ORIGINAL ARTICLE

Knowledge formalization for product–process integrationapplied to forging domain

Alexandre Thibault & Ali Siadat & Mohsen Sadeghi &Régis Bigot & Patrick Martin

Received: 25 June 2008 /Accepted: 6 January 2009 / Published online: 29 January 2009# Springer-Verlag London Limited 2009

Abstract Efficient and effective forging process selectionfor a given set of product characteristics and requirementsis a multicriterion problem strongly influenced by inter-dependent factors like product complexity, design require-ments, product quality, resource availability, and cost.These factors are formalized based on the informationprovided regarding the role and experiences of experts inproduct–process design; however, design representation isconsidered as a network of product and process parametersand expert’s knowledge as a set of constraints applied onthe parametric network. This paper proposes an integratedproduct–process approach to evaluate its consistency and isuseful in selecting suitable forging process and productdesign parameters. Computer support tool has been devel-oped to present and to integrate the product parameters,the process characteristics, and the expert’s knowledgerelated to forging domain to select an appropriate forgingprocess evaluated through a constraint propagation algo-rithm. This approach is validated through a case studypresented at the end.

Keywords Concurrent engineering . Product–process planintegration . Knowledge formalization . Forging

1 Introduction

Forged products have a wide range of industrial application,e.g., automotive and aerospace industries, but principal

activities involved in the forged parts development includeforged part design, process design, suitable manufacturingprocess selection, and planning. These activities dependhighly on the expert’s experience and product and processknowledge accumulated in the industry over a long periodof time.

Recent activities in concurrent engineering [1] aim toprovide computer-aided tools that are able to integrateproduct and process development activities, increase productquality, create most consistent and productive manufacturingprocess, and reduce product and development cost. Sinceproduct–process integration [2] for forged manufacturingplays one of the key issues in forging product and processdevelopment, hence, it can be considered as one of the mostimportant areas of concurrent engineering.

In this context, this research paper seeks to establish amethodology to practice a concurrent manufacturing pro-cess development for forged products. We focus moreparticularly on the relationships and links that exist withinthe product design and the related process plan. Themanagement of these links is what we call “product–process plan integration” which can be decomposed intotwo main aspects (the two directions of product–processplan integration), i.e., product and process parameters andconstraints. This point of view is inspired by Coyne [3]who identified two phases:

& Analyses: the selection of the manufacturing processes,& Synthesis: the multidisciplinary constraints integration

due to the already defined parameters.

As it can be seen on Fig. 1, the goal of integration is tolink the set of the data as product parameters and theprocess plan parameters. For each set of data, someconstraints and parameters may be already defined, so theother set of data must be defined according to predefined

Int J Adv Manuf Technol (2009) 44:1116–1132DOI 10.1007/s00170-009-1928-8

A. Thibault :A. Siadat (*) :M. Sadeghi :R. Bigot : P. MartinLGIPM–ENSAM Metz,4 rue Augustin Fresnel,57078 Metz Cedex 3, Francee-mail: ali.siadat@ensam.fr

constraint and parameter. There are two kinds of reasoningduring product–process integration:

& Product design parameters: reasoning is considered todetermine the constraints that must be respected on theprocess plan parameter selection (manufacturing pro-cesses selection),

& Process plan design parameters: reasoning is based todetermine which constraints must be considered duringthe definition of product parameters (design for manu-facturability [DFM]).

The links between the product and process parameters inforging domain are defined according to product develop-ment properties [4]:

& The geometrical and mechanical properties of the partare modified globally during the definition of a forgingprocess. It is opposite to the machining process where amachining operation modifies the part locally (boring,surfacing, etc.).

& There is a significant correlation between the modifica-tion of geometrical parameters and the variation of themechanical parameters. For example, the cold drawingof a billet will modify not only the length of the billetbut also the mechanical resistance of the billet.

These properties imply (1) the necessity for the globalconsideration of part in order to determine the process plan,hence, the use of an entity-based approach is unadaptable atthis level and (2) consideration of the advantage to bederived from the correlation between the geometricalparameters and the mechanical parameters to improve themechanical characteristics.

