In the scientific research and production practice, we have encountered a variety of components similar to those shown in the drawing, the end cover 2 and the housing 5 (material ZL105), and the two sliding bearings 6 are respectively assembled with the end cover 2 and the housing 5, The end cover 2 and the housing 5 are positioned by the positioning pin 1, and the end cover 2 and the housing 5 are fixedly coupled by the screw 3 washer 4. It is required to ensure that the inner holes of the two sliding bearings 6 are coaxial with the reference hole A after assembly. The degree is φ0.02 mm, the cylindricity of the two holes is 0.006 mm, and the surface roughness value Ra = 0.8 μm.
The material of the sliding bearing 6 is graphite M233H. This material is a non-metallic material which is pressed by powder. It is brittle and has low hardness. It is easy to have defects such as chipping, slag, cracking during processing; end cover 2 and housing 5 After the combination, the φ14.5H7 hole depth is 170mm, and it is required to ensure the coaxiality φ0.02mm and the cylindricity 0.006mm to the reference surface A at the same time. This requires high turning tools and machine tools, and is difficult to turn.
1. Comparison of process plans
(1) Process plan one
First, the end cap 2 and the sliding bearing 6, the housing 5, and the sliding bearing 6 are respectively assembled by an interference fit, and then two φ 14.5H7 holes are separately processed.
In this process scheme, the size and cylindricity requirements of the φ 14.5H7 hole are easy to guarantee, and the requirements for turning tools and machining are not high. The tool does not need to be overhanging very long, and the tool bar is rigid, but it is twice loaded. The clips are aligned separately, and the coaxiality φ 0.02 mm of the reference A cannot be guaranteed.
(2) Process plan 2
The end cover 2 and the housing 5 are positioned by the positioning pin 1, and the end cover 2 and the housing 5 are fixedly coupled by the screw 3 and the washer 4, so that the positioning can be positioned once, the reference hole A can be aligned, and the turning processing can be performed. Hole φ 14.5H7 and end face.
In this process scheme, the housing 5 and the locating pin 1 are interference fits, and the end cap 2 and the locating pin 1 are clearance fits, thus avoiding double clamping and direct machining directly. However, due to the hole depth of 170mm, special special lengthening arbor is required. The tool overhangs too long and the hole is small during processing. The rigidity of the shank is poor. It is easy to generate vibration during turning, which makes the inner hole of φ 14.5H7 taper and cylindricity. It cannot be guaranteed and also affects the surface roughness of the workpiece. If the inner hole is remedied by grinding, the processing of the grinding sleeve is difficult.
Can you find a way to locate the clamping at one time and the tool without overhanging too long? To this end, we combine the advantages and disadvantages of the first and second options, and come up with a combined processing method to effectively solve the above processing problems.
(3) Process plan three
é•— soft claw clamping end cover 2, firstly cut the left end sliding bearing 6 hole and its end face, under the premise of not removing the end cover 2 on the lathe, the end cover 2 and the housing 5 are positioned by the positioning pin 1, and then The end cover 2 and the housing 5 are fixedly coupled by the screw 3 and the washer 4, and the right end hole and the reference hole are machined.
In this process scheme, the positioning and alignment of the clamping is achieved once, and the cumulative error caused by the two clamping and alignment is avoided, because the two holes are separately processed, and only the saddle of the machine tool is moved, the tool does not need to be suspended. Stretched too long, the shank is rigid and the cylindricity is easy to guarantee.
2. Preparation of processing technology
Based on the advantages of the third scheme, the processing of the part is arranged as follows: In the drawing, the thick solid lines indicate the parts to be processed in the assembly, and the two φ 14.5H7 holes and the φ 62H8 holes have a radial one-sided margin of 0.3. Mm, the end faces to be machined have a margin of 0.2mm, and all other dimensions are machined into place in a single part. The key process is the finishing process during combined machining. For this reason, we choose high-precision turning machine according to the brittle and soft material of the material. The tool is made of hard alloy YG8, which has good wear resistance and can effectively Improve the surface quality of the workpiece; tool geometry: 10° for the front angle, 15° for the back angle, R1mm for the tool nose radius; cutting parameters: cutting speed 350~480m/min, feed rate 0.06~0.1mm/r. The selection of cutting tools and cutting parameters can effectively prevent the occurrence of defects such as chipping and slag, and can effectively ensure the requirements of deep hole cylindricity 0.006mm and end face flatness 0.006mm.
The key process is as follows: firstly, the end cover 2, the sliding bearing 6 and the housing 5, and the sliding bearing 6 are assembled by an interference fit; the soft jaws are clamped to the end cover 2, and the front end face B and the outer C face are beaten. Within 0.01mm, the inner end of the left end of the sliding bearing 6 and its end face; without removing the end cover 2, the housing 5 and the positioning pin 1 are firstly interference fit, and the positioning pin 1 is further spaced from the end cover 2 Cooperate, fixedly coupled by the screw 3 washer 4, turning the inner hole of the right end sliding bearing 6 and its end face and the reference hole φ62H8 and its end face. Small cutting and multiple feeds can be used for turning to ensure the requirements of the drawings. After processing, according to the design requirements, the screw 3 and the washer 4 coupling can be removed, and the components formed by the end cover 2 and the housing 5 are paired and marked, and stored in pairs.
3. Processing verification
A batch of parts processed by the scheme prepared by the scheme 3 is tested by a three-coordinate measuring instrument, and the qualification rate of the dimensional and geometrical tolerances is 97%. After analysis, some of the unqualified parts are the looseness of the graphite bearing material of the sliding bearing 6 itself. Some, the shape tolerance is out of tolerance. The assembly formed by the end cap 2, the sliding bearing 6 and the housing 5, the sliding bearing 6, and the positioning pin 1 are paired and stored, and the coaxiality φ 0.02 mm cannot be measured because it is a positioning and positioning process. At the time of assembly, the inner holes φ14.5H7 of the two sliding bearings 6 are both ends mounted on the same long shaft, and can be finely adjusted by the gap between the end cover 2 and the positioning pin 1, and have no influence on the assembly. Other components like this one in our unit are also processed in this combination, with good processing quality and efficiency, and can meet the assembly requirements of the design.
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