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This paper describes an automated design system developed for design of progressive die. The proposedsystem is organized in 27 knowledge-base modules. The production rule based knowledge-base system(KBS) approach is utilized for constructing the system modules. Modules are user interactive anddesigned to be loaded into the prompt area of AutoCAD. The system is capable of automating all majoractivities of design of progressive die such as checking the design features of sheet metal parts, designof strip-layout, selection of progressive die components, modeling of die components and die assembly,and selection of materials for progressive die components. 33292
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The system is implemented on a PC havingAutoCAD software and therefore its low cost of implementation makes it affordable by small andmediumsize enterprises. 1. IntroductionA progressive die is used worldwide for mass production ofsheet metal parts. Design of progressive die is a complex andhighly specialized procedure and typically progressive die designtakes 20% of the lead time from the concept design to the finalstamping manufacture. The perse nature of products producedby progressive die demands a high level of knowledge on the partof the die designer that can only be achieved through years of prac-tical experience. Checking the design features of sheet metal parts,design of strip-layout, selection of die components, selection ofmaterials for die components; and modeling of die componentsand die assembly are major activities for designing a progressivedie. The traditional methods of carrying out these tasks requireexpertise and are largely manual and therefore tedious, time con-suming and error-prone. The quality of die design depends to alarge extent on the designer’s skill, experience and knowledge. Anumber of researchers have tried to develop computer aided sys-tems for progressive die. For example, Murikama and Shirai(1989) developed a CAD/CAM system which is capable of generat-ing assembly and dimensioned part drawings as the final outputbut the strip and die layouts have to be done manually by the de-signer. Researchers at National University of Singapore and Insti-tute of High Performance Computing, Singapore also reported tohave developed an integrated modelling and process planningsystem (2002) for planning bending operations of progressive dies.Sima, Lee, and Jang (2004) carried out the study on the develop- ment of center carrier type progressive die for U-bending part pro-cess. Ghatrehnaby and Arezoo (2009) reported to develop anautomated nesting and piloting system for progressive dies. Someresearchers reported to have developed intelligent CAD systems forprogressive die. For example, Duffy and Sun (1991) developed aknowledge-based system for the design of progressive stampingdies using a feature-based approach. Lee, Lim, and Nee (1993)developed IKOOPP, an intelligent knowledge-based process plan-ning system for the manufacture of progressive die plates. Cheok,Foong, and Nee (1996) reported to have developed an intelligentplanning aid for progressive die design using PC developmenttools. Ismail, Chen, and Hon (1996) have also worked on expertsystems for progressive piercing and blanking die design. Zheng,Wang, and Li (2007) have developed intelligent CAPP system forautomobile panels.Commercially available CAD/CAM systems are providing a greatdeal of assistance in drafting and analysis in die design process, buthuman expertise is still needed to arrive at the final design. Also,the high cost associated with setting up such systems is quite oftenbeyond the reach of small-scale sheet metal industries. Someresearchers have used AI techniques to conserve experiencedbased knowledge of die design experts. But the use of these sys-tems is very limited. They can either handle only blanking andpiercing operations or parts with relatively simple geometry. Itappears that the development in progressive die automation havenot kept pace with advancement in AI technology. Thus, there is astern need to develop an automated design system for progressivedies having low cost of implementation using both CAD and AIapproach collectively, which can be easily affordable by smalland medium scale sheet metal industries. This paper describes anautomated design system for accomplishing the tedious and time consuming design task of progressive die with very ease and in avery short time period.2. Considerations for design of progressive die2.1. Strip-layout designAs a first step in the planning of manufacture of a sheet metalpart, it is useful to check whether certain of its design featuresare conducive to ease of manufacture. Such checks are useful toavoid manufacturing defects, section weakness, and need of newdies, tools or machines. Dimensions and location of internal andexternal features such as holes, extended holes, internal contours,external contours, cuts, notches, bosses, cups, slots and bendsshould be tested against rules of good practice. Strip-layout designis to arrange layout of the operations and subsequently determinethe number of stations required. Strip layout is mainly governed bythe geometrical features of the part, tolerance on dimensions of thepart, direction of sharp edge of stock strip and other technicalrequirements. There is no unique best solution for the strip-layoutdesign but the some basic guidelines (Kumar, 2006) are generallyconsidered during this important activity.2.2. Selection of die componentsDie block, die gages, stripper plate, punch plate, back plate,punches, pilots, die-set and fasteners are major components of aprogressive die. The size of the die block depends on sheet thick-ness, direction of sharp edge, strip-width, type of die materialand length of strip-layout. Size of die