Fine machining of functional surfaces in grey cast iron materials
To fulfil the function of highly complex assemblies, ever higher requirements are placed on the machining in relation to the macro geometric part properties such as dimensional, shape and position accuracy as well as micro geometric part properties such as the surface finish. Compliance with the required tolerances necessitates the usage of fine machining methods and precision machining methods; special tools and cutting materials adapted to the machining task are also needed. In addition, increasingly cast iron materials with improved mechanical and thermal properties are used; as a consequence machinability is made more difficult due to embedded carbides as well as higher strength pearlite phases. The general requirement for the more productive machining of cast iron parts therefore requires the holistic consideration of the process. The requirement for higher machining speeds necessitates an increase in the cutting parameters. These increases are achieved by means of optimisation of the cutting geometry, the cutting material and the cutting material coating. In addition, the development of innovative concepts for the reduction of the tool setting time and tool changing time is essential to improve the productivity during the fine machining of functional surfaces on cast iron materials and in the end to reduce the tool stock at the customer. Due to new innovative tool technologies, in future it will be possible to realise both more productive and also more cost-effective machining processes on cast iron parts.
Motivation
Grey cast iron continues to be a material in high demand because the manufacturing costs are low and its properties can be specifically adjusted using alloying elements. In this way it is possible to obtain optimal combinations of properties for specific applications. The excellent tribological sliding and dry-running properties are further special material-related aspects of cast iron. These properties result from exposed graphite layers in the cast iron material and are retained even if graphite is lost during the usage phase because voids act as solid lubricant reservoirs. Cast iron materials can be categorised into white and grey cast iron, refer to Cast steel and special cast alloys also belong to this material group. Due to the characteristics stated above and the good mechanical properties, such as high strength and rigidity along with excellent damping characteristics, among other areas grey cast iron materials are currently used in diesel engines subjected to high loads (heavy duty, lorry engines). Here cast iron with lamellar graphite (GJL), cast iron with vermicular graphite (GJV) and cast iron with spheroidal graphite (GJS) compete with each other.
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