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International Journal of Production Research Vol 46 No 22 15 November 2008 6269 6304 Mould data management in plastic injection mould industries M L H LOW and K S LEE Department of Mechanical Engineering National University of Singapore 9 Engineering Drive 1 Singapore 117576 Revision received September 2006 In the current mould making industries the challenge is to shorten the mould lead time while maintaining the desired quality This is one of the main demands from customers so as to maintain a competitive edge over the competition While mould industries are always improving on their systems to cater to the rapidly changing plastics industry one of the common issues that are still plaguing them is the management of large quantities of data within a mould project In the current practice of local mould making industries almost all the data for the mould design manufacture and testing stage are often either confused or duplicated unnecessarily As a result it becomes less responsive when changes are required since manual decision making and sorting of these data are required With the increasing complexity of plastic part design the corresponding mould design manufacturing and testing data also increase in both quantity and complexity The usual method of managing these data would take up a substantial amount of time This issue could be resolved by incorporating a data management system that specifically caters to mould making industries into their practice This paper presents a framework for how the data from the different stages of the mould project could be managed more efficiently through the use of templates This framework is divided into modules to cater for the various stages of the mould project A case study is presented to illustrate the proposed framework for mould data management Keywords Mould data management Plastic injection mould Templates Mould design Mould manufacture Mould testing 1 Introduction Plastic injection moulding is a precise manufacturing method of mass producing plastic components Nowadays it produces most of the components of consumer medical electronics and automobile products Lightweight the use of fewer components and having a more versatile design are just some of the reasons for replacing the traditional metallic components with plastic components in these products The product life cycle for most consumer products today is getting shorter as newer and perhaps more trendy designs are made available This is also true for the product life cycles of medical electronics and automobile products when newer and more efficient designs are produced As a result the lead time required for producing the injection moulds for these plastic products gets shorter Corresponding author Email mpeleeks nus edu sg International Journal of Production Research ISSN 0020 7543 print ISSN 1366 588X online 2008 Taylor Francis http www tandf co uk journals DOI 10 1080 00207540701305522 Thus mould making industries have to bear the responsibility of producing the moulds in a shorter period of time Besides having the challenge of producing the moulds at a faster rate product manufacturers customers are also demanding that the mould industries maintain the desired quality of the moulds These demands are to ensure that the customers themselves are able to maintain their competitive edge over the rest While the mould industries are always improving on their systems to cater to the rapidly changing plastic industry one of the common issues that are still plaguing them is on the management of the large quantities of data within a mould project In the current practice of local mould making industries almost all these data were either confused or duplicated unnecessarily As a result it becomes less responsive to changes since manual decision making is required to sort these data The quantity of these mould project data increases as the plastic part design becomes more complex and complicated The corresponding mould manufacturing and mould testing data also increases in both complexity and quantity thus they too contributed to the increase in quantity of the mould project data of a mould project Pressure to improve on the mould making practices have prompted many researchers to research into various methods to help alleviate the many problems faced in the process of design manufacturing and testing of plastic injection moulds Much research work has been done over the years by researchers in the area of the plastics industry which includes the study of the polymer characteristics mould design mould manufacturing and moulding machines parameters etc Much effort has been made by these researchers to achieve the ultimate common goal to bring about an increase in the efficiency in the production of the final plastic products from their resin state namely in the areas of mould design manufacture and testing 1 1 Resin material selection HyperQ Plastic Beiter et al 1991 CIMP Cornell Injection Molding Program Jong and Wang 1989 MAPS Material and Process Selection Lovrich and Tucker 1986 GERES Nielsen et al 1986 etc are systems that have been developed for the selection of plastic materials for the plastic part based on part requirements using a knowledge based approach These systems use searching mechanisms and heuristics to select the material for the plastic part in both a qualitative and a quantitative manner Although selecting the best material for a plastic part is an important issue not to be missed in the design process most of these systems are developed as a stand alone system and were not integrated into the design of both the plastic part and mould 1 2 CAD mould design systems Many knowledge based systems KBS for the design of plastic injection moulds have been developed over the years some of which have emerged as commercial software IMOLD Intelligent Mould Design Lee et al 1997a is one of the knowledge based systems that have been marketed as commercial mould