Machining is the process of changing the external dimensions or properties of a workpiece using machining machinery.
The process of CNC machining
With the development of the manufacturing industry, many precision parts are now CNC machined, this is because CNC machining is not only easy to operate, but also has good processing results. So what is the process of CNC machining?
- According to the program list check the length, width and height of the workpiece (workpiece size).
- Place the workpiece according to the direction of the program sheet (workpiece placement)
- Copy the program with the same name according to the program list (program check)
- Check on the machine whether the flatness, verticality and right angle of the workpiece meet the process requirements (workpiece correction)
- Minute take number to do the second minute to avoid workpiece bias clock (operation first check)
- Check the tool used in processing according to the program sheet, the tool type, diameter, clamping length and the length of the tool to avoid empty (tool check)
- Check the correct position of the lower tool when the machine is running close to the workpiece (operation second check)
- After the rough machining is completed, use the calibration table to check if the workpiece is offset (operation third check)
- Check the flatness of the workpiece according to the 2D drawing after the machining is completed to see if it reaches the work difference requirement, and if the shape of the workpiece is missing the machining situation (operation fourth check)
The above process on CNC processing is shared here, CNC processing can logically handle the program with control codes or other symbolic instructions, through the computer will be decoded, so that the machine tool to perform the prescribed action.
What do I have to do to solve problems in CNC machining?
Because CNC machining is programmed and computer-controlled machining, CNC machining has the advantages of stable machining quality, high machining accuracy, high repeatability, the ability to process complex profiles and high machining efficiency. However, in the actual processing process, there are often some problems, how to solve this time?
1.Workpiece overcut.
Causes.
- 1, popping knife, tool strength is not long enough or too small. Resulting in the tool popping knife.
- 2, operator improper operation.
- 3, cutting allowance is not uniform. (e.g. leave 0.5 on the side of the surface and 0.15 on the bottom)
- 4, improper cutting parameters (e.g.: tolerance too large, SF set too fast, etc.).
Solution.
- 1, the principle of using the knife: can be large, not small, can be short not long.
- 2, add clear angle program, the margin as much as possible to stay even, (side and bottom margin to stay consistent).
- 3, reasonable adjustment of cutting parameters, the margin of large corners to repair round.
- 4, the use of machine tool SF function, the operator fine-tune the speed of the machine tool cutting to achieve the best results.
2.The division in.
Causes.
- 1, the operator manual operation is not accurate, manual operation number of errors.
- 2、There are burrs around the mould.
- 3, the centering bar has a magnetic.
- 4、The four sides of the mould are not perpendicular.
Improvement.
- 1、Manual operation should be repeatedly double-checked, and the parting centre should be at the same height at the same point as far as possible.
- 2、Deburr the periphery of the mould with an oil stone or file before wiping it clean with a rag, and finally confirm by hand.
- 3、Demagnetise the centre of the mould before dividing it (use a ceramic centre stick or other).
- 4、School table to check whether the four sides of the mould is vertical, (verticality error large need to review the program with the pliers).
3.To the knife.
Causes.
- 1, the operator manual operation is not accurate, manual operation number is wrong.
- 2, tool clamping error.
- 3, flying knife on the blade is wrong, (flying knife itself has a certain error).
- 4, R knife and flat bottom knife and flying knife between the error.
Solution.
- 1, manual operation should be repeatedly double-checked, to the knife as far as possible in the same point.
- 2, tool clamping with a wind gun blow clean or rag wipe clean.
- 3, flying knife on the blade to measure the tool bar, light bottom surface when available a blade.
- 4, a separate pair of knife program, can avoid the error between the R knife flat knife flying knife.
4.the collision machine – programming.
Causes.
- 1, safety height is not enough or not set (fast feed G00 when the knife or collet hit on the workpiece).
- 2, the tool on the program list and the actual program tool is written wrong.
- 3、The tool length (edge length) on the program sheet and the actual depth of machining are written wrongly.
- 4、The wrong number of Z-axis depths and the wrong number of Z-axis depths on the program sheet.
