K356-錐齒輪座加工工藝及鉆3-M6螺紋孔夾具設(shè)計(jì)【版本2】,k356,齒輪,加工,工藝,m6,螺紋,羅紋,夾具,設(shè)計(jì),版本 , J.M. Superior 2, Cranfield accepted 26 relies requirements, taking this as a general concept, is to make should be always linked to a requirement, and its purpose is International Journal of Machine Tools Fixture knowledge modelling, Fixture functional requirements 1. Introduction The main objective of any design theory is to provide a suitable framework and methodology for the definition of a sequence of activities that conform the design process of a product or system 1. In general, all of them identify requirements as the starting point in the design process. In fact, the engineering discipline dealing with product design can be defined as the one that considers scientific and engineering knowledge to create product definitions and design solutions based on ideas and concepts derived from requirements and constraints 24. For this research, a relevant issue when considering explicit the meaning of two main terms: Functional Requirement (FR) and Constraint (C). A functional requirement, as it stated by different authors, represents what the product has to or must do independently of any possible solution, 2,4. A FR is a kind of requirement, and considering some basic principles widely recognized in the field of Requirements Engineering, we could add it is a unique and unambiguous statement in natural language of a single functionality, written in a way that it can be ranked, traced, measured, verified, and validated. A constraint can be defined as a restriction that in general affects some kind of requirement, and it limits the range of possible solutions while satisfying the requirements. So, a constraint A functional approach for the formalization R. Hunter a , J. Rios b, * a Department of Mechanical and Manufacturing Engineering, Escuela Tecnica Jose Gutierrez Abascal, b Currently in Enterprise Integration (Bldg 53), Received 14 January 2005; Available online Abstract The design of machining fixtures is a highly complex process that of the fixture design process Perez a , A. Vizan a de Ingenieros Industriales, Universidad Politecnica de Madrid, 28006 Madrid, Spain University, Cranfield, MK43 0AL, UK 14 April 2005 August 2005 on designer experience and his/her implicit knowledge to achieve Manufacture 46 (2006) 683697 functional requirements should be defined in the functional domain, which brings on the scene the issue of how to define and represent the functionality of a product. The way used to represent it will affect the reasoning process of the designer, and in that sense, the mapping between the functional 0890-6955/$ - see front matter q 2005 Elsevier Ltd. All rights reserved. doi:10.1016/j.ijmachtools.2005.04.018 * Corresponding author. Tel.: C44 1234 754936; fax.: C44 1234 750852. to narrow the design outcome to acceptable solutions. Considering the Theory of Axiomatic Design 4, ably, the first aspect to think about is how the requirements are represented or declared. As it has been previously and the physical domains, being the later the one where the design solutions are developed. Several authors have investigated the concept of functionality and functional representation 2,58. Their design approach provides a view based on the Function-Behaviour-Structure frame- work, where function is defined using structure and behaviour 6. The objective is to fill the gap that allows a designer to progress from FRs to physical design solutions. The approach is that product functions are achieved by means of its structure, which seems to lead to an iterative causal approach, where solutions are sought until the selected structure causes the intended functionality. The approach adopted in the research presented in this paper is based on the definition of Fixture Functional Components (FFC), which can satisfy the fixture functionality, and on the mapping between such FFC and fixture commercial elements. An advanced approach to the definition of requirements and functions comes from the creation of ontologies. The ontological approach pursues the definition of the meaning of terms making use of some kind of logic, and the definition of axioms to enable automatic deduction and reasoning 9. The ontological approach has got a higher relevance since the representation of knowledge is considered the key factor in whatever engineering process, and it has been recognized as a way to facilitate the integration of engineering applications 10, to describe functional design knowledge 7, and to define requirements 11. Considering a purist approach, if an ontology does not include axioms to enable reasoning then it could be considered more like an information model, and in this sense, this is the approach developed in the work presented in this paper. When considering the methodologies developed for the design of fixtures, it can be stated that in general they are rational and propose a series of steps to follow. For example, the methodologies proposed by Scallan and Henriksen 12, 13, make use of this approach to describe in general terms the information needed in each stage of the fixture design process. Basically, the importance of modelling in detail such information, which mainly is related to fixture requirements, fixture functionality, fixture components, manufacturing resources, manufacturing processes, and design rules; resides on the possibility to automate the design process through the development of a knowledge- based application or system. It is relevant to mention that several authors have already aimed to develop knowledge- based applications for fixture design, none of them based on a functional approach, some of the most recently published works can be found in the Refs. 1419. In the following sections, this paper presents a methodology to formalize the design process of machin- ing fixtures based on the engineering concepts of functional requirements and fixture functions 20. The formalization of the functional requirements is achieved through the application of a structured way of specifica- R. Hunter et al. / International Journal of Machine684 tion via natural language. Additionally, IDEF0, MOKA mentioned, the way of expressing requirements definitively affects their interpretation and the creation of a design solution. In this sense, it is widely accepted, that the use of natural language is the most common way of expressing requirements and in consequence, their writing becomes an important issue. The anatomy proposed by Alexander et al. 24 to write requirements in a semi-structured way is used as basis to declare the functional requirements and constraints of fixtures 20. In