In order to support the two directions of product–processintegration, we present a research background on the themeof product–process integration in Section 2 to establish the

fact that experts are trying to organize solutions to these issuesthrough knowledge integration within product–process defi-nition. In Section 3, a methodology for the representation ofprocess plan schemas is explained using elementary ele-ments to represent forging process sequences. Subsequently,the rule-based technique is implemented to precise the linkbetween product and process plan parameters that serve asthe basis for the preparation of process sequencing selection.The proposed formalism is implemented as a computer sup-port tool in Section 4 along with a case study to validate ourapproach. The paper concludes with a summary of theresults and presents future research perspectives in Section 5.

2 Research background

2.1 Product–process integration

The product–process integration can be defined in twomanners [5]: (1) selection of the manufacturing process and(2) design for manufacturability.

2.2 Manufacturing processes selection

Manufacturing process selection involves two steps: step 1involves the evaluation of available processes for theirtechnical capability to make a design and step 2 ranksresulting successful processes using economic criteria [6].Many methods have been proposed to support these steps.Ashby [7] proposes the selection of manufacturing pro-cesses considering their compatibility with the geometricalparameter and the material followed by rating based on thecost. The final choice is performed with respect to therating, industrial knowledge, and available manufacturingresources; however, the approach adopted in this researchpaper does not assume a specific manufacturing domain.

P1

P2

P3

…

Pi

Pj

…

Product definition

Integration direction « selection ofmanufacturing processes » : Repercussion of the constraints due to the already defined product data

Product data (already defined)

Integration direction « Design for manufacturing » : Repercussion of the constraints due to the already definedprocess plan data

Product data (to be defined)

K1

K2

K3

…

Ki

Kj

…

Process plan definition

Process plan data (already defined)

Process plan data (to be defined)

Each Ki and Pi may depend on other Kj or Pj (already defined or to be defined)

Kj and Pi are valuable data

Fig. 1 The two directions ofproduct–process planintegration

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Lovatt [8] describes the framework based on the definitionof process plan with different manufacturing tasks (steelcutting, steel heat treatment, casting, etc.) to determine thesequences of specific manufacturing process. The processselection is carried out by the combination of manufactur-ing process attributes, material parameters, and productspecifications to satisfy the design requirements [9]. Theapproach proposed by Gupta [10] consists of three phases:(1) identification of the pairs of material/process thatsatisfy the required conditions (economical and geometricalspecifications), (2) generation of the possible process plansfrom identified material/process pairs, and (3) selection ofthe most interesting process plans considering the eco-nomical indicators. In Ishii’s work [11, 12], the processselection is decomposed into two steps: (1) the first step isthe identification of relevant parameters that affect manu-facturing processes selection and (2) the second stepconsists in developing the representation schemas forknowledge used during the manufacturing processes selec-tion. This knowledge is used to determine compatibilitybetween product specifications and process parametersand to rank more precisely the possible manufacturing pro-cesses according to the economical indicators. Boothroyd[13] propose the selection of the material/process pairsbased on the process capability in terms of geometricalspecifications realization and material constraint. The finalselection is determined by the elimination of the unaccept-able material/process pairs, considering the related con-straints and predefined indicators, such as the cost. Table 1summarizes the characteristics of different manufacturingprocess selection approaches.

2.3 Design for manufacturability

DFM is a two-step product design approach according tothe predefined process plan that involves constraints relatedto product parameters and characteristics. In step 1, a set ofpossible solution propositions in the product parametersdefinition are identified, followed by step 2 that ensures itsmanufacturability. Step 2 can be decomposed into threephases [14]: (1) verification: determine whether the product

is reasonably manufacturable or not (according to theavailable resources, the existing knowledge); (2) quantifi-cation: time, quality, and cost; and (3) optimization on threelevels: human knowledge, resources (machines, tools,computer applications), and product (design) [15].

Few researches deal more precisely with the productdesign under constraint and correspond more to the designfor manufacturability. Feng [16] propose the constraintsprogramming method to integrate the manufacturing pro-cess constraints at the design level. This approach is entity-based and applied to the machining domain. More recently,Kumar [17] describe a knowledge-based system consistingof set of rules to assess the manufacturability of deep-drawnparts. Skander [18] proposes the consideration of a partdesign with skin and skeleton features in order to integratemanufacturing constraints.