design software This system is built on Unigraphics platform and uses IntelliCAD ICAD as a tool to process design knowledge Other knowledge based systems developed for plastic injection moulds include IKMOULD Mok et al 2001 ESMOLD Chin et al 1996 the KBS of the National Cheng Kang University at 6270M L H Low and K S Lee Taiwan Lee et al 1997b and the KBS of Drexel University Tseng et al 1990 etc However all these systems did not consider the initial design before actual mould design though some of them have a comprehensive library of standard components A parametric controlled cavity layout design system for a plastic injection mould that makes use of only standard layout designs has been developed Low and Lee 2003a and since this system utilizes configurations database this system can be easily incorporated into the initial design of plastic injection moulds This research work attempts to introduce standardization into the cavity layout design by having only standard cavity layout designs in its database 1 3 Parting design The parting design of plastic injection moulds has been explored by a number of researchers The methods used for the parting line and direction search includes using topological based graph described by a B rep solid model multi objective function criteria fuzzy decision making and feature recognition etc Chen et al 1993 gave algorithms for dividing a given object into pockets for which visibility and demouldability can be determined independently for constructing visibility maps and for selecting an optimal pair of parting directions for a mould that minimizes the number of cores Chen et al 2000 researched into a method of automatic mould parting direction selection in computer aided design of moulds and dies The minimum volume bounding box of the model is found first for a given 3D CAD model A dexel model is constructed along each of the three pairs of parting directions which is defined based on the bounding box surface normal vectors Parting lines corresponding to the three possible parting directions are estimated using a slice method A designer s preferences coded as fuzzy weighting factors are set up for the evaluation of the most promising parting direction Weinstein and Manoochehri 1997 present a methodology for obtaining an optimal design of a mould tool for an injection moulded or a die cast part based on part geometry The methodology uses multi objective function criteria It considers how parting line complexity draw depth number of undercuts number of unique side cores and mould complexity affect manufacturability and cost The design variables selected are draw direction range and parting line location The draw direction range limits possible parting line locations to those not associated with undercuts These design variables can be extracted from the part geometry by dividing the surfaces into concave and convex regions The concave and convex regions determine the allowable draw range and parting line location for the part respectively A non linear programming technique generates the optimal mould configuration solution Li et al 2005 proposed a new approach to automate the design of parting surfaces for plastic injection moulds The new method tackles the issue of the automatic generation of a polygonal complex that is required for boundary curve interpolation The mesh that defines the interior of the surface patch is generated using medial axis transform and optimization Upon subdivision the mesh generates a smooth surface patch that connects to neighbouring patches to form the entire parting surface The major advantage of this new approach is that the subdivision surface is generated by a standard subdivision scheme that facilitates the Mould data management in plastic injection mould industries6271 development of any downstream applications such as CNC tool path extraction on the surface These methods are capable of auto parting line and direction search to a certain extent until the plastic product becomes more complex At this stage some user intervention is needed to select and create the parting line 1 4 Undercuts interference elements detection Like the parting design the detection of undercuts or interference elements has captured the attention and interest of many researchers Based on the concept of blockage in a given direction a subdivision technique is developed by Hui 1997 to evaluate the geometry of an undercut With the notion of internal and external undercut the mouldability of a component is studied External undercuts can be resolved with side cores while internal undercuts can be resolved by the use of split cores However the use of split cores requires considerations as to whether sufficient space is available for their movement A local and a global blockage test are introduced to detect any interference between the moulded component and a side core or a split core A search strategy is also developed for selecting a suitable combination of main parting side core and split core directions Fu et al 1999 developed an algorithm for the automated recognition of undercut features for determining the optimal parting direction of injection moulded parts Based on the 3D solid model of a moulded part described in boundary representation B Rep the geometrical entities and the information of a solid model and their topological relationships are extracted According to this information the criteria under which the undercut feature is formed are set up and the undercut feature directions the withdrawal directions of side cores or side cavities are identified The optimal parting direction is chosen based on the criterion of maximizing undercut feature volumes in each undercut feature group On the other hand Ye et al 2001 describes a hybrid method to recognize undercut features from moulded parts with planar quadric and free from surfaces The hybrid method takes advantage of graph based and hint based approaches Various undercut features including interacting undercut