General CNC machining usually refers to computer digital control precision machining, CNC machining lathes, CNC machining milling machines, CNC machining boring and milling machines, etc. CNC is a kind of automatic machine tool equipment, that has the logic of processing control code or other symbols in accordance with procedures prescribed by the instruction, and the decoding, to make machine movement and machining parts. CNC machining automation degree, with stable processing quality, but also according to the machine, tool, blank and fixture information, to simulate machining CNC program, and can identify the error in the process of processing. A CNC machining center is a kind of CNC machine tool with a tool library, that can automatically change the tool, to a certain range of the workpiece for a variety of processing operations. Therefore, CNC machining has the advantages of stable processing quality, high processing precision, high repetition precision, complex surface processing, and high processing efficiency. In the actual process of processing, human factors, and operational experience, to a large extent, will affect the final processing quality.
When using CNC machine tools, first of all, the geometric information and technological information of the drawings of the machined parts should be written into the processing program with the specified code and format; Then the processing program input into the numerical control device, according to the requirements of the program, through the numerical control system information processing, distribution, so that the coordinates move a number of small displacement, to achieve the relative motion of the tool and the workpiece, complete the parts processing.
CNC machine tool is a set of machine tools, computer, motor and drive control, and detection technology as one of the automation equipment. The basic components of CNC machine tools include a control medium, CNC device, servo system, feedback device, and machine body.
1, Greatly reduce the number of tooling, processing complex shape parts do not need complex tooling. If you want to change the shape and size of the parts, only need to modify the parts processing program, suitable for new product development and modification.
2, Stable machining quality, high machining accuracy, high repetition accuracy, and adaptation to the processing requirements of aircraft.
3, The production efficiency is higher under the condition of multi-variety and small-batch production, which can reduce the time of production preparation, machine tool adjustment, and process inspection, and reduce the cutting time due to the use of optimal cutting quantity.
4, It can process complex surfaces that are difficult to be processed by conventional methods, and even some parts that cannot be observed.
The division of CNC machining procedures can generally be carried out according to the following methods:
1, The tool concentrated sequencing method is according to the tool used to divide the process, with the same tool CNC machining parts can be completed on all the parts. With a second knife and a third knife to do whatever else they can. This can reduce the number of tool changes, compress the space-time, and reduce unnecessary positioning errors.
2, To machining parts sequencing method for CNC processing content of a lot of parts, according to its structural characteristics will be processed into several parts, such as inner shape, shape, surface, or plane. Generally, first processing plane, positioning the surface, after processing holes; First processing simple geometric shapes, then processing complex geometric shapes; Machining the parts with lower precision first, and then machining the parts with higher precision requirements.
3, With rough and fine CNC processing sequencing method for CNC machining deformation prone parts, due to the deformation may occur after rough machining and need to be calibrated, so generally speaking, where rough and fine machining should be separated from the process. To sum up, in the division of the process, we must depend on the structure and technology of the parts, the function of the machine tool, the number of parts CNC processing content, installation times, and the production organization of the unit flexible grasp. It is also suggested that the principle of process concentration or the principle of process dispersion should be determined according to the actual situation, but it must be reasonable.
The arrangement of the processing sequence should be considered according to the structure of the parts and the blank condition, as well as the need for positioning clamping, focusing on the rigidity of the workpiece, which is not destroyed. The order should generally follow the following principles:
1, The CNC machining of the previous process cannot affect the positioning and clamping of the next process, and the general machine tool processing process interspersed between them should also be considered comprehensively.
2, Advanced machining sequence of inner shape and inner cavity, and then shape machining process.
3, With the same positioning, clamping, or same knife CNC processing process is best connected, in order to reduce the number of repeated positioning, the number of tool changes,s and the number of moving plates.
4, In the same installation of multiple processes, should be arranged first to the workpiece rigid damage small process.
The following three points should be paid attention to when determining the positioning datums and clamping schemes:
1, Strive to design, process, and program the calculation of the benchmark unity.
2, As far as possible reduce the number of clamping, as far as possible after a positioning can CNC machining out of all the surfaces to be processed.
3, Avoid the use of manual adjustment schemes.
4, The fixture should be open, and its positioning and clamping mechanism can not affect the CNC machining of the knife (such as collision), encounter this kind of situation, can be used with the vise or add the bottom plate screw clamping.
The tool point can be located on the machined parts, but pay attention to the tool point must be the reference or has been finished parts, sometimes in the first process after the tool point was CNC machining damage, will lead to the second process, and after the tool point can not be found, Therefore, in the first process of the tool, attention should be paid to set up a relative position of the tool in the place where there is a relatively fixed size relationship with the positioning datum so that the original tool point can be retrieved according to the relative position relationship between them. This relative-to-tool position is usually located on the machine table or fixture. The selection principle is as follows:
1, Finding the right is easy.
2, Easy programming.
3, Small error in the toolset.
4, It is convenient and searchable to check during processing.
The origin of the workpiece coordinate system is set by the operator, it is in the workpiece after clamping, through the knife to determine, it reflects the distance between the workpiece and the machine zero position relationship. Once the workpiece coordinate system is fixed, it is generally not changed. The workpiece coordinate system and the programming coordinate system must be unified, that is, when machining, the workpiece coordinate system, and the programming coordinate system are consistent.
The cutting path is the motion path and direction of the tool relative to the workpiece in the process of exponential controlled machining. The reasonable choice of machining route is very important because it is related to the CNC machining precision and surface quality of the parts. In determining the knife route is the main consideration of the following points:
1, Ensure the machining accuracy requirements of parts.
