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Computer-aided die design for axis-symmetric cold forging products by feature elimination
Journal of Materials Processing Technology 137 (2003) 138–144
Computer-aided die design for axis-symmetric cold forging products by feature elimination Takahiro Ohashia,*, Satoshi Imamuraa, Toru Shimizub, Mitsugu Motomurac a
b
Digital Manufacturing Research Center, AIST, 1-2-1 Namiki, Tsukuba, 305-8564, Japan Institute of Mechanical Systems Engineering, AIST, 1-2-1 Namiki, Tsukuba, 305-8564, Japan c Waseda University, Tokyo, Japan
Abstract The authors consider forging to be a procedure for adding features to a raw material, and process planning to be the inverse procedure. Each step of the forging process is thought of as a combination of feature eliminating processes. Depending on the above, the authors have developed a CAD system to design forging sequences and die profiles. The system designs the forging sequences and die profiles from the product to its raw material by eliminating features, which is the inverse of forging processes. First, the system detects features from a product’s shape. A shape is represented by its cross-section including the axis with free curves. Its outline is described as successive finite vectors. The system extracts features by using the change of the vector direction. Second, the system searches a database of ‘‘manufacturing cases’’ using features such as search keys to find a candidate case in which the manufacturing process can be applied to the product. A manufacturing case is a data set having three kinds of data; search key, validity checking procedure of itself, and eliminating the procedure to get a partial preform after the elimination of the feature. Search key is the name of the feature to which a case can be applied. If the system finds a matched case by using the search key, it applies a validity checking procedure described in the matched case data. Please note that, by only eliminating features it is not possible to obtained a process plan. Each case must represent an actual forging method by which the feature can be manufactured. The validity checking procedure ensures that the eliminating process is actually to be realized as the inverse of forging. The system checks if the case can be applied on the feature or not by the validity checking procedure. If it passes, it eliminates the feature by the eliminating procedure described in the case. The procedures in each case are independent, but they exchange information about the cases and dimensions by using a working memory like a blackboard. Using the working memory, the system combines eliminating procedures automatically to get an actual manufacturing process. Thus, the system designs one forging process and preform, and after then, it also does the internal profiles of dies and exports them as point line into general purpose CAD systems. Repeating the above procedures, the system generates process plans and die profile design from the product’s shape to its raw materials. Multiple plans and profiles are designed by repeating the procedure recursively. # 2002 Elsevier Science B.V. All rights reserved. Keywords: Cold forging; Expert system; Process planning; CAPP; CAD; Dies
1. Introduction Several methods for computer-aided cold forging process planning and die design have been proposed. However, most of their applications are restricted to simple shapes which are represented by combinations of primitive shapes or their sections drawn with lines and circles. This is primarily due to two reasons. First, cold forging products tend to have simple shapes. Second, the systems often restrict product shape to facilitate building a knowledge-base and understanding the process. Furthermore, development of forging technology enables the manufacture of increasingly more complex shaped cold forging products in actual shops. These * Corresponding author. Tel.: þ81-298-61-7877; fax: þ81-298-61-7129. E-mail address: [email protected] (T. Ohashi).
products often have free curved sections, so it has been difficult to treat them using conventional systems. The author have therefore developed a computer-aided cold forging process and die design system that can accommodate axi-symmetrical products having a free curved section by the ‘‘feature elimination method’’. It designs process plans and the internal profiles of dies and exports the data to a general purpose CAD system as point line.
2. Process planning by feature elimination 2.1. Basic idea [2] Forging is considered to be a procedure for adding features to a raw material, and process planning to be the
0924-0136/02/$ – see front matter # 2002 Elsevier Science B.V. All rights reserved. PII: S 0 9 2 4 - 0 1 3 6 ( 0 2 ) 0 1 1 0 1 - 9
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Fig. 1. Model of the process planning.
inverse procedure (i.e., eliminating features from a manufactured product by manufacturing process). A forging expert seems to extract form features from the product and consider how he would manufacture it when he develops the forging process plan. If he finds how to manufacture one of the features, he eliminates it from his mind and continues the process planning. The process is compiled into the computer-software model shown in Fig. 1. In this model, the system first extracts features from the postform. It then picks one of the features and eliminates it by means of the actual forging process. This is done by using a database of processes. Thus, the system plans the forging process by repeating extraction and elimination as described above. 2.2. Extraction of form features The system extracts features from the free curved crosssection drawn by counter-clockwise successive points (Fig. 2). It then draws a vector line tying points with the neighbor. When the change of the angle of the vector from a
Fig. 2. Shape representation for an axis-symmetrical forging by the vector line and the angle symbol line.
