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journal of materials processing technology 1 9 5 ( 2 0 0 8 ) 94100 journal homepage: Automation of strip-layout design for sheet metal work on progressive die S. Kumara, R. Singhb a Department of Mechanical Engineering, Hindu College of Engineering, Sonepat, Haryana, India b Department of Mechanical Engineering, CRSCE, Murthal, Haryana, India a r t i c l ei n f o Article history: Received 13 November 2006 Accepted 18 April 2007 Keywords: Automation Strip-layout design Sheet metal work Progressive die Expert system a b s t r a c t Strip-layout design is an important step in the planning stage of sheet metal work on pro- gressive die. It is an experience-driven activity and the quality of strip-layout is highly dependent on the knowledge and skill of die designers. This paper presents an expert system for automation of strip-layout design process. The proposed system is developed using the production rule-based expert system approach of Artifi cial Intelligence (AI). It comprises six modules to impart expert advices to the user for identifying sheet metal oper- ations, sequencing of operations, selection of proper piloting scheme, number of stations, staging of operations on progressive die and selection of proper dimensions of stock strip. Finally, the system models the strip-layout automatically in the drawing editor of AutoCAD using the output data fi les of other modules. Usefulness of the system is demonstrated through an example of an industrial component. The system is fl exible and has low cost of implementation. 2007 Elsevier B.V. All rights reserved. 1.Introduction Strip-layout design has an extreme importance during the planning stage of progressive die design as the productivity, accuracy, cost and quality of a die mainly depends on the strip-layout (Tor et al., 2005). Traditional strip-layout design is manual, highly experience-based activity and therefore tedious,timeconsuminganderror-prone(Lietal.,2002;Ridha, 2003). Four decades earlier strip-layout problems were solved manually. The blanks cutting from cardboard were manip- ulated to obtain a good strip-layout. This trial and error procedure of obtaining suitable strip-layout with maximum material utilization is still being used in most of the small scale and even in some medium scale sheet metal industries worldwide. The quality of strip-layout achieved by using tra- ditional methods depends on the experience and knowledge of designers. On the advent of computer aided design (CAD) Corresponding author. Tel.: +91 9416942082; fax: +91 1302212755. E-mail address: skbudhwar2003yahoo.co.in (S. Kumar). systems around 3 decades earlier, the process of strip-layout design was somewhat made easier and the design lead-time was reduced from days to hours. However, well-trained and experienced die designers were still required to operate these CAD systems. Most of the applications of CAD in strip-layout design are aimed mainly at achieving better material utiliza- tion by rotating and placing the blanks as close as possible in the strip. However, the strip-layout with maximum mate- rial saving may not be the best strip-layout, indeed the die construction may become more complex, which could offset the savings due to material economy unless a large num- ber of parts are to be produced. The system developed by Schaffer (1971) in 1971 reported to calculate the stresses due to bending moment on cantilevered die projections and if the system fi nds that the stress level is above the yield stress of die steel material, then the system distributes the cutting operations over several stages in order to keep the stresses 0924-0136/$ see front matter 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.jmatprotec.2007.04.119 journal of materials processing technology 1 9 5 ( 2 0 0 8 ) 9410095 Table 1 A sample of production rules incorporated in the proposed system Serial numberIFTHEN 10.001minimum accuracy required on part in mm0.2 and feature required on part=hole or slot or internal contour cut Required operation=piercing 20.001minimum accuracy required on part in mm0.2 and feature required on part=small cut or notch on external boundary or contour Required operation=notching 30.001minimum accuracy required on part in mm0.2 and feature required on part=complete cut on one side of part Required operations=parting off/cut off 4Required operations: notching, blanking/parting off, piercingPreferred sequence of operation: 1st, piercing; 2nd, notching; 3rd, blanking/parting off 5Number of holes exist on the part2, shape of holes=circular, diameter of holes1.0mm, hole pitch2.0 times of sheet thickness, distance of holes from the edge of part2.0 times sheet thickness, specifi ed tolerance on holes0.05mm, and holes are located on opposite sides of the part Select the two largest holes for piloting 6There are suitable holes available in the component Pierce these holes at fi rst station and use them for piloting 7The minimum distance between the edge of the internal feature and edge of die block2.0 times of sheet thickness (but not less than 3.0mm) OR there is any possibility of future engineering changes in the design of part Left idle station 8Required operations on part=notching (2), piercing (any number of holes) and parting off; distance of hole(s) from edge of part and hole pitch2.0 times of sheet thickness Number of stations=5. Preferred staging: 1st station, piercing; 2nd station, notching and piloting; 3rd station, notching and piloting; 4th station, parting off 9Sheet thickness1.4mm; 25blank contour width75mm; sharp edge (along width of sheet) exists in the edge perpendicular to the moving direction of the sheet Select sheet width in mm=(blank contour width+3.2) 10Sheet thickness0.8mm; blank contour length25mm; sharp edge (along length of sheet) exists in the edge parallel to the moving direction of the sheet (along width of sheet) Select feed distance in mm=(blank contour length+2.0) within