Application of Electric Current in Friction Stir Welding

Friction Stir Welding (FSW) is a relatively new joining technique and has many applications. In FSW, heat generated due to friction between FSW tool and work-piece material softens the material and allows the materials in work-pieces to be stirred and joined together. FSW allows the work-pieces to be joined without reaching the melting point of the material, thus resulting in better welds. However, a large amount of mechanical energy has to be consumed for FSW of high-strength, difficult-to-weld metals such as titanium alloys. Hence, new FSW methods should be investigated to reduce the required energy. In this study, an innovative electrically-enhanced friction stir welding (EEFSW) has been developed. Electric current is passed in welding coupons of Aluminum 6061 plates and its effect on welding process and welds are examined. The results indicate that, with the aid of electric current, improvement in welding speed and reduction in energy consumption is obtainable, which enhances the productivity and widens the range of applications of FSW. Weld properties are found to be affected by the introduced current as well.

Wear of a Tool in Double-Disk Lapping of Silicon Wafers

Silicon wafers are the most widely used substrates for fabricating integrated circuits. A sequence of processes is needed to turn a silicon ingot into silicon wafers. One of the processes is flattening by lapping or by grinding to achieve a high degree of flatness and parallelism of the wafer [1, 2, 3]. Lapping can effectively remove or reduce the waviness induced by preceding operations [2, 4]. The main aim of this paper is to compare the simulation results with lapping experimental data obtained from the Polish producer of silicon wafers, the company Cemat Silicon from Warsaw (www.cematsil.com). Proposed model is going to be implemented by this company for the tool wear prediction. Proposed model can be applied for lapping or grinding with single or double-disc lapping kinematics [5, 6, 7]. Geometrical and kinematical relations with the simulations are presented in the work. Generated results for given workpiece diameter and for different kinematical parameters are studied using models programmed in the Matlab environment.

Effects of Carrier Material and Design on Microalgae Attachment for Biofuel Manufacturing: A Literature Review

Continuous use of petroleum derived fuels is widely recognized as unsustainable due to depleting supplies and the accumulation of greenhouse gases in the environment. Renewable, carbon neutral transport fuels are needed for environmental and economic sustainabilities. Algae have been demonstrated to be one of the most promising sources for biofuel production. However, large-scale algae production and harvesting for energy manufacturing are too costly using existing methods. The approach of growing algae on solid carriers is innovative and can potentially lead to cost-effective manufacturing of algae biofuels. As cells approach to the solid surface, many factors come in to influence microbial attachment such as the surface wettability, free energy, polarity, roughness and topography. Surface wettability plays an important role in the initial cell attachment. For further contact, surface free energy and polarity are more directly related to cell-substratum attachment strength. Surface roughness and texture are species-specific parameters and have been applied widely in attachment studies.

Optimization on the Production of Variable Thickness Aluminium Tubes

The variable thickness tube drawing is a new modification in the tube drawing methods which enables production of axially variable thickness tubes faster and easier in comparison with other similar methods like radial forging or indentation forging. The production of this type of tubes can be used in optimum design of mechanical parts which do not necessarily need constant thickness along the axis of tube and this method can strikingly reduce the overall weight of parts and mechanical assemblies like cars. In this paper, the variable thickness tube drawing were parameterized in a MATLAB code and optimized with the Ls-Opt software as an optimization engine and Ls-Dyna as a FE solver. The final objective of this optimization study is to determine the minimum thickness which can be produced in one step by this method with various tube dimensions (tube thickness and outer diameter). For verification of results, some experiments were performed in the tube drawing machine which was fabricated by this research group and acceptable correspondence was observed between numerical and experimental results.

Emergent Structure Detection for Multi-Axis Machining

This paper examines the phenomenon of emergent structures that occur in the transient stock material during multi-axis rough machining from a plurality of fixed orientations. Taking the form of thin webs and strings, emergent structures are stock material conditions that can lead to catastrophic failure during machining, even when tool path verification is successful. We begin by discussing the motivation for use of fixed orientations in multi-axis machining using multiple automated setups via rotary axes, which enables fast processing and ‘first part correct’ machining. Next, we demonstrate how unintended emergent structures occur in this paradigm of machining and can lead to catastrophic failure of the tool or work piece. Our original work focuses on the problem of geometric detection of these structures during process planning and prior to tool path planning, to the end of altogether avoiding emergent structure formation. To quickly simulate the machining process, we present an object-space method for determining the transient state of stock material based on the inverse tool offset. To identify emergent structures within this transient stock state, we propose a metric based on the medial axis transformation. Finally, we present our implementation of these methods and demonstrate realtime computation appropriate for an optimization scheme to eliminate emergent structures. Our methods provide consistent and logical results, as demonstrated with several freeform component examples. This work enables the development of robust algorithms for autonomous tool path planning and machining in multi-axis environments.