neighbor exceeds 1808, the system marks it with ‘‘’’. If the angle is equal to 1808, the system marks it with ‘‘0’’, and if the angle is less than 1808, the system marks it with ‘‘þ’’. In the above, the system produces an angle symbol line consisting of symbols ‘‘þ’’, ‘‘’’, and ‘‘0’’. When the system finds consecutive identical symbols in the line, it combines them into one segment symbol (Fig. 3). Next, the system searches the feature database for a feature having the same segment symbol line as a part of the symbol line of the section. If the system finds the data, it extracts a feature using it. Features that the system extracts are shown in Fig. 4. The feature data set consists of the following four parts: (a) Symbol line composing the feature. This part of the data set is used as the searching key. (b) Name of the feature. This just represents the name of the feature. (c) Procedure to check whether or not it is able to apply itself. When the system finds a feature from the database using the symbol line, it checks whether it is able to apply the feature by running this procedure. This procedure checks conformity by using Euclid’s
Fig. 3. Example of the segment symbols and their line. In this case, there are four segments and their segment symbol line is expressed as ‘‘( . . . , , 0, , þ, . . . )’’.
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Fig. 4. Features that the system extracts [2].
distance [3] and checks for geometrical contradiction between the axis or other features. (d) Procedure to fix the scope of the feature in the line. This procedure is used to fix the scope of the feature in the product shape. This data set is prepared in the form of object-oriented data, and all the above data and procedures are built into the set. The system first runs checking procedure (c). If this check is satisfactory, the system creates a new segment symbol list by replacing part of the segment symbol list with the
detected feature name. Finally, it enters the information of the extracted feature (i.e., the feature’s name and scope on the point list of the product) into the feature pool using data (b) and procedure (d). The system extracts features by repeating this process for all the candidate feature data and combinations of segment symbols. The system does not use only symbols (i.e. ‘‘þ’’, ‘‘’’, and ‘‘0’’) for extraction but also feature names. Features extracted from first generation symbol list are called ‘‘first features’’, and those from the second and third generations, ‘‘second features’’ and ‘‘third features’’. Fig. 5 shows a typical result of extracting features
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‘‘actual manufacturing process’’ to plan a process. The system has a database of such ‘‘actual manufacturing processes’’, and uses it to eliminate features from a product until it finally obtains the raw material, as shown in Fig. 6. These are called ‘‘processing (or eliminating) cases’’. The processing case is the data set which ensures the elimination relates to the actual manufacturing process. It eliminates features in the manner of an actual forging process. The processing case consists of the following four parts: (a) Feature which can be eliminated by the case. (b) Name of the process. (c) Procedure to check whether it is able to apply itself certainly. (d) Procedure to create a post-eliminate shape, i.e., ‘‘preform’’.
Fig. 5. Example of feature extraction.
of the axis-symmetrical product, a ball-stud, having a free curved section. It can be seen that different features are extracted for the same part, for example ‘‘shaft’’ and ‘‘double_shaft’’, because of recursive execution of feature extraction. 2.3. Feature elimination by using a database of processing cases [2,4] Features are eliminated using a database of processing cases. Note that process planning cannot be performed by just eliminating features geometrically. The system must eliminate features from the manufactured shape by using an
This data set is composed of object-oriented data the same as ‘‘feature data’’ in Section 2.2. In an actual manufacturing process, several features are produced at a time. This means that the system must combine the elimination of several features. We developed an algorithm using a ‘‘constraint-blackboard’’ for this purpose (see Fig. 7). Elimination of each feature is considered as the inverse of a virtual manufacturing process and corresponds to one ‘‘processing case’’. An actual manufacturing process is composed of these virtual processes. A combination of virtual processes is called a ‘‘combined process’’. When the system designs a combined process, the procedures in the ‘‘processing case’’ must exchange information concerning the ‘‘case’’ because virtual processes affect each other through their limits of deformability, compressing direction, and geometrical feasibility. For example, in Fig. 7, the first virtual manufacturing step, forward extrusion, can be executed if its reduction is less than 0.86 and if it is not a combined process but a simple, independent, forward extrusion process. However, the reduction must be less than 0.8, and the stem diameter must be 0.4 times larger than the outer diameter of the cup-shaped part of the product when it is combined with hollow backward extrusion. This means that ‘‘hole’’ of the product cannot be eliminated by ‘‘backward extrusion’’ with ‘‘elimination of shaft by forward extrusion’’ in a single step if the latter condition is not satisfied. This control is implemented as follows by using the ‘‘constraint-blackboard’’. The ‘‘constraint-blackboard’’ is a common working memory like a blackboard (for example [1]) through which the procedures exchange data on case constraints. First, information on the previously planned virtual manufacturing process [5], forward extrusion in this case, is entered onto the ‘‘constraint-blackboard’’ using the procedure described in a formerly applied processing case when the shaft is eliminated. The information consists of the name of the applied case, dimensions, compressing direction, and list of processing cases that can be combined. The system then extracts features again from the shape of which ‘‘shaft’’ is eliminated. Next, the system attempts to extract features.
