Due to the complexity of CNC machining (such as different machine tools, different materials, different tools, different cutting methods, different parameter settings, etc.), it is decided to engage in CNC machining (whether machining or programming) to reach certain Level must pass a relatively long period of time. This manual is a summary of some experiences in the long-term actual production process, related to CNC machining processes, processes, selection of common tool parameters, monitoring during processing, etc. For reference.
How to divide the processing process:
The division of CNC machining operations can generally be carried out as follows:
(1) According to the processing part sorting method For parts with a lot of processing content, the processing part can be divided into several parts according to its structural characteristics, such as inner shape, shape, curved surface or plane. Generally, the plane, the positioning surface, and the rear processing hole are first processed; the simple geometric shape is processed first, and the complicated geometric shape is processed; the lower precision part is processed first, and the processing precision requirement is higher.
(2) The tool concentration sorting method is to divide all the parts that can be completed on the part with the same tool according to the dividing process of the tool used. In the other parts that can be completed with the second knife and the third. This reduces the number of tool changes, compresses the dead time, and reduces unnecessary positioning errors.
(3) In the rough and fine processing, the parts that are prone to processing deformation need to be shaped due to the deformation that may occur after roughing. Therefore, in general, the rough and fine machining must be separated. .
In summary, when dividing the process, it must be based on the structure and process of the part, the function of the machine tool, the amount of CNC machining content of the part, the number of installations and the production organization status of the unit. It is also recommended to adopt the principle of process concentration or the principle of process dispersion, which should be determined according to the actual situation, but it must be reasonable.
What principles should be followed in the arrangement of processing orders?
The order of the processing sequence should be considered according to the structure of the part and the condition of the blank, as well as the need for positioning and clamping. The key point is that the rigidity of the workpiece is not destroyed. The order should generally be based on the following principles:
(1) First, the inner cavity is added, and then the outer shape processing step is performed.
(2) The processing of the previous process cannot affect the positioning and clamping of the next process, and the intermediate machining process must be considered in the middle.
(3) In the multiple processes carried out in the same installation, the process of reducing the rigidity of the workpiece should be arranged first. (4) It is best to connect the same positioning, clamping method or the same knife processing to reduce the number of repeated positioning, the number of tool changes and the number of moving plates.
three. What should be noted in the determination of the way the workpiece is clamped?
The following three points should be noted when determining the positioning reference and clamping scheme:
(1) Avoid using the manual adjustment scheme.
(2) Minimize the number of clamping operations and, as far as possible, machine all the surfaces to be machined after one positioning.
(3) Strive to unify the benchmarks of design, process, and programming calculations.
(4) The fixture should be opened smoothly, and its positioning and clamping mechanism can not affect the cutting in the machining (such as collision). When such a situation is encountered, it can be clamped by means of a vise or a bottom plate.
How to determine the correct point of the knife? What is the relationship between the workpiece coordinate system and the programmed coordinate system?
1. The tool point can be set on the part to be machined, but note that the tool point must be the reference position or the finished part. Sometimes the tool point is destroyed after the first process, which will lead to the second process and After the tool setting point is not searchable, it is necessary to set a relative tool setting position in the relative fixed size relationship with the positioning reference in the first process, so that the original position can be retrieved according to the relative positional relationship between them. The point of the knife. This relative pair of tool positions is usually located on the machine table or fixture. The selection principle is as follows:
1) Easy to program.
2) It is easy to find.
3) The tooling error is small.
4) Easy inspection during processing.
2. The origin position of the workpiece coordinate system is set by the operator. After the workpiece is clamped, it is determined by the tool setting. It reflects the positional relationship between the workpiece and the machine zero. Once the workpiece coordinate system is fixed, it is generally not changed. Both the workpiece coordinate system and the programmed coordinate system must be uniform, that is, the workpiece coordinate system and the programmed coordinate system are identical during machining.
How to choose a route?
The path of the tool is the trajectory and direction of the tool relative to the workpiece during the index control process. A reasonable choice of the machining route is very important because it is related to the machining accuracy and surface quality of the part. The following points are mainly considered in determining the route:
1) It is convenient for numerical calculation and reduces the amount of programming work.
2) Guarantee the machining accuracy requirements of the parts.
3) Minimize the number of blocks.
4) Seek the shortest machining route and reduce the emptying time to improve the processing efficiency.
5) To ensure the roughness of the contour surface of the workpiece after processing, the final contour should be arranged for the last pass to be continuously processed.
6) The path of the tool's advance and retraction (cut-in and cut-out) should also be carefully considered to minimize the stopping of the knife at the contour (the elastic change of the cutting force caused by the sudden change of the cutting force) and leave the tool marks, and also avoid the vertical deviation on the contour surface. Scratch the workpiece with a knife.
How to monitor and adjust during processing
After the workpiece is aligned and the program is commissioned, it can enter the automatic machining stage. During the automatic machining process, the operator monitors the cutting process to prevent workpiece quality problems and other accidents caused by abnormal cutting.
