Abstract
The paper presents an overview of the ways of data exchange between CAD and CAPP systems. The exchange was described using neutral data exchange formats and applications programming interfaces. New possibilities in the area of data exchange with the use of solutions enabling full specification of the designed part based on the 3D CAD model have been described. It was presented how such data can be exported from the CAD system to the STEP 242 file format and how to further use this data in planning production processes in the CAPP system. This study proposes the configuration of an IT environment that streamlines and organizes the work related to product development departments of manufacturing enterprises. The mechanisms and interfaces that automate the flow of data between CAD/CAPP systems have been proposed.
Keywords
1 Introduction
The traditional approach to the development of technical documentation in the area of product development assumes that process planning is executed on the basis of CAD 2D drawings. Such documents are usually prepared in the computer aided design systems - CAD. Work in these systems usually takes place sequentially; at first CAD 3D models are prepared, in the next step CAD 2D drawings are developed. CAD 2D drawings can be based on CAD 3D models for both individual parts and assemblies, which greatly speeds up the creation of documentation. In popular CAD systems, there are functions supporting the preparation of 2D drawings based on a 3D model such as: automatic projection, inserting views, simple and aligned sections, hatching, scaling, importing dimensions and annotations from a 3D model. 2D drawings are parametrically linked to the 3D model. If one of them is modified, the system also updates the related document. The drawing for the part should contain all the information and requirements necessary to produce it. Despite many functions automating the creation of 2D documents based on 3D models, it is still a time-consuming task, costly and requiring specialist knowledge in the field of mechanical design. The modern approach to design in CAD systems allows to save product and manufacturing information (PMI) directly on the 3D model [1]. In such a model, it is possible not only to insert classical dimension values in 2D sketches and 3D design operations, but also to add tolerance dimensions. Similarly, on the 3D model of the part it is possible to add surface finishing and datum identifier symbols, position and shape tolerances, material definitions, weld symbols and much more about the presented part. Such solutions allow for a full description of the parts with information necessary for its production, disregarding the phase of preparing the 2D drawing [2]. Taking into account the solutions described above, the further part of the article describes possible ways of using data related to the 3D model of parts directly in Computer Aided Process Planning systems.
2 Process Planning in CAPP – Identification of a Problem
Production enterprises wanting to control and automate business processes taking place in the company implement IT systems that improve the management of various departments of the company. Usually, ERP systems (Enterprise Resources Planning) are implemented in the hope that they will provide functions supporting the work of all company departments, ensure their integration and provide access to current data at various decision-making levels. The implementation of the ERP system, however, does not exhaust the topic of computerization of the enterprise. It turns out that there are many areas without proper support. One of them is the product development area and more specifically process planning, which is based on CAD data and data collected in ERP systems. Many companies decide to implement additional software that will fill functional gaps. These deficiencies are as follows:
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lack of a common repository of technological knowledge in the form of: templates of reference processes, previously made processes for re-use, operation templates, production resources, mechanisms supporting decision making,
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lack of standards in the scope of circulation and approval of documentation, usually data are stored locally on users’ computers and documents are created using popular office packages,
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it is not possible to draw sketches for operations based on design data and it is not possible of storing them in relation to the product structure,
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no mechanisms for automatically entering route data into ERP systems.
The function of the integrator of these areas can be performed by the CAPP system, which will enable the management of data related to the production technology in connection with the product structure and data from the ERP system. Additionally, an appropriately configured IT environment will provide the opportunity for concurrent work, which will result in shortening the time of preparation of the project documentation. The following approaches are used in the CAPP systems [7,8,9]:
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variant - based on similarity of manufactured parts and processes templates,
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generative - the system automatically generates a technological process on the basis of principles and knowledge stored in the form of rules,
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semi-generative - combining the benefits of the variant and the generative approach.
In manufacturing enterprises, there is a need to implement CAPP solutions. There is a general tendency to gather engineering knowledge and make it available in design processes. Such activities additionally bring benefits in the form of an increase in the quality of the developed processes through total or partial independence from the individual knowledge and experience of the employees of the technological planning departments.
