Machining Datum of choice examples
Figure 1 Lathe Feed Shaft Bracket
[HC Machinery Industrial Network] Guan Key Words: Example 1 Figure 1 shows the feed axis lathe parts rack, where they already know these processes are:
(1) liner; (2) coarse planing bottom and convex sets;
(3) coarse and fine boring 32H7 hole;
(4) drilling, expanding, hinge l6H9 hole.
Test selection and the process of positioning base a few degrees of freedom to determine the limit.
Solution: The first process crossed. When the blank is large, the method can be used both crossed to several non-processing area of the location of the face processing requirements. Choose not to process surface R22? Cylindrical and R15? Cylindrical coarse base, taking into account the non-processing of the plane and distance from the bottom 18? Requirements, draw the bottom and the boss of the processing line.
Second search process by being crossed, planing bottom, and Boss. The third process
32H7 coarse boring holes. Processing requests for the size of 32 ± 0.1?, 6 ± 0.1? And Boss K, parallel side of 0.03?. According to the principle of superposition benchmark selection and boss for the localization bottom base, the bottom limit of three degrees of freedom, two degrees of freedom restrictions boss, no benchmarks do not overlap error.
Drilling the fourth working procedure, expand, hinge 16H9 hole. In addition to precision hole itself, this process should ensure that the position required for the size of 4 ± 0.1?, 51 ± 0.1? And two holes in the parallel requirements of 0.02?. According to the principle of intensive benchmark selection, can have three different options:
(1) the bottom limit of three degrees of freedom, K surface limited to two degrees of freedom with two holes of this program a benchmark process unifying principle. Fixture is relatively simple. Design size 4 ± 0.1? Base overlap; size 51 ± 0.1? Processes benchmark hole 32H7 the center line, and positioning base is K surface localization size of 6 ± 0.1?, There is no overlap base error, its size is equal to 0.2? ; two holes parallel 0.02? also do not coincide base error, its size is equal to 0.03?. Can see, this program does not overlap error basis over the allowed range, not feasible.
(2) 32H7 hole limit of four degrees of freedom, a freedom bottom limit on the size of this program 4 ± 0.1? A benchmark does not overlap the error, and the positioning Pin Slender, less rigid, so not good.
(3) restrictions on the underside of the three degrees of freedom, 32H7 Kong limited to two degrees of freedom that this option could be a long piece set up to achieve diamond sales for the three design requirements are the basis of coincidence, the only 32H7 holes for the bottom The parallelism error will affect the two holes in the vertical plane parallel degree, should be restricted boring 32H7 holes.
In summary, the third program reference basically coincide, fixture structure is not very complicated, clamping convenient, it should be.
I am an expert from China Quality Dress, usually analyzes all kind of industries situation, such as electric actuated ball valves , foundation drilling equipment.
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