Research on BOM structure in CAPP

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Research on the structure of BOM in CAPP


capp (Computer Aided Process Planning) as a carrier for the automation of process design process, has made great progress in research and development. With the continuous deepening and development of advanced manufacturing technology, the integration degree of CAPP and CAD, PDM, MRP and other systems is required to be higher and higher, and the core of integration is to realize the consistency, sharing and maintainability of product data. In order to realize product lifecycle management (PLM) of product data, the author of this paper proposes to use the concept of bill of materials (BOM) to design the process data structure

in actual production, most of the business and production processes of enterprises are actually an order oriented product design and manufacturing process. It can be seen that an enterprise must first configure products according to the user's order to obtain a product structure tree or BOM that meets the order requirements, and then use the BOM as basic data to guide the production activities of the enterprise. However, people's understanding of BOM is not deep enough. They think that BOM is a simple bill of materials, that is, a descriptive document of product data structure. The understanding of BOM only stays on the basis of product structure or bill of materials. In fact, this is not enough. As a BOM that conforms to the production of modern enterprises, we must consider the process flow in order to form a perfect basic product data for the full life cycle management (PLM) of products. Therefore, BOM should be understood as: product structure + process flow. Based on this, the author of this paper focuses on the structure of bill of materials in process planning (ppbom) in CAPP system

1 process design idea based on BOM

process design method based on BOM is to establish complex engineering data on relational database, so that CAPP can be integrated into a unified product data management system (PDMS), which effectively solves the integration of cad/CAPP system and ERP system. BOM oriented process design is divided into four stages: BOM acquisition, BOM adjustment, process design implementation, and integration with ERP. Each stage needs to realize corresponding tasks, as shown in Figure 1. No matter which stage of process design, process design always focuses on the main line of BOM. The process of process design is actually the process of BOM generation, organization, evolution and transmission

2 Relationship between process design and BOM

in the process of process design, the management of process information mainly includes process card management and statistical data summary. The management of process cards mainly refers to the production, storage and query of cards (process flow cards, welding process cards, forging process cards, etc.) used for process route design. The general principle of data collection refers to the statistics of data in the above cards according to material consumption, tooling and equipment usage, so as to transmit these information to cam and other systems for production preparation and cost accounting. The basis of realizing the above functions in CAPP system is the design of ppbom

The narrow understanding of BOM refers to the technical description document of product data structure, which indicates the structural relationship between product components, sub parts, parts and raw materials, as well as the number of subordinate components required for each component. EBOM (engineering BOM) produced by CAD is a kind of narrow BOM. It only describes the assembly and geometric information of products on the basis of product design, and lacks the corresponding process information. Therefore, the design of ppbom is mainly based on the modification of data structure and the expansion of data relationship of EBOM, so as to increase the process information of products and realize the data visualization, query and summary at all levels

3 data structure design of ppbom

data structure analysis of EBOM

ebom comes from the engineering design department, and its main structure is hierarchical and parent-child, among which parent-child BOM is more commonly used. In EBOM, two types of data relationships are mainly described: (1) the relationship between the assembly quantity of products, that is, the parts and their number that make up a certain assembly. (2) The natural attribute relationship of a part, that is, the size, material, weight and other characteristics of a part

the relationship between EBOM and ppom

ppom and EBOM are related and different from each other. Their connection is mainly manifested in that the prototype of ppbom is EBOM, and most of the basic data in ppbom (such as the assembly relationship of parts, the size of parts, etc.) comes from EBOM. Their differences mainly include three aspects:

(1) different product data structures. The difference of data structure is mainly due to the difference between process and design, which leads to three situations: A. virtual parts. Some assembly parts will appear in product design, which are represented as branch nodes in EBOM. However, in the actual process, due to the assembly process, an assembly will not be manufactured in the form of a component, but will be installed on the product in the form of a separate part. At this time, it is necessary to change this branch node into a group of leaf nodes in the ppbom. b. Middleware. In the actual production process of products, assemblies composed of a group of the same parts are often used. The manufacturing and processing processes of such assemblies and their subordinate parts are exactly the same. Therefore, in order to simplify the process design process and facilitate management, it is necessary to define them as a branch node in ppbom. c. Outsourced parts. Such components only need to be defined as outsourcing in the routing and appear as a leaf node in the ppbom

