Computer-Based Techniques for Analyze and Simulate of Plastic Part and Mold Design Process

5th International DAAAM Baltic Conference “INDUSTRIAL ENGINEERING – ADDING INNOVATION CAPACITY OF LABOUR FORCE AND ENTREPRENEURS” 20–22 April 2006, Tallinn, Estonia

CUSTOMIZATION OF CAD SYSTEM FOR DECISION SUPPORT OF MOULD DESIGN PROCESS

Hermaste, A., Sutt, A., Kyttner, R.

Abstract: Today, there is a clear trend to predominantly based upon the experience use more plastics and composites in of the mould designer. Mould designers are engineering industry. The time to market required to possess thorough and broad for plastic injection products is becoming experience, because detailed decisions shorter and more crucial, thus the lead require knowledge of the interaction time available to making the injection between different parameters. moulds is decreasing. Proper design of the Today, many CAD systems provide the injection moulding is crucial to producing geometric modeling functions which functional and quality plastic component. facilitate the drafting operations of mould This will need an integrated optimizing of design, but do not provide to mould mould, process and material properties. To designers the inexpensive solution of achieve mould and process optimization, necessary knowledge to develop good early decisions in design process must be mould designs. supported. Computer-aided engineering packages are This paper introduces a decision analyze usually good at data processing for approach to examine the best praxis’s of information-intensive problems. However, companies and use the results of analyzes in mould design a substantial practical to improve the computer supported mould knowledge is needed. Therefore the design process. The pattern recognition methods, how to describe the data of best technique is used together with the practices and to put it into the CAD system questionnaires developed by the authors to to develop the good mould designs, must evaluate technically and economically be taken under consideration. Previous acceptable variations of different plastic works in applying computer techniques in product and injection mould parameters. the field of injection moulding covered To collect the information about best many aspects of injection moulding and praxis’s from different Estonian mould design activities. companies, the developed questionnaires The knowledge based engineering systems were used. [1,5] have demonstrated great potential to Keywords: injection mould design, assist designers in interacting with a CAD decision analysis and support system, system for conceptual design as well as for questionnaires to evaluate the best the final engineering design of a mould by engineering praxis’s, pattern recognition using engineering rules of thumb with methodology, Knowledge Based extensive analytical procedures. The major Engineering advantage of a knowledge based engineering system for mould design is the 1. INTRODUCTION explicit representation and manipulation of knowledge, representing human judge- Nowadays, mould design faces increasing ment, such as rules of thumb and best deadline pressure and the design itself is practices of companies. Knowledge Based

121 Engineering is fundamentally about design  Finding a good reduct (sometimes re-use [2]. It concerns being able to take called feature selection) from advantage of any experience, expertise and attributes of a decision system. other information relevant to each phase of  Extracting knowledge from a the engineering life cycle of a mould decision system. design.  Testing the rules and applying them These knowledge bases can exist in many to make decisions. forms, such as: Our approach was to develop a helpful – spreadsheets system to support effective and rational – engineering formulas decision making in a mould design process – handbooks that uses existing CAD elements described – proprietary software through MS Excel spreadsheets to In this paper an approach to develop a represent collected knowledge. Therefore supportive technique for CAD-based standard MS Excel techniques were used mould design is described. The for modeling decisions. Unigraphics NX MOLDWIZARD has Our proposed decision analysis technique been chosen as base. helps:  To model plastic part, technology 2. APPROACH AND planning and solve mould design METHODOLOGY problems as decision trees.  Analyze decision based models & Engineering Decision Analysis is a process make better design decisions based that allows examining decisions in a on best praxis of companies and structured and efficient manner. Decision using pattern recognition technique. Analysis uses techniques such as Pattern  Customize CAD system (UG NX Recognition [8], Artificial Intelligence [7], MOLDWIZARD with UG Machine Learning [7] and others in order to Knowledge Fusion technique) for discover decision patterns and relationships plastic part and mould design in data, to integrate existing analytical design methods and instruments. It can be  Communicate results of effective viewed as computer automated analysis design options, underlying analysis, and exploration of data and knowledge best design decisions and supporting (best practices) used in companies to assumptions design of plastic parts, their manufacturing The approach is deeply integrated into the technologies, including the design of system processes and not just a simple add injection moulds. on, or interface to an existing system. Knowledge discovery, machine learning or data mining often involve large databases. 2.1 Knowledge acquisition However, the databases are usually built for purposes other than knowledge The overall plastic part manufacturing discovery, and there are often many process includes product design, material redundant attributes in the databases. This selection, manufacturing process selection, increases the complexity of knowledge mould design and mould manufacturing discovery and decreases the quality of the process selection. Mould design process, discovered knowledge. shown in Fig. 1, includes mould base The knowledge discovery requires the design, core/cavity design, etc. In mould following steps: base design process engineers have to  Pre-processing of continuous select mould type, mould dimensions, attributes, optimizing the values machining methods and mould material and eliminating useless attributes. according to plastic product parameters.