gages mainly depend onthe sheet thickness. But the minimum thickness of die gauges isalso restricted by risk of camber, which may occur during heattreatment process of their manufacturing. The width of die gagesmay sometimes be increased to maintain the symmetry of progres-sive die. Strippers are of two types: fixed or stationary and springloaded or movable. The size of stripper plate corresponds to thesize of die block. The width of channel in the stripper should beequal to the strip width plus adequate clearance to allow for vari-ations in the strip width. The punch plate is used to position andsupport the punches. The punch plate should have sufficient thick-ness for providing enough support, good dowelling to ensure accu-rate alignment and adequate screws to overcome the stampingload. The thickness of punch plate is a function of punch diameter.In case two or more than two punches are mounted, the punchhaving biggest diameter is considered for selecting suitable thick-ness of punch plate. Punch plate thickness should also be propor-tional to the overall punch height. The length and width of thepunch plate is usually same as of die block. Hardened back-upplates are normally interposed between small perforator punchesand the punch holder. The backup plate is generally about 10–12 mm thick. In the selection process of die-set of progressivedie, one should consider part quantity, dimensional tolerance ofthe component, clearance between punch and die, and clearancebetween guideposts and bushings. It is considered a good practiceto use steel die-sets to prevent fractures of the die holder. Themainsteps usually carried out for selecting a die-set are determinationof the type of the die-set (two pillar, four pillar, rear pillar, centerpillar, diagonal pillar, etc.), selection of the die area and choice ofthe die holders. Selection of the kind of die-set depends upon thetype of sheet metal operation, part quantity and job accuracy.The dimensions of the die-set depend upon the length and widthof the die and its placement in the die-set. If available, standarddie-sets can be used or these can be custom-built. In industries,the number and size of fasteners (screws and dowels) are selectedon the basis of size of die block. Dowels are usually located neardiagonally opposite corners of the die block, for maximum locatingeffect. Screws and dowels are preferably located about 1.5–2.0times their diameter from the outer edges or the blanking contour.Screws are used to assemble the die details on top and bottom bol-ster of die-set. The number and size of screws may be calculated byestimating the space available and the load to be resisted.2.3. Selection of materials for die componentsSelection of materials for progressive die components for a gi-ven application depends on which die failure mechanisms domi-nates. For selecting the suitable material for a progressive diecomponent, the die designer properly investigates the functionalrequirements of that component and then a critical study is carriedout to identify the required mechanical properties and possiblecauses, which may result the failure of the component. The basicidea of a die designer is to select a suitable material for a particulardie component such that all other failure mechanisms except wearare eliminated. The wear can then be optimized to match the re-quired production quantity of sheet metal parts. To obtain longerdie life and hence higher productivity, tool steels are being widelyused as materials for die components. One of the most importantadvantages of using steels as cutting tool materials is that, theyare originally soft and machineable, by applying suitable heattreatment, they become extremely hard and wear resistant. Selec-tion of suitable hardness range of selected materials of die compo-nents depends on the geometry of the part to be manufactured onprogressive die.2.4. Modeling of die components and die assemblyModeling of progressive die involves the modeling of plate ele-ments and die-set. Modeling of plate elements requires the dimen-sional data of die block, die gages, stripper plate, punch plate andback plate. The dimensions of plate elements as recommendedby an intelligent system and stored in various output data filescan be utilized for their modeling. Drawing commands of AutoCADsuch as LINE, PLINE, CIRCLE, FILLET, LAYER etc. can be invoked formodeling of plate elements. Further for automatic modeling ofplate elements, one may recall the strip-layout stored in a fileand may insert it appropriately in the plan view of plate elements.For automating modeling of die-set, the dimensional data of bot-tom and top bolster of die-set, diameters of guide pillars and guidebushes stored in an output data file can be utilized.Based on the above considerations, an automated systemnamely INTPDIE is developed for design and modeling of progres-sive die components.3. Automated design system: INTPDIE3.1. Procedure for development of the proposed automated designsystemThe procedural steps for the development of the proposed auto-mated system include knowledge acquisition, framing of produc-tion rules, verification of production rules, sequencing ofproduction rules, identification of hardware and computer lan-guage, construction of knowledge base, choice of search strategy,and preparation of user interface. The technical knowledge forthe development of system is collected through die design hand-books, industrial brochures, technical reports, and highly experi-enced progressive die designers and tool manufacturers. Theknowledge thus acquired is analyzed and tabulated in form of pro-duction rules of ‘IF-THEN’ variety. The production rules so framedare verified from a team of progressive die design experts and tool manufacturers. Production rules in each module of the proposedsystem are arranged in a structured manner.