Process design analysis of the hottest bearing bus

2022-08-07
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Process design and analysis of bearing bush broaching machine

1 introduction to bearing bush

bearing bush is a sliding bearing used in the crankshaft journal and other parts of the engine. It is composed of a bimetallic steel strip with a steel strip as the substrate and a layer of bearing alloy attached to the surface, and is formed through a series of processing. This layer of bearing alloy usually has three kinds: Babbitt alloy, aluminum tin alloy and copper lead alloy. This machine is an internal finishing broaching machine designed and manufactured for Shaoxing textile machinery factory to process EQ main shaft flanging bush (Fig. 1). The bearing alloy of the flanging bush of the main shaft is aluminum tin alloy, and the part cut by the broaching machine is the part of the bearing alloy layer

2 inner circle finishing process and characteristics of bearing bush

there are two main methods for inner circle finishing of bearing bush, one is boring and the other is broaching. See Table 1 for their respective characteristics

table 1

3 current status of domestic shaft pad internal circular broaching machine

the general status of domestic shaft pad internal circular broaching machine at present is:

the fixture adopts gantry structure, but its rigidity is not strong and it is inconvenient to adjust; The special sliding table for broach adopts the traditional sliding guide rail. The clearance of the guide rail is large, the linear motion accuracy of the sliding table is poor (0.016/1000), and the friction resistance is large, resulting in large heat output of the driving oil cylinder and poor stability of the mechanical accuracy. Generally, it needs to be adjusted 2 ~ 3 times a day; In addition, the cutting and chip removal of the machine tool are manual operation, which has high labor intensity and low production efficiency. In order to improve the precision and output of product parts, we redesigned the broaching machine to solve the problems of poor precision, low productivity and poor stability

4 overall layout of the machine tool

the machine tool adopts a horizontal layout (referring to the horizontal layout of the sliding table, see Figure 2), which is composed of fixtures, broaching tires, sliding tables, broaches, feeding devices, feeding devices, electrical and hydraulic components. The processing process is as follows: put the parts into the aggregate chute of the feeding device, the sliding table starts from point B to point a, automatically takes a piece of material from the aggregate chute, then goes back to point B on the right, and brings the material to point C at the same time; The ejector pushes the material into the drawing tire at point C, the clamping device in the fixture clamps the parts, and the ejector returns; The slide table moves to the left again to drive the broach to broach the workpiece to point a; Take the material again, and cut the material just pulled at point C; The blanking device will take away the pulled parts along with the right side of the sliding table again and push them into the blanking device's material handling groove for collection; Take it away manually after the tank is full. In this way, an action cycle is completed. All actions of the cycle are automatically carried out under the control of the PLC machine

1. Bed 2 Feeding device 3 Fixture 4 Broach 5 Blanking device

6 Material handling trough 7 Cylinder 8 Control cabinet 9 Hydraulic station

Figure 2 overall layout of the machine tool

5 main components and technical requirements of the machine tool

the fixture of the machine tool adopts the gantry structure (see Figure 3), which has the function of supporting the tire pulling and clamping the workpiece. Since the fixture must bear all broaching forces, it must have enough rigidity to withstand the impact force of about 20000n during broaching

Figure 3 fixture

the clamping mechanism is the key component of the fixture. First, it is required that the broaching process will not be affected during clamping. Since the clamping point of the bearing bush is on the steel back of the opposite face of the bearing bush, the thickness of the steel back is 2.15mm, and the maximum clamping width is 2mm, the position of the pressing plate must be accurate during each action, so as to avoid too much pressing against the knife and too little pressing. Therefore, the pressing plate shall be set with a positioning step. When loosening, the pressing plate shall be fully retracted to avoid touching the parts during blanking. Second, the clamping force should be appropriate. Generally, the clamping pressure is 150% of the force applied when detecting the bearing bush height. This machine is 11000n, which is more appropriate. If the clamping force is too large, the clamping mark will be left on the clamping point of the bearing bush; If the clamping force is too small, the fitting ratio between the bearing bush locating surface and the broaching locating surface will not reach more than 80%, which will affect the stability of broaching accuracy. Third, the clamping pressure on the two mating surfaces of the bearing bush should be equal, otherwise the bearing bush will rotate in the tyre. The machine tool adopts a symmetrical pull rod force application mechanism, which can make the clamping pressure on both sides equal. Fourth, the clamping shall be self-locking, so as not to cause oil pressure fluctuation and affect the stability of product accuracy when a large amount of oil is fed into the oil cylinder during broaching. The machine tool adopts a slope self-locking device with a self-locking angle of 13 ° (see Figure 3), which can be locked reliably

tire pulling is a high-precision ordinary car. It is required to select the parts of the electronic material change testing machine that meet the following requirements, and the clamp specific tire pulling bearing surface also requires high precision. However, since the curve of the circular surface of the tyre drawing after installation is difficult to be concentric with the axis of the circular broach, the tyre drawing fixture should be slightly adjusted up, down, left and right, as shown in Figure 3. The machine adopts 1 ∶ 100 inclined plane for adjustment, which is convenient and reliable, and has good accuracy retention

as the bearing bush is an elastic part, when the clamping pressure plate is loosened, the part will not fall off by itself, so it needs to be struck on the steel back. In order not to damage the parts, part of the striking lever in the material device (see Figure 3) is intentionally cut off to form a weak gap, so as to increase the elasticity and buffer the strike force, so as to avoid damaging the parts and not affect the processing beat

