Roughing has an important influence on the machining process and the quality of the workpiece. In the machining of the engine seat hole surface, better product quality is achieved due to the improvement of the rough machining tool. In actual machining, the proper matching and use of tools and the use of tools for finishing the seat ring must be taken seriously. Taking a rough tool as an example, due to the material difference of the seat ring, the difference in the final machining condition will be directly affected. Therefore, choosing a reasonable roughing tool can create the conditions for the next final processing, on the contrary, it will directly affect the quality of the final processing. Therefore, we must pay attention to the rational use of relevant parameters of rough machining tools and the selection of suitable rough machining tools. The production of defects Take the displacement of a cylinder block of a certain engine as an example. In order to further improve the performance of the engine, our factory adjusted the material of the intake seat ring, mainly to increase the surface hardness of the material. However, in the subsequent trial cut processing, it was found that after the normal use of the tool in the processing of 30 to 50 pieces of the workpiece with a new seat installed, the 60 ° surface of the seat ring sealing surface has a burst phenomenon (Figure 1), tool The service life is only 15% of its previous actual life. After technicians visually inspected the workpieces with burst ports on the edges of all the intake seats, we found that not all of the eight intake seats in the cylinder head have a bursting phenomenon, and some have an edge on the seat ring. 1 to 3 bursts, some 2 to 3 seats, 1 to 3 bursts at the edges. Figure 1 Defects on the raceway problem analysis According to the phenomenon of edge collapse during processing, we analyze the following aspects: Failure analysis If the machining defect shown in Fig. 1 is not discovered in time, it will cause serious problems such as carbon deposition, leakage, insufficient fuel combustion, power drop, and black smoke during the use of the engine. Therefore, such defects must be completely resolved. 2 seat ring material composition The material composition of the seat ring is shown in the table, and it can be seen that the content of chromium, molybdenum, and cobalt increases, which directly increases the difficulty of processing (hardness value control: 222HV=95HRB, 372HV=110HRB). The hardness difference between the new and old seats is very obvious. Therefore, in comparison, the requirements for machining tools have been improved. 3. Analysis of appearance According to the visual inspection of the defected seat ring, we found that the air intake seats that produced the burst mouth were all pressed and installed, and the end face of the seat ring was slightly higher than the hole face of the bottom hole of the seat ring. 4. Processing technology analysis The engine's cylinder head, a total of 8 intake seats, 8 exhaust seats, the seat ring processing coarse, finishing to complete. After the seat ring is pressed in, first the rough surface of the seat ring 44.7° is taken over by the cemented carbide insert (Fig. 2), and the first 60°, 44.7° and 30° bevels of the finish machining are first processed into 44.7°. Slant; Next, the tool with tool material CBN assumes the finishing of 60°, 44.7°, and 30° (Fig. 3), and roughing and finishing are done on the same machine, ie one clamping is completed The coarse and fine processing content of the seat ring. According to the above-mentioned processing technology, the workpiece quality and the tool life meet the set technical requirements in the actual production at ordinary times (the rough-cutting carbide cutting tool life is 340 pieces, and the finishing machining CBN cutting tool life is 340 pieces). Figure 2 Finishing the roughing of the 44.7° face of the seat Figure 3 Finishing the rest of the processing surface Solution process To solve the problem, the following principles should generally be followed: the order of selection is from simple to complex, the possible main direction to possible reasons for general analysis, and the possibility of high probability to low frequency. 1. Adjust the height of the fit to verify Based on the above analysis, we first verify the height of the fitting after the seat is pressed. This small drop will affect the bursting defects that appear in the process. Reason for selection: Because the surface hardness of the seat ring is higher than the original hardness, it also increases its brittleness, and the end face of the seat ring is slightly higher than the hole of the bottom hole. Under the extrusion of the cutter, there is no resistance on the side of the seat ring. Bursting is easy to produce. The original tool was used for machining verification. The results were as follows: 10 specimens were cut, and 10 pieces of the workpiece did not burst. Based on the improvement of the situation, deepen the bottom hole as much as possible to allow the pressed-in seat to be lower than the blank and verify the machining. The original CBN tool FT01 (new blade) was used for testing. After the 50 pieces were processed, the bursting phenomenon was found. This shows that the drop in the fit between the seat ring and the bottom hole is not a direct cause. 