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英文原文
CONCURRENT DESIGN OF PLASTICS INJECTION MOULDS
Assist.Prof.Dr. A. YAYLA /Prof.Dr. Pa? a YAYLA
Abstract
The plastic product manufacturing industry has been growing rapidly in recent years. One of the most popular processes for making plastic parts is injection moulding. The design of injection mould is critically important to product quality and efficient product processing.
Mould-making companies, who wish to maintain the competitive edge, desire to shorten both design and manufacturing leading times of the by applying a systematic mould design process. The mould industry is an important support industry during the product development process, serving as an important link between the product designer and manufacturer. Product development has changed from the traditional serial process of design, followed by manufacture, to a more organized concurrent process where design and manufacture are considered at a very early stage of design. The concept of concurrent engineering (CE) is no longer new and yet it is still applicable and relevant in today’s manuf acturing environment. Team working spirit, management involvement, total design process and integration of IT tools are still the essence of CE. The application of The CE process to the design of an injection process involves the simultaneous consideration of plastic part design, mould design and injection moulding machine selection, production scheduling and cost as early as possible in the design stag
This paper presents the basic structure of an injection mould design. The basis of this system arises from an analysis of the injection mould design process for mould design companies. This injection mould design system covers both the mould design process and mould knowledge management. Finally the principle of concurrent engineering process is outlined and then its principle is applied to the design of a plastic injection mould.
Keywords :Plastic injection mould design, Concurrent engineering, Computer aided engineering, Moulding conditions, Plastic injection moulding, Flow simulation
1. Introductio
Injection moulds are always expensive to make, unfortunately without a mould it can not be possible ho have a moulded product. Every mould maker has his/her own approach to design a mould and there are many different ways of designing and building a mould. Surely one of the most critical parameters to be considered in the design stage of the mould is the number of cavities, methods of injection, types of runners, methods of gating, methods of ejection, capacity and features of the injection moulding machines. Mould cost, mould quality and cost of mould product are inseparable
In today’s completive environment, computer aided mould filling simulation packages can accurately predict the fill patterns of any part. This allows for quick simulations of gate placements and helps finding the optimal location. Engineers can perform moulding trials on the computer before the part design is completed. Process engineers can systematically predict a design and process window, and can obtain information about the cumulative effect of the process variables that influence part performance, cost, and appearance.
2. Injection Moulding
Injection moulding is one of the most effective ways to bring out the best in plastics. It is universally used to make complex, finished parts, often in a single step, economically, precisely and with little waste. Mass production of plastic parts mostly utilizes moulds. The manufacturing process and involving moulds must be designed after passing through the appearance evaluation and the structure optimization of the product design. Designers face a huge number of options when they create injection-moulded components. Concurrent engineering requires an engineer to consider the manufacturing process of the designed product in the development phase. A good design of the product is unable to go to the market if its manufacturing process is impossible or too expensive. Integration of process simulation, rapid prototyping and manufacturing can reduce the risk associated with moving from CAD to CAM and further enhance the validity of the product development.
3. Importance of Computer Aided Injection Mould Design
The injection moulding design task can be highly complex. Computer Aided Engineering (CAE) analysis tools provide enormous advantages of enabling design engineers to consider virtually and part, mould and injection parameters without the real use of any manufacturing and time. The possibility of trying alternative designs or concepts on the computer screen gives the engineers the opportunity to eliminate potential problems before beginning the real production. Moreover, in virtual environment, designers can quickly and easily asses the sensitivity of specific moulding parameters on the quality and manufacturability of the final product. All theseCAE tools enable all these analysis to be completed in a meter of days or even hours, rather than weeks or months needed for the real experimental trial and error cycles. As CAE is used in the early design of part, mould and moulding parameters, the cost savings are substantial not only because of best functioning part and time savings but also the shortens the time needed to launch the product to the market.
