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The Computer Aided Die Design System(CADDS)developed by Prasad and Somasundaram (1992) also has onemodule for the strip-layout for progressive die. In thismodule,the die type is selected, depending on the input parame-ters. If the selected die is progressive, strip development issubsequently carried out according to the rules incorporatedin the strip-layout module. But the major limitation of thesystemis that it supportsmainly blanking and piercing opera-tions. Singh and Sekhon (2001) developed a low cost modellerfor two-dimensional metal stamping layouts. The software isbased on AutoCAD and AutoLISP. The system is capable ofmodeling circular, polygonal and components having curvedsegments. Alternative strip-layouts are also generated andtested for optimality. The main limitation of the system isthat it deals with single operation stamping dies. Kim etal. (2002) developed a system using AutoLISP language. Thesystem decides the sequencing process of electric productswith intricate piercing and bending operations by consider-ing several factors on bending and adopting fuzzy set theory.It constructs fuzzy matrix for calculating fuzzy relationshipvalue and determines the optimum bend by combining sev-eral ruleswith fuzzy reasoning. The strip-layoutmodule of thesystem is able to carry out bending and piercing operations of3D electric product. Themain limitation of this systemis thatit deals with only bending and piercing operations on progres-sive die. Venkata Rao (2004) presented a strip-layout selectionprocedure pertaining to metal die stamping work. The pro-cedure is based on analytic hierarchy process (AHP). But, thedeveloped procedure is applicable only for simple blankingand piercing dies. Chu et al. (2004) proposed a mathematicaltechnique capable of generating a stamping sequence auto-matically in the design of progressive stamping dies.Agraph isused to represent a stamping part and define the relationshipsbetween its stamping features. The graph is partitioned intosets ofmutually independent vertices using a clustering algo-rithm. Finally, the clustered sets are ordered to give the finalsequence of workstations. Completion and development of asoftware prototype of the system is still in progress and has to be tested against real industrial sheet metal parts havingdifferent shapes.The foregoing literature review reveals that only a fewresearch and development works have been carried out inthe area of automation of strip-layout design for sheet metalwork on progressive dies. Most of the works are concentratedon process planning for sheet metal blanking and piercingoperations. Some commercial computer aided systems areavailable to assist die designers but these are limited only tosimple calculations, strip nesting, retrieval of catalogue dataand compiled database of standard die components, none ofthem directly addressed the problem of strip-layout design.The dependence on experience coupled with the mobility ofdie 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 andexperience of die designers into an expert system so that itcan be retained and utilized suitably for future application anddevelopment purposes. Although some expert systems havebeen developed for die design area, but most of the researchworks are concentrated on nesting and process planning ofsheetmetal forming and drawing.No specific systemhas beendeveloped for solving strip-layout design problem of progres-sive dies. To improve productivity and to build a computerintegrated manufacturing environment, automatic modelingof strip-layout design is essential. The objective of the devel-opment work presented in this paper is to concentrate on theautomation of strip-layout design using production rule-basedexpert systemapproach of Artificial Intelligence (AI). The sys-tem is implemented on PC having AutoDesk AutoCAD 2004software and designed to be loaded in the prompt area ofAutoCAD.2. Recommendations for strip-layoutdesignStrip-layout design for progressive die is to arrange layout ofthe operations and subsequently determine the number ofstations required. For design of strip-layout, the die designerdetermines the sheet metal operations required for manu-facturing the parts, sequencing of operations, selection ofpiloting method, number of stations required and the oper-ations stamped at each station of progressive die. Strip-layoutis determined by the shape of a part and its technical require-ments. It is generally governed by the geometrical features of the part, tolerance on dimensions of the part, direction ofsharp edge of stock strip and other technical requirements.One important, but very difficult task in strip-layout design isthe determination of a proper sequence of stamping opera-tions so that the part can be stamped correctly and efficiently.The sequence of operations on a strip and the details of eachoperation must be carefully developed to ensure that thedesign will produce good sheet metal parts without produc-tion or maintenance problems. Normally there is no uniquebest solution for the strip-layout design but certain commonrules can be used to guide the design of strip-layout. Some ofthe important rules generally used for strip-layout design areas follows:(1) The initial operations such as side cuts or cropping,whichdo not directly affect the shape of the final product shouldbe made in the first stage.(2) If there are suitable holes available in the sheet metalpart, these holes should be used for piloting; otherwiseexternal pilot holes should be introduced according tothe progression. Piercing of these pilot holes is done inthe first stage or just after cropping stage. The loca-tion of pilot holes should always be the far oppositesides of the strip, with the greatest possible gap inbetween. This is to secure the best fixation and position-ing of the strip, once the pilots engage in their respectiveopenings.(3) Distances between the holes punched on one stationmust be larger than a certain value to ensure the diestrength. Pierced holes may be distributed over severalstages, if they are closely located and functionally notrelated.(4) Holeswith high position accuracy requirement should bepunched in one station.(5) Narrow slots and projections should not be allowed in adie as fracture may occur.(6) If the external profile of the blank is complex, then theprofile may be split into simple sections by projecting allthe vertices of the blank vertically up to the edge of thestrip.(7) Idle stations may be used to avoid crowding of punchesand die blocks together. An added advantage is thatFig. 3 – Strip-layout generated by the proposed system forexample component.future engineering changes can be incorporated at lowcost.(8) Bending should preferably be done in the last station orprior to the parting stage, and the rest of the strip shouldbe 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 bestaged.(10) Sufficient bridgewidth should be used in order to providemaximum strength for the bridges.(11) Finally, design the strip in such a way that it enables thecomponent and scrapes to be ejected without interfer-ence.Piloting is an important factor in strip-layout design for pro-gressive die. The strip must be positioned accurately in eachstation so that the operations can be performed at the properlocations. The task of selection of piloting scheme shouldbe viewed as interdependent task in the strip-layout designprocess. A strip-layout design system should support directpiloting, semi-direct piloting and indirect piloting scheme. Ahole is considered to be suitable for use as a pilot hole if it is cir-cular in shape, specified size tolerance is not high, big enoughfor use as a pilot hole, does not lie on the folded portion of theworkpiece, not too close to the edge of the workpiece, and nottoo close to another hole on the workpiece.