When the eccentric shaft is turned on the three-jaw chuck (only the eccentric gasket is used instead of the auxiliary tool such as the jacket), the eccentricity tolerance is high. In the actual processing, the thickness of the eccentric gasket needs to be adjusted based on the measured actual value, not only It takes a long time, and its position accuracy is difficult to guarantee. The eccentric shaft of the vehicle is now reversed, which is both accurate and quick. For ease of description, this article takes the two different machining processes of the eccentric shaft shown in Fig. 1 as an example to describe in detail the processes and their sequence in the two process processes so as to facilitate understanding and analysis. prototype machined parts
1. Traditional process
The principle of traditional craftsmanship is that the benchmark is first. For example, the traditional eccentric shaft technology plan is to machine the center hole at both ends first, and then install the workpieces at the two tops. Then, after machining the reference outer circle, correct the machining eccentricity.
The traditional process method is generally only suitable for one-piece stock preparation. The processing steps are as follows: (1) Check whether the billet size meets the requirements of the drawings. prototype machined parts
2 At least one third of the clamping blanks are long and round, with a moderate extension, a flat end face, and an outer circle of the car. Because the surface of the blank can only be used once as a coarse reference, this step provides a fine reference for the next process. About 3 to 5 mm from the claw, the outer circle is left with a moderate margin and then hit the center hole. 3 Turn around at least one-third of the length of the outer circle, take the total length to the size and hit the center hole. 4 two top clips, except the outer circle of the eccentric outer circle to the size of the car (guaranteed coaxiality), the eccentric outer circle machining to its basic size plus twice the eccentricity plus 2mm. (5) Eccentric gaskets and copper skins are to be calibrated to correct eccentric eccentricity of the outer rear car to chamfering of the size (including the value of the straightness and eccentricity of the outer round busbars). 6 Machining the remaining elements (such as threads). 7 Check the processing elements and remove them. prototype machined parts . prototype machined parts
2. Reverse process
Different from the traditional process, the reverse process method adopts the following technological scheme: first machining the main surface and then processing the reference surface. Contrary to the traditional process, it is called the reverse process. The following describes the process steps when the reverse processing method is used to process the preparation of a single piece and a component as a whole.
The process steps when processing a single piece using the reverse process method are as follows:
(1) Check whether the billet size meets the requirements of the drawings.
(2) Grinding blanks are about 30mm long and the outer circle of the blanks is about 3 to 5mm away from the claws, and the outer circle is left at 1.5~2mm. This step provides the fine reference needed for the clamping process in the next process. To ensure the positioning stability of the workpiece in the machining process, there is no car end face; in order to reduce the effect of radial forces, the outer circle with less radial force is used. Turning.
(3) U-turn and holding the fine reference outer circle (thread outer circle part), according to the drawing ratio not less than one-third of the total length of the workpiece, flat end face, and then the small outer circle of the eccentric outer left end face The length of the car to the size, the outer circle left 2mm left and right margins (to reduce car eccentric eccentric cutting allowance). prototype machined parts
(4) The workpiece is not re-turned, and the eccentric gasket and copper skin are added to prepare the eccentricity of the machining. The precision reference outer circle (screw outer circle part) is clamped and turned, and the drawing ratio is not less than three-thirds of the total length of the workpiece. First, after correcting eccentricity (coarse correction), vehicle eccentricity and length to size requirements, and chamfer deburring (including the straightness and eccentricity of the outer busbar).
(5) The workpiece does not turn around, remove the eccentric gasket and clamp it again, and make a fine reference outer circle (thread outer circle part) of a circle of copper skin, and reversely measure the reference center hole for measuring the eccentricity. The specific process is: appropriately increase or decrease the thickness of the copper skin, use the dial indicator to correct the eccentricity to the left and right clamping, correct again, ensure the eccentricity and straightness of the eccentric part of the busbar (precision correction) to play the center hole to the size. If the tailstock and the tip are of high accuracy and reliability, then the rest of the elements that need to be machined can be machined against the center hole. Otherwise, the coaxiality between the outer circle and the center hole reference cannot be ensured. The cutting amount during processing can be appropriately improved. Consider the direction of efficiency. prototype machined parts
(6) To process the remaining elements to their dimensional accuracy requirements, it shall be ensured that the outer circle is first machined, the other elements are processed afterwards, and finally the chamfer is deburred and the inspection is removed.
