The parts processed by cnc are composed of several surfaces with certain dimensions and mutual position requirements. The relative position requirements between the surface of the mold parts processed by cnc include two aspects: distance dimensional accuracy between surfaces and relative positional accuracy (such as coaxiality, parallelism, verticality and round runout). The relative positional relationship between the surfaces of the parts processed by cnc is inseparable from the reference, and the position of the surface of the part cannot be determined without an explicit reference. In its general sense, a datum is a point, line, or surface on which a part is used to determine the position of other points, lines, and faces. Benchmarks can be divided into design categories and process benchmarks according to their roles.
1. Benchmark design for cnc processing
The reference on the part drawing to determine other points, lines, and faces is called the design basis. Design benchmarks are given by part drawings, and there are many different options for positioning benchmarks. Generally, in the first process, only the surface of the blank can be used for positioning, and in the subsequent process, the surface that has been processed can be used for positioning. Sometimes it may be the case that there is no suitable surface on the workpiece that can be used as a positioning reference. In this case, the base surface must be specially set or machined on the workpiece, called the auxiliary reference.
2, cnc processing process benchmark
The reference used in the machining and assembly process of cnc-machined parts is called the process reference. Process benchmarks are divided into positioning benchmarks, measurement benchmarks, and assembly benchmarks, depending on the application.
(1) The reference used to position the workpiece in the correct position in the machine tool or fixture during positioning reference machining is called the positioning reference.
(2) When measuring the reference part, the reference used to measure the size and position of the machined surface is called the measurement reference.
(3) Assembling the basis of the assembly to determine the position of the part in the part or product, called the assembly basis.
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