- Email: [email protected]
Process Planning: From Automation to Integration
Copyright CO IFAC Information Control in Manufacturing, Nancy - Metz, France, 1998
PROCESS PLANNING: FROM AUTOMATION TO INTEGRATION Daniel BRISSAUD (1), Patrick MARTIN (2)
(1) Laboratoire Sols Solides Structures, BP 53 38041 GRENOBLE cedex 9, France, E-mail: [email protected] (2) ENSAM- 4 rue Augustin Fresnel 57078 METZ cedex 3 [email protected] At the head of the GAMA group
Abstract : Process planning has been studied since years. Many systems are in laboratories and some in the market. They assist the process planner in his activity. Nowadays, the challenge is the integration of process planning in the product design. This communication deals with the evolution of the process planning problem and the questions to challenge. The automation of process planning has integrated the feature recognition before becoming an assistance of process planners and then of designers. Copyright ©1998IFAC
Key words: manufacturing process, concurrent engineering, integration.
imposes the process planner's activity and tools to be revised. The integration of product design and process planning consists in ensuring that a part has the intrinsic possibility of being manufactured.
1. INTRODUCTION
The problem of process planning has advanced through the changes of the manufacturing concepts. Classically about twenty years ago, process planning is reduced toward the production tasks and must prepare the elements for a production of quality without incidents. It was a problem of planning and one tried to solve it with automatic systems, particularly expert systems. For a use by less experienced engineers, it was necessary to include the definition of machining features into the process planning system. It was the age of feature recognition which did not change the problem of planning. The big change is due to the emergence of the concurrent engineering which requires the process planner's role to be thought. The duty of cooperation between the actors of the product life cycle
Here is the challenge of nowadays for the process planning research area. In France, the GAMA group gathers the research laboratories in process planning domain. They worked first on automatic process planning and proposed many systems as PROPEL, LURPA-TOUR, Generation Ascendante de Processus, OMEGA, Generation Ascendante de Gamme d'Usinage (GAMA, 1990). The group is now also working on the integration problem. This paper shows the evolution of the process planning problem and the skills and abilities of process planners to challenge the integration problem.
271
system based on knowledge base (Brissaud 1992).
2. AUTOMATIC PROCESS PLANNING
3. FEATURE RECOGNITION
Elaborating a process plan for a part under consideration consists in proposing an ordered set of actions to be performed in order to transform a roughed part to a finished part. The process plan is suggested from the finished part definition, the technology for the initial part to be obtained (it allows to have an approximate representation of the roughed part), the production context and the production capabilities which are considered used (Fig. 1). An action can be performed only if the resources necessary for its complete success are defined and available.
The main drawback of the automatic process planning quickly appeared: the part description which needs machining features is an expert work. This cannot be accepted a priori for two reasons. Needing an expert person into the automatic system does not cross the mind and integrating process planning into a CAD-CAM environment comes up against the required abilities for its use. The process planning problem advanced from giving a solution to the planning problem to automatically obtaining the machining features (Fig. 2) .
It is the matter of a planning problem which can be classically expressed: what is the sequence of actions which allows the initial state of the part (the roughed part) to be transformed in the expected state of the part (the finished part) ? It is a non linear planning problem, the subgoals which can be considered are dependent on themselves. This first problem is coupled with a problem of allocation and sharing out of resources. An action becomes effective when a cutting tool, a fixture and a machine-tool belonging to the capable and available resources are allotted to it. The difficulty lies in the fact that the capability of the resource to achieve the required quality for the action to be performed is difficult to evaluate and that the economic objective imposes the maximum use of each resource. As this problem is a planning problem. it is normal to search an automatic process planning system. Numerous ways have been tested and it is not the matter to be exhaustive here: let you see (EIMaraghy, 1993; Leung, 1996) for a complete review on process planning and (Case and Gao, 1993; Lenau and Mu, 1993; Salomons, et al., 1993) for a complete review on features. Different classifications have been proposed for process planning resolution techniques: let us notice variant vs. generative systems, process plan architecture vs. set-up planning, A.1. techniques vs. algorithm. Let you see for a representative system the PROPEL expert system which is interested by the elaboration of the process plan architecture with a generative
