注塑模具冷却系统的自动设计

1、Computer-Aided Design 37 (2005) 645662Automatic layout design of plastic injection mould cooling systemC.L. Li*, C.G. Li, A.C.K. MokDepartment of Manufacturing Engineering and Engineering Management, The City University of Hong Kong, Tat Chee Avenue, Kowloon, Hong Kong, ChinaReceived 22 March 2004;

2、received in revised form 29 July 2004; accepted 10 August 2004AbstractThis research extends our previous investigation of the automation of the preliminary design stage to the layout design stage of the cooling system design process. While the functional aspects of the cooling system are considered

3、during the preliminary design stage, the layout design stage addresses both the functionality and manufacturability of the design. A graph structure is devised to capture a given preliminary design and a graph traversal algorithm is developed to generate candidate cooling circuits from the graph str

4、ucture. Heuristic search is employed to develop the cooling circuits into the layout designs by generation of tentative manufacturing plans. A framework for fuzzy evaluation of the layout designs is developed to rate the various design alternatives generated. An experimental system is implemented to

5、 verify the feasibility of the approach, and examples generated from the system are presented to illustrate the major steps of the automatic design process.q 2004 Elsevier Ltd. All rights reserved.Keywords: Design automation; Automatic design synthesis; Plastic injection mould; Cooling system design

6、1. IntroductionThe function of the cooling system of a plastic injection mould is to provide thermal regulation in the injection moulding process. When the hot plastic melt enters into the mould impression, it cools down and solidifies by dissi- pating heat through the cooling system. As the cooling

7、 phase generally accounts for about two-thirds of the total cycle time of the injection moulding process, efficient cooling is very important to the productivity of the process. The cooling system also plays an important role in the product quality. A cooling system that provides uniform cooling acr

8、oss the entire part ensures product quality by preventing differential shrinkage, internal stresses, and mould release problems. In addition to the functional aspects, the design of a cooling system should also consider the manufacturability of the system to control the cost of mould construction.Th

9、e process of cooling system design is a complicated process and can be distinguished into three phases:* Corresponding author. Tel.: C852 2788 8432; fax: C852 2788 8423.E-mail address: .hk (C.L. Li).preliminary design, layout design, and detail design. Although, CAD/CAM systems are wi

10、dely used in the design of injection moulds, they are mainly limited to providing geometric modeling tools in the detail design phase. Specialized stand-alone or add-on software packages that provide interactive geometric modeling tools for designing various components or sub-systems of the mould st

11、ructure are also commercially available. However, limited research works on automation tools that can play a more active role in the preliminary and layout design phases have been reported. In a previous research project, we developed a feature-based method which creates the preliminary design autom

12、atically 1,2. Given a plastic part with a complex shape, the feature-based method decomposes the part into simpler shape features, called cooling features. Cooling sub-circuits are then generated automatically to provide the required cooling function for each recognized feature. In the present resea

13、rch, automation in the design process is extended to the layout design phase. Techniques are developed which generate the layout design automatically from the preliminary design by considering both the functional and manufacturing aspects of the cooling system.0010-4485/$ - see front matter q 2004 E

14、lsevier Ltd. All rights reserved. doi:10.1016/j.cad.2004.08.0032. Related workThere are four major areas of research related to plastic injection mould cooling system, namely, computer-aided engineering (CAE) analysis, design optimization, new fabrication technology, and automatic design synthesis.

15、Most of the early research work 37 focused on CAE analysis. After more than two decades of extensive research, commercial CAE packages such as MOLDFLOW and Moldex3D are now widely used in practice to analyze a given design. These CAE methods predict the temperature profile that changes with cooling

16、time. Efficiency and quality can thus be estimated before the actual mold fabrication. While CAE methods are able to analyze a given design, they do not suggest design changes when problems are detected from the results of an analysis. Optimization methods 810 are reported which utilize the CAE anal

17、ysis results to optimize a design. Given an initial cooling configuration design, an objective function is formulated as a measure of the temperature uniformity and cooling efficiency. The objective function is expressed in terms of parameters relating to the configuration of the cooling system and

18、processing conditions. By integrating an optimization algorithm with a cooling analysis algorithm, the initial design can be fine-tuned to optimize the cooling system design.Recently, methods that build better cooling systems by using new fabrication technology have been reported. Instead of the con

19、ventional hole-drilling method to produce straight-line channels, Sachs et al. 11,12 reported a method that takes the advantage of solid freeform fabrica- tion technology to produce conformal cooling channels. Such channels maintain a constant distance from the mould impression, so that accurate tem

20、perature control is possible, even for a part with a complex shape. It has been reported that a more uniform temperature distribution and better dimensional control of the moulded part can thereby be achieved. Sun et al. 13 used CNC milling to produce U-shape milled grooves for cooling channels. Thi

