Study of machining accuracy in ultrasonic elliptical vibration cutting

The cutting speeds of the tool, the rake angle and clearance angle through the cycles of elliptical vibration cutting for separating type ultrasonic elliptical vibration cutting are defined initially in the present paper. Subsequently, a theoretical model of the thrust cutting force in ultrasonic elliptical vibration cutting is proposed, and the reason of the machining accuracy improvement by applying ultrasonic elliptical vibration is clarified theoretically. Finally, the effect of ultrasonic elliptical vibration cutting on machining accuracy is verified experimentally by utilizing an ultrasonic elliptical vibration cutting system.     

Suppression of burrs in turning with ultrasonic elliptical vibration cutting

The approximate cutting force models in three-dimensional separating type ultrasonic elliptical vibration cutting are proposed in present paper. The theoretical models of the stresses of deformation zone on the workpiece edge in burr formation in ultrasonic elliptical vibration cutting are derived based on three-dimensional cutting model, and the reason for the burr being suppressed by applying ultrasonic elliptical vibration is clarified theoretically. Finally, the effect of ultrasonic elliptical vibration cutting on the burr is verified experimentally.     

Experimental study on ultrasonic elliptical vibration cutting of hardened steel using PCD tools

Diamond tools cannot usually be applied for machining hardened steels while applying conventional cutting technique. As an alternative, ultrasonic elliptical vibration cutting (UEVC) technique was successfully applied for obtaining mirror surface on such steels using single crystal diamond (SCD) tools. In order to reduce production cost without compromising mirror surface quality, polycrystalline diamond (PCD) tools may be tested against highly expensive SCD tools. However, study on machining of hardened steel using PCD tools applying the UEVC technique has not yet been reported. The current research presents an experimental study on UEVC of hardened stainless steel (a typical Stavax, hardness 49 HRC) using the PCD tools. Face turning experiments were carried out to investigate the effects of three machining parameters: nominal depth of cut, feed rate, and nominal cutting speed on output performances such as cutting force, tool flank wear, surface roughness, and chip formation. Experimental results show that nominal cutting speed has very strong influence on the output performances, compared to the other two parameters. The surface roughness improves with a decrease in cutting speed. A mirror-like surface of approximately 804 mm² with a roughness value R_a of 11 nm was achieved at a lower cutting speed. Theoretical explanations have been given to support the results drawn from the UEVC experiments. It can be concluded that, while applying the UEVC technique, the inexpensive PCD tools instead of the SCD tools can be effectively applied to obtain optical surface for producing precise molds from the hardened steel.     

Effect of machining parameters in ultrasonic vibration cutting

The ultrasonic vibration cutting (UVC) method is an efficient cutting technique for difficult-to-machine materials. It is found that the UVC mechanism is influenced by three important parameters: tool vibration frequency, tool vibration amplitude and workpiece cutting speed that determine the cutting force. However, the relation between the cutting force and these three parameters in the UVC is not clearly established. This paper presents firstly the mechanism how these parameters effect the UVC. With theoretical studies, it is established that the tool–workpiece contact ratio (TWCR) plays a key role in the UVC process where the increase in both the tool vibration parameters and the decrease in the cutting speed reduce the TWCR, which in turn reduces both cutting force and tool wear, improves surface quality and prolongs tool life. This paper also experimentally investigates the effect of cutting parameters on cutting performances in the cutting of Inconel 718 by applying both the UVC and the conventional turning (CT) methods. It is observed that the UVC method promises better surface finish and improves tool life in hard cutting at low cutting speed as compared to the CT method. The experiments also show that the TWCR, when investigating the effect of cutting speed, has a significant effect on both the cutting force and the tool wear in the UVC method, which substantiates the theoretical findings.     

A study on the effect of tool nose radius in ultrasonic elliptical vibration cutting of tungsten carbide

Nowadays, ultrasonic elliptical vibration cutting (UEVC) technique is being successfully applied for ultraprecision machining of difficult-to-cut materials. Previous study reported that the tool geometry especially tool nose radius notably influences the performance of 1D ultrasonic vibration cutting (UVC). However, the effect of tool nose radius in the UEVC technique is yet to be studied. This study aims to investigate the effects of tool nose radius on the UEVC performance in terms of cutting force, tool wear and surface finish when machining a hard-to-cut material, sintered tungsten carbide (WC), using PCD tools. The experimental results show that the UEVC technique performs remarkably better in all aspects at a 0.6 mm nose radius compared to a lower (e.g. 0.2 or 0.4 mm) and a higher nose radius (e.g. 0.8 mm). When machining about 412 mm² surface area, an average surface roughness, R_a of 0.010 μm is achieved with a 0.6 mm nose radius. Analyses are conducted to justify the findings in this study.     

An integrated model for analysing the effects of ultrasonic vibration on tool torque and thermal processes in friction stir welding

An integrated model of ultrasonic vibration enhanced friction stir welding (UVeFSW) is developed by integrating the thermal-fluid model with the ultrasonic field model and tool torque model. The tool torque and the heat generation rate at tool/workpiece contact interfaces are coupled with the interfacial temperature, strain rate and ultrasonic energy density. The model is used in quantitatively analysing the effects of ultrasonic vibration on tool torque and thermal processes in friction stir welding (FSW). The results show that ultrasonic vibration reduces the flow stress, which results in a decreasing of tool torque, interfacial heat generation rate and interfacial temperature. The complicated interaction of ultrasonic energy with the thermal processes in FSW leads to a gentle thermal gradient and an enhanced plastic material flow in UVeFSW. The model is validated by a comparison of the calculated thermal cycles and tool torque at various welding parameters with the experimentally measured ones.