Helical milling is an alternative hole-making machining process which presents several advantages when compared to conventional drilling. In the helical milling process, the tool proceeds a helical path while rotates around its own axis. Due to its flexible kinematics, low cutting forces, tool wear, and improved borehole quality may be achieved. In this study, a new helical milling process to create holes in hardened steel with a hardness of HRC 52 was used. Carbide inserts with PVD TiN coating were applied. Input parameters including cutting speed and feed rate were considered in 4 and 2 levels, respectively. In order to increase the reliability of the results, experiments were repeated 4 times and the total of 32 tests were performed. Other cutting parameters, such as axial and radial depth of cut were constant. Machining process was performed in dry state and without any lubricant. Output characteristics were tool wear, surface roughness, cutting force, machining time and material removal rate. Tool wear, surface roughness and forces, were measured by tool maker microscopy, roughness tester and dynamometer, respectively. The results showed that increasing the cutting speed on this type of hardened steel, decreases the surface roughness, machining forces and machining time. However, increasing the cutting speed and the feed rate enhances the tool wear and material removal rate considerably. Cutting speed and Feed rate of 50 m/min and 0.05 mm/tooth, offered the best mechanical properties of the Machining. پرونده مقاله

The widespread application of thermoplastic polymers in different aspects of industries has motivated researchers and companies to improve and upgrade their forming, joining and assembling processes to overcome their limitations. One of the newest joining methods of thermoplastics is friction stir welding which is based on frictional heat generated through contact between a rotating tool and the workpiece.The aim of this study is to investigate the weldability of dissimilarpoly methyl methacrylate and polycarbonatesheets via friction stir welding approach.The effects of process parameters such as rotational and traverse speeds and the heater temperature on the mechanical properties of the joints were studied comprehensively. Rotational and traverse speeds and heater temperature of 2100 rpm, 8 mm/min and 120 °C, offered the optimized mechanical properties of the joint. In the optimum joining condition, welded joint with strength equal to 98% of polycarbonate and with higher hardness than the polycarbonate was obtained. پرونده مقاله