1 1 feature recognition The CAD CAPP integration methods mainly include: feature recognition method, data exchange method and feature design. This system uses feature recognition method to develop feature-based CAPP system. The feature recognition method is to analyze the output of CAD, extract the process design features according to certain algorithms and recognition rules, to overcome the various drawbacks of manual input, and realize the automatic transmission of CAD information of parts to CAPP, CAM and other systems. UG is a feature-based high-end 3D CAD CAM CAE integration software that provides built-in feature modeling capabilities and maintains a library of feature instances. The system uses the UG OPEN API programming interface to obtain part feature instance information for feature recognition. The part model features in UG software are divided into shape features and non-shape features (material features, precision features, technical features and management features, etc.), and non-shape features are assigned as attributes to shape features to establish a relationship between the two. And can be called. The main steps for character recognition are as follows. 1) Select objects by rules or interactively. 2) Identify the shape features of the object using the API function of UG. 3) Extracting the non-shape features associated with the shape feature, the operation function for the component or object property in UG is located in uf attr..h. 4) Store the identification results in a database for decision making. 1 2 knowledge base design and process optimization design rules 1 2 1 Knowledge indicates that the knowledge required to store the system solving problem in the knowledge base requires that the expression of the knowledge is simple and easy to understand, and the domain expert knowledge can be clearly and clearly expressed. The organizational structure should be modular to expand, Modifications and applications. The commonly used knowledge representation methods of artificial intelligence are: semantic network representation, rule representation, frame representation, first-order predicate representation, and so on. In this system, production rules are used to describe process design knowledge. The production rule is an antecedent expression model consisting of two parts. The former part is called condition, such as state, premise, reason, etc. The latter part is called result, such as activity, conclusion, consequence, etc. The general form is: IF premise THEN Conclusion (or action). For example: IF processing features flat bottom groove THEN flat bottom cylindrical end mill 1 2 2 process optimization design rules To obtain better processing quality, while ensuring production efficiency, it is particularly important to choose appropriate process parameters and elements. The general principles of process design are: to ensure the machining accuracy and surface roughness requirements of the parts; to shorten the path of the cutting, to reduce the time of entering and retracting and other auxiliary time; to use the large cutting amount as much as possible to improve the processing efficiency; to facilitate numerical calculation and reduce Programming workload. This paper mainly analyzes the factors affecting the processing quality of parts, discusses the principle of determining the corresponding processing parameters, and comprehensively analyzes the factors affecting the selection of these parameters, and initially draws some ideal selection schemes and determination principles to ensure the processing quality. Improve processing efficiency under the premise to more effectively guide process design and NC programming. 1 2 2 1 Optimizing the selection of cutting tools In general, ball-end knives are suitable for surface machining, especially finishing, because spherical surface contact with curved surfaces can achieve better surface roughness and also improve machining accuracy. Quality and efficiency are the goals of CNC machining. Tools should choose materials with high hardness and rigidity as much as possible. This article focuses on commonly used high speed steel (HSS) and cemented carbide materials. 1 2 2 2 step depth and cutting width According to the actual machining experience, the reference values ​​of the depth of cut and the cutting width during roughing are summarized for different workpiece materials. 1 2 2 3 Feed rate Since the feed rate is affected by many complicated factors, it is difficult to give a quantitative optimal range. Factors affecting the ratio of feed rate to spindle speed include part machining accuracy, surface roughness, tool material, blank material, tool diameter, depth of cut and cutting width. The UGII software platform provides a feedrate calculation function that automatically determines the spindle speed and cutting speed based on the last five parameters. These two parameters are calculated using the feedrate automatic generator provided by UG. The generator searches the feed speed table for different cutting methods, blank materials, tool materials and depth of cut to obtain surface speed and feed per tooth. This calculates the spindle speed, cutting speed, and so on. 1 2 2 4 Optimization of the advance and retraction modes In the CNC milling process, the advance and retract modes affect the safety of the tool path. In view of safety, the knife is retracted in the direction of the tool axis. The choice of the feed method requires consideration of factors such as tool type, workpiece material, and processing method. If a flat-blade is used, it is generally not allowed to feed perpendicular to the surface of the workpiece. It should be cut sideways along the workpiece or fed from the pre-drilled hole. If the ball-cutting knife is used to machine the free-cutting material, the knife can be fed vertically. For roughing, the same feed method as the flat cutter can be used, or a spiral feed can be used. Finishing is suitable for slash feeds. The 1 2 2 5 pass mode determines the surface texture of the part. The CAM software provides the cutting and milling method to determine the grain direction by setting the cutting direction. For general-purpose surfaces, it is generally in the form of row milling or ring milling. The cutting direction of row milling is generally parallel to the X or Y axis. For the surface of the rotor, the direction of the busbar is the cutting direction. The concentric pattern is mainly used for flat surfaces with a rounded boundary. The radial mode is more suitable for a centrally symmetrical surface. These methods can basically meet the processing requirements of general parts, and the line milling and ring milling methods are most commonly used in surface machining. The actual surface setting should be as close as possible to ensure the surface texture of the parts. 