Machining Center Positioning Benchmark Selection

- Nov 03, 2017 -

As with normal machine tools, when machining in the machining center, the parts are still attached according to the 6-point positioning principle.

In selecting the positioning benchmark, we must fully consider the processing of each station, to achieve three purposes:

① The selected reference should be able to ensure that the workpiece positioning accuracy, easy loading and unloading workpieces, the workpiece can quickly complete the positioning and clamping, reliable clamping, and fixture structure is simple.

② The selected benchmark and the processing of various parts of the size of the calculation is simple, minimize the size of the chain calculation, to avoid or reduce the calculation and calculation errors.

③ ensure the accuracy of the processing. In determining the specific positioning of the benchmarks, to follow the following principles:

a) Try to choose the design basis of the part as a positioning reference. In the development of parts processing program, we must first select the best precision machining center for processing. This requires that in the roughing, consider what kind of rough reference to the precision machining of the reference surface, that is used in the machining center of the various positioning standards should be processed in front of normal machine or machining center process, it is easy to ensure that all workers Bit machining surface accuracy relationship between each other, and when the surface still need to rely on multiple clamping or other machine to complete, select the same design and benchmark reference positioning, not only to avoid the reference misalignment caused by positioning error , To ensure processing accuracy, and to simplify programming.

b) When the processing center including the design basis can not be completed simultaneously in the machining center, the positioning reference and the design basis should be as far as possible. At the same time also consider the use of the benchmark positioning, a fixture will be able to complete all parts of the key precision machining. In order to avoid finishing parts after multiple non-critical dimensional processing, multiple turnaround, resulting in deformation of the parts, bump scratch, to consider as much as possible to complete a multi-processing content (such as screw holes, free holes, chamfer, Non-important surface, tool inspection, etc.) at the same time, the machining center to complete the process is usually arranged at the end.

c) When both the machining center in the machining center and the completion of the processing of the station, the positioning of the benchmark to consider the completion of the processing as much as possible. To this end, to consider the ease of positioning of the various surfaces are processed, such as the box, the best one-two pin positioning, so that the tool on the other surface processing.

d) When the positioning of the parts is difficult to coincide with the design basis, the assembly drawing should be carefully analyzed to determine the design function of the design basis of the part. Through the calculation of the dimension chain, the range of geometric tolerances between the positioning reference and the design reference should be strictly regulated to ensure Precision. For the machining center with automatic measurement function, the coordinate system can be arranged in the process to check the work step, that is, the program controls the touch probe to test the design standard automatically before each part is processed. The CNC system automatically calculates and corrects the coordinate system to ensure that each Geometrical relationship between processing site and design basis.

e) The origin of the workpiece coordinate system, that is, the "programming zero point" does not necessarily coincide with the part positioning datum. However, there must be a definite geometric relationship between the two. The origin of the workpiece coordinate system to choose the main consideration to facilitate programming and measurement. For the parts with high dimensional accuracy requirements, the positioning datum should be considered whether the origin of the coordinates can be accurately measured by the positioning datum while taking into consideration the measurement method.

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