- Email: [email protected]
Integration of Manufacturing Processes in Design
Integration of Manufacturing Processes in Design S. Tichkiewitchl (Z),M. Veron2 (1) Institute National Polytechnique. Grenoble, France * Universite de Nancy, Vandeuvre-les-Nancy, France Received on January 10,1998 1
Abstract Constraints concerning the manufacturing of product parts must be integrated as early as possible in the product design process, in order to reduce costs and time to market. For this, a part of manufacturing knowledge must be at the design team's disposal all through the design process. In order to facilitate the consideration of machining and forging capabilities by a group of designers, we have developed computer tools. This paper describes the linkage of these tools with our CAD system and the benefits of such integration in the form of shape and cost evaluation. Keywords : Design, Integration, Manufacturing
1. I n t r o d u c t i o n In order to be competitive in the global market, it is increasingly important to reduce costs and time to market of a new product. Industrial design and engineering design has to be performed in parallel, as shown by Kimura [3]. With the simultaneous involvement of the marketing agents, technologists, manufacturers, IT technologists, aesthetics, ergonomics, or people from maintenance or recycling, the use of a suitable data structure is required. This structure must allow everyone to use at the same time their own language, based on features, in order to be productive [4]. The design system must also allow dialogue between participants [6] in order to settle conflicts as soon as possible. The structure of such a system and the associated data model has been shown in [8]. In the following sections, the methodology of integrated design is reviewed. Manufacturability of a product is considered and the relationship between functional surfaces of a part and forging or machining processes are discussed. Computer
aided tools useful for such an approach are detailed. 2. The integrated desian context With integrated design context, each participant of the design process has access to a unique data base where the different decisions previously taken are stored in a form of the product model. In [8], we explain our multiview product model. A first system view contains the specifications of the desired system in terms of functionalities. These functionalities are given as relations which specify links. Each link is a particular way to address the component we are designing. The work of technologists i s to transform the total specifications in terms of structural parts, using for this a lot of physical principles. Doing this, the technologists create sub-components in order to describe how the initial system is conceived, until the lowest possible description of the system as a lot of parts is reached. Each part is decomposed in a frame view and a geometric view. The frame view is built with the skin features,
m COPEST Forgeable
I
I
simulation
Presto preform
I
Yes
Preform
Figure 1 : The complementary forging tools
Annals of the ClRP Vol. 47/7/7998
99
Figure 2 : Some stamped cross-sectionson 3D parts given by COPEST representations of the functional surfaces with allowance and roughness and, with the skeleton features, links between the skins in order to give the topology of the part. The geometric view is built with the corresponding theoretic surfaces and is the traditional support of CAD representation. The frame view and the geometric view are shared views. That is to say, that each actor is able to obtain their own representation of each part. We show in the next sections how the forging process engineer can use such information in order to propose a rough stamped part and how the machining process engineer can add his constraints in order to reduce the global cost of the part [5].
3. The foraina view The goal of the forging process engineer during the design process is to determine how the rough stamped part can be produced at the least expensive way considering the final global cost of the tooled part. In order to assist the forging process engineer, we have integrated the forging knowledge in a set of forging software tools. These tools are operational today for revolute parts, and presently are being extended to 3D parts. They successively transform the functional frame of the part into a forged section, verify the ability to stamp the proposed shape, generate the preforms if necessary, and finally evaluate the cost of the stamping operations (see Figure 1). As an interactive process, the forging process engineer can propose some modification to the frame data in order to reduce the cost of his rough part. COPEST is our software tool that transforms the topology and geometry of a part described in terms of their frame and geometric views in a forgeable shape. It adds specific stamping features such as allowances, edge fillets, draft angles, web and flash [l]. This design tool is mainly based on expertise and on specific deformation modes. Its specificity is to be able to connect the radii dimensions to the local pressure distribution. In 30, COPEST always transforms cross-sections, ensuring the coherence of the pressure distribution in the whole part. Results are shown in Figure 2. ForgeRond is a software which performs fast simulation of the forging deformation for an axisymmetrical part (71.The basic pressure model is an expertise model, but we have added new
100
models in order to take into account the evolution of the free form surfaces during stamping, with thermal and dynamic behaviour. This software is very important in the design context, as it gives the possibility to simulate the forgeability of a part without using finite element method. That has the advantage that it can be translated in a very short time. This is due to the integration of knowledge on the modes of deformation of a billet inside the dies and, with this integration, to a strong reduction of the degrees of freedom compared to a FEM problem. ForgeRond provides information such as shape evolution during the stamping process, the forging load and the energy consumption in only a few seconds. It also gives information on the filling of the dies. Most of the time, it is not possible to transform a cylindrical billet into the stamped part in only one blow, and the simulation with ForgeRond indicates where the dies are unfilled. In such a case, intermediate shapes are obtained with preforming dies, mainly in 3 consecutive blows : flattening, preforming and finishing. Our Presto software proposes to the user a preform in the case that unfilled areas are detected with ForgeRond. The main target of preform dies are to insure a good distribution of material in the finishing dies, so as to permit the filling of these dies without any defects, minimize the metal losses, with the smallest possible flash, and reduce the finishing die wear in order to increase its time life. Presto uses some rules elaborated by skilled designers, depending on the material used and the machine chosen. The simulation of the deformation for obtaining the preform may be done with ForgeRond and in some case can induced as it a preliminary forging step. One of the results of ForgeRond is the energy required to transform a shape into another one, with a forging press. Chamouard’s experiences allow us to determine an energy equivalence between presses and hammers, and so to determine parameters which make up the total forging cost, depending on the size of production run, the chosen machine and the dimensions of the initial billet. This cost estimate method has been established in ForgeRond software, and has to be increased in order to take into account administration overheads or firm margin.
