The application of state of the art manufacturing processes has always been constrained by the capabilities either from technical limitations such as limited materials and complex part geometries or production costs. As a result, hybrid manufacturing processes – where varied manufacturing operations are carried out – are emerging as a potential evolution for current manufacturing technologies. However, process planning methods capable of effectively utilising manufacturing resources for hybrid processes are currently limited. In this paper, a hybrid process, entitled iAtractive, combining additive, subtractive and inspection processes, along with part specific process planning is proposed. The iAtractive process aims to accurately manufacture complex geometries without being constrained by the capability of individual additive and subtractive processes. This process planning algorithm enables a part to be manufactured taking into consideration, process capabilities, production time and material consumption. This approach is also adapted for the remanufacture of existing parts. Four test parts have been manufactured from zero and existing parts, demonstrating the efficacy of the proposed hybrid process and the process planning algorithm.
Manufacturing technology has gone through a number of evolutionary developments over the past decades [1]. However, due to the technological constraints of individual manufacturing processes, it is not always feasible to produce components in terms of material, geometry, tolerance and strength etc. [2]. Additive manufacturing methods provide the capability to automatically produce components with various part designs including complex internal features. However, a number of limitations hinder its further development, such as limited materials available, long production times, diminished surface quality and reduced dimensional accuracy, compared to computer numerically controlled (CNC) machining. On the other hand, CNC machining technology, a subtractive process, is typically used for hard material machining, due to high accuracy and the relatively short production times achievable. Nevertheless, certain features like internal cavities are still difficult to produce due to limited tool accessibility. In recent years, the on-going industrial trend towards energy efficiency and material consumption requires new technology to be developed. As a result, the concept of hybrid manufacturing begins to emerge [1]. However, none of these hybrid processes addresses the material consumption issue. Products that are out of tolerance are abandoned resulting in considerable waste and in turn, increased overall production and part cost.
Process planning techniques have nowadays been widely used in various domains of production. Generally, process planning comprises of the selection and sequencing of processes and operations to transform a chosen raw material into a finished component [3]. Nonetheless, the majority of process planning research focuses on machining technology. Furthermore only limited process planning approaches have been developed for the hybrid processes.
In this paper, a hybrid process entitled iAtractive, combining additive (i.e. Fused Filament Fabrication, FFF [4]), subtractive (i.e. CNC machining) and inspection, along with a reactionary process planning algorithm is proposed. This will provide the designer with enhanced manufacturing capability and flexibility. The process planning algorithm enables a part to be manufactured either from zero or an existing part. The major elements for realising such an algorithm are described in detail in the proceeding sections. Finally, two case studies were conducted. In the first case study, the test part consists of internal features has been accurately manufactured as one complete unit. Three identical parts in the second case study were manufactured from three existing parts with different features. These case studies demonstrate the efficacy of the proposed hybrid process and the process planning algorithm.
A number of inherent technical limitations of individual manufacturing processes stimulate this research on hybrid manufacturing. This paper introduced a novel hybrid process combining additive, subtractive and inspection processes in a serial manner. A reactionary process planning algorithm is proposed, organising manufacturing operations and sequences, and determining appropriate parameters during production. It provides an intelligent solution to accurately manufacture complex products (i.e. internal features) in terms of production time, material consumption and reuse. Based on the given part design and available manufacturing resources, a static plan is first generated, which is ready for use but will be further updated according to the feedback of inspection operations during production. The case study demonstrated the efficacy of the proposed process planning algorithm and indicates that the iAtractive process has better flexibility and capability as compared to individual additive and subtractive processes. Future work will focus on developing and extending RP2A for accurately manufacturing parts with sculptured and internal features. A modified ESO method will also be developed, further reducing material consumption and introducing the concept of dematerialisation and re-densification.
