Abstract: Rock cuttability is expressed by specific energy (SE) that is defined as the energy required for cutting unit volume of rock. Direct determination of SE requires a rock cutting rig and is expensive and time-consuming. Therefore, empirical models have been alternative methods for predicting SE from rock properties. Two different predictive models of SE have been developed in this study using regression tree and artificial neural network (ANN) methods. Both empirical models employed the uniaxial compressive strength (UCS) and Mode I fracture toughness (KIC), being derived from tensile strength (t), as predictors. Data from four different studies have been used to develop the models. Statistical analyses on the data set have shown that both UCS and KIC are closely related to SE in a nonlinear form. Numerical and graphical measures of the goodness of the fit and ANOVA test have shown that regression tree and ANN models have performed similarly.
Abstract: After the grinding process, the cutting edges of cemented carbide milling tools tend to chipping. Chipping has a strong influence on the tool performance. For this reason, the cutting edges are further prepared. Additionally, a cutting edge rounding has an impact on the wear behavior and the process stability. For the cutting edge preparation of milling tools, magnetic finishing is a promising process. This paper describes the process of magnetic finishing. The influencing parameters, i.e. the process time and the distance between the cutting tool and the magnetic disks, are investigated. Furthermore, the effect of magnetic finishing on the tool life is demonstrated using the example of a milling process with titanium.
Abstract: The purpose of this paper is to investigate the performance of grinding alumina for the specific designed tools containing a controlled diamond protrusion and arrangement. The grinding forces, workpiece roughness and diamond wear at changing the depth of cut and feed under a fixed spindle speed were studied in the experiments. The experiment results showed that the grinding forces with the increase of feed slowly increased. However, the grinding forces with the increase of depth of cut showed a relatively larger rise. When the depth of cut reached to 0.09 mm that is about one fourth of diamond size, the axial grinding force obtained above about 20 N to cause some weaker or higher protrusive diamonds to produce a relatively larger fracture or pull-out. Furthermore, under a larger depth of cut and a larger feed rate the workpiece roughness obtained was the poorer. When diamond tool was employed for a longer time test under the depth of cut less than about one fourth of grit diameter, diamonds mainly displayed an attritious wear and the alumina roughness was about Ra 1.2-2.2 μm. This designed diamond tools are feasible for grinding alumina.
Abstract: The effect of microstructure of cemented tungsten carbide materials on their mechanical properties and wear characteristics was investigated using nanoindentation and nanoscratch methods. The results indicated that the variation in grain size insignificantly affected the hardness, elastic modulus and friction coefficient of the work materials, but considerably influenced their removal rates. The carbide with coarser grains exhibited a much higher removal rate was obtained during scratching.
Abstract: Titanium alloy is a kind of typical difficult-to-machine materials. In this study, the surface integrity of titanium alloy Ti-6Al-4V machined by electrical discharge machining (EDM) method are experimentally investigated and analyzed in term of surface roughness, SEM micrographs and microcracks. Effect of discharge energy and material properties on surface integrity are presented in this paper.
Abstract: A study of helical drill points for drilling carbon fiber reinforced plastics (CFRP) is presented. A helical drill point has an “S” contour with a radiused crown chisel that reduces the thrust force and make the drills self-centering. The S-shape chisel edge has a lower negative rake angle than a conventional chisel edge, and therefore may cut rather than extrude material. Experiments of drilling CFRP with helical drill points and conventional drill points were conducted. The results indicate that the helical drill points can reduce delamination significantly as compared to the conventional drill points under same cutting condition. Otherwise, delamination size decreases with increasing the cutting speed and increases with increasing the feed
Abstract: A dynamics model is established considering gyroscopic effects due to high speed rotating spindle-tool system in ultra-high speed milling (USM). The proposed method for predicting stability enables a new 3D stability lobe diagram to be developed in the presence of gyroscopic effects, to cover all the intermediate stages of spindle speed. The influences of the gyroscopic effects on dynamics and stability in USM are analyzed. It is shown that the gyroscopic effects lower the resonance response frequencies of the spindle-tool system and the stable critical depth of cut in ultra-high speed milling.
Abstract: In order to improve machining accuracy and surface quality effectively in ECM (electrochemical machining), a novel pulse inversion power supply has been presented, which has following merits such as high-frequency short pulse, high-power, and compact size. The scheme of full bridge inversion has been selected in this power supply model, and feedback circuit realizes voltage adjusted automatically, and guarantees to stability of voltage. Protect circuit has designed to avoid the problem of workpiece-burn. Finally, a series of electrochemical mechanical polishing tests using the power supply have been carried out, and the results have proved that it helps to achieve well surface quality processed, and improve machining accuracy, and also verify feasibility of its scheme.
Abstract: A new active cooling method is proposed for increased cooling effectiveness of coolant in grinding. It is based on variable strength activation of coolant together with active cooling to allow better machining heat transfer through mist evaporation. Multiple actuators are used through superposition and focusing. A device of variable strength coolant activation has been developed. Preliminary experimental tests were conducted to test the feasibility of the proposed cooling method. It is found that, using the proposed variable strength activation, an improvement of 87.6% in Ra value and 71.9% in Rq value were obtained when compared with the existing activated and cooled coolant cooling method.
Abstract: To allow better machining heat transfer through mist evaporation, a new active cooling method is proposed. It is based on variable strength activation of coolant together with active cooling. A key issue in the proposed method is the use of multiple actuators of high frequency vibration for extra strength increase. This will rely on the idea of focusing and superposition. In this project, experimental tests were conducted to test the idea for the proposed variable strength activation of coolant in precision machining. Experimental test results show that the effects of ejection distance de on the vibration sensor output amplitude Aa and output frequency fa are not significant. The output amplitude Aa has a linear relationship with the number of actuator na. The effects of na on fa is not obvious. Based on the results, the idea of using multiple actuators for focusing and constructive superposition in variable strength activation is confirmed.