Things to consider when programming
Due to the high accuracy requirements for our processed products, there are several factors to consider when programming, such as:
First, let’s consider the processing sequence of the parts:
Start by drilling with a flat end to prevent shrinkage during the drilling process.
Perform rough turning before finishing turning to ensure the accuracy of the parts.
Process parts with larger tolerances first before moving on to smaller tolerances to avoid scratching the smaller tolerance surfaces and to prevent deformation of the parts.
Drilling process
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
Tool setting can be divided into two categories: setting with a tool setting gauge, which is known as direct setting, and direct tool setting, which is used when a lathe does not have a tool setting gauge.
Common tool setting gauge
To set the tool setting point, first select the center of the right end face of the part and set it as the zero point. Once the machine tool returns to the original point, each tool to be used should be 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 will automatically record the measured value, ensuring that the Z axis is correctly aligned.
The X-axis tool setting is known as the trial cutting tool setting. Use a cutter tool to reduce the outer circle of the part and measure the outer circle value of the tool (e.g. x = 20mm). Enter x20 and click to measure. This ensures that the X axis is correctly aligned.
This tool setting method can be used for mass production of the same part for a long time, as the tool setting value remains unchanged even after the machine tool is powered off and restarted. Furthermore, the tool does not need to be reset during shutdown.
Debugging skills
After programming the part and setting the tool, there is a need to perform trial cutting and debugging to prevent program errors and tool setting errors from causing a collision accident.
Firstly, carry out the empty stroke simulation processing 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 before starting the simulation process.
After completing the simulation process, confirm that the program and tool setting are correct before processing the part.
Once the first part is processed, perform a self-inspection to ensure it is qualified. Then, ask a full-time technician to check the part.
After confirming that the full-time inspection is qualified, commissioning is complete.
Complete the processing of parts
After completing the initial trial cut, batch production is necessary. However, qualifying the first part does not guarantee the entire batch of parts will meet the required standards.
During the processing stage, tools wear due to variations in the materials being processed. The degree of wear depends on the hardness of the material; softer materials lead to less wear, whereas harder materials result in faster wear.
Therefore, frequent inspections are necessary during the processing stage. It is also important to adjust the cutter compensation value in a timely manner to ensure the parts meet the required standards.
Tool wear process and blunt standards
As an example, let’s consider the parts we processed earlier, using K414 as the processing material, with a total processing length of 180mm. However, due to the material’s extreme hardness, the tool wears out quickly during the processing. Consequently, a slight deviation of 10-20mm is generated from the beginning to the end, resulting from tool wear.
To ensure the parts’ qualification, we must artificially add a slight degree of 10-20mm in the program.
The basic principles of processing
First, rough machining should be performed to remove excess material from the workpiece, followed by finishing machining.
During processing, it is crucial to avoid any vibration or thermal degeneration. Vibration can be caused by various factors, such as excessive load, machine tool and workpiece resonance, insufficient machine tool rigidity, or tool passivation.
To minimize vibration, the following methods can be used:
- 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
The collision of the machine tool can significantly damage its accuracy, and the impact varies across different types of machine tools.
In general, machines with less rigidity are more susceptible to damage from collisions. Therefore, it is crucial to avoid collisions in high-precision CNC lathes. With careful operation and the use of specific anti-collision techniques, collisions can be completely prevented.
The primary reasons for collisions are:
- Errors in tool diameter and length input, incorrect workpiece and other geometrical dimensions input, as well as incorrect initial positioning of the workpiece can cause problems during machining.
- Inaccurate setting of the workpiece coordinates or resetting of the machine zero point during machining can also result in changes, and most collisions occur when the machine tool is moving rapidly. Therefore, it is crucial for the operator to be vigilant during the initial stages of executing the program and changing tools. Mistakes in program editing or incorrect input of tool dimensions can easily lead to collisions at this time.
- At the end of the program, improper sequencing of the CNC axis retracting motion can also cause collisions. It is important to take special precautions to avoid collision during these critical stages of the machining process.
To avoid collisions as mentioned above, the machine operator must utilize their five senses fully while operating the machine tool. The operator needs to observe if there are any abnormal movements, sparks, noises, vibrations, or burnt smells from the machine tool. If any of these situations are detected, the operator should immediately stop the program, and the machine should not be used until the problem is resolved.
Mastering the operation skills of CNC machine tools is a gradual process and cannot be achieved overnight. It requires mastering the basic operation of machine tools, as well as basic machining and programming knowledge.
The operation skills of CNC machine tools are not static; they require an organic combination of the operator’s imagination and hands-on ability, making it a type of innovative labor.
