Timothy W. Deines

Edge chipping in rotary ultrasonic machining of silicon

With the increase in demand of energy, more and more silicon-based solar panels are used to convert solar energy to electricity. In solar panel manufacturing, to increase the efficiency of solar cells, electrical contacts of the front side need to be connected to the back side of the panel. Therefore, holes of different sizes need to be drilled in silicon solar panels of certain designs. Because silicon has high brittleness and hardness, drilling of silicon solar panels using traditional drilling methods might lead to solar panel cracking and low tool life. Rotary Ultrasonic Machining (RUM) is one of the nontraditional drilling processes. It has been used to drill holes in many brittle materials. However, there is no report in the literature on RUM of silicon. This paper presents a study on edge chipping in RUM of silicon. Two-level three-factor full factorial design was employed to experimentally determine effects of input variables on edge chipping and cutting force. The experimentally determined relation between edge chipping and cutting force was compared with that obtained by Finite Element Analysis (FEA). Higher tool rotation speed, higher ultrasonic power and lower feedrate led to smaller edge chipping and lower cutting force. An important influencing parameter on edge chipping is cutting force. Large edge chipping is almost always accompanied by higher cutting force.

Dry Machining of Carbon Fiber Reinforced Plastic Composite by Rotary Ultrasonic Machining: Effects of Machining Variables

Rotary ultrasonic machining (RUM) has been used to drill holes in brittle, ductile, and composite materials. However, all these experiments were conducted with help of water or oil based coolant. This paper presents an experimental study on RUM of carbon fiber reinforced plastic (CFRP) composite using cold air as coolant. It reports effects of machining variables (ultrasonic power, spindle speed, and feedrate) on outputs (cutting force, torque, surface roughness, and burning) in RUM of CFRP using vortex-tube (VT) generated cold air as coolant.Copyright

Rotary Ultrasonic Machining of stainless steels: empirical study of machining variables

Stainless steels have a variety of engineering applications and have been machined using many processes. The composite/steel stacks are used increasingly in new generations of aircraft industry, presenting new challenges in drilling holes in these stacks. It has been reported that Rotary Ultrasonic Machining (RUM) could drill composite materials effectively. The feasibility to use RUM to drill stainless steel was also reported. However, there is no report on systematic study on effects of different machining variables in RUM of stainless steel. This paper presents an experimental study on RUM of stainless steels. Cutting force, torque and surface roughness in RUM of stainless steels have been investigated using different machining variables (including spindle speed, feedrate and ultrasonic power). [Received 17 October 2009; Revised 9 February 2010; Accepted 1 March 2010]

Development of an innovative coolant system for rotary ultrasonic machining

Rotary ultrasonic machining (RUM), a hybrid machining process combining the material removal mechanisms of diamond grinding and ultrasonic machining, has been recognised as a reliable and cost-effective machining method for hard-to-machine materials such as advanced ceramics. There exist a number of articles on this process, but no one has reported systematic studies on coolant effects. In this paper, the air-operated double diaphragm pump is used for the first time in rotary ultrasonic machining to develop a novel coolant system to study the coolant effect on RUM performances, including vertical cutting force, material removal rate and surface roughness. Experiments with different coolant delivery modes are conducted and the material removal process in rotary ultrasonic machining when employing the new coolant system is discussed.

Ultrasonic-vibration-assisted pelleting of wheat straw: an experimental investigation

Energy security, economy, environment sustainability are all driving the USA to develop alternative liquid transportation fuels that are domestically produced and environmental friendly. Bioethanol produced from cellulosic biomass can significantly reduce the use of fossil fuels in the transportation section. However, significant hurdles must be overcome for cost-effective manufacturing of cellulosic bioethanol. Cellulosic feedstocks have a low bulk density, causing high costs in transportation and storage. To address this problem, this paper reports an experimental investigation on ultrasonic-vibration-assisted (UV-A) pelleting of wheat straw. Results show that pellet density and durability were greatly improved with the assistance of ultrasonic vibration.