3.1 Formfeature recognition.
The part is defined by geometrical and topological elements which are classically (CSG or Brep for instance) in a CAD database. It is a question of building the machining features from the CAD database contents. This approach can charm because it assures that the works of the product engineer and the process planner are independent The translation between the two trades becomes evident: no expert is needed, only a geometrical analysis can perform the translation. The numerous works on this area lead us to think that this approach has globally failed (Cugini, et al. 1992; De Martino, et al. , 1996; Gardan and Minich, 1990). Although very numerous algorithms solve locally recognition problems (essentially with Brep representation), no solution appears to recognise all the features of the part what the type is and what the representation is. The machining feature used in process planning is semantically very rich and carries the know-how of the trade. Characterising a machining feature only by a geometrical and topological signature seems deny the trade culture. For instance, why recognising two co-axial cylinders when the engineer has thought a counterbored hole and the process planner knows how machine it.
trade knowledge
~~~~rt~~:;!rl:~:.::"~~"
machining features capabilities ",
; ~,-. j: ;: : ~'~;::~H*~ ;~;
' ::"
Process planning system
Fig.1: An automatic process planning system
272
trade knowledge part . design features capabilities
Machining feature recognition system
Process planning system
"
l
process plan
Fig. 2: Process planning and feature recognition.
two kinds of data are needed (Fig.3). First, many information on the part must be available: a classically CAD model (surfacic and volumetric models) which can be defined in the designing view, a model for process planner (machining features) which is defined in a machining view, a model for forgers or casters which is defined in their own view and gives the representation of the roughed part, the functions of the part which are defined in a specific view (the functional one) or eventually in the designing view. All this information is complementary and necessary for the building of flXturing features. The building can be effective because at each step of the recognition the know-how of a process planner helps the system. Knowledge on points of part location, types of location, techniques and technologies for clamping, characterisation of a good fixturing (here in the form of indicators on sliding, revolving, clamping force, assured quality, best use of capabilities) is captured and encapsulated into the system or brought by the process planner.
3.2 Design by features.
This approach comes from a simple idea. The process planner must handle machining features . If the engineer handles too features - and why not features close to machining features - the recognition, therefore the mapping from engineer to process planner no longer remains a problem. The first sense of this principle fails. The features that the engineer naturally handles are far from the machining features; he cannot handle machining features because his nature and skills are not here [Midler 91 J. Those works have therefore be interesting because they have contributed to stabilise the parametric and variational geometry concepts. The new sense of design by feature is more attractive because each trade is accepted; the engineer works with designing features and the process planner with machining features. The difficulty comes from the fact that it is necessary to have a mapping between the different kinds of features. The research questions deal with the characterisation of designing features and the mechanisms which will allow the mapping. Shah et al. (1994) proposes to slit up , then make up, features with a set of elementary volumes and an adapted algebra. The force of this proposition consists in postulating a neutral format. The limit comes from the fact that Shah reduces the design problem to the handling of nominal geometry form.
4. INTEGRATION OF PRODUCT MODELLING AND PROCESS PLANNING The context of concurrent engineering imposes that the process planner is one of the actors which participate to the product definition. The process planner, as the product engineer does for his own objective, gives the constraints due to the machining process of the part. the problem of process planning becomes a problem of designing for process planning and can be asked like that (Fig. 4). Is the part under design machinable ? If not, what are the obstacles which prevent the part from machining ? If yes, can part improvements be proposed for a less expensive solution ? The most important change with this new process planning problem is the fact that process planning activity becomes an activity with a creation of part geometry. Or classically process planning begins with the complete geometrical definition of the part.
33. Trade-orientedfeature recognition.
Now it seems that the system of feature determination must be a mixed system: a recognition of trade-oriented features. It groups the advantages of the two systems: a recognition of the features extracted from the engineer data (the interest is the generality of a such system) and features oriented by the trade under consideration (the efficiency comes from the direct management of trade data). Let us take for example the recognition of fixturing features in a process planning approach (paris 1996). For this extraction,
273
BEGINNING Recognition of the geometrical elements and their technological functions
.:~, ~
..
