First, STEP technology application
1 STEP-UP
STEP-NC is a new interface standard (ISO14649) based on STEP between the design module and the manufacturing module. It is an extension of STEP to the manufacturing field. It requires the CNC system to directly use the CAD 3D data model that conforms to the STEP standard, plus the process information and tool information to directly generate the machining program to drive the machine.
The basic principle of STEP-NC is to program based on manufacturing characteristics. It tells the CNC what to "machine", rather than programming the tool movement directly, and telling the CNC how to "process". The processing flow is based on the working step as the basic unit, and the feature and technical information are linked together. Each work step defines only one operation ("what to do, how to do, etc.", only one tool and one Kind of strategy. STEP-NC passes the workpiece processing program to the processing workshop through the task description (drilling center hole, drilling, roughing, finishing...), and the machining program can be modified according to actual needs in the workshop. Process information can be saved and returned to the design department, allowing for better exchange and retention of experience and knowledge, as well as sharing of product lifecycle data.
2 STEP-NC data model
In order to fully and comprehensively express information during the exchange of information between the CAM system and the CNC system, a suitable data model must be established (as shown in the figure above). ISO14649 uses an object-oriented way to define the data model to avoid the loss of information. Each processing step is defined as a separate object, each of which contains various descriptive properties. By strictly separating the geometric data, operating data, processing data and other data, the storage and access of information is simplified, and information can be exchanged between different modules. The machining process of the part is defined as a sequence of steps, and a step based on the geometric information determines which operations are executed, and the object-oriented operation itself contains process information, tool information, machining strategy, and the like.
Second, the key technology of CNC based on STEP-NC
1 Automatic identification of manufacturing features
The Manufacturing Feature in STEP-NC refers to the shape of the portion of material that is removed from the part blank in order to obtain the final shape of the part. It differs from the concept of features in general CAD, mainly because the manufacturing features must be obtained by removing the material (except for rapid prototyping). The definition of manufacturing features in STEP-NC comes from the common features defined in STEPAP224, STEP AP224. There are: holes, grooves, steps, planes, bosses, contours, etc.
The first task of generating a CNC machining program (AP238 file) in accordance with STEP-NC is to identify the manufacturing features to be machined from the geometric model of the part (output from the CAD system) and generate the STEP AP224 file as a subsequent process design. basis.
2 Simulation of STEP-NC CNC program
The STEP-NC NC program can be dynamically linked to the CNC company's MasterCAM software using STEP TOOLS's ST-Machine toolkit. ST-Machine can be connected to software such as MastercAM and GibbCAM to convert the medium-sized data information of the STEP-NC NC program into a specific tool path. MasterCAM is a CAD/CAM integrated software with three-dimensional modeling, tool path generation, NC program generation, and simulation processing. Under the platform of MastercAM software, the St machine.dll dynamic library is used to connect the st-machine toolkit, and the STEP-NC medium file is simulated and processed to generate the tool path trajectory of the STEP-NC NC machining program. The purpose of the connection is to use the process and tool parameters defined in the AP238 file, perform the functions of the MasterCAM software and finally generate the tool path in accordance with the AP238 file, and clearly analyze the processing strategy of the AP238 file and the path of the tool entry and exit (approach-retract-strategy) And other information. On this basis, optimize the tool path and process parameters of the STEP-NC NC machining program, set a reasonable forward and backward tool path, prevent overcutting and interference of the tool, optimize the design of the NC program, and also use the post processing of MasterCAM software. The function generates the G and M codes of the STEP-NC NC program, and verifies the manufacturing characteristic information of the STEP-NC NC program under the traditional controller.
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