Experimental and finite element modelling of ultrasonic cutting of food

In recent years ultrasonic cutting has become an established technology in a variety of industries including the food processing industry to cut a variety of materials. An ultrasonic cutting system consists of a generator, transducer and either a single or multiple blade cutting devices tuned to a specific mode of vibration, commonly the longitudinal mode, between 20 and 100 kHz. High power ultrasonic cutting device design has traditionally relied on the cut requirements of the product, the use of empirical approaches where ultrasonic cutting system parameters such as cutting speed, frequency of vibration, mode of vibration, blade tip amplitude, gain and cutting orientation are determined from experimental and experience of the tool designers. Finite element (FE) models have also been used to predict the vibrational behaviour of the cutting tool. However, the performance of an ultrasonic device critically relies on the interaction of the cutting tool and material to be cut. Currently the interaction between the resonant blade and the material to be cut is neglected but the cutting mechanism at the interface is of significant importance and knowledge of this mechanism would be of considerable benefit to designers when developing ultrasonic cutting blade concepts and processing requirements. Simulations of the cutting process would also enable designers to conduct parametric studies quickly using computational methods instead of conducting lengthy, laborious experimental tests. The research reported in this thesis provides an insight into the requirements of the tool-material interaction to allow optimal cutting parameters to be estimated as an integral part of designing cutting blades for use in the food industry. A methodology is proposed for modelling the interaction between the resonant blade and the material to be cut using the finite element method, to gain an understanding of the cutting mechanism. The effect of ultrasonic cutting parameters, such as resonant frequency, mode of vibration, blade tip sharpness, cutting force, cutting speed, blade tip amplitude and are also investigated. Knowledge of the temperature distribution at the interface between the resonant blade and the substrate material would also be of benefit as currently experimental determination of the temperature at the interface is impractical using current measuring systems. Two thermo-mechanical FE models of ultrasonic cutting are developed which simulate the cutting tool and material interaction to allow cutting parameters to be derived numerically to enhance cutting blade design. The FE models incorporate experimentally derived mechanical and thermal properties of the common engineering thermoset Perspex and also of the following food materials; toffee, cheese, chocolate and jelly. The combined thermo-stress FE model allows the temperature at the cut interface to be determined under various loading conditions and provides a method for investigating the effects of blade design on temperature at the blade-material interface. Estimations of accurate mechanical and thermal properties of foodstuffs for inclusion in the FE models are determined experimentally using materials testing techniques such as tension and compression tests. Ultrasonic cutting blades are designed using finite element analysis and experimental investigations are performed on an ultrasonic cutting rig to validate the FE models. Two different generic 2D modelling approaches to simulate ultrasonic cutting are presented. One uses the debond method in ABAQUS standard and the alternative uses the element erosion method in ABAQUS explicit. Progression of the element erosion method into a 3D model is also presented with the intension of improving the accuracy of the modelling technique and to offer the flexibility to model complex geometries or cutting orientations. The models are presented and validated experimentally against a common engineering material, Perspex, and parametric studies are presented and discussed for the food materials; toffee, cheese, chocolate and jelly. For accurate modelling of any process, accurate material data is required and for common engineering materials such as Perspex accurate data is readily available in the literature. For food products however, the mechanical and thermal properties are not readily available and are often batch dependent. Methodologies for testing and determining the mechanical and thermal properties of two selected food materials, toffee and cheese, are also presented and the results from these experimental tests are incorporated in the finite element models to simulate the food materials during ultrasonic cutting. Models of ultrasonic cutting are for both single layer materials and also for multi layer material architectures.EThOS - Electronic Theses Online ServiceGBUnited Kingdo