Fig. 3: Algorithm for building the fixturing features in a CAD environment capabilities !1
trade . knowledge ~;' ,...-----'-------'--, part with supplementary partial definition elements of definition of the part Process ::S'!:!z:!!tt!!:':-::!:~ !~~;;;J. planning process plan system :jji'
~~~t::!!f!:::~i:'~:~l:::~: ~~;~
~----------------~
Fig. 4: Process planning in design activity
4.1 New concepts must be developed.
The machinability of a design feature is defined by the capacity of this feature to be machined. A design feature is machinable if a set of machining features can be created from the design feature under study and at least one capable machining process can perform that set of machining features. A design feature is not machinable if no machining feature or no capable machining process exist
There are in fact two complementary problems. An analysis problem: is the designed part machinable ? The design problem is complete seeing that the part has been already designed and all the parameters are therefore defined. The question is reduced to modifying the value of parameters. It is a verifying problem, classical approach even if the nature of knowledge engaged in this check is not classical here. An synthesis problem: is the part under design machinable ? Here the design problem is not complete seeing that the work is not finished and all the parameters are not defined. The question is, from an analysis of a partial problem, proposing trade knowledge to participate to the definition of the missing or incomplete parameters. This knowledge is generally brought in terms of constraints due to the manufacturing process on the design choices.
An indicator of machinability concept is proposed as a place where the co-operation between the engineer and the process planner can be developed. An indicator asks it about the current design model and its role is to propose actions onto this current design model in order to improve and complete it The body of the indicator is made up by a system of measure which captures information on design parameters and a system of interpretation which transform the design information into an action onto the design parameters through a machining reasoning (Fig. 5). The measure and the interpretation is not neutral but depends on the manufacturing objective: process planning, verifying the designed product, assisting the designing for choosing for instance.
4.2. Indicators as a co-operation between engineers and process planners.
274
Objective t---~-------t
t---'''----i
action proposals
Measure Interpretation
Fig. 5: the model of an indicator of machinability. There are a lot of difficulties for the implementation of an indicator and many questions have to be answered before having efficient indicators. About capture: what is the mapping from design parameters to machining features? Nowadays it is only succeed for obvious cases. When must this mapping be done? It is a strategic question. All the time during the design process? At key moments? At the designer's request for an information ? Being the answer, the mechanism of capture is not the same. About interpretation: the body is of course the process planner's know-how. But it needs a representation of designer's activity and the freedom which can be allowed onto the design parameters. About the action proposals, the opposite mapping from machining parameters to design parameters is still a problem and it is necessary to know what are the possible actions onto a current design model.
complexity of the problem. The subtasks are very dependent. • The production and economic contexts are advanced and the typology of the process planning problems is increased needing new optimisation techniques. • The use of emerging A.I. techniques is necessary: expert systems, constraints propagation, neural networks, genetic algorithms, fuzzy logic are complementary techniques which have proved their efficiency in local tasks in process planning. For the integration problem in a concurrent engineering context, it is only the beginning. The indicators are only one way and their most important interest is the fact that they can be activated all along the design process, in particular when the part is not entirely defined. More the concept of machnining feature can be use also for designing the manufaturing system itself (Garro, 1992, Jacobe, 1992). It is not the place here to make an exhaustive list of the possible research developments in this field but only notice that the stake is important and the process planners have skills and abilities to challenge it.
Some indicators of machinability have been developed. The fixturing indicator assures that the fixturing of the part during machining can be realised with the required quality, particularly about displacements of the part under forces or clamping possibilities (Brissaud 1997a). The cost indicator is of course an important information; it is completed by a machining direction indicator which analyses the machining directions needed for machine the part and proposes improvements of the part in modifying the feature direction when it is possible (Brissaud 1997b). We are also developing a burr indicator in order to foresee the burrs and pilot them, and more classical indicators on the form which can be obtained and the quality which can be achieved.