Figure 3 : an integrated fixturing application : example of a plan primary locating region The output of these softwares are included in a forging view of the product model. The stamped part is considered as a specific component with cost, energy and number of strikes as links, and with its specific frame and geometric views. 4. The machinina view At this stage of the design process, the manufacturers have at their disposal the frame and geometric view of each initial part, and are also connected to the frame and geometric view of the corresponding stamped part. The rough and the finished part are known and the manufacturer has to validate these shapes. We think that it is possible at this stage of the design to use two different types of tools : integrated manufacturing tools in a CAD environment and tools adding manufacturing constraints to the design process.
4.1 Integrated manufacturing tools in a CAD environment While in such a case, we can use integrated manufacturing tools in order to indicate if a process plan is allowable for the part under study, with the given machining facilities. The PROPEL tool, an automatic machining process planner, has been built in our laboratory to support this goal. Most of the time, the process plan allows the calculation of machining costs and consequently a cost estimate. With the forging cost, we obtain a global manufacturing cost of the part. In order to run PROPEL, a first application determines the part machining fixturing, which involves both locating and clamping [2].This has been developed within a commercial CAD environment. Choosing a machining fixture depends on the machining direction, which must necessarily be accessible, on the behaviour of the part during machining, which has to be respect, and on the accuracy of the machining operation that the design requires. The first entry of this application is the geometric model of the part. Then, we ask the process
planning expert to transfer geometric features to machining features, and to give the relationships between them. The system needs no supplementary particular handling when compared to classical CAD systems. For the language, standard notions for a mechanical specialist were chosen and the geometry of the part, its stability during machining process, the transmitted forces and the accuracy achieved, are used in natural language. The result of the module is a set of possible appropriate machining fixtures of the part. This set can be visualized in the CAD environment. The module also shows the links with the machining fixtures. The expert has six properties available that can be analysed to advance the work. These six properties are : (1) visualization of the possible locating regions (see Figure 3); (2) visualization of the possible clamping regions, dependent on the locating region (see Figure 4); (3) visualization of accessible machining features, dependent on the locating and clamping regions (see Figure 5); (4) intensity of the global clamping force necessary for the part to be stable, dependent on the locating region, clamping region and machining operation: (5) part stability factor, dependent on the locating region, clamping region and machining operation; (6) value of the required accuracy levels for the locating region, dependent on the specified relationship and the machining operation. With this last result, and a set of machining facilities, PROPEL is able to run and to propose a set of process plans and the associated cost. PROPEL is an expert system written in Le Lisp. 4.2 Developing a tool which adds machining constraints to the design process Using the part machining fixturing application, the most important piece of information for the design team is perhaps the absence of an adapted fixturing for the current part, or that the quality 101
expert has machining tools to validate these rough parts, to verify that he can obtain the expected quality, and to give the corresponding process plan and associated cost of machining. Integration of manufacturing processes during the design process avoids the cost of the late backtracking and increases the overall quality of the design.
