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ABSTRACT
Lightweight structure is a new trend in machine tool design to ensure higher speed and higher acceleration of elements. The drive and control systems in mechanical engineering requires lightweight design provided by the recently developed light materials thus resulting in economical advantages. The hollow-sphere-composites (HSCs) consist of hollow spheres up to 80 of the volume and a reactive resin system as binder. The recently developed HSC materials, the hollow sphere bodies, are made from ceramics, silicates, plastics or metals and provide a range of structural materials of different chemical composition, grain size distribution, density, bulk density, softening temperature and compression. Therefore, a vast palette of HSC-variants can be obtained with different properties for a variety of applications. The mechanical properties of HSC materials depend on the properties of the spherical hollow bodies. The mechanical and thermal behavior of HSC materials can be characterised by using dynamic mechanical analysis (DMA), differential scanning calorimetry (DSC) and thermomechanical analysis (TMA). The thermal and mechanical properties of selected HSC structures, e.g. machine tool components, robot arms, demonstrate the flexibility and application feasibility of this new material.
CHAPTER I
INTRODUCTION
In mechanical engineering, including automotive and aircraft manufacture, the same lightweight building principles are used to meet various and often complex demands in shape-, structure-, material coupled with the need for optimized production process selection for technology needs and financial considerations. The optimised design of machine tools using finite element methods may lead to substantial improvements in the acceleration or damping behaviours. The application of new, alternative materials in machine tool design provides dramatic improvements in mass reduction through the full utilisation of material, high strength and stiffness as well as maximum functional integrity and economy. The requirements for the lightweight machine structures are characterised by the optimal use of material quantity. These demands can rarely be satisfied with monolithic structures. As a result, the application of cellular materials, e.g. honeycomb, metal foams or syntactic foams will soon gain significance. A combination of metals and fibrous materials can be used adaptively to different conditions, similar to natural structures, like the hand bones as shown in Fig. 1. This is a foam structure connected with the supporting system, where muscles and sinews are utilised for movements.
Fig. 1. Cellular structure of human hand.
CHAPTER II
HOLLOW-SPHERE-COMPOSITES
An alternative method in reducing the mass of materials is to use a mixture of high percentage volume of hollow spheres containing air or gas, and a reactive resin system. In this research hollow-sphere-composites consisting of corundum based (0.5–1 mm) macro-hollow-spheres and aluminium-silicate Fillite (5–300_m) micro-hollow-spheres are used as shown in Fig. 2.
In the recent research programme 12 different types of hollow spheres were used in combination with cold and warm hardener epoxy resin (EP) and with and without fibre reinforcement, resulting in excess of 20 HSC-variants with different properties. The hollow spheres vary in diameter between 10 and 2000 _m and the wall thickness is only 10% of the diameter size. The round shape of the spheres provides a high package density and a minimal viscous drag.
Fig. 2. (a) Bulk material of corundum 0.5–1 mm; (b) interior of Fillite (SEM); © hollow-sphere-composite (corundum and Fillite); (d) interior of hollow-sphere-composite (SEM).