Turning Method and Process Analysis of Single Turning Crankshaft

First, technical requirements and process analysis (Figure 1)

figure 1

1, the main technical requirements:

(1) Cylindrical A total of three, A total of 4 places A total of 2 places.

(2) There are 2 places of 25 mm in length, 4 places in 4 mm, and 1 place in each of 8 mm, 5 mm, 300+0.1, 46 mm, and 160±0.1 mm.

(3) Two 45o angles.

(4) The tolerance between the eccentricity of the eccentricity of the geometric tolerance and the axis is 0.05mm.

2, process analysis:

In the machine, from turning motion to reciprocating motion, it is often done by an eccentric mechanism or a crankshaft; eccentric workpieces and crankshafts are generally machined on a lathe.

Eccentric workpieces, crankshafts and cylindrical turning have a lot in common, but eccentric workpieces and crankshafts have their special points. This is the axis of the workpiece between the outer circle and the outer circle is parallel and does not coincide. The outer axis of the workpiece is parallel. This phenomenon is called "eccentricity." The distance between these two axes is called "eccentricity."

The eccentricity of the car is the same as other parts of the car. The processing method is not fixed, but different methods are adopted according to the different quantities, shapes and precision requirements of the workpiece.

The first thing to consider is the shape, dimensional accuracy, and tolerances of the part. Select the appropriate process. Therefore, the prior process analysis must be accurate. Of course, reliable processing methods and steps are also crucial.

(1) The shape of the eccentric workpiece depends entirely on turning. Therefore, it should be carefully considered and the machining process and processing steps must be selected.

(2) Eccentric workpieces can be turned by two top-clamping methods. In order to ensure the parallelism of the eccentric outer circle and the axis of the shaft and other related accuracy requirements, turning the eccentric part, the turning tool must have sufficient strength. It should be noted that the carbide turning tool is easily damaged during turning, the top force of the eccentric workpiece is uneven, and the front top is easily damaged or displaced. Therefore, it must be checked frequently.

(3) Before using two top car eccentric workpieces, first use a three-jaw automatic centering chuck to clamp the outer circle of one end of the workpiece, turn the plane at the other end of the work piece to drill the center hole, and clamp the top clamp to turn the outer circle. Dimensions require that the length be as long as possible. Turn the head and then use the three-jaw automatic centering chuck to clamp the processed outer circle, set the total length of the workpiece, the flat end surface, drill the center hole, and the surface roughness of the workpiece at both ends of the surface should meet the requirements.

Second, processing difficulties and solutions:

1. The machining quality of the center hole of the eccentric workpiece has a great influence on the machining accuracy of the workpiece. The position requirements of the center holes at the two ends of the eccentric workpiece correspond one to one. If the center holes at both ends are not on the same line, the axis skew, or the center hole The surface machining is not round and smooth; it will seriously cause the shape error and position error of the crankshaft workpiece after machining. Therefore, for eccentric workpieces with high precision requirements, the center hole should generally be machined on a high-precision coordinate boring machine.

2. Eccentric workpieces are mounted on the two tops. Because the distribution of force points on the outer circle of the workpiece is uneven, the clamping is not firm. After driving or machining, large centrifugal force and shock vibration will occur, which will cause the workpiece to appear. Out-of-roundness and vibrations on the outer circle of the workpiece may even cause serious accidents.

3, when processing a long crankshaft workpiece, the most prominent contradiction is the poor rigidity of the workpiece, unbalanced rotation, easy deformation, processing is more difficult; supporting the method of supporting the screw after the crankshaft can increase the workpiece rigidity, reduce deformation and vibration; but Be sure to pay attention to the top and support screws can not be too tight, too tight will cause the workpiece bending deformation; if the support screw is too loose, it will not be supported, the screw in the processing is easy to fly out of the accident.

4. After the eccentric workpiece is clamped, the original center line has been offset by a certain distance. In order to prevent accidents from being damaged by the turning tool, it is necessary to start from the highest point of the workpiece when cutting.

5. When checking the eccentricity e, the workpiece should be measured at the top between the two tops. (Maximum reading on the dial indicator - minimum reading = 2e). If the dial gauge is not measuring enough, add a block gauge or install a dial indicator and measure on a high vernier scale.

6. Turning the eccentric workpiece, the cutting speed should not be selected too high, and the front and back angles of the turning tool should not be worn too much.

7. When the eccentric workpiece is eccentric, the top force is uneven, and the front top is easily damaged or displaced. Therefore, it must always check and ensure that the two tips are in friction and clearance.

8. Pay attention to adjust the clearance of the lathe spindle, especially when the lathe accuracy is poor, it is even more important.

Third, the examples of processing methods and steps

1, spare parts for the 45 # steel bar stock. The three-jaw self-centering chuck holds the outer circle of the blank, and the long correcting is extended. The end face is flat and the center hole is drilled. Hold the outer circle again and use a top-down method with the top of the action. Roughing, finishing Φ60 0 -0.1 mm to the size requirements, and then adjust the end of the car, pay attention to the package of thin copper, anti-clamping the surface of the workpiece, the total length of 160 ± 0.1 mm in size requirements. Drill Φ3mm center hole. (Figure II)

figure 2

2. Paint on both sides of the shaft and place the workpiece on the V-shaped frame for scribing. Use the scribing disk (or vernier height scale) to first draw a contour line equal to the centerline of the workpiece on the end face and the outer circle. (image 3)

image 3

Rotate the workpiece by 90°, align the centerline with a 90° square rule, draw a vertical centerline on the end face and the outer circle Φ60mm, and draw a centerline with an eccentricity of 13±0.1mm at both ends. At the two ends, draw another center line with eccentricity of 13±0.1mm, see (Figure 4), (Figure 5). Accurately drill 4 3mm center holes in 4 eccentric centers.