- 5、The coordinates are incorrectly set during programming.
Solution.
- 1、The height of the workpiece should be measured accurately to ensure that the safety height is above the workpiece.
- 2、The tool on the program sheet and the actual program tool should be the same (try to use automatic program sheet or program sheet with pictures).
- 3、Measure the actual depth of machining on the workpiece, and write down the length and edge length of the tool on the program sheet (generally 2-3MM above the workpiece for the tool clamping length and 0.5-1.0MM for the edge length to avoid emptying).
- 4, the actual Z axis on the workpiece to take the number, write clearly on the program sheet. (This operation is generally a manual operation to write a good to double check).
5.Crash machine – operator.
Causes.
- 1, depth Z-axis tool alignment error.
- 2, divided in touch with the number and manipulation of the number of errors (such as: single-sided take the number of no radius into the tool, etc.).
- 3, with the wrong knife (such as: D4 knife with D10 knife to process).
- 4, the program to go wrong (such as: A7.NC go A9.NC).
- 5、The hand wheel is shaken in the wrong direction during manual operation.
- 6, manual rapid feed when pressed in the wrong direction (for example: -X press +X).
Solution.
- Depth Z-axis tool setting must pay attention to what position the tool is on. (bottom surface, top surface, analysis surface, etc.).
- Sub-centre touch number and manipulation number to be repeatedly checked after completion.
- When clamping the tool should be repeatedly and the program list and the program cross-checked after loading.
- Procedures should be followed one by one in order.
- When using manual operation, the operator himself should strengthen the proficiency of the machine tool operation.
- When moving manually and quickly, the Z-axis can be raised to the top of the workpiece before moving.
6. Surface accuracy.
Causes.
- 1、The cutting parameters are unreasonable and the surface of the workpiece is rough.
- 2、The cutting edge of the tool is not sharp.
- 3, tool clamping is too long, the edge of the tool to avoid empty too long.
- 4、Chip removal, blowing and oiling are not good.
- 5、Programming the way to go, (you can try to consider going smooth milling).
- 6、The workpiece has burrs.
Solution.
- 1, cutting parameters, tolerances, allowances, speed feed settings to be reasonable.
- 2, the operator is required to check the tool from time to time, not regularly replaced.
- 3, the operator is required to clamp the tool as short as possible, the edge of the tool to avoid empty not too long.
- 4、For the flat knife, R knife, round nose knife undercutting, the speed feed setting should be reasonable.
- 5, the workpiece has burrs: the root of our machine tools, tools, tool walking way has a direct relationship. So we need to understand the performance of the machine tool, the side of the burr to make up the knife.
Safety rules for CNC machining
General CNC machining usually refers to computer digital control of precision machining, CNC machining lathes, CNC machining milling machines, CNC machining boring mills, etc. CNC machining is a new processing technology, the main work is the preparation of processing programs, that is, the original manual work to computer programming. So what are the safety rules of CNC machining?
- 1. must comply with the machining centre safety operating procedures.
- 2. Before working according to the provisions should wear protective equipment, tie the cuffs, not allowed to wear scarves, gloves, ties, aprons, female workers should pull the hair braid in the hat.
- 3. Check whether the tool compensation, machine zero point and workpiece zero point are correct before starting the machine.
- 4. The relative position of the buttons should be in accordance with the operating requirements. Prepare and enter the CNC program carefully.
- 5. To check the equipment on the protection, insurance, signal, position, mechanical transmission parts, electrical, hydraulic, digital display and other systems operating conditions, in all normal circumstances before cutting processing.
- 6. Machine tool test run before processing, should check the lubrication, mechanical, electrical, hydraulic, digital display and other systems operating conditions, in all normal circumstances before cutting processing.
- 7. Machine tool according to the program into the processing operation, the operator is not allowed to touch the moving workpiece, tool and transmission part, forbidden to pass or take tools and other items across the rotating part of the machine.