The following aspects are mainly considered for monitoring the cutting process:
1. Monitoring of cutting sound during cutting In the automatic cutting process, when the cutting is started, the sound of the cutting workpiece is stable, continuous and brisk, and the movement of the machine is stable. As the cutting process progresses, the cutting process becomes unstable when there are hard spots on the workpiece or tool wear or tool feeding. The unstable performance is that the cutting sound changes, and the tool and the workpiece will collide with each other. Sound, the machine will vibrate. At this time, the cutting amount and cutting conditions should be adjusted in time. When the adjustment effect is not obvious, the machine should be suspended and the condition of the tool and workpiece should be checked.
2. Machining Process Monitoring Roughing primarily considers the rapid removal of excess allowance on the surface of the workpiece. During the automatic machining of the machine tool, the tool automatically cuts according to the predetermined cutting path according to the set cutting amount. At this time, the operator should pay attention to observe the change of the cutting load during the automatic machining process through the cutting load table, adjust the cutting amount according to the bearing capacity of the tool, and maximize the efficiency of the machine tool.
3. The finishing process monitors the finishing, mainly to ensure the machining size and surface quality of the workpiece, the cutting speed is high, and the feed rate is large. At this time, attention should be paid to the influence of the built-up edge on the machined surface. For the cavity machining, it should also pay attention to the machining of the cut and the knife at the corner. For the solution of the above problems, one should pay attention to adjust the spray position of the cutting fluid, so that the machining surface is always in the optimal cooling condition; the second is to observe the quality of the machined surface of the workpiece, by adjusting the amount of cutting, avoid as much as possible Changes in quality. If the adjustment still has no obvious effect, it should be reasonable to stop the inspection of the original program.
It is important to note that when you pause or stop the inspection, pay attention to the position of the tool. If the tool stops during the cutting process, a sudden spindle stop will cause a tool mark on the surface of the workpiece. Generally, stop the machine when the tool leaves the cutting state.
(4) The quality of the tool monitoring tool determines the processing quality of the workpiece. In the automatic machining and cutting process, it is necessary to judge the normal wear condition and abnormal damage of the tool through sound monitoring, cutting time control, pause check during cutting, and surface analysis of the workpiece. According to the processing requirements, the tools should be processed in time to prevent the processing quality problems caused by the tools not being processed in time.
Seven. How to choose a reasonable processing tool? What are the major factors in the amount of cutting? Are there tools for several materials? How to determine the speed of the tool, cutting speed, cutting width
1. Non-reground carbide end mills or end mills should be used for face milling. Generally, when milling, try to use secondary cutting. The first pass is preferably rough milling with end mill and continuous cutting along the surface of the workpiece. The width of each pass is recommended to be 60% - 75% of the tool diameter.
2. End mills and end mills with carbide inserts are mainly used for machining bosses, grooves and box faces.
3. Ball knives and round knives (also known as round nose knives) are often used to machine curved surfaces and beveled contours. Ball knives are mostly used for semi-finishing and finishing. Round knives with carbide tools are often used for roughing.
8. What is the role of the processing program? What should be included in the processing program list?
(1) In the processing program list, it should include: drawing and programming file name, workpiece name, clamping sketch, program name, tool used in each program, maximum depth of cutting, processing properties (such as roughing or finishing) ), theoretical processing time, etc.
(2) The processing program list is one of the contents of the NC machining process design. It is also a procedure that requires the operator to abide by and execute. It is a specific description of the machining program. The purpose is to let the operator clarify the contents of the program, the clamping and positioning methods, and each The tool selected for the machining program should be concerned with the problem.
9. What to do before NC programming
After determining the processing technology, you should know before programming:
1. Workpiece clamping method;
2, the size of the workpiece blank ---- to determine the scope of processing or whether multiple clamping is required;
3, the material of the workpiece ---- to choose which tool to use for processing;
4. What are the knives in stock----avoid to modify the program during machining because there is no such tool, if you must use this tool, you can prepare in advance.
X. What are the principles for setting the safe height in programming?
The principle of setting the safety height: generally higher than the highest point of the island. Or set the programming zero point to the highest surface, so as to avoid the danger of collision.
XI. After the tool path is compiled, why should it be post-processed?
Because the address code and NC program format that can be recognized by different machine tools are different, it is necessary to select the correct post-processing format for the machine tool used to ensure that the programmed program can run.
XII. What is DNC communication?
(1) The mode of program transmission can be divided into two types: CNC and DNC. The CNC means that the program is transported to the memory of the machine tool through the media medium (such as floppy disk, tape reader, communication line, etc.), and is transferred from the memory during processing. The program is processed. Since the capacity of the memory is limited by the size, when the program is large, the DNC method can be used for processing. Since the machine tool directly reads the program from the control computer during the DNC processing (that is, it is done while sending), it is not subject to the memory capacity. Subject to size.
(2) According to the classification of materials, the tools are generally divided into ordinary hard white steel knives (materials are high-speed steel), coated tools (such as titanium plating), alloy tools (such as tungsten steel, boron nitride tools, etc.).
(C). There are three major factors in the amount of cutting: cutting depth, spindle speed and feed rate. The overall principle of the choice of cutting amount is:
Less cutting, fast feed (ie small depth of cut, fast feed rate)[/link]
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