2.4 Knowledge management applied to integration

The product–process integration requires the collaborationof experts from different skills and from many disciplineswho often work in distributed environment and may not beusing the same description for the same object. Everyexpert has his own knowledge, formalisms, and toolsresulting in the integration and collaboration of the expertactivities as an active research issue. The link between theproduct and its associated process plan belongs to knowl-edge formalization: experts use their knowledge to deter-mine the selection of the manufacturing processes or todefine the product parameters considering the manufactur-ing constraints.

Researches with a specific focus on the application in theproduct–process integration activities have been widelyexpanded to investigate the applicability of knowledgeformalization technologies and concepts in engineeringcontexts such as expert system [19], group technology[20], ontology [21], and case-based reasoning [22]. Table 2gives a synthesis of the main characteristics of the proposedconcepts.

2.5 Product–process integration in forging domain

Several research activities are reported in the forgingdomain to integrate product–process design. The develop-ment of a knowledge-based concurrent engineering systemfor closed die hot forging processes is described by Esche[23]. As a result, the development of the AutomatedConcurrent Engineering Software (ACES) forging moduleand its capabilities for material and machine selection,process design, process sequencing, die design, and earlycost estimation has been explained.

Tsai [24] presented a remote collaborative forging engi-neering system for a concurrent product and process

Table 1 Comparison of the approaches “manufacturing processesselection”

Approach Choice ofmanufacturingprocesses

Choice ofmaterials

Associatedtool

Economicalevaluation

Ishii Yes No HyperQ/Process YesAshby Yes Yes CES n.a.Gupta Yes Yes Seer-DFM YesBoothroyd Yes Yes DFMA YesLovatt Yes n.a. n.a. Yes

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development environment. Activities of conventional forgingengineering design, manufacturing processes modeling, andplanning were analyzed to propose a structural model forforging enterprises.

The design of a web-based cold forging process generationsystem is the focus of a system developed by Zhang [25]. Inthis system, key issues on the development of computer-aided intelligent design system are addressed in great detailto include system structure, knowledge representation,knowledge-based design, problem-solving paradigms,knowledge-based management system, knowledge acquisi-tion, Extensible Markup Language model of the product,and the transition and display of the drawing through theInternet.

Kingsly [26] has explained the development of a feature-based design system that is applied in the concept-to-manufacturing stages of the forging process. The system isbroadly divided into four modules, namely, feature-baseddesign (FBD), virtual factory environment (VFE), featuremapping for forging (FMF), and process planning (PP). TheFBD module is used for design, modeling, analysis,representation, and validation of the component for forgingapplication. The VFE module defines the layout model ofthe factory on the computer and provides database formachines, machine tools, tools, workpieces, etc. The FMFmodule contains the knowledge base to prepare a forgemodel, die impressions, parting line/surface, etc. The PPstage is used to find the process parameters like formingsequence, shape of preform and finisher die sets, temper-ature of billet and dies, forming speed, die stroke, materialfor die sets and workpieces, etc.

Zdrahal [27] has proposed ontology-based forgingknowledge integration. The selection of forging processes isrealized using a classification process. The process capabili-ties and product parameters are considered to generate a set ofclassification.

Kulon [28] has described a knowledge-based design toolenabling the generation of hot forging die designs from acomponent profile. The system integrates the hot forging

die design process into a single framework and guides theuser through the design process enabling the generation offorgeable geometry from a component profile taking intoaccount machine, material and forging company specificdata, and design considerations.

Yang [29] has explained a concurrent engineeringconcept in order to integrate CAD/CAM/CAE and rapidprototyping and manufacturing for the development of themetal-forming process. The process characteristics such asgeometrical complexity, effects of process parameters, flowpattern of workpiece, and deformation-induced defects areconsider to reduce trial and errors in the design stage.

3 Development of the formalism

3.1 Choice of the formalism

The expert system and group technology are considered inour proposed framework. An expert system is a computerapplication that represents the knowledge and reasoningprocess of experts based on a series of rules provided withinspecific domain area. Group technology is the process usedto identify and compare the design and manufacturingcharacteristics of parts in order to group them into familiesassociated to the generic standard process plans.