Ultrasonic-Vibration-Assisted Pelleting of Cellulosic Biomass: Effects of Moisture Content

Cellulosic biomass is an important source for making biofuels. However, there are several barriers to cost-effective manufacturing of biofuels using cellulosic biomass. One such barrier is related to the high transportation cost due to the low density of cellulosic biomass. Pelleting of cellulosic biomass is one way to increase its density. This paper reports an experimental study on ultrasonic vibration-assisted pelleting of cellulosic biomass. The study was focused on the effects of moisture content (MC) on pellet density of three kinds of cellulosic biomass (wheat straw, switchgrass, and sorghum). The experimental results show that sorghum has the highest density with three levels of MC among these biomass materials. The highest density was found with sorghum of 20% MC.

Effects of Mechanical Comminution on Enzymatic Conversion of Cellulosic Biomass in Biofuel Manufacturing: A Review

It is imperative to develop alternative fuels to replace current petroleum-based liquid transportation fuels. Biofuels produced from cellulosic biomass (forest products and residues, agricultural residues, and dedicated energy crops) is one such alternative. Manufacturing biofuels from cellulosic biomass requires reduction of the material size using mechanical comminution methods. This paper reviews these mechanical comminution methods. It presents their effects on biomass particle size, cellulose crystallinity, and sugar yield. It also discusses the characteristics of each method and future research directions.

Manufacture of Aerospace Components With Pressure Welding

Pressure welding technology is a solid state bonding process and generally involves heating the metal surfaces and then applying a suitable amount of axial pressure. In this state the metal components being joined undergo only microscopic deformation and the joining region is homogeneous and complete metallurgical bonding is possible without secondary materials or liquid phases. In the present work, pressure welding of titanium alloys has been investigated to fabricate several aerospace components with various complex configure. The result shows that the pressure welding method has been successfully applied with blow forming for near net shape forming of aerospace components, including high pressure tank for attitude control of spacecraft, and other lightweight structural panels.

Method for Evaluating Machining Toolholder-Spindle Unbalance Due to Chips at the Toolholder Interface

Machining process monitoring method is developed for detecting and diagnosis of the presence of chips at the toolholder-spindle interface. Although toolholders can be simply balanced before they are placed in the spindle, there can be some balancing problems remaining when one or more loose machining chips are attached at the toolholder-spindle interface(s) during a tool change. A method is developed by considering the natural and geometric unbalances of the toolholder-spindle system combined with an analysis of the toolholder tilt due to the presence of loose machining chips around the spindle. The method can be integrated on-line as a real-time expert diagnostic system for toolholder tilt due to the presence of loose machining chips at the spindle nose. The expert diagnostic system makes intelligent decisions on toolholder unbalance and concerns with chips at the interface that result in unwanted tilting and vibrations. The tool unbalance algorithm was able to monitor the toolholder tilting according to the results of this study.

Effects of Deformation Speed and Type of Alloy on Friction and Lubrication by Tip Test

The tribological conditions in cold forging operations are extremely severe, especially with high ram speed, due to large surface expansion and normal pressure at the tool/workpiece interface. The effects of deformation velocity and type of alloy were determined in the two sets of experiments carried out in the present study. In the first set, two different deformation speeds of 0.1 and 1mm/s were used for the aluminum alloys of 6061-O, 1050-O and copper alloys tests. The results were further confirmed with the second sets of experiments using AA2024 and AA6061 and three deformation speeds of 0.1, 1 and 5mm/s to evaluate the performance of each lubricant under increasing ram speed. Four lubricants such as grease, corn oil, VG100 and VG32 were used. While all the lubricants show a reduction in maximum load with increasing deformation speed, grease shows a rise in the maximum load from zero to a maximum at a deformation speed of 1mm/s and then descends gradually to a minimum load at a speed of 5mm/s for AA2024-O and AA6061-O. Since the load reduction seen, with grease as lubricant, is probably due to thermal softening, it will not be considered a desirable lubricant under increasing deformation speed because of the adverse effects on the tooling. It is found that in choosing lubricant for cold forging operations the type of workpiece material and deformation speed should be properly considered. Of the liquid lubricants (corn oil, VG100 and VG32) considered, corn oil shows the best lubricant for cold forging operations of copper, aluminum 6061-O, 1050-O and 2024-0 under increasing speed magnitude.