Factors affecting dimensional accuracy and improvement measures.

1. Measurement error. Because of the manufacturing errors of measuring tools, the error of measurement method leads to the fact that the measurement results can not reflect the actual size of the workpiece, and will directly affect the dimensional accuracy of the machined surface. Improve measures: according to the accuracy requirements, reasonable selection of measuring methods and measuring instruments; control measurement conditions, such as control measurement environmental temperature.

2. Adjustment error. The use of adjusting method in Machining, the size of the measuring sample can not fully reflect the size fraction caused by various random errors in the machining, thus affecting the correctness of the size adjustment, resulting in dimensional error. Improvement measures: Trial-machining a set of workpieces, and adjust the tool position on the basis of the average position of their size distribution. The quantity of the trial-cutting work shall be determined by the required dimensional tolerances and the dispersion range of the actual machining size.

3. Tool error and tool wear. Sizing tool error and wear directly affects the machining dimensions; In adjustment method machining, the cutting tool abrasion will make one batch workpiece have different size; In CNC Machining, tool manufacture, installation, adjustment error and tool wear directly affects the machining size. Improvement measures: control the size of the cutter; adjust the machine tools in time; ensure the accuracy of tool installation; master the rules of tool wear and make compensation.

4. Positioning mechanism repeated positioning accuracy. Improvement measures: to improve the rigidity, accuracy and sensitivity of the positioning mechanism.

5. Feed error. The drive error of the feed mechanism and the "crawl" caused by the micro feeding, make the actual feed amount not consistent with the graduation indicating value or the program control value, thus producing the machining size error. Improvement measures: to improve the accuracy of the feed mechanism; direct measurement feed by micrometer ; adopts closed loop control system.

6. Thermal deformation of process system. The measured size on the just finished workpiece can't reflect the actual size of the workpiece; When using adjustment method machining a batch of workpiece, the workpiece size dispersion range increased by machines and tools thermal deformation; When using sizing tool method machining, tool thermal deformation directly affects the machining size. Improvement measures: separate the fine machining and rough machining; sufficient and effective cooling; reasonable adjustment dimensions; according to the thermal deformation law of workpiece, appropriate compensation when measuring, or measured under cold state; Waite the machine to be heat balanced and then machining; control the environmental temperature.

7. Workpiece installation error. Caused by the fixture manufacturing error, positioning errors, orientation and tool setting errors, clamping deformation and alignment errors. So that the design benchmarks of the machined surface changes with the relative position of the tool, which results in the position size error of the machined surface. Improvement measures: correctly select the positioning benchmark; improve the fixture manufacturing accuracy; reasonably determine the clamping method and the size of clamping force; careful alignment and clamping.