Efficiency Improvement of Aluminum Recycling Process

AbstractAluminum has been used as a raw material in the automotive, aerospace, cookware and construction industries, including daily appliances. The manufacturing of aluminum ingot from aluminum scraps involves the recycling process where the aluminum scraps are melted and recast together with the modification of chemical composition. Since the recycling process has to account some operations to prepare and manage the scraps, the process is generally ineffective in terms of time and activities related. This in turn leads to the increased waiting time and cycle time of the process. This research therefore aims at increasing the efficiency of aluminum recycling process with emphasizing on the cycle time reduction. The ECRS technique and 5W1H activity analysis were employed to eliminate wastes in each operation of the process. The casting techniques were used to reduce scarp melting time which shared the largest portion of the whole production time. After the process improvement, wastes can be eliminated, thus increasing the efficiencies of man and machines from 34.12% and 59.46% to 50.68% and 61.95%, respectively. The average production cycle time can be reduced from 25.91 hours to 20.13 hours, thus saving the manufacturing cost by 421,327.65 baht accordingly

Towards damage-free micro-fabrication of silicon substrates using a hybrid laser-waterjet technology

A novel hybrid laser-waterjet machining technology is developed in this thesis using a new material removal concept to achieve near damage-free micromachining. Using this concept, a laser is used to heat and soften the material while a waterjet is used to expel and remove the laser-softened material in a layer by layer manner, so that material is removed in its solid-state below its melting temperature. Water also takes a cooling action. An experimental rig has been built to realize this novel concept and an extensive experimental investigation has been carried out to understand the process and the effect of various parameters on the process using a single-crystalline silicon as the specimen material. It has been found that near free of heat-affected zone and high material removal rate can be achieved when using this hybrid laser-waterjet technology, as compared to the dry laser micromachining process. Specifically, a laser Raman spectroscopy study has found that a much thinner amorphous layer within 40 nm was formed than that found in the dry laser machining process. In order to understand the coupled effect of laser and waterjet on the material removal process and to predict and control the process on a mathematical and quantitative basis, a temperature-field model has been developed whereby a model for the dry laser machining process is developed first before it is extended to the hybrid laser-waterjet process incorporating the waterjet cooling and expelling effects. The parabolic heat conduction associated with enthalpy method is numerically solved by using an explicit finite difference scheme for predicting the two-dimensional temperature field. The thermal model has been verified by comparing the predicted temperatures with the temperatures measured by an infrared camera. The simulated groove depths are also compared with the experimental data under the corresponding conditions and it is found that they are in good agreement. A simulation study of the hybrid laser-waterjet process is finally reported which provides an in-depth understanding of the material removal process and mechanisms and the interaction between laser, waterjet and material under the coupled effect of laser heating and waterjet cooling and expelling

Continuous trench, pulsed laser ablation for micro-machining applications

The generation of controlled 3D micro-features by pulsed laser ablation in various materials requires an understanding of the material's temporal and energetic response to the laser beam. The key enabler of pulsed laser ablation for micro-machining is the prediction of the removal rate of the target material, thus allowing real-life machining to be simulated mathematically. Usually, the modelling of micro-machining by pulsed laser ablation is done using a pulse-by-pulse evaluation of the surface modification, which could lead to inaccuracies when pulses overlap. To address these issues, a novel continuous evaluation of the surface modification that use trenches as a basic feature is presented in this paper. The work investigates the accuracy of this innovative continuous modelling framework for micro-machining tasks on several materials. The model is calibrated using a very limited number of trenches produced for a range of powers and feed speeds; it is then able to predict the change in topography with a size comparable to the laser beam spot that arises from essentially arbitrary toolpaths. The validity of the model has been proven by being able to predict the surface obtained from single trenches with constant feed speed, single trenches with variable feed speed and overlapped trenches with constant feed speed for three different materials (graphite, polycrystalline diamond and a metal-matrix diamond CMX850) with low error. For the three materials tested, it is found that the average error in the model prediction for a single trench at constant feed speed is lower than 5 % and for overlapped trenches the error is always lower than 10 %. This innovative modelling framework opens avenues to: (i) generate in a repeatable and predictable manner any desired workpiece microtopography; (ii) understand the pulsed laser ablation machining process, in respect of the geometry of the trench produced, therefore improving the geometry of the resulting parts; (iii) enable numerical optimisation for the beam path, thus supporting the development of accurate and flexible computer assisted machining software for pulsed laser ablation micro-machining applications

Laser Micromachining of Silicon Substrates

Laser micromachining has been widely used for micro-component fabrication of various materials, such as silicon substrates where silicon wafer is ablated accurately and precisely through marking, scribing, drilling or dicing. Thermal damages can occur on the substrates when improper process parameters and methods are used. This paper presents a review on the micromachining of silicon substrates using conventional and novel lasers as well as water-assisted laser micromachining technologies. The basic concepts and approaches of the technologies are discussed along with the challenges to damage-free laser micromachining at commercially acceptable cutting rates.</jats:p

Underwater Laser Turning of Commercially-Pure Titanium

Underwater laser machining process is a material removal technique that can minimize thermal damage and offer a higher machining rate than the laser ablation in ambient air. This study applied the underwater method associated with a nanosecond pulse laser for turning a commercially pure titanium rod. The effects of laser power, surface speed and number of laser passes on machined depth and surface roughness were investigated in this work. The results revealed that a deeper cut depth and smoother machined surface than those obtained from the laser ablation in ambient air were achievable when the underwater laser turning process was applied. The machined depth and surface roughness were found to significantly increase with the laser power and number of laser passes. The findings of this study can disclose the insight as well as potential of the underwater laser turning process for titanium and other similar metals.</jats:p