The need to meet set tolerances of plastic part ties in to all aspects of the moulding process, including part size and shape, resin chemical structure, the fillers used, mould cavity layout, gating, mould cooling and the release mechanisms used. Given this complexity, designers often use computer design tools, such as finite element analysis (FEA) and mould filling analysis (MFA), to reduce development time and cost. FEA determines strain, stress and deflection in a part by dividing the structure into small elements where these parameters can be well defined. MFA evaluates gate position and size to optimize resin flow. It also defines placement of weld lines, areas of excessive stress, and how wall and rib thickness affect flow. Other finite element design tools include mould cooling analysis for temperature distribution, and cycle time and shrinkage analysis for dimensional control and prediction of frozen stress and warpage.
The CAE analysis of compression moulded parts is shown in Figure 1. The analysis cycle starts with the creation of a CAD model and a finite element mesh of the mould cavity. After the injection conditions are specified, mould filling, fiber orientation, curing and thermal history, shrinkage and warpage can be simulated. The material properties calculated by the simulation can be used to model the structural behaviour of the part. If required, part design, gate location and processing conditions can be modified in the computer until an acceptable part is obtained. After the analysis is finished an optimized part can be produced with reduced weldline (known also knitline), optimized strength, controlled temperatures and curing, minimized shrinkage and warpage. Machining of the moulds was formerly done manually, with a toolmaker checking each cut. This process became more automated with the growth and widespread use of computer numerically controlled or CNC machining centres. Setup time has also been significantly reduced through the use of special software capable of generating cutter paths directly from a CAD data file. Spindle speeds as high as 100,000 rpm provide further advances in high speed machining. Cutting materials have demonstrated phenomenal performance without the use of any cutting/coolant fluid whatsoever. As a result, the process of machining complex cores and cavities has been accelerated.
It is good news that the time it takes to generate a mould is constantly being reduced. The bad news, on the other hand, is that even with all these advances, designing and manufacturing of the mould can still take a long time and can be extremely expensive.
Figure 1 CAE analysis of injection moulded parts
Many company executives now realize how vital it is to deploy new products to market rapidly. New products are the key to corporate prosperity. They drive corporate revenues, market shares, bottom lines and share prices. A company able to launch good quality products with reasonable prices ahead of their competition not only realizes 100% of the market before rival products arrive but also tends to maintain a dominant position for a few years even after competitive products have finally been announced (Smith, 1991). For most products, these two advantages are dramatic. Rapid product development is now a key aspect of competitive success. Figure 2 shows that only 3–7% of the product mix from the average industrial or electronics company is less than 5 years old. For companies in the top quartile, the number increases to 15–25%. For world-class firms, it is 60–80% (Thompson, 1996). The best companies continuously develop new products. At Hewlett-Packard, over 80% of the profits result from products less than 2 years old! (Neel, 1997)
Figure 2. Importance of new product (Jacobs, 2000)
With the advances in computer technology and artificial intelligence, efforts have been directed to reduce the cost and lead time in the design and manufacture of an injection mould. Injection mould design has been the main area of interest since it is a complex process involving several sub-designs related to various components of the mould, each requiring expert knowledge and experience. Lee et. al. (1997) proposed a systematic methodology and knowledge base for injection mould design in a concurrent engineering environment.
