Research On The Influence Of Heat Treatment Parameters On The Machinability Of Austempered Ductile Iron

Austempered Ductile Iron(ADI) is a new type ductile iron material, which has been used for a wide variety of applications in aerospace, ships, vehicles and heavy industry due to its high strength, high hardness, excellent toughness, high ductility and excellent comprehensive mechanical properties, and has obtained both economic and social benefits obviously. The excellent mechanical and physical properties of ADI is attributed to the austempering heat treatment technology, especially the heat treatment temperature and time, which makes it become hard-machining material represented not only the high contact stresss on rake face but also aggravating wear for friction between tool and high hardness, wear resistance chip while improves the remarkable mechanical properties. It has seriously affected application of the ADI products in more newer fields, especial in China.According to the present situation of domestic and foreign research, a proper range of austempering temperature and time is selected to prepare for a series of ADI samples austenitized at 900℃for 1.5h followed by austempered at 250, 300 and 350℃for 1, 2, 3hour, which were in Applied Process Company(America) for heat treatment by single temperature isothermal quenching process from horizontal continuous casting ductile iron. All of these workpieces whose properties are similar to ASTM Grade 2~4 were tested the mechanical properties, analyzed and compared the metal organization. Precise dry cutting experiment was done on Austempered Ductile Iron samples with CC6050, CB7025 and GC2025 which are manufactured by Sandvik(Sweden). In this paper, the influence of austempering temperature and time on tool wear, cutting forces and surface roughness are systematically studied at the first time, provided scientific basis for the heat treatment process in the preparation of ADI and the selection of cutting parameters in the process of cutting.The main contents of this thesis are summarized as follows:1. The wear width of cutting tool was recorded when cutting ADI workpieces with three cutting tools, followed by analyzing the influence of austempering temperature and time, cutting tool materials on tool wear. Wear profile of cutter's surface(rake face and flank face) was observed by means of S-4700 scanning electron microscope(SEM), after which discussed wear mechanism and performance of the cutter, in addition, recommending an ultrasonic technique based on the theory of wavelet to detect the cutter wear.2. Cutting forces were measured by Kistler three-dimensional force dynamometer in machining, and analyzed the effect of austempering temperature and time, cutting tool and strain hardening on cutting forces. The effects of cutting parameters on cutting forces were analyzed separately by means of the Orthogonal test including respectively penetrating the impact of each cutting parameter on cutting force by single-factor analysis method as well as observing chip shape as cutting parameters varies.3. Further experiment study was done to measure the surface soughness with 2205 surface roughness measuring instrument, after what exploring the influence of austempering temperature and time, cutting tool and cutting parameters on surface roughness.4. Research was done on cutting parameters identification of surface roughness and cutting force predictive models based on particle swarm optimization algorithm, and furtherly made Fuzzy inference model which explored the relation among cutting force, austempering temperature and time with the help of Matlab Fuzzy Logic toolbox.Research showed that this paper focuse on the experimental study on tool wear, cutting forces and surface roughness of ADI, providing theoretical references for high quality, low cost, high efficiency process of ADI in future. The fuzzy inference model among austempering temperature and time offers theoretical basis for the parameter setting of heat treatment, also the surface roughness and cutting force predictive models can offer scientific basis for the selection of cutting parameters, predicting the cutting forces and surface quality effectively in turning ADI workpieces.