The

slide (see Figure 4) is a power component that drives the broach to cut, and its quality directly affects the machining accuracy of parts. The sliding table of the machine tool is an oil pressure driven sliding table, which should have high linear motion accuracy, large driving force (the oil cylinder thrust of the machine is 35000n) and high motion speed. This can not only improve efficiency, but also improve the surface roughness of parts and reduce cutting resistance. The broaching speed of the sliding table is 20m/min and the return speed is 34m/min. However, the old sliding guide rail and sliding table are difficult to meet these requirements. Therefore, the machine tool adopts the gapless rolling guide rail and selects six sliding blocks (three sliding blocks for each guide rail, see Figure 4), which improves the rigidity and bearing capacity of the sliding saddle. Because the rolling guide rail has high linear motion accuracy (0.008/1000) and small rolling friction coefficient (0.005), it can pre tighten the guide rail to form gapless rolling, so as to ensure that the sliding table can move smoothly in a straight line under large load resistance. It is not only less heated, but also convenient for maintenance and replacement

1. Slider 2 Slide saddle 3 Cylinder 4 Pressing plate 5 Pressure block 6 Cylinder support 7 Guide rail 8 Bed

Figure 4 sliding table

sliding table oil cylinder is also a key component. Due to the high movement speed of the sliding table, the oil cylinder should have a good buffer device to reduce the impact. The front and rear cover adjustable buffer devices are used for this oil cylinder, as shown in Figure 5. Taking the rear cover as an example, the principle is as follows: When Part 4 enters Part 3, the triangle groove starts throttling, and the oil in chamber a enters chamber B through the triangle groove; When the triangle groove is closed, the oil in chamber a enters chamber B through the adjustable flow cone valve, thus forming a smaller throttling than the triangle groove and forming a buffer. The buffer effect produced by this structure is ideal. Even if the machine tool stops after high-speed operation, no impact phenomenon can be felt

1. Piston 2 Cylinder barrel 3 Throttle ring 4 The damping sleeve is respectively installed on the objective lens base and in the eyepiece barrel 5 Throttle cone valve 6 Oil port 7 Retaining iron 8 Rear cover 9 Piston rod 10 Steel ball 11 Spring 12 Triangle groove

Fig. 5 buffer device

tool has the closest relationship with the machining quality of parts. The broach of this machine tool is made of 9 circular blades which are locked through the mandrel (see Fig. 6). The 1st ~ 4th blades are rough cutting blades, and each tooth lift is 0.1mm. The 5th ~ 8th blades are cutting and checking teeth. See Table 2 for the tooth lift. The 9th piece is installed eccentrically (there is a 2mm downward eccentric step at the rear of the spindle) to cut the oil grooves on both sides of the bearing bush. The whole broach is fixed on the sliding saddle by the tool holder, and each blade can rotate when it is loosened. When the blade is worn, turn the blade 180 ° to continue to use. In addition, it is better to grind the broach before use, so that the precision of the drawn bearing bush is stable, the cutting surface is as bright as a mirror, and the roughness can reach ra0.1 μ m; Otherwise, there are traces on the surface of the pulled parts

the automatic loading and unloading device plays a very important role in the high-speed, stable and reliable operation of the machine tool. The feeding device consists of an aggregate chute and a separator (see Fig. 7). The aggregate chute can collect 15 bearing shells vertically. During feeding, the spacer separates the upper material from the lowest material to avoid feeding two pieces at the same time during automatic feeding. The blanking device is composed of a sliding block type feeder and a material handling groove (see Figure 8). Their actions are completed by colliding the sliding table when it moves left and right. The action is as follows: when the sliding table moves to point a on the left, the impact separator moves to the left - to separate the material, at this time, the lowest piece of material will fall into the ejector on the sliding table (when the ejector returns to point C with the sliding table, the material will be pushed into the puller). At the same time, the processed bearing bush at point C will be knocked down onto the material receiving groove of the blanking slider; The sliding table moves to the right, and the material separator moves to the right under the action of the spring - discharging. When it reaches point B, the discharging slider collides with the material handling groove fixed on the bed, and the materials are automatically moved to the material handling groove for collection. When it is full (15 pieces), they are taken away by the workers. Thus, a loading and unloading cycle is completed. The loading and unloading device has simple and reliable structure and is very convenient to use

1. Support plate 2 Aggregate chute 3 Spring 4 Spacer plate 5 Nut 6 Jacking opening 7 Impactor 8 Slide table 9 Bracket

1 Slide table 2 Ejector 3 Slide 4 Slider 5 Tension spring 6 Material handling trough 7 Support

Figure 7 feeding device

figure 8 feeding device

6 conclusion

the machine tool has been used by the user for several years. It has been shown that it can automatically operate normally, with few faults and stable accuracy. The stability accuracy is: the wall thickness tolerance is 0.007mm, and the surface roughness is ra0.1 for graphene like materials μ m. The production rate is 11.36 billion yuan and 650 pieces/hour for the base. This machine tool can adapt to the processing of bearing shells of different types, specifications and materials only by replacing the tire pulling parts, Broaches (not for the same diameter) and adjusting the aggregate chute. Its deficiency is that the chip removal is not ideal

1. Trim nut 2 Clamping cylinder 3 Clip details 4, 6, 10 Pull rod 5 Chute slide 7 Balance levers 8, 9 Fine adjust the swash block 11 Pressing plate 12, 21 Tire pulling 13 Tool 14 Slide 15 Rotating shaft 16 Transfer pin 17 Charging cylinder 18 Punching lever 19 Stop 20 Punching slider

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