2, Convenient numerical calculation, reduces programming workload.
3, Seek the shortest CNC machining route and reduce the empty cutting time to improve CNC machining efficiency.
4, Minimize the number of program segments.
5, Ensure that the workpiece contour surface after CNC machining roughness requirements, the final contour should be arranged at the last cut continuous processing out.
6, The advance and retreat of the tool (cut and cut out) line should also be seriously considered, in order to minimize the contour of the stop tool (cutting force sudden change caused by elastic deformation) and leave the mark, but also to avoid in the contour of the vertical under the knife and scratch the workpiece.
After the workpiece is found and the program debugging is completed, it can enter the automatic processing stage. In the process of automatic machining, the operator should monitor the cutting process to prevent abnormal cutting caused by workpiece quality problems and other accidents.
Monitoring the cutting process mainly considers the following aspects:
1, The main consideration of processing monitoring rough machining is 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 tool automatically cuts according to the predetermined cutting path. At this time, the operator should pay attention to observing the change of the cutting load in the process of automatic machining through the cutting load table, according to the bearing condition of the tool, adjust the cutting parameters, and play the maximum efficiency of the machine tool.
2, In the process of cutting the monitoring of cutting sound in the automatic cutting process, generally start cutting, the sound of the tool cutting workpiece is stable, continuous, and light, at this time the movement of the machine tool is stable. With the progress of the cutting process, when the workpiece has a hard point or tool wear or tool clamping and other reasons, the cutting process is unstable, unstable performance is the change of cutting sound, there will be a collision between the tool and the workpiece, the machine will appear vibration. At this time, the cutting parameters and cutting conditions should be adjusted in time. When the adjustment effect is not obvious, the machine tool should be suspended to check the condition of the tool and the workpiece.
3, Monitoring the finishing process is mainly to ensure the machining size and surface quality of the workpiece. The cutting speed is higher and the feed quantity is larger. At this time, attention should be paid to the impact of debris accumulation on the surface of the processing, for the cavity processing, should also pay attention to the corner processing and letting the knife. To solve the above problems, one is to pay attention to adjusting the spraying position of the cutting fluid, so that the machining surface is always in cooling conditions; The second is to pay attention to observe the quality of the workpiece that has been processed surface, by adjusting the cutting parameters, as far as possible to avoid quality changes. If the adjustment still has no obvious effect, the machine should be shut down to check whether the original program is reasonable. In particular, pay attention to the position of the tool when suspending or stopping the inspection. If the tool stops in the cutting process, the sudden spindle stop, will make the workpiece surface produce tool marks. Stop should be considered when the tool leaves the cutting state.
4, Tool monitoring tool quality largely determines the quality of the workpiece processing. In the process of automatic machining cutting, it is necessary to judge the normal wear condition and abnormal damage condition of the tool through sound monitoring, cutting time control, suspension inspection in the process of cutting, workpiece surface analysis, and other methods. According to the processing requirements, timely processing of the tool, to prevent the occurrence of processing quality problems caused by the tool is not timely processing.
1, Surface milling should choose not heavy grinding carbide end milling cutter or end milling cutter. In general milling, as far as possible to use the second cutting processing, the first cutting is best with end milling cutter rough milling, continuous cutting along the workpiece surface. The recommended width of each cutting tool is 60%- 75% of the diameter of the tool.
2, End milling cutter and end milling cutter with cemented carbide blade are mainly used for machining boss, groove, and box mouth surface.
3, Ball knife, round knife (also known as round nose knife) is often used for machining curved surfaces and variable bevel contours. The ball knife is mostly used for semi-finishing and finishing. Round knives with carbide inserts are often used for rough cutting.
1, machining program is one of the contents of the CNC machining process design, but also the need for the operator to comply with, the implementation of the procedures, is the specific description of the processing program, the purpose is to let the operator clear the content of the program, clamping and positioning, each processing program selected tools should pay attention to the problems.
2, In the processing program, it should include: the drawing and programming file name, workpiece name, clamping sketch, program name, the tool used by each program, the maximum depth of cutting, processing properties (such as rough machining or fine machining), theoretical processing time, etc.
After determining the processing technology, it is necessary to understand before programming:
1, Workpiece clamping method;
2, The size of the workpiece hair embryo —- in order to determine the scope of processing or whether the need for multiple clamping;
3, The workpiece material —- in order to choose the processing tool used;
4, The inventory of the knife —- to avoid processing because there is no tool to modify the procedure, if you must use the tool, you can prepare in advance.
Safe altitude setting principle: generally above the highest side of the island. Or the programming zero is set on the highest surface, which can also maximize the risk of knife collision.
Because different machine tools can recognize the address code and the NC program format is different, so it is necessary for the use of machine tools to choose the correct post-processing format to ensure that the program can run.
The way of program transportation can be divided into CNC and DNC two kinds, CNC refers to the program through the media (such as floppy disk, tape reading machine, communication line, etc.) transported to the machine memory storage, processing from the memory out of the program to process. Because the capacity of the memory is limited by the size, so when the program is large, DNC can be used for processing, because the DNC processing machine directly from the control computer reads the program (that is, to do while sending), so the capacity of the memory is not limited by the size.
1, Cutting parameters have three major elements: cutting depth, spindle speed, and feed speed. The overall principle of selection of cutting parameters is: less cutting, fast feed (i.e. cutting depth is small, fast feed speed)
2, According to the material classification, the tool is generally divided into ordinary hard white steel knife (material for high-speed steel), coating tool (such as titanium plating, etc.), alloy tool (such as tungsten steel, boron nitride tool, etc.).