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The formulation of CNC turning process
Release date:2022-04-01

Process division method

When machining parts on a CNC lathe, the process should be divided according to the principle of process concentration, and most or even all surfaces should be processed as much as possible under one clamping. According to different structural shapes, usually choose the outer circle, end face or inner hole, end face clamping, and strive to unify the design basis, process basis and programming origin. In mass production, the following methods are often used to divide the process.

1. Divide the process according to the machining surface of the part

That is to say, the part of the process that completes the same profile is a process. For parts with many and complex surfaces, they can be divided into multiple processes according to their structural characteristics (such as inner shape, shape, curved surface and plane, etc.).

Finish the surface with high positional accuracy in one clamping, so as to avoid the error caused by multiple positioning and clamping to affect the positional accuracy. For the workpiece shown in Figure 1, according to the process characteristics of the part, the roughing and finishing of the outer contour and the inner contour are completed in one process, which reduces the number of clamping times and is conducive to ensuring the coaxiality.

2. Divide the process according to roughing and finishing

That is, the part of the process completed in roughing is a process, and the part of the process completed in finishing is a process. For parts with large blank allowance and high machining accuracy requirements, rough turning and fine turning should be separated into two or more processes. Arrange rough turning on CNC machine tools with lower precision and higher power, and arrange fine turning on CNC machine tools with higher precision.

This division method is suitable for parts that have large deformation after processing and need to be separated from roughing and finishing, such as parts whose blanks are castings, welded parts or forgings.

Divide the process according to the type of tool used

3. Divide the process according to the type of tool used

Taking that part of the process completed by the same tool as a process, this method is suitable for the situation that there are many surfaces to be machined on the workpiece, the continuous working time of the machine tool is long, and the preparation and inspection of the machining program are difficult.

4. Divide the process according to the number of installations

Take that part of the process that is completed in one installation as a process. This method is suitable for workpieces with little processing content, and can reach the state to be inspected after the processing is completed.

After careful and careful analysis of the part drawing, the following basic principles should be followed to formulate a machining plan - first rough and then fine, first near and then far, cross inside and outside, few program segments, and short tool paths.

(1) Coarse first and then fine

It refers to gradually improving the machining accuracy in the order of rough turning, half fine turning and one fine turning. In order to improve the production efficiency and ensure the finishing quality of the parts, during the cutting process, the roughing process should be arranged first. Even amount.

(2) first near and then far

The far and near mentioned here are in terms of the distance of the machining part relative to the tool setting point. Under normal circumstances, especially in rough machining, the parts close to the tool setting point are usually processed first, and the parts far from the tool setting point are processed later, so as to shorten the tool moving distance and reduce the idle travel time.

(3) Crossover inside and outside

For parts that need to be machined both the inner surface (inner cavity) and the outer surface, when arranging the machining sequence, the inner and outer surfaces should be roughed first, and then the inner and outer surfaces should be finished.

Determine the path of the tool

Tool path: in CNC machining, the movement path and direction of the tool position relative to the workpiece. That is, the path that the tool travels from the tool setting point to the end of the processing program, including the cutting path and the non-cutting idle strokes such as cutting in and out of the tool.

The general principle of determining the tool path: on the premise of ensuring the machining accuracy and surface quality of the parts, the tool path should be shortened as much as possible to improve productivity; it is convenient for coordinate value calculation, reducing programming workload and facilitating programming. For multiple repeated tool paths, subroutines should be written to simplify programming.

Commonly used tool paths when machining parts on CNC lathes:

Analysis of the cutting path of the turning arc

When actually turning the arc, multi-tool processing is required, most of the allowance is cut off first, and then the required arc is turned after Z.

Analysis of the tool path for grooving

When turning a rectangular groove with low precision and a narrow width, a turning tool with a tool width equal to the groove width can be used, and the straight-in method is used to feed and turn out at one time. The grooves with high precision requirements are generally formed by two-feed turning, that is, when feeding the groove for the first time, leave a fine-turning allowance on both sides of the groove wall, and trim it with a constant-width knife when feeding the groove for the second time.

The wider grooves can be cut by the straight-forward method for many times, and the finishing allowance is left on the groove wall and bottom surface.

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