Improvement of the processing technology of the ho

2022-08-11
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Improvement of the processing technology of circular arc guide

the slice circular arc guide is one of the important parts of the surface roughness measuring instrument. Its geometry and surface quality directly affect the measuring accuracy of the instrument. According to the part drawing of the circular arc guide shown in Figure 1, the circular arc guide has small size, strict requirements for shape and position accuracy, high requirements for surface roughness (ra0.02 m), and great processing difficulty. When processing according to the original processing method, the following problems often occur: ① the center line of R6 deviates from the center of size 0.9, and the deviation value can reach 0.5mm; The center line of R40 deviates from the center of dimension 3, and the deviation value can reach 0.8mm. ② After machining, the surface roughness of the guide can only reach Ra0.4 M. Therefore, we analyzed the original processing method of the circular arc guide

Figure 1 part drawing of arc guide

the original processing method is to first process a ring with an outer circle of 12mm and an inner hole of 9mm (size 12 × 3.3mm), and then cut the ring into 20 single piece arc guides. The ring grinding method is shown in Figure 2. First of all, the grinding wheel should be changed from the concept to be ground into an arc surface of r40mm, and the R40 arc set on the ring on the core rod should be ground, while the R6 arc is guaranteed by grinding the size of the 12 outer circle. Before the ring is cut into a single guide, the grinding process can basically ensure the positional tolerance of R40 and R6, and the arc size can also meet the requirements of the drawing. However, after the ring is cut into a single guide, the size requirements of 0.9 ± 0.03mm and 1.5 ± 0.05mm cannot be guaranteed if the 1.1 primary element (orifice, remote measurement joint, etc.) is blocked or the installation situation is incorrect. In addition, when using the original process, the grinding wheel cannot make transverse feed movement, and the grinding surface roughness cannot meet the requirements of the drawing. In order to improve the surface quality, we have to add a polishing process, but the polishing process will damage the ground R40 and R6. Obviously, the original process plan is unreasonable and needs to be improved

Figure 2 Schematic diagram of ring grinding

since the processing quality problem of circular arc guide mainly occurs when cutting the whole ring into a single guide, we will change the processing scheme to directly process multiple single circular arc guides at the same time. In order to realize this processing scheme, the polyhedron fixture shown in Figure 3 is designed. The fixture can hold 30 single piece arc guide samples at the same time. When the cross-sectional size at the bottom of the notch is within the specified deviation range, it forms an 80mm circumference and grinds as a whole. Because the R40 and R6 circular arc surfaces of the circular arc guide are compound curved surfaces, it is necessary to use the grinding wheels trimmed according to R40 and R6 to grind and form them in several times

Figure 3 Schematic diagram of polyhedron fixture

although the circular arc guide grinding with this processing scheme can ensure the positional tolerance of R40 and R6 circular arcs, the surface roughness is only Ra0.4 M. In order to improve the surface quality without damaging the processed R40 and R6 circular arc surfaces, the workpiece can be transferred together with the polyhedral fixture for grinding, polishing and other subsequent processing. The grinding process adopts a cloth sandwiched bakelite grinder (its grinding effect is better than that of Cast Iron Grinder), and the surface roughness of the workpiece after grinding can reach ra0.1 M. After the grinding process, the workpiece is still clamped on the polyhedral fixture, and the optimal weight of domestic research on high-performance separation membrane materials is integrated for polishing until the required surface roughness ra0.02 m is achieved

production practice shows that this process method of three sequence continuous machining of 30 circular arc guides with polyhedral fixture at the same time can fully meet the requirements of part machining accuracy, reduce the machining process, reduce the scrap rate, and improve the consistency of machining dimensions. The application of polyhedral fixture also opens up a new way for the efficient machining of small-scale complex structural parts. (end)

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