21、s tech- nique is similar to the conformal cooling method, in that the channels are able to follow the shape of the mould impression. As with the conformal cooling method, an improvement in temperature control has also been reported. The focus of our work is in the automatic design synthesis of the c

22、ooling system, which is an area that has not been well investigated. In our previous work 1,2, a feature- based technique for automatic preliminary design genera- tion was developed. The work reported in this paper concentrates on the automation of the layout design. The automatic layout design proc

23、ess is formulated as a heuristic search process. Design automation by heuristic search is a commonly used technique, and has been investigated by the author in the design automation of mechanical devices 14,15. The heuristics that guide the layout design process are based on fuzzy evaluation of the

24、cooling performance and manufacturability of candidate designs. Automaticmanufacturability analysis in various application domains has been studied extensively, and Grupta et al. 16 reported a comprehensive survey. The evaluation method developed in this research was inspired by the method reported

25、by Ong and Chew 17 in the manufacturability evaluation of machined parts and setup plans. The use of fuzzy logic in the evaluation was inspired by the successful applications of fuzzy logic in various aspects of injection mould design research, including parting direction determination 18 and moulda

26、bility analysis 19.3. Overview of the methodIn the preliminary design stage, the major issue to be addressed is the functional requirement, that is, the cooling requirement, of a given plastic part. The preliminary design specifies the type (e.g. U-circuit, parallel channels, bubblers, cooling tower

27、s, etc.), size (e.g. channel length and diameter), and the approximate locations of the cooling elements that form the cooling sub-circuits. Each sub-circuit provides the cooling function that carries away the heat from a region of the part. Our previous research 1,2 shows that the preliminary desig

28、n can be determined mainly from the geometric shape of the part, and a feature recognition approach for automating the design was developed. Given the preliminary design, complete cooling circuits are developed in the layout design phase by connecting the individual sub-circuits and cooling elements

29、 together. The layout design process considers the manufacturability and the feasibility of the physical realization of the cooling circuits.In the current research, the investigation is focused on cooling systems that do not use parallel cooling and have only one cooling circuit. The major items to

30、 be addressed include: the location of the main cooling elements, the channels that interconnect the cooling elements and the sub-circuits, and the locations of the inlet and outlet of the cooling system. The design of each item is inter-related and the layout design process is divided into four maj

31、or stages of operation.1. The derivation of a graph structure that represents the preliminary design and modification of the graph to facilitate subsequent operation.2. The generation of candidate cooling circuits from thegraph structure.3. The generation of layout designs from the candidate cooling

32、 circuits by developing tentative manufacturing plans.4. The evaluation of the candidate layout designs with respect to cooling performance and manufacturability.The first stage of the design process is a preparation step, which serves to derive a representation of the preliminary design in a form t

33、hat facilitates the subsequent operation.C.L. Li et al. / Computer-Aided Design 37 (2005) 645662649Starting from the second stage, a control structure is employed in the layout design process to control the transition of the process from one stage to the next, and the backtracking from a later stage

34、 to a previous stage. The design process is formulated as a searching process, whereby at each stage a candidate design is selected for processing. A search tree is devised to represent the design process, as illustrated in Fig. 1. Each node in the search tree represents either an operation or an ou

35、tput from an operation. As a selection at one stage may eventually lead to a dead-end at a later stage, backtracking is important in the design process. For example, one candidate cooling circuit may eventually lead to a layout design that has a very low rating in cooling performance. To search for

36、an alternative solution, the design process backtracks to the second stage to investigate (i) an alternative cooling circuit from the same inlet; or (ii) an alternative inlet and generate a new cooling circuit, and then repeats the subsequent stages to develop an alternative design. Fig. 2(a) shows

37、the preliminary design of the cooling system of an example part. For illustration purposes, only the core half of the mould is shown. Fig. 2(b) shows the final layout design generated by the design process. Fig. 2(c) shows two of the alternatives generated in the second stage of the design process.F

38、ig. 1. The search tree that represents the layout design process.4. Graph representation and operation on the preliminary designGiven a preliminary cooling system design in the form of a set of sub-circuits consisting of various type of cooling elements, a basic problem in generating the layout desi

39、gn is to identity appropriate connections within the sub-circuits (e.g. the interconnections between a set of parallel channels) and between adjacent sub-circuits (e.g. the connection between two U-circuits in two adjacent layers) so that they can be connected to form a complete cooling circuit. A g

40、raph-based technique is used to solve this problem, and this includes three major steps.1. Devise a graph representation of the preliminary design.2. Add extra nodes and edges to the graph so as to represent the various possible connections between and within the sub-circuits.3. Employ a specific gr

