Automated Generation of Lifters for Injection Moulds
An algorithm for automated identification of undercuts 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 subassembly 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 undercut 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 presented 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; Undercut
1. Introduction
As one method for the manufacture of plastic parts, injection
moulding has been well developed. An injection mould
assembly, as shown in Fig. 1, typically consists of a mouldbase,
runners, core and cavity, cooling channels, ejectors, and
other auxiliary 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 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 toggle cam can be adopted. For an internal undercut, a
lifter mechanism (sometimes referred to as angled action split
Correspondence and offprint requests t Dr Y. F. Zhang, Department
of Mechanical Engineering, National University of Singapore, Singapore
119260. E-mail: mpezyfnus.edu.sg
core) is probably the most commonly used method. This
mechanism is illustrated by the example shown in Fig. 2.
During the ejection stroke, the lifter is driven inwards, thereby
withdrawing the obstruction and allowing the moulding to be
extracted 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. 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 [1], were developed
to meet such a need. These packages provide some commonly
used mould layouts and various component libraries for the
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 still
at an experimental stage. None of them have been reported in
any industrial application. This paper focuses on the automated
Fig. 1. An injection mould assembly. |
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发表于 2005-3-2 11:46:00
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