JCR CNC Models has been engaged in precision parts for more than 10 years. From the initial optical communication parts processing to the current military parts processing, the difficulty coefficient is getting bigger and bigger, so how to design the process allowance of complex precision parts processing? For a brief share:
In the process of precision machining, we change the geometry of the parts to process the cutting size, which I call as the processing allowance. The size of the processing allowance has a great impact on the processing speed, quality and processing cost. If the processing allowance is too large, it will not only increase the processing labor amount, reduce the production efficiency, but also increase the consumption of materials, tools and power, and increase the processing cost. If the processing allowance is too small, it can not eliminate various surface defects and the error of the previous process, nor can it compensate for the installation error of the workpiece in the process of processing, which is easy to make the workpiece scrapped.
Cutting margin is commonly used in our processing by the following methods:
1. Check the table
According to the processing allowance data provided by the relevant processing manual, combined with the actual production situation of our factory, the processing allowance is determined after correction, which is a common method in large processing plants.2. The empirical estimation method
Determine the processing allowance according to the processing experience of the processing technicians. What is the main basis that processing process personnel determines processing allowance standard?
(1) The minimum processing allowance is used to shorten the processing time and reduce the workpiece manufacturing cost.
(2) There should be sufficient processing allowance, especially for the final processing procedure. The machining allowance shall ensure the surface roughness, size, shape and position accuracy specified in the machining drawings (3) sufficient machining allowance to eliminate the workpiece deformation caused by heat treatment.
(4) When processing allowance, the possible changes of processing methods, processing equipment and workpieces in the processing process should be considered.(5) When formulating the processing allowance, the size, shape and other factors of the work piece should be considered.3. Analysis and calculation method
According to the theoretical formula and related experimental data, the factors affecting the processing allowance are analyzed and calculated to determine the processing allowance. What is the calculation formula of the processing allowance?
(1) The minimum allowance is calculated as follows:
Surface treatment: zbmin = aamin abmax
Cylinder processing: 2 zbmin = Damin dbmax
Internal surface treatment: zbmin =abmin aamax
Inner hole processing: 2zbmin =dbmin damax
Note: zbmin (minimum margin on one side in this process), 22 bmin (minimum margin of double-sided diameter in this process), aamin, amin, aamax, damaX (minimum and maximum limit size of previous process), abmin, dbmin, abmax, dbmax (minimum and maximum limit size of this process (after processing))
(2) The calculation formula of the maximum tax exemption is as follows
Zbmax =Zbmin + Ta + Tb
2Zbmax=2Zbmin +Tda +Tdb
Note: TA, TDA (dimensional and diameter tolerances for the previous process), TB, TDB (dimensional and diameter tolerances for this process)
(3) Calculation formula of the basic tolerance of internal and external surface processing:
Unilateral allowance: ZB basic =zbmin + ta
Column allowance: 2 ZB base = 2 zbmin + TDO
Inner hole allowance: 2 ZB base =2zbmin + TDA
The above is the design method of the processing process of complex precision parts, which is often used by the personnel engaged in engineering design, or the programming technicians will also refer to it.
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