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Fig. 6. Process planning using a database of processing cases. The checking procedure includes judgement for deformability.
The system chooses one feature and searches the database of processing cases. If it finds a hopeful case, it runs a checking procedure for that case. The procedure checks the conditions for both an independent process and combined processes such as the example condition described above by referring
to information on the blackboard. If the check is successful, ‘‘hole’’ is eliminated and ‘‘backward extrusion’’ is combined with ‘‘forward extrusion’’. If not, the system continues searching for other processing cases or features to continue elimination until there is no available case or feature. It then
Fig. 7. Example of combined elimination with ‘‘constraint-blackboard’’. In this case, backward extrusion can be combined with forward extrusion only when the forward extrusion ratio is smaller than 0.8 and the forward extrusion diameter is 0.4 times larger than the outer diameter of the backward-extruded cup.
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clears the blackboard and assembles virtual processes into one real process. Repeating the above, the system obtains several manufacturing plans to compose the multiple forming stage. 2.4. Phase and peculiar case on cold forging process planning In multiple stage cold forging, the ‘‘forming direction’’ (i.e., the material flow direction) is restricted primarily to three kinds, the direction of punch stroke, its opposite direction, and the lateral direction because a large forming force is generally required in cold processes. The forming direction of each processing case thus plays an important role in process planning. Fig. 7 shows two processes having different forming directions that combine one-to-one. However, it is also possible to combine multiple feature elimination having the same forming direction as shown in Fig. 8. Two backward extrusion processes, which have forming directions opposite to the compressing direction, and a forward extrusion, which has a forming direction the same as the compressing direction, are combined into one manufacturing process. In this case, process planning for combined processes having the same forming directions differs from that for ones having different directions. To fix the dimensions of combined processes having the same forming directions, processes can be calculated only by applying the volume constancy law with choosing appropriate dies and punches. However, the dimensions of different forming directions are not determined by just the volume constancy law but also by the volume balance of material flow. In addition, the manner of judging processing limits differs largely between the former and the latter. The authors think that it makes building a knowledge-base easier if the tactics are taken that the system first combines elimination having the same forming direction then does it for features with different forming directions. In addition, the system should run a checking procedure after all combinations are completed based on the conditions, such as processing limit. The authors therefore divided the system elimination operation into two phases according to the forming direction. In addition, a new phase in which the deformability of the combined processing is checked comprehensively and was added checking of each processing case was restricted to basic conditions. These phases are called the ‘‘feature combination phase’’, ‘‘process combination phase’’, and ‘‘deformability checking phase’’. Phase a (feature combination phase). In this phase, only the features having the same forming direction are eliminated, such as ‘‘forward extrusion’’ with ‘‘forward extrusion’’, ‘‘backward extrusion’’ with ‘‘backward extrusion’’, and ‘‘upset’’ with ‘‘upset’’. Phase b (process combination phase). In this phase, features having different forming directions can be combined for elimination. For example, ‘‘forward-and-backward
Fig. 8. Example of combined process.