(7) U-turn the large cylindrical surface, take the total length, use the dial indicator to correct the reference surface and then hit the center hole.
(8) Process remaining elements such as threads to dimensions.
(9) Remove the inspection after checking the processing elements.
When the components are processed by the reverse process, the schematic diagram of the eccentric shaft is shown in Fig. 2. The process steps are as follows:
(1) Check whether the billet size meets the drawing processing requirements, and calculate whether the component cutting allowance and the remaining amount of the car flat end face left after cutting off satisfy the processing requirements.
(2) Clamping blanks protrude approximately 30-50mm long outer circle, the flat face of the car hits the center hole, and then clips a top to clamp the whole material, the car is blank and the outer circle is round, the outer circle is turned as long as possible, and the outer circle is set aside. 1.5 ~ 2mm margin.
(3) U-turn clamping of the finished fine reference outer circle, extending the outer circle of about 30-50mm, flat end face can be, and then the small outer circle on the left side of the eccentric outer car to the length dimension. Under normal circumstances, the outer circle of the feed direction is preferentially machined so that its diameter does not touch the eccentric outer circle of the vehicle. In contrast, when the vehicle is eccentric, the aperture needs to be large, and it is inconvenient to prevent the secondary eccentricity and chamfering from being deburred.
(4) The workpiece is not re-turned and the eccentric gasket and copper skin are added to prepare the eccentricity of the machine. The fine-circled outer circle (threaded outer circle portion) of the machined turning is fine. After eccentricity (coarse correction), eccentric eccentricity of the car and length to size, and chamfer deburring (including values of linearity and eccentricity of the outer bus bar).
(5) The workpiece does not turn around, remove the eccentric gasket, and then clamp the fine reference circle (the outer circle of the assembly) with a circle of copper skin, and the extension length is between 150-155mm (ie the length of the workpiece to be processed plus The width of one cutting blade plus the retracting amount of 2 to 3 mm) reverses the reference center hole for measuring the eccentricity. The specific approach is: appropriately increase or decrease the thickness of the copper skin, correct the eccentricity of the dial indicator to the left and right clamp, correct again, ensure the straightness of the eccentricity and the eccentric part of the bus (precision correction), hit the center hole to the size requirements, the workpiece After moving to the top, the remaining machinable elements are machined to their dimensional accuracy requirements. Should ensure that the first processing of the outer circle, after the processing of grooves, threads, etc. can be processed on the remaining surface, the final chamfer deburr, cut off the test (total length left a little margin).
(6) The surface of the large outer circle of the cut copper piece is clamped and the total length is taken. The center hole is drilled after the dial indicator corrects the outer circle surface. prototype machined parts
The position and size of the eccentricity on the cylindrical part are different. Therefore, the developed process plan should be optimized according to the actual situation. The principle of the chemical process selection is: 1 When the eccentricity is located at or close to the axial end of the workpiece, the eccentric process plan is used to preferentially process the eccentricity. . 2 When the eccentricity is located at or near the center of a long workpiece, the traditional process scheme is preferentially used to process the eccentricity, and eccentricity may also be performed by using a reverse process method. However, as the workpiece is longer and the fixture and correction are inconvenient, the two-point method is used as far as possible. . 3 When eccentric or end eccentric machining, correct processing according to the conventional scheme. prototype machined parts
3. Conclusion
The reverse process method is contrary to the principle of processing preceded by the benchmark, and adopts the process method of the post-processing reference for vehicle eccentricity. Especially in the process scheme adopted for component preparation, the center hole is machined and the entire part is processed. Compared with the two process methods, the traditional process is relatively easy to accept, but due to the use of two top, the top of the front of the car, the assembly and disassembly of the heart chuck, splitting chucks and other methods, the time is relatively more, the quality of machining eccentricity by the machine precision The influence of processing techniques is difficult to guarantee. The reverse process method not only saves time and effort, but also guarantees the quality of eccentric machining, and reduces the process of correcting the eccentricity to the eccentric eccentric turning. This not only eliminates the machining error caused by the operation method, but also eliminates the factors such as machine tool errors. Eccentricity error makes its processing quality stable and reliable. prototype machined parts