CAD/DFM integrated solution for sheet metal parts


Abstract: Aiming at the structural characteristics of Fanjin parts, using feature technology, a CAD/DFM integrated prototype system for Fanjin parts based on the Pro/E platform is established on the basis of feature modeling, so as to realize DFM technology in the field of Fanjin zero-price processing The sharing and integration of design and manufacturing information in the entire life cycle of applications and products. Introduced the architecture, design principles and key technologies of the Fanjin parts CAD/DFM integrated system, as well as the evaluation process of the manufacturability evaluation module; the STEP neutral file is used as the source file to describe the product data information, and the product design features The database and manufacturing feature database are used as intermediaries for obtaining and transmitting product information, so as to realize the true integration of CAD and DFM. The results of the process and economic evaluation of the parts using the method provided by the system show that the application of DFM technology in the field of metal processing can reduce product costs, increase productivity, and speed up the market speed of products.

1 Introduction
DFM is the core technology and implementation method of concurrent engineering. It is a practical technology that starts from the entire life cycle of the product and considers the cost of the product in the early conceptual design stage of the product. DFM software integrates the knowledge of design, materials and processing technology, and independent designers can use this knowledge to make reasonable decisions immediately without having to work hard to obtain first-hand information or consult experts. The development team can use DFM to let everyone think about the same problem at the same time. In short, compared with current product development methods, the result of applying DFM is to obtain higher-quality products at lower cost and in a shorter time. Practice shows: DFM can shorten the product development cycle by 40%-60% and reduce product cost by 30%-40%.

At present, as far as the research objects are concerned, most of the DFM field is for box parts and revolving parts, and there is relatively little research on the DFM design method and process of Fanjin parts. In recent years, with the rise and application of a small amount of cutting and rapid prototyping processing technology, the research on the parts/products processed by the forming technology and its process design and system structure has become an important direction.

Since the research on DFM technology, various manufacturability evaluation methods have been proposed. At present, these methods have two problems: the content of manufacturability evaluation is not comprehensive (the focus is on solving the problem of knowledge-based manufacturing cost evaluation), and the function of features and parts, structural manufacturability and processing manufacturability are not considered; DFM and CAD are not implemented. Information sharing and integration.

This paper analyzes the characteristics of Fanjin parts, adopts the feature-based part manufacturability evaluation method, establishes a reasonable feature and part manufacturability evaluation system, comprehensively and reasonably evaluates the manufacturability of the parts, so as to guide the part design and research integration The integrated DFM method of parts realizes the information integration of CAD/DFM.

2 CAD/DFM integrated system structure of Fanjin parts
Since concurrent engineering was put forward, well-known domestic and foreign companies have implemented concurrent engineering in the field of new product development, and have achieved significant economic benefits. As the core technology of concurrent engineering, DFM has also attracted the attention of various enterprises. At present, in China, the development of DFM software is still in its infancy, and its application is mainly concentrated in the field of mechanical processing. In order to further promote the development of DFM technology and expand the application fields of DFM, this article established a knowledge-based CAD/DFM Integrative Prototype System for Sheet-Metal Products (CAD/DFM Integrative Prototype System for Sheet-Metal Products) based on previous studies. Sheet-Metal CAD/DFM system).

2.1 Sheet-Metal DFM system function
The main functions of the Sheet-Metal DFM system (see Figure 1): Based on the company’s mechanical design automation system Pro/Engineer as the software platform, it is oriented to fan-metal parts and realizes automatic feature recognition, extraction and matching on the basis of feature modeling. Part feature information model; then through feature mapping technology to realize the feature mapping from the design domain to the manufacturing domain, and use STEP development tools to generate STEP neutral files according to the system application protocol; finally complete the technology and economics of the manufacturability of the fan gold parts Evaluation of the nature; the information integration between CAD and DFM is realized on the feature layer, so as to truly realize integrated and parallel product parts development.

2.2 The key technology adopted by the Sheet-Metal DFM system
According to the overall requirements of the subject and the definition and analysis of the system information model, the system adopts the following key technical implementation schemes:

(1) Use STEP standard to realize the integration scheme based on the system information model. The data model design of each system module is completely in accordance with the system application protocol to ensure the sharing and exchange of information, and to realize the real STEP-based product data integration.

(2) Adopt feature design technology, so that in the design stage, design and manufacturing intentions other than product geometric topology information can be captured. Feature extraction and matching of product feature models based on feature design, instead of using complex feature recognition technology based on geometric models, can accelerate the exploration of methods and approaches for concurrent engineering implementation.

Establish the Sheet-Metal DFM system with the existing commercial software as the development platform. According to the in-depth investigation and study of the CAD system and the use of domestic CAD software data, this system uses PTC's parametric CAD software Pro/Engineer as the software development platform to establish a Sheet-Metal DFM manufacturability evaluation system to achieve matching Technical and economic evaluation of gold parts.

2.3 Design principles of Sheet-Metal DFM system
In order to ensure the realization of Sheet-Metal DFM system functions, the following main principles were followed during the design of the system:

(1) Construct a part design model based on feature design. The feature model used in the design model is the requirement and prerequisite for the implementation of feature mapping in the feature information processing module, otherwise the information transmission on the feature layer cannot be realized. When performing shape feature mapping, it is necessary to analyze and discriminate the underlying information. Therefore, a geometric reasoning mechanism based on features must be established to identify features from discrete geometric and topological relationships.