Proposed formalism is a compromise between grouptechnology and expert system. The objective is to structureand aggregate the information and knowledge related to thefamily of product–process using the intelligent reasoningmethods. The goal is to associate these approaches in orderto limit the proliferation of families while preserving acertain level of precision in the possible deductions. Theaddition of rules allow to determine the precise the linkbetween product and process plan parameters for an addedadvantage to be associated to families, i.e., to limit theirpossible inconsistency to a certain extent.

The process plans manipulated with the proposedformalism are what we call “high-level process plans.”

Table 2 Synthesis of the different approaches for knowledge management

Formalism Interpretation system Existing tools Limitations

Expert system Rules Algorithms of forward, backward,or mixed chaining

CLIPS, Prolog Opaqueness of the reasoning,difficulty to maintain

Ontology Description logic Use of reasoners: consistencychecking, classification

Protégé, Growl, pOWL, Swoop Complicated interface,difficulty to maintain

Case-basedreasoning

Case: pair problemdescription/solutiondescription

Similarity research, adaptation n.a. Booting of the case base,adaptation rules

Group technology Part families associatedto consequences

Classification in part families andapplication of the consequences

n.a. Definition of part families,proliferation of part families

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They consist of a simple sequence of elementary stepsnamed as “elementary transformations” to describe the useof a manufacturing process. The idea of this formalism is tofactorize high-level process plans into schemas by stronglylinking product parameters. The structure of a process planschema will allow formalizing knowledge relative to therelations between process plan parameters and product partparameters. Furthermore, this formalization shall be pro-cessed in order to produce deductions on process plan andon the definition of product part.

3.2 Description of the proposed formalism

3.2.1 Building of process plan schemas

A process plan schema can be viewed as a factorization ofseveral high-level process plans associated to rules that wecall “conditions.” More precisely, a process plan schema isdescribed with objects called “transformation.” There existfour types of transformations:

1. elementary transformation,2. sequence transformation,3. choice transformation,4. loop transformation.

Elementary transformations have already been men-tioned in the previous section. It is used to describe an

elementary step included in a manufacturing process. Thethree other types of transformation are called “composedtransformations.” Sequence transformation represents anordered sequence of transformations (of all types). Choicetransformation represents several possibilities of transfor-mations for a step; however, choice between these differenttransformations is exclusive. Loop transformation can beused to represent a repeated nature transformation.

Sequence transformation and choice transformationallow factorizing several high-level process plans: inFig. 2, two process plans are shown. The only differencebetween them is on the first elementary transformation: thefirst uses the sawing process, whereas the second uses theshearing process. These two process plans can be factorizedusing a choice transformation that gives two possibilities:elementary transformation with sawing process or elemen-tary transformation with shearing process.

Conditions may be defined for all transformations of aprocess plan schema (example on Fig. 3). Conditions arerules that define some physical or logical conditionsconcerning product parameters that must be satisfied inorder to select an acceptable transformation (for example,the conditions which are used to indicate the possible andnot possible transformation or the recommended transfor-mation). The root transformation of the schema may alsohave a condition; if this is not satisfied, the schema will notbe considered.

Fig. 2 Factorization of severalhigh-level process plans

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Four types of conditions have been defined in order tocategorize them and to facilitate the collection of knowl-edge during expert’s interviews:

– conditions of elimination relative to the limits of themanufacturing processes,

– conditions of elimination linked to the uselessness of amanufacturing processes,

– conditions of elimination according to the knowledgeof an expert,

– conditions of recommendation.

A condition of elimination, if satisfied, will eliminate theconcerned transformation; however, a condition of recom-mendation, if satisfied, will privilege the concerned transfor-mation (the other concurrent possibilities will be eliminated).

3.2.2 Exploitation of a process plan schema

The exploitation of a process plan schema can be decom-posed into three phases:

1. scrutiny of a process plan schema,2. deduction of the process plans,3. consideration of the constraints on the process plan.

The scrutiny of a process plan schema implies theschema simplification by eliminating the possibilities thatare not compatible with part characteristics. The schema isbrowsed to evaluate each condition. If conditions of elimina-tion are satisfied, it results in the elimination of concernedtransformations, whereas if conditions of recommendation aresatisfied, it results in the elimination of the transformations in

competition with concerned transformation. In Fig. 4, theprocess plan schema is simplified: assuming that the partconsidered implies a billet with diameter too high forshearing, the condition of elimination on the elementarytransformation using the shearing process is true and thenthis transformation is eliminated. On Fig. 5, if the conditionof recommendation is verified, all the transformations inconcurrence with the considered one are eliminated (unlessthey are recommended too).

