1 Introduction
The FANUC system is one of the commonly used control systems for CNC machine tools, and its control commands are divided into single cycle commands and multiple cycle commands.
2 programming ideas
The essence of the program is to find out the characteristics of the tool trajectory, and realize the repeated statements in the program through mathematical algorithms. According to the above part characteristics, we find that the X coordinate value gradually decreases. Therefore, you can use the FANUC system to change the X wear value, customize the turning cycle processing, control the tool with a fixed value from the part of the tool's contour distance each time, and use the system condition jump after processing in each machining cycle before modification, and return Modify the statement accordingly. After the rough machining cycle is completed, determine the workpiece to determine the finishing amount, modify the tool compensation parameters, and then jump to complete to complete the turning.
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3 Correctly choose the loop starting point
When the cyclic program ends, the tool automatically returns to the starting position of the cyclic program execution at the end of the cycle. Therefore, it is necessary to ensure that the tool returns safely to the starting point at the end of the cycle. When the cycle instruction is programmed, it is easy to use the safety hazards that cause major problems. Of course, safety cannot be guaranteed. The starting point is set too far away from the workpiece, resulting in long and empty tool paths. affect processing efficiency. Is it safe to return to the start of the cycle, the start of the cycle program, the tool position at the end of the last line of the finishing process, the shape of the workpiece at the end of the cycle, the tool holder and other tool mount locations for the shape. In either case, it is ultimately possible to ensure that cycling does not interfere with rapid retraction by changing the starting position of the cycling program. You can use mathematical calculation methods, CAD software query base point coordinate method to determine the reasonable and safe start position of the cycle, or in the program debugging stage, use single-stage operation and low-magnification feed, try cutting, and modify the program start point coordinates step by step Determine a reasonably safe starting location. After considering the above factors, it is necessary to determine the starting point of the cycle, and special attention should be paid: if machining and cutting are added to the measurement and debugging program before machining, if the machine tool runs to the Nth line, the spindle stops, the program is paused, and retracts to the appropriate position after measurement. Then enter the position near the workpiece manually or manually, and execute the finishing cycle command automatically, and then the starting point of the cycle program is a point. If you choose an incorrect position, there may be interference. It is best before the finishing cycle. Before the program line, add instructions to quickly enter the reasonable starting position of the cycle program to ensure safety.
4 Reasonable combination of loop instructions
Usually, the finishing G70 command is used in combination with the roughing G71, G73, and G74 commands to complete the rough machining of the workpiece. However, in the case of a workpiece with a concave structure, for example, if the FANUCTD system G71 cycle command is used for roughing, use G71 for roughing, because this command performs the last cycle of roughing according to the contour. For example, use the FANUCTC system G71 cycle command for rough machining, and set the trimming edge allowance to be smaller than the depth of the concave surface structure. The trimming allowance is insufficient, and the workpiece is scrapped.
In order to solve this problem, we can use the rough machining method of G71 and G73, that is, first use the G71 cycle to remove most of the cutting edge, then use the G73 cycle to remove the concave structure with the processed edge, and finally use the G70 cycle for finishing or still use G71 And G70 processing, the depth of the concave-convex structure left in the rough machining stage exceeds the finishing allowance, in G70 processing, use the X-direction length compensation value of the tool or set the wear compensation method, after processing, for example, in G71 , set the finishing allowance in the X direction to 3.5, after the rough machining is finished, set a positive value input in the corresponding tool X direction compensation (for example, 0.5 is the finishing allowance), the tool is recovered and filled, and processed according to the G70 command , implement semi-finishing, cutting depth 3, after semi-finishing, the X direction compensation of the corresponding tool is set to -0.5 cumulative input, call the tool again, process according to the G70 command, execute
Finishing, with a depth of cut of 0.5. In order to keep the machining program consistent, and the X direction tool setting value for the semi-finishing and finishing stages is also called a different compensation number.
5 CNC lathe programming skills
5.1 Setting the initial state of the CNC system with a safety block
When programming, the planning of safety blocks is very important. Before starting the tool and spindle, in order to ensure the safety of machining, please set the start or initial state in the start block. Although a CNC machine is set to default values after power-up, there should be no chance of a programmer or operator relying on the system defaults due to their ease of change. Therefore, when writing NC programs, develop a safe program to set the initial state of the system. Good programming habits will not only ensure the absolute safety of programming, but also allow you to operate in debugging, tool path inspection and size adjustment, etc. The program is more convenient to use. At the same time, it also enhances the portability of the program because it does not depend on the default settings of the specific machine tool and CNC system. In the FANUC system, when machining parts with a small diameter, the safety program segment can be set as: G40G97G99G21.
5.2 Skillful use of M commands
CNC lathes have multiple M instructions, and the use of these instructions is related to the needs of machining operations. Using these M commands correctly and skillfully, these parts will bring a lot of convenience. Add the M05 (spindle stop rotating) M00 (program stop) command after finishing the part, which allows us to measure the size of the part easily to ensure the machining accuracy of the part. In addition, after the thread is completed, use the M05 and M00 commands to facilitate the detection of the thread quality.
5.3 Reasonably set the starting point of the cycle
Before using these cycle commands, FANUCCNC lathe has many cycle commands, such as simple fixed cycle command G92, compound fixed cycle command G71, G73, G70, thread cutting cycle command G92, G76, etc., the tool must first be positioned to the beginning of the cycle The starting point of the cycle not only controls the safe distance of the tool close to the workpiece and the actual cutting depth of the first roughing, but also determines the distance of the cycle hollow stroke. The starting point of G90, G71, G70, and G73 commands is usually set at the corner of the workpiece closest to the start of rough machining, the X direction is generally set to X (rough diameter), and the Z direction is generally set 2-5mm from the workpiece. The starting direction of the thread cutting cycle commands G92 and G76 is usually set outside the workpiece. When processing external threads, the X direction is generally set to X (thread diameter + 2). When processing internal threads, the X direction is generally set to X (thread diameter - 2) and the Z direction is generally set to thread 2-5mm.
5.4 Using abrasion skillfully to ensure the dimensional accuracy of parts
Tool compensation is divided into geometric offset and wear offset. Geometric offsets determine the position of the tool relative to the program origin, and wear offsets are used for precise dimensioning. When machining parts on a CNC lathe, in order to prevent waste, the wear compensation value can be input before machining the parts. When setting the wear compensation value of the part, the sign of the wear compensation value should have the allowance of the machined part. When machining the outer ring, a positive wear offset should be preset. When machining holes, a negative wear offset should be preset. The size of the wear offset is preferably the size of the finishing allowance.
6 Conclusion
In short, before the CNC lathe processing operation, the writing of instructions is the foundation, and it is the key to the lathe operation. We must do a good job in the writing and application of instructions.
