Discussion on standardization of NC programming

2022-09-27
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Here we will not discuss the programming method to obtain the machining program for the time being. Let's discuss from another angle, whether there should be a standard for processing procedures? In production, we often encounter problems when managing and applying these processing programs, and how to solve them

we first propose a concept here - standardization of NC machining program. The "standardization" mentioned here does not simply define the format of the processing program. It refers to the setting of relevant cutting parameters, the selection of tools and the standardization of tool path design ideas in the process of compiling machining programs. Why do we have the idea of NC machining program standardization? Let's take a look at which links are often repeated and easy to make mistakes in the process of NC machining, so these links are our focus for standardization. For the workpiece with the simplest process flow, the process in Figure 1 is required to complete NC machining

when the processing program is completed, every detail of all links in the diagram must be consistent with the requirements of the processing program, and the negligence of every detail may bring disastrous results. For example, the clamping position and mode in the blank clamping process, the size of the pressing plate bolt, the error of the blank size, the size parameters of the tool and the position of the tool in the tool magazine, the setting of the machining origin, the name of the machining program, the tool guidance in the machining process, the setting of the cutting parameters and the initial termination position, etc. We cannot absolutely avoid errors, but we can find a safe way to minimize the probability of errors. Now we see that as long as these links are set as a standard, the operators will have rules to follow, and the probability of mistakes can be greatly reduced. The standardization of these links depends on the support of the processing program, so we have the idea of standardizing the processing program. At the same time, the standardization of the processing program also has a guiding direction

now we know the purpose of the standardization of processing procedures, so the links that need standardization in actual production, once some implemented standards are formulated, how can we realize them? In general, we can formulate an enterprise standard as detailed as possible, and then reach the production workshop and relevant departments in the form of documents, and require machine tool operators to operate the equipment in strict accordance with the standard, and require programmers to write processing procedures in strict accordance with the standard. The machine tool operators in the workshop are relatively easy to accept this method, because the standardized operation process can not only reduce the labor intensity, but also reduce the operation risk. But for programmers, the first thing they need to consider is the processing process, possible problems and solutions. Some "flexible" content is often set at will according to their own habits. Especially for manual programmers, they often choose the simplest and most convenient way to deal with these "flexible" problems. If the processing program is written according to the specified standard, it is equivalent to limiting the processing method of some "flexible" problems, which virtually increases the content they need to think about and increase the workload. Therefore, it will be more difficult to implement, and this kind of problem that depends on human brain thinking and processing is prone to negligence. This is also an insurmountable obstacle for manual programming, so we recommend using cam auxiliary programming software, but not any CAM software can handle this problem well. It is best to choose CAM software with secondary development and customization functions to implement enterprise standards into the software platform. In this way, programmers do not have to look through documents all the time and restrict their programming ideas by referring to the rules and regulations in enterprise standards. The operators in the production workshop only need to produce according to the requirements of the standard documents

next, we will use several examples to further elaborate some contents contained in the subject of machining program standardization and the solutions in CAM software. On the one hand, it provides you with some ideas on the standardization of processing procedures. On the other hand, we have a preliminary understanding of how to customize these standardized contents in CAM software

workpiece clamping

in addition to customized tooling equipment, most of the general tooling has been standardized, as long as the enterprise introduces it on demand when purchasing. For the most commonly used bolt pressing plates, enterprises should use unified standards as far as possible. The fewer categories, the easier it is to manage. While we manage the sampling quantity in 7.4.2 according to table 4, the information of such tools should also be shared by programmers. When designing the tool path, the programmer can take the fixture shape and clamping method into account. At the same time, the operator must install the workpiece according to the standard specifications, which can not only reduce the interference between the tool and the fixture, but also improve the processing efficiency. Taking sheet metal processing as an example, pressing plates and bolts can be selected according to standards. At the same time, a standard can be specified for the clamping position in advance, such as the installation with a distance of 200mm on the long side, the installation with a distance of 100mm on the short side, and the tool always advances and retreats from the beginning of the long side. Even the fixture and machine tool can be built into a 3D mathematical model to form a tooling equipment database. In the cam environment, programmers can clearly understand the clamping state of the workpiece. The operator can also install the workpiece according to the established standard. In Edgecam, the seamlessly integrated data interface can load any 3D model built by CAD or even assembly model at the same time (Figure 2). It not only provides data guarantee for creating a real programming environment, but also provides a seamless integrated data platform for enterprises and upstream and downstream related units. Especially for enterprises that have implemented or will implement pdm/erp, there is no need to worry about data incompatibility in cam