The deduction of the process plans consists in extractingall possible high-level process plans from the scrutinizedprocess plan schema obtained during the previous step.During deduction, the scrutinized process plan schema isbrowsed; each time, a choice transformation is found and anew process plan is created for each alternative presented inthe choice transformation. For example, on Fig. 6, theschema is composed of a sequence with three elementarytransformations and a choice transformation with twoalternatives. The deduction process produces two processplans based on these alternatives.

The consideration of the constraints on the process planis realized at two levels:

1. the set up of the constraints on the process plan schema,2. the repercussion of the constraints to the part

characteristics.

A constraint on the process plan schema can be consideredto represent the usage and no usage of the transformations. If aconstraint represents the no usage of transformation, then thistransformation is eliminated from the schema. If a constraintindicates the use of the transformation, then the concurrent

Fig. 3 Conditions on a processplan scheme

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transformations are eliminated from the process schema. Therepercussion of the constraints to the part characteristics isrealized through the consideration of the proposed conditions.All elimination conditions on the route to imposed trans-formations must be satisfied to keep these transformationsavailable; hence, the constraints on the part characteristics canbe determined with respect to the ones on the process plan.

Remark 1: use of the conditions The different types ofconditions provide several levels of schema processing. Ifthe scrutiny process is realized by one type of condition,

then the other type of condition and the associatedconstraint do not get involved in the scrutiny process.

Remark 2: applied reasoning The applied reasoning con-sider the following hypothesis: a nonevaluated conditionwill not intervene during the processing.

Remark 3: metadata and reliability percentage Metadatathat are not exploited within the reasoning process can beintegrated to this formalism in order to improve the schemacomprehension and the reliability percentage can be

Recommended transformation

Eliminated transformations because of competition with the recommended transformation.

SequenceTE: Hot flashing

TE: Hot borningChoice

Choice

TE: void process

TE: Hardening &Tempering

TE: Controlled Cooling

TE: Simple Cooling

Fig. 5 Pruning of a processplan scheme (condition ofrecommendation)

If the part implies a too large billetdiameter, then the shearing processmust be eliminated.

Condition : Fig. 4 Pruning of a processplan scheme (condition ofelimination)

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associated to each condition in order to provide the degreeof reliability of the defined condition.

3.2.3 Conclusion on the proposed formalism

A process plan schema permits to factorize several high-levelprocess plans with rules called conditions that are linked tothe part parameters and allow the elimination or recommen-dation of transformations during processing. The conditiondefined on the root transformation of a process plan schemagathers the criteria that must be respected for the applicationof the schema. In this study, a connection can be made withformalism, like group technology: this condition on the roottransformation defines a kind of part family associated to aunique process plan schema. Thus, each process plan schemarepresents a part family, and the classification to the partfamily is realized using the condition on the root transfor-mation of the schemas.

An example of a process plan schema is shown on Fig. 7(drawn from [30]) centered on the extrusion process. It hasbeen built with an expert from the French Industrial andMechanical Technical Centre (http://www.cetim.fr).

The difficulty to carry out this formalization is to findthe right size of a schema:

– Too complete schemas lead to difficult readability andmaintainability; however, it is theoretically possible tofactorize many process plans in a unique schema but itshall result in the loss of clarity.

– Too short schemas could possibly lead to a prolifera-tion of the schemas if the covered domain ofpossibilities is large.

4 Implementation and case study

The implementation of this formalism should respond to thefollowing objectives:

– specification of the description parameters of a part inorder to render the application entirely configurable,

– definition of the process plan schemas,– definition of the parts to be analyzed,– reasoning on the process plan schemas, considering a

given part.

The structure of the data and associated reasoningalgorithm are detailed in the following subsections.

4.1 Data structure

4.1.1 Description parameters

Description parameters are used for the description of apart and for the composition of the conditions in aprocess plan schema and are useful if it is used at leastonce in a condition; otherwise, it cannot intervene in thereasoning. All the description parameters are configu-rable: a special data structure has been proposed for thispurpose.

