CNC machining occupies an important position in the CNC machining and manufacturing industry. The advanced level and the dimensional accuracy of CNC machining parts directly determine the performance of mechanical equipment. The machining and manufacturing industry with high-performance mechanical equipment can greatly enhance the overall economic strength of the country.
CNC lathe is one of the pillars supporting the modern manufacturing industry. It is responsible for the manufacture of CNC machining parts for a large number of equipment. The control of the dimensional accuracy of CNC machining parts is the focus of our technicians.
We analyze the causes of machining errors from CNC machining parts, and study how to solve them and avoid recurrence. CNC lathes mainly process rotary parts, and the main components of most CNC machined parts are holes, outer circles, grooves, and threads. Next, I will study from three aspects: the machining principle of CNC lathes, the causes of machining errors of CNC lathes, and the methods of error adjustment.
1. Processing principle of CNC lathe
The CNC lathe uses the CNC device to control the movement of the tool holder and the rotation of the spindle to process the workpiece. Before CNC lathes process parts, the technicians need to analyze the drawings to prepare the processing technology and programs. The debugging personnel input the program into the CNC machining lathe control system, and the workpiece is processed by the operator after debugging. In the process of CNC machining parts, the spindle drives the workpiece to rotate, the servo system drives the tool to process the workpiece under the control of the commands issued by the CNC device, and the operator checks the size of the CNC machined parts and uses the compensation function to correct the size.
2. Reasons for errors in CNC machining parts
When CNC machine tools are CNC machining parts, the dimensional accuracy of CNC machined parts will be affected by factors such as machine tool rigidity, workpiece deformation, tool wear, etc. In the process of CNC machining, we must analyze the reasons and solve them.
2.1 Machining tool wear affects machining accuracy
When CNC lathes are CNC machining parts, the tools will wear out. When machining the outer circle, the size of the outer circle will increase after the tool is worn, which will cause the size to be out of tolerance. In the process of CNC machining of the inner hole, the inner hole size will become smaller after the tool wears, causing the size to be out of tolerance. In CNC machining of threaded parts, after the thread cutter is worn, the internal and external threads are out of tolerance, and the ring gauge and plug gauge are unqualified.
2.2 The lack of rigidity of the machine tool and the rigidity of the tool causes the size to be out of tolerance
In the process of CNC machining parts, due to the excessive processing volume and insufficient rigidity of the machine tool, vibration is caused, and the surface quality of CNC machining parts is too poor. In the process of excessive cutting, the tool will wear faster, resulting in poor surface quality of the workpiece, and even causing the tool to break.
2.3 Insufficient coolant supply causes size error
In the process of metal CNC machining, a large amount of heat is generated due to the high cutting speed. During the cutting process, if the cooling is not timely enough, there will be a lot of iron cutting, winding the CNC machined parts and damaging the tool, resulting in the final size out of tolerance.
2.4 The size is out of tolerance due to the operation error of the technician
Enterprise technicians input the program and debug after the installation of the tool and CNC machined parts. During the debugging process, tool setting and size measurement are required. When setting the tool length compensation, the accuracy of the CNC machined parts will be out of tolerance due to operation errors. During the measurement of CNC machining parts, due to the insufficient size measurement, the measured size is too large or too small, which eventually causes the size to be out of tolerance.
3. The solution to the out-of-tolerance of the parts processed by the CNC lathe
Enterprise technicians input the program and debug after the installation of the tool and CNC machined parts. During the debugging process, tool setting and size measurement are required. When setting the tool length compensation, the accuracy of the CNC machined parts will be out of tolerance due to operation errors. When measuring the cutting parts, because the size measurement is not standardized, the measured size is too large or too small, which eventually causes the size to be out of tolerance.
In the normal CNC machining process, it is found that the size of the CNC machined parts is out of tolerance. We need to analyze it. If the tool is found to be good, we need to adjust the size according to the measurement results. Poor, many operators directly modify the size through tool compensation after measuring the final size. Often, the dimensional stability after such modification is not good. The ultimate reason is that the roughing allowance is too large.
In the actual CNC machining process, such as cutting a 45# steel outer circle with a diameter of 60 mm, the tolerance is generally set to -0.02 to 0, which requires us to perform roughing and finishing. After roughing, the outer circle size of the part should be 50.5– Between 50.3 and 3, we often neglect to measure the allowance after rough machining in the process of CNC machining parts. If cutting is performed under the condition that the finishing tool and cutting parameters are unchanged, the size will be too large.
After rough machining, the measurement result is 50.6 mm. We need to set the tool compensation through the offset interface. The final input value needs to be calculated. It is necessary to input –0.1 mm in the X-axis parameter setting to meet the requirements, but we generally adjust the size to smaller than the maximum size. Size adjustment to 50.45 mm is the best size value.
After the roughing dimension is qualified, we need to debug the finishing dimension. The outer circle dimension of 60 mm is debugged according to the tolerance value of –0.02 to 0. The optimal dimension is 59.99 mm. If the measured dimension is 60.02 mm, we It is necessary to calculate the difference between 60.02 mm and 59.99 mm, and make compensation in the X-axis direction of the finishing tool – 0.03 mm, measure again, and the size is qualified, then you can disassemble the part and continue processing. When setting the tool compensation, we must To be clear, the CNC lathe is parameterized according to the diameter.
When measuring the outer circle, if the length of the outer circle surface of the size is too long, we need to measure in sections. After finding that the outer circle has a taper, it needs to be debugged through the program. For example: the same outer circular surface is 80 mm long, and the taper in the diameter direction is 0.04 mm. When it is a forward taper, the adjustment program is G01X–0.04Z–80.F0.1, and when it is a reverse taper, the adjustment program is G01X0.04Z–80.F0. 1. The operator must detect the size accurately when the first piece of trial cutting is CNC machining, so as to prevent the occurrence of scrapping in batches. During the CNC machining process, the on-site operators should observe the liquid level of the cutting fluid on time. When the liquid level is too low, we should add the cutting fluid in time to prevent the occurrence of entanglement.
After performing routine inspection and correct judgment, the operator can well control the size of common parts processed by CNC lathes according to the above debugging methods. During the CNC machining process, the operator should also submit the inspection according to the regulations and make a record while doing the self-inspection, so that there is a “double insurance” for the inspection quality of the CNC machining parts.