3 Data Exchange Between CAD and CAPP Systems
During the development of CAD and CAPP systems many methods and tools have been developed for sending geometrical data, dimensions, tolerances, surface finish parameters, and position and shape tolerances [3]. Data transfer from CAD systems can be implemented in two main ways: with the use of dedicated data exchange formats and through direct communication with the CAD system in which the considered part geometry model is active. The first approach assumes the ability to read data connected with the geometry of the part from files with an ordered, standardized structure.
For this purpose, the following file formats can be used: DXF (Data eXchange Format) Parasolid, IGES (Initial Graphics Exchange Specification) or STEP (STandard for the Exchange of Product model data). The use of 3D part model data from such file formats requires a thorough knowledge of the file structure and the assumption that the files are unified. This assumption often turns out to be problematic, because apparently consistent file formats differ from each other depending on which CAD system has been generated [4,5,6]. Despite the many years of development, the IGES format has not been formalized in the form of a record, which hinders its analysis and processing [7]. As a result IGES development was discontinued and work was focused on the STEP format. The STEP is a continuation after the development of the IGES standard [7]. The popular STEP format is AP203, later AP214 and recently developed AP242. AP214 is considered an extension of AP203. This format was created as a result of combining two standards AP 203 and AP 214 and was approved by ISO in 2014 [1]. Regarding the development of CAPP systems, high hopes are associated with the latest version of the STEP protocol - AP242 due to the fact that in addition to the geometry, information about production and assembly are stored, such as: assembly tolerances, surface finishing and other information about the production process. The STEP 242 format is a neutral standard, so it is not related to a specific CAD system. It turns out that there is no need to generate 2D drawings, store them, analyse them or even print them. Production companies can exchange such files and complete the task of process planning more quickly.
It is a file format independent of the system so it provides flexibility in data exchange. It can successfully replace the existing approaches in the field of data exchange: neutral and native formats. Additionally, it can be used for data archiving.
Software developers of popular CAD systems (SolidWorks, Inventor, Solid Edge, Siemens NX and others), as part of development work have added functionality in the possibility of adding product and manufacturing information - PMI directly on the 3D CAD model. In addition, the export of this data is possible to the STEP 242 format. Assuming that the PMI data are complete, it is possible to skip the 2D drawings preparation.
In addition to the neutral formats in CAD systems, there are still direct formats available (Direct CAD Interfaces) that allows to load files in the form of a specific system. Data exchange takes place without conversion and without need to be saved as an additional file. These formats are unlikely to apply to data exchange with CAPP systems due to the fact that the file structure is not widely available by CAD software vendors.
Another way to access the part data is based on direct communication with the CAD system. It is possible through programming interfaces built into CAD systems. Application Programming Interface - API allow access to data by offering appropriate functions. This approach requires the use of external software tools supporting coding processes that allows to apply the methods and properties provided by the programming interface. Written computer programs enable capturing of any parameters and data of the CAD model, regardless of the method of design and parameterization of the geometry or order of design operations. The data set obtained in this way can be processed practically in any way. One of the application areas is the possibility of using data collected from the CAD system to process planning in the CAPP system. Such a method requires the collection of two data classes: geometrical data that characterizes the geometry of the designed part and dimensional and precision data, which indicate the dimensions and acceptable tolerances in which the part is to be made. The use of API programming interfaces for CAD and CAPP integration entails the need to low-level data processing. It is necessary to accurately identify the way the geometry is representing and the data structure characterizing the dimensions, tolerances, surface finishing values or shape tolerances. The next task is to link these data structures and use it to processes planning in the CAPP system. This task is quite complex and often leads to limited functionality in terms of the completeness of the description of the geometrical data needed for manufacturing. The development of the data exchange interface in the API environment is possible for one particular CAD system or even one version of it, which is a big limitation. The code can not be used in other CAD systems due to differences in the syntax of the methods of access to objects. Along with the update version of the CAD program may change the method of access to objects or attributes, which results in that the programming code will need to be updated. The advantage of this approach is that the interface refers directly to the CAD model, analyzes it and transfers data to the CAPP system. With this approach, it is easier to control design changes and make appropriate adjustments of processes in the CAPP system.