Fig. 6 Deduction of processplans

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Four types of parameters are available in the developedimplementation:

1. unordered list,2. ordered list,3. integer,4. float.

Figure 8 summarizes the data structure of the parameters.Two main classes permit the specification and the use of theparameters:

1. The class ParameterSpecification: an instance from thisclass contains the specification of the parameter (name,description, possible values).

Fig. 7 Example of a process plan scheme (from [22])

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2. The class ParameterValue: an instance of this class hasa reference with an instance of the class ParameterSpecification and contains a defined value for theconcerned parameter. Instances from this class are usedfor the effective allocation of the parameters in theconditions or in a part description.

4.1.2 Storage of process plan schemas

Two significant observations can be drawn from the storageof a process plan schema:

– the storage of the tree structure composed by thetransformations,

– the storage of the conditions associated to thetransformations.

The model realized for the implementation is presentedon Fig. 9. A process plan schema (class ProcessPlan-Schema) is associated to a unique transformation: the roottransformation of the schema. In the implementation, wedecided to impose the root transformation as a sequencetransformation.

The tree structure of the schema is represented with thecomposite pattern; the nodes of the tree are instances fromthe class ComposedTransformation, whereas the leaves areinstances from ElementaryTransformation. These latterinstances have a reference to an instance from the classProcess to express the fact that they use a manufacturingprocess. Each instance from the class ComposedTransfor-mation have a collection of instances of the class Trans-formation which may be instances from ComposedTransformation or from ElementaryTransformation.

ParameterValue

UnorderedListParameterValue

OrderedListParameterValue

IntegerParameterValue

RealParameterValue

ParameterSpecification

UnorderedListParameterSpecification

OrderedListParameterSpecification

IntegerParameterSpecification

RealParameterSpecification

0..* 1..1

Fig. 8 Structure of parameter data

Fig. 9 Data structure for process plan scheme

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Concerning the conditions, each instance of the Trans-formation class has a list of four references to instancesfrom the Condition class:

– A condition of elimination linked to the limit ofmanufacturing processes.

– A condition of elimination linked to the uselessness ofmanufacturing processes.

– A condition of elimination from the know-how of anexpert.

– A condition of recommendation.

Each condition of a transformation is described with a tree-based structure, thanks to a pattern composite (Fig. 10). Thenodes are instances of the ANDCondition or ORConditionclasses, whereas the leaves or instances of the GreaterThanElementaryCondition or EqualsElementaryConditionclasses.

Each instance from the ElementaryCondition class has areference to an instance of the ParameterValue class: it

allows knowing on which parameter the condition isapplied and what is the considered value.

4.1.3 Definition of the parts to be analyzed

The parts to be analyzed are described with parameters. Ifno parameter are filled, it shall result in no evaluation ofschema conditions; hence, no scrutiny of schemas. Themodel used is very simple: an instance of the Part class willhave a list of references to instances of the ParameterValueclass. Figure 11 shows the link between the part and theprocess plan thanks to the conditions.

4.2 Reasoning

There exist three phases for reasoning:

– The first phase consists of marking the schemas. Theprinciple of marking is to browse the schemas and

Fig. 10 Data structure for the conditions

Fig. 11 Data structure for a partand link with the process plan

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evaluate each condition of each transformation withrespect to the considered part. New working processplan schemas are generated in this phase whichstores the evaluation results. This processing isadjustable: the user can select types of conditionsto be evaluated.

– The second phase is implemented by the user: hedecides where the transformation are kept, suppressed,or imposed (to express the fact that, for instance, hewants to keep the possibility of using a certainmanufacturing process in the process plan) on eachworking process plan schema. Ultimately, thesedecisions are constraints on the process plan and shallnot necessarily match the definition of the part.Inconsistencies should be shown after the deductionof the process plans which means that nonrespected or

nonevaluated conditions will be displayed for eachprocess plan deducted.

– The third phase is the deduction of the process plansfrom the working process plan schemas on which theuser has fixed his constraints. This last phase is realizedonly if the number of the extractable process plans isnot too high. In the implementation, it has been fixed at20 for computational time and display reasons. Eachextracted process plan has a reference to an instance ofthe condition class that corresponds to the necessarycondition for the considered process plan. This neces-sary condition is built during the construction of theprocess plan and gathers all the conditions that are notevaluated or not respected by the definition of the part.Then, the user can be informed about the demands onthe part parameters for each deducted process plan.

