Things to consider when programming
Because the high requirements for the accuracy of the processed products we have, the things to consider when programming are:
First, consider the processing sequence of the parts:
- Drill first and then flat end (this is to prevent shrinkage during drilling);
- Rough turning first, then finishing turning (this is to ensure the accuracy of parts);
- First processing the large tolerance one then the small one(this is to ensure that the small tolerance size surface will not be scratched and to prevent parts from being deformed).
According to the hardness of the material, choose a reasonable speed, feed rate and cutting depth:
- Forcarbon steel material, choose high speed, high feed and large cutting depth. For example: 1Gr11, select S1600, F0.2, and cutting depth 2mm;
- Forhard alloy,choose low speed, low feed and small cutting depth. For example: GH4033, select S800, F0.08, cutting depth 0.5mm;
- For titanium alloy,choose low speed, high feed and small cutting depth. For example: Ti6, select S400, F0.2, and cutting depth 0.3mm. Take the processing of a part as an example: the material is K414, this material is a very hard material. After many tests, the final selection is S360, F0.1, and the cutting depth 0.2mm.
Tool setting skills
The tool setting can be divided into setting with tool setting gauge which means direct setting. Some lathes do not have a tool setting gauge, so the following tool setting technique is direct tool setting.
Common tool setting gauge
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 tool returns to the original point, each tool to be used is centered on the right end face of the part as the zero point. When the tool touches the right end surface, enter Z0 and click to measure. The tool compensation value of the tool will automatically record the measured value. This means that the Z axis is aligned correctly.
The X-axis tool setting is called trial cutting tool setting.Use a cutter tool to reduce the outer circle of the part. Measure the outer circle value of the tool (such as x is 20mm). Enter x20, click to measure. The X axis is aligned correctly.
This tool setting method, even if the machine tool is powered off, will not change the tool setting value after power on and restart, can be applied to mass production of the same part for a long time, and the tool does not need to be reset during the shutdown.
After the part is programmed, tool is set, there’s a need to to perform trial cutting and debugging. In order to prevent program errors and tool setting errors from causing a collision accident.
We should first carry out the empty stroke simulation processing, and in the coordinate system of the machine tool, translate the tool to the right as a whole by 2 to 3 times the total length of the part. Then start the simulation process.
After the simulation process is completed, confirm that the program and tool setting are correct, and then start processing the part.
After the first part is processed, first perform a self-inspection to confirm that it is qualified, and next find a full-time technician to check.
This is the end of the commissioning after the full-time inspection is confirmed to be qualified.
Complete the processing of parts
After the first trial cut is completed, batch production is required, but the qualification of the first part does not mean that the entire batch of parts will be qualified.
Because in the processing process, the tool will wear due to the different processing materials.
The softer the processing material, the less the tool wear, the harder the processing material, the faster the tool wear.
Therefore, in the process of processing, it is necessary to perform frequent inspections, increase and decrease the cutter compensation value in time, and ensure the qualification of the parts.
Tool wear process and blunt standards
Take the parts we processed before as an example, the processing material is K414, and the total processing length is 180mm. Due to the extremely hard material, the tool wears very quickly during processing. From the beginning to the end, a slight degree of 10-20mm is generated due to tool wear.
Therefore, we must artificially add a slight degree of 10-20mm in the program to ensure the qualification of the parts.
The basic principles of processing
First, rough machining, remove excess material from the workpiece, and then finish machining.
Vibration should be avoided during processing
Thermal degeneration during workpiece processing should also be avoided. There are many reasons for the vibration, which may be excessive load, the resonance of the machine tool and the workpiece, the insufficient rigidity of the machine tool, or the passivation of the tool.
We can reduce the vibration by the following methods:
- Reduce lateral feed and machining depth.
- Check whether the workpiece is clamped securely.
- Increase the speed of the tool, or reduce the speed to reduce resonance.
- In addition, check if it is necessary to replace with a new tool.
Experience in preventing machine tool collisions
Collision of the machine tool greatly damages the accuracy, and affects different types of machine tools differently.
Generally speaking, it has a greater impact on machines with less rigidity. Therefore, for high-precision CNC lathes, collisions must be avoided. As long as the operator is careful and masters certain anti-collision methods, collisions can be completely prevented and avoided.
Main reasons for the collision:
- Incorrect input of tool’s diameter and length;
- Incorrect input of workpiece dimensions and other related geometrical dimensions and incorrect positioning of the initial position of the workpiece;
- The workpiece coordinates of the machine tool are set incorrectly, or the machine zero point is reset during the machining process, resulting in changes. Most machine tool collisions occur during the rapid movement of the machine tool. The danger of collision at this time is also the greatest and should be absolutely avoided. Therefore, the operator should pay special attention to the machine tool in the initial stage of executing the program and tools changing progress. Because at this time, if the program is edited incorrectly, and the diameter and length of the tool are entered incorrectly, collision will be easy to happen. At the end of the program, if the sequence of the retracting motion of the CNC axis is wrong, collision may occur.
In order to avoid the above-mentioned collision, the operator must give full play to the functions of the five senses when operating the machine tool. The operator need to observe whether the machine tool has abnormal movements, sparks, noises, abnormal sounds, vibrations, or any burnt smell. If an abnormal situation is found, the operator should stop the program immediately, the machine can not be used until the problem is solved.
Anyway, mastering the operation skills of CNC machine tools is a gradual process and cannot be achieved overnight.
It is based on mastering the basic operation of machine tools, as well as basic machining and programming knowledge.
CNC machine tool operation skills are not static, it is an organic combination that requires the operator to give full play to imagination and hands-on ability, and it is a kind of innovative labor.