Based on the above considerations, it can be concluded that the greatest possibilities in the field of communication and data exchange between CAD systems and CAPP are offered by the STEP 242 format. It can be the basis for the operation of systems supporting the design of technological processes due to the fact that it contains all the necessary data for these activities. This format is so neutral in the event of a change in the CAD model will be required to perform a re-export data which can be considered a disadvantage of this approach.
4 Process Planning in CAPP Systems Based on PMI Annotations Saved in CAD Systems
During the development of the product, the constructor should consult his ideas with the technology department, who analyzes the technological character of the structure and proposes possible design changes. These changes may result in production costs, delivery time and the decisions on the implementation of production using the available production resources in the company or in cooperation. Without access to design data and set requirements for a product, it is difficult to make such decisions and choose the most economical variant of the manufacturing process. This allows to detect problems in the early stages of product development and avoid inserting costly changes while already at the production stage. The modern approach to design assumes that the work of product development departments does not include the stage of creating 2D drawings. This is possible due to new CAD system functions that have MBD (Model Based Definition) modules that allow to store data about the designed part directly on the 3D model and production requirements, without the need to create and store 2D technical drawings. The use of PMI annotations brings benefits in the form of reduced design costs (shorter time) and, as a result, speed up the time of product launch on the market. An annotation mechanism is used, which is defined on specific views directly on the 3D model. The use of this approach to design can completely eliminate the need to create 2D documentation. There is a significant reduction in the time of preparation of design and technological documentation due to the possibility of concurrent work on the project. Both the designer and the process planner can work on the same 3D models. The process planner can also apply his comments to the 3D model in the form of a comments. In this way, it is possible to precisely identify problem areas in the project and avoid misunderstandings. Another factor is the ability to correctly interpret 2D documentation, which can be very troublesome with complex shapes. Incorrectly interpreted design documentation may result in errors in the selection of manufacturing technology. If such documentation is transferred to production, it can bring about large losses. The benefit of using this part description is that all design and technological documentation is available in one file, which simplifies product data management in the company. CAD systems offer 3D file viewers, which have a number of useful functions to view the annotations attached to the 3D model. Parts with annotations can be saved in formats that do not require a license for the CAD program in which the model was prepared and even a specialized browser. The part with PMI annotations can be saved as a 3D PDF file and opened with the help of popular free browsers for this format. This facilitates cooperation between companies at the stage of determining design or technological requirements for products. Popular CAD systems can save geometric data in the form of the Step 242 (Managed Model Based 3D Engineering) neutral format.
The two basic methods of data exchange between CAD systems and CAPP are discussed above: neutral and direct formats and through interfaces. Interfaces work as add-inns to CAD system and are developed in internal programming languages available in the API environment.
Figure 1 presents the concept of an integrated product development environment based on interfaces enabling data exchange between CAD and CAPP systems. Two ways of communication were proposed: through a dedicated interface developed in the CAD system’s API environment and using the STEP 242 neutral file format. Other neutral file formats and direct methods were discarded due to a number of limitations described above.
In the first step, the part model is analyzed and the data is prepared in the form of a list of geometric features along with the annotations assigned to them. On the basis of such data, the CAPP system, guided by the knowledge base rules, may propose a set of data in the form of technological operations. Technological operations can be grouped in the form of a classifier for different types of geometric features. Such a system could propose several solutions (processes) and leave the final decision to the user.
As a result of exporting the part model from the CAD system to the STEP 242 format, a text file with an ordered structure is obtained. For example, for holes, both the nominal dimension and tolerance values are available in explicit form - Fig. 2
This form of data can be used to automate traditional technology design using CAPP systems. Figure 3 presents an example of PMI for counterbore holes.
