I. What are the characteristics of CNC milling machines?
1. Processing characteristics
For machining areas that are frame-shaped planes or steps of varying heights, a point-to-line CNC milling machine is sufficient. If the machining area is a curved contour, the choice between a two-axis or three-axis linkage system should be determined based on the geometry of the surface. Alternatively, depending on the part's machining requirements, a CNC indexing head or a CNC rotary table can be added to a standard CNC milling machine. In this case, the machine tool becomes a four-axis CNC system, capable of machining spiral grooves, blade parts, etc.
2. Dimensions
Smaller CNC milling machines with lifting tables typically have a table width of less than 400mm, making them ideal for machining small to medium-sized parts and contour milling of complex surfaces. Larger machines, such as gantry milling machines, have table widths of 500-600mm or more, and are used to machine large, complex parts.
3. Accuracy
my country has established precision standards for CNC milling machines, including specialized standards for CNC vertical milling machines and lifting table milling machines. These standards specify a linear motion coordinate positioning accuracy of 0.04/300mm, a repeatability of 0.025mm, and a milling circle finish of 0.035mm. In reality, machine tools typically have a considerable margin of error in their factory-set precision, often compressing the tolerances by about 20% compared to the national standards. Therefore, from a precision selection perspective, general CNC milling machines can meet the machining needs of most parts. For parts requiring higher precision, a precision CNC milling machine should be considered.
4. Batch
For large-scale production, users can use dedicated milling machines. For small to medium-batch production with frequent, repetitive cycles, CNC milling machines are highly suitable, as the initial batch of tools, fixtures, and programs can be stored and reused. In the long run, the trend of highly automated milling machines replacing ordinary milling machines, reducing labor and increasing productivity, is inevitable.
II. Precautions for operating CNC milling machines
(I) Basic Matters
1. When entering the workshop for internship, wear work clothes, ensuring the cuffs are tightly rolled up and the shirt is tucked into the trousers. Female students must wear safety helmets and tuck their braids inside. Sandals, slippers, high heels, vests, skirts, and scarves are not allowed in the workshop. Note: Gloves are not permitted when operating machine tools.
2. Take care not to move or damage the warning signs installed on the machine tool;
3. Avoid placing obstacles around the machine tool; the workspace should be large enough.
4. When a task requires two or more people to complete together, attention should be paid to coordination and consistency among them;
5. Compressed air is not permitted for cleaning machine tools, electrical cabinets, and NC units;
6. Practice should be conducted on the designated machine tools and computers. No other machine tools, equipment, or electrical switches may be tampered with without permission.
(II) Preparatory Matters
1. Before operation, you must be familiar with the general performance, structure, transmission principle, and control program of the CNC milling machine, and understand the functions and operating procedures of each operating button and indicator light. Do not operate or adjust the machine tool before you understand the entire operation process.
2. Before starting the machine tool, check whether the electrical control system is normal, whether the lubrication system is unobstructed and whether the oil quality is good, and add enough lubricating oil as required. Check whether all operating handles are correct, whether the workpiece, fixture and cutting tool are firmly clamped, and whether the coolant is sufficient. Then run the machine tool at low speed for 3 to 5 minutes to check whether all transmission components are normal. Only after confirming that there are no faults can it be used normally.
3. After the program is debugged, you must obtain the instructor's permission before proceeding step by step. Skipping steps is not allowed. Unauthorized operation or violation of regulations without the instructor's permission will result in a score of zero. Those who cause accidents will be punished according to relevant regulations and will be required to compensate for the corresponding losses.
4. Before machining parts, it is essential to strictly check whether the machine tool origin and tool data are normal and to perform a no-cutting trajectory simulation.
(III) Precautions during the process
1. When processing parts, the protective door must be closed. Do not put your head or hands inside the protective door. The protective door must not be opened during processing.
2. During processing, the operator must not leave the machine tool without authorization and should maintain a high level of concentration, observing the machine tool's operating status. If any abnormal phenomena or accidents occur, the program should be stopped immediately, the power supply cut off, and the instructor notified promptly; no other operations are permitted.
3. Do not strike the control panel or touch screen with force. Do not strike the worktable, indexing head, fixtures, or guide rails.
4. It is strictly forbidden to open the CNC system control cabinet for viewing or touching without authorization;
5. Operators must not arbitrarily change the machine tool's internal parameters. Trainee students must not access or modify programs not written by themselves.
6. On the machine tool control microcomputer, no operations other than program manipulation, transmission, and program copying are permitted;
7. CNC milling machines are precision equipment. Except for the fixtures and workpieces placed on the worktable, it is strictly forbidden to pile any tools, clamps, cutting tools, measuring instruments, workpieces, or other miscellaneous items on the machine tool.
8. Do not touch the blade tip or metal filings with your hands. Metal filings must be removed with a metal hook or brush.
9. Do not touch the rotating spindle, workpiece, or other moving parts with your hands or in any other way;
10. Measuring the workpiece or manually changing speeds during processing is prohibited. Wiping the workpiece with cotton or cleaning the machine tool is also strictly forbidden.
11. Trial operations are prohibited;
12. When moving the positions of each axis using the handwheel or rapid traverse method, always carefully check the "+" and "-" markings on the X, Y, and Z axes of the machine tool before moving. Before moving, slowly turn the handwheel to check that the machine tool is moving in the correct direction, and only increase the moving speed after confirming this.
13. When it is necessary to pause the measurement of workpiece dimensions during program operation, the measurement should only be carried out after the machine tool has completely stopped and the spindle has stopped rotating, in order to avoid personal injury accidents;
14. If the machine tool is not used for several days, the NC and CRT sections should be powered on for 2-3 hours every other day;
15. When shutting down, wait 3 minutes after the spindle stops rotating before turning off the machine.