(2) extension or change of basic attributes of parts. In the specific ppbom, you must add corresponding basic attributes such as routing and working hours for each part. In the use of materials, sometimes due to inventory and other reasons, the raw materials defined during design may not be available. At this time, the process department will select new materials according to the material substitution rules, and the information of the process bom will be changed accordingly

(3) expansion of product data relationship. In ppbom, in addition to inheriting the product assembly quantity relationship and the natural attribute relationship of parts in EBOM, the mapping relationship between parts and process documents must also be defined. This kind of relationship mainly describes the relationship between parts and various process cards processing the parts

through the analysis and comparison of EBOM and ppbom, we can know that in ppbom, the product is taken as the object, including the design information and process information of the product, realizing the one-to-one correspondence between the design information and process information, and improving the product data structure, which has a 10 minute wide speed regulation range and beam movement spacing structure

data structure design of ppbom

according to the above structure and relationship description, in the logical structure design of the database, ppbom is designed as a four layer structure, as shown in Figure 2, in which the process card layer is mainly used to fill in each process card and summarize the process document directory; At the component level and the part level, it mainly reflects the assembly process relationship of parts and components, as well as the summary of material consumption quota, design and manufacturing special process equipment and other information at these levels; Various summary tables generated at the product level will describe the assembly attribute relationship, natural attribute relationship and process design information of parts, mainly including parts list, material quota and process route

4 realization of ppbom function

visualization of data in ppbom

realization of data visualization is mainly to make various data relationships of ppbom change from logical structure to physical structure. The CAPP system based on the design idea of this paper selects treect RL control to display the assembly relationship of products, components and parts and the corresponding process card information, as shown in Figure 3. In this way, it is also easy to add, delete, modify and other operations of ultrasonic vibration atomization pulverization technology at each node

in terms of data display, reading and storage methods, the author of this paper uses XML technology to realize. For each process card, it is described with XML code, as shown in Figure 4, which is part of the cells of a process card:

the XML description of the table shown in Figure 3 is:

process number

process name

process content


after describing the process card in XML language, According to the characteristics of the data filled in each table in each card, after Abstract sorting, each card is divided into five parts: cardhead, cardbody, edition, revision and appendix. The program abstracts these five parts into five classes using object-oriented ideas, and defines the methods and attributes of the corresponding classes. When reading the data, the card format information described in XML will be read, Then read the corresponding data from the database according to the corresponding data table of different classes and fill it in the correct position of the card. During data storage, the completed table data is parsed from XML format and stored in the corresponding data table according to the class of each part of the table

query and summary of data in ppbom

after the process card is described in XML language, the data information of each card is stored in the ppbom

table in XML format, while some key information of the process card, such as part list drawing number, part drawing number, etc., is stored in the form of fields. Therefore, when querying data, you need to find the corresponding table in the database according to the key information of the card, get the corresponding XML document description, and then retrieve XML metadata. This query process can be realized by using simple structured query language (SQL) in relational database, and only string matching operation is required in program development language

during data summary processing, due to the diversity of summary input conditions and structured output data, it is necessary to write corresponding stored procedures in the database operating system. The summary is based on the query of data. In the program, the equipment can be used not only for the material, but also for the mechanical testing of other non-woven fabrics of the same type. Different query conditions can be programmed into the program. The corresponding stored procedures are executed in the database operating system. After retrieving the required data, some post-processing, such as sorting, classification or mathematical calculation, is carried out. Finally, it is output in the form of XML document or displayed in CAPP, Or for other systems. (end)

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