the reasonable limit. One of the limitations of the sys- tem is that it does not give any importance to the complexity of die and punches during staging of operations. Adachi et al. (1983) developed an integrated CAD system for design of progressive die. The system outputs also include generation of strip-layout for progressive die. But the user has to specify the sequence of operations himself to obtain the strip-layout. Nee (1984a,b, 1985) developed some experimental packages for analysis on press capacity, the use of coiled or strip stock and cost factors in order to solve for near-optimum layout and nesting problems for both sheet metal and metal stamping blanks. All of his work focused on the general strip-layout design process and the expert rules involved do not tackle other stamping operations such as piercing, bending, form- ing, etc. The system developed by Duffy and Sun (1991) used knowledge-based system approach to generate strip-layout for progressive stamping dies. The system was implemented in IDL, which is a knowledge-based system language. The sys- tem has the capability to generate strip-layout; however, it has not been implemented and its capabilities in real life have not been tested. The Computer Aided Die Design System (CADDS) developed by Prasad and Somasundaram (1992) also has one module for the strip-layout for progressive die. In this module, the die type is selected, depending on the input parame- ters. If the selected die is progressive, strip development is subsequently carried out according to the rules incorporated in the strip-layout module. But the major limitation of the system is that it supports mainly blanking and piercing opera- tions. Singh and Sekhon (2001) developed a low cost modeller for two-dimensional metal stamping layouts. The software is based on AutoCAD and AutoLISP. The system is capable of modeling circular, polygonal and components having curved segments. Alternative strip-layouts are also generated and tested for optimality. The main limitation of the system is that it deals with single operation stamping dies. Kim et al. (2002) developed a system using AutoLISP language. The system decides the sequencing process of electric products with intricate piercing and bending operations by consider- ing several factors on bending and adopting fuzzy set theory. It constructs fuzzy matrix for calculating fuzzy relationship value and determines the optimum bend by combining sev- eralruleswithfuzzyreasoning.Thestrip-layoutmoduleofthe system is able to carry out bending and piercing operations of 3D electric product. The main limitation of this system is that it deals with only bending and piercing operations on progres- sive die. Venkata Rao (2004) presented a strip-layout selection procedure pertaining to metal die stamping work. The pro- cedure is based on analytic hierarchy process (AHP). But, the developed procedure is applicable only for simple blanking and piercing dies. Chu et al. (2004) proposed a mathematical technique capable of generating a stamping sequence auto- maticallyinthedesignofprogressivestampingdies.Agraphis used to represent a stamping part and defi ne the relationships between its stamping features. The graph is partitioned into sets of mutually independent vertices using a clustering algo- rithm. Finally, the clustered sets are ordered to give the fi nal sequence of workstations. Completion and development of a software prototype of the system is still in progress and has 96journal of materials processing technology 1 9 5 ( 2 0 0 8 ) 94100 Fig. 1 Execution of the proposed system. to be tested against real industrial sheet metal parts having different shapes. The foregoing literature review reveals that only a few research and development works have been carried out in the area of automation of strip-layout design for sheet metal work on progressive dies. Most of the works are concentrated on process planning for sheet metal blanking and piercing operations. Some commercial computer aided systems are available to assist die designers but these are limited only to simple calculations, strip nesting, retrieval of catalogue data and compiled database of standard die components, none of them directly addressed the problem of strip-layout design. The dependence on experience coupled with the mobility of die designers in stamping industries has caused much incon- venience to the sheet metal industries all over the world. Therefore, it has become essential to capture knowledge and experience of die designers into an expert system so that it canberetainedandutilizedsuitablyforfutureapplicationand development purposes. Although some expert systems have been developed for die design area, but most of the research works are concentrated on nesting and process planning of sheetmetalforminganddrawing.Nospecifi csystemhasbeen developed for solving strip-layout design problem of progres- sive dies. To improve productivity and to build a computer integrated manufacturing environment, automatic modeling of strip-layout design is essential. The objective of the devel- opment work presented in this paper is to concentrate on the automationofstrip-layoutdesignusingproductionrule-based expert system approach of Artifi cial Intelligence (AI). The sys- tem is implemented on PC having AutoDesk AutoCAD 2004 software and designed to be loaded in the prompt area of AutoCAD. 