The hottest solid carbide precision and efficient

2022-08-15
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Solid carbide precision and high-efficiency straight groove expanding and extruding cutter

expanding and extruding cutter is a special tool for high-precision hole machining of automobile engine. The intake pipe of automobile engine is an important part of the engine. The processing quality of the fuel injection nozzle hole of the intake pipe directly affects the fuel saving performance of the automobile. In the past, precision expanding and extruding knives imported from abroad were mostly used to process the nozzle holes, which were expensive and costly. In order to reduce processing costs and improve the market competitiveness of products, the localization of automotive cutting tools is imperative. The design and manufacturing points of the precision straight groove expanding and extruding cutter developed by our company are introduced below

1 Characteristics of machined holes

Jinan testing machine factory of engine oil injection holes Jinan testing machine we can say that we are studying the machining process all the time, as shown in Figure 1. The workpiece material is alsi12 (Cu); The processing machine is German dmg60h horizontal machining center; The cutting parameters are v = 3.5m/s, f = 0.14mm/r. More and more new composite materials are used to manufacture body in white and sunroof. The cooling method adopts emulsion external cooling

figure 1

it can be seen from the figure that the processing parts are as follows: expand F11 ± 0.1mm and F14 ± 0.1mm holes, spot facer f20mm counterbore and formed chamfer surface, of which the surface roughness of F14 ± 0.1mm holes is required to reach Ra1.6 M

in the processing process, due to the low strength of aluminum alloy and large chip deformation, the processing effect will be affected. Increasing the cutting speed and increasing the feed can reduce the chip deformation coefficient. Therefore, using high speed and large feed can offset part of the chip deformation. In order to ensure that the surface roughness value of the machined hole is below Ra1.6 m, it is necessary to design a reasonable tool structure and parameters, reduce or even eliminate the chip buildup, avoid the generation of scale thorns, and prevent vibration. At the same time, measures should also be taken to squeeze the machined surface to further reduce the roughness value

2 tool design requirements

1) eliminate chip build-up tumors

chip build-up tumors are caused by cold welding between the chip base metal and the rake face. Appropriately increasing the rake angle and improving the smoothness of the rake face are the main measures to eliminate chip build-up tumors. Generally, the main method to increase the rake angle is to use the right helicoid and the negative offset plane, but the helicoid is synthesized by the grinding wheel and the workpiece through the spiral motion, and the grinding process is poor in stability, so it is difficult to obtain a high finish rake surface, and the negative offset plane will reduce the strength of the tool and is not suitable for use. At this time, the positive offset plane can be used. Although it reduces the front angle, it will increase the brittleness of the chip and make it easy to fracture. It is an effective measure to eliminate the chip buildup

2) eliminate scale spikes

it can be seen from the metal cutting principle that when the cutting speed is high, reducing the front angle can inhibit the generation of scale spikes. Therefore, the use of positive offset plane can not only eliminate the chip deposition tumor, but also effectively inhibit the generation of scale spikes

3) vibration prevention

vibration is usually divided into three types: free vibration, forced vibration and self-excited vibration (i.e. flutter). Free vibration and forced vibration are independent of the tool; Chatter is the vibration itself from the one-way external force to obtain energy to maintain its own vibration, also known as self-sustaining vibration. The magnitude of this vibration is closely related to whether the tool design is reasonable or not. The stress condition of the tool during cutting is shown in Figure 2 and figure 3

Figure 2 figure 3

when the hard points of the processed material are encountered in the cutting process, the main cutting forces FZ1 and FZ2 on the two main cutting edges of the tool are not equal, and their radial components FY1 and FY2 are not equal, resulting in the radial vibration of the tool and the appearance of vibration marks on the machined surface, thereby increasing the damping of the elastic system (tool) and suppressing the generation of vibration. The cutter tooth a in Figure 3 can play this role. In addition, the machined surface can also be ironed to reduce the surface roughness value of the hole

