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10 Valuable Lessons in CNC Machining
Jin Ming Auto Parts Manufacturing Technology Limited | Date:2023/8/2 | View:91
First, how to divide the CNC machining process?
CNC machining process can be divided generally according to the following methods:

1. Tool focused sub-processing method is to divide the process according to the tool used, with the same tool cnc machining finished all the parts on the part can be completed. In the second knife, the third knife to complete the other parts they can complete. This reduces the number of tool changes, compressed air time, reducing unnecessary positioning errors.

2. The processing part of the sequential method for CNC machining content of many parts, according to its structural characteristics of the machining part into several parts, such as internal shape, shape, surface or plane. General first processing plane, positioning surface, after processing holes; first processing simple geometry, and then processing complex geometry; first processing parts with lower precision, and then processing parts with higher precision requirements.

3. To rough and finish CNC machining sub-processing method for parts prone to CNC machining deformation, due to the deformation that may occur after rough machining and the need for calibration, so generally speaking, where rough and finish machining are to be separated from the process. In summary, in the division of the process, must be depending on the structure of the parts and process, the function of the machine tool, the number of parts CNC CNC machining content, the number of installations and the unit''s production organisation status and flexibility. Another suggestion is to use the principle of process concentration or the principle of process dispersion, according to the actual situation to determine, but must strive to be reasonable.

Second, CNC machining sequence should be arranged in accordance with what principles?
The machining sequence should be arranged according to the structure of the parts and blank conditions, as well as the need to consider the positioning and clamping, focusing on the rigidity of the workpiece is not destroyed. The sequence should generally be carried out in accordance with the following principles:

1. The previous process of CNC machining can not affect the positioning and clamping of the next process, interspersed with general-purpose machine tool machining processes should also be considered comprehensively.

2. The first internal cavity plus process, followed by the shape of the machining process.

3. With the same positioning, clamping mode or the same knife CNC machining process is best to connect to reduce the number of repetitive positioning, the number of times the knife and move the number of times the pressure plate.

4. In the same installation of multiple processes, should be arranged first on the workpiece rigidity of small damage to the process.

Third, the determination of workpiece clamping should pay attention to those aspects?
In determining the positioning reference and clamping programme should pay attention to the following three points:

1. Strive to design, process, and programming calculations of the benchmark unity.

2. Try to reduce the number of clamping, as far as possible to do in a positioning can be CNC machined out of all the surfaces to be machined.

3. Avoid the use of accountable machine manual adjustment programme.

4. The fixture should be open and smooth, its positioning, clamping mechanism can not affect the CNC machining in the knife (such as collision), encountered such a situation, can be used with a vise or add a base plate to draw the screws of the clamping method.

Fourth, how to determine the tool point is more reasonable? What is the relationship between the workpiece coordinate system and programming coordinate system?

1. The tool setting point can be located in the processed parts, but note that the tool setting point must be the reference position or has been machined parts, sometimes in the first process after the tool setting point is destroyed by CNC machining, will lead to the second process and after the tool setting point to look for, so in the first process to the knife to pay attention to the positioning of the datum in the relative size of the relative size of the relationship between the establishment of a relative tool position, so that according to the relative position relationship between them to retrieve the original. Relative position relationship between them to find the original tool setting point. This relative to the tool position is usually located on the machine table or fixture. Its selection principles are as follows:

(1) Easy to find the right.
(2) Programming convenience.
(3) Tool setting error is small.
(4) Easy to check when processing, can be checked.

2. The origin position of the workpiece coordinate system is set by the operator himself, it is determined by tool setting after the workpiece is clamped, it reflects the distance position relationship between the workpiece and the zero point of the machine tool. Once the workpiece coordinate system is fixed, it is generally not changed. Workpiece coordinate system and programming coordinate system must be unified, that is, in the processing, workpiece coordinate system and programming coordinate system is consistent.

Fifth, how to choose the tool route?
Tool route is the index control machining process of the tool relative to the machined part of the trajectory and direction. Reasonable choice of machining route is very important, because it is closely related to the CNC machining accuracy and surface quality of parts. In determining the tool route is the main consideration of the following points.

1. To ensure that the machining accuracy requirements of the parts.

2. To facilitate numerical calculation, reduce programming workload.

3. Seeking the shortest CNC machining route, reduce the empty knife time to improve cnc machining efficiency.

4. Minimise the number of program segments.

5. To ensure that the surface of the workpiece contour CNC machining roughness requirements, the final contour should be arranged for the last knife continuous processing out.

6. The tool in and out of the knife (cut in and cut out) route should also be carefully considered to minimise stopping the knife at the contour (cutting force caused by a sudden change in elastic deformation) and leave a knife mark, but also to avoid the contour of the surface vertically under the knife and scratch the workpiece.