REFERENCES
Brissaud D. (1992). Systeme de conception automatique de gamme d'usinage pour les industries manufacturieres, These de Doctorat, Universite Joseph Founa, Grenoble . Brissaud D., Paris H., Tichkiewitch S. (1997a), Assisting designers in the forecasting of surfaces used for easier fixturing in a machining process, International journal of materials processing technology, VoL65, nOl-3, pp 26-33, 1997. Brissaud D. (1997b), Integration des savoir-faire du gammiste dans des outils d'aide a la conception de produits. Universite d'ete, Bucarest, 1997 Case K., Gao J. (1993), Feature technology : an overview, Int. Journal of Computer Integrated
5. PERSPECTIVES Process planning has been largely studied now and strong concepts have emerged. Nevertheless the production context advances and new problems must be integrated into process planning. Six results or research ways can be put forward. • Solid modelling has long been considered as the CAD model for CAPP systems but the evidence is that feature models are stronger for process planning. • The concept of variant process planning is revitalised by the argument that its strength can be combined with the generative concept. • The concept of decomposing process planning into subtasks is no longer so obvious because the
Manufacturing, Vo1.6 nOl&2. Cugini U., Mandorli F., Vicini I. (1992), Form feature recognition as a technique for CAD / CAM integration, proceedings of MICAD 92, Paris. ElMaraghy H.A. (1993), Evolution and future
275
perspectives of CAPP, An1UlIs of the CIRP, Vol.4212. GAMA (1990) La gamme automatique, Hermes, Paris Gardan Y. , Minich C. (1990), La modelisation geometrique et l'extraction de caracteristiques de forme, La gamme automatique, pp. 19-38, Hermes, Paris Garro O. (1992), Conception d'tHements physiq ues de systemes de production. Application aux machines-outils a architecture parallele, these de l'Universite de Nancy 1, 18-0592. Jacobe P. (1992) Generation ascend ante de gamme d'usinage, these de I'Universite de Franche Cornte, 16-12-92 Lenau T., Mu I. (1993), Features in integra ted modell ing of produc ts and their produc tion, Int.
Journal of Computer Integrated Manufacturing,
vol.6 n01&2. Leung H.C. (1996), Annota ted bibliography on compu ter-aid ed process planning, Int. Journal of Advanced Manufacturing Technology, Vol.12. De Martino T., Falcidieno B., Giannini F. (1996), Feature-based modeli ng as a solutio n for concur rent engine ering design, Rensselaer's fifth internatio1UlI conference CIMA T, Grenoble, may 1996. Midler C. (1991), L'apprentissage de la gestion par projet dans l'indus trie automobile, An1Ulles des Mines, sme Realites Industrielles, octobre 1991. Paris H., Brissaud D. (1996), Une vue usinag e d'un produi t dans un environnement CFAO,
revue internatio1Ulle de CFAO et d'infographie,
Vol.ll n06. Salomons O.W., Van Houten F.J.A.M., Kals H.J.J. (1993), Review of research in featurebased design, Journal of Manufacturing Systems, vol.12 n02. Shah J.J;, Shen Y., Shirur A. (1994), Determ ination of machin ing volum es from extensible sets of design features in Advanced in feature based manufacturing, Shah, Mantyla, Nau editors, Elsevier.
276
PROCESS PLANNING: FROM AUTOMATION TO INTEGRATION Daniel BRISSAUD (1), Patrick MARTIN (2)
(1) Laboratoire Sols Solides Structures, BP 53 38041 GRENOBLE cedex 9, France, E-mail: [email protected] (2) ENSAM- 4 rue Augustin Fresnel 57078 METZ cedex 3 [email protected] At the head of the GAMA group
Abstract : Process planning has been studied since years. Many systems are in laboratories and some in the market. They assist the process planner in his activity. Nowadays, the challenge is the integration of process planning in the product design. This communication deals with the evolution of the process planning problem and the questions to challenge. The automation of process planning has integrated the feature recognition before becoming an assistance of process planners and then of designers. Copyright ©1998IFAC
Key words: manufacturing process, concurrent engineering, integration.
imposes the process planner's activity and tools to be revised. The integration of product design and process planning consists in ensuring that a part has the intrinsic possibility of being manufactured.
1. INTRODUCTION
The problem of process planning has advanced through the changes of the manufacturing concepts. Classically about twenty years ago, process planning is reduced toward the production tasks and must prepare the elements for a production of quality without incidents. It was a problem of planning and one tried to solve it with automatic systems, particularly expert systems. For a use by less experienced engineers, it was necessary to include the definition of machining features into the process planning system. It was the age of feature recognition which did not change the problem of planning. The big change is due to the emergence of the concurrent engineering which requires the process planner's role to be thought. The duty of cooperation between the actors of the product life cycle
Here is the challenge of nowadays for the process planning research area. In France, the GAMA group gathers the research laboratories in process planning domain. They worked first on automatic process planning and proposed many systems as PROPEL, LURPA-TOUR, Generation Ascendante de Processus, OMEGA, Generation Ascendante de Gamme d'Usinage (GAMA, 1990). The group is now also working on the integration problem. This paper shows the evolution of the process planning problem and the skills and abilities of process planners to challenge the integration problem.