extrusion’’. This phase must follow the ‘‘feature combination phase’’. Phase c (deformability checking phase). In this phase, the system checks whether the process satisfies the deformability criteria. This phase is meaningful only for a combined process. If the designed process is not a combined one, this check was already performed in phase a using the checking procedure of each processing case. In such a case, this phase becomes a dummy phase in which nothing is done. The authors made a peculiar case having only a checking procedure that determines the deformability of combined processing for this phase; only these peculiar cases are used. The system can assemble virtual processes only after this phase. Phases are controlled using the ‘‘constraint-blackboard’’ and a peculiar case by which the system changes phase. The flag of the current phase is written on the ‘‘blackboard’’ by the first processing case. It is rewritten by a peculiar case which has its function restricted to only the changing of the phase. All the processing cases can access the ‘‘constraintblackboard’’ by their checking procedure to determine the current phase. Thus, the check result is evaluated considering the phase, and appropriate processing cases are chosen at each phase.
3. Example process planning and discussion Fig. 9 shows an example of process planning by the system. The target product is a ball-stud identical to the one shown in Fig. 5. This product has a free curved section at its head. First, the system detects the features, three ‘‘shafts’’, one ‘‘flange’’ and one ‘‘double_shaft’’. The system finds ‘‘flange’’ can be manufactured by ‘‘upsetting’’. It then eliminates ‘‘flange’’ by ‘‘upsetting’’ under the volume constancy law to obtain a preform. Next, the system extracts features from the preform to get two ‘‘shafts’’ and one ‘‘double_shaft’’. The system finds ‘‘double_shaft’’ can be manufactured by ‘‘forward extrusion’’ and eliminates it to obtain the raw material. In this case, ‘‘shaft’’ can also be manufactured by ‘‘forward extrusion’’. When a ‘‘shaft’’ is eliminated before ‘‘double_shaft’’, the system performs the
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that it is more efficient to let the user choose an appropriate plan rather than to attempt to build completely automatic systems. The result is exported to an external general CAD program as point line on the internal profile of dies and used to draw die design with library of die set parts.
4. Conclusion and further study
Fig. 9. Example process plan developed by the system.
extraction procedure again, detects the other ‘‘shaft’’, and eliminates it in a combination process with the former ‘‘forward extrusion’’. Finally, it manufactures the ‘‘double_shaft’’. In the system, there is little knowledge about the order of manufacturing. As a result, some manufacturing plans suggested by the system for one product may be unrealistic, for example, the plan for the product in Fig. 5 in which ‘‘double_shaft’’ is eliminated earlier by ‘‘forward extrusion’’ and manufactured after upsetting. These unrealistic plans could be reduced by putting general rules into the system such as ‘‘upsetting must be done last’’. However, this has the risk of removing rare possibilities. Removing all unrealistic plans may result in removing a rare good plan as well. In addition, the authors did not seek to realize a completely automatic design system in this paper, but rather a support system for forging designers. They therefore think
In this paper, the authors have reported a developed computer-aided process planning and die design system for axissymmetric cold forging products having a free curved section. They consider process planning and die profile design to be the inverse procedure of manufacturing, eliminating features from a manufactured product. The eliminating procedure is realized using a database of processing cases. The cases represent actual manufacturing processes and ensure that the elimination will be the inverse of the actual forging process. The system develops process plans and inside profile of dies by repeated feature extraction and elimination from the product until the raw material is obtained. In future work, it is planned to combine this system and a deformation analyzer. The system will be used to design temporary plans of complex forging processes as the inverse of manufacturing, and the analyzer as a normal simulator of manufacturing. By realizing an algorithm correcting temporary process design with the analysis results, it is expected to develop a system capable of designing more precise and complex forging process plans. References [1] Ohsuga, Introduction to Knowledge Based Engineering, Ohm Corp, 1986, 184 pp. (Tisiki-besu-nyumon in Japanese). [2] T. Ohashi, M. Motomura, Trans. Jpn. Soc. Mech. Eng. Ser. C 64 (618) (1998) 707–712 (in Japanese). [3] G.J. Schmucker, Fuzzy Set, Natural Language Computations, and Risk Analysis, Keigaku-Shuppan, 1990 (T. Onizawa, Transl. to Japanese). [4] T. Ohashi, M. Motomura, Proceedings of the 18th International Manufacturing Conference, China, pp. 245–250. [5] T. Ohashi, M. Motomura, Trans. Jpn. Soc. Mech. Eng. Ser. C 64 (620) (1998) 1450–1455 (in Japanese).