2. Adjust parameters The adjustment of cutting parameters is a convenient means to solve the problem. This state is changed by reducing the cutting force of the finishing tool. For different tools, tests are performed with different processing parameters. For CBN tool with FT05 material, the original 0.09mm/r is reduced to 0.07mm/r, the status still has not changed, and then it is adjusted to 0.06mm/r, 0.05mm/r, or even to 0.04mm/r. The situation still occurs. Therefore, the adjustment of the feed rate has no effect. Next, the change of cutting material and the change of the cutting angle were selected to test and solve this problem. The replacement of pre-prepared tools of different materials and different back angles did not achieve the desired results. Some only processed 1 to 2 pieces with bursts, and some processed 10 pieces with bursts. Therefore, attempts to eliminate the burst condition by changing the existing finishing tool material are not possible. Re-review the various processes and tools in the machining process. If the rough-cutting cemented carbide inserts are subjected to more rapid wear than when the harder material is being machined, the passivation of the tool will directly increase the crowding of the seat ring. Pressing and bursting. Although the roughing is 44.7°, the roughing process is to machine the entire seat to 44.7°, and the 60° is the finishing work based on the 44.7°. If it is processed at 44.7°, it has already been produced. Burst, and if the 60 ° surface finishing can not be completely cut off the burst, that is, the final 60 ° surface will have a burst phenomenon. According to this analysis, the third trial cutting process still used the original tool and cutting parameters. When the roughing tool was cut to 40, 50, and 60 pieces, they were examined separately and found to be basically 50 to 60. In the case of rough machining, the wear of the tool has become more severe. Therefore, the life of the rough-cutting carbide cutting tool was set at 60 pieces, and then the test was conducted without bursting. solution The test results tell us that the previously used tool products could not meet the service life requirements, and the rough tool materials must be replaced or re-selected. Cutting edge sharp carbide cutting tools have advantages in machining softer materials, so the tool life is also higher. However, when the sharp edge is used to process harder materials, the wear of the cutting edge is accelerated, which easily causes the extrusion of the processing surface, and the edge collapses directly. Therefore, the idea to solve the problem is adjusted to: increase the wear resistance of the blade surface; micro-blunt treatment of the cutting edge of the main cutting edge of the blade, reducing the acceleration of the initial wear. The currently available solution is to adjust the tool material so as to reduce the wear rate and thus increase the service life of the tool. Change the rough tool material from the original cemented carbide to the coated cemented carbide insert, select the main cutting edge with a micro-blunt edge, such as a carbide insert coated with TiAlN. Restore the depth of the bottom hole of the seat ring, adjust it to the middle value, and then perform a test, and get a very good effect. The tool life before the bursting of the seat ring sealing surface is about 600 pieces, and the service life is greatly improved. Conclusion In general machining, we usually do not pay much attention to the processing of roughing tools. We think that roughing is only to reduce the machining allowance in finishing, and it is the pre-machining for the finishing machining quality, while the finishing tool only It is the key to the quality of the product. Therefore, when it is actually used, it pays more attention to the condition of finishing and ignores the rough machining condition.
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In the machining of the seat ring of the engine cylinder head, the usual machining processes are: rough machining of a bottom hole of a seat ring, a bottom hole of a finishing seat ring, a press-fit seat ring, a rough machining seat ring sealing surface and a finishing seat ring sealing surface. In the entire process, every step is an important part. Because, processing a good seat tube is the key to engine head machining. 
According to this hypothesis, under the premise of not exceeding the tolerance, the processing depth of the bottom hole of the seat ring is increased as much as possible, so that the pressed-in seat ring is substantially lower than the hole mouth surface of the seat bottom hole.
3. Roughing parameter adjustment
From the above cases, it can be seen that rough machining plays a key role in finishing. Therefore, “coarseness†is not a matter of concern, and the conditions before and after processing often directly affect the final quality. Whether the choice of roughing tool is appropriate or not should be given enough attention in the machining process.
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