Affect the factor of mental allowance

When the specific content of affirmatory working procedure, one of its jobs decide working procedure mental allowance reasonably namely. The size of mental allowance all has bigger effect to the treatment quality of the spare parts and production economy. Mental allowance is too big, the amount of labor that raises machining necessarily, reduce productivity; Increase what raw material, equipment, tool reachs electric power to wait to use up. Mental allowance is too small, blemish of all sorts of surface of sum of errors that cannot ensure the working procedure on excision is formed again, affect the quality of the spare parts, produce waste product even. By graph 1-9 knowable, working procedure mental allowance (nominal value, be the same as below) outside expressing except the working procedure dimension of working procedure of usable photograph adjacent, still can use additional, kind the method expresses, namely: Working procedure mental allowance is equal to the smallest mental allowance and before the sum of public errand of dimension of working procedure working procedure. Accordingly, when discussing the factor that affects mental allowance, answer to consider to affect the factor of the smallest mental allowance above all. The factor that affects the smallest mental allowance is more, assign main influencing factor individual event introduction to be as follows now. (1) before the exterior surface roughness that working procedure forms and blemish layer deepness (Ra and Da) rise to make the treatment quality of workpiece progressively, general every working procedure should cut the normal metal organization under work surface, will go up the exterior surface roughness that working procedure forms and blemish layer cut away. (2) before the position error of appearance sum of errors that working procedure forms (△ X and △ W) mix when appearance public errand, position public errand the relation between dimension public errand is independent principle when, dimension public errand is not controlled form tolerancepublic errand. Right now, the smallest mental allowance should assure will before the appearance that working procedure forms and position error cut away. The error in above influencing factor reachs blemish, can overlap together sometimes, if graph 1-10 place is shown, the △ X in the graph is parallelism alignment error for W of flatness error, △ , but machine quality to assure, can undertake simple overlay to each, so that be excised thoroughly. Blemish of afore-mentioned each sum of errors are before working procedure forms, to can excise its entirely, the outfit that considers this working procedure even places the effect of error ε B. If graph 1-11 place is shown, because 3 claw forbid from centering chuck centering, make E of axis of rotation of main shaft of workpiece axes deviate is worth, cause mental allowance inhomogenous, to ensure will before the blemish of each sum of errors of working procedure is excised entirely, the surplus on the diameter should increase 2e. Hold the amount that places error ε B, can be in those who beg clamping apparatus of sum of errors of a fixed position error, clamp is right after deciding an error, get. The error of clip of outfit of element graph 1-11 that graph 1-10 affects the smallest mental allowance is narrated on the influence put together to mental allowance, the factor that affects working procedure mental allowance but a few reduce is following: The public errand of working procedure dimension of the working procedure before ● (Ta) . The exterior surface roughness that the working procedure before ● forms and deepness of exterior blemish layer (Ra+Da) . The position error of appearance sum of errors that the working procedure before ● forms (W of △ X, △ ) . The error holding clip of this ● working procedure (ε B) . CNC Milling