Super practical NC machining experience!

Due to the complexity of NC machining(such as different machine tools,different materials,different cutting tools,different cutting methods,different parameter settings,etc.),it is determined that engaging in NC machining(whether machining or programming)must continuously accumulate experience in the long-term actual production process.

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

The arrangement of machining sequence shall be considered according to the structure and blank condition of parts and the needs of positioning and clamping,with the focus on the rigidity of the workpiece not being 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 general machine tool processing process interspersed in the middle shall also be comprehensively considered.

(2)The inner cavity processing sequence shall be carried out first,and then the contour processing sequence shall be carried out.

(3)It is better to connect the processes processed with the same positioning,clamping mode or the same knife,so as 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 damage to the rigidity of the workpiece shall be arranged first.

2、What aspects should be paid attention to in determining the clamping mode of workpiece?

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

(1)Strive to unify the basis of design,process and programming calculation.(2)reduce the clamping times as much as possible and process all the surfaces to be processed after one positioning.

(3)Avoid using the manual adjustment scheme of occupying the machine.(4)the fixture shall be open,and its positioning and clamping mechanism shall not affect the tool walking in processing(such as collision).In such cases,it can be clamped by using vise or adding base plate to extract screws.

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

1.The tool setting point can be set on the of the machined parts,but note that the tool setting point must be the reference position or the finished part.Sometimes the tool setting point is machined and damaged after the first process,which will make it impossible to find the tool setting point in the second process and after,Therefore,during tool setting in the first process,pay attention to set a relative tool setting position where there is a relatively fixed dimensional relationship with the positioning datum,so that the original tool setting point can be retrieved according to the relative positional 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 alignment 2)convenient programming 3)small tool setting error 4)convenient inspection during machining

2.The origin position of the workpiece coordinate system is set by the operator.It is determined by tool setting after the workpiece is clamped.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 not changed.The workpiece coordinate system and the programming coordinate system must be unified,that is,during machining,the workpiece coordinate system and the programming coordinate system are consistent.

4、How to select the cutting route?

Tool path refers to the motion path and direction of the tool relative to the workpiece in the process of NC machining.The reasonable selection 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 cutting route:

1)Ensure the machining accuracy requirements of parts.2)Facilitate numerical calculation and reduce programming workload.3)Find the shortest processing route and reduce the empty tool time to improve the processing efficiency.

4)Minimize the number of segments.5)Ensure the requirements of the roughness of the workpiece contour surface after machining,and the final contour shall be processed continuously with the last tool.

6)The forward and backward(cut in and cut out)route of the tool should also be carefully considered to minimize the knife marks caused by stopping the tool at the contour(elastic deformation caused by sudden change of cutting force)and avoid scratching the workpiece by cutting vertically on the contour surface.

5、How to monitor and adjust during processing?

After the workpiece is aligned and the program is debugged,it can enter the automatic machining stage.In the process of automatic machining,the operator shall monitor the cutting process to prevent workpiece quality problems and other accidents caused by abnormal cutting.

Monitoring the cutting process mainly considers the following aspects:

1.Machining process monitoring rough machining mainly considers the rapid removal of excess 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 shall observe the change of cutting load in the automatic machining process through the cutting load table,and adjust the cutting parameters according to the bearing force of the tool to give full play to the maximum efficiency of the machine tool.

2.Monitoring of cutting sound in the cutting process in the automatic cutting process,generally,when cutting,the sound of the tool cutting the workpiece is stable,continuous and light.At this time,the movement of the machine tool is stable.With the progress of the cutting process,when there are hard spots on the workpiece,tool wear or tool clamping,the cutting process is unstable.The unstable performance is that the cutting sound changes,the tool and workpiece will collide with each other,and the machine tool will vibrate.At this time,the cutting parameters and cutting conditions shall be adjusted in time.When the adjustment effect is not obvious,the machine tool shall be suspended to check the condition of tools and workpieces.

3.Finish machining process monitoring finish machining is mainly to ensure the machining size and surface quality of the workpiece,high cutting speed and large feed.At this time,attention should be paid to the influence of chip accumulation on the machining surface.For cavity machining,attention should also be paid to over cutting and tool yield at the corner.To solve the above problems,first,pay attention to adjusting the spraying position of cutting fluid to keep the machining surface in the best]cooling condition at all times;Second,pay attention to the quality of the machined surface of the workpiece,and avoid the change of quality as much as possible 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 pausing the inspection or stopping the inspection.If the cutting tool stops in the cutting process,the sudden spindle stop will produce tool marks on the workpiece surface.In general,shutdown should be considered when the tool leaves the cutting state.

4.Tool monitoring tool quality largely determines the machining quality of the workpiece.In the process of automatic machining and cutting,the normal wear and abnormal damage of the tool should be judged by means of sound monitoring,cutting time control,pause inspection in the cutting process,workpiece surface analysis and so on.Timely handle the cutting tools according to the processing requirements to prevent the failure of the cutting tools.

Keyword:NC machining

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