Aviation complex products have the characteristics of customer demand, product composition, product technology, subject discipline, manufacturing process, test maintenance, project management, working environment, etc., and have long product life cycle, high technical content, strict production and quality requirements. Assembly is an important part of the aviation complex product design process, and the results are directly related to product quality, performance, life and maintainability. In the manufacturing process, the assembly time accounts for about 20% to 50% of the total production time, and the assembly cost accounts for 20% to 30% of the total manufacturing cost. In order to shorten the assembly cycle of the product, reduce the assembly cost, and improve the assembly quality, the assembly process planning and design of the aerospace product must be changed from the traditional model based on 2D drawings to the new model based on the 3D model for the product life cycle.

The promotion and application of 3D CAD software in China has greatly improved the design efficiency of mechanical products. Some large aviation companies have begun to promote the 3D model design of MBD-based products, and no longer draw 2D drawings, but today's mainstream 3D CAD systems can only be realized. The assembly structure design and the simple interference relationship inspection function can not realize the assembly process design, and can not check whether the product and process equipment have interference relationship during the assembly process. The well-known digital assembly software in foreign countries mainly includes Visualization Mockup, Tecnomatix and DELMIA. These systems provide assembly simulation functions, but can not realize information integration in design, process and manufacturing departments and full lifecycle management of product data.

The Computer Aided Assembly Process Planning (CAAPP) system for PLM (Product Lifecycle Management) is a three-dimensional model that spans the entire life cycle of a product, and the assembly and assembly process of the product through the computer. Rationality, applicability of process equipment, etc. Analyze, simulate, evaluate and optimize product assembly models to achieve the goals of shortening product development cycle, improving assembly quality and efficiency, reducing production costs, and optimizing product performance. In this paper, the key technology research and system development of CAAPP system are carried out, and the application mode of the system is discussed.

3D Assembly Process Requirements Analysis for PLM

Aviation complex products have complex shapes, small batch sizes, large differences in part specifications, and high reliability requirements. Product stereotypes are a complex and sophisticated process that often requires multiple designs, tests, and improvements, which are costly and time consuming. The assembly process characteristics of aerospace complex products are as follows:

(1) The assembly process of aviation products is complicated, and it is generally decomposed into assembly, assembly and assembly; the assembly process of each group and components is generally performed by cleaning, assembly tolerance calculation, mechanical part assembly, electronic component assembly, wiring, testing, etc. Composition, product assembly is a process of machine, electric, and cloth mixing.

(2) The structure of aviation products is generally compact, and the assembly space is small. It is not convenient to use tooling and equipment. In the assembly process, the tooling and fixture design are often unreasonable and cannot be assembled. Therefore, tooling and fixtures have high repair rates, long development cycles, and high R&D costs.

(3) The production volume of the product is small. If all models are tested and assembled, the production cost of the product will be further increased and the product life cycle will be extended.

(4) The shape and structure of the product is complicated, and the assembly path of the parts is tortuous. It is difficult to reflect the actual assembly situation by relying on the space imagination of the craftsman, and the assembly process is difficult to prepare.

(5) The number of parts is large, the size is very different, and the parts are misplaced and missing. It is difficult to understand the assembly process by relying on the two-dimensional assembly process. It is necessary for the assembly technician to instruct the workers to assemble at the assembly site.

There are a lot of problems in the traditional assembly process planning mode, including: the assembly process personnel should extract a large amount of assembly process information from the 2D drawings, and the workload is very large; the assembly process is mainly based on the text description, and is assisted by the process drawings. Workers understand complex tooling and key processes. Assembly workers do not have an intuitive understanding of the overall structure of the product. It is difficult to match the process equipment in the assembly process with the assembly resources at the assembly site. The number of tooling, fixtures, and instruments at the assembly site is large. There are many kinds of process equipments, and the process equipment designed by the craftsmen relying on the two-dimensional drawings is often unreasonable, and even interferes with the products during the assembly process, which makes it impossible to assemble. Due to the lack of reliable simulation verification methods, assembly problems can only be found at the assembly site. Redesigning the process equipment, the whole process is very cumbersome, extending the product development cycle.

The assembly process personnel completes the division of labor and the division of tasks according to the three-dimensional model of the product and the assembly process standard specification; acquires the three-dimensional model of the group and components, and performs assembly sequence planning, designing the assembly process route; performing detailed design of the assembly process to determine the assembly steps Work step content, and design of tooling and fixtures, distribution of assembly process equipment; assembly path planning, assembly simulation and interference inspection, adjustment of assembly path if interference occurs; output assembly simulation picture, video, assembly process PDF Files to support assembly site visual browsing.

CAAPP system development

An aviation company in China has a compact product layout, complex shape structure, large number of parts, large size difference, small production batch, fast product upgrade; complex assembly process, many on-site tooling and fixtures, and often misplaced and leaked Happening. At present, the company's Product Data Management (PDM) system is Siemens' Teamcenter 8.3, Computer Aided Process Planning (CAPP) system is CAPPFramework 2007 of Northwestern Polytechnical University, and 3D CAD system is NX 6.0. Based on the actual production of the enterprise, the author developed the assembly process, design and simulation system for aviation complex products for PLM using Visual Basic 6.0. The system software platform is Tecnomatix software of Siemens, and the database is Oracle 10g.