machining, work holding is a key aspect, and fixtures are the elements responsible to satisfy this general goal. In their design process, the starting point is the definition of the machining fixtures functional requirements and constraints. Usually, a fixture solution is made of one or several physical elements, as a whole the designed fixture solution must methodology, and UML diagrams are used to capture, represent and formalize knowledge, being the ultimate goal to facilitate the automation of the fixture design process. The IDEF0 method is used to create an activity model of the fixture design process, allowing the identification of the information used in each one of the different tasks it comprises. UML has been used to complement the IDEF0 model by representing the interaction between the activities of the process. The MOKA methodology together with UML, are used to capture and represent knowledge involved in the fixture design process. Finally, to validate the proposed methodology, partial results obtained from the development of a prototype knowledge-based application are presented. 2. Analysis of machining fixtures requirements In Section 1, two terms have been defined: functional requirement and constraint. Requirements have always existed, the way in which they are expressed, and how they are integrated in the product design process, are aspects that are addressed from different disciplines, for example: product design engineering and requirements engineering among others. In general, Requirements Engineering refers to the discipline dealing with the capture, formalization, representation, analysis, management and verification of requirements fulfilment. However, all these aspects need to be integrated in the product design process, and require- ments should lead to the definition of the possible product design solutions, which in general demands an integrated view of the requirements issue. It is important to keep in mind that the development of such discipline is strongly related to Software Engineering and Systems Engineering, and in fact much of the research related to requirements come from authors from these engineering areas 2123. When considering the analysis of requirements, prob- Tools in this case a KBE application for the design of machining fixtures; and the second one is the functional requirements of the components subject of the application; in this case machining fixtures. An example of the former ones for an application developed in collabor- ation with an industrial partner is presented by Rios et al. 28. For this kind of FRs specification, UML seems to be for fixture FRs. MOKA ICARE: ENTITY Name Reference Entity Type Function Constraints Functional Requirements for the Fixture Constraints Functional Requirements (CFR) Structure Define constrains to Functional Requirements for the fixture t support the fun e structur de of the fixtur Re 03-07-04 1.0 In progres form R. Hunter et al. / International Journal of Machine Tools it is independent of the knowledge representation to be used in the implementation, and it does not require from the fixture designer a deep knowledge of any software modelling technique. The definition of these fixture functions is a first step in the modelling needed for a KBE application development. For example, considering stability as one of the main constraints affecting the fixture FRs, any fixture functional solution should satisfy this constraint. To achieve that, it would be necessary to define a fixture function (FF) for stability methodology. Part machining: operations strategies cutting parameters cutting tool parameters volume to remove Optimization method Analysis model Constraints: Deformation Stability Interference Part orientation Part support: support points support vectors support surfaces Determine cut Determ Determine cl Determine cl Determ Determ R. Hunter et al. / International Journal of Machine Tools & Manufacture 46 (2006) 683697 689 Part location: locating points locating vectors locating surfaces Part information: mechanical properties friction coefficient raw material shape and dimensions part shape and dimensions tolerances evaluation, and this function could be called from the fixture function clamp (clamp_FF) presented as example in the Fig. 6. From a high level perspective, the stability_FF would need as input: part information (i.e.: material mechanical properties, shape, dimensions and tolerances), machining process information (i.e.: machining operations, machining strategies, volumes to remove, cutting parameters, cutting tool parameters), and fixture functional element information (i.e.: function, constraints, rules, containing volume, point and vector of application). Part of this information will have to be used to determine some derived parameters like cutting and allowed clamping forces. Making use of such infor- mation together with an analysis model, for example the one proposed by Liao et al. 32, and optimization methods, for example the one proposed by Pelinescu et al. 33, such stability_FF could be developed and implemented. The complexity in the detailed specification of such stability_FF is extremely high, and demands its own research by itself Fig. 6. High-level function template Fig. 7. Structure of the AFNOR fixture Fixture functional elements: function constraints rules containing volume Function Clamp (clamp_FF) F4 ting forces ine clamping surface amping points amping orientation ine clamping forces ine clamping elements 32,34,35, but the definition of a high level function where all the information needed for its development could be represented, is one of the objectives of the research presented in this paper. Phase 3: The third phase, functional design (FD), is aimed to create a set of functional solutions for the fixture design. A functional solution is independent of any particular commercial fixture component, and it is rep- resented by means of a set of fixture functional elements. A fixture functional element satisfies at least one of the functions identified as inherent to a fixture, i.e.: centre, position, orientate, clamp, and support. These elements are represented by means of graphical symbols, also called functional symbols, which apart from the functionality also represent some qualifiers that affect them. Such fixture functional symbols are based on the technological elements defined in the AFNOR standard NF E 04-013 - 1985 36. Fig. 7 presents their structure, which comprises: kind of representation. technological elements. Type Function *Surface class: Machined *Type contact surface: Punctual technology, state of the part surface, function of the