Figure 4 is a partial enlarged view of Figure 3 when cutter tooth a extrudes the workpiece. In Figure 4, F1 = fcosa. When f is constant, the smaller A is, the greater the extrusion force is, which is conducive to reducing the machined surface roughness. In this design, the Q surface is ground with a grinding wheel of ﹤ 300mm according to the parameters in Figure 5, which can reduce the value of a and obtain better extrusion effect

Figure 4

determination of specific parameters

there are 6 parameters of the main structure of the straight groove expanding and extruding cutter, and the specific distribution is shown in Figure 5

Figure 5

1 not only has excellent appearance quality and small performance loss), the offset l

l affects the rake angle of the tool, the inclination of the edge and the flow direction of the chip, and affects the stability of cutting in and cutting out. The larger the L value is, the longer the cutting edge is, and the more stable the cutting process is. However, if the L value is too large, the sharpness of the tool will be reduced, which is extremely detrimental to the inhibition of the growth of debris accumulation tumors and scales. Generally, l = 0.7mm

2) the value of core thickness K

k directly affects the size of chip holding space and tool strength, usually k = 2.9mm

3) the included angle of the groove q

q mainly affects the size of the chip holding space, which is usually taken as q=105 °

4) the fillet radius at the bottom of the groove r

r affects the smoothness of the chip holding groove, which is usually taken as R = 1mm

5) cylindrical blade width b

blade width affects the extrusion effect and processing stability of the tool. The appropriate blade width has the functions of support, guidance, stability and vibration elimination. Generally, B = 0.8mm

6) the back diameter dr

dr affects the value of a in Figure 4. The smaller DR is, the smaller A is. The Dr value is usually 0.4 ~ 0.6mm smaller than the workpiece diameter

4 manufacturing points

two points should be paid attention to when manufacturing precision and efficient straight groove expanding and extruding cutter: ① try to improve the smoothness of the rake face and keep the roughness value below Ra0.2 m; ② Determine a reasonable rake angle and keep the roughness value of the rake face below Ra0.4 M

1) machining of rake face

in order to obtain high-quality rake face, fine-grained diamond grinding wheel should be selected, and the grinding linear speed should reach more than 50m/s. The grinding direction is shown in Figure 6. It can be seen from the figure that the rake face is ground by the side of the grinding wheel, and it should be ground in place along the groove depth direction at one time, so that the grinding wheel is not easy to vibrate, and the ideal roughness value can be obtained

figure 6

2) machining of the flank

the condition of the machined flank is shown in Figure 7. It can be seen from the figure that if the workpiece is tilted for shovel grinding and the X angle is increased, the C1 value can be increased and a larger axial shovel grinding amount can be obtained. In this way, a larger axial back angle can be obtained, while the cutters for processing aluminum alloy usually need a larger back angle

figure 7

there are two kinds of flank structures: one is to process the flank into a plane back angle. From figure 8, it can be seen that the cutting direction of the grinding wheel should be parallel to the broken line L to make the flank have no high point, so it needs three times of cutting. In addition, due to the inconsistent direction of each cutting, there must be obvious traces of cutting, which will affect the appearance and cost man hours. The other is to process the flank into a relief grinding surface. As can be seen from Figure 9, circle C is the cutting direction of the grinding wheel, and the relief grinding motion is synthesized by using circular motion and linear movement. It is easy to complete the machining of the flank with one-time cutting. The machining efficiency is high, the dimensional accuracy is easy to control, there is no trace of cutting, and the appearance is beautiful

figure 8 figure 9

5 test effect

Figure 10 shows the final design of the expanding and extruding knife. After the test of an engine manufacturer (the use of machine tools and cutting parameters are the same as those listed in Section 1 of this paper), the surface roughness value of the machined ﹤ 14 ± 0.1mm hole is below Ra1.6 m, and the surface quality of the hole is stable. Domestic expanding and extruding tools can process 28000 holes continuously, while imported tools can only process 210. But when we don't need them, we hope they can completely disappear 00 holes

figure 10

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