Design of special tooling for processing the hotte

Design of special tooling for vertical screw hole machining

in the process of machining and maintenance, we often encounter workpieces that process vertical screw holes on cylinders. As shown in Figure 1: for batch processing of 1000 sets of trapezoidal nuts, the processing difficulty is that the symmetry of the axis of the vertical screw hole to the outer circle of the workpiece is not more than 0.05 mm, the perpendicularity is not more than 0.05 mm, and the size is not more than 0.05 mm away from the end of the workpiece. The tolerance requirements are high geometric tolerance accuracy requirements of ± 0.05 mm. The conventional processing method of this kind of workpiece is to first process the excircle, and then use the four jaw chuck to find the axis of the screw hole on the lathe by marking, and then process the thread. Obviously, this kind of alignment method is relatively difficult, especially the geometric tolerance accuracy requirements of various parts are relatively high, and it is difficult to achieve the required high geometric tolerance accuracy through scribing, especially in mass production, with low efficiency and high cost. Because the CNC lathe cannot. When the workpiece is processed by secondary clamping, there is also the accuracy error of repeated positioning of multiple clamping. In view of the above problems, the solution of using special tooling to process vertical screw holes is proposed

1. The design of tooling is shown in Figure 2. It is a special tooling for machining vertical screw holes with high geometric tolerance accuracy requirements. The technical core of the tooling is: on the basis of ensuring the geometric tolerance accuracy of the tooling base and V-shaped block, the V-shaped block locates the axis of the workpiece; The locating pin and tightening nut are used for axial positioning of the workpiece; Clamp the workpiece. So as to ensure the machining accuracy of the workpiece and improve the production efficiency

the machine has the following advantages:

(1) stably ensure the machining accuracy of the workpiece. The form and position tolerance accuracy of the vertical screw hole of the workpiece, and the position of the rigid workpiece relative to the tool and machine tool are guaranteed by the tooling

(2) it is convenient and fast to improve labor productivity. The operator does not need to correct the workpiece, which can significantly reduce the auxiliary working hours. After the workpiece is clamped in the tooling, the rigidity of the workpiece is improved, so the cutting amount can be increased and the labor productivity is improved

(3) reduce costs. The tooling can be used on ordinary lathes or economical CNC lathes without adding high-precision machine tools; In batch production, the larger the batch size of the workpiece, the more significant the economic benefits obtained

2. Manufacturing of tooling

the key components of the tooling are the V-shaped block and tooling base in Figure 2, and its manufacturing accuracy is the key to whether the tooling can meet the requirements of workpiece shape and position tolerance accuracy

(1) the manufacturing process of V-shaped block

is also a high-end machine. 3 is the part drawing of V-shaped block. The machining difficulty of this part is that the V-shaped surface with an included angle of 90 ° and φ 32 shape and position tolerance requirements between holes. Therefore, unconventional processing technology must be adopted

Figure 4 is the schematic diagram of V-block processing technology. On completion of V-block φ After finishing the 32 holes, bottom surface and two sides, fix the V-shaped block on the rotary workbench. The center hole of the rotary table and the V-shaped block must be used before φ 32 holes are accurately positioned, and the error must be within 0.005 mm. Install the rotary table on the 45 ° inclined iron, use the dial indicator to correct the parallelism between the inclined iron and the guide rail of the grinder table, then fix the inclined iron on the grinder table, then rotate the rotary table, use the dial indicator to correct the parallelism between the side of the V-block and the guide rail of the grinder table, and finally fix the rotary table, so that a V-shaped surface can be ground. After finishing the grinding work, rotate the rotary table 180 °, and use the dial indicator to correct the parallelism of the side of the V-block on the other side and the guide rail of the grinder table again. After fixing the rotary table, you can grind the v-surface on the other side

the above processing technology can ensure that the V-shaped surface of the V-shaped block with an included angle of 90 degrees and φ 32 shape and position tolerance requirements between holes

(2) manufacturing requirements of tooling base

Figure 5 is the part drawing of tooling base. The manufacturing of tooling base can adopt conventional processing technology. But it should be emphasized: φ 32 boss and

φ The plane and outer circle of 170 and the outer circle of Mohs No. 6 taper must meet the requirements of coaxiality

(3) installation of tooling

the installation of this tooling is a conventional process. However, after installation, you must φ Take the flatness of L70 as the benchmark to detect the parallelism of V-shaped block items. If the error exceeds 0.005mm, it must be reinstalled