(2) The manufacturability evaluation module of the Sheet-Metal DFM system takes manufacturing features as input. In order to facilitate the reading of the obtained manufacturing feature information into the database, the feature mapping must eventually generate a STEP-neutral description of the manufacturing features with certain engineering semantics. file.

(3) Handle the relationship between system specificity and versatility. The Sheet-Metal DFM system is mainly for the technical and economic evaluation of Fanjin parts, without considering other production areas. However, the generality of this system is not lost. In order to make this system not dependent on any CAD system, the following factors have been considered during the research and development of this system:

1) The data description format must be consistent.
2) Data exchange must comply with STEP standards.

2.4 Architecture of Sheet-Metal DFM system
Sheet-Metal DFM system is an integrated evaluation system for manufacturability of Fanjin parts, as shown in Figure 2. The main features of the system are:

(1) Obtain the design features of the fan gold parts by reading the STEP neutral file, so that the system does not depend on any CAD system, so it has universality.

(2) When illegal geometric types and wrong designs are discovered, an Unknown entity is established for processing, which increases the fault tolerance of the system.

(3) Users can add, delete and update records in the knowledge base and database according to specific conditions, making the system open.

(4) The system has good integration and uses standard data interfaces to access data information, reducing human-computer interaction.

(5) Analyze and evaluate the manufacturability of Fanjin parts based on knowledge, and realize the concurrent design of products. The system is mainly composed of 5 parts (see Figure 3):

(1) Design feature model (CAD system) The design feature model is constructed using Pro/Engineer software. One of the most obvious features of this software is its strong feature modeling function.
    (2) Design feature information processing module This module uses geometric reasoning and a knowledge-based hybrid method to automatically extract all the design information of the part from the STEP file generated by the CAD system. And automatically carry out feature reorganization and feature recognition for each entity that composes the part, identify and classify each design feature into different feature subsets (internal feature set and external feature set), and give the features of each design feature at the same time The class code and the corresponding characteristic attribute value provide the necessary information for realizing the conversion of design features to manufacturing features. It is worth pointing out that the semantics of the modeling features extracted by this module are not necessarily clear. For example, if all trace features are extracted, the shape semantics are not clear at this time, so it needs to be finalized by the feature mapping module.
    (3) Feature Mapping Module The function of the feature mapping module is to convert design features into manufacturing features, and generate the processing method and initial process design plan for each design feature. It includes shape feature mapping, dimensional accuracy mapping, surface roughness mapping and material feature mapping. The manufacturing features obtained after mapping are information units with certain engineering semantics. The result of feature mapping is an important prerequisite for manufacturability evaluation.
    (4) Manufacturability evaluation module The manufacturability evaluation module is the core of a Sheet-Metal DFM system. Its function is to evaluate the feasibility, reliability and economy of the design of Fanjin parts. In order to evaluate the design model comprehensively and accurately, manufacturability evaluation is divided into two processes: technical evaluation and economic evaluation.
    1) Technical evaluation Technical evaluation is mainly to evaluate the degree to which the design plan meets the design requirements and technical performance. Evaluation indicators can be divided into: structural manufacturability, machinability, processing manufacturability, etc.; some of the technical indicators are technical issues that have nothing to do with the actual manufacturing resources of the enterprise, aiming to carry out the structure and accuracy information of the parts based on the manufacturability knowledge. Analyze, evaluate the possibility and difficulty of processing, identify designs that cannot be processed by conventional methods, and those that are difficult to process by conventional methods; the other part is manufacturability issues that are closely related to the actual manufacturing resources of the enterprise. The actual resource needs of the enterprise are used to examine whether the production equipment can meet the requirements of various aspects such as the size range and accuracy characteristics of parts processing.
    2) Economic evaluation The economic evaluation mainly focuses on the evaluation of the economic benefits of the product design plan, including the cost of the plan, the cost of implementation, the utilization rate of materials, etc. The costs included in the manufacturability include: material cost, labor cost, Manufacturing expenses, non-production expenses and tooling expenses. The time included in manufacturability mainly includes: processing time, preparation time for handover, and tooling preparation time.
    (3) Multi-domain knowledge base and database Multi-domain expert knowledge base and database are important technical support for realizing the manufacturability evaluation of parts/products. It has relevant expert knowledge and databases (such as mold design and manufacturing costs, parts processing time, processing costs, processing methods and processing technology guidelines, etc.) required for the manufacturability evaluation of Fanjin parts. The core of constructing this system is how to acquire and express knowledge in different fields and the mechanism of management and application of this knowledge.

3 Conclusion
    Based on the structure and process characteristics of Fanjin parts, this paper uses STEP technology to establish a CAD/DFM integrated prototype system for Fanjin parts. The system fully considers the features and parts' function, structure and processability, and can perform a comprehensive and detailed evaluation of the parts; adopts the feature-based part manufacturability evaluation method to establish a reasonable feature and part manufacturability evaluation The system can comprehensively and reasonably evaluate the manufacturability of the parts, thereby guiding the design of the parts: the use of STEP neutral files for product data description, and the realization of information sharing and integration between CAD and DFM.