At present, the manufacturing industry has two requirements for CNC vertical lathes, one is to have high precision in processing, and the other is to have high productivity in the manufacturing process.
CNC vertical lathe machining precision, X-axis, Z-axis are full closed-loop geometric axis, mechanical transmission is completed by high-precision ball screws, stable working condition, machine accuracy, repeatable positioning accuracy is high.
Due to the machine operator’s lack of operating experience, although the CNC vertical lathe has superior machining flexibility than ordinary lathe, it is not much different from ordinary lathe as far as the productivity of turbine parts is concerned.
Therefore, in order to reduce the manufacturing cost, improve the efficiency of CNC vertical lathe becomes the top priority of the turbine manufacturer, and the reasonable use of programming skills, mastering the characteristics of CNC vertical lathe machine tool, to improve the processing efficiency has an unexpected effect.
How to improve the efficiency of CNC vertical lathe?
1. Flexible setting of tool stop reference point
CNC lathe a total of X, Z two geometric axes, the geometric center of the turbine cylinder for the origin of the coordinate system, the tool is close to the workpiece, the coordinate value decreases, called into the tool;
On the contrary, the coordinate value increases, away from the workpiece, known as the retreat. When the tool back to a safe position, this point is convenient to enter and exit the tool, and at the same time conducive to the replacement of inserts, this position is called the stop reference point.
The reference point is a very important concept in programming. After each execution of an automatic cycle, the tool must return to this position in preparation for the next cycle.
Therefore, the actual position of the tool relative to the workpiece must be adjusted before executing the program. Due to the complexity of the internal structure of the turbine cylinder, it is very critical to choose a reasonable retraction point; if the empty stroke is too long, machining time is wasted; if it is too close, the tool may collide with the workpiece when the machine is rapidly feeding the tool.
At the same time, the actual position of the tool stop reference point is not fixed, the programmer can adjust the position of the tool stop reference point according to the diameter of the workpiece, the shape of the workpiece, the type of tool used, etc., which can effectively shorten the empty stroke of the tool and thus improve efficiency.
2. Reduce the tool empty stroke
Empty stroke refers to the distance run by the tool to approach the workpiece and return to the stopping point after cutting is completed. The external dimensions of the front cylinder and middle cylinder of the steam turbine are large, and the empty stroke of the machine tool is longer when the inner cavity is sized, taking the front cylinder of the 50MW back-pressure steam turbine as an example, the distance from the vertical flange surface to the steam seal groove is 2600mm.
As long as the tool empty stroke is reduced and the retraction point is reasonably designed, the operating efficiency of the machine can be improved. For example, when machining the front cylinder of the turbine, the following points need to be considered when machining each spacer groove:
(1) Calculate and analyze the workpiece drawings to determine the clamping length of the tool, the adjustment height of the machine tool crossbar, the height of the machine tool crossbar is very critical, in order to meet the case of tool change as far as possible to adjust the height of the crossbar, otherwise the ram overhangs out longer, the toolbar stiffness when cutting is poor, affecting the machining accuracy;
(2) Reasonable programming, through the Z, X tool setting reference, to determine the tool programming processing size, through a tool setting, you can complete the processing of each groove, to avoid the operator needs to adjust the tool when machining each groove, to improve machining accuracy.
Ordinary vertical lathe machining each groove needs to be measured, repeated tool setting in machining, each time the human occupation of the machine operation will produce tool setting error, the size of the cumulative error, and ultimately affect the accuracy of the product.
Through the CNC vertical lathe can control the empty stroke of the tool in the smallest range, to avoid each spacer slot tool setting, thus improving the efficiency of machine tool processing.
3. Optimize tool selection, extend tool life
The turbine cylinder structure is so varied that each model of turbine needs to be equipped with a set of tools. In this case, in order to reduce the number of tools and optimize the tool magazine, it is recommended that the general-purpose tools be placed in order, and the professional tools be well labeled and placed in a fixed position.
Due to the differences in the geometry of the tools themselves, there are large differences in the stiffness and strength of different tools, for example, between an internal circular tool and a cut-off tool.
If these differences are not considered when programming. Roughing with a weak stiffness of the tool to withstand a large cutting load, it will lead to abnormal wear or even damage to the tool, and the machining quality of the part does not meet the requirements, or even digging into the processing defects such as.
Therefore, the programming must analyze the structure of the parts, with higher strength, stiffness of the tool to withstand a larger cutting load, with strength, stiffness of the tool to withstand a smaller cutting load, roughing tool, finishing tool with a reasonable cutting dosage, reduce the number of times grinding and replacing the tool, to extend the service life of the tool, improve productivity.
