Standard process for CNC programmers

CNC machining, as a representative of advanced productivity in the machinery manufacturing industry, has played a huge role in the automotive, aviation, aerospace and mould 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, because of the different levels of CNC programming personnel, there is a need to avoid low-level errors and repetitive problems by establishing certain specifications.

A, CNC 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 position trajectory, machining trajectory simulation, post-processing, CNC machining program simulation simulation, CNC machining program proof checking, issuing the site processing and CNC machining program finalization.

1. Determine the basis of programming

CNC programming basis mainly includes three-dimensional models, engineering drawings and parts manufacturing instructions (CNC process procedures), through the CNC programming basis can obtain the following information: part information, CNC machining process scheme, CNC machine tool type, clamping and positioning methods, tools, processes and work steps, processing program number and product processing state, etc.

2. Establish the process model

On the basis of the three-dimensional model of the part and engineering drawings for the design of the process model, mainly including: trimming of the three-dimensional model of the part, the establishment of the process reference surface, the establishment of the process positioning holes, platen and position design and machining surface allowance processing.

3. Define machining operations to generate toolpaths

Define the machining operation to generate the toolpath, the main content includes: define the programming coordinate system, fully consider the processing material characteristics, tool cutting characteristics, machine tool cutting characteristics and parts need to remove the material condition and other factors, according to the process requirements to define the processing mode (including a variety of tooling strategy, etc.), process parameters (including margin, feed rate, spindle speed and span of the machining toolpath, etc.) and auxiliary attributes (including to the tooling point, safety surface and the toolpath). including tooling point, safety surface and CNC machine tool properties, etc.), and finally generate the tool position trajectory.

4. Machining trajectory simulation verification

Machining trajectory simulation verification mainly includes: check whether the definition of tools, machine tools, workpieces and fixtures is complete and accurate in size; check whether the machining operation, the definition of each process should achieve the correct size of the part; check whether the machining mode in the definition of the machining operation (such as roughing strategy, tool complement machining and cavity machining and other options)

whether correct and reasonable; check the machining process between the CNC machine table, the machined parts, tools and fixtures whether there is overcutting, undercutting or collision interference and other problems; check whether the process parameters are reasonable, etc.

5. Post-processing

Post-processing can be an independent process, can also be combined with the generation process of tool position files into one, according to the function of the processing software, choose the appropriate processing method, and for post-processing have the following requirements.

Generate a specific CNC system-specific processing program, should choose its specific post-processing software; post-processing software development or customisation, to be combined with a specific control system and machine tool motion structure type; post-processing software to ensure that the tool position processing information is fully converted, and to meet the requirements of the control system syntax; post-processing, automatically add the necessary notes to the processing program.

6. CNC machining program simulation verification

On the basis of the programming software or the combined CNC simulation software (Vericut) function, the various aspects involved in the CNC machining program are verified as far as possible to ensure the correctness of the final machining program, and the corresponding CNC machining program simulation verification is recorded.

Simulation verification mainly includes the following: check the processing program, whether the comment information is correct; check the CNC machining program, whether the choice of processing mode is correct; check the processing program, whether the tool size information is correct; check the CNC machining program, each process should achieve the correct part size information; check the CNC machining program, whether the tool compensation information is correct; check the CNC machining program, whether there is overcutting, undercutting or collision interference problems; check the CNC machining program, the spindle speed, feed speed and the current CNC machine matching, etc.

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7. CNC machining program calibration check

CNC program proofreading and process file proofreading is completely different, the program format is a coordinate point, if line by line proofreading program content, it takes a lot of time, but also is impractical.

The proofreading of the program is mainly considered from the following aspects.

① The model. The model is a fundamental element of the correct procedure and needs to be proofread for correctness, analysing whether all the data in the model is consistent with the elements of the process documentation.

② Coordinate system. Check that the direction of the programmed machining coordinate system is consistent with that required by the process documentation, that it is easy to operate, that the coordinate system is reasonably chosen and that it is easy to control dimensions.

③ Machining strategy. Different machining strategies generate very different programs, and the volume of the program varies, while the analysis of the rationality of the machining strategy is mainly to control the tool trajectory of the program and control the quality and efficiency of machining.

④ Tooling. Tool materials, specifications and forms are determined according to the part material and part processing parts, different tools directly affect the processing efficiency and processing quality.

⑤In and out points. The entry and exit points are the main factors that cause knife gnawing and stabbing of the part, and are also important aspects that affect surface quality.

⑥Program format. Different CNC systems require different formats for the program, generally through the editing of the post-processing program, generated to meet the requirements of different control systems machining program, program format proofreading is mainly in the first and last part of the program, does not affect the processing quality of the program.

The CNC program must be complete, correct, uniform and coordinated to ensure that the operator can use the program correctly and process a qualified product. The CNC machining program should be able to guarantee the rationality, safety and stability of the entire process.

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8.CNC program field trial processing and processing program finalization

For some parts with complex technology, difficult processing, high dimensional accuracy or large quantities, the CNC programming staff, workshop process supervisors, operators and inspectors should be organised to follow up and record the on-site trial processing, in order to instantly correct unreasonable clamping and positioning methods and cutting parameters, etc.