122 Cooling and Cavity number Mould base venting system selection design design

Cavity layout Ejection Mould design design system design

Feed system Mould material design selection

Fig. 1. Stages in mould design process

For every decision making stage there has choose from the UG NX MOLDWIZARD, to be developed the most reasonable and shown in Fig. 2. Each mould type has its suitable technique to evaluate collected own specification and number of plates (of knowledge. In this paper we choose, as an type TCP, AP, BP, CP, etc) which depends example, mould base assembly related on different plastic product parameters. decisions making (mould type and Product parameters are also input features dimension selection) to show how the in pattern recognition technique. proposed methodology could be used in the The fundamental objective for pattern Unigraphics NX MOLDWIZARD recognition is to provide a meaningful environment. categorization of the input. It can be considered to be a two stage process: 3. EVALUATION OF COLLECTED feature extraction and pattern classification. A feature is a measurement taken KNOWLEDGE on an input pattern that is to be classified. A suitable feature is one which will Mould base assembly design during provide a definite characteristic of the various stages is different. Mould base input. The pattern classifier is then design includes mould type selection, supplied with a set of features which are mould dimension selection, machining then mapped onto a classification state. methods selection and mould material Given the input features, the classifier must selection. Therefore, these different design decide which type of category matched stages cannot be represented just by one most closely. Classifiers typically rely on kind of knowledge representation. distance metrics and probability theory to Depending on what kind of decisions we do this [8]. have to make, reasonable method or As pattern classifier we choose Bayesian mechanism must be chosen. Each classifiers theory. Based on this theory, manufacturer has developed its own mould decision rule calculation uses the following type standards. Our example based on equation: DME mould base standard components. DME provide six different mould types to

123 (1) 1 T –-1 gi(x) = – (x – μi) Σ i(x – μi) + ln P(ωi) + ci, 2

Type 1 Type 2 Type 3

Type 4 Type 5 Type 6

Fig. 2. Types of mould constructions: TCP, BCP – clamping plates, AP, BP – cavity plates, CP – risers, SPP – support plate, NP1 – intermediate plate number 1, NP2 – intermediate plate number 2. where x is a given feature vector mould base type according to input (parameters of product, cavity layout and criterions of plastic product. After that number), ωi is classes (types of mould numerical values are sorted increasingly. construction), μi is the mean value of the ωi Resorted list is reflected in mould base class and Σi is covariance matrix defined as selection type area (Fig. 3). T Σi = E[(x – μi)( x – μi) ]. Also the appended parameters or indexes 4. INTEGRATION THE DESIGN are used in different Excel spreadsheet files KNOWLEDGE INTO CAD SYSTEM in this paper. Design parameters can capture and represent the information Computer-aided knowledge based which reflects the usability of certain types engineering technique [2] has been used to of elements in mould design process. represent the injection moulding process to Accordingly to these parameters, the assist the overall mould design. The mould designers can evaluate which researchers have started to adopt a elements are the most suitable in a specific knowledge-based approach to solving the mould design project. The meaning of the injection moulding and mould design formula (1) of pattern recognition problems in recent years. DTMOULD-1 [1] technique is to calculate the different is a knowledge based system for injection numerical values for various mould base mould cost estimation. MOULDX [1] and types. It reflects the most approximate EIMPPLAN-1 [1] incorporated