Computer-aided die design for axis-symmetric cold forging products by feature elimination Takahiro Ohashia,*, Satoshi Imamuraa, Toru Shimizub, Mitsugu Motomurac a
b
Digital Manufacturing Research Center, AIST, 1-2-1 Namiki, Tsukuba, 305-8564, Japan Institute of Mechanical Systems Engineering, AIST, 1-2-1 Namiki, Tsukuba, 305-8564, Japan c Waseda University, Tokyo, Japan
Abstract The authors consider forging to be a procedure for adding features to a raw material, and process planning to be the inverse procedure. Each step of the forging process is thought of as a combination of feature eliminating processes. Depending on the above, the authors have developed a CAD system to design forging sequences and die profiles. The system designs the forging sequences and die profiles from the product to its raw material by eliminating features, which is the inverse of forging processes. First, the system detects features from a product’s shape. A shape is represented by its cross-section including the axis with free curves. Its outline is described as successive finite vectors. The system extracts features by using the change of the vector direction. Second, the system searches a database of ‘‘manufacturing cases’’ using features such as search keys to find a candidate case in which the manufacturing process can be applied to the product. A manufacturing case is a data set having three kinds of data; search key, validity checking procedure of itself, and eliminating the procedure to get a partial preform after the elimination of the feature. Search key is the name of the feature to which a case can be applied. If the system finds a matched case by using the search key, it applies a validity checking procedure described in the matched case data. Please note that, by only eliminating features it is not possible to obtained a process plan. Each case must represent an actual forging method by which the feature can be manufactured. The validity checking procedure ensures that the eliminating process is actually to be realized as the inverse of forging. The system checks if the case can be applied on the feature or not by the validity checking procedure. If it passes, it eliminates the feature by the eliminating procedure described in the case. The procedures in each case are independent, but they exchange information about the cases and dimensions by using a working memory like a blackboard. Using the working memory, the system combines eliminating procedures automatically to get an actual manufacturing process. Thus, the system designs one forging process and preform, and after then, it also does the internal profiles of dies and exports them as point line into general purpose CAD systems. Repeating the above procedures, the system generates process plans and die profile design from the product’s shape to its raw materials. Multiple plans and profiles are designed by repeating the procedure recursively. # 2002 Elsevier Science B.V. All rights reserved. Keywords: Cold forging; Expert system; Process planning; CAPP; CAD; Dies
1. Introduction Several methods for computer-aided cold forging process planning and die design have been proposed. However, most of their applications are restricted to simple shapes which are represented by combinations of primitive shapes or their sections drawn with lines and circles. This is primarily due to two reasons. First, cold forging products tend to have simple shapes. Second, the systems often restrict product shape to facilitate building a knowledge-base and understanding the process. Furthermore, development of forging technology enables the manufacture of increasingly more complex shaped cold forging products in actual shops. These * Corresponding author. Tel.: þ81-298-61-7877; fax: þ81-298-61-7129. E-mail address: [email protected] (T. Ohashi).
products often have free curved sections, so it has been difficult to treat them using conventional systems. The author have therefore developed a computer-aided cold forging process and die design system that can accommodate axi-symmetrical products having a free curved section by the ‘‘feature elimination method’’. It designs process plans and the internal profiles of dies and exports the data to a general purpose CAD system as point line.
2. Process planning by feature elimination 2.1. Basic idea [2] Forging is considered to be a procedure for adding features to a raw material, and process planning to be the
0924-0136/02/$ – see front matter # 2002 Elsevier Science B.V. All rights reserved. PII: S 0 9 2 4 - 0 1 3 6 ( 0 2 ) 0 1 1 0 1 - 9
T. Ohashi et al. / Journal of Materials Processing Technology 137 (2003) 138–144
139
Fig. 1. Model of the process planning.
inverse procedure (i.e., eliminating features from a manufactured product by manufacturing process). A forging expert seems to extract form features from the product and consider how he would manufacture it when he develops the forging process plan. If he finds how to manufacture one of the features, he eliminates it from his mind and continues the process planning. The process is compiled into the computer-software model shown in Fig. 1. In this model, the system first extracts features from the postform. It then picks one of the features and eliminates it by means of the actual forging process. This is done by using a database of processes. Thus, the system plans the forging process by repeating extraction and elimination as described above. 2.2. Extraction of form features The system extracts features from the free curved crosssection drawn by counter-clockwise successive points (Fig. 2). It then draws a vector line tying points with the neighbor. When the change of the angle of the vector from a
Fig. 2. Shape representation for an axis-symmetrical forging by the vector line and the angle symbol line.
