The concept of mental allowance

Mental allowance is the metallic layer ply that in pointing to treatment process, cuts. Surplus has the branch of total mental allowance and operation allowance. In the process that is a spare parts by semifinished product change, machine in some apparently the total ply that excises metallic layer, the total mental allowance that calls this surface (also call semifinished product surplus) ; Usually, total mental allowance is not excision, divide in each working procedure to be excised gradually however, the metallic layer ply that place of every working procedure excises reason calls mental allowance of this working procedure (abbreviation operation allowance) . Operation allowance is photograph adjacent the difference of the working procedure dimension of two working procedure, semifinished product surplus is the difference of the design dimension of semifinished product dimension and hardware design. Because working procedure dimension has noncombatant duty, the surplus size that incident excises actually differs. Graph 1-8 expresses the concern of operation allowance and working procedure dimension. By the graph knowable, the basic measure of operation allowance (abbreviation is basic surplus or nominal surplus) Z can press type calculates to be being included face: Order of Z= go to work is basic dimension, this process is primary dimension to including face: This Z= process is primary dimension, operation allowance of 1-8 of basic measure graph and working procedure dimension reach order of go to work the relation of its public errand (A) is included face (axis) (B) includes face (aperture) machine to facilitate, working procedure dimension is pressed " the principle that enter system " tag extreme deviation, be included namely the working procedure dimension of the face takes error for 0; Include the working procedure dimension of the face gets off deviation is 0. Semifinished product dimension is pressed two-way decorate on, next deviation. The computation of operation allowance and working procedure dimension and its public errand is formulary: The Zmin in type of Z=Zmin+Ta (1-1)Zmax=Z+Tb= Zmin+Ta +Tb (1-2) -- the smallest operation allowance; Zmax -- the biggest operation allowance; Ta -- the public errand of dimension of foreword of go to work; Tb -- the public errand of this working procedure dimension. The working procedure dimension as a result of semifinished product dimension, spare parts dimension and each working procedure is put in the error, so no matter be total mental allowance, or working procedure mental allowance is a fluctuant value, appeared the biggest with the smallest mental allowance, the relation of they and working procedure dimension and its public errand can use graph 1-9 specification. Can see by the graph, the working procedure before nominal mental allowance is and the difference of this working procedure dimension, the difference of the least value of dimension of the working procedure before the smallest mental allowance is and the maximum of this working procedure dimension; The difference of the maximum of dimension of the working procedure before the biggest mental allowance is and the least value of this working procedure dimension. The fluctuant limits of working procedure mental allowance (the difference of the biggest mental allowance and the smallest mental allowance) the working procedure before be equal to and the sum of public errand of working procedure dimension of this working procedure. Mental allowance of graph 1-9 working procedure reachs its public errand CNC Milling