When adding annotations, the CAD system automatically detects geometrical features and suggests a description. In the case of the above there are 6 holes with a diameter of 4.5 mm and a depth of 16 mm. The counterbore has a diameter of 9 mm and a depth of 3.1 mm. By analyzing the model using the API interface or by interpreting the STEP 242 file format, it is possible to obtain a hole pattern with the parameters necessary to select the manufacturing technology.
5 Conclusion
Process planning is a rather complex issue. Includes selection of: material, operations, machine tool, tools, machining parameters, tooling, time and material norms, cost analysis, etc. Currently, in manufacturing companies, process planning takes place largely manually and is based on the experience of process planners. This way of working is time-consuming, requires a lot of work and it is easy to make mistakes of a different kind. Access to information necessary while creating processes is also difficult due to the lack of central knowledge bases and resources databases. The presented approach gives the opportunity to quickly create new technological documentation by associating technological features with the process models available in the CAPP system. This will increase the efficiency of work in the area of product development, giving the opportunity to re-use the data available in the system. Implementation of the CAPP system with a central database gives the opportunity to technological knowledge acquisition from process planners and writing it to knowledge base. The use of such accumulated knowledge means that the quality of process plans may be at least partly independent from the knowledge and experience of single process planners. In addition, the system gives you the opportunity to optimize production costs by analyzing various process variants.
This study proposes the configuration of an CAPP system that streamlines and organizes the work of product development departments of manufacturing enterprises. Mechanisms and interfaces have been proposed that automate the data exchange between CAD and CAPP systems. In future work, it is planned to implement the presented concepts in the form of computer system modules.
References
Lipman, R., Lubell, J.: Conformance checking of PMI representation in CAD model STEP data exchange files. Comput. Aided Des. 66, 14–23 (2015)
Witherella, P., Herronb, J., Ametac, G.: Towards annotations and product definitions for additive manufacturing. In: 14th CIRP Conference on Computer Aided Tolerancing (CAT). Procedia CIRP, vol. 43, pp. 339–344 (2016)
Jeon, S.M., Lee, J.H., Hahm, G.J., Suh, H.W.: Automatic CAD model retrieval based on design documents using semantic processing and rule processing. Comput. Ind. 77, 29–47 (2016)
Waiyagan, K., Bohez, E.L.J.: Intelligent feature based process planning for five-axis mill-turn parts. Comput. Ind. 60, 296–316 (2009)
Rameshbabu, V., Shunmugam, M.S.: Hybrid feature recognition method for setup planning from STEP AP-203. Robot. Comput. Integr. Manuf. 25, 393–408 (2009)
Marjudi, S., Mohd Amran, M.F., Abdullah, K.A.S., Widyarto, N.A., Majid, A., Sulaiman, R.: A review and comparison of IGES and STEP. In: Proceedings of World Academy of Science, Engineering and Technology, vol. 62, pp. 1013–1017 (2010). ISSN: 2070-3724
Schuh, G., Prote, J.-P., Luckert, M., Hünnekes, P.: Knowledge discovery approach for automated process planning. In: The 50th CIRP Conference on Manufacturing Systems, Procedia CIRP, vol. 63, pp. 539–544 (2017)
Kumar, S.P., Jerald, J., Kumanan, S.: Automatic feature extraction and CNC code generation in a CAPP system for micromachining. Procedia Mater. Sci. 5, 1986–1997 (2014)
Chwastyk, P., Kolosowk, M.: CAD/CAPP/CAM integration system in design process of innovative products. In: Proceedings of the 23rd International DAAAM Symposium, vol. 23, no. 1 (2012). ISSN: 2304-1382
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Krot, K., Czajka, J. (2019). Processing of Design and Technological Data Due to Requirements of Computer Aided Process Planning Systems. In: Burduk, A., Chlebus, E., Nowakowski, T., Tubis, A. (eds) Intelligent Systems in Production Engineering and Maintenance. ISPEM 2018. Advances in Intelligent Systems and Computing, vol 835. Springer, Cham. https://doi.org/10.1007/978-3-319-97490-3_26
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