n Figure 4 : Example of clamping regions opposite to the primary locating region of the possible fixturing is insufficient. The sooner this problem is detected the sooner solutions are proposed. This avoids expensive backtracking that is inevitable when this problem is detected late in the manufacturing process. It is better to adapt as soon as possible suitable measures and to create specific features if necessary. The quality of the fixturing is directly linked to the quality of the machining operation and, as a result, to the quality of the part. If the cost is too high because the fixturing conditions are too restrictive, the design team can impose new features without any functionality from the usage point of view, to solve the fixturing quality problem. With the machining fixturing application, the designer can visualize the geometrical behaviour in a 3D space, and have the following advantages : (1) the possible machining directions are known and he can try to correctly locate the other features to machine. In this way, the designer can locate features in a consistent way, taking into account clamping constraints, in order to decrease the numbers of set-ups, if possible; (2) the available design space is assessed. Notably, for prismatic parts with strap-type clamping, physical clamping clutters up the work space enormously and imposes substantial constraints on the access to machining features; (3) a feature without potential locating region can be spotted and the design can be review. 5. Conclusion In this paper, we show how it is possible to add to our Computer-Aided-Integrated-Design modeller some additional tools relative to the manufacturing processes. The forging process engineer can use forging tools in order to give to the best rough parts he can forge relative to the desired finished parts of a system, and the costs of the stamping operations, as soon as the frame and the geometric views of the parts are known. The process planning
102
u
/ I
Figure 5 : Example of double-strap clamping and paths of the cutting tools. 5. References (1) Boujut, J.F., Tichkiewitch, S., 1995, COPEST : a co-ordination tool in the design process of stamped part, Proc. of Advances in Materials and Processing Technologies, Dublin, 8-12 Aug., 857866 (2) Brissaud, D., Paris, H., Tichkiewitch, S., 1997, Assisting designers in the forecasting of surfaces used for easier fixturing in a machining process, Journ. of Materials Processing Technology,, 65 : 26-33 (3) Kimura, F., 1997, Issues in Styling and Engineering Design, Annals of the CIRP, 4612 (4) Krause, F.L., Kimura, F., Kjellberg, T., Lu, S.C-Y., 1993, Product Modelling : a keynote paper, Annals of the CIRP, 4212: 695-706 (5) Liebers, A., Kals, H.J.J., 1997, Cost decision support in product design, Annals of the CIRP, 46/1: 107-1 12 (6) Lu, S.C.-Y., Li, D., Cheng, J., Wu, C.L., 1997, A model fusion approach to support negotiations during complex engineering system design, Annals of the CIRP, 4611: 89-92 ( 7 ) Tichkiewitch, S., Boujut, J.F., Marin, Ph., 1993, Toward a fast simulation system of stamping deformation, Proc. of 14rh Int. Forging Cong., Venise, 27-29 Sept., 53-64 (8) Tichkiewitch, S., Veron, M., 1997, Methodology and Product Model for Integrated Design Using a Multiview System, Annals of the CIRP, 4611 :81-84
Abstract Constraints concerning the manufacturing of product parts must be integrated as early as possible in the product design process, in order to reduce costs and time to market. For this, a part of manufacturing knowledge must be at the design team's disposal all through the design process. In order to facilitate the consideration of machining and forging capabilities by a group of designers, we have developed computer tools. This paper describes the linkage of these tools with our CAD system and the benefits of such integration in the form of shape and cost evaluation. Keywords : Design, Integration, Manufacturing
1. I n t r o d u c t i o n In order to be competitive in the global market, it is increasingly important to reduce costs and time to market of a new product. Industrial design and engineering design has to be performed in parallel, as shown by Kimura [3]. With the simultaneous involvement of the marketing agents, technologists, manufacturers, IT technologists, aesthetics, ergonomics, or people from maintenance or recycling, the use of a suitable data structure is required. This structure must allow everyone to use at the same time their own language, based on features, in order to be productive [4]. The design system must also allow dialogue between participants [6] in order to settle conflicts as soon as possible. The structure of such a system and the associated data model has been shown in [8]. In the following sections, the methodology of integrated design is reviewed. Manufacturability of a product is considered and the relationship between functional surfaces of a part and forging or machining processes are discussed. Computer
aided tools useful for such an approach are detailed. 2. The integrated desian context With integrated design context, each participant of the design process has access to a unique data base where the different decisions previously taken are stored in a form of the product model. In [8], we explain our multiview product model. A first system view contains the specifications of the desired system in terms of functionalities. These functionalities are given as relations which specify links. Each link is a particular way to address the component we are designing. The work of technologists i s to transform the total specifications in terms of structural parts, using for this a lot of physical principles. Doing this, the technologists create sub-components in order to describe how the initial system is conceived, until the lowest possible description of the system as a lot of parts is reached. Each part is decomposed in a frame view and a geometric view. The frame view is built with the skin features,
m COPEST Forgeable
I
I
simulation
Presto preform
I
Yes
Preform
Figure 1 : The complementary forging tools
Annals of the ClRP Vol. 47/7/7998
99
Figure 2 : Some stamped cross-sectionson 3D parts given by COPEST representations of the functional surfaces with allowance and roughness and, with the skeleton features, links between the skins in order to give the topology of the part. The geometric view is built with the corresponding theoretic surfaces and is the traditional support of CAD representation. The frame view and the geometric view are shared views. That is to say, that each actor is able to obtain their own representation of each part. We show in the next sections how the forging process engineer can use such information in order to propose a rough stamped part and how the machining process engineer can add his constraints in order to reduce the global cost of the part [5].
