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Procedure of CNC programming

As a representative of advanced productivity in the machinery manufacturing industry, CNC machining has played a huge role in the automotive, aviation, aerospace, and mold industries after more than 10 years of introduction and development.
CNC programming is an important aspect that affects the quality and efficiency of CNC machining, especially in high-speed and precision machining. In the machinery industry, due to the different levels of CNC programmers, it is necessary to establish certain specifications to allow everyone to avoid low-level errors and repetitive problems.
One, NC machining programming process
The general process of CNC machining programming includes: determining the programming basis, establishing the process model, defining the machining operation, generating the tool path, machining path simulation, post-processing, simulation of the CNC machining program, proofreading and checking of the CNC machining program, issuing on-site machining and CNC machining Procedures are finalized, etc.
1. Determine the basis for programming
The basis of CNC programming mainly includes three-dimensional model, engineering drawings and part manufacturing instructions (NC process regulations). The following information can be obtained through the basis of CNC programming: part information, CNC machining process plan, CNC machine tool type, clamping and positioning method, tool, process and Work step, processing program number and product processing status, etc.
2. Build process model
The process model design is based on the part three-dimensional model and engineering drawings, which mainly includes: trimming the part three-dimensional model, establishing process reference surface, establishing process positioning hole, pressing plate and position design, and processing surface margin processing.
3. Define machining operations to generate tool path
Define machining operations and generate tool location trajectories. The main contents include: define the programming coordinate system, fully consider factors such as the characteristics of the processed material, the cutting characteristics of the tool, the cutting characteristics of the machine tool, and the material condition of the part that need to be removed, and define the processing method (including various A kind of tooling strategy, etc.), process parameters (including margin, feed speed, spindle speed and processing tool path span, etc.) and auxiliary attributes (including tool setting point, safety surface, CNC machine tool attributes, etc.), and finally generate tool Bit track.
4. Simulation verification of machining trajectory
The main content of the processing path simulation verification includes: check whether the definitions of tools, machine tools, workpieces, and fixtures are complete and whether the dimensions are accurate; check the processing operations and define whether the size of the parts that each process should reach is correct; check the processing methods in the definition of the processing operations (such as (Rough machining strategy, tool offset machining and cavity machining options)
Whether it is correct and reasonable; check whether there are over-cutting, under-cutting, or collision interference between the CNC machine tool worktable, processed parts, tools and fixtures during processing; check whether the process parameters are reasonable, etc.
5. Post-processing
Post-processing can be an independent process, or it can be integrated with the tool location file generation process. According to the function of the processing software, select an appropriate processing method. The post-processing has the following requirements:
To generate a special processing program for a specific CNC system, the specific post-processing software should be selected; the development or customization of the post-processing software should be combined with the specific control system and machine tool motion structure type; the post-processing software should ensure the tool position processing information It is fully converted and meets the grammar requirements of the control system; in post-processing, the necessary notes are automatically added to the processing program.
6. Simulation verification of NC machining program
On the basis of the programming software or combined with the functions of the numerical control simulation software (Vericut), all aspects involved in the numerical control processing program are verified as much as possible to ensure the correctness of the final processing program, and the corresponding numerical control processing program simulation verification is carried out recording.
The simulation verification mainly includes the following contents: check whether the annotation information in the processing program is correct; check whether the selection of the processing method in the CNC processing program is correct; check whether the tool size information in the processing program is correct; check whether each process in the CNC processing program Whether the size information of the parts that should be reached is correct; check whether the tool compensation information is correct in the CNC machining program; check whether there are over-cutting, under-cutting or collision interference in the CNC machining program; check the CNC machining program, spindle speed, advance Whether the feed speed matches the current CNC machine tool, etc.
7. Proofreading and checking of CNC machining program
The proofreading of the numerical control program is completely different from the proofreading of the craft file. The program format is a coordinate point. It takes a lot of time to proofread the content of the program line by line, which is also impractical.
The proofreading of the program is mainly considered from the following aspects.
①Model. The model is the basic element to ensure the correctness of the program. It is necessary to check the correctness of the model, and analyze whether all the data of the model are consistent with the process document elements.
②Coordinate system. Check whether the programmed processing coordinate system direction is consistent with the requirements of the process file, whether it is easy to operate, whether the coordinate system selection is reasonable, and whether it is convenient to control the size.
③Processing strategy. The programs generated by different processing strategies are completely different, and the amount of programs is also different. The rationality of the processing strategy is analyzed, mainly to control the tool path of the program, and control the processing quality and efficiency.
8. On-site trial processing of CNC program and finalizing of processing program
For some parts with complex craftsmanship, difficult processing, high dimensional accuracy or large batches, it is necessary to organize CNC programmers, workshop process supervisors, operators, and inspectors to track and record the on-site trial processing conditions, so as to correct errors immediately. Reasonable clamping and positioning methods and cutting parameters.
For some single-piece production parts, in the case of good manufacturability and low dimensional accuracy, try cutting processing should be avoided as much as possible, but left to the NC machining simulation link to find problems and correct them in order to improve programming efficiency and reduce production costs. For mass-produced parts, after the first batch is produced, the CNC machining program should be finalized and warehoused for unified management.
