A Functional-Based Stack-up Design System for Stamping Dies.pdf

1、A Functional-Based Stack-Up Design System for Stamping Dies 1Bor-Tsuen Lin and 2Ming-Ren Chang 1Dept. of Mechanical and Automation Engineering National Kaohsiung First University of Science and Technology Kaohsiung 824, Taiwan, R.O.C. 2Institute of Engineering Science and Technology National Kaohsiu

2、ng First University of Science and TechnologyKaohsiung 824, Taiwan, R.O.C. bt_.tw ,.tw Keywords:functional-based; functional feature; stack-up design; stamping die Abstract.The aim of this paper is to develop a functional-based stack-up design system for stamping dies.

3、 By performing function analysis, function decomposition, and geometric analysis, design engineers are able to identify a particular dies functional features and their main variables, which are used as the basic units for the stack-up design. This stack-up design system includes a die design knowled

4、ge base, a functional feature module, and graphic user interfaces. A functional- based stack-up design system has been implemented on a Windows operation system through interfacing Visual Basic codes with commercial software, CATIA and Automation API. To showcase the power of the system, an example

5、of designing a lower of the drawing dies for roof outer panels is provided. Based on the experimental results, the system is an efficient, flexible and accurate stack-up system for designing die structures. Introduction Today, stamping parts are widely used in large-scale and high-precision products

6、, such as vehicle, communication, computer and consumer products. Therefore, the stamping process has been identified as one of the most important manufacture techniques in the industry. Stamping dies are classified into drawing dies, trimming dies, and flange dies based on their functionalities. As

7、 a result of the competitive market, the stamping die manufacturers must be able to develop high- quality dies in a relatively short time with a relatively low cost. Using a computer aided design (CAD) system is one of the most effective ways to increase a companys competitiveness. Currently, 3D CAD

8、 systems are only able to build models based on geometric parameters provided by design engineers. They fail to provide the designer with sufficient design knowledge, which is essential to the design tasks. Therefore, many researchers try to combine the 3D models with a design knowledge base or to b

9、uild expert systems 1-6. Some researchers carry on the design method. Andrews et al. 7 bring up the concept of design reuse in a CAD environment. Myung and Han 8 take advantage of the commercial expert system shell and combine the design knowledge base with a commercial CAD system to propose a knowl

10、edge-based parametric design of mechanical product based on a configuration design method. When designing complex stamping dies, die design engineers are required to customize systems to facilitate the design process 9. Nowadays, specialized software, such as CADCEUS, is available for designing stam

11、ping dies. These systems are focused on the automation of the design process of die layout and die faces 10. In addition, software that provides add-ons to CATIA, such as VAMOS, is also available. The design of dies with VAMOS is based on building blocks of components, which are provided from VAMOS

12、11. However, at present, only limited die structure automated capabilities exist 12-15, and their design procedure and design parameter value are fixed based on experience formula of current die Industry. In order to provide a flexible, effective, and accurate method of designing dies, we proposed a

13、 functional-based stack up design system for stamping dies. Applied Mechanics and Materials Vols. 110-116 (2012) pp 1447-1457 Online available since 2011/Oct/24 at (2012) Trans Tech Publications, Switzerland doi:10.4028/ All rights reserved. No part of contents of this paper may be reproduced or tra

14、nsmitted in any form or by any means without the written permission of TTP, . (ID: 35, National Cheng Kung University, Tainan, Taiwan-10/01/14,12:13:32) Functional-based Design In general, the purpose of designing a new mechanical structure is to support a certain function. However, addi

15、tional assistance or extended functions is required for achieving this goal. Unfortunately, these additional functions make the mechanical structure even more complex 16. For example, the purpose of drawing dies is to draw parts to achieve the desired shape. However, in the entire drawing process, w

16、e need positioning panels, guiding dies, and other operations. As shown in Figure 1, these extended sub-functions are essential to the drawing process. After a close look at each type of mechanism design method, we find that a particular mechanism has its own design method because of certain externa

17、l conditions, such as manufacture processes, production methods or other specific requirements. In other words, the layouts of the mechanism have a limited number of modes. Once the layout is fixed, the parts that are included in this layout are also fixed. For instance, a press is used to process s

18、tamping dies. There must be some features, which is called U-groove, on the stamping die to have the die fixed on the press. Therefore, every design feature in a structure provides at least one function. This paper proposes a functional-based stack-up design system. A functional feature is the minim

19、al unit in this system. We employ a bottom-up approach, where several functional features form a functional part, related functional parts then form a design unit or sub-design unit, and those design units finally form the desired mechanical structure. Punch Stopper Machine Center Guide Box Security

20、 Area Guide Plate Base Strengthening Rib Nest Guide Hole Key Slot Guide Plate Base U-Groove Pocket Cushion Pin Hole Strengthening Rib Lifting Eye Figure 1. The lower die of drawing die The feature-based design approach, also known as design-by-feature or feature-based modeling, provides the designer