neighbor exceeds 1808, the system marks it with ‘‘’’. If the angle is equal to 1808, the system marks it with ‘‘0’’, and if the angle is less than 1808, the system marks it with ‘‘þ’’. In the above, the system produces an angle symbol line consisting of symbols ‘‘þ’’, ‘‘’’, and ‘‘0’’. When the system finds consecutive identical symbols in the line, it combines them into one segment symbol (Fig. 3). Next, the system searches the feature database for a feature having the same segment symbol line as a part of the symbol line of the section. If the system finds the data, it extracts a feature using it. Features that the system extracts are shown in Fig. 4. The feature data set consists of the following four parts: (a) Symbol line composing the feature. This part of the data set is used as the searching key. (b) Name of the feature. This just represents the name of the feature. (c) Procedure to check whether or not it is able to apply itself. When the system finds a feature from the database using the symbol line, it checks whether it is able to apply the feature by running this procedure. This procedure checks conformity by using Euclid’s
Fig. 3. Example of the segment symbols and their line. In this case, there are four segments and their segment symbol line is expressed as ‘‘( . . . , , 0, , þ, . . . )’’.
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Fig. 4. Features that the system extracts [2].
distance [3] and checks for geometrical contradiction between the axis or other features. (d) Procedure to fix the scope of the feature in the line. This procedure is used to fix the scope of the feature in the product shape. This data set is prepared in the form of object-oriented data, and all the above data and procedures are built into the set. The system first runs checking procedure (c). If this check is satisfactory, the system creates a new segment symbol list by replacing part of the segment symbol list with the
detected feature name. Finally, it enters the information of the extracted feature (i.e., the feature’s name and scope on the point list of the product) into the feature pool using data (b) and procedure (d). The system extracts features by repeating this process for all the candidate feature data and combinations of segment symbols. The system does not use only symbols (i.e. ‘‘þ’’, ‘‘’’, and ‘‘0’’) for extraction but also feature names. Features extracted from first generation symbol list are called ‘‘first features’’, and those from the second and third generations, ‘‘second features’’ and ‘‘third features’’. Fig. 5 shows a typical result of extracting features
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‘‘actual manufacturing process’’ to plan a process. The system has a database of such ‘‘actual manufacturing processes’’, and uses it to eliminate features from a product until it finally obtains the raw material, as shown in Fig. 6. These are called ‘‘processing (or eliminating) cases’’. The processing case is the data set which ensures the elimination relates to the actual manufacturing process. It eliminates features in the manner of an actual forging process. The processing case consists of the following four parts: (a) Feature which can be eliminated by the case. (b) Name of the process. (c) Procedure to check whether it is able to apply itself certainly. (d) Procedure to create a post-eliminate shape, i.e., ‘‘preform’’.
Fig. 5. Example of feature extraction.
of the axis-symmetrical product, a ball-stud, having a free curved section. It can be seen that different features are extracted for the same part, for example ‘‘shaft’’ and ‘‘double_shaft’’, because of recursive execution of feature extraction. 2.3. Feature elimination by using a database of processing cases [2,4] Features are eliminated using a database of processing cases. Note that process planning cannot be performed by just eliminating features geometrically. The system must eliminate features from the manufactured shape by using an
This data set is composed of object-oriented data the same as ‘‘feature data’’ in Section 2.2. In an actual manufacturing process, several features are produced at a time. This means that the system must combine the elimination of several features. We developed an algorithm using a ‘‘constraint-blackboard’’ for this purpose (see Fig. 7). Elimination of each feature is considered as the inverse of a virtual manufacturing process and corresponds to one ‘‘processing case’’. An actual manufacturing process is composed of these virtual processes. A combination of virtual processes is called a ‘‘combined process’’. When the system designs a combined process, the procedures in the ‘‘processing case’’ must exchange information concerning the ‘‘case’’ because virtual processes affect each other through their limits of deformability, compressing direction, and geometrical feasibility. For example, in Fig. 7, the first virtual manufacturing step, forward extrusion, can be executed if its reduction is less than 0.86 and if it is not a combined process but a simple, independent, forward extrusion process. However, the reduction must be less than 0.8, and the stem diameter must be 0.4 times larger than the outer diameter of the cup-shaped part of the product when it is combined with hollow backward extrusion. This means that ‘‘hole’’ of the product cannot be eliminated by ‘‘backward extrusion’’ with ‘‘elimination of shaft by forward extrusion’’ in a single step if the latter condition is not satisfied. This control is implemented as follows by using the ‘‘constraint-blackboard’’. The ‘‘constraint-blackboard’’ is a common working memory like a blackboard (for example [1]) through which the procedures exchange data on case constraints. First, information on the previously planned virtual manufacturing process [5], forward extrusion in this case, is entered onto the ‘‘constraint-blackboard’’ using the procedure described in a formerly applied processing case when the shaft is eliminated. The information consists of the name of the applied case, dimensions, compressing direction, and list of processing cases that can be combined. The system then extracts features again from the shape of which ‘‘shaft’’ is eliminated. Next, the system attempts to extract features.