Fig. 12 General structure of theapplication

Fig. 13 Configuration tab

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4.3 User interfaces

The organization of the process plan schemas is realizedwith libraries called Referentials. The analysis of a part ismade based on referential models selected by the user.

In order to clarify the structure of the application andto facilitate the saving of the data, a class calledEnvironment has been created (Fig. 12). This class hasreferences to the different classes that compose our

Fig. 14 Knowledge tab

Fig. 15 Case studies tab

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application to specify parameters, manufacturing process-es, schemas, and parts to be analyzed.

Before the effective use of the application, the user mustconfigure before the first time:– The context: specifies the description parameters of a

part, the manufacturing processes that may be used.

– The expert knowledge: creates the process plan schemathat could be used.

– These two first steps are essential and made oncebefore any analysis, but the context and the knowledgemight be completed later.

– Then, for an intuitive use, the interface is composed ofthree tabs:

Fig. 16 Process plan schemefor hot forging

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– the configuration tab (for the context specification),– the knowledge tab (for editing the expert knowledge),– the case studies tab (for the edition and analysis of the parts).

The configuration tab is presented on Fig. 13. The inter-face for the specification of part parameters permits togive a name and a description, to choose the type, and todefine the possible values of the parameter. Manufacturingprocesses can also be created. For the moment, only thename of the process can be filled in but other metadatacould be added in the next versions of this application.

The knowledge tab (Fig. 14) allows creating differentreferential models and schemas contained in these referen-tial models. A schema can be browsed and modified, thanksto the tree viewer and the different buttons besides. Byselecting a transformation on the schema, the associatedconditions can be viewed or modified on the conditionseditor on the right.

Finally, the case studies tab (Fig. 15) is split into twoparts: the definition of the parts (above) and the analysis of apart (below). For a change in the part, the user is not requiredto define all the possible parameters for a part: parametersthat are not filled in will not be considered in the reasoning.

For the analysis of a part, the user must select:

– the part to be analyzed,– the referential models to be considered during the analysis,– the types of conditions to be considered during the analysis.

The results are displayed with a color code: each analyzedschema can be shown in the tree viewer with the eliminatedtransformations highlighted in red and the recommendedtransformations highlighted in blue. Transformations withnonevaluated conditions are not highlighted.

The user can choose to impose, keep, or suppresstransformations with the three buttons on the right of theschema viewer. If the number of the deducible processplans is less than 20, the user can launch the deduction ofthe process plans displayed on the right.

By selecting a process plan in the list of deductedprocess plans, the sequence of this process plan is shownand the necessary condition (to apply this process plan) canbe viewed on the conditions viewer.

4.4 Case study

Some interviews have been conducted with forging experts ofthe French Industrial andMechanical Technical Centre in orderto build a consistent process plan schema shown on Fig. 16.

For this case study, we have taken into account sevenparameters which are as follows:

1. morphological class,2. section variations number,3. boring presence,

4. bending presence,5. revolution presence,6. quality level,7. batch size.

Twenty-three manufacturing processes are used in thisschema; however, two remarks can be observed during thedevelopment of this schema:

1. A manufacturing process called “empty process” mustbe created in order to express the optional steps (usingor not using the optional manufacturing process).

2. A set of conditions associated to the manufacturingprocess permit to integrate experts’ knowledge, whichcontains the conditions related to limitation of theprocess and the conditions related to uselessness of theprocess.

The schema is composed of 50 transformations: threesequences, 14 choices, and 33 elementary processes. Thereare 21 conditions which are associated to 16 transforma-tions. The analysis of the schema without considering theconstraint permits to deduce 7,680 process plans.

In order to test this schema and the application, thefollowing plan is carried out: starting from a part definition,the user deducts the parameters considered in this schema.Application deduces the consequences on the process plan(eliminated or recommended transformations). The userfurther applies constraints on the process plan (he imposesor suppresses some transformations), and finally, someprocess plans are deducted with necessary conditions onsome part parameters. The part for the example is aconnecting rod, as it can be seen on Fig. 17.