For some single production parts, in the case of good craftsmanship and low dimensional accuracy, trial machining should be avoided as far as possible, but left to the CNC machining simulation link to discover problems and correct them, in order to improve programming efficiency and reduce production costs. For mass-produced parts, the CNC machining program should be finalised and warehoused for unified management after the first batch of production.

Second, the management of CNC programs and manufacturing outline (FO)

1. Naming of CNC programs

For easy access, easy to identify, call and management, the first CNC program file must be named reasonably. CNC machine tools are coded in different multiples, and generally only identify the numbers and letters, different CNC system identified by the program format is also different.

Therefore, the form of CNC program naming is generally: name + suffix.

(1) name composition is generally: product code _ processing type + process number _ program version.

Which "product code" that is the reference to the parts involved in the drawing number; "processing type" that is milling (M) or turning (L); "process number" that is, the process number in the process documentation; The "program version" is the new version (NEW), after the change of version can be managed by 001, 002 ......, etc. in turn.

(2) Suffix composition: generally txt, mpf, etc.

(3) CNC program naming example: a product code for D25-1155-12-00, there are three processes require CNC machining, which process 15 for CNC milling process, the first time the preparation of CNC programs, then the corresponding CNC program files in the program library name as shown in Figure 2 shown.

(4) The naming of CNC programs to meet the requirements of the control system, as well as easy to identify, call and management as the principle.

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2. Naming of the tool

In the preparation of the machining process, it is necessary to define various tool types, tool materials and the geometric parameters of the tool itself.

Before the establishment of cutting parameters database, can only rely on manual input, CNC programming UG learning QQ group: 304214709, want to learn CNC programming to receive free learning materials plus this group therefore less efficient, and the completion of a simple repetition of labor, the final generated program is not intuitive for the operator, the level of the process personnel requirements.

Through the actual processing in the experience summed up, can be through the corresponding CAM software (NX software) to establish processing database, in the future operation can be directly from the library call. The establishment of the library should be preceded by the definition of the tool number, for easy identification can be indicated in the NX tool library in the following way.

(1) End mill: LX + D + diameter + L + tool extension length + La + tool edge length + Z + number of edges + R + bottom tooth radius. Such as LXD25L50La25Z3R1.5_L7 said: the diameter of the end mill is 25mm, the working length requires a minimum of 50mm, the edge length requires a minimum of 25mm, the number of edges is 3 edges, the bottom angle is R1.5mm; L7 for processing 7075 imported aluminium.

(2) Drill: ZT+D+diameter+tool extension length+La+tool edge length+Z+number of edges+J+drill angle. For example, ZTD6.5L30La20Z2J120 means: the diameter of this drill is 6.5mm, the working length is required to be a minimum of 30mm, the edge length is required to be a minimum of 20mm, the number of edges is 2 edges and the drill tip angle is 120°.

In the post, its tool information is required to be output together so that the operator can be prevented from running the program without changing the tool number or the tool length. Its main purpose is to establish a unified standard for CNC programming and program simulation, but also to facilitate the unified issuance of tools and proofreading.

3. CNC machining process content requirements

In the manufacturing outline (FO), it is necessary to put forward some requirements for the content of the CNC machining process to prevent inconsistencies between the manufacturing outline (FO) and the CNC program, resulting in the scrapping of parts.

Specific requirements are as follows.

(1) to clearly indicate the blank or part of the clamping positioning surface and workpiece coordinates and coordinate system, and to ensure that the coordinates of the origin and coordinate system and processing procedures consistent;

(2) to clearly indicate the position of the platen pressing the part or blank, and the limit height of the top surface of the platen bolt;

(3) To briefly describe the necessary specifications of the tool required, and the part of the part to be machined by the tool;

(4) To accurately express the name of the CNC program for the machined part;

(5) To accurately express the tooling used to machine the part.

CNC technology as years of advanced manufacturing technology, its technical content is very high, involving a variety of aspects, especially the rapid and efficient CNC machining programming, the application of high-speed cutting, CNC process programming standardization and standardization.

The efficiency of CNC machining technology is to a large extent related to the technical management model of the enterprise itself. The standardization and standardization of CNC machining program preparation, to a certain extent, reflects the enterprise's own CNC machining technology application level, through the standardization to constrain the diversity of CNC programs, improve the quality of tool trajectory, such as in the process file to indicate the positioning reference, tool reference, coordinate system, tool parameters and cutting parameters; for the preparation of the program can be from two-dimensional contour processing, three-dimensional surface processing, fixed cycle For the preparation of the program can be from two-dimensional contour machining, three-dimensional surface machining, fixed cycle, tool compensation and tool path machining strategy and other aspects of standardized programming; in the typical part machining process based on experience, the establishment of standardized, standardized CNC program template, can significantly improve the quality of programming and product processing efficiency.

For the enterprise's successful product processing technology and CNC machining experience, can be saved in the form of templates, both for the reuse of resources, but also as a resource for technical exchange.

Therefore, effective CNC machining processes and CNC programming templates, the use of the corresponding specifications can largely reduce quality accidents, reduce costs and improve the efficiency of processing.