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Fig. 6. Process planning using a database of processing cases. The checking procedure includes judgement for deformability.
The system chooses one feature and searches the database of processing cases. If it finds a hopeful case, it runs a checking procedure for that case. The procedure checks the conditions for both an independent process and combined processes such as the example condition described above by referring
to information on the blackboard. If the check is successful, ‘‘hole’’ is eliminated and ‘‘backward extrusion’’ is combined with ‘‘forward extrusion’’. If not, the system continues searching for other processing cases or features to continue elimination until there is no available case or feature. It then
Fig. 7. Example of combined elimination with ‘‘constraint-blackboard’’. In this case, backward extrusion can be combined with forward extrusion only when the forward extrusion ratio is smaller than 0.8 and the forward extrusion diameter is 0.4 times larger than the outer diameter of the backward-extruded cup.
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clears the blackboard and assembles virtual processes into one real process. Repeating the above, the system obtains several manufacturing plans to compose the multiple forming stage. 2.4. Phase and peculiar case on cold forging process planning In multiple stage cold forging, the ‘‘forming direction’’ (i.e., the material flow direction) is restricted primarily to three kinds, the direction of punch stroke, its opposite direction, and the lateral direction because a large forming force is generally required in cold processes. The forming direction of each processing case thus plays an important role in process planning. Fig. 7 shows two processes having different forming directions that combine one-to-one. However, it is also possible to combine multiple feature elimination having the same forming direction as shown in Fig. 8. Two backward extrusion processes, which have forming directions opposite to the compressing direction, and a forward extrusion, which has a forming direction the same as the compressing direction, are combined into one manufacturing process. In this case, process planning for combined processes having the same forming directions differs from that for ones having different directions. To fix the dimensions of combined processes having the same forming directions, processes can be calculated only by applying the volume constancy law with choosing appropriate dies and punches. However, the dimensions of different forming directions are not determined by just the volume constancy law but also by the volume balance of material flow. In addition, the manner of judging processing limits differs largely between the former and the latter. The authors think that it makes building a knowledge-base easier if the tactics are taken that the system first combines elimination having the same forming direction then does it for features with different forming directions. In addition, the system should run a checking procedure after all combinations are completed based on the conditions, such as processing limit. The authors therefore divided the system elimination operation into two phases according to the forming direction. In addition, a new phase in which the deformability of the combined processing is checked comprehensively and was added checking of each processing case was restricted to basic conditions. These phases are called the ‘‘feature combination phase’’, ‘‘process combination phase’’, and ‘‘deformability checking phase’’. Phase a (feature combination phase). In this phase, only the features having the same forming direction are eliminated, such as ‘‘forward extrusion’’ with ‘‘forward extrusion’’, ‘‘backward extrusion’’ with ‘‘backward extrusion’’, and ‘‘upset’’ with ‘‘upset’’. Phase b (process combination phase). In this phase, features having different forming directions can be combined for elimination. For example, ‘‘forward-and-backward
Fig. 8. Example of combined process.