2.Recommendations for strip-layout design Strip-layout design for progressive die is to arrange layout of the operations and subsequently determine the number of stations required. For design of strip-layout, the die designer determines the sheet metal operations required for manu- facturing the parts, sequencing of operations, selection of piloting method, number of stations required and the oper- ations stamped at each station of progressive die. Strip-layout is determined by the shape of a part and its technical require- ments. It is generally governed by the geometrical features journal of materials processing technology 1 9 5 ( 2 0 0 8 ) 9410097 Fig. 2 Example component (brass, sheet thickness=0.6mm). of the part, tolerance on dimensions of the part, direction of sharp edge of stock strip and other technical requirements. One important, but very diffi cult task in strip-layout design is the determination of a proper sequence of stamping opera- tions so that the part can be stamped correctly and effi ciently. The sequence of operations on a strip and the details of each operation must be carefully developed to ensure that the design will produce good sheet metal parts without produc- tion or maintenance problems. Normally there is no unique best solution for the strip-layout design but certain common rules can be used to guide the design of strip-layout. Some of the important rules generally used for strip-layout design are as follows: (1) Theinitialoperationssuchassidecutsorcropping,which donotdirectlyaffecttheshapeofthefi nalproductshould be made in the fi rst stage. (2) If there are suitable holes available in the sheet metal part, these holes should be used for piloting; otherwise external pilot holes should be introduced according to the progression. Piercing of these pilot holes is done in the fi rst stage or just after cropping stage. The loca- tion of pilot holes should always be the far opposite sides of the strip, with the greatest possible gap in between. This is to secure the best fi xation and position- ing of the strip, once the pilots engage in their respective openings. (3) Distances between the holes punched on one station must be larger than a certain value to ensure the die strength. Pierced holes may be distributed over several stages, if they are closely located and functionally not related. (4) Holes with high position accuracy requirement should be punched in one station. (5) Narrow slots and projections should not be allowed in a die as fracture may occur. (6) If the external profi le of the blank is complex, then the profi le may be split into simple sections by projecting all the vertices of the blank vertically up to the edge of the strip. (7) Idle stations may be used to avoid crowding of punches and die blocks together. An added advantage is that Fig. 3 Strip-layout generated by the proposed system for example component. future engineering changes can be incorporated at low cost. (8) Bending should preferably be done in the last station or prior to the parting stage, and the rest of the strip should be arranged around such a requirement. (9) Finally, the parting off or blanking operation(s) and inter- nal holes used as semi-piloting holes (if any) should be staged. (10) Suffi cient bridge width should be used in order to provide maximum strength for the bridges. (11) Finally, design the strip in such a way that it enables the component and scrapes to be ejected without interfer- ence. Pilotingisanimportantfactorinstrip-layoutdesignforpro- gressive die. The strip must be positioned accurately in each station so that the operations can be performed at the proper locations. The task of selection of piloting scheme should be viewed as interdependent task in the strip-layout design process. A strip-layout design system should support direct piloting, semi-direct piloting and indirect piloting scheme. A holeisconsideredtobesuitableforuseasapilotholeifitiscir- cular in shape, specifi ed size tolerance is not high, big enough for use as a pilot hole, does not lie on the folded portion of the workpiece, not too close to the edge of the workpiece, and not too close to another hole on the workpiece. From the list of suitable pilot holes, the best piloting holes should be selected based on the following priority: (1) If only one hole is available, it must be considered in the fi rst instance. (2) If there are a number of holes, then the location of these holes should be examined. 98journal of materials processing technology 1 9 5 ( 2 0 0 8 ) 94100 Table 2 Typical prompts, user responses and expert advices generated during execution of the proposed expert system for example component (Fig. 2) PromptExample data entryAdvice to the user Please enter sheet materialBrassModel the blank using AutoCAD commands Please enter sheet thickness in mm0.6Please enter the command OPRPLAN OPRPLANWelcome to the module OPRPLAN, developed for identifi cation of operations Enter type of feedAutomatic Is camber present in the strip?NoPlease enter the geometrical features of the part in form of questionnaire (Yes/No) Is small cut(s) or notch(es) existing on external boundary or contour? Yes Is hole(s) or slot(s) or internal contour cut exist- ing? Yes Is sheet edge(s) rough?No Does bend along a straight axis exists?No Is curved bend or forming existing?No Is complete cut required at any side of blank?YesFollowing operations are requirednotching, piercing and parting off. Please enter the command OPRSEQ OPRSEQWelcome to the module OPRSEQ developed for identifying the proper sequence of operations. The proper sequence of operations is as follows: 1st, piercing; 2nd, notching; 3rd, parting off. Please enter the command PLTSEL PLTSELWelcome to the module PLTSEL, developed for selection of piloting scheme Is any folded portion on the part?No Enter specifi ed tolerance (in mm) on hole(s)0.05 Are holes located on opposite sides of the part?YesSelect the two largest holes located on opposite sides of part for piloting (direct piloting). Please enter the command OPRSTAGE OPRSTAGEWelcome to the module OPRSTAGE developed for deciding number of stations and staging of operations on progressive die. Please enter the command OPRSTAGE1 OPRSTAGE1 Is the center-to-center distance between holes has tolerance range within 0.05mm? YesPierce these holes at the same station Are there any complex or weak sections in the external profi le of the part? No Is the minimum distance between the edge of the internalfeatureandedgeofdieblock2.0times of sheet thickness (but not less than 3.