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Home - News - 12 items Summary of CNC processing experience, what is CNC processing?

12 items Summary of CNC processing experience, what is CNC processing?

January 29, 2021

CNC machining, also known as CNC machining, refers to the machining with CNC machining tools. Because CNC machining is controlled by computer after programming, CNC machining has the advantages of stable processing quality, high processing precision, high repeatability, complex surface machining and high processing efficiency. In the actual process of processing, human factors and operating experience, to a large extent, will affect the final processing quality. Below, let's take a look, a veteran driver with 10 years of CNC machining experience, summed up the 12 valuable experience.


How to divide CNC machining process?


CNC machining process can generally be divided according to the following methods:


The method of centralized tool ordering is to divide the working procedure according to the tool used, and use the same tool CNC to finish all the parts that can be completed. Use the second knife and the third to do whatever else they can. This can reduce the knife change times, compress the space time, reduce the unnecessary positioning error. For CNC parts with a lot of processing content, the processing part can be divided into several parts according to their structural characteristics, such as internal shape, shape, surface or plane. Generally, the plane and positioning surface are processed first, and the hole is processed later. The simple geometry is processed first, and then the complex geometry is processed. The parts with low precision are machined first, and the parts with high precision are machined again. For parts prone to CNC machining deformation, the rough and fine CNC machining sequence method, due to the deformation may occur after the rough machining and need to be shaped, so generally speaking, coarse and fine processing should be separated from the process. To sum up, in the division of the process, must be based on the parts of the structure and technology, the function of the machine tool, parts CNC machining content, the number of times of installation and the unit's production organization flexibly master. Suggest to use the principle of working procedure concentration to still use the principle of working procedure dispersedly additionally, want to decide according to actual circumstance, but certainly do one's best is reasonable.


The arrangement of the processing sequence should be considered according to the structure of the parts and the condition of the blank, as well as the need for positioning and clamping, the focus is that the rigidity of the workpiece is not destroyed. The sequence should generally follow the following principles:


The CNC machining of the previous process should not affect the positioning and clamping of the next process, and the general machine tool machining process should also be considered comprehensively. Advanced inner - shaped inner - cavity processing sequence, after the contour processing procedures. With the same positioning, clamping way or the same cutter CNC machining process is best connected to reduce the number of repeated positioning, knife changes and moving the number of pressing plate. In the same installation of multiple processes, should be arranged first to the workpiece rigid damage of the process.


Which aspects should be paid attention to in the determination of workpiece clamping mode?


The following three points should be paid attention to when determining the positioning datum and clamping scheme:


Strive to design, process, and programming calculation benchmark unified. As far as possible to reduce the number of clamping, as far as possible after a positioning can CNC machining all surfaces to be processed. Avoid using mechanical adjustment schemes. Fixture to open, its positioning, clamping mechanism can not affect the CNC machining tool (such as collision), encounter such a situation, you can use a vise or add the bottom plate screw clamping way.


How to determine the reasonable knife point? What is the relationship between artifact coordinates and programming coordinates?


The knife point can be processed in parts, but pay attention to the knife point must be the benchmark or has been processed, sometimes after the first step in the knife point was destroyed by the CNC machining, can lead to the next working procedure and after to don't find the cutting point, so the first step in the attention to the knife to have relatively fixed size relations with the locating datum places set up a location relative to the knife, so that we can according to the relative position between them relations back to the original cutting point. The opposable cutter position is usually located on the machine bench or jig.


The selection principles are as follows:It's easy to find the right one. Easy to program. Little error in tool setting. Easy to check when processing.


The origin position of the workpiece coordinate system is set by the operator. After the workpiece is clamped, it is determined by the tool. It reflects the distance and position relation between the workpiece and the zero point of the machine tool. Once the workpiece coordinate system is fixed, it generally does not change. Workpiece coordinate system and programming coordinate system must be unified, that is, workpiece coordinate system and programming coordinate system are consistent during machining.


How to choose the knife route?


The tool path is the path and direction of the tool relative to the workpiece being processed in the process of exponential control. The reasonable choice of machining route is very important, because it is related to CNC machining precision and surface quality. The following points are mainly considered in determining the route:


Ensure the machining accuracy of the parts. Convenient numerical calculation, reduce the programming workload. Seek the shortest CNC machining route, reduce the time of empty tool to improve CNC machining efficiency. Minimize the number of segments. To ensure the roughness of the workpiece contour surface after CNC machining, the final contour should be processed continuously with the last tool. The advance and retreat of the tool (cut and cut) line should also be carefully considered, in order to minimize the stopping of the tool at the contour (cutting force sudden change caused by elastic deformation) and leave the mark, but also to avoid the vertical knife in the contour surface and scratch the workpiece.


How to monitor and adjust CNC machining process?