3. The foraina view The goal of the forging process engineer during the design process is to determine how the rough stamped part can be produced at the least expensive way considering the final global cost of the tooled part. In order to assist the forging process engineer, we have integrated the forging knowledge in a set of forging software tools. These tools are operational today for revolute parts, and presently are being extended to 3D parts. They successively transform the functional frame of the part into a forged section, verify the ability to stamp the proposed shape, generate the preforms if necessary, and finally evaluate the cost of the stamping operations (see Figure 1). As an interactive process, the forging process engineer can propose some modification to the frame data in order to reduce the cost of his rough part. COPEST is our software tool that transforms the topology and geometry of a part described in terms of their frame and geometric views in a forgeable shape. It adds specific stamping features such as allowances, edge fillets, draft angles, web and flash [l]. This design tool is mainly based on expertise and on specific deformation modes. Its specificity is to be able to connect the radii dimensions to the local pressure distribution. In 30, COPEST always transforms cross-sections, ensuring the coherence of the pressure distribution in the whole part. Results are shown in Figure 2. ForgeRond is a software which performs fast simulation of the forging deformation for an axisymmetrical part (71.The basic pressure model is an expertise model, but we have added new
100
models in order to take into account the evolution of the free form surfaces during stamping, with thermal and dynamic behaviour. This software is very important in the design context, as it gives the possibility to simulate the forgeability of a part without using finite element method. That has the advantage that it can be translated in a very short time. This is due to the integration of knowledge on the modes of deformation of a billet inside the dies and, with this integration, to a strong reduction of the degrees of freedom compared to a FEM problem. ForgeRond provides information such as shape evolution during the stamping process, the forging load and the energy consumption in only a few seconds. It also gives information on the filling of the dies. Most of the time, it is not possible to transform a cylindrical billet into the stamped part in only one blow, and the simulation with ForgeRond indicates where the dies are unfilled. In such a case, intermediate shapes are obtained with preforming dies, mainly in 3 consecutive blows : flattening, preforming and finishing. Our Presto software proposes to the user a preform in the case that unfilled areas are detected with ForgeRond. The main target of preform dies are to insure a good distribution of material in the finishing dies, so as to permit the filling of these dies without any defects, minimize the metal losses, with the smallest possible flash, and reduce the finishing die wear in order to increase its time life. Presto uses some rules elaborated by skilled designers, depending on the material used and the machine chosen. The simulation of the deformation for obtaining the preform may be done with ForgeRond and in some case can induced as it a preliminary forging step. One of the results of ForgeRond is the energy required to transform a shape into another one, with a forging press. Chamouard’s experiences allow us to determine an energy equivalence between presses and hammers, and so to determine parameters which make up the total forging cost, depending on the size of production run, the chosen machine and the dimensions of the initial billet. This cost estimate method has been established in ForgeRond software, and has to be increased in order to take into account administration overheads or firm margin.
Figure 3 : an integrated fixturing application : example of a plan primary locating region The output of these softwares are included in a forging view of the product model. The stamped part is considered as a specific component with cost, energy and number of strikes as links, and with its specific frame and geometric views. 4. The machinina view At this stage of the design process, the manufacturers have at their disposal the frame and geometric view of each initial part, and are also connected to the frame and geometric view of the corresponding stamped part. The rough and the finished part are known and the manufacturer has to validate these shapes. We think that it is possible at this stage of the design to use two different types of tools : integrated manufacturing tools in a CAD environment and tools adding manufacturing constraints to the design process.
