An Integrated DEM-FEM Model for Shot Peening Applications

Shot peening is a commonly used technique for improving the fatigue life of machine components by inducing compressive residual stresses in the surface layers. This process involves plastically deforming the surface layers by impacting with spherical particles at high speeds. The induced residual compressive stresses resist crack propagation and thus increase the fatigue life. The intensity of shot peening, measured using the Almen test, is an essential quantity for ensuring shot peening effectiveness and repeatability. It depends on various process parameters such as the shot speed, shot size, shot material, impact direction, and flow rate. In this study, a novel computational model is developed to simulate the Almen intensity tests on a Type-C strip accurately. The model uses a coupled technique based on the discrete element method (DEM) and the conventional finite element method (FEM). The predicted Almen intensity values agree with analytically calculated values. Results from the parametric studies conducted to analyze the influence of various parameters on the Almen intensity indicate that many different combinations of these parameters can obtain a given Almen intensity although the residual stress fields may vary.

On the 3D Printability of Multi-Walled Carbon Nanotube/High Density Polyethylene Composites

This study focuses on 3D printing of multi-walled carbon nanotube/high density polyethylene (MWCNT/HDPE) composites. First, rheological properties of 0.1, 1, and 5 wt.% MWCNT/HDPE composites were investigated to estimate the 3D printability window. Second, filaments with 1.75 mm diameter were fabricated and subsequently extruded by a commercial 3D printer. Finally, the filaments and 3D printed parts were tested to correlate the rheological, mechanical, and electrical properties with processing parameters. Experimental results show that flow behavior of MWCNT/HDPE composites is a critical factor affecting the 3D printability. The shear viscosity exhibits good shear thinning behavior at high shear rates and significantly increases with increasing nanotube loading from 0.1 to 5 wt.%, at low shear rates. Reliable MWCNT/HDPE filaments were obtained with smooth surface finish and good mechanical and electrical properties. The 0.1 and 1 wt.% MWCNT/HDPE filaments exhibit very good printing characteristics. However, under the flow conditions of a standard 0.4-mm nozzle, 3D printing of 5 wt.% MWCNT/HDPE filament can be rather difficult primarily due to high shear viscosity and nozzle clogging. Thus, further investigation is needed to fully optimize the 3D printing of MWCNT/HDPE composites.

Rotary Ultrasonic Machining of Basalt Rock Using Compressed Air As Coolant: A Study on Edge Chipping and Surface Roughness

The aim of this study is to investigate the edge chipping and surface roughness of basalt rock processed by rotary ultrasonic machining (RUM) using compressed air as coolant. Basalt rock is commonly used as a building and construction material for foundations and dams, as well as in architectural designs such as constructing thin veneers and facades. Rotary ultrasonic machining, a hybrid process of grinding and ultrasonic machining, is employed to drill difficult-to-machine materials such as ceramics, composites, titanium alloys, stainless steel, etc. RUM has many advantages over conventional machining processes such as twist drilling. These advantages include lower cutting force, higher surface quality, lower tool wear, etc. This paper is the first in literature to report a study on edge chipping and surface roughness on RUM of basalt rock using cold compressed air as coolant. The effects of three input variables (tool rotation speed, feedrate, and ultrasonic power) on cutting force, torque, edge chipping, and surface roughness were studied. Experimental results obtained from this investigation show that RUM with cold air as the coolant has the capability to machine holes in basalt rock with a surface roughness of less than 3.5 μm without severe edge chipping.

Ultrasonic Welding of Soft Polymer and Metal: A Preliminary Study

Joining soft polymers and metals is receiving increasing attention in both industry and academia to enable the manufacturing of innovative products. One motivation arises from the production of next-generation heat exchanges, the structure of which is primarily composed of polymers and metals. Waste heat coming from low temperature exhaust gas stream is significant in industries in the U.S. However, traditional heat exchangers that are available to recover heat in the presence of small temperature difference are large and costly, restricting the wide application of such heat exchangers. To address this challenge, a hybrid materials design is proposed to achieve a balance between thermal conductivity and mechanical strength. High quality requirement induced by the changing operating conditions necessitates a strong bonding between polymers and copper. In this research, the possibility of using ultrasonic welding, which is conventionally employed to join dissimilar or similar metal layers, is explored. Preliminary results from welding experiments and tensile shear tests reveal that two bonding modes exist in the welding of PET and copper. Furthermore, analysis of power signals collected during welding shows that one can potentially monitor and optimize welding processes using monitoring signals. It is concluded from this study that ultrasonic welding has excellent potential in joining soft polymers and metals. Future work is also discussed on the process improvement and mechanism investigation.

Comparison of Commercially Available Thread Forming Profiles on Flow Drill Joining of 6061-T6 Aluminum to Thermoset Carbon Fiber Reinforced Composite

Flow Drill Screws are self-piercing, self-tapping screws used for single sided joining of light metals, such as aluminum. This technology has been adopted by many automotive OEMs for use in metals. Thread forming profiles exist for material stackups that are made of entirely metals and entirely polymers/composites. This research evaluated the effectiveness of these thread profiles in dissimilar metal-on-composite stackups. Thread profiles designed for use in polymers/composites and aluminum were compared with a traditional machine screw thread profile for flow drill joining of 1mm and 2mm thick 6061-T6 aluminum to 3mm thick thermoset carbon fiber reinforced polymer. The three thread profiles were manufactured as M5x25mm flow drill screws in their commercially available configurations and materials. Two parameter sets from the FDS equipment manufacturer were evaluated, the first designed for use with the polymer thread forming profile, the second designed for use with the aluminum thread forming profile. The thread profiles were evaluated based on outputs of process time, peak torque, and lap shear strength. The polymer thread profile had shorter process times than the other 2 profiles but caused more damage to itself and its mating material. All 3 thread profiles exhibited greater shear strength when aluminum was used as the lower sheet material.