features are defined by extended attributed face edge graphs EAFEG Unlike conventional graph based methods which recognize features by graph matching the new approach recognizes the undercut features by searching the cut sets of subgraphs Face properties and parting lines are used as hints to guide the search of cut sets To recognize undercut features from parts with free form surfaces a convex hull algorithm is used to determine the face properties positive negative and horizontal Lu and Lee 2000 introduced a three dimensional ray detection method to detect the interference elements The method includes sweeping a solid model recognizing the geometric feature and extracting the shell of the interference element A vector plane approach is proposed to solve release directions of the interference shell The approach uses vector planes to collect the normal vectors of the shell surface and then the release direction of a vector plane is determined by two extreme vectors on the plane The release directions of an interference element are obtained by intersecting the release directions of all vector planes The common techniques that are being used are graph based methods recognition of interacting features Minimal Condition Subgraph MCSG and 6272M L H Low and K S Lee visibility map V map etc These techniques are otherwise collectively known as feature recognition techniques These research works have found usefulness in the creation of side cores slider heads and lifter heads all of which are designs that cater specifically to the external and internal undercuts of the plastic part This is to ensure a smooth release without causing any damage to the moulded part during ejection due to interference of the part and mould 1 5 Filling design The filling design involves the design of both the gate and runner An abductive network method has been used to design the gate of freeform injection moulds Lin 2001 This research makes use of simulation annealing SA optimization algorithm with a performance index to obtain a perfect part Another system CADFEED Computer Aided Design of the FEED system of the plastic injection mould was developed by Ong et al 1995 to design accurately and efficiently the type location and size of a gating system of a plastic injection mould However CADFEED is not a viable system in the current CAD industry because it uses AutoCAD a 2D CAD software though it may be a low cost system The current CAD industry is moving towards 3D CAD because of the many benefits derived from it On the other hand some researchers such as Irani et al 1995 and Lee and Stevenson 1999 have made use of finite element analysis to assist them in the design of the runners for plastic injection moulds 1 6 Cooling design Meanwhile many researchers have also done impressive works for the cooling design of plastic injection moulds They have made much effort and the techniques that they used include simulation annealing SA optimization boundary element design sensitivity analysis finite element analysis and feature based approach A 3D numerical simulation using the boundary element method is proposed by Zhou et al 2002 which can predict the cavity temperature distributions in the cooling stage of injection moulding The radii and positions of cooling lines are chosen as design variables and the boundary integral sensitivity formulations are deduced For the optimum design of cooling lines the squared difference between the objective temperature and the temperature of the cavity is taken as the objective function Based on the optimization techniques with design sensitivity analysis an iterative algorithm to reach the minimum value of the objective function is introduced which leads to the optimum design of cooling lines at the same time Tang et al 1997 presented a methodology for optimal design of cooling systems for multi cavity injection mould tooling After the part layout and the injection mould are designed the methodology optimizes cooling system layout in terms of cooling channel size locations and coolant flow rate The mould cooling design is modelled as a non linear constrained optimization problem The objective function for the constrained optimization problem is stated as minimization of both a function related to part average temperature and temperature gradients throughout allthecavities Theconstrainedoptimaldesignproblemissolvedusing Powell s conjugate direction with the penalty function method The objective function is evaluated using finite element analysis solving the transient heal Mould data management in plastic injection mould industries6273 conduction problem A matrix free Jacobi conjugate gradient algorithm of Galerkin finite element method is utilized to simulate transient heat conduction Li 2001 researched into using a feature based approach to design the cooling system A plastic part with a complex shape is decomposed into simpler shape features The cooling systems of the individual features are first obtained and they are then combined to form the cooling system of the entire part Decomposing a complex shape into shape features is a feature recognition problem in which a new algorithm for the recognition of features specific to cooling system design is developed Lin 2002 uses the cooling system as the major control parameter to achieve an optimal design for a simulated injection mould model When the cooling system parameters are given i e cooling channel diameters cooling channel spacing and cooling line equations the product performance warpage can be predicted accurately by the developed abductive network model The injection mould part line of the parameter equation is formulated by the abductive network method to limit the number of parameters in the cooling system The optimal cooling system parameters can then be reached through a SA optimization algorithm with a performance index to obtain perfect parts Sun et al 2004 proposed a milled groove insert method in mould cooling for cooling of medium and larg