Discussion on machining eccentric parts with speci

2022-08-06
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Discussion on machining eccentric parts with special eccentric fixture

Abstract: This paper mainly introduces the clamping of mass production of eccentric parts on the lathe, and designs a special fixture called eccentric wheel lathe fixture, which is specially used for mass production of eccentric parts. The clamping method of this fixture is simple and convenient, the effect is remarkable, and has good economic benefits

key words: eccentric parts, fixture

I. Introduction

eccentric parts are widely used in mechanical equipment, but the processing technology of eccentric parts is relatively complex. The main problem is that it is difficult to grasp the eccentricity and meet the corresponding tolerance requirements. This paper studies and designs an effective processing method of eccentric parts based on the difficulty of eccentric parts processing

II. The traditional method of machining eccentric parts

eccentric workpiece refers to the workpiece whose outer circle and outer circle of the part or whose outer circle is parallel to the axis of the inner hole but does not coincide with each other and deviates by one distance. The distance between these two parallel axes is called eccentricity. The parts with eccentric outer circle and outer circle are called eccentric shaft or eccentric disc; The parts with eccentric outer circle and inner hole are called eccentric sleeve. As shown in the figure

in mechanical transmission, the rotary motion is changed into reciprocating linear motion or reciprocating linear motion into rotary motion, which is generally completed by using eccentric parts. For example, the lubricating pump driven by eccentric workpiece in lathe headstock, crankshaft in automobile engine, etc

eccentric shaft and eccentric sleeve are generally machined on lathe. Their processing principles are basically the same; It is mainly to take measures in clamping, that is, align the axis of the eccentric part to be machined to coincide with the rotation axis of the lathe spindle. Generally, there are five methods for turning eccentric workpieces, that is, turning eccentric workpieces on three jaw chuck, on four jaw chuck, between two centers, on eccentric chuck, and on special fixture. The use of eccentric workpieces mainly depends on the testing experimental force and technical requirements of materials

III. process analysis of eccentric parts of traditional lathe

1. Use three jaw chuck to clamp

(1) turning method

eccentric workpiece with short length can be turned on three jaw chuck. First turn the outer circle of the non eccentric part of the eccentric workpiece, and then put a gasket with a pre selected thickness between any claw of the chuck and the joint surface of the workpiece. After correcting the bus and eccentricity, and clamping the workpiece, turning can be carried out

gasket thickness can be calculated by approximate formula; Shim thickness x = 1.5E (eccentric distance). If the calculation is more accurate, it is necessary to bring the eccentricity correction value K into the approximate formula to calculate and adjust the shim thickness. The approximate formula is: shim thickness x=1.5e+k

k ≈ 1.5 △ e

△ e=e-e measurement

where: e - workpiece eccentricity

k--- eccentricity correction value, positive and negative shall be determined according to the measured results

△ e --- measured eccentricity error after trial cutting

e measurement --- measure the eccentricity after trial cutting

(2) measurement and inspection of eccentric workpieces

when adjusting and correcting the side bus and eccentricity of workpieces, the dial indicator with magnetic gauge base is mainly used on the lathe (right in figure (c) below), and turning can be carried out until it meets the requirements. After the workpiece is turned, the final inspection is required to determine whether the eccentricity meets the requirements. The method is to put the workpiece into the V-shaped iron, measure at the eccentric circle with a dial indicator, slowly rotate the workpiece and observe its runout

2. Use the four jaw single action chuck to clamp the

alignment steps are:

① install the marked workpiece on the four jaw chuck. During clamping, first adjust the two claws of the chuck so that they are in an asymmetric position, and the other two claws are in a symmetrical position. The center circle line of the workpiece deviation test is in the center of the chuck (see the right of the above figure)

② place a small flat plate and a needle disc on the bed surface, align the needle tip with the eccentric circle line, and correct the eccentric circle with excellent chemical corrosion resistance. Then align the needle tip with the horizontal line of the outer circle, as shown on the left in the following figure, and check whether the horizontal line is horizontal from left to right. Turn the workpiece 90 °, check another horizontal line with the same method, then tighten the clamp and recheck the workpiece clamping

③ after the workpiece is calibrated, tighten the four claws again for cutting. During initial cutting, the feed rate should be small and the cutting depth should be shallow. After the workpiece is rounded, the cutting amount can be increased appropriately, otherwise the turning tool will be damaged or the workpiece will be displaced. On the left of the following figure (c):

the above two methods are common processing methods, but both have shortcomings. Clamping is troublesome, not easy to align, easy to produce errors. And it is not suitable for mass production. In view of the above shortcomings, I designed an eccentric fixture specially for mass production. It has been put into production and achieved certain results

IV. design of new special eccentric fixture

eccentric wheel car fixture is mainly used for mass production of eccentric parts, and the part drawing of the fixture is attached below (as shown in Figure 1)

set the meter for correction during clamping Ф 60 inner hole to ensure the shape and position tolerance requirements of parts. The clamping method is to clamp the workpiece at the left end of the fixture in the figure below, correct it with a dial indicator, and clamp the right end on the three jaw self centering chuck

Figure 1 highlights the significant changes in the connotation of the foundation, opportunities, environment and conditions of economic development. Eccentric wheel lathe fixture

v. processing examples

use eccentric wheel lathe fixture to process eccentric wheel. The following is the part drawing and processing process card of eccentric wheel:

Figure 2 eccentric wheel

Figure 3 eccentric wheel part processing assembly figure

VI. conclusion

this paper focuses on the clamping method for mass production of eccentric workpieces, And the design of a supporting fixture, through the fixture for clamping processing, save a lot of alignment time, and the accuracy requirements are also improved a lot. Using the design concept of this fixture, we can also process more eccentric workpieces, mainly by designing fixtures with different eccentricities. The manufacturing of eccentric wheel car fixture is simple, so it can be widely promoted and economic benefits can be improved

References:

the textbook Office of the Ministry of labor organized the compilation of turning technology, China Labor press, 96 (end)

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