Reasonable machining program
1. Workpiece clamping
The workpiece is mainly clamped by the jaws to tighten the workpiece, and the auxiliary support is added to enhance the rigidity of the workpiece. The turbine is an irregular workpiece, and its geometric center of gravity is difficult to determine, which requires many years of experience and practice by the operator.
Especially the front cylinder seal section is downward, the workpiece is big at the top and small at the bottom, the center of gravity is high, the unreasonable clamping scheme will lead to high-frequency vibration during the machining process of the workpiece, and the finishing tool, due to its high hardness, is very prone to chipping, which affects the surface roughness and machining dimensions.
Workpiece clamping defects will lead to more unfavorable factors.
The front cylinder of the turbine, in the case of conventional clamping methods, needs to choose a better auxiliary support. After the auxiliary support point is selected, the pressure plate is used to press and fix the point, and the size of the pressure force is moderate, and too large leads to the deformation of the workpiece.
In processing, because the height of the workpiece reaches 2800mm, by welding clamping hitch in the cylinder body, as the pressure plate support point.
When machining is completed, the welded hitch is milled off on the boring machine, and the clamp is ground flat.
2. Alignment of workpiece
Workpiece alignment is a key factor in ensuring machining accuracy, to ensure that the geometric center of the workpiece and the rotary center of the worktable back.
In order to improve the accuracy of calibration and unify the datum with the previous process, it is recommended to process the calibration circle and calibration plane when the turbine front cylinder and middle cylinder are processed in the previous process.
In the CNC boring machine fine milling center parting surface, after the completion of fine milling, the horizontal center parting surface will be calibrated, the workpiece will be calibrated with the vertical flange surface, the cat’s paw surface will be milled flat, and the horizontal center parting surface will be the center, and the fine milling of the calibration plane and the calibration inner circle will be done.
Through this, the lathe can greatly save correction time when correcting the workpiece, and the correction accuracy is much higher than the conventional method.
3. Reasonable control of machining allowance
Control the machining allowance of each process, can effectively shorten the production cycle of the product. Generally should be too much blank on the margin, especially containing forging, casting hard skin layer of the margin arrangements in the ordinary lathe processing, CNC vertical lathe for semi-finishing and finishing.
If you must use CNC vertical lathe processing, you need to pay attention to the reasonable preparation of the program to control the machining allowance of each knife.
Workpiece machining allowance needs to be reasonably controlled, if the allowance is large, the machining load increases, and the workpiece needs to be cut several times, which affects the machining efficiency; finishing allowance left less, in the finishing process, the semi-finishing cutter pattern can not be completely eliminated, which affects the surface roughness.
When semi-finish machining the front and middle cylinders of the turbine, leave a finishing allowance of 1mm on the diameter and 0.5mm on the plane.
Reasonable use of machine advantage precision
Reasonable use of the advantages of machine tool function, that is, to improve the productivity of the machine tool and product machining accuracy. Some CNC vertical lathes are equipped with a power head at the end of the square pillow, which can complete the boring and milling of the workpiece.
As a CNC machine tool operator, you must fully grasp the machine tool, understand the processing characteristics of the machine tool, in order to be able to give full play to the advantages of the machine tool in the processing of precision, the choice is conducive to the protection of the machine tool accuracy of the processing program.
CNC vertical lathe itself weighs more, by its own gravity, the machine tool in the long-term fast start or fast stop, resulting in machine tool accuracy is affected, affecting the service life of the machine tool.
In order to improve the machining efficiency and protect the accuracy of the machine tool, the G0 instruction is reasonably invoked when writing the program, and the G64 function is enabled in the main program, so that the machine tool has a buffer when the feed axes are started and stopped.
When manually executing the empty stroke of the machine tool, it is prohibited to make an emergency stop during high-speed operation.
The type of products processed by the CNC vertical lathe is rotary body parts, when turning the workpiece plane, the finishing allowance is controlled between 0.5-0.9mm, and the surface roughness is able to reach Ra1.6-3.2μm.
Boring machine adapted to box parts processing, in the processing of flat surface, finishing allowance control 0.015-0.04mm between, the surface roughness can reach Ra0.8 ~ 1.6μm. this is the machine tool characteristics of the impact on the processing of parts.
Conclusion
Through the analysis of the above large-scale CNC vertical lathe processing factors, combined with the steam turbine industry processing experience, can greatly improve production efficiency and ensure product quality.
Maximize the processing advantages of CNC vertical lathe, reduce the manufacturing cost of enterprises, and at the same time have a certain reference role in peer processing.