41、aph traversal method to find paths that correspond to candidate cooling circuits.Steps 1 and 2 are described in the following sub-sections, and step 3 will be described in the next section.4.1. Graph representationThe graph that represents the preliminary design is initially constructed with a set o

42、f disjointed sub-graphs, such that each sub-circuit specified in the preliminary design is represented by a sub-graph. Each edge in the sub-graph represents a cooling channel and each node represents an inlet, outlet, or a connection point between adjacent channels. The edges in the graph are labele

43、d with one of the attributes: L-edge, C-edge, or X-edge. L-edge is used for edges that represent straight-line cooling channels (L-channel). C-edge is used for edges that represent cooling channels with complex shapes (C-Channel). X-edge is used for edges that represent channels, which serve to inte

44、r- connect sub-circuits or cooling elements within a sub-circuit (X-channel). Their cooling effects, if any, are not considered and are not specified in the preliminary design. An X-edge is created only during the layout design process.The cooling elements in each sub-circuit are represented as foll

45、ows: for an individual cooling channel, two nodes connected by an L-edge are used; for a planar cooling element (such as a U-circuit or V-channel), a simple path consisting of an alternate sequence of nodes and L-edges is used; for an element with an inlet and outlet that are geometrically close to

46、each other (such as bubblers and baffles), or an element with a complex 3D cooling channel (such as a cooling tower), two nodes connected by a C-edge are used.4.2. Graph modificationA cooling system that does not use parallel cooling and has only one cooling circuit corresponds to a simple path inFi

47、g. 2. The automatic layout design process.the proposed graph representation. To search the graph for an appropriate simple path that connects all or most of the cooling elements specified in the preliminary design, the graph should be a connected graph. However, the graph initially constructed to re

48、present the preliminary design is not connected, because there is no connection between the sub-graphs that correspond to the individual sub-circuits, and a sub-circuit itself may not be represented by a connected component in the graph. Therefore, the initial graph has to be modified by a set of op

49、erations so that the graph becomes connected.4.2.1. Modification of L-graphsThose sub-graphs that contain only L-edges, which have the channels represented by these L-edges lying on the same plane, are labeled as L-graphs. Typical cooling elements captured by L-graphs include U-circuits, V-channels,

50、 and sets of parallel cooling channels lying on the same plane. Each L-graph is investigated and modified, if necessary, to form a connected sub-graph with at least one cycle. The modification is achieved by adding additional channels that connect the end points of the existing channels. Fig. 3(a) s

51、hows the resulting graph structure derived from a simpleFig. 3. Graph representation of the preliminary design of cooling system.example of preliminary design given in Fig. 2(a). Notice that the graph structure consists of two connected sub- graphs, and that each sub-graph is composed of L-edges whi

52、ch represent the cooling elements specified in the preliminary design, and X-edges which are added during graph modification.4.2.2. Merging of sub-graphsThe purpose of merging the sub-graphs is to connect the individual sub-graphs to form a connected graph. As each sub-graph represents a sub-circuit

53、 specified in the prelimi- nary design, the merging process should (i) avoid any major modifications in the sub-graphs; and (ii) use the shortest possible X-edge whenever an X-edge is needed to establish a connection. These ensure that the merging process does not cause signification deviations from

54、 the preliminary design that is represented in the individual sub-graphs. The merging process consists of two stages.In the first stage, only L-graphs are considered. Consider two L-graphs LGi and LGj lying on the planes PLi and PLj. They are merged if either (i) PLi and PLj are parallel and the geo

55、metric distance between them is less than a threshold value; or (ii) PLi and PLj are on the same plane, and there exists a pair of parallel channels, one from LGi and the other from LGj such that the geometric distance between them is less than a threshold value. In the former case, LGi and LGj are

56、merged into a single sub-graph by adding nodes and edges according to the method described below. The corresponding channels represented in the original L-graphs are translated to the plane that is at equal distance from PLi and PLj. In the latter case, LGi and LGj are merged by replacing the pair o

57、f channels (and thus the corresponding edges in the sub-graphs) by a single channel that lies between the two channels.In the second stage, all sub-graphs are considered. Any two sub-graphs are merged if the distance between them is the smallest. The distance between two sub-graphs Gi and Gj is defi

58、ned as the smallest distance among the distances between an edge of Gi and an edge of Gj. The distance between edge ei of Gi and edge ej of Gj is defined as the shortest geometric distance between the channels that are represented by ei and ej. The merging is executed iteratively until all sub-graphs are merged into a single graph.To merge two sub-graphs Gi and Gj (not necessary L-graphs), an X-edge (and possibly an extra node) is added; this corresponds to adding a channel that connects the two sub-circuits represented by Gi and Gj. As the cooling effect of this chann