4. Concurrent Engineering in Mould Design
Concurrent Engineering (CE) is a systematic approach to integrated product development process. It represents team values of co-operation, trust and sharing in such a manner that decision making is by consensus, involving all per spectives in parallel, from the very beginning of the product life-cycle (Evans, 1998). Essentially, CE provides a collaborative, co-operative, collective and simultaneous engineering working environment. A concurrent engineering approach is based on five key elements:
1. process
2. multidisciplinary team
3. integrated design model
4. facility
5. software infrastructure
Figure 3 Methodologies in plastic injection mould design, a) Serial engineering b) Concurrent engineering
In the plastics and mould industry, CE is very important due to the high cost tooling and long lead times. Typically, CE is utilized by manufacturing prototype tooling early in the design phase to analyze and adjust the design. Production tooling is manufactured as the final step. The manufacturing process and involving moulds must be designed after passing through the appearance evaluation and the structure optimization of the product design. CE requires an engineer to consider the manufacturing process of the designed product in the development phase. A good design of the product is unable to go to the market if its manufacturing process is impossible. Integration of process simulation and rapid prototyping and manufacturing can reduce the risk associated with moving from CAD to CAM and further enhance the validity of the product development
For years, designers have been restricted in what they can produce as they generally have to design for manufacture (DFM) – that is, adjust their design intent to enable the component (or assembly) to be manufactured using a particular process or processes. In addition, if a mould is used to produce an item, there are therefore automatically inherent restrictions to the design imposed at the very beginning. Taking injection moulding as an example, in order to process a component successfully, at a minimum, the following design elements need to be taken into account:
1. . geometry; . draft angles, . Non re-entrants shapes, . near constant wall thickness, . complexity, . split line location, and . surface finish, 2. material choice; 3. rationalisation of components (reducing assemblies);
4. cost.
In injection moulding, the manufacture of the mould to produce the injection-moulded components is usually the longest part of the product development process. When utilising rapid modelling, the CAD takes the longer time and therefore becomes the bottleneck.
The process design and injection moulding of plastics involves rather complicated and time consuming activities including part design, mould design, injection moulding machine selection, production scheduling, tooling and cost estimation. Traditionally all these activities are done by part designers and mould making personnel in a sequential manner after completing injection moulded plastic part design. Obviously these sequential stages could lead to long product development time. However with the implementation of concurrent engineering process in the all parameters effecting product design, mould design, machine selection, production scheduling, tooling and processing cost are considered as early as possible in the design of the plastic part.
When used effectively, CAE methods provide enormous cost and time savings for the part design and manufacturing. These tools allow engineers to virtually test how the part will be processed and how it performs during its normal operating life. The material supplier, designer, moulder and manufacturer should apply these tools concurrently early in the design stage of the plastic parts in order to exploit the cost benefit of CAE. CAE makes it possible to replace traditional, sequential decision-making procedures with a concurrent design process, in which all parties can interact and share information, Figure 3. For plastic injection moulding, CAE and related design data provide an integrated environment that facilitates concurrent engineering for the design and manufacture of the part and mould, as well as material selection and simulation of optimal process control parameters.
Qualitative expense comparison associated with the part design changes is shown in Figure 4 , showing the fact that when design changes are done at an early stages on the computer screen, the cost associated with is an order of 10.000 times lower than that if the part is in production. These modifications in plastic parts could arise fr om mould modifications, such as gate location, thickness changes, production delays, quality costs, machine setup times, or design change in plastic parts.
Figure 4 Cost of design changes during part product development cycle (Rios et.al, 2001)
At the early design stage, part designers and moulders have to finalise part design based on their experiences with similar parts. However as the parts become more complex, it gets rather difficult to predict processing and part performance without the use of CAE tools. Thus for even relatively complex parts, the use of CAE tools to prevent the late and expensive design changesand problems that can arise during and after injection. For the successful implementation of concurrent engineering, there must be buy-in from everyone involved.
5.Case Study
Figure 5 shows the initial CAD design of plastics part used for the sprinkler irrigation hydrant leg. One of the essential features of the part is that the part has to remain flat after injection; any warping during the injection causes operating problems. Another important feature the plastic part has to have is a high bending stiffness. A number of feeders in different orientation were added to the part as shown in Figure 5b. These feeders should be designed in a way that it has to contribute the weight of the part as minimum as possible.
Before the design of the mould, the flow analysis of the plastic part was carried out with Moldflow software to enable the selection of the best gate location Figure 6a. The figure indicates that the best point for the gate location is the middle feeder at the centre of the part. As the distortion and warpage of the part after injection was vital from the functionality point of view and it has to be kept at a minimum level, the same software was also utilised to yiled the warpage analysis. Figure 5 b shows the results implying the fact that the warpage well after injection remains within the predefined dimensional tolerances.