271
system based on knowledge base (Brissaud 1992).
2. AUTOMATIC PROCESS PLANNING
3. FEATURE RECOGNITION
Elaborating a process plan for a part under consideration consists in proposing an ordered set of actions to be performed in order to transform a roughed part to a finished part. The process plan is suggested from the finished part definition, the technology for the initial part to be obtained (it allows to have an approximate representation of the roughed part), the production context and the production capabilities which are considered used (Fig. 1). An action can be performed only if the resources necessary for its complete success are defined and available.
The main drawback of the automatic process planning quickly appeared: the part description which needs machining features is an expert work. This cannot be accepted a priori for two reasons. Needing an expert person into the automatic system does not cross the mind and integrating process planning into a CAD-CAM environment comes up against the required abilities for its use. The process planning problem advanced from giving a solution to the planning problem to automatically obtaining the machining features (Fig. 2) .
It is the matter of a planning problem which can be classically expressed: what is the sequence of actions which allows the initial state of the part (the roughed part) to be transformed in the expected state of the part (the finished part) ? It is a non linear planning problem, the subgoals which can be considered are dependent on themselves. This first problem is coupled with a problem of allocation and sharing out of resources. An action becomes effective when a cutting tool, a fixture and a machine-tool belonging to the capable and available resources are allotted to it. The difficulty lies in the fact that the capability of the resource to achieve the required quality for the action to be performed is difficult to evaluate and that the economic objective imposes the maximum use of each resource. As this problem is a planning problem. it is normal to search an automatic process planning system. Numerous ways have been tested and it is not the matter to be exhaustive here: let you see (EIMaraghy, 1993; Leung, 1996) for a complete review on process planning and (Case and Gao, 1993; Lenau and Mu, 1993; Salomons, et al., 1993) for a complete review on features. Different classifications have been proposed for process planning resolution techniques: let us notice variant vs. generative systems, process plan architecture vs. set-up planning, A.1. techniques vs. algorithm. Let you see for a representative system the PROPEL expert system which is interested by the elaboration of the process plan architecture with a generative
3.1 Formfeature recognition.
The part is defined by geometrical and topological elements which are classically (CSG or Brep for instance) in a CAD database. It is a question of building the machining features from the CAD database contents. This approach can charm because it assures that the works of the product engineer and the process planner are independent The translation between the two trades becomes evident: no expert is needed, only a geometrical analysis can perform the translation. The numerous works on this area lead us to think that this approach has globally failed (Cugini, et al. 1992; De Martino, et al. , 1996; Gardan and Minich, 1990). Although very numerous algorithms solve locally recognition problems (essentially with Brep representation), no solution appears to recognise all the features of the part what the type is and what the representation is. The machining feature used in process planning is semantically very rich and carries the know-how of the trade. Characterising a machining feature only by a geometrical and topological signature seems deny the trade culture. For instance, why recognising two co-axial cylinders when the engineer has thought a counterbored hole and the process planner knows how machine it.
trade knowledge
~~~~rt~~:;!rl:~:.::"~~"
machining features capabilities ",
; ~,-. j: ;: : ~'~;::~H*~ ;~;
' ::"
Process planning system
Fig.1: An automatic process planning system
272
trade knowledge part . design features capabilities
Machining feature recognition system
Process planning system
"
l
process plan
Fig. 2: Process planning and feature recognition.
two kinds of data are needed (Fig.3). First, many information on the part must be available: a classically CAD model (surfacic and volumetric models) which can be defined in the designing view, a model for process planner (machining features) which is defined in a machining view, a model for forgers or casters which is defined in their own view and gives the representation of the roughed part, the functions of the part which are defined in a specific view (the functional one) or eventually in the designing view. All this information is complementary and necessary for the building of flXturing features. The building can be effective because at each step of the recognition the know-how of a process planner helps the system. Knowledge on points of part location, types of location, techniques and technologies for clamping, characterisation of a good fixturing (here in the form of indicators on sliding, revolving, clamping force, assured quality, best use of capabilities) is captured and encapsulated into the system or brought by the process planner.
