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journal of materials processing technology 195 (2008) 94100 journal homepage: Automation of strip-layout design for sheet metal Sonepat, India Strip-layout design Sheet metal work Progressive die Expert system an important experience-dri wledg of rule-based to oper 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 files of other modules. Usefulness of the system is demonstrated through an example of an industrial component. The system is flexible 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, time consuming and error-prone (Li et al., 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 finds 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 work on progressive die S. Kumar a, , R. Singh b a Department of Mechanical Engineering, Hindu College of Engineering, b Department of Mechanical Engineering, CRSCE, Murthal, Haryana, article info Article history: Received 13 November 2006 Accepted 18 April 2007 Keywords: Automation abstract Strip-layout design is gressive die. It is an dependent on the kno system for automation using the production comprises six modules ations, sequencing of Haryana, India step in the planning stage of sheet metal work on pro- ven activity and the quality of strip-layout is highly e and skill of die designers. This paper presents an expert strip-layout design process. The proposed system is developed expert system approach of Artificial Intelligence (AI). It impart expert advices to the user for identifying sheet metal oper- ations, selection of proper piloting scheme, number of stations, journal of materials processing technology 195 (2008) 94100 95 Table1Asampleofproduction rules incorporated in the proposed system Serial number IF THEN 1 0.001minimum accuracy required on part in mm0.2 and feature required on part=hole or slot or internal contour cut Required operation=piercing 2 0.001minimum accuracy required on part in mm0.2 and on external Required operation=notching mm side off, of holes part 0.05 the internal kness e cing om edg width edg sheet 2 e par sheet) within tem of al. pr of the Nee for and nesting b design other ing, kno for in tem not been de module the ters. subsequentl in system tions. feature required on part=small cut or notch boundary or contour 3 0.001minimum accuracy required on part in feature required on part=complete cut on one 4 Required operations: notching, blanking/parting 5 Number of holes exist on the part2, shape diameter of holes1.0mm, hole pitch2.0 times thickness, distance of holes from the edge of sheet thickness, specified tolerance on holes holes are located on opposite sides of the part 6 There are suitable holes available in the component 7 The minimum distance between the edge of and edge of die block2.0 times of sheet thic than 3.0mm) OR there is any possibility of futur changes in the design of part 8 Required operations on part=notching (2), pier of holes) and parting off; distance of hole(s) fr and hole pitch2.0 times of sheet thickness 9 Sheet thickness1.4mm; 25blank contour sharp edge (along width of sheet) exists in the perpendicular to the moving direction of the 10 Sheet thickness0.8mm; blank contour length edge (along length of sheet) exists in the edg moving direction of the sheet (along width of the reasonable limit. One of the limitations of the sys- is that it does not give any importance to the complexity die and punches during staging of operations. Adachi et (1983) developed an integrated CAD system for design of ogressive die. The system outputs also include generation strip-layout for progressive die. But the user has to specify sequence of operations himself to obtain the strip-layout. (1984a,b, 1985) developed some experimental packages analysis on press capacity, the use of coiled or strip stock cost factors in order to solve for near-optimum layout and problems for both sheet metal and metal stamping lanks. All of his work focused on the general strip-layout process and the expert rules involved do not tackle stamping operations such as piercing, bending, form- etc. The system developed by Duffy and Sun (1991) used wledge-based system approach to generate strip-layout progressive stamping dies. The system was implemented IDL, which is a knowledge-based system language. The sys- has the capability to generate strip-layout; however, it has been implemented and its capabilities in real life have not tested. The Computer Aided Die Design System (CADDS) veloped by Prasad and Somasundaram (1992) also has one for the strip-layout for progressive die. In this module, die type is selected, depending on the input parame- If the selected die is progressive, strip development is y carried out according to the rules incorporated the strip-layout module. But the major limitation of the is that it supports mainly blanking and piercing opera- Singh and Sekhon (2001) developed a low cost modeller 0.2 and of part Required operations=parting off/cut off piercing Preferred sequence of operation: 1st, piercing; 2nd, notching; 3rd, blanking/parting off =circular, of sheet 2.0 times mm, and Select the two largest holes for piloting Pierce these holes at first station and use them for piloting feature (but not less engineering Left idle station (any number e of part Number of stations=5. Preferred staging: 1st station, piercing; 2nd station, notching and piloting; 3rd station, notching and piloting; 4th station, parting off 75mm; e Select sheet width in mm=(blank contour width+3.2) 5mm; sharp allel to the Select feed distance in mm=(blank contour length+2.0) 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- eral rules with fuzzy reasoning. The strip-layout module of the 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 define 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 final sequence of workstations. Completion and development of a software prototype of the system is still in progress and has 96 journal of materials processing technology 195 (2008) 94100 Fig. 1 Execution of the 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 can be retained and utilized suitably for future application and 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 sheet metal forming and drawing. No specific system has been developed for solving strip-layout design problem of progres- proposed system. 