- 8. Adjusting the machine, clamping workpieces and tools and wipe the machine, must be stopped.
- 9. No tools or other objects are allowed to be placed on electrical appliances, operating cabinets and guards.
- 10. No direct removal of chips by hand, special tools should be used for cleaning.
- 11. If abnormal conditions and alarm signals are found, stop immediately and ask the relevant personnel to check.
- 12. Not allowed to leave the work station when the machine is running, for some reason to leave, the table will be placed in the middle position, the tool bar returned, must stop, and cut off the host power.
The Key points of CNC machining operation
- 1. In order to simplify positioning and security, each positioning surface of the fixture should have precise coordinate dimensions relative to the machining centre’s machining origin.
- 2. To ensure that the orientation of the part is consistent with the workpiece co-ordinate system and machine co-ordinate system selected in the programming, and the orientation of the installation.
- 3. To be able to be dismantled in a short time and changed into a fixture suitable for the new workpiece. As the auxiliary time of the machining centre has been compressed to a very short time, the loading and unloading of the fixture should not take up too much time.
- 4. The fixture should have as few components as possible and a high degree of rigidity.
- 5. The fixture should be as open as possible, the spatial position of the clamping elements should be as low as possible, and the mounting fixture should not interfere with the tool path of the work step.
- 6. Ensure that the workpiece is fully machined within the travel range of the spindle.
- 7. For machining centres with interactive tables, the design of the fixture must prevent spatial interference between the fixture and the machine tool due to the movement of the table, the upper support, lower support and rotation.
- 8. As far as possible, all machining is done in one clamping. When it is necessary to replace the clamping point, special care should be taken not to damage the positioning accuracy by replacing the clamping point, if necessary, in the process documentation.
- 9. The contact between the bottom surface of the fixture and the table, the bottom surface flatness of the fixture must be guaranteed to be within 0.01-0.02mm, with a surface roughness no greater than Ra3.2um.
The Advantages of CNC machining
CNC machining belongs to a processing method in aluminum processing, general CNC machining usually refers to computer digital control precision machining, CNC machining lathe, CNC machining milling machine, CNC machining boring and milling machine, etc., industrial aluminum processing in it belongs to the finishing process, then what are the advantages of CNC machining?
1, CNC can be automatically processed
CNC machining usually refers to the precision machining controlled by computer digital control. Therefore, it can be controlled by the program instructions of CNC machine tools, and the whole processing process is carried out automatically according to the program instructions. The high degree of automation of the machine tool greatly reduces the labour intensity of the workers.
Many CNC machines can now be run unattended throughout the machining cycle, freeing up the operator for other tasks. This brings a number of ancillary benefits to CNC users, including reduced operator fatigue, fewer errors caused by human error and consistent and predictable machining times for each workpiece.
2. High CNC machining accuracy
The second major advantage of CNC technology is the consistency and accuracy of the workpiece. The typical accuracy of today’s CNC machines has reached two to four thousandths of an inch or 0.05 to 0.10 millimetres, with repeatability close to or better than eight thousandths of an inch or 0.02 millimetres. This means that once a program has been validated, two, ten or a thousand identical parts can easily be produced with the same accuracy and consistency. Mass production is possible and product quality is easily controlled.
3. CNC machining flexibility
As these machines are run by a computer programme, running different workpieces is as simple as loading different programs.
This also brings another benefit in the form of quick changeovers. Because these machines are so easy to set up and run and can easily load programs, they have very short set-up times.
4. Highly efficient CNC machining
CNC machining allows for multi-coordinate linkage and can machine complex zero points. When the shape and size of the part needs to be changed, only the CNC program needs to be changed, saving production preparation time.
5, CNC processing complex profiles
It can process complex profiles that are difficult to process by conventional methods, and can even process some unobservable processing parts.
6, CNC processing reduces cutting time
In the case of multi-species and small batch production, the production efficiency is higher, and the time for production preparation, machine tool adjustment and process inspection can be reduced, and the cutting time can be reduced due to the use of the best cutting volume.