21、 with a set of features in a feature library 17. However, functional-based design differs from feature-based design in that feature-based design is a design method that is based on form features, such as pad, pocket, hole, etc. These features on a particular part are used to acquire particular shape

22、s. In contrast, functional-based design is a design method that is based on functional features, such as boss, rib, hook, and etc. The purpose is to add the functional features that carry design intents into the mechanical structure directly 18. These functional features must satisfy the following r

23、equirements: (a) may include design intent; (b) sets of features related to specific function; (c) main variables related to function; and (d) performance 18. When constructing a 3D model, most systems make use of Boolean operations on features. Consider the design of a U-groove, for example. Suppos

24、e we have a base, F0. Then, the union of a U_Pad, F1, with F0 gives P1. Finally, the difference of P1 and U_Pocket, F2, gives the final U- groove, P2, as shown in Figure 2. 1448Mechanical and Aerospace Engineering, ICMAE2011 U P0 - F0 (Base) P1 P2 F1 (U_Pad) F2 (U_Pocket) Figure 2. An example of fea

25、ture-based u-groove modeling Though the functional-based design approach also uses Boolean operations, the difference is that the combination is functional-based. Therefore, it is important for the designer to treat every functional feature as a unit. Whenever the designer wants to construct a featu

26、re, the unit representing the feature can be loaded and put into the CAD environment. The union of base, F0, and U-groove (functional feature), FF1, gives us the final design P1, as shown in Figure 3. Figure 3. An example of functional-based u-groove modeling Methodology of Functional Reasoning In o

27、rder to construct the mechanical structure in a stack-up manner, we need to get a full understanding of the die structure and design options. Moreover, we need to decompose the die into various functional features. In order to simplify the stacking process, we also need to identify the main variable

28、s and the connections between various functional features. This section explains how to identify the design options, the functional features, and their main variables. This process of function reasoning includes function analysis, and function decomposition is shown in Figure 4. Figure 4. The proces

29、s of functional reasoning Function Analysis.The purpose of the function analysis is to identify design options by finding the functions of which a particular stamping die consists. The purposes (why) and capabilities (how) of a die are called functions. Purposes are the anticipated results after cer

30、tain actions are preformed, Applied Mechanics and Materials Vols. 110-1161449 while capabilities are the tasks that need to be carried out to achieve the purposes 19. A function is expressed using a verb plus a noun. Taking a U-groove of a stamping die as an example, the purpose of this U-groove is

31、to fix the die. Therefore the function is expressed as “fixed die”. The function analysis of a drawing die makes use of a functional tree. First, by identifying the forming sheet metal as its main function, we perform a backward searching to get all assistant and extended functions where we further

32、identify all available design options. As shown in Figure 5, some of the design options provide more than one option. For example, hooks have three different types: lifting eye bolts, cast in lifting bushings, and bolts. Designers need to make their choices based on design needs. In terms of represe

33、ntation, we use OR to indicate that there are multiple options which are available. Figure 5. Functional tree of a drawing die Function Decomposition. In the previous section, we performed the function analysis of the drawing die and identified the design options for the structural design. However,

34、design options are only representations a partial structure, it may include more than one functional feature 20. As shown in Figure 1, the guide box structure only guides the die toward the correct direction, but this structure includes three functional features: the guide plate base, the stopper, a

35、nd the strengthening rib. Generally speaking, when facing complex design tasks, engineers usually employ a divide-and- conquer approach. They first divide the big complex design task into several sub-tasks and perform analysis on each of the sub-tasks in turn. This divide-and-conquer method ensures

36、that the task can be fully covered and clearly illustrated. Therefore, we need to perform a hierarchical function analysis until a functional feature is reached. The process of decomposing the design options of a drawing die is shown in Figure 6. First, the die structure is divided into four levels

37、21: design units, sub-design units, functional parts and functional features. The hierarchy of functional features in a drawing die is shown in Figure 6. 1450Mechanical and Aerospace Engineering, ICMAE2011 Design Object Drawing Die Design Unit Upper Die Design Unit Blank Holder Design Unit Lower Die

38、 Design Sub-Unit Die Set Functional Part Locating Structure Functional Part Periphery Structure Functional Part Punch Key-Slot Functional Feature Guiding Plane Functional Feature Bolt Hole Functional Feature Hook Functional Feature Pocket Functional Feature Guide Plate Base Functional Feature Stoppe

39、r Functional Feature Functional Part Guide Box U-Groove Functional Feature Strengthening Rib Functional Feature Nest Guide Hole Functional Feature Cushion Pin Functional Feature Figure 6. Hierarchy of functional features in a drawing die Geometric Analysis.The objective of the geometric analysis is

40、finding the key variables of the functional features in order to manipulate stably and easily them. The key variables of the geometric analysis include entities and constraints of the functional features. Most 3D CAD systems keep a history of every object and procedure during building solid model. T