Multiphase Flow Distribution in MQL Drilling Using Optical Intensity Distribution Based Approach

Oil flow distribution in Minimum Quantity Lubrication (MQL) plays an important role in the efficiency of machining processes, but it remains challenging to measure experimentally. This paper presents a new method to measure the oil flow distribution in through-channel drill bits based on the reflected light intensity. Measurements were conducted from multiple angles in order to map the flow distribution across the channel cross-sectional area. The method is applied to drill bits of a circular cross-section channel and two helix angles, 0° and 30°. The results show that, for the 0° helix angle channel, the oil concentrates near the periphery of the channel, while for 30° helix angle channel, the oil concentrates towards the center of the drill point. Furthermore, Computational Fluid Dynamics (CFD) simulation was conducted to compare with the measurement results, and it was observed that the oil distribution is correlated to the velocity field. Oil flow concentration is high in low velocity regions. Though preliminary, this study has concluded that the velocity field generated using single-phase CFD is a critical indicator for oil distribution in an MQL flow.

Preliminary Results on Finishing of WC-Co Coating by Magnetorheological Finishing Process

Thermal spray coating has the ability to enhance the lifetime of engineering components by reinforcing the surface properties. The surface roughness of the as-sprayed coatings needs to be suitably finished for its end use. The nanofinished WC-Co coatings are widely used in aerospace and automobile industries. In this present investigation, surface grinding followed by the magnetorheological finishing (MRF) processes is employed for finishing of WC-Co coating. Boron carbide (B4C) powder is used as the abrasive particles in the MRF process. MRF spot finishing technique is performed on the ground coating. The plastically deformed layer from the ground surface is removed completely by the gentle mechanical abrasion of MR fluid ribbon. The surface roughness and volume of material removed are measured over the finishing time. It is perceived that the surface roughness of the finishing spot is increased after a threshold machining time. This is attributed to the aging of MR fluid and the mechanical abrasion of wear debris. The experiment is also performed with the assistance of Murakami’s reagent to perform etching and finishing, simultaneously. A comparatively higher finishing rate is observed in this case.

Some Observations on How Mechanochemical Effect Determines Deformation Mode and Chip Morphology in Cutting of Metals

We analyze unsteady plastic flow modes in cutting of metals using high-speed imaging of the deformation zone, in situ. For metals which exhibit high levels of strain hardening, the commonly assumed steady (smooth) flow is inherently unstable. Instead, the cutting is characterized by unsteady sinuous flow, with large-amplitude folding, that is triggered by a plastic buckling instability linked to the material microstructure. A mechanochemical effect caused by Al-Alcohol chemical reaction on workpiece surface, which is coupled to the unsteady flow mode, is highlighted. Experimental results reinforce the hypothesis pertaining to flow stability governing the deformation mode and chip type.

Bending and Springback Analysis on Sheet Metal Material Discontinuity

Origami concept came up as an emerging technique for sheet metal bending or folding and is called as Origami-based sheet metal (OSM) folding. This process fits right in criteria of effectiveness, efficiency, and sustainable manufacturing due to minimal resources required to make the fold or bend. In this process, the line was created on which the bend was supposed to perform. Traditionally the intermittent material was removed from that line with a through cut. Then the bend was performed. During bending the force required was very less and thus it can also be called as easy bend operation. Because the material and removed all the way through the thickness of the metal, these part after bending cannot be used to contain particles smaller than the cut width or liquid solution due to leakage issue. To overcome this issue, this paper investigates the material discontinuities with a blind cut, where the material through the thickness was not completely removed. For this 4 sample types were created. Three additional variables were added in placing the sample during bend operation. Experiments were performed and bending deformation and springback were analyzed. After analyzing the results, it was found that significant thickness difference regions in the sample, smaller clearance, smaller width or cut, and width of cut facing punch are the best variable to have a better bending and less springback.

Pressurization and Annealing Effect Analysis Through Hole Expansion

Due to continuous push towards environmental regulations to reduce the impact on the environment by reducing the fuel consumption, and concerns on limited resources, the more sustainable manufacturing is in demand. More abundance material like iron-carbon based alloy are higher strength and easily formable but ways are research to reduce the weight of created part by reducing the thickness due to density issue. Some low dense material is the alternatives but they miss the easy to deform spot. The present study is focused on how to make the material more deformable in the process by evaluating the parameters in deformation through the hole expansion process. For this study, four tests were chosen hemispherical dome test, cylindrical tool test, conical tool test, and biaxial test. In all tests, only the biaxial test machine does not use the rigid tool to deform the hole while all other test used the rigid tool punch to deform the hole. Cruciform specimen dimension was used to make the sample, which fits in all of the considered tests. A hole was created at the center of the specimen which will be expanded in all tests. In all tests the deformation mechanics and hole expansion was studied. Force-displacement curves were plotted and discussed. In addition, tests were also performed on annealed material to understand the hole expansion in ductile material. Based on the results it was observed that biaxial tests do not provide any pressurization effect and all test which includes the rigid tool to deform the hole does. Due to the pressurization effect, the hole was expanded more. It was also noted that the hole expansion was more in ductile material and pressurization effect increases with ductile material.