2 system implementation 2 1 Basic components and functions of the system This system is based on the UG platform and is embedded in the UG Application Module. 1) Import the process defined in the typical process library into the CAM module of the current UG file. 2) Identify the part features and complete the configuration in the operation navigator of the UG CAM module. 3) According to the processing requirements input by the user, the similar required surfaces are classified into the operation groups in the operation navigator. 4) Query the process knowledge base, determine the machining parameters such as step allowance, process tolerance and line spacing through inference, generate the step group and automatically generate the NC machining process in the UG CAM module. The specific algorithm is as follows: (1) Obtain the material properties of the part and the minimum radius of curvature of the surface; (2) Select the tool type, and query the knowledge base according to the material properties of the part, select the appropriate tool material, and select the tool radius according to the minimum radius of curvature of the surface; 3) Obtain the machining requirements (surface roughness, machining accuracy) defined by the user for the feature surface; (4) Query the knowledge base, and find the corresponding process margin for fine, semi-finish, rough machining according to the processing requirements (s 1, s 2 , s 3) and maximum depth of cut dM, and suggested routing (fine, semi-finished number n 1 , n 2); (5) to obtain the feature size values ​​of the user input surface; (6) determine the fine according to the milling method , semi-precision, rough machining economic accuracy, and calculate the corresponding deviation value i 1 , o 1 , i 2, o 2, i 3, o 3; (7) obtain the user input actual margin value astock value; (8) Initialization total margin stock = 0, upper and lower deviation intol = i 0, outtol = o 0, loop variable j = 0; (9) when stock < astock (loop condition while); (10) create a new step, pre Set parameters; set the step Measured value = stock; set the upper and lower deviations of the step to intol, outtol; set the step (stepover), feedrate (feedrate) and other parameters; (11) the following steps are to set the balance of the next step according to the rules And the deviation parameter variable; if j < n 1, indicating that the current is finishing, the remaining margin stock = stock + s 1; if j < n 1 - 1, the economic precision of the reference finishing i 1 , o 1, The upper and lower deviations i 0 and o 0 of the machining are slightly adjusted and assigned to intol and outtol; if n 1 j < n 1 + n 2, that is, if it is semi-finished, the remaining margin stock = stock + s 2 If n 1 - 1 j < n 1 + n 2 - 1, the economic precision deviation of the semi-finishing i 2, o 2 is slightly adjusted and then assigned to intol, outtol; if jn 1 + n 2, ie if it is thick Machining, leaving the remainder stock= stock+ s 3; if jn 1 + n 2 - 1, intol and outtol respectively take the economic precision deviation of the rough machining i 2, o 2 moderate adjustment value; (12) j = j + 1; return to the while loop judgment; (13) post work, end. 2 2 system development key technology Using the secondary development tools provided by the software platform, users can develop automated tools that are highly integrated with the system according to actual needs, and realize the expansion of CAD CAM functions. The secondary development tools provided by UGNX mainly include Open API, Open GRIP, UIStyler, Menu Script, etc. UIStyler and MenuScript are used to create the shell of the extended application (such as program interface). Open API and Open Grip are the core program and database interface. Writing tool. Open GRIP is one of the secondary development tools provided by UGII. Its program structure is similar to FORTRAN and is tightly integrated with the UG system. Various common interactions with the UG system can be accomplished using the GRIP program. The Open API is also one of the secondary development tools provided by UGII. It is the interface between UG and external applications. It is a collection of functions that can be called through C programming to extend the functionality of UG applications. 3 application examples Select the surface features in the graphics area, define the processing requirements, the system writes the relevant information to the data file, and classifies the similarly required surfaces into the operation groups in the operation navigator. Select a set of curved surfaces with similar processing requirements in the graphics area. The system will obtain a set of curved surfaces with the same processing requirements on the same azimuth surface selected by the user, and then according to the workpiece material, surface characteristics and processing requirements (surface roughness, accuracy grade) and other conditions. , query the rules in the process knowledge base, determine the processing parameters such as step allowance, process tolerance, line spacing, etc. by reasoning, generate the step group and in the UG CAM module 4 Conclusion This paper introduces the CAPP system of NC machining based on the secondary development and knowledge base of UG platform. By referring to the existing process design experience and the proven process parameters, a set of process optimization design rules and a knowledge base are established. Based on the rapid processing of the machining process corresponding to the machining features and the automatic generation of the NC program, the integrated operation of CAD CAPP and NC programming and the effective integration of information are realized, which improves the efficiency and quality of CNC programming and helps the craftsman to be fast and precise. Finish the processing of parts. (Finish)
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1 CNC machining process decision mechanism based on feature and knowledge base