环境下的电话机底座模具设计外文翻译.docx

1、环境下的电话机底座模具设计外文翻译外文翻译专 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 undercut

2、s and the creation 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 subassem

3、bly and places it 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 und

4、ercut group is found. 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 prese

5、nted that illustrates 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 inj

6、ection mould assembly, 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 moul

7、ding that prevents 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

8、toggle cam can be 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 extracte

9、d in the parting 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.

10、It is therefore desirable 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 t

11、he user to choose 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

12、still at an experimental 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

13、 of identification 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 unde

14、rcuts. The following 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 ultim

15、ately affect the 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 an

16、d Tan developed a 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 interse

17、cting vectors along a candidate parting direction from randomly created points on the part model, coupled with a genetic algorithm. Chen et al. employed the visibility map method to identify potential undercuts, leading to the selection of the optimal parting direction. One problem with the above me

18、thods is that optimising the parting direction without considering parting lines is incomplete,as a potential undercut could be avoided by appropriately placing the parting lines. Tan et al. presented a method for generating parting lines by adding artefacts to vertical side faces with respect to th

19、e parting direction. However, this task has to be done by the user. At present, the techniques reported for the automatic determination of the parting direction and lines are still far from mature.2.2 Resolving UndercutsOnce the parting direction and lines are determined, the mouldcore and cavity ca

20、n be generated by subtracting the part froma block and subsequently splitting the block along the partingsurface. At this level, the core and cavity are referred to asvirtual core (v-core) and virtual cavity (v-cavity), as the sliders and lifters are yet to be incorporated. In respect to the parting

21、direction, the undercuts on both the v-core and the v-cavitycan be identified, and sliders and/or lifters designed.Shin and Lee presented a method that identifies undercut faces from the v-core and the v-cavity. Side cores are generated by manually specifying the releasing directions. The v-core and

22、 v-cavity are then modified to incorporate the side cores. Rosen also developed an algorithm using a similar approach for creating sliders and lifters. Strictly speaking, the sliders and lifters generated by both of the above methods are only at an abstract level, which is far from being usable in i

23、ndustry.Many more aspects must be considered and designed to make the mechanism a complete functional part in the whole mould assembly.The present study aims at creating complete lifter subassemblies for industrial use. In industrial practice, the parting direction and lines are mainly predetermined

24、 by the plastic part designer, rather than by the mould designer. Apart from the number of undercuts, the appearance of the parting line on the part is also an important factor to consider. The present algorithm takes the v-core and the v-cavity as the input. In addition, the mould-base which is to

25、be used to incorporate the lifter subassembly is already determined. First, the silhouette curves of the faces on the v-core, with respect to the parting direction, are extracted and used to split the corresponding faces. Secondly, undercut faces are derived based on their surface normal and grouped

26、 into individual undercuts. Thirdly, releasing directions are identified for each undercut. Fourthly, for each undercut, a lifter head is generated based on its releasing direction. Finally, other standard components are selected and added to each lifter head to form a whole lifter subassembly.3. Id

27、entifying Internal UndercutsOn the v-core, a face that is adjacent to the part surface is referred to as a CoF. The moving direction of the core during mould opening is specified by “PD-” . For lifter design, the first step is to extract undercut faces from all CoFs. Ideally, the normal at every poi

28、nt on a CoF should be checked. A point whose normal has a positive element along PD- is said to be blocked during mould opening, and its parent CoF is a undercut face. However, it is possible that not all the points on a undercut face are blocked, and a complete search of all the points is not possi

29、ble. Therefore, we propose a preprocessingmethod for the CoFs. The idea is to split a CoFso that the points on each resulting face have a homogeneous normal element along PD. To achieve that, the silhouette curves on each CoF in respect to PD- are extracted and used to split the CoF. For each result

30、ing face, a single point is checked. If it is blocked, its parent face and subsequently the parent CoF is an undercut face. This approach is further illustrated by the example shown in Fig. 3. The part has two undercuts, one of them has a freeform surface. Figure 3(d) shows the extracted silhouette

31、curves and the four faces after splitting where two of them are found to be undercut faces.Once all of the individual undercut CoFs are identified, the next step is to allocate them to different undercut groups (UGp), where each UGp can be handled by a single lifter. Since a lifter moves along its l

32、ateral direction during mouldopening , any two undercut CoFs that are overlapping, viewed from the parting direction, should be handled by a single lifter. Although in industrial practice, two or moreUGps found using this heuristic are sometimes handled by a single lifter, such practice depends main

33、ly on the designers experience and thus is not considered in this study. In each UGp, the undercut CoFs may not be adjacent (or they cannotbe sewed into a single face). In such cases, the non-undercut CoFs that are adjacent to the undercut CoFs will be identified and added to the UGp. Finally, the CoFs in an UGp are se