Experience summary of NC machining

Because of the complexity of NC processing (such as different machine tools, different materials, different tools, different cutting methods, different parameter settings, etc.), it is decided that the experience must be accumulated continuously in the long-term actual production process to engage in NC processing (whether processing or programming).

1、 What principles should be followed for the arrangement of processing sequence?

The processing sequence shall be arranged according to the structure and blank condition of the parts, as well as the needs of positioning and clamping. The emphasis is that the rigidity of the workpiece will not be damaged. The sequence shall generally follow the following principles:

1) The processing of the previous process shall not affect the positioning and clamping of the next process, and the processing of general machine tools interspersed between them shall also be considered comprehensively.

2) The internal cavity processing sequence shall be followed by the contour processing sequence.

3) It is better to connect the processes of the same positioning, clamping method or the same knife processing to reduce the times of repeated positioning, tool change and moving the pressing plate.

4) For multiple processes in the same installation, the process with small rigid damage to the workpiece shall be arranged first.

2、 What aspects should be paid attention to when determining the clamping mode of workpieces?

When determining the positioning datum and clamping scheme, attention shall be paid to:

1) Strive to unify the design, process and programming calculation.

2) The clamping times shall be reduced as far as possible, and all surfaces to be machined can be machined after one positioning.

3) Avoid using manual adjustment scheme for machine occupation.

4) The fixture shall be open smoothly, and its positioning and clamping mechanism shall not affect the tool path during processing (such as collision). In such cases, it can be clamped with a vise or by adding a base plate to draw screws.

3、 How to determine a reasonable tool setting point? What is the relationship between workpiece coordinate system and programming coordinate system

1. The tool setting point can be set on the part to be machined, but it should be noted that the tool setting point must be the reference position or the part that has been finished. Sometimes the tool setting point is destroyed after the first process, which will lead to no way to find the tool setting point in the second process and the subsequent process. Therefore, when aligning the tool in the first process, it should be noted that a relative tool setting position should be set where there is a relatively fixed dimension relationship with the positioning reference, In this way, the original tool setting point can be found according to the relative position relationship between them. This relative tool setting position is usually set on the machine tool workbench or fixture. The selection principles are as follows:

1) Easy to find

2) Easy programming

3) Small tool setting error

4) Convenient inspection during processing

2. The origin position of the workpiece coordinate system is set by the operator. After the workpiece is clamped, it is determined by tool setting. It reflects the distance position relationship between the workpiece and the zero point of the machine tool. Once the workpiece coordinate system is fixed, it is generally unchanged. The workpiece coordinate system and the programming coordinate system must be unified, that is, during processing, the workpiece coordinate system and the programming coordinate system are consistent.

4、 How to select the tool path?

Tool path refers to the path and direction of the tool relative to the workpiece in the process of NC machining. The reasonable choice of machining route is very important, because it is closely related to the machining accuracy and surface quality of parts. The following points are mainly considered when determining the tool path:

1) Ensure the machining accuracy requirements of parts.

2) It is convenient for numerical calculation and reduces programming workload.

3) Find the shortest processing route, reduce the empty tool time to improve the processing efficiency.

4) Minimize the number of program segments.

5) Ensure the roughness requirements of the workpiece contour surface after machining. The final contour shall be

processed continuously with the last cutter.

6) The advance and retreat (cut in and cut out) route of the tool shall also be carefully considered to minimize the tool marks caused by tool stopping at the contour (elastic deformation caused by sudden change of cutting force), and also to avoid scratching the workpiece due to vertical cutting on the contour surface.

5、 How to monitor and adjust during processing?

The workpiece can enter the automatic processing stage after the alignment and program debugging are completed. In the automatic machining process, the operator shall monitor the cutting process to prevent the workpiece quality problems and other accidents caused by abnormal cutting.

The monitoring of cutting process mainly considers the following aspects:

1) The main consideration of the rough machining process monitoring is the rapid removal of the surplus allowance on the workpiece surface. In the automatic machining process of the machine tool, the tool automatically cuts according to the predetermined cutting path according to the set cutting parameters. At this time, the operator should observe the change of cutting load during automatic processing through the cutting load table, and adjust the cutting parameters according to the bearing force of the tool to maximize the efficiency of the machine tool.

2) Monitoring of cutting sound in the cutting process In the automatic cutting process, the sound of the tool cutting the workpiece is stable, continuous, and light at the beginning of cutting, and the machine tool movement is stable at this time. With the progress of the cutting process, when there are hard spots on the workpiece or the tool is worn or the tool is clamped, the cutting process becomes unstable. The unstable performance is that the cutting sound changes, the tool and the workpiece will collide with each other, and the machine tool will vibrate. At this time, the cutting parameters and cutting conditions should be adjusted in time. When the adjustment effect is not obvious, the machine tool should be paused to check the condition of the tool and workpiece.

3) The finishing process is monitored to ensure the machining size and surface quality of the workpiece. The cutting speed is high and the feed rate is large. At this time, attention should be paid to the influence of chip buildup on the machined surface. For cavity machining, attention should also be paid to over cutting and tool passing at corners. To solve the above problems, first, pay attention to adjusting the spraying position of cutting fluid, so that the machined surface is always in the best cooling condition; Second, pay attention to the quality of the machined surface of the workpiece, and try to avoid quality changes by adjusting the cutting parameters. If the adjustment still has no obvious effect, stop the machine to check whether the original program is reasonable.

In particular, pay attention to the position of the tool when suspending inspection or stopping inspection. If the tool stops in the cutting process and the spindle stops suddenly, tool marks will be generated on the workpiece surface. In general, shutdown shall be considered when the tool leaves the cutting state.

4) The quality of the tool monitoring tool largely determines the processing quality of the workpiece. In the process of automatic machining and cutting, it is necessary to judge the normal wear condition and abnormal damage condition of tools by means of sound monitoring, cutting time control, pause inspection during cutting, workpiece surface analysis, etc. Tools shall be handled timely according to the processing requirements to prevent them from being handled in time.