124 mouldability considerations into part In mould base register file “mouldbase_- designs and addressed the conceptual reg_mm.xls”, pattern design development of injection moulded recognition technique was used, to find parts. ICAD [1], the knowledge based what type of mould base components are system of Drexel University [1], was most suitable for different specific developed for injection mould design. criteria’s (for instance DME metrical The commercially available package mould base components). The goal is to Unigraphics NX MOLDWIZARD is a sort different mould base types so what the convenient program to customize the most reasonable mould base type is the different mould design scenarios. first selectable in the “Mold base The single standard elements or Management” dialog window (Fig. 3). It subassemblies could be described in Excel helps the mould designer, to select the spreadsheet format. These available most reasonable mould base type to his spreadsheets could be customized specific mould design project. Also, as according to the specific enterprise needs. more specific data which correspond to To analyze decision based models and input classifier are entered to the mould make design decisions based on best praxis base register file, the overall mould base of companies, the pattern recognition type selection becomes more accurate. technique described afore was applied to Additionally, new parameter called “Index the Excel spreadsheet. The goal was to of usability” was entered. The meaning of extend existing possibilities in the “Index of usability” is to record every Unigraphics NX MOLDWIZARD. It helps single selection of a mould base variant to support the mould design process in tool with specific dimensions in “Moldbase making companies. Management” dialog window and copy For example, if Mouldbase Management that information back to the mould base dialog window in NX MOLDWIZARD database file. It gives to mould designer the was selected (Fig. 3), it is clearly possibility to evaluate which mould base noticeable that two Excel spreadsheet file variants are mostly used in same kind of are used: projects. 1. Mould base register file and 2. Corresponding mould base database file.

125 Type of mould The resorted mould types base catalogue. according to pattern recognition technique in mould base register file.

The indexes which The shortcuts to two reflect the different Excel spreadsheet dimensions of file (mould base selected mould register file and type. specific database file.

Additional variable “Index of usability”.

Fig. 3. Mold base Management dialog window Additional variable “Index of usability” is In the implementation of the proposed visible in MOLDWIZARD “Moldbase methodology in CAD could facilitate the Management” dialog window, in variable utilization of specific knowledge in tool sector (Fig. 3). making companies. The suitability of this methodology was The future direction of this research is to tested on practical examples based on integrate the presented approach with developed questionnaires and pattern Unigraphics Knowledge Fusion language. recognition technique. The results indicates Due to Knowledge Fusion , Unigraphics that pattern recognition technique as CAE system takes advantage of additive element in NX MOLDWIZARD’s engineering knowledge bases in mould base register file and additional conjunction with mould making design variables is a convenient base for further rules and. Therefore the possibilities to research. deliver powerful solutions while permitting knowledge based extension of Unigraphics 5. CONCLUSION by a mould designer could be available.

This paper has presented an approach and 6. ACKNOWLEDGEMENTS methodology of supportive technique of CAD-based mould design procedure based The research was supported by the on existing CAD resources (Unigraphics Estonian Science Foundation (Grant 5620). NX MOLDWIZARD and Unigraphics NX Knowledge Based Engineering approach) with collected experimental data. 7. REFERENCES The proposed methodology does not aim to 1. Mok C. K., Chin K. S. and John K. replace existing systems in companies but L. Ho. An Interactive Knowledge- rather to be a supportive tool for Based CAD System for Mould communicating and sharing specific Design in Injection Moulding heuristical and empirical data. Processes. The International Journal of Advanced Manufac-

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Corresponding author: M.Sc. Aigar Hermaste Department of Machinery Faculty of Mechanical Engineering Tallinn University of Technology, TUT Ehitajate tee 5, 19086 Tallinn, Estonia Tel: Int +372 620 3269 Fax: Int +372 620 3250 E-mail: [email protected]