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1、外文翻译专 业 材料成型及控制工程 学 生 姓 名 班 级 材控08-1 学 号 指 导 教 师 Automated Generation of Lifters for Injection MouldsY. F. Zhang, H. H. Liu and K. S. LeeDepartment of Mechanical Engineering, National University of Singapore, Republic of SingaporeAn algorithm for automated identification of undercuts and the creatio
2、n of the lifter subassembly in plastic injection mould design is described. The algorithm is suitable for injection mould design in a 3D mode. The input to the software is a 3D part model, parting direction and lines, and a mould-base. The software then generates the lifter subassembly and places it
3、 properly in the mould-base. This is accomplished in four steps. First, the so-called virtual core and cavity are generated without considering any undercuts. Undercut faces on the part are then identified and undercut groups are formed. Secondly, the releasing direction of each undercut group is fo
4、und. Thirdly, for each undercut group, a lifter head based on its releasing direction is created. Fourthly, other standard components of a lifter assembly are retrieved and attached to the corresponding lifter head within the mould-base at the correct location. A case study is presented that illustr
5、ates the efficacy of the technique for the automated design of lifters to fulfil a real industrial requirement.Keywords: CAD; Injection mould design; Lifter; Undercut1. IntroductionAs one method for the manufacture of plastic parts, injection moulding has been well developed. An injection mould asse
6、mbly, typically consists of a mouldbase, runners, core and cavity, cooling channels, ejectors, and otherauxiliary components. Among these functional parts, the core and cavity, which form the shape of the moulding, are at the centre of a mould. An undercut is any portion of the moulding that prevent
7、s it from being extracted from the impression, along the parting direction. An undercut adjacent to the cavity is usually referred to as an external undercut, and one adjacent to the core as an internal undercut. For an external undercut, a slider mechanism, such as a finger cam or toggle cam can be
8、 adopted.For an internal undercut, a lifter mechanism is probably the most commonly used method. This mechanism is illustrated by the example shown . During the ejection stroke, the lifter is driven inwards, therebywithdrawing the obstruction and allowing the moulding to be extracted in the parting
9、direction.Traditionally, mould design is typically carried out on the drawing board or by using 2D computer-aided drawing packages. With the development of 3D computer-aided design (CAD) techniques, product design and NC tool-path generation are commonly carried out in the 3D mode. It is therefore d
10、esirable to design the mould in the 3D mode, in order to shorten the lead time. Recently, it has been observed that several CAD packages, such as IMOLD , were developed to meet such a need. These packages provide some commonly used mould layouts and various component libraries for the user to choose
11、 from. The design tasks involving geometric reasoning,such as slider and lifter design, are still performed interactively. There has also been some published work on undercut detection and the design of side cores (slider and lifter). However, the reported automation techniques are still at an exper
12、imental stage. None of them have been reported in any industrial application. This paper focuses on the automated identification of internal undercuts and the generation of lifers.However, the technique developed could be extended to the design of sliders.2. Previous WorkIn the area of identificatio
13、n and resolving undercuts for mould design, most of the published work focuses on searching for the optimal parting direction and the parting lines, in order tominimise the number of undercuts. There are also a few reported techniques on how to incorporate side cores to resolve undercuts. The follow
14、ing sections review some of the previous work in these two categories.2.1 Optimisation of Parting Direction and LinesThe selection of the parting direction and the parting lines of a part is critical to the mould design, as the decision will decide the number of undercuts, and ultimately affect the
15、cost of the mould. Ravi and Srinivasan proposed a set of criteria that affect the parting direction and line selection. From a geometric point of view, the possible candidates for such selection are infinite. Various knowledge-based or optimization schemes have been proposed. Hui and Tan developed a
16、 heuristic-based approach for determining parting directions based on the balance of the preference value (the ratio of the projected area in a given direction to the maximum projected area) and the blocking factor. Sawai and Kakazu constructed a similar evaluation factor by intersecting vectors along a candidate parting direction fro