3.2 Design by features.
This approach comes from a simple idea. The process planner must handle machining features . If the engineer handles too features - and why not features close to machining features - the recognition, therefore the mapping from engineer to process planner no longer remains a problem. The first sense of this principle fails. The features that the engineer naturally handles are far from the machining features; he cannot handle machining features because his nature and skills are not here [Midler 91 J. Those works have therefore be interesting because they have contributed to stabilise the parametric and variational geometry concepts. The new sense of design by feature is more attractive because each trade is accepted; the engineer works with designing features and the process planner with machining features. The difficulty comes from the fact that it is necessary to have a mapping between the different kinds of features. The research questions deal with the characterisation of designing features and the mechanisms which will allow the mapping. Shah et al. (1994) proposes to slit up , then make up, features with a set of elementary volumes and an adapted algebra. The force of this proposition consists in postulating a neutral format. The limit comes from the fact that Shah reduces the design problem to the handling of nominal geometry form.
4. INTEGRATION OF PRODUCT MODELLING AND PROCESS PLANNING The context of concurrent engineering imposes that the process planner is one of the actors which participate to the product definition. The process planner, as the product engineer does for his own objective, gives the constraints due to the machining process of the part. the problem of process planning becomes a problem of designing for process planning and can be asked like that (Fig. 4). Is the part under design machinable ? If not, what are the obstacles which prevent the part from machining ? If yes, can part improvements be proposed for a less expensive solution ? The most important change with this new process planning problem is the fact that process planning activity becomes an activity with a creation of part geometry. Or classically process planning begins with the complete geometrical definition of the part.
33. Trade-orientedfeature recognition.
Now it seems that the system of feature determination must be a mixed system: a recognition of trade-oriented features. It groups the advantages of the two systems: a recognition of the features extracted from the engineer data (the interest is the generality of a such system) and features oriented by the trade under consideration (the efficiency comes from the direct management of trade data). Let us take for example the recognition of fixturing features in a process planning approach (paris 1996). For this extraction,
273
BEGINNING Recognition of the geometrical elements and their technological functions
.:~, ~
..
Fig. 3: Algorithm for building the fixturing features in a CAD environment capabilities !1
trade . knowledge ~;' ,...-----'-------'--, part with supplementary partial definition elements of definition of the part Process ::S'!:!z:!!tt!!:':-::!:~ !~~;;;J. planning process plan system :jji'
~~~t::!!f!:::~i:'~:~l:::~: ~~;~
~----------------~
Fig. 4: Process planning in design activity
4.1 New concepts must be developed.
The machinability of a design feature is defined by the capacity of this feature to be machined. A design feature is machinable if a set of machining features can be created from the design feature under study and at least one capable machining process can perform that set of machining features. A design feature is not machinable if no machining feature or no capable machining process exist
There are in fact two complementary problems. An analysis problem: is the designed part machinable ? The design problem is complete seeing that the part has been already designed and all the parameters are therefore defined. The question is reduced to modifying the value of parameters. It is a verifying problem, classical approach even if the nature of knowledge engaged in this check is not classical here. An synthesis problem: is the part under design machinable ? Here the design problem is not complete seeing that the work is not finished and all the parameters are not defined. The question is, from an analysis of a partial problem, proposing trade knowledge to participate to the definition of the missing or incomplete parameters. This knowledge is generally brought in terms of constraints due to the manufacturing process on the design choices.
An indicator of machinability concept is proposed as a place where the co-operation between the engineer and the process planner can be developed. An indicator asks it about the current design model and its role is to propose actions onto this current design model in order to improve and complete it The body of the indicator is made up by a system of measure which captures information on design parameters and a system of interpretation which transform the design information into an action onto the design parameters through a machining reasoning (Fig. 5). The measure and the interpretation is not neutral but depends on the manufacturing objective: process planning, verifying the designed product, assisting the designing for choosing for instance.