4.1 Integrated manufacturing tools in a CAD environment While in such a case, we can use integrated manufacturing tools in order to indicate if a process plan is allowable for the part under study, with the given machining facilities. The PROPEL tool, an automatic machining process planner, has been built in our laboratory to support this goal. Most of the time, the process plan allows the calculation of machining costs and consequently a cost estimate. With the forging cost, we obtain a global manufacturing cost of the part. In order to run PROPEL, a first application determines the part machining fixturing, which involves both locating and clamping [2].This has been developed within a commercial CAD environment. Choosing a machining fixture depends on the machining direction, which must necessarily be accessible, on the behaviour of the part during machining, which has to be respect, and on the accuracy of the machining operation that the design requires. The first entry of this application is the geometric model of the part. Then, we ask the process
planning expert to transfer geometric features to machining features, and to give the relationships between them. The system needs no supplementary particular handling when compared to classical CAD systems. For the language, standard notions for a mechanical specialist were chosen and the geometry of the part, its stability during machining process, the transmitted forces and the accuracy achieved, are used in natural language. The result of the module is a set of possible appropriate machining fixtures of the part. This set can be visualized in the CAD environment. The module also shows the links with the machining fixtures. The expert has six properties available that can be analysed to advance the work. These six properties are : (1) visualization of the possible locating regions (see Figure 3); (2) visualization of the possible clamping regions, dependent on the locating region (see Figure 4); (3) visualization of accessible machining features, dependent on the locating and clamping regions (see Figure 5); (4) intensity of the global clamping force necessary for the part to be stable, dependent on the locating region, clamping region and machining operation: (5) part stability factor, dependent on the locating region, clamping region and machining operation; (6) value of the required accuracy levels for the locating region, dependent on the specified relationship and the machining operation. With this last result, and a set of machining facilities, PROPEL is able to run and to propose a set of process plans and the associated cost. PROPEL is an expert system written in Le Lisp. 4.2 Developing a tool which adds machining constraints to the design process Using the part machining fixturing application, the most important piece of information for the design team is perhaps the absence of an adapted fixturing for the current part, or that the quality 101
expert has machining tools to validate these rough parts, to verify that he can obtain the expected quality, and to give the corresponding process plan and associated cost of machining. Integration of manufacturing processes during the design process avoids the cost of the late backtracking and increases the overall quality of the design.
n Figure 4 : Example of clamping regions opposite to the primary locating region of the possible fixturing is insufficient. The sooner this problem is detected the sooner solutions are proposed. This avoids expensive backtracking that is inevitable when this problem is detected late in the manufacturing process. It is better to adapt as soon as possible suitable measures and to create specific features if necessary. The quality of the fixturing is directly linked to the quality of the machining operation and, as a result, to the quality of the part. If the cost is too high because the fixturing conditions are too restrictive, the design team can impose new features without any functionality from the usage point of view, to solve the fixturing quality problem. With the machining fixturing application, the designer can visualize the geometrical behaviour in a 3D space, and have the following advantages : (1) the possible machining directions are known and he can try to correctly locate the other features to machine. In this way, the designer can locate features in a consistent way, taking into account clamping constraints, in order to decrease the numbers of set-ups, if possible; (2) the available design space is assessed. Notably, for prismatic parts with strap-type clamping, physical clamping clutters up the work space enormously and imposes substantial constraints on the access to machining features; (3) a feature without potential locating region can be spotted and the design can be review. 5. Conclusion In this paper, we show how it is possible to add to our Computer-Aided-Integrated-Design modeller some additional tools relative to the manufacturing processes. The forging process engineer can use forging tools in order to give to the best rough parts he can forge relative to the desired finished parts of a system, and the costs of the stamping operations, as soon as the frame and the geometric views of the parts are known. The process planning
102
u
/ I
Figure 5 : Example of double-strap clamping and paths of the cutting tools. 5. References (1) Boujut, J.F., Tichkiewitch, S., 1995, COPEST : a co-ordination tool in the design process of stamped part, Proc. of Advances in Materials and Processing Technologies, Dublin, 8-12 Aug., 857866 (2) Brissaud, D., Paris, H., Tichkiewitch, S., 1997, Assisting designers in the forecasting of surfaces used for easier fixturing in a machining process, Journ. of Materials Processing Technology,, 65 : 26-33 (3) Kimura, F., 1997, Issues in Styling and Engineering Design, Annals of the CIRP, 4612 (4) Krause, F.L., Kimura, F., Kjellberg, T., Lu, S.C-Y., 1993, Product Modelling : a keynote paper, Annals of the CIRP, 4212: 695-706 (5) Liebers, A., Kals, H.J.J., 1997, Cost decision support in product design, Annals of the CIRP, 46/1: 107-1 12 (6) Lu, S.C.-Y., Li, D., Cheng, J., Wu, C.L., 1997, A model fusion approach to support negotiations during complex engineering system design, Annals of the CIRP, 4611: 89-92 ( 7 ) Tichkiewitch, S., Boujut, J.F., Marin, Ph., 1993, Toward a fast simulation system of stamping deformation, Proc. of 14rh Int. Forging Cong., Venise, 27-29 Sept., 53-64 (8) Tichkiewitch, S., Veron, M., 1997, Methodology and Product Model for Integrated Design Using a Multiview System, Annals of the CIRP, 4611 :81-84