3. Clamping and calibration of tooling

Figure 6 is the schematic diagram of clamping and calibration of tooling. First, remove the chuck on the lathe, clamp the excircle of the tooling Mohs No. 6 taper to the taper hole half of the earth shaft of the lathe with standard accuracy, and fix the tooling on the earth shaft with M20 pull rod. Rotate the soil shaft dynamically and check the dial indicator positions 1 and 2, and the runout reading should be within 0.005 mm. Then move the middle carriage of the lathe, fine tune the rotating spindle, and correct the side of the V-shaped block at the position 3 of the dial indicator. After confirming that the runout reading of the dial indicator is within the range of 0.01 113113, do not rotate the spindle slowly. Move the middle carriage of the lathe, check the V-shaped surface of the V-shaped block at the position 4 and 5 of the dial indicator, and its runout reading is within the range of 0.01 113113. Finally, rotate the spindle 180 °, calibrate the other side of the V-shaped block at the position 3 of the dial indicator again, and repeatedly check the V-shaped surface of the V-shaped block at the positions 4 and 5 of the dial indicator. If it is found that its runout reading exceeds the range of 0.01131113, the tooling must be reworked

after completing the calibration and verification of tooling, install the standard bar into the V-shaped block φ 22 hole. Adjust the adjustable locating pin (see Figure 2), measure with the measuring block, and make its end point to the V-shaped block φ The distance between the center lines of 22 holes is 40+0.01mm

finally, install fixtures and workpieces and conduct commissioning

4. Machining accuracy analysis of workpiece

(1) workpiece T20 × 4-6h vertical screw hole axis pair φ 35. The symmetry of the outer circle is required to be 0.05 mm, and the perpendicularity is required to be 0.05 mm. The cumulative error of the tooling is as follows:

① positioning error Δ D。 The V-shaped block has alignment, which can make the positioning datum of the workpiece always lie in the symmetrical plane of the V-shaped block. Because the cylindricity of the workpiece is required to be 0.01 mm, and its maximum eccentricity error is 0.005 mm, the maximum

positioning error of the workpiece to the tooling is 0.005 mm

② tooling depends on how customers say manufacturing errors Δ J。 Curved limit face of tooling V-block φ 32. The allowable error of the symmetry of the positioning hole is 0.005mm; φ 32 locating hole and tooling base φ The maximum machining error of 32 boss is the same as 0.01mm. Therefore, the cumulative maximum error of tooling manufacturing is 0.025 mm

③ installation error of tooling Δ A。 The maximum installation error of the tooling is limited to 0.01mm

④ machining error Δ G。 The machining error of the lathe, such as the error between the fixture datum installed on the lathe spindle and the rotation axis of the earth shaft, the radial runout of the spindle, the parallelism or verticality between the feeding direction of the lathe carriage and the spindle axis, etc. Its size depends on the manufacturing accuracy of the machine tool, the overhang length of the fixture and the centrifugal force. Therefore, it is necessary to regularly check the temperature and vibration of the electromechanical system and the size of the internal wires

integrate the above positioning errors Δ D. Tooling manufacturing error Ⅳ, tooling installation error m, processing error Δ G. The cumulative maximum error σ of the tooling fixture can be obtained Δ：

accuracy reserve jc= (0.05-0.032) =0.01 8mm

(2) workpiece T20 × 4-6h dimension of the distance between the axis of the vertical screw hole and the end face of the workpiece. It is required to be 40 ± 0.05 mm, and the cumulative error of tooling is as follows:

① positioning error Δ D。 Since the standard bar is used to install the V-block φ 22. Measure with a measuring block, adjust the adjustable locating pin, and make its end point to the V-shaped block φ The distance between the center lines of 22 holes is 40 ± 0.0 1mm, so the maximum positioning error of the workpiece for assembly under working conditions should be 0.01mm

② tooling manufacturing error Ⅳ. Tooling V-block φ 22 hole pairs φ 32. The maximum error of the cylindricity of the positioning hole is 0.005 mm; φ The maximum machining error of 32 locating hole and 32 boss of tooling base is 0.005 mm, that is, the maximum error of shaft hole is 0.01mm; work clothes φ The maximum machining error of 170 excircle for Lu 32 boss is also 0.01mm. Therefore, the cumulative maximum error of tooling manufacturing is 0.025 mm

③ installation error of tooling Δ A。 Limit the maximum installation error of tooling to 0.01 mm

④ machining error Δ G。 Similarly: Δ G=0.05/3=0.016mm

integrate the above positioning error Δ D. Tooling manufacturing error Ⅳ. Tooling installation error Δ A. Machining error Δ G. The cumulative maximum error σ of the tooling fixture can be obtained Δ：

accuracy reserve jc= (0.05-0.033) =0.017 mm

according to the above analysis, the processing method of this workpiece is desirable

5. Test run workpiece measurement

after testing three workpieces, a T20 with a length of 50mm was made × 4-6g standard bolts are used as calibration rods. Install the calibration rods on the workpieces one by one, and measure the size by the projector. As shown in Table 1

the test results of the commissioning workpiece show that the T20 of the workpiece processed on the tooling × 4-6h vertical screw hole axis pair φ 35 the symmetry of the outer circle is not more than 0.028mm, the verticality is not more than 0.035mm, and the maximum error of the distance between the vertical screw hole and the end is ± 0.037 mm, which fully meets the machining accuracy requirements of the workpiece

6. Conclusion

the special device of this design has been applied in batch production. The practical application shows that the device has stable accuracy and can meet the machining requirements of high-precision parts; The use of this device greatly reduces the auxiliary time required for processing workpieces, effectively improves the processing efficiency of parts, reduces costs, and achieves good economic benefits