The plan permits to deduct the following morphologicalcharacteristics:

– morphological class no. 315 (ASM handbook classifi-cation available at [31]),

– section variations number=2,– boring presence=true,– bending presence=false,– revolution presence=false,– quality level=E (norm EN 10243-1: 1999).

Fig. 17 Connecting rod

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Moreover, in this case study, the client needs a quantity of30,000 parts per year. Using these information, and con-sidering all associated conditions to the manufacturingprocesses, the number of deducible process plans becomes80 due to the fact that four transformations have beendirectly eliminated and four others have been recommended.

The user then imposes an upset operation, a controlledcooling, and a shot-blasting operation and he suppresses thegalvanization operation. In consequence, the number ofresting process plans becomes eight.

The upset operation should be eliminated due to theparameter section variations number that is too high. Thisnecessary condition is indicated for each process plandeduced where this operation appears.

The schema used in this study is created based on theelementary information collected. More details in theproduct and process definition must be considered to createthe complete process schema and associated conditions tothis schema. However, the functionality of the applicationcorresponds to the following specifications:

– the possibility to show the constraints on the processschema, owning to part parameters and the deductionof the possible process plans;

– the possibility to show the requirements on the partparameters, considering the constraints imposed by theuser on the process schema.

5 Conclusion and perspectives

The proposed methods provide the functionalities to definethe referential process schema in an industry. Expert’sknowledge integration during process schema definition isthe most suitable process.

Some disadvantages can be emphasized on the approach:

– The formalism is not really easy to understand on thefirst view: the proposed methods must be well-understood in order to create the right schemas. Forinstance, the writing of the elimination condition is notobvious: the user has to keep in mind that the trans-formation will be eliminated when the condition isevaluated at true (and not at false).

– The user-friendliness of the interfaces has to be improvedto make the use of the application easier. For instance, theconfiguration of the usable parameters, the manufacturingprocesses, and the schemas must be reserved for experts.Only the case studies tab has to be used during part designand its associated process plan.

The direction “choice of manufacturing processes” issupported by the tool with the display of the consequences

on the schemas: eliminated or recommended transforma-tions. Moreover, possible process plans can be deducted ifthey are not exhaustive.

The direction “design for manufacture” is supported bythe application, thanks to the possibility to imposeconstraints on the process plan schema (suppressed orimposed transformations). These constraints are reflectedon the part parameters as necessary conditions whenpossible process plans are deducted. The necessary con-ditions displays:– parameters that are not in compliance with constraints

imposed on the process plan,– parameters that are not filled in and have to respect

some constraints imposed on the process plan.

Several evolutions concerning the presentation and thefunctionalities are conceivable. We cite here some mainenhancements coming from the experimentations withsome users:

– Permit the definition of default conditions applied for amanufacturing process: some manufacturing processeswill be independent from the context in which theywould be used. For instance: the shearing or sawingprocesses. Conditions defined on the transformationsthat use these processes are a priori invariant from oneschema to another. A default condition could then beinteresting: when the manufacturing process is used inan elementary transformation, the default conditionwould be directly applied on this transformation. Theedition of the condition would be always possible but itcould let the creation of a schema be faster.

– Permit a consistency checkout of a schema: in order tohelp the user in the definition of a correct schema, acheckout would be interesting to correct some mistakessuch as defining some conflicting conditions or definingseveral times the same transformation after a choicetransformation, which corresponds to nothing.

– Use of indicators: the idea is to realize a ranking of thededucted process plans according to indicators. Thisranking will be based on one or several indicators thatthe user could choose. Indicators could be mechanical(e.g., security factor) or economical.

– The development of another tab has been planned: theresources tab in order to complete the integration withresources. The user could create one or several work-shops that could have one or more machines. Whilereasoning on the process plan schema or deducting theprocess plans, it would be possible to select not onlythe referential models and the types of conditions butalso the workshops that would be considered. Areflection has to be lead so as to define the link thatmay be established between resources, manufacturingprocesses, parts, and process plans.

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All these evolutions will be examined in a next versionof the application. A first phase of test is planned with someforging companies in order to detect other possible needsand to build a first feedback.

Acknowledgments We would like to particularly thank MM. PierreRavassard, Patrick Marchand, and Pierre Krumpipe from the FrenchIndustrial and Mechanical Technical Centre (http://www.cetim.fr) fortheir active collaboration in this project.

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