2. Management of NC program and manufacturing outline (FO)
1. Naming of NC programs
For the convenience of reference, easy identification, call and management, the first NC program file must be named reasonably. Numerical control machine tools have different coding multiples, and generally only recognize numbers and letters, and the program formats recognized by different numerical control systems are also different.
Therefore, the form of NC program naming is generally: name + suffix.
(1) The name composition is generally: product code_processing type + process number_program version.
Among them, "product code" refers to the drawing number of the referenced part; "processing type" refers to milling (M) or turning (L); "process number" refers to the process number in the process file; "program version" refers to New version (NEW), after changing the version, you can use 001, 002... and so on for management.
(2) Suffix composition: generally txt, mpf, etc.
(3) Example of NC program naming: A product code is D25—1155—12—00. There are three processes that require NC machining. Process 15 is a NC milling process. The NC program compiled for the first time is the corresponding NC program The name of the file in the library is shown in Figure 2.
(4) The naming of NC programs is based on the principle of conforming to the requirements of the control system and being easy to identify, call and manage.
④ Tool. The tool material, specification and form are determined according to the part material and the part processing position. Different tools directly affect the processing efficiency and processing quality.
⑤The entry point and the exit point. The entry point and the exit point are the main factors that cause the knife to bite and puncture parts, and they are also important aspects that affect the surface quality.
⑥Program format. Different numerical control systems have different requirements for the program format. Generally, processing programs that meet the requirements of different control systems can be generated by editing the post-processing program. The proofreading of the program format is mainly at the beginning and the end of the program, which does not affect the processing quality of the program.
The CNC program must be complete, correct, unified and coordinated to ensure that the operator can use the program correctly and process qualified products. The NC machining program should be able to ensure the rationality, safety and stability of the whole process.
2. Naming of the tool
When programming the machining process, it is necessary to define various tool types, tool materials and geometric parameters of the tool itself, etc.
Before the cutting parameter database is established, the micro signal; SGLS93 can only receive data by manual input, so the efficiency is low, and the completion is only simple repetitive labor. The final generated program is not intuitive to the operator and is not intuitive to the process. The level of personnel is relatively high.
Based on the experience in actual processing, the processing database can be established through the corresponding CAM software (NX software), which can be directly called from the library in future operations. To establish a library, you should first define the tool number. For easy identification, it can be expressed in the NX tool library as follows.
(1) End mill: LX+D+diameter+L+tool extension length+La+tool blade length+Z+blade number+R+bottom tooth radius. For example, LXD25L50La25Z3R1.5_L7 means: the diameter of the end mill is 25mm, the minimum working length is 50mm, the minimum blade length is 25mm, the number of blades is 3 blades, and the base angle is R1.5mm; L7 is for processing 7075 imported aluminum.
(2) Drill: ZT+D+diameter+tool extension length+La+tool blade length+Z+blade number+J+drilling angle. For example, ZTD6.5L30La20Z2J120 means: the diameter of the drill bit is 6.5mm, the minimum working length is 30mm, the minimum blade length is 20mm, the number of blades is 2 blades, and the drill point angle is 120°.
In the post-positioning, the tool information is required to be output together, which can prevent the operator from running the program without changing the tool number or tool length. Its main purpose is to establish a unified standard for NC programming and program simulation, and to facilitate uniform distribution and proofreading of tools.
3. Content requirements of CNC machining process
In the manufacturing outline (FO), it is necessary to put forward some requirements for the content of the CNC machining process to prevent the manufacturing outline (FO) from being inconsistent with the CNC program, resulting in scrapped parts.
Specific requirements are as follows:
(1) It is necessary to clearly indicate the clamping and positioning surface of the blank or part and the origin and coordinate system of the workpiece coordinate, and ensure that the origin and coordinate system are consistent with the processing program;
(2) Clearly indicate the position of the pressing plate pressing parts or blanks, and the limit height of the top surface of the pressing plate bolts;
(3) Briefly describe the necessary specifications and parameters of the required tool and the parts processed by the tool;
(4) It is necessary to accurately express the name of the CNC program of the processed part;
(5) To accurately express the tooling for processing the part.
As an advanced manufacturing technology for many years, CNC technology has a high technical content, involving many aspects, especially the rapid and efficient CNC machining programming, the application of high-speed cutting, and the standardization and standardization of CNC process programming.
The efficiency of CNC machining technology is largely related to the technology management model of the enterprise itself. The standardization and standardization of numerical control processing programming reflects the application level of the enterprise’s own numerical control processing technology to a certain extent. Through standardization, the diversification of numerical control programs is restricted and the quality of tool trajectories is improved. Tool reference, coordinate system, tool parameters and cutting parameters; for programming, standardized programming can be carried out from multiple aspects such as two-dimensional contour processing, three-dimensional surface processing, canned cycles, tool compensation and tool path processing strategies; in typical parts processing technology On the basis of experience, the establishment of standardized and standardized CNC program templates can greatly improve the programming quality and product processing efficiency.
The successful product processing technology and CNC processing experience of the enterprise can be stored in the form of a template, which is not only conducive to the reuse of resources, but also as a resource for technical exchanges.
Therefore, the effective use of CNC machining technology, CNC programming templates, and corresponding specifications can greatly reduce quality accidents, reduce costs, and improve processing efficiency.

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