This thesis presents the development of a novel robotically effected plastic foam sculpting system for rapid prototyping and manufacturing purposes. The developed system is capable of rapidly sculpting physical objects out of expanded and extruded polystyrene using an electrically heated Nichrome sculpting tool. An overview of current conventional rapid prototyping systems indicated that the main disadvantages lie in the limited size of objects which can be built, the relatively long time involved to produce one part and the high cost of the systems and materials. An extensive literature and technology review was conducted on work which was similar to the novel system presented in this thesis. The literature provided many good ideas which could be applied. Two sections of experimental work were conducted. The first was aimed at simply proving the concept of robotically effected sculpting of plastic foams. A crude procedure was developed which proved to be rather tedious and manual, especially in terms of generating the tool paths. Qualitative observations of the cut surfaces were used to change the testing parameters to explore their effects and discover which parameters produced accurate and smooth sculpted surfaces. 12 tests were documented and proved that the sculpting of satisfactory surfaces was achievable. The second section of experimental work involved developing the aforementioned crude procedure to make it more automated, especially in terms of the tool path generation and optimisation step. An innovative five step procedure was developed which if followed can produce accurately sculpted artefacts using CAD models of the artefacts as the primary input. Two artefacts were successfully sculpted using the developed procedure. The first was a simple lofted surface; the CAD model of which was created in SolidWorks. The second artefact was a patient customised medical radiation therapy head and neck support; the CAD model of which was created by scanning the back of the author's head and neck with a 3D scanner. The sculpted support fitted the author perfectly. The implementation of the procedure in the two tests highlighted several points including the speed in which the whole process can be carried out. The time taken from the scanning of the authors head and neck with the 3D scanner through to the physical sculpted artefact, was a mere 80 minutes; of which only 13 minutes was consumed in the actual setup and sculpting step! This is extremely quick when compared to conventional rapid prototyping systems and CNC milling. Several areas of future work were outlined and included, tool and fixture design, automation and integration of the system procedure, tool pathing strategy for foam cutting and robot control system issues. The work presented in this thesis provides an excellent foundation for future development of the robotic foam sculpting system.

For several years, research work has been carried out at the University of Canterbury aimed at the development of a rapid prototyping and manufacturing process referred to as Robotic Foam Sculpting (RFS). This system uses a six-axis industrial robot and electrically-heated hot-wire and hot-blade tools to sculpt desired parts from blocks of polystyrene foam. The vision for this system is that it will be able to rapidly create large volume foam models at low cost, for a range of potential applications. Parts produced by the RFS system can potentially be used as investment casting patterns, cores for sculptures and architectural details, demonstration and testing models, wind tunnel test models, and many other potential applications. At the beginning of the work reported in this thesis, there was very little understanding of the nature of the surfaces produced by hot-tool cutting of foam, very little knowledge of the range of input cutting conditions that affected the surface quality, and almost no understanding of the relationships between the cutting strategy and the nature of the surfaces being produced. In addition, there was little evidence of published work on these subjects that was sufficiently robust to be applicable to the RFS system. This research was concerned with rectifying this gap in the existing knowledge. There were a number of different focal areas for this research. These included the surface texture of surfaces cut with hot tools, the effects of cutting strategy on the surface quality in single-pass cutting of foam, the effects of cutting strategy on the surface quality in multi-pass cutting, and the application of a current-control system to control the surface quality in real time during a cut. In each of the focal areas the goal was to develop a detailed understanding of the nature of the different aspects of surface quality, to map the factor interactions and dependencies that controlled these aspects of surface quality, to develop methods for predicting the expected surface quality based on cutting strategy (and vice versa) and to develop techniques for minimising the surface errors. The detailed investigation of the surface texture of surfaces produced with hot-tool cutting is presented in Chapter 4. This chapter explores the characteristic nature of foam surfaces, presents the development of a method of measuring the surface texture of foam, and investigates the usefulness of a range of standard texture parameters for assessing foam surface quality. It is concluded in this chapter that common texture parameters based on the relative heights of surface features are not capable of reliably discriminating between different foam surfaces, so a new texture parameter (the 10%-Height Contiguous Diameter) is developed and implemented. Using this parameter, it is possible to reliably predict the surface texture to be expected for a given set of cutting conditions. Investigations of the cutting strategy in single-pass cutting are presented in Chapter 5. This chapter identifies the two key aspects of surface quality in single-pass cutting, the kerfwidth and the surface barrelling. Experimental work is carried out to investigate the relationships between these errors and the cutting strategy, and the factors that influence each of them are identified. In addition, statistical models are developed for the kerf along the length of a cut so that the kerf can be predicted based on cutting conditions. This chapter also includes a study of the cutting force in single-pass cutting, and develops models that allow the prediction of the expected cutting force for a given cutting strategy. A detailed study of the cutting strategy for multi-pass cutting is presented in Chapter 6. This study identifies the most significant surface errors in multi-pass cutting and determines the causes of each of these errors and the factor interactions and dependencies that have to be considered when developing a multi-pass cutting strategy. Once again, statistical models that allow the prediction of these surface errors based on cutting strategy, or the evaluation of cutting strategy parameters to achieve a desired surface quality, are developed. The models for cutting force in single-pass cutting are applied to multi-pass cutting, and it is found that these models can accurately predict the force in multi-pass cutting as well. The characterisation of the acoustic output in hot-tool cutting forms the subject matter of Chapter 7. This study establishes that the magnitude of the acoustic output is proportional to the cutting force experienced during the cut, and is therefore potentially suitable for use as a trigger signal for feedback current control. This would allow an acoustic signal to be used instead of the current force signal, which has a number of drawbacks that will be discussed in Chapter 2, the Background Material chapter. The specific trigger signal identified as being of most use is the acoustic output in the 4 – 12 kHz band, where the presence of any non-zero acoustic output above background noise is a reliable and repeatable indicator of the presence of thermomechanical cutting. The work presented in this thesis provides a detailed, quantitative, evidence-based and reliable understanding of the nature of the cutting strategy in hot-tool cutting of foam. The key cutting strategy parameters and the important aspects of surface quality for different cutting types are identified, the relationships between all these parameters are mapped, and quantitative models are developed that allow the output metrics like the surface quality or the cutting force to be predicted with a high degree of accuracy based on the input cutting strategy conditions. Armed with this understanding, it is possible to determine the most suitable cutting strategy for sculpting a given part, and to assess whether a given part can be sculpted with the RFS system. As such, the research problem posed at the start of this thesis has been largely solved, and the stage is set for further research to optimise the cutting strategy for sculpting different parts and to correct the remaining drawbacks of the RFS system to complete the development of a commercially-useful manufacturing system.