Selection of eccentric shaft counterweight

Because of the asymmetry of the shape of the eccentric shaft, it will inevitably cause unbalance during processing, so the first problem to be solved before processing the eccentric shaft is the counterweight. Selecting the appropriate counterweight can make the transmission of the workpiece stable during processing, thus meeting the processing accuracy of the product.

There are three common methods of counterweight. One is to leave a collet on the workpiece and connect the special counterweight with the reserved collet by means of keys and pins. The advantages of this connection method are high assembly accuracy, no relative movement between the workpiece and counterweight, and the disadvantages are high manufacturing costs, and special site and personnel are required for installation during the installation process. The second is to directly carry out the counterweight on the workpiece. The counterweight and the workpiece are fastened on the workpiece by clamping. The advantages are simple installation, low production cost, no need to process various auxiliary keyways and pin holes on the workpiece before installation, and the disadvantages are that the counterweight and the workpiece are easy to move relative during the processing, which affects the processing accuracy of the product. The third method is chuck counterweight, which is simple but not accurate. Because the grinder has no chuck, this counterweight method cannot be applied to the grinder.

The above three common methods have their own advantages and disadvantages. According to the structural characteristics of the eccentric shaft, a set of new tooling with large clamping force, natural indexing and simple counterweight adjustment has been designed. Its design principle is: (1) ∑ T=0. By adjusting the left and right counterweights, the workpiece can rotate smoothly in the eccentric cylindrical machining process, and the machining difficulty caused by the workpiece eccentricity can be solved. (2) The principle of improving the machining accuracy of the workpiece. (3) The principle of increasing clamping force, reducing machining difficulty and improving machining efficiency. (4) The principle of reducing processing procedures.

This new set of tooling is mainly composed of five parts - counterweight, three-jaw self-centering chuck, eccentric tailstock, indexing chuck and eccentric cushion block.

① The eccentric pad is fixed between the four-jaw single-acting chuck and the three-jaw self-centering chuck. Its function is to fix and adjust the eccentric position of the three-jaw self-centering chuck relative to the spindle axis. Considering the need of counterweight, the eccentric cushion block is designed as an axisymmetric part, weighing about 24kg.

② Indexing chuck This disc is fixed on the back of the centering chuck. After the workpiece is clamped, it will be integrated with the centering chuck and the workpiece. Its function is: when machining the eccentric circle again, the three-jaw self-centering chuck is positioned and the natural indexing is realized through the three-jaw slot.

Note: According to the assembly drawing, the maximum impact of eccentric spacer block and indexing chuck groove tolerance on the center deviation of three-jaw self-centering chuck is 0.10 mm. According to the function calculation, the maximum deviation angle from the center of gravity of the workpiece to the center of the spindle is 0.115 ° ≈ 6 ′ 52 ″, and the impact on the 50mm eccentricity is 0.00 001 mm. The maximum impact of the displacement relative to the 50mm eccentricity on the processing quality of the workpiece is equal to zero, which fully meets the processing requirements.

③ The eccentric tailstock eccentric hole is used in conjunction with the eccentric shaft outer circle, with a distance of 50mm as a central hole, and is used in conjunction with the tailstock center. When in use, tighten the fastening bolts, eliminate the fit clearance of the shaft hole, and control the eccentricity of 50mm within 0.05mm. Its function is: the tailstock accurately locates the axis position of the eccentric circle of the eccentric shaft, and adds a part of counterweight to the tail.

④ Counterweight weight: 12mm × 60mm × 160mm steel plate. It is connected under the eccentric cushion block by two M12 bolts, and the weight of counterweight is about 0.8kg, a total of 10. Its function is to balance the difference between the rotary moment generated by the eccentric shaft and the tooling during the processing.

Moment calculation The moment generated by the cushion block is:

T1=F? L=G1? L=24 × 90=2160(㎏?mm)=21.6N? m

Where, G1 - mass of eccentric cushion block

L -- the distance from the center of gravity of the cushion block to the center of the four-jaw single-acting chuck. The total torque generated by the indexing chuck, the three-jaw self-centering chuck, and the workpiece after rough turning is:

T2=F? L=G2? L=90 × 50=4500(kg?mm)=45N? m

Where: G2=p? V=(60 × two hundred and eighty-five × one hundred and thirty × 7.85)/100000=17.5(N)

Where, G2 --- total mass of indexing chuck, three-jaw self-centering chuck and workpiece after rough turning

The moment generated by eccentric tailstock is: T3=F? L=G3? L=17.5 × 40=700(kg?mm)=7(N?m)

Where G3 -- mass of eccentric tailstock

L -- distance from center to spindle center

Through torque calculation, we can see that the torque generated by indexing chuck, three-jaw self-centering chuck and workpiece after rough turning is 45N? m. However, the adjusting torque generated by eccentric cushion block and eccentric tailstock is only 2160+700=28.60N? m. The difference is 16.40N? m。 In order to balance the torque, the tooling solves this problem by adding counterweight.

Counterweight moment calculation: T4=n? F? L=n? G? L=10 × zero point eight × 200=16 (N? M) can basically achieve torque balance.

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