Figure 4 Figure 53

The outer circle of Φ60 0 -0.1 mm is clamped with a parallel clamp and clamped between the centers of the two crankshafts. The outer diameters of the crankshafts of the rough and fine cars are Φ28-0.010 -0.035 mm×40mm, and Φ20 -0.010 -0.018mm×30 +0.1 0mm.

Note the processing of the final note R1. (Figure 6)

Figure 6

4. Use a parallel clamp to clamp the outer circle of Φ60 0 -0.1 mm, clamp the workpiece between the center holes of the two bearing journals, and install the support screws in the middle groove of the machined crankshaft to increase the rigidity of the crankshaft; when using the supporting screws, , to ensure that the screw has enough support to prevent the screw from throwing. More attention should be paid to the prevention of excessive support force and deformation of the crankshaft. Rough car Φ30mm×74mm, control the middle wall thickness 8mm and chamfer 45° and length. (Figure 7)

Figure 7

5. Turn the head: clamp the outer circle of Φ30mm with parallel clamps, and clamp the workpiece between the center centers of the two bearing journals. Coarse and fine cars Φ25 0-0.05 mm×29mm and Φ20mm-0.010-0.018×25mm are required and inverted. Angle 1 × 45 °, control the thickness of the intermediate wall 8mm and chamfer 45 ° and length. (Figure 8)

Figure 8

6. Turn the head: clamp the outer circle of Φ20 mm with a parallel clamp, and clamp the workpiece between the center centers of the two bearing journals. Thick and fine cars Φ28 0 -0.05 mm×75mm and Φ20mm-0.010 -0.018×71mm and taper 1: 5 to size requirements, control the thickness of the intermediate wall 8mm and chamfer 1 × 45 °. (Figure 9)

Figure 9

At this point, the processing process has been basically completed, chapped after deburring for inspection.

Fourth, the inspection method

1, using two top methods (see Figure 10), the dial indicator is installed on the knife holder, the contact of the dial indicator refers to the fine wheel Φ60 ± 0.1 of the outer circle, the crankshaft for a small amount of rotation up and down, At the highest point, the dial indicator is set to zero, and then the dial indicator contacts at the lowest point of the outer circle of Φ60±0.1. The crankshaft is rotated in a small amount and read at the lowest point. The highest number-lowest number = actual eccentricity. Use the same method to take the actual eccentricity in two places respectively. The average of the two values ​​is the eccentricity of the workpiece. However, this method is only suitable if the eccentricity is smaller than the measurable range of the dial indicator. For the larger eccentricity (such as eccentricity of 26 in this example), the following method should be adopted.

Figure 10

2, still using two top methods (see Figure 11), the dial indicator is installed on a high-end vernier, a high-scale vernier on the small skateboard has been removed from the knife holder, the contact indicator of the dial indicator has been fine On the outer circle of the car Φ60±0.1, a full-scale reading was made using a high-size vernier, and a micrometer was taken from the dial indicator. The reading at the highest point and the lowest point was subtracted to find the eccentricity. Block eccentricity can also be used to determine the eccentricity, the rest can be according to the above method.

Figure 11

3, the parallelism measurement (Figure 12), the workpiece at both ends of the shaft properly placed on a special inspection tool, and then in the vertical and horizontal four different positions to check the crankshaft axis parallel to the axis of both ends of the axis, the average The error should be less than the 0.05mm tolerance specified on the drawings.

Figure 12

During turning, the workpiece is first driven to the required diameter and length, and the two ends are flattened. The eccentric part can then be turned by inserting a washer of the appropriate shape and thickness on one or both jaws of the three-jaw chuck. The shape and thickness of the gasket can be selected according to the size of the eccentricity. Because of the different shapes of the gaskets, the thickness of the gasket is also calculated differently. 1. Calculation of square spacer thickness: For eccentric workpieces with small eccentricity (e ≤ 5 ~ 6mm), square spacers can be used as shown in Fig.13.

Figure 13

The gasket thickness can be calculated using the following approximate formula:

X = 1.5e(1-e/2d)

In the formula: X-gasket thickness (mm)

E—eccentricity of eccentric workpiece (mm)

d—The diameter (mm) of the clamped portion of the eccentric workpiece.

The eccentric clamping jaw shown in the figure has a diameter of 60 mm and an eccentricity of 4 mm. The spacer thickness is:

X = 1.5×4 ( 1-1/2*60) = 6×0.9917 = 5.95 (mm)

2, the calculation of the sector gasket thickness

When turning workpieces with large eccentricity (e>6mm), fan-shaped spacers can be applied as shown in Fig.14.

Figure 14

The thickness of the sector shim can be calculated using the following approximate formula:

X = 1.5e ( 1 + e/2d+6e)

Such as an eccentric workpiece diameter of 36mm, eccentricity of 10mm, the thickness of its fan-shaped gasket:

X = 1.5 × 10 × (1 + 10/2*36+6*10 ) = 16.14 (mm)

3, gasket thickness correction

Since the calculated thickness of the gasket is only an approximate value, the accuracy of the three-jaw chuck, the hardness and strength of the gasket material also affect the eccentricity; and in practice, the use of the calculated thickness of the gasket Eccentric parts are often larger than the required eccentricity, which requires the use of test methods to correct the gasket thickness. Generally, an eccentric workpiece is first turned according to the calculated thickness of the spacer, and then the eccentricity of the workpiece is checked, the eccentricity error value is measured, and the thickness of the spacer is properly corrected until a part with a qualified eccentricity is machined.

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