6.Conclusions
In the plastic injection moulding, the CAD model of the plastic part obtained from commercial 3D programs could be used for the part performance and injection process analyses. With the aid of CEA technology and the use of concurrent engineering methodology, not only the injection mould can be designed and manufactured in a very short of period of time with a minimised cost but also all potential problems which may arise from part design, mould design and processing parameters could be eliminated at the very beginning of the mould design. These two tools help part designers and mould makers to develop a good product with a better delivery and faster tooling with less time and money.
Referenc
1.Smith P, Reinertsen D, The time-to-market race, In: Developing Products in Half the Time. New York, Van Nostrand Reinhold, pp. 3–13, 1991
2.Thompson J, The total product development organization. Proceedings of the Second Asia–Pacific Rapid Product Development Conference, Brisbane, 1996
3.Neel R, Don’t stop after the prototype, Seventh International Conference on Rapid Prototyping, San Francisco, 1997
4.Jacobs PF, “Chapter 3: Rapid Product Development” in Rapid Tooling: Technologies and Industrial Applications , Ed. Peter D. Hilton; Paul F. Jacobs, Marcel Decker, 2000
5.Lee R-S, Chen, Y-M, and Lee, C-Z, “Development of a concurrent mould design system: a knowledge based approach”, Computer Integrated Manufacturing Systems, 10(4), 287-307, 1997
6.Evans B., “Simultaneous Engineering”, Mechanical Engineering , Vol.110, No.2, pp.38-39, 1998
7.Rios A, Gramann, PJ and Davis B, “Computer Aided Engineering in Compression Molding”, Composites Fabricators Association Annual Conference , Tampa Bay, 2001
中文譯文
塑料注射模具的并行設(shè)計
摘要
塑料產(chǎn)品制造業(yè)已在近幾年迅速增長。用于制造塑料部件的最流行的過程之一是注塑。注塑模具的設(shè)計是非常重要的產(chǎn)品質(zhì)量和高效的產(chǎn)品加工。