Figure 2 in Edgecam, the seamlessly integrated data interface can load any 3D model built by CAD or even assembly model at the same time

tool selection and number

generally speaking, there are two principles for tool selection. One is that data can be easily imported into excel table, which is the most efficient processing principle; The second is the principle of minimum tool cost. On the basis of meeting these two principles, the choice of cutting tools is still quite flexible, so what conditions should be followed? When programmers consider this problem, they need to understand the existing tool resources of the enterprise. Therefore, the enterprise should have a complete, unique and timely updated tool database, which is open not only to programmers, but also to workshops. When selecting tools, programmers can find available tools in the tool library, and ensure that the equipment operator can also find the corresponding tools in the tool library of the machine tool. In the process of designing the tool path, the programmer can set the tool number according to the diameter (from large to small) or length (from long to short) of the selected tool, so that the operator can follow the rules when preparing the tool. Edgecam provides a tool database based on SQL, which can be set as a tool library, and set permissions for different users, which is not only convenient for maintenance and management, but also can be associated with the programming environment (Figure 3)

Figure 3 Edgecam provides a tool database with SQL as the platform, and can be set as a winding tool library

origin definition

in principle, the programming origin is best to coincide with the design origin of the part, which can reduce the cumulative error. However, in actual processing, it is often difficult to find the design origin position of the workpiece in the initial blank state. In order to facilitate tool setting, programmers often specify an origin position, This is very random. For example, when defining the Z origin, if the Z origin is defined on the lower surface of the workpiece (the upper surface of the machine tool workbench or cushion block), it is a very good choice. The program is not only easy to interpret (in this case, the Z value is always positive, if there is a negative value, it must be wrong), but also easy to be accepted by people, so its surface is generally not or rarely decorated with fabric or leather to form a system, And implement it is very simple. In the programming software, adjusting the origin is a very simple operation. Edgecam also provides the "automatic alignment" function, which can automatically adjust the position of the workpiece by clicking the plane of the Z origin with the mouse (Fig. 4). Even if the tool path has been generated, you can move the origin position again, and the tool path will be updated automatically

Figure 4. The "automatic alignment" function of Edgecam can automatically adjust the position of the workpiece by clicking the plane of the Z origin with the mouse

parameters related to the generation of tool path

the import and export distance and angle of the tool are generally related to the size of the tool. At the same time, the position of the fixture is also a factor that needs to be considered. Combined with the clamping position standards mentioned above, we can also set unified import and export conditions. As for the cutting parameters, such as the axial and radial cutting depth of the tool, we can refer to the tool diameter setting. The feed and revolution are from the tool database (some expert data can be provided in the tool library for selection). The connection mode and safety distance of the tool path can be fixed in the processing strategy. When programming, you only need to pay attention to the main parameters, and other parameters can be set a standard value in advance. All of the above can be implemented in Edgecam

there are two ways to realize this function in Edgecam. The first way is relatively simple. Using the group processing method provided by Edgecam, the processing parameters that need to be set are relatively simple. Some common parameters, such as safety distance, connection mode, angle and distance of import and export, can be set uniformly in the system in advance, and the programming operation is also very simple

Figure 5 processing strategy file is actually a flow chart

another method is to use the secondary development tool - policy manager provided by Edgecam. This is a tool for customizing machining strategies, which can combine Edgecam's existing machining strategies arbitrarily, and fix all the contents of model feature parameters, tool parameters and project management related parameters in the machining strategy in the form of constant values or variables. In the actual programming process, you only need to apply the relevant strategy files to the characteristics of the processed model

the machining strategy file is actually a flowchart. Each machined feature successively calculates the tool path according to the node content set in the flowchart (Fig. 5). The basic unit of each node is each "process" visible in the browser, which can be copied in Edgecam. It can be a processing method or a combination of multiple processing methods. The judgment node is particularly important, which is the soul of the processing strategy, and it gives life to the processing strategy. A processing strategy can be simple or complex; The processing strategy is OK

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