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 Artificial 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 195 (2008) 94100 97 F thic of sharp One the tions The oper design tion best rules the as 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 ig. 2 Example component (brass, sheet kness=0.6mm). the part, tolerance on dimensions of the part, direction of edge of stock strip and other technical requirements. important, but very difficult task in strip-layout design is determination of a proper sequence of stamping opera- so that the part can be stamped correctly and efficiently. sequence of operations on a strip and the details of each ation must be carefully developed to ensure that the will produce good sheet metal parts without produc- or maintenance problems. Normally there is no unique solution for the strip-layout design but certain common can be used to guide the design of strip-layout. Some of important rules generally used for strip-layout design are follows: (1) Theinitialoperationssuchassidecutsorcropping,which donotdirectlyaffecttheshapeofthefinalproductshould be made in the first 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 first 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 fixation 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 profile of the blank is complex, then the profile 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) Sufficient 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- holeisconsideredtobesuitableforuseasapilotholeifitiscir- cular in shape, specified 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 first instance. (2) If there are a number of holes, then the location of these holes should be examined. 98 journal of materials processing technology 195 (2008) 94100 Table2Typical prompts, user responses and expert advices generated during execution of the proposed expert system for example component (Fig. 2) Prompt Example data entry Advice to the user Please enter sheet material Brass Model the blank using AutoCAD commands Please enter sheet thickness in mm 0.6 Please enter the command OPRPLAN OPRPLAN Welcome to the module OPRPLAN, developed for identification of operations Enter type of feed Automatic Is camber present in the strip? No Please 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? Yes Following operations are requirednotching, piercing and parting off. Please enter the command OPRSEQ OPRSEQ Welcome 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 PLTSEL Welcome to the module PLTSEL, developed for selection of piloting scheme Is any folded portion on the part? No Enter specified tolerance (in mm) on hole(s) 0.05 Are holes located on opposite sides of the part? Yes Select the two largest holes located on opposite sides of part for piloting (direct piloting). Please enter the command OPRSTAGE OPRSTAGE Welcome 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? Yes Pierce these holes at the same station Are there any complex or weak sections in the external profile of the part? No Is the minimum distance between the edge of the internalfeatureandedgeofdieblock2.0times of sheet thickness (but not less than 3.0mm)? R There is any possibility of future engineering changes in the part? No Please enter command OPRSTAGE2 OPRSTAGE2 Enter number of notches in the part 2 Enter number of holes in the part 2 Number of stations required=5. Preferred staging of operations: 1st station: piercing; 2nd station: punching, notching and piloting; 3rd station: notching and piloting; 4th station: notching and piloting; 5th station: parting off. Please enter command SWLSEL SWLSEL Welcome to the module SWLSEL developed for determining strip width and feed distance Enter blank contour width in mm 62.0 Enter the sharp edge direction of the sheet (along width of sheet) ptmds a Select strip width in mm=65.2 Enter blank contour length in mm 12.7 Enterthesharpedgedirectionofthemovingsheet (along the length of sheet) partmds b Select feed distance (or pitch) in mm=14.7. Please enter command STRPLYT STRPLYT Welcome to the module STRPLYT, developed for automatic modeling of strip-layout Select a start point (220,100) The strip-layout modelled by the system is shown in the drawing editor of AutoCAD a ptmds, perpendicular to the moving direction of strip. b partmds, parallel to the moving direction of strip. journal of materials processing technology 195 (2008) 94100 99 (a) If holes are located in the same direction as feed of the strip, then select one hole, which is nearest to the centroid of the part. (b) If holes are located in the perpendicular direction as that of feed, then select the two largest holes (which are equal in diameter) and that are located at a dis- (3) mendations, design oped. under 3. pr Kno system ing design trial sour ing pr pr ules, and w pr THEN v system of allo tr langua ing base anism, base tion enough necessar of in using data thr stor The the the data of ommendations for the type of sheet metal operations required tomanufacturethepart.ThenextmoduleOPRSEQdetermines the sequencing of recommended sheet metal operations. It takes its input directly from the output data file OPRPLAN.DAT generated during