模具制造公司，誰愿意以保持競爭優(yōu)勢，縮短應(yīng)用系統(tǒng)的模具設(shè)計過程中，設(shè)計和制造領(lǐng)先時代的欲望。模具行業(yè)在產(chǎn)品開發(fā)過程中的重要支撐產(chǎn)業(yè)，作為產(chǎn)品的設(shè)計者和制造商之間的一個重要環(huán)節(jié)。從產(chǎn)品的發(fā)展，改變了傳統(tǒng)的串行設(shè)計過程中，其次是制造，一個更有組織的并發(fā)設(shè)計和制造過程中被認(rèn)為是在一個非常早期的設(shè)計階段。并行工程（CE）的概念已不再是新鮮事，但它仍然是適用的，在今天的化學(xué)品制造acturing環(huán)境相關(guān)。團(tuán)隊合作精神，管理人員的參與，整個設(shè)計過程和集成的IT工具仍然是CE的本質(zhì)。同時考慮應(yīng)用的CE程序設(shè)計的一個注入進(jìn)程涉及的塑料零件設(shè)計，模具設(shè)計和注塑機選擇，生產(chǎn)調(diào)度和成本盡早在設(shè)計雄鹿
本文介紹了注塑模具設(shè)計的基本結(jié)構(gòu)。這個系統(tǒng)的基礎(chǔ)上產(chǎn)生的注塑模具設(shè)計過程的分析，模具設(shè)計公司。注塑模具設(shè)計系統(tǒng)涵蓋了模具設(shè)計工藝和模具知識管理。最后的原則的并發(fā)工程過程的概述，然后被施加到其原理的塑料注射模具的設(shè)計。
關(guān)鍵詞：注塑模具的設(shè)計，并行工程，計算機輔助工程，成型條件，注塑成型，流程模擬
1.導(dǎo)論
注塑模具往往成本很大，不幸的是沒有的模具，它不能是可能浩有一個模制產(chǎn)品。每一個模具制造商都有他/她自己的方式來設(shè)計模具，模具的設(shè)計和建設(shè)一個有許多不同的方式。當(dāng)然，模具的設(shè)計階段，要考慮的最重要的參數(shù)之一是空腔，注射方法，跑步者的類型的，選通的方法，噴射，容量和特性的注塑機的方法的數(shù)量。模具成本，模具的模具產(chǎn)品的質(zhì)量和成本是分不開的。
在今天的環(huán)境，計算機輔助模具填充仿真工具包，可以準(zhǔn)確地預(yù)測任何部分的填充圖案。這可以快速模擬的門安置，并幫助找到最佳的位置。以前的部分設(shè)計完成后，工程師可以在電腦上進(jìn)行成型試驗。工藝工程師可以系統(tǒng)地預(yù)測設(shè)計和工藝窗口，可以獲取信息的過程變量影響性能，成本和外觀的累積效應(yīng)。
2.注塑成型
注塑成型是最好的塑料帶出最有效的方法之一。這是普遍使用的，往往是在一個單一的步驟，使復(fù)雜，成品零件經(jīng)濟(jì)，精確和廢物少。大規(guī)模生產(chǎn)的塑料部件大多采用的模具。后通過的外觀評價及結(jié)構(gòu)優(yōu)化的產(chǎn)品設(shè)計，制造過程中，涉及模具的設(shè)計必須。設(shè)計人員面臨的注塑成型部件的選擇，當(dāng)他們創(chuàng)建一個龐大的數(shù)字。并行工程要求工程師在開發(fā)階段考慮制造過程的設(shè)計的產(chǎn)品。一個好的設(shè)計的產(chǎn)品是不能去的市場，如果其生產(chǎn)過程中是不可能的，或過于昂貴。與從CAD到CAM過程的仿真，快速原型制造的集成可以降低風(fēng)險，進(jìn)一步提升產(chǎn)品開發(fā)的有效性。
3.計算機輔助注塑模具設(shè)計的重要性
注塑模具設(shè)計任務(wù)可以是非常復(fù)雜的。計算機輔助工程（CAE）分析工具使設(shè)計工程師提供了巨大的優(yōu)勢，幾乎和零件，模具及注塑參數(shù)沒有真正的使用任何制造和時間的考慮。嘗試另一種設(shè)計或概念在計算機屏幕上的可能性給出了工程師的機會，以消除潛在的問題，然后再開始真正的生產(chǎn)。此外，在虛擬環(huán)境中，設(shè)計人員可以快速，方便地評估特定的成型參數(shù)對最終產(chǎn)品的質(zhì)量和可制造性的靈敏度。所有theseCAE工具，使所有這些分析，在一米的幾天甚至幾個小時內(nèi)完成，而不是幾周或幾個月需要對實際的試驗和錯誤周期。由于采用的是早期設(shè)計的零件，模具和成型工藝參數(shù)CAE不僅是因為最佳的功能的一部分，節(jié)省時間，也縮短了所需的時間向市場推出的產(chǎn)品，節(jié)約成本是巨大的。
需要設(shè)定的公差，以滿足的塑料部分關(guān)系到成型過程中的各個方面，包括零件的尺寸和形狀，樹脂的化學(xué)結(jié)構(gòu)，使用的填料，模腔布局，澆注，模具冷卻和釋放機制。鑒于這種復(fù)雜性，設(shè)計人員經(jīng)常使用電腦的設(shè)計工具，如有限元分析（FEA）和模流分析（MFA），以減少開發(fā)時間和成本。有限元分析確定應(yīng)變，應(yīng)力和偏轉(zhuǎn)通過劃分成小的元素，這些參數(shù)可以很好地定義的結(jié)構(gòu)的一部分中。 MFA評估澆口位置和大小以優(yōu)化樹脂流動。它還定義的焊接線，過度緊張的地區(qū)，壁和肋骨厚度如何影響流量的位置。其他有限元設(shè)計工具，包