China
Africa
Explore chapters and articles related to this topic
Machine Tools
Published in David A. Stephenson, John S. Agapiou, Metal Cutting Theory and Practice, 2018
David A. Stephenson, John S. Agapiou
The machine tool structure supports the various parts of the machine tool, as well as the part and fixture, and provides rigidity to ensure accuracy. In general, a machine tool structure consists of a bed or base, column, ram, or saddle (carriage). Fixed components such as the base are most commonly made of cast iron, nodular iron, steel weldments, or composites with polymer, metal, or ceramic matrices. Castings must be aged and stress relieved. Reinforced or polymer concrete and epoxy granite are sometimes used for machines subjected to high levels of vibration; their application has been limited mainly to grinding machines due to warping, thermal gradients, and the absorption of coolant. Moving components are made of cast iron, steel, aluminum, and sheet metal. The design of moving columns is becoming increasingly critical as machine travel speeds increase, since the weight must be reduced to reduce inertia while maintaining high stiffness. Steel weldments can reduce the structural weight significantly but require careful design to resist vibration and deformation. Welded bases can be designed with high stiffness and good control of damping because welds in the bases block vibration transmission. Machines using weldment structures are often classified as light-duty machine tools unsuitable for rough cutting or precision applications. Metal-matrix composites, ceramics, and reinforced concrete materials are most often applied in precision or high-speed applications [88–94]. The machine damping obtained from the structural material itself can be improved significantly by internal means, including (1) filling structural cavities with oil, lead, sand, or concrete [1,2,6]; (2) circulating coolant through the machine structure; (3) allowing for microslip at the joints; and (4) attaching a viscous material layer between joints. Damping can also be improved by using shear plates, tuned mass dampers, viscous shear dampers, and active dampers [6,95–98]. Polymer or concrete-filled bases are preferred for grinding machines because they increase system damping and stability. The ideal machine configuration is application dependent as discussed in standards [99].
Multi-attribute optimization of end milling epoxy granite composites using TOPSIS
Published in Materials and Manufacturing Processes, 2019
Arunramnath R, Thyla P.R, Mahendrakumar N, Ramesh M, Aravind Siddeshwaran
Epoxy granite composites gaining more importance in machine tool industries are replacing conventional cast iron materials due to their lightweight and better damping properties. Recently several research works have been carried out in replacing conventional materials with fiber reinforced polymer matrix composites for fabrication of machine tool structures with enhanced static and dynamic stability. Epoxy granite particulate composites are replacing conventional materials because of their lightweight and low thermal expansion. These composites molded require machining operations for final assembly. Machining of particulate composites results in tool wear and high surface roughness. Ramnath et al. [1] analyzed and reviewed machining processes of different materials and machining parameters considered for investigations on milling study of epoxy granite composites. Sener[2] investigated the surface roughness and cutting forces of AA7039 and Al2O3 composite by milling using uncoated carbide inserts. The experimental investigations reveal that material structure significantly affects surface roughness and feed rate was the most critical factor affecting cutting force. Mudhukrishnan et al.[3] evaluated the influence of tool materials on dimensional inaccuracies and machined surface quality of glass fiber reinforced polypropylene composites. It is observed that desired dimensional and surface quality are attained with a speed of 2500 rpm and feed rate of 0.05 mm/rev.