Sixth, how to monitor and adjust the CNC machining process?
The workpiece can enter the automatic machining stage after the alignment and programme debugging are completed. In the automatic machining process, the operator should monitor the cutting process to prevent abnormal cutting caused by workpiece quality problems and other accidents.

Cutting process monitoring mainly consider the following aspects:

1. The machining process monitoring rough machining is mainly considered to be the workpiece surface of the excess margin of the rapid removal. In the automatic machining process, according to the set amount of cutting, the tool automatically cuts according to the predetermined cutting trajectory. At this time, the operator should pay attention to the cutting load table to observe the automatic machining process of the cutting load changes, according to the cutting tool bearing capacity, adjust the cutting amount, play the maximum efficiency of the machine tool.

2. The cutting process of cutting sound monitoring in the automatic cutting process, generally start cutting, the sound of the tool cutting the workpiece is stable, continuous, brisk, at this time the movement of the machine tool is smooth. With the cutting process, when the workpiece has a hard point or tool wear or tool feed clip and other reasons, the cutting process appears unstable, unstable performance is the cutting sound changes, the tool and the workpiece will appear between the sound of mutual impact, the machine tool will appear vibration. At this point should be timely adjusted cutting dosage and cutting conditions, when the adjustment effect is not obvious, should pause the machine tool, check the status of the tool and workpiece.

3. Finishing process monitoring finishing, mainly to ensure that the workpiece processing size and processing surface quality, cutting speed is higher, feed is larger. At this time should pay attention to the chip tumour on the machining surface, for cavity machining, should also pay attention to the corners of the processing of overcutting and let the knife. For the solution of the above problems, one should pay attention to adjusting the spray position of the cutting fluid, so that the machined surface is always in the cooling conditions; secondly, pay attention to observe the quality of the machined surface of the workpiece, by adjusting the amount of cutting, as far as possible to avoid changes in quality. If the adjustment is still no obvious effect, it should be stopped to check whether the original programme is programmed reasonably. Special attention should be paid to the position of the tool when pausing for inspection or stopping for inspection. If the tool stops during the cutting process, the sudden spindle stoppage will produce knife marks on the surface of the workpiece. Generally should be considered when the tool leaves the cutting state, stopping the machine.

4. Tool monitoring tool quality largely determines the quality of the workpiece processing. In the automatic machining cutting process, through the sound monitoring, cutting time control, cutting process pause check, workpiece surface analysis and other methods to determine the normal wear condition of the tool and abnormal breakage conditions. According to the processing requirements, the tool to timely processing, to prevent the occurrence of processing quality problems arising from the tool is not processed in a timely manner.

Seven, how to reasonably select the processing tool? Cutting amount of several elements? How many kinds of material cutting tools? How to determine the rotational speed of the tool, cutting speed, cutting width?

1. Plane milling should be used without regrinding carbide end mill or end mill. General milling, as far as possible, the use of secondary tooling processing, the first tooling is best to use the end milling cutter rough milling, continuous tooling along the surface of the workpiece. Recommended width of each cutter to 60% to 75% of the diameter of the tool.

2. End milling cutter and end milling cutter with carbide inserts are mainly used for machining the cam, groove and box mouth surface.

3. Ball cutter, round cutter (also known as round nose cutter) is commonly used for machining curved surfaces and variable bevelling contour profile. The ball cutter is mostly used for semi-finishing and finishing. The round cutter with carbide tool is mostly used for roughing.

Eight, what is the role of machining programme? What should be included in the machining programme?

1. The machining programme is one of the contents of the CNC machining process design, but also need to be observed by the operator, the implementation of the protocol is a specific description of the machining process, the purpose is to allow the operator to specify the content of the program, clamping and positioning, the various machining procedures selected by the tool should pay attention to issues such as both.

2. In the machining programme should include: drawing and programming file name, workpiece name, clamping sketches, the name of the program, the tool used in each program, the maximum depth of cut, the nature of machining (such as roughing or finishing), the theoretical machining time and so on.

Nine, CNC programming to do before the preparation?
After determining the machining process, programming before to understand:

1. The workpiece clamping method;

2. The size of the workpiece embryo - in order to determine the scope of machining or the need for multiple clamping;

3. The material of the workpiece - in order to select the type of tool used for machining;

4. What are the tools in stock - to avoid the lack of this tool in the processing to modify the programme, if you must use this tool, you can prepare in advance.

Ten, in the programming of the safety height of the setting of what principles?
Safety height setting principle: generally higher than the highest surface of the island. Or set the programming zero point at the highest surface, which can also minimise the risk of tool collision.