actual processing, use the sharpened Walter φ The surface finish of the workpiece machined with 16mm cemented carbide end milling cutter can reach Ra1.6

4 summary

by analyzing the damage causes of carbide forming milling cutters, according to the different damaged parts of scrapped carbide milling cutters and the length of available parts, the scrapped carbide milling cutters can be reused, the service life and milling efficiency are improved, and the processing cost is greatly reduced by manually grinding the damaged parts of micro chipping cutting edges, increasing the arc transition edge, and changing the scrapped tool handle into a single tool

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