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CNC Machining Process Principle

CNC Machining

Processing process planning refers to the whole process, which can not be judged by the nature of a process and the processing of a surface. For example, some positioning datum planes need to be processed very accurately in the semi-finishing stage or even in the rough processing stage. Sometimes in order to avoid dimension chain conversion, semi-finishing of some secondary surfaces can also be arranged in the finishing stage.

After determining the processing method and stage of the part surface, the processing of each surface in the same processing stage can be combined into several steps. 1. Processing procedure division method

Parts processed on CNC machine tools are generally divided into working procedures according to the principle of centralized working procedures. There are several methods of division:

(1) According to the cutter used

Taking the process completed by the same tool as a process, this method can be applied to the case of more surface to be machined. Machining centers often use this method to complete.

(2) According to the number of workpiece installation

The process that can be completed by one clamping of parts is regarded as a process. This method is suitable for parts with little processing content. On the premise of guaranteeing the processing quality of parts, the whole processing content can be completed by one clamp.

(3) According to roughing and finishing

The part of the process completed in roughing is regarded as one process, and the part of the process completed in finishing is regarded as another process. This method is suitable for parts with strength and hardness requirements, need heat treatment or parts with high accuracy requirements, need to effectively remove internal stress, and parts with large deformation after processing, need to be divided into rough and finish processing stages of parts processing.

(4) According to the processing location, the part of the process that completes the same profile is regarded as a process.

For parts with more and more complex machined surfaces, the sequence of NC machining, heat treatment and auxiliary processes should be reasonably arranged, and the problem of linking processes should be solved. 2. The principle of the division of processing procedures is that parts are made up of multiple surfaces, which have their own accuracy requirements, and there are corresponding accuracy requirements between the surfaces. In order to meet the design accuracy requirements of parts, the processing sequence arrangement should follow certain principles.

(1) The principle of “first rough, then fine”

The order of surface processing is roughing, semi-finishing, finishing and finishing. The aim is to gradually improve the accuracy and surface quality of the machined surface of parts. If all surfaces of parts are processed by CNC machine tools, the process arrangement is generally in the order of roughing, semi-finishing and finishing, that is, semi-finishing and finishing after the roughing is completed. When roughing, most of the machining allowance can be removed quickly, and then each surface can be processed in turn. This can improve the production efficiency, and ensure the processing accuracy and surface roughness of parts. This method can be applied to machined surfaces with high position accuracy. This is not absolute. For some machined surfaces which require high dimensional accuracy, considering the stiffness, deformation and dimensional accuracy of parts, it is also possible to consider that these machined surfaces are finished in the order of rough, semi-finish and finish respectively. For the machined surface with high precision, it is better to shelve the parts for a period of time between rough and finish processes, so that the surface stress of the parts after rough processing can be completely released, and the degree of stress and deformation of the Parts’surface can be reduced, which is conducive to improving the machining accuracy of the parts.

(2) Processing principle of datum level first

At the beginning of the processing, the surface used as the reference for finishing is always processed. Because the surface of the positioning datum is accurate and the clamping error is small, the roughing and semi-finishing of the positioning datum are always carried out for any part in the processing process. If necessary, the finishing is also carried out. For example, the axle parts are always roughed and semi-finished for the positioning datum, and then refined. Processing. For example, the axis parts always process the center hole first, then the center hole and the positioning hole are used as the precise benchmark to process the holes and other surfaces. If there is more than one precise datum, the processing of datum should be arranged in accordance with the order of datum conversion and the principle of improving the processing accuracy step by step.

(3) The principle of face before face

For box, bracket, body and other parts, the plane outline size is larger, and the plane positioning is more stable and reliable. Therefore, the plane should be processed first, and then the hole should be processed. In this way, not only can follow-up processing have a stable and reliable plane as the positioning datum, but also the processing of holes on a flat surface becomes easier, which is also conducive to improving the processing accuracy of holes. Usually, the process can be divided according to the Parts’processing position. Generally, the simple geometry shape is processed first, then the complex geometry shape is processed; the parts with lower precision are processed first, then the parts with higher precision are processed; the plane is processed first, and then the hole is processed.

(4) Internal-external principle

For the precision sleeve, the coaxiality between the outer circle and the hole is higher. Generally, the principle of first hole and then the outer circle is adopted, that is, the outer circle is used as the positioning datum to process the hole, and then the higher precision hole is used as the positioning datum to process the outer circle. This can ensure the higher coaxiality between the outer circle and the hole, and the clamp structure used is also simple.

(5) Principles for reducing the number of tool changes

In NC machining, the processing sequence should be arranged as far as possible according to the order in which the cutter enters the processing position.


Post time: Apr-25-2019
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