Energy consumption study in ultrasonic vibration-assisted pelleting of wheat straw for cellulosic biofuel manufacturing

Cellulosic biofuels are an alternative to petroleum-based transportation fuels. Ultrasonic vibration-assisted (UV-A) pelleting can increase density of cellulosic feedstocks, reduce transportation and storage costs, and increase sugar yield. However, energy consumption in UV-A pelleting has not been fully investigated. This paper presents an experimental study on energy consumption in UV-A pelleting of wheat straw. Effects of pelleting input variables (sieve size used in size reduction, pelleting pressure, ultrasonic power, and pellet weight) and size reduction machine type (knife milling versus hammer milling) are investigated. Results show that energy consumption in UV-A pelleting increased as sieve size, ultrasonic power, and pellet weight increased, and as pelleting pressure decreased. Energy consumption in UV-A pelleting of wheat straw particles processed by knife milling was higher than that in UV-A pelleting of those processed by hammer milling.

A Study on Amount of Biomass Pellets Used in Durability Testing

Biofuels are an alternative to petroleum-based liquid transportation fuels. Cellulosic biomass can be used as feedstocks for befoul manufacturing. Low density of cellulosic feedstocks causes difficulties in handling them during transportation and storage, thus hindering large-scale and cost-effective manufacturing of cellulosic biofuels. Pelleting can increase the density of cellulosic feedstocks by compacting bulky biomass into pellets. Pellet durability, an important quality parameter, measures the ability of pellets to withstand impact and other destructive forces during transportation and handling. ASABE standard S269.4 specifies a procedure to determine pellet durability using 500 grams of pellets. However, it does not provide any justification of choosing this amount of pellets. This paper investigates the feasibility of using a smaller amount of pellets (50 grams) to determine pellet durability. Results show that 50 grams of pellets can generate comparable durability results as 500 grams of pellets.Copyright

Surface roughness in rotary ultrasonic machining: hypotheses and their testing via experiments and simulations

Rotary ultrasonic machining (RUM) is a non-traditional drilling process. It has been used to drill not only brittle but also ductile materials. It was observed that the surface roughness of the drilled hole near the entrance side was better than that near the exit side. However, explanations about this observation could not be found in the literature. This paper aims to provide explanations about this observation. It presents three hypotheses and their testing via experiments and simulations.

Ultrasonic-Vibration Assisted Pelleting for Cellulosic Ethanol Manufacturing: Effects of Particle Size and Moisture Content on Power Consumption

Ethanol produced from cellulosic materials is an alternative to petroleum-based transportation fuels. However, its manufacturing costs are too high to be competitive at present. Raw cellulosic biomass materials have low density, causing their transportation and handling expensive, contributing to high manufacturing costs of cellulosic ethanol. Pelleting can increase the density of cellulosic biomass and reduce their transportation and handling costs. Ultrasonic vibration-assisted (UV-A) pelleting is a new pelleting method. Earlier studies show that moisture content and particle size have significant effects on pellet quality and sugar yield. However, their effects on power consumption in UV-A pelleting have not been studied. Since power consumption directly affects ethanol manufacturing costs, it is desirable to understand how input variables affect power consumption. The objective of this paper is to study effects of moisture content and particle size on power consumption in UV-A pelleting of wheat straw. Results show that higher moisture content and larger particle size result in higher power consumption.Copyright

Size Reduction of Poplar Wood Using a Lathe for Biofuel Manufacturing: A Preliminary Experiment

Poplar wood can be used as feedstocks for manufacturing of cellulosic biofuels (e.g., ethanol) as liquid transportation fuels. Producing ethanol from poplar wood involves reducing poplar wood into small particles, hydrolyzing cellulose inside poplar particles to fermentable sugars, and converting these sugars to ethanol. Size reduction is usually done by wood chipping and biomass milling. In the literature on poplar biofuels, there are no reports on particle formation mechanisms or effects of size reduction on sugar yield. One important reason for the lack of such knowledge is that particle formation in current size reduction methods is not well controlled. This paper presents the first attempt to use a lathe to generate poplar particles (or chips) with well controlled mechanisms of chip formation. The objective is to experimentally determine relations among chip thickness, uncut chip cross-section area, shear angle (representing the deformation severity of the chips), crystallinity index, and sugar yield.© 2011 ASME