Sheet Metal · 2022年5月12日

The operation skills and experience shared by the masters of CNC lathes

Time has passed. I have been operating CNC lathes for ten years in a blink of an eye. Ten years of experience has allowed me to accumulate some machining skills and experience on CNC lathes and communicate with colleagues.
Due to frequent replacement of processed parts and limited factory conditions, we have programmed ourselves for ten years, set the tool ourselves, debug and complete the processing of the parts by ourselves. In summary, the operating skills are divided into the following points:
1. Programming skills
Because our factory has high requirements for the accuracy of processed products, the things that need to be considered when programming are:
(1) The processing sequence of the parts: drill first and then flat end (this is to prevent shrinking when drilling); first rough turning, then finish turning (this is to ensure the accuracy of the parts); first processing with large tolerances and final processing with small tolerances (This is to ensure that the surface of the small tolerance size is not scratched and to prevent deformation of the parts).
(2) Choose a reasonable speed, feed and depth of cut according to the hardness of the material. I personally summarize it as follows:
1. The carbon steel material chooses high speed, high feed rate and large cutting depth. Such as: 1Gr11, select S1600, F0.2, cutting depth 2mm;
2. Low speed, low feed rate and small cutting depth are selected for cemented carbide. Such as: GH4033, select S800, F0.08, cutting depth 0.5mm;
3. Choose low speed, high feed rate and small cutting depth for titanium alloy. Such as: Ti6, select S400, F0.2, and cut depth 0.3mm. Take a part that I process as an example: the material is K414, which is an extra-hard material. After many tests, the final selection is S360, F0.1, and the depth of cut 0.2 before processing qualified parts. There are still many programming skills, and I personally sum it up like this.
2. Knife setting skills
Tool setting is divided into tool setting instrument setting and direct tool setting. Most of the lathes in our factory do not have tool setting instruments, which are direct tool setting. The tool setting techniques mentioned below are direct tool setting. First select the center of the right end face of the part as the tool setting point, and set it as the zero point. After the machine returns to the origin, each tool that needs to be used will be set with the center of the right end face of the part as the zero point; when the tool touches the right end face, enter Z0 and click to measure. The tool compensation value of the tool will automatically record the measured value, which means that the Z-axis tool setting is done, and the X tool setting is the trial cutting tool setting. The outer circle of the part is turned with the tool, and the outer circle value of the machine is measured ( If x is 20mm) input x20, click Measure, the tool compensation value will automatically record the measured value, then the x axis is also correct; this method of tool setting, even if the machine is powered off, the setting will not change after the power is turned on. The tool value is suitable for mass production of the same part for a long time, during which the lathe is closed and there is no need to recalibrate the tool.
Three, debugging skills
After the parts are programmed, the tool needs to be trial cut and debugged. In order to prevent errors in the program and error in the tool setting, causing machine collision accidents, we should first perform idle stroke simulation processing, and perform the calibration in the coordinate system of the machine tool. The tool moves to the right by 2-3 times the total length of the part; then start the simulation processing. After the simulation processing is completed, confirm that the program and tool setting are correct, and then start processing the part. After the first part is processed, self-check first to confirm that it is qualified , And then find a full-time inspection and inspection, after the full-time inspection is confirmed to be qualified, this means that the debugging is over.
Fourth, complete the processing of the parts
After the first piece of trial cutting is completed, the parts will be mass-produced, but the first piece of qualification does not mean that the entire batch of parts will be qualified, because in the process of processing, the tool will wear out due to the difference in processing materials. Soft, the tool wear is small, the processing material is hard, and the tool wears quickly. Therefore, in the process of processing, it is necessary to check frequently to increase and decrease the tool compensation value in time to ensure the qualification of the part. Take a part as an example, the processing material is K414 , The total processing length is 180mm. Because the material is extremely hard, the tool wears very quickly during processing. From the starting point to the end point, the tool wear will produce a slight degree of 10-20mm. Therefore, we must artificially add 10-20mm in the program. In this way, the qualified parts can be guaranteed.
In short, the basic principle of machining: rough machining first, remove the excess material of the workpiece, and then finish machining; avoid vibration during machining; avoid thermal denaturation during workpiece machining. There are many reasons for vibration caused by excessive load. Large; it may be due to the resonance of the machine tool and the workpiece, or it may be caused by insufficient rigidity of the machine tool, or it may be caused by the tool passivation. We can reduce the vibration by the following methods; reduce the transverse feed and the processing depth, and check Whether the workpiece is clamped firmly, increase the rotation speed of the tool and reduce the rotation speed to reduce the resonance. In addition, check whether it is necessary to replace a new tool. The above is a summary of my skills in CNC lathe machining over the years.
In addition, in order to safely operate the cnc machine tool and prevent the machine from colliding, I have the following points:
I often hear others say that you can’t learn to operate the machine without touching the machine. This is a very wrong and harmful understanding. The collision of the machine will greatly damage the accuracy of the machine, and it will have different effects on different types of machine tools. Generally speaking, , It has a greater impact on machine tools with low rigidity, such as the T6 horizontal lathe we currently use, once the machine tool collides, the impact on the accuracy of the machine tool is fatal. Therefore, for high-precision CNC lathes, collisions must be absolutely eliminated. As long as the operator is careful and masters certain anti-collision methods, collisions can be prevented and avoided. The following are some tips on anti-collision of CNC lathes: The main reason for the collision is: one is the input error of the diameter and length of the tool; the other is the input error of the size of the workpiece and other related geometric dimensions and the initial position of the workpiece Positioning error; Third, the workpiece coordinate system of the machine tool is set incorrectly, or the zero point of the machine tool is reset during the machining process, and changes occur. Machine tool collisions mostly occur during the rapid movement of the machine tool. The collisions that occur at this time are also the most harmful. Avoid absolutely. Therefore, the operator should pay special attention to the machine tool in the initial stage of executing the program and when the machine tool is changing tools. At this time, once the program is edited incorrectly, and the diameter and length of the tool are entered incorrectly, collisions are likely to occur. At the end of the program, if the NC axis retracts the tool in a wrong sequence, then a collision may also occur. In order to avoid the above collisions, the operator should give full play to the features of the five senses when operating the machine tool, and observe whether the machine tool has abnormal movements, sparks, noises and abnormal noises, vibrations, and burnt odors. If an abnormal situation is found, the program should be stopped immediately. After the standby bed problem is solved, the machine tool can continue to work. In short, mastering the operation skills of cnc machine tools is a gradual process and cannot be accomplished overnight. It is based on mastering the basic operation of machine tools, basic machining knowledge and basic programming knowledge. The operating skills of CNC machine tools are not static, it is an organic combination that requires the operator to give full play to their imagination and hands-on ability, and is an innovative work. At the same time, I hope my skills and experience can bring some help to my colleagues.

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