41、aking the U-groove as an example, the main variables are in the 2D draft of the solid model and the extracted 2D draft of U- groove is shown in Figure 7. Input.1 Sketch.1: Create Outer U-Shape Feature Type: Extrude (5mm) Sketch.2: Create Inner U-Shape Feature Type: Pocket (to last) Take out 2D draft

42、 (sketch.1) of U- groove from the solid model. Line.1 Line.2 Line.3 Point.1 Point.2 Point.5 Point.4 Point.3 Arc.1 (a) (b) Figure 7. The extracted 2D draft of a U-groove: (a) the features of the U-groove; (b) 2D draft of the U-groove Then, we analyze the geometric information of the 2D draft of U-gro

43、ove by performing the classifying object, re-named object and identifying relationship shown in Table 1. In the classifying object, we need to identify the basic entities, geometry entities, geometry constrains, and dimension constraints from all objects of 2D draft of U-groove. In the re-named obje

44、ct, every object are named based on the name of their type plus their serial numbers in the CAD system, and we only re-name the variables that need control. In the identifying relationship, we analyze the associations Applied Mechanics and Materials Vols. 110-1161451 among objects and identify the k

45、ey variables. This step helps the program engineers ensure that their programs give the correct results. The U-Center renamed from Length. 1 shown in Table 1 is a main variable of the U-groove, because the position and the dimension of the U-groove are changed based on the value of the U-Center. Bes

46、ides U-Center, Input.1 is also need to identify as the initial position of U-groove. When a point in the screen for design module of the CAD system is picked as an initial position of the U- groove, the Input.1 value is assigned to the position value. Tab1. The geometry analysis of U-groove Category

47、 Name Relationship Category Name Relationship Basic Entity Origin - Geometric Entity Line.3 S: Point.4, E: Point.5 H direction - Arc.1 Point.3 V direction - Dimension Constraint U-Center (Length.1) Point.3, Absolute X(Y) Geometric Entity Point.1 Line.1, Line.2 Length.2 Line.2, Line.3 Point.2 Line.2,

48、 Arc.1 Radius.1 Arc.1 Point.3 Arc.1 Geometric Constraint Coincidence.1 Line.1, Input.1(Side Face) Point.4 Arc.1, Line.3 Tangency.1 Line.1, Arc.1 Point.5 Line.3, Line.1 Tangency.2 Line.2, Arc.1 Line.1 S: Point.5, E: Point.1 Perpendicular.1 Line.1, Line.3 Line.2 S: Point.1, E: Point.2 Perpendicular.2

49、Line.2, Line.3 *S: start point of the line; E: end point of the line Implementation Issues In addition to the aforementioned functional reasoning, the functional-based stack-up design system also includes die design knowledge-base, functional feature library, functional feature modules, and graphic

50、user interfaces, as shown in Figure 8. The system is designed for use on personal computers. It uses CATIA V5 as the CAD environment and MS Visual Basic 6.0 as the system language. CAA V5 Automation Application Programming Interface (API) is used to interact with CATIA. Functional Feature Geometry M

51、odeling Die Structure Functional Feature Module Graphic User Interface Design Rules, Formulas, Tables, Validation Conditions Die Design Standard Die Design Criteria Die Design Knowledge Base Figure 8. The schema of functional-based stack-up design system 1452Mechanical and Aerospace Engineering, ICM

52、AE2011 Die Design Knowledge Base.In order to establish a fast and easy connection between the design data and the computer aided design system, we need to convert the design data into a die design knowledge base compatible format that can be processed by the computer system. As shown in Figure 9, a

53、table shows the design standard of a U-groove. Figure 9. Design standard of a U-groove Managing the die design in a systematic way is a process for classifying and compiling a huge die design data based on each functional feature, where each functional feature is the result of the aforementioned fun

54、ctional reasoning. By mapping the design standards and design criteria with each functional feature, the design data for each functional feature is made available to the designer, so that the system can adopt a functional-based approach when designing dies. In this paper, the conversion of the desig

55、n data of a die is a two-step process. The first step is to convert the dimension variables, which are defined in the design standards, into design tables. The next step is to convert the design criteria into design rules, design formulas, and verification conditions, so that design engineers are ab

56、le to impose limits on dimension, to calculate the values of the variables, and to further make sure that the result meets the design criteria. In this step, we adopt a grammatical approach. Since CATIA can be connected to MS Excel, we transfer all dimension variables into an Excel table. By fetchin

57、g the related dimension variables from the table when constructing an entity, the system is able to convert the design data in digital form. Because the dimension of the U-groove is strongly related to the weight of the die, the functional feature library and the design table must be used together.

58、When constructing the structure of a functional feature, the system reads the dimension variables so that the functional feature can be created to meet its standard Functional Feature Module.The purpose of constructing the functional feature module is to integrate the functional feature library and

59、the die design knowledge base into each functional feature module. In order to build the functional feature library, we perform a classification of the functional features, which are identified using the aforementioned functional reasoning. This process assigns each functional feature a category based on their functional characteristics. When the classification is finish