4.2. Indicators as a co-operation between engineers and process planners.
274
Objective t---~-------t
t---'''----i
action proposals
Measure Interpretation
Fig. 5: the model of an indicator of machinability. There are a lot of difficulties for the implementation of an indicator and many questions have to be answered before having efficient indicators. About capture: what is the mapping from design parameters to machining features? Nowadays it is only succeed for obvious cases. When must this mapping be done? It is a strategic question. All the time during the design process? At key moments? At the designer's request for an information ? Being the answer, the mechanism of capture is not the same. About interpretation: the body is of course the process planner's know-how. But it needs a representation of designer's activity and the freedom which can be allowed onto the design parameters. About the action proposals, the opposite mapping from machining parameters to design parameters is still a problem and it is necessary to know what are the possible actions onto a current design model.
complexity of the problem. The subtasks are very dependent. • The production and economic contexts are advanced and the typology of the process planning problems is increased needing new optimisation techniques. • The use of emerging A.I. techniques is necessary: expert systems, constraints propagation, neural networks, genetic algorithms, fuzzy logic are complementary techniques which have proved their efficiency in local tasks in process planning. For the integration problem in a concurrent engineering context, it is only the beginning. The indicators are only one way and their most important interest is the fact that they can be activated all along the design process, in particular when the part is not entirely defined. More the concept of machnining feature can be use also for designing the manufaturing system itself (Garro, 1992, Jacobe, 1992). It is not the place here to make an exhaustive list of the possible research developments in this field but only notice that the stake is important and the process planners have skills and abilities to challenge it.
Some indicators of machinability have been developed. The fixturing indicator assures that the fixturing of the part during machining can be realised with the required quality, particularly about displacements of the part under forces or clamping possibilities (Brissaud 1997a). The cost indicator is of course an important information; it is completed by a machining direction indicator which analyses the machining directions needed for machine the part and proposes improvements of the part in modifying the feature direction when it is possible (Brissaud 1997b). We are also developing a burr indicator in order to foresee the burrs and pilot them, and more classical indicators on the form which can be obtained and the quality which can be achieved.
REFERENCES
Brissaud D. (1992). Systeme de conception automatique de gamme d'usinage pour les industries manufacturieres, These de Doctorat, Universite Joseph Founa, Grenoble . Brissaud D., Paris H., Tichkiewitch S. (1997a), Assisting designers in the forecasting of surfaces used for easier fixturing in a machining process, International journal of materials processing technology, VoL65, nOl-3, pp 26-33, 1997. Brissaud D. (1997b), Integration des savoir-faire du gammiste dans des outils d'aide a la conception de produits. Universite d'ete, Bucarest, 1997 Case K., Gao J. (1993), Feature technology : an overview, Int. Journal of Computer Integrated
5. PERSPECTIVES Process planning has been largely studied now and strong concepts have emerged. Nevertheless the production context advances and new problems must be integrated into process planning. Six results or research ways can be put forward. • Solid modelling has long been considered as the CAD model for CAPP systems but the evidence is that feature models are stronger for process planning. • The concept of variant process planning is revitalised by the argument that its strength can be combined with the generative concept. • The concept of decomposing process planning into subtasks is no longer so obvious because the
Manufacturing, Vo1.6 nOl&2. Cugini U., Mandorli F., Vicini I. (1992), Form feature recognition as a technique for CAD / CAM integration, proceedings of MICAD 92, Paris. ElMaraghy H.A. (1993), Evolution and future
275
perspectives of CAPP, An1UlIs of the CIRP, Vol.4212. GAMA (1990) La gamme automatique, Hermes, Paris Gardan Y. , Minich C. (1990), La modelisation geometrique et l'extraction de caracteristiques de forme, La gamme automatique, pp. 19-38, Hermes, Paris Garro O. (1992), Conception d'tHements physiq ues de systemes de production. Application aux machines-outils a architecture parallele, these de l'Universite de Nancy 1, 18-0592. Jacobe P. (1992) Generation ascend ante de gamme d'usinage, these de I'Universite de Franche Cornte, 16-12-92 Lenau T., Mu I. (1993), Features in integra ted modell ing of produc ts and their produc tion, Int.
Journal of Computer Integrated Manufacturing,
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