The International Journal of Advanced Manufacturing Technology

In cutting process, the insufficiency in grasp of the tool vibration characteristics of spindle system seriously hinders the improvement of machining quality and efficiency. Thus, this paper develops a novel dynamic model of spindle system in ball end milling process considering the nonlinear contact behavior of bearings. For the sake of coupling with the motion differential equations of spindle shaft, a general analytical expression for the nonlinear contact force of matched angular contact ball bearings is proposed. Then, dynamic cutting force model during ball end milling is established with consideration of the influence of tool vibration on the uncut chip thickness. Furthermore, the effectiveness and feasibility of the proposed model is confirmed by some cutting tests. Finally, the effects of rotation speed, bearing preload, and cutting parameters on the tool end vibration response of spindle system are analyzed in detail. The investigations reveal that the main resonance frequency increases and the corresponding resonance amplitude decreases as bearing preload increases. The larger bearing preload can improve cutting stability and machining quality. It is also concluded that the change regarding axial depth of cut considerably affects the vibration behaviors of tool end. The proposed dynamic model can be applied to predict the vibration of spindle system during ball end milling, especially the tool vibration.

A novel flame-retarded polymer composites using cow horn ash particles (CHAp) were investigated. The cow horn ash particles were varied in the polyester from 5 to 20 wt% with 5 wt% interval. Thermogravimetric analysis (TGA) and cone calorimeter test were used to determine the flame-retarded properties of the developed composites. Weight of 5.28, 5.285, 8.47, 11.64, and 17.67% were left at 0, 5, 10, 15, and 20 wt% CHAp. Twenty percent of the weight remained at around 500 °C as the weight percentage addition of CHAp increased up to 20 wt%. The introduction of CHAp particles to polyester induces protective barriers against thermal decomposition and retards the thermal decomposition of polyester/CHAp composite. This work shows that at 20 wt%, CHAp can serve as flame retard in the sense that the CHAp delays the ignition time by 39.93% of the composite and the end of burning time by 30.59% and reduced the total heat release rate by 34.07%. Waste cow horn can be used as flame retardant to polymer composites.

Severe plastic deformation processes (SPDs) have been developed over the past decades to produce bulky parts with proper mechanical and microstructural properties. Equal-channel angular pressing (ECAP) is a method in which a metal is subjected to severe plastic straining through simple shear. The combined extrusion-equal channel angular pressing (C-Ex-ECAP) is proposed in this paper as a new method of SPD. This process is a combination of extrusion and ECAP processes. The new process contains two shear zones which can lead to UFG structure in fewer passes compared with ECAP. In the proposed method, there is the capability of fabricating longer specimens because of the presence of the extrusion process. This investigation has been performed up to six passes, and the microstructural, mechanical, and electrical properties have been studied in the deformed workpieces. The samples produced in six passes of this process showed a 480% increase in yield strength compared to the annealed sample, and a decrease in grain size from 18 μm to 820 nm, as well as an increase in hardness from 41.8 to 125 HV. The electrical conductivity study also showed that the six-pass specimens had a 5% reduction in electrical conductivity compared to the annealed specimens.

Due to environment-friendly nature, water-soluble binder systems have received much attention in recent years. Polyethylene glycol (PEG) and polymethyl methacrylate (PMMA) binder system is one such example and has been widely reported in the literature. In this paper, a comprehensive investigation of PEG/PMMA binder system has been carried out. Feedstocks were made using stainless steel 17-4PH powder, and subsequently, conventional and micrometal injection moulding (μMIM) processes were carried out. Differential scanning calorimetry (DSC) and fracture surface analysis of moulded samples were performed for complete evaluation. It was found that despite great potential, there are certain drawbacks associated with this binder system. The main problem is the formation of shrinkage voids during solidification. It is proposed that this binder system is more suitable for μMIM process that has an inherently higher cooling rate.

A solder bump is regarded as a specular-dominant shiny component that distorts the height profile and causes poor repeatability during the bump height measurement. In this paper, we analyze the relationship between the projection angle and other factors based on the general reflectance mechanism of the specular surface. An optimum projection angle exists, such that can produce the best repeatability of the bump height measurement; therefore, we propose a convenient experimental system with a circular motion guide that can evaluate the optimum projection angle experimentally. The experimental results show that best repeatability is obtained with the optimum projection angle. The proposed method to find the optimum projection angle in this paper can therefore be applied to the many cases of measurement for ball grid array samples having specular-dominant shiny component.

Al-7075 alloys are drilled using an inverted drilling method to investigate the effect of hole performances (enlargement, roundness, and surface roughness). Additionally, this study uses a gray-Taguchi methodology to optimize the multiple performance characteristics for the machining parameters in the dry drilling of Al-7075 alloy. The experimental results indicated that holes are enlarged using TiAlN- and TiN-coated drills by only 68.9% and 75.0% more than if an uncoated drill is used. The analysis of variance (ANOVA) results for the multiple performance characteristics in dry drilling Al-7075 alloys show that the spindle speed has a significant effect among all drilling parameters. Uncoated drill experiences the maximum wear, followed by the TiN-coated drill and then the TiAlN-coated drill. In an inverted drilling machine arrangement, chips fall out of the workpiece that is being drilled to prevent chips clogging and tool wear caused by secondary cutting. The values for the enlargement, roundness, and surface roughness for the inverted drilling are 95.5%, 88.8%, and 83.0% that for standard drilling, respectively. Using inverted drilling creates better hole quality and less tool wear than standard drilling.

In this paper, an evaluating method of laser welding quality for stainless steel lap joint has been studied based on the ultrasonic nondestructive testing technology. The two-dimensional array ultrasonic probe is used to inspect the weld joint, analyzing the effect of fusion state on A-scan echo amplitude, and C-scan image of internal contact surface is established. A concept of equivalent weld width as the quantitative characterization of fusion state is defined, and a computational model of equivalent weld width is discussed based on statistical method. Testing results show that this method is simple and feasible, and its accuracy could completely meet the requirements of engineering application.

Graphene-reinforced metal matrix composites have received a lot of attention from academia and industry due to their excellent mechanical properties. In this paper, the machinability of graphene-reinforced aluminum metal matrix composites (Gr/Al MMCs) during micro-machining is investigated by finite element method. A three-dimensional modeling program based on the Python language is developed independently; this program can generate graphene with random distribution of orientation and position. A three-dimensional two-phase finite element model considering the cutting edge radius is established to simulate the micro-machining process of Gr/Al MMCs. Embedded element method is used in the model to more efficiently simulate the interaction behavior between graphene and aluminum matrix during micro-machining. The accuracy of the model is verified by indirect experiments. Stress distribution, tool-graphene interaction, chip formation, cutting force, and specific cutting energy during micro-machining are investigated with different uncut chip thickness. The simulation results show that graphene inhibits stress propagation, resulting in the formation of a stress field with irregular contours within the matrix. Continuous serrated chips are generated during the cutting process. The addition of graphene increases the magnitude and fluctuation of cutting forces.