1 system's functional architecture

The CAAPP system consists of assembly process planning, design and assembly process simulation, assembly process file generation module, and database system, CAPP system, PDM system, and 3D CAD system.

The main components of the system function as follows:

(1) 3D CAD system: 3D model of design products and process equipment (full-format 3D model, expressed as "*.PRT").

(2) PDM system: process division, task division, process personnel authority management, assembly process approval and release.

(3) Assembly process planning and design module: assembly sequence planning, assembly process route design, assembly process detailed design.

(4) Assembly process simulation module: plan the assembly path and perform assembly process simulation and interference check, generate assembly simulation pictures (JPG format, represented by "*.JPG"), and simulation video (AVI format, with "*" .AVI"), simulation animation (general three-dimensional graphics format, expressed as "*.U3D").

(5) Assembly process file generation module: Generate assembly process (Excel file, indicated by "*.XLS") to support the technician preview and convert the simulation animation into 3D PDF file.

(6) CAPP system: According to the process information and simulation files, the assembly process specification is formed.

The system is integrated with the PDM system, and the 3D model is acquired through the integrated interface of the Tecnomatix software and the PDM system, and the basic attribute information of the component is mapped through a predefined XML file to obtain related information.

The system is integrated with the CAPP system to generate an assembly process information file (expressible Markup Language file, represented by "*.XML") in the assembly process planning and design module according to the assembly process planning, design and simulation results, including the assembly simulation file. The save path information, the CAPP system parses the file and obtains the assembly simulation file to form an assembly process specification.

2 Division of labor and division of tasks

The process department of an aviation enterprise is generally divided into an enterprise-level process department and a shop-level process department. The enterprise-level process department can perform assembly process review on the product, design PBOM (process BOM); determine the assembly workshop of each group of components in the PDM system and The assembly shop, and the sub-unit catalogue report is generated to complete the process division; the workshop-level process department assigns process designers to prepare the assembly process in the PDM system according to the results of the process division to achieve the task division.

3 Product 3D model acquisition

In order to prepare the assembly process, the system needs to obtain the 3D model of the product and the basic attribute information such as name and code number from the PDM system. Due to the difference between the PDM system and the assembly process planning and design module, the definition of the same attribute may be different, so that the basic attribute information of the component cannot be directly obtained from the PDM system, and the mapping relationship between the attributes needs to be defined through the XML file. Figure 3 shows a three-dimensional model of a product acquired through an integrated interface.

4 Assembly process planning

The system supports product 3D model browsing, can display the assembly structure of the product, and adjust the position of each component in the assembly structure to complete the assembly sequence planning. The assembly process can be established under the assembly process node, the attribute information of each process can be improved and the components can be assigned through the Pert diagram. Figure 4 shows the assembly process planning in the CAAPP system.

5 assembly process design

Under the assembly process node, assembly steps can be established and the attribute information of each step can be improved. The assembly process equipment can be imported into the system assembly resource library and distributed. The system can automatically collect the assembly process information and display it in the property interface of the process, process and work step, which is convenient for the process personnel to view and modify and improve. Figure 5 shows the assembly process design in the system.

6 assembly process simulation

The system's motion navigation tool can drag and rotate components, remove them from the assembly, use the "inversion" tool to convert the disassembly path into an assembly path, and the system can automatically plan the assembly path. Dynamic interference checking can be performed during assembly process simulation to verify the rationality of the assembly path and assembly process equipment design. Figure 6 shows the assembly process simulation in the system.

7 Assembly process file generation and assembly site visual browsing

The preparation, approval and release of the assembly process of the aviation enterprise are completed in the integrated system of PDM and CAPP. The special symbols in the assembly process need to be filled in the CAPP. After the assembly simulation is completed, the process can be marked in the 3D model. Requirements and comments, intercept the assembly simulation picture, record the simulation video, and make the assembly simulation U3D file. The CAAPP system can automatically convert the U3D file into a 3D PDF file, and the assembly process information and the simulation file save path are counted and output in the form of a process XML file; the CAPP system can parse the assembly process XML file and generate an assembly process file, according to the simulation. The file save path acquires the simulation file to support the assembly site visual browsing, as shown in Figure 7. Since the 3D PDF file is associated with the craft card, there is no need to include textual process information.

Conclusion

Through the research on the characteristics of aviation complex products and their assembly process, the problems of traditional assembly process planning and design mode are illustrated, and the functional structure and general structure of the assembly process, design and simulation system of aviation complex products for PLM are proposed. The process discusses the assembly field application model. According to the actual production of an aviation company, an assembly process planning, design and simulation system based on Tecnomatix software was developed. At present, the system has been running in the aviation enterprise for more than one year, and more than 30 components have been assembled. Design and simulation, and can support assembly site browsing assembly simulation pictures, video, 3D PDF moving surface, effectively guide the assembly site to carry out assembly work, improve production efficiency, and shorten the product pre-research cycle. However, at present, the system cannot model and assemble cables and electronic components. These will be the next step in the research.

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