Some operating skills and experience in CNC lathe machining
Published Time:
2020-03-17
I. Programming skills The precision requirement for processed products is high. Matters to be considered during programming include: 1. Machining order of parts: Drilling first, then end milling (this is to prevent material shrinkage during drilling); rough machining first, then finish machining (this is to ensure part precision); machining parts with large tolerances first, then those with small tolerances (this is to ensure that the surface of small tolerance dimensions is not scratched and to prevent part deformation). 2. Select reasonable speed, feed rate, and depth of cut according to material hardness: 1) For carbon steel materials, select high speed, high feed rate, and large depth of cut. For example: For 1Gr11, select S1600, F0.2, and a depth of cut of 2mm; 2
I. Programming Techniques
The processing of products requires high precision. Here are some things to consider when programming:
1. Part Processing Order:
Drill holes before end-facing (this is to prevent shrinkage during drilling);
Rough machining before fine machining (this is to ensure part accuracy);
Process large tolerances before small tolerances (this ensures that the surface of small tolerance dimensions is not scratched and prevents part deformation).
2. Select appropriate speeds, feeds, and depths of cut based on material hardness:
1) For carbon steel, select high speed, high feed, and deep cut. For example: 1Gr11, select S1600, F0.2, depth of cut 2mm;
2) For hard alloy, select low speed, low feed, and shallow cut. For example: GH4033, select S800, F0.08, depth of cut 0.5mm;
3) For titanium alloy, select low speed, high feed, and shallow cut. For example: Ti6, select S400, F0.2, depth of cut 0.3mm. Taking the processing of a certain part as an example: the material is K414, which is an extra-hard material. After multiple tests, S360, F0.1, and a depth of cut of 0.2 were finally selected to produce qualified parts.
II. Tooling Techniques
Tooling is divided into tooling using a tooling instrument and direct tooling. Most of the lathes in our factory do not have tooling instruments, so they use direct tooling. The following tooling techniques refer to direct tooling.
First, select the center of the right end face of the part as the tooling point and set it as the zero point. After the machine returns to the origin, each tool to be used is tooled using the center of the right end face of the part as the zero point; when the tool touches the right end face, input Z0 and click "measure"; the measured value will be automatically recorded in the tool compensation value. This indicates that the Z-axis tooling is complete. For X-axis tooling, perform a test cut. Use the tool to machine a small amount of the outer circle of the part, measure the machined outer circle value (e.g., x is 20mm), input x20, click "measure", and the tool compensation value will automatically record the measured value. At this time, the X-axis is also tooled. With this tooling method, even if the machine power is off, the tooling value will not change after restarting, suitable for large-scale, long-term production of the same part, and the machine does not need to be re-tooled during shutdown.
III. Debugging Techniques
After the part program is written and the tools are tooled, a test cut and debugging is needed. To prevent errors in the program and tooling errors that cause collisions, a dry run simulation should be performed first. The tool is moved to the right by 2–3 times the total length of the part in the machine's coordinate system; then simulate the processing. After the simulation is complete, confirm that the program and tooling are correct before machining the part. After the first part is machined, perform a self-inspection. If it is qualified, ask the specialized inspector to check. Only after the specialized inspector confirms that it is qualified is the debugging considered complete.
IV. Completing Part Machining
After the first part is test-cut, batch production begins. However, the qualification of the first part does not mean that the entire batch of parts will be qualified, because during machining, the different materials being processed will cause tool wear. If the material is soft, the tool wear is small; if the material is hard, the tool wear is fast. Therefore, during processing, frequent measurement and inspection are needed to increase or decrease the tool compensation value in a timely manner to ensure the quality of the parts.
Taking a certain part as an example, the machining material is K414. The total machining length is 180mm. Due to the extra-hard material, tool wear is very fast during machining. From the starting point to the end point, due to tool wear, a taper of 10–20mm will occur. Therefore, we must artificially add a taper of 10–20mm in the program to ensure the quality of the parts.
In short, the basic principle of processing is: rough machining first to remove excess material, then fine machining; avoid vibration during machining; avoid thermal deformation of the workpiece during machining. Vibration can occur for many reasons: excessive load; resonance between the machine and the workpiece; insufficient rigidity of the machine; or tool dulling. We can reduce vibration by the following methods: reduce the transverse feed and machining depth; check whether the workpiece clamping is firm; increase or decrease the tool speed to reduce resonance; and check if it is necessary to replace new tools.
V. Experience in Preventing Machine Collisions
Machine collisions cause significant damage to the machine's accuracy, and the impact varies depending on the type of machine. In general, the impact is greater on machines with low rigidity. Therefore, for high-precision CNC lathes, collisions must be absolutely avoided. As long as the operator is careful and masters certain collision prevention methods, collisions can be completely prevented and avoided.
The main causes of collisions are: 1. Incorrect input of tool diameter and length; 2. Incorrect input of workpiece dimensions and other relevant geometric dimensions, as well as incorrect initial positioning of the workpiece; 3. Incorrect setting of the workpiece coordinate system of the machine, or the machine zero point being reset and changed during the machining process. Most machine collisions occur during rapid movement of the machine, and the damage caused by collisions at this time is also the greatest and should be absolutely avoided. Therefore, the operator must pay special attention to the initial stage of the machine executing the program and when the machine is changing tools. At this time, if the program is edited incorrectly or the tool diameter and length are input incorrectly, a collision is likely to occur. In the program termination stage, if the tool retraction sequence of the CNC axis is incorrect, a collision may also occur.
To avoid the above collisions, when operating the machine, the operator should make full use of their five senses to observe whether the machine has any abnormal movements, sparks, noise or unusual sounds, vibrations, or burning smells. If an abnormal situation is found, the program should be stopped immediately, and the machine can only continue to work after the machine problem is solved.
In short, mastering the operation skills of CNC machine tools is a gradual process and cannot be achieved overnight. It is based on mastering basic machine operation, basic mechanical processing knowledge, and basic programming knowledge. CNC machine tool operation skills are not static; they require the operator to fully utilize their imagination and hands-on ability in an organic combination, a creative labor.
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