After alignment and program debugging, the workpiece can enter the automatic machining stage. During automatic machining, the operator should monitor the cutting process to prevent abnormal cutting from causing quality problems and other accidents.


Monitoring the cutting process mainly considers the following aspects:


Monitoring of machining Rough machining is mainly concerned with the rapid removal of excess on the workpiece surface. In the automatic machining process of the machine tool, according to the set cutting parameters, the cutter automatically cuts according to the predetermined cutting track. At this time, the operator should pay attention to observe the change of the cutting load in the automatic machining process through the cutting load table, and adjust the cutting dosage according to the bearing state of the tool, so as to give full play to the maximum efficiency of the machine tool. Monitoring of cutting Sound in the process of automatic cutting, generally at the beginning of cutting, the sound of the tool cutting workpiece is stable, continuous, light, at this time the motion of the machine tool is stable. As the cutting process, when the workpiece has hard point or tool wear or tool feed after the reason, the cutting process appears unstable, unstable performance is the change of cutting sound, the tool and the workpiece will appear between each other hit sound, the machine will appear vibration. At this point should be timely adjustment of the cutting dosage and cutting conditions, when the adjustment effect is not obvious, should stop the machine, check the cutter and workpiece condition finishing process monitoring finishing, mainly to ensure the workpiece processing size and surface quality, cutting speed is higher, larger feed. At this point, we should pay more attention to the effect of chip nodules on the processed surface. For the cavity processing, we should also pay attention to the corner of the processed cutting and letting knife. To solve the above problems, one is to pay attention to adjust the cutting fluid spray position, so that the machining surface is always in cooling conditions; The second is to pay attention to observe the quality of the processed surface of the workpiece, by adjusting the cutting dosage, to avoid quality changes as far as possible. If the adjustment still has no obvious effect, it should be shut down to check whether the original program is reasonable. It is important to pay attention to the position of the tool during the pause or stop inspection. If the tool stops in the cutting process, the spindle will stop suddenly, and the workpiece surface will produce a cut mark. In general, when the tool leaves the cutting state, consider stopping. Tool monitoring tool quality largely determines the workpiece.


Non - grinding carbide end - milling cutter or end - milling cutter should be used for surface milling. General milling, as far as possible to use the second cutting tool processing, the first cutting tool had better use end milling cutter rough milling, along the workpiece surface continuous cutting. It is recommended that the width of each tool should be 60% to 75% of the diameter of the tool. End mills and carbide inserts are mainly used for machining lugs, grooves and box orifices. Ball knife, round knife (also known as round nose knife) is often used to machining curved surfaces and variable bevel contour shape. The ball knife is mainly used for semi-finishing and finishing. Carbide tipped knives are mostly used for roughening.


What is the function of the machining procedure sheet? What should be included in the process sheet?


Machining procedure sheet is one of the content of CNC machining process design, but also needs the operator to comply with, the implementation of the regulations, is the specific description of the machining procedure, the purpose is to let the operator clear the content of the program, clamping and positioning, the tool selection of each processing procedure should pay attention to the problem. In the processing program list, it should include: drawing and programming filename, workpiece name, clamping sketch, program name, tool used in each program, maximum depth of cutting, processing nature (such as rough or finishing), theoretical processing time, etc.


What should Be done before nc programming?

After determining the processing technology, understand before programming:


Workpiece clamping mode; The size of the workpiece's hair embryo -- in order to determine the processing scope or whether multiple clamping is required; The materials of the workpieces -- to choose which tools to use in the processing; What tools are in stock -- avoid modifying the program without this tool during machining. If you must use this tool, prepare it in advance.


What are the rules for setting safety levels in programming?


Rule of safety: generally above the highest surface of the island. Or the programming zero set in the highest plane, which can also minimize the risk of knife collision.


After the tool path is programmed, why do we need to do post-processing?


Because different machine tools can recognize the address code and NC program format is different, so for the use of machine tools to choose the correct post-processing format to ensure that the program can run.


What is DNC communication?


The way of program transmission can be divided into CNC and DNC, CNC refers to the program through media (such as floppy disk, tape reader, communication line, etc.) transferred to the memory of the machine to be stored, and the program is called out from the memory for processing. Because the storage capacity is limited by the size, so when the program is large, DNC processing can be used. Because the DNC processing machine directly from the control computer to read the program (that is, while doing), so it is not limited by the storage capacity by the size.


Cutting parameters have three main factors: cutting depth, spindle speed and feed speed. The general principle of the choice of cutting dosage is: less cutting, fast feed (that is, cutting depth is small, fast feed) according to the material classification, tools are generally divided into ordinary hard white steel (material for high-speed steel), coating tools (such as titanium plating), alloy tools (such as tungsten steel, boron nitriding tools). If you want to switch from CNC machining operator to programmer, these are the most important things to know. Besides the above, what else do you think you should know? Is it also important to improve efficiency? Is it also important to avoid collision and empty knives?