This paper presents a methodology of a computer-aided process planning system for an injection mould component, slider, which will facilitate the standardisation of process planning and significantly reduce lead-time. A combination of generative and variant approach is used for the development of the system. The input to the system is a 3D slider model. Firstly, the system classifies the slider types and extracts the feature parameters from the model. Each slider type refers to a standard process plan template, in which a set of processes in sequence is presented. Secondly, the system selects machines, cutters, fixtures and cutting parameters for each process in the plan template based on the actual dimensions of features and the available machining resources. The process plan execution is then simulated on the screen step by step. Although the system is developed for sliders, the approach is generic in nature and could be easily extended to include other mould components, such as lifters, mouldbases, etc.
Process planning is a systematic determination of the detailed methods by which parts can be manufactured from raw material to a finished product. It is an important stage linking design and manufacturing in an industrial organisation. In general, it includes material selection, process selection, machine tool selection, tool selection, sequence of operation, fixture selection, process plan documentation and so on. As process planning is a very complex job, a computer needs to be used if the task is to be accomplished within a feasible period of time. On the other hand, optimal process plans do not usually remain static but change with changing conditions, such as lot sizes, availability of equipment, and any emerging new technology. It is, therefore, a major advantage of computer-aided process planning (CAPP) that it accounts for any variation in the manufacturing parameters. It has been recognised that CAPP bridges the gap between engineering design and manufacturing and forms a key factor in integrating the activities in a manufacturing organisation [1].
With the rapid development of computer-aided techniques in the last two decades, many CAPP systems have been developed and reported [2]. These developed CAPP systems are based on variant approach or generative approach. In the variant approach, a new process plan is produced by retrieving the plan for a similar part and manually modifying the plan to fit the part at hand; but in the generative approach the system uses the knowledge about the manufacturing processes to create the process plan from scratch. Some variant systems include AUTOPLAN [3], AUTOCAP [4], and generative systems include KAPLAN [5], QTC [6], GENPLAN [7], and TVCAPP [8]. The presence of difficulties with a purely generative system resulted in some researchers proposing a semi-generative approach to CAPP, which is basically a combination of the variant and generative methods. The aim of such system is to reduce user interaction by incorporating standard operation sequences, heuristic, rules and mathematical formulae to the system [9]; COMPLAN [10] is such a system.
In spite of enormous efforts, reported CAPP systems still lack industrial acceptance. The researchers have restricted their problem domains to handle only certain aspects. Some considered only rotational parts while others concentrated on prismatic ones only, thus incorporating a very limited number of manufacturing features. Furthermore, currently there are no CAPP systems for mould manufacturing and it leads to motivate this research.
This paper presents a CAPP for the manufacture of sliders. A combination of variant and generative approach is used for the development of the system. The input to the system is a 3D slider model. Firstly, the system classifies the slider types and extracts the feature parameters from the model. Each slider type refers to a standard process plan template, in which a set of processes in sequence is presented. Secondly, the system selects machines, cutters, fixtures and cutting parameters for each process in the plan template based on the actual dimensions of features and the available machining resources. The process plan execution is then simulated on the screen step by step. The tests demonstrated that such an approach is very close to the current industrial practice and has high adaptability.
In this paper, a hybrid approach is proposed to develop a CAPP system for the manufacture of sliders. The idea and methodology demonstrates an approach to CAPP which is generic in nature and can be used for the development of the process plan for other components of an injection mould. It is hoped that the developed methodology would make a significant contribution in moulding industry. The advantages of the developed CAPP system are given as follows:
1.
The system is industry-based and user friendly.
2.
It updates process plans easily whenever a design is changed and it is flexible and expandable.
3.
It can be easily adaptable in any mould shop by simply keying in the relevant information of resources available in that shop and it can work when new machines or cutters are made available by only updating the databases.
4.
The system enables a reduction of overall lead-time and improves the quality of mould significantly.
However, the developed system has some limitations too. The major limitations are that customisations are needed and the system can only be interfaced with IMOLD.