extrusion’’. This phase must follow the ‘‘feature combination phase’’. Phase c (deformability checking phase). In this phase, the system checks whether the process satisfies the deformability criteria. This phase is meaningful only for a combined process. If the designed process is not a combined one, this check was already performed in phase a using the checking procedure of each processing case. In such a case, this phase becomes a dummy phase in which nothing is done. The authors made a peculiar case having only a checking procedure that determines the deformability of combined processing for this phase; only these peculiar cases are used. The system can assemble virtual processes only after this phase. Phases are controlled using the ‘‘constraint-blackboard’’ and a peculiar case by which the system changes phase. The flag of the current phase is written on the ‘‘blackboard’’ by the first processing case. It is rewritten by a peculiar case which has its function restricted to only the changing of the phase. All the processing cases can access the ‘‘constraintblackboard’’ by their checking procedure to determine the current phase. Thus, the check result is evaluated considering the phase, and appropriate processing cases are chosen at each phase.
3. Example process planning and discussion Fig. 9 shows an example of process planning by the system. The target product is a ball-stud identical to the one shown in Fig. 5. This product has a free curved section at its head. First, the system detects the features, three ‘‘shafts’’, one ‘‘flange’’ and one ‘‘double_shaft’’. The system finds ‘‘flange’’ can be manufactured by ‘‘upsetting’’. It then eliminates ‘‘flange’’ by ‘‘upsetting’’ under the volume constancy law to obtain a preform. Next, the system extracts features from the preform to get two ‘‘shafts’’ and one ‘‘double_shaft’’. The system finds ‘‘double_shaft’’ can be manufactured by ‘‘forward extrusion’’ and eliminates it to obtain the raw material. In this case, ‘‘shaft’’ can also be manufactured by ‘‘forward extrusion’’. When a ‘‘shaft’’ is eliminated before ‘‘double_shaft’’, the system performs the
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that it is more efficient to let the user choose an appropriate plan rather than to attempt to build completely automatic systems. The result is exported to an external general CAD program as point line on the internal profile of dies and used to draw die design with library of die set parts.
4. Conclusion and further study
Fig. 9. Example process plan developed by the system.
extraction procedure again, detects the other ‘‘shaft’’, and eliminates it in a combination process with the former ‘‘forward extrusion’’. Finally, it manufactures the ‘‘double_shaft’’. In the system, there is little knowledge about the order of manufacturing. As a result, some manufacturing plans suggested by the system for one product may be unrealistic, for example, the plan for the product in Fig. 5 in which ‘‘double_shaft’’ is eliminated earlier by ‘‘forward extrusion’’ and manufactured after upsetting. These unrealistic plans could be reduced by putting general rules into the system such as ‘‘upsetting must be done last’’. However, this has the risk of removing rare possibilities. Removing all unrealistic plans may result in removing a rare good plan as well. In addition, the authors did not seek to realize a completely automatic design system in this paper, but rather a support system for forging designers. They therefore think
In this paper, the authors have reported a developed computer-aided process planning and die design system for axissymmetric cold forging products having a free curved section. They consider process planning and die profile design to be the inverse procedure of manufacturing, eliminating features from a manufactured product. The eliminating procedure is realized using a database of processing cases. The cases represent actual manufacturing processes and ensure that the elimination will be the inverse of the actual forging process. The system develops process plans and inside profile of dies by repeated feature extraction and elimination from the product until the raw material is obtained. In future work, it is planned to combine this system and a deformation analyzer. The system will be used to design temporary plans of complex forging processes as the inverse of manufacturing, and the analyzer as a normal simulator of manufacturing. By realizing an algorithm correcting temporary process design with the analysis results, it is expected to develop a system capable of designing more precise and complex forging process plans. References [1] Ohsuga, Introduction to Knowledge Based Engineering, Ohm Corp, 1986, 184 pp. (Tisiki-besu-nyumon in Japanese). [2] T. Ohashi, M. Motomura, Trans. Jpn. Soc. Mech. Eng. Ser. C 64 (618) (1998) 707–712 (in Japanese). [3] G.J. Schmucker, Fuzzy Set, Natural Language Computations, and Risk Analysis, Keigaku-Shuppan, 1990 (T. Onizawa, Transl. to Japanese). [4] T. Ohashi, M. Motomura, Proceedings of the 18th International Manufacturing Conference, China, pp. 245–250. [5] T. Ohashi, M. Motomura, Trans. Jpn. Soc. Mech. Eng. Ser. C 64 (620) (1998) 1450–1455 (in Japanese).