technological element, and the kind of contact between the part surface and the fixture element. In order to progress from the functional design to the detailed one, which is the next phase, it has been defined a mapping table between functional symbols and commercial fixture elements 20, Table 2 represents an example. For the creation of the possible functional solutions a set of input information, analysis models, optimization func- tions, and rules has to be included in the software functions previously defined in the second phase. Basically, the inputs defined are: Part information: material mechanical properties, shape and dimensions of the part to be machined, and the associated tolerances. Functional element information: functions, associated restrictions, orientation, containing volume, contact parameters, and location point. Part manufacturing process: sequence of operations, and for each operation: machining strategy, cutting para- meters, cutting tool, and volume to remove. Production estimation of: number of set-ups, set-up times, batch size, production rate, and target cost. Resource information: machine morphology, and machine capacity. Functional design brings benefits to design environments Table 2 Relation between AFNOR elements and fixture commercial components Fixture function Functional representation Clamp function (Attribute) Type technology Surface Class *Type technology *Surface class *Type contact surface *Type function R. Hunter et al. / International Journal of Machine690 where the solution is mainly driven by the satisfaction of quantitative functions, as opposite to environments where subjective aspects like aesthetics has a major relevance. In particular, in the fixture design environment, the advantage of creating a functional solution derives from not using a full library of commercial fixture elements but a reduced number of basic functional elements, which can be transformed into the former ones in a second design phase. And this is particularly relevant when some kind of artificial intelligence technique is going to be applied in the implementation phase, since many of these techniques are based on the initial generation of a complete design space where the possible solutions are contained, if the design space can be reduced then the determination of the solutions can be done more efficiently. And with the functional design approach the design space is divided in two subsets, one subset dealing with the functional solution and other dealing with the physical one. Phase 4: The fourth phase, detailed design (DD) comprises the creation of detailed solutions from a functional one. To undertake this phase the mapping tables previously mentioned and the corresponding interpretation rules have to be used. To mention as well, that the fixture software functions apply in a similar way, but with a different input, which basically is the geometry (containing volume) associated with the fixture element, this is particularly relevant for the interference checking. How- ever, in this case the space of possible solutions is reduced by the fact that only those commercial elements that can be mapped to the functional ones can be used, and that a point of application and an orientation vector for the elements to be used are data as well. A detailed solution contains the finalfixturecommercialelementstobeusedinthe machining of the part and their set-up. Finally, the fifth phase, validation of the design (FV), is aimed to make a final evaluation and validation of the functional requirements and their associated constraints defined in the first phase. However, it is important to mention that in addition to a final validation, the functional approach, with the separation of the design spaces in two parts, allows implementing the validation in two prior stages. First in the functional design phase, so the possible functional design Type contact surface *Type function: Machining Fixture Commercial elements selected type *Type technology: Clamp Tools & Manufacture 46 (2006) 683697 solutions fulfil the imposed requirements, and second in the detailed design phase. This can be made by means of the optimization method that can be included in the Fixture Function (FF), as it was previously mentioned in the Phase 3. Based on this methodology, a detailed definition of the fixture functional design process is presented in the next section. 4. Fixture functional design process model As it was mentioned in the introduction, the functional approach to design has drawn the attention of several researchers 2,5,6,7,8. However, as it is pointed out by Kitamura 7, in general, the functional knowledge is left implicit, there are not clear definitions of the functional concepts, and the generic functions proposed in the literature are too generic to be used by designers. In this sense, the ontological approach is an interesting contri- bution to formalize the functional design knowledge. The approach adopted in this research deals with the definition of what would be the first step in a fixture ontology development, which is the modelling of the fixture information. The functional approach to fixture design, based on an information model definition, has some characteristics that can be deduced from the facts presented in the previous sections, that is: a reduced number of functions that a fixture has to perform, the possibility of formalizing the FRs specification with quantitative qualifiers, and the reduction of the design space by using functional elements. However, prior to the definition of any fixture information model, it is necessary to define the fixture design process and the information flow along it. Following is the activity model developed in this research to represent the fixture design process. The model is represented using the IDEF0 technique and UML, and it allows identifying the knowledge units needed during such process, and the interaction among used modelling techniques to represent the process and part of the information related to the fixture design process 37,38, but without taking a functional approach to it. Starting with the input knowledge units related to part geometry, manufacturing process plan, machining resources, and following the IDEF0 methodology, the first step is to create a context diagram or highest-level diagram, of the fixture design process. The knowledge units that constitute the final output to the process are the fixture detailed design, and the fixture assembly plan. The resource knowledge units are the machine-tool unit and the modular fixture elements one. The IDEF0 methodology is based on the definition of a hierarchical b