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Kamath G.R.,Hypertherm Inc.
2014 IEEE International Conference on Power Electronics, Drives and Energy Systems, PEDES 2014 | Year: 2014

This paper presents an analysis of the skin and proximity effects produced by line frequency harmonic currents in a 33 kW 12-pulse rectifier transformer using its 'Double-2D' FEA model. The model is first validated with experimental data obtained from a series of standard impedance voltage tests with a proof-of-concept transformer prototype. Good agreement is observed between model results and experimental data. The model is then used to study the 12-pulse harmonic current conditions and represent the associated winding losses as equivalent resistances. It is seen that harmonic current losses account for as much as 8-11% of the secondary winding and 4-6% of the total winding power loss, indicating their significance in this application. © 2014 IEEE.

Ebner R.L.,Mitre Corporation | Mehdi F.,Hypertherm Inc. | Klewicki J.C.,University of New Hampshire | Klewicki J.C.,University of Melbourne
Journal of Fluid Mechanics | Year: 2016

The structure of smooth- and rough-wall turbulent boundary layers is investigated using existing data and newly acquired measurements derived from a four element spanwise vorticity sensor. Scaling behaviours and structural features are interpreted using the mean momentum equation based framework described for smooth-wall flows by Klewicki (J. Fluid Mech., vol. 718, 2013, pp. 596-621), and its extension to rough-wall flows by Mehdi et al. (J. Fluid Mech., vol. 731, 2013, pp. 682-712). This framework holds potential relative to identifying and characterizing universal attributes shared by smooth- and rough-wall flows. As prescribed by the theory, the present analyses show that a number of statistical features evidence invariance when normalized using the characteristic length associated with the wall-normal transition to inertial leading-order mean dynamics. On the inertial domain, the spatial size of the advective transport contributions to the mean momentum balance attain approximate proportionality with this length over significant ranges of roughness and Reynolds number. The present results support the hypothesis of Mehdi et al., that outer-layer similarity is, in general, only approximately satisfied in rough-wall flows. This is because roughness almost invariably leaves some imprint on the vorticity field; stemming from the process by which roughness influences (generally augments) the near-wall three-dimensionalization of the vorticity field. The present results further indicate that the violation of outer similarity over regularly spaced spanwise oriented bar roughness correlates with the absence of scale separation between the motions associated with the wall-normal velocity and spanwise vorticity on the inertial domain. © 2016 Cambridge University Press.

McQuade K.,Hypertherm Inc.
Welding and Cutting | Year: 2010

Back to the original question as to which process is the best. Hopefully the answer "it depends" now makes sense as it does depend on each specific cutting operation. Laser is often used when cutting thin plate (less than 6 mm) and where tight tolerances are required. The capital cost and operating cost are both high. Oxyfuel is mainly used for cutting only thick carbon steel (greater than 50 mm) when cut quality is not a requirement. Oxyfuel has the lowest capital cost and operating cost, but the cost per part is higher due to slow cutting speeds and lower quality which often requires rework.Plasma provides a good balance in terms of capital cost, cut quality, productivity and operating cost. It has a broad thickness range, material flexibility and provides high cutting speeds.

Kim S.,University of Minnesota | Kim S.,Hypertherm Inc. | Heberlein J.,University of Minnesota | Lindsay J.,Hypertherm Inc. | Peters J.,Hypertherm Inc.
Plasma Chemistry and Plasma Processing | Year: 2012

Highly constricted plasma arcs are widely used for metal cutting. One important characteristic of the cutting process is the consistency of the cut edge around the perimeter of the workpiece. Cut edge properties, including surface roughness, edge shape and dross formation, are presumed to depend on the local temperature and chemical composition of the cutting arc adjacent to the cut edge. Fluid dynamic instabilities in the arc boundary leading to entrainment of the low temperature ambient gas can have a strong effect on cutting performance. This paper describes the use of micro-jets to suppress fluid dynamic instabilities in the boundary layer of a plasma cutting arc. Previously developed optical diagnostics and analysis methods are used to characterize the arc boundary layer. Multiple nozzle designs have been investigated to quantify the effects of utilizing micro-jet flow around the arc column, and some relationships between nozzle design and cut quality are presented. © Springer Science+Business Media, LLC 2011.

Kim S.,University of Minnesota | Kim S.,Hypertherm Inc. | Heberlein J.,University of Minnesota | Lindsay J.,Hypertherm Inc. | Peters J.,Hypertherm Inc.
Journal of Physics D: Applied Physics | Year: 2010

Plasma cutting is commonly used to cut metals in a variety of applications. This research is motivated by the lack of fundamental understanding of the dynamics of the plasma flow interacting with cold gas environment. It is focused on the characterization of the arc instabilities that affect the quality and consistency of a cut. The characterization of instabilities has been performed with high-speed Schlieren imaging technology to visualize the arc width and the light intensity fluctuations in the arc boundary layer. Measurements of arc symmetry using Fourier and wavelet transforms of the light intensity fluctuations in individual pixels in the Schlieren images are able to provide a quantitative measure for the degree of instability. Ambient gas entrainment into the plasma jet is measured using a CCD camera with a narrow bandpass filter centred on the nitrogen atomic line to detect nitrogen concentrations throughout the arc, thus showing the penetration of shield and ambient gas into the pure oxygen plasma. The effects of torch design features on these characteristics are investigated by comparing two different torch designs. The results show that the developed diagnostics are useful for evaluating new torch designs. © 2010 IOP Publishing Ltd.

When it comes to cutting metal, there are several options; important is figuring out which option is right for your business. Choosing the right process is dependent upon the cutting needs of your business: cut quality, productivity, operating costs, profitability, process flexibility or investment costs. This article explores the three major thermal cutting technologies - oxyfuel, laser and plasma - and provides insight into what is important to consider when deciding which cutting process would be best for you.

Osterhouse D.J.,University of Minnesota | Lindsay J.W.,Hypertherm Inc. | Heberlein J.V.R.,University of Minnesota
Journal of Physics D: Applied Physics | Year: 2013

Plasma arc cutting is a widely used industrial process in which an electric arc in the form of a high velocity plasma jet is used to melt and blow away metal. The arc attaches inside the resulting cut slot, or kerf, where it both provides a large heat flux and determines the flow dynamics of the plasma. Knowledge of the position of the arc attachment is essential for understanding the phenomena present at the work piece. This work presents a new method of measuring the location of the arc attachment in which the arc voltage is measured during the cutting of a range of work piece thicknesses. The attachment location is then interpreted from the voltages. To support the validity of this method, the kerf shape, dross particle size and dross adhesion to the work piece are also observed. While these do not conclusively give an attachment location, they show patterns which are consistent with the attachment location found from the voltage measurements. The method is demonstrated on the cutting of mild steel, where the arc attachment is found to be stationary in the upper portion of the cut slot and in reasonable agreement with existing published findings. For a process optimized for the cutting of 12.7 mm mild steel, the attachment is found at a depth of 1.5-3.4 mm. For a slower process optimized for the cutting of 25.4 mm mild steel, the attachment is found at a depth of 3.4-4.8 mm, which enhances heat transfer further down in the kerf, allowing cutting of the thicker work piece. The use of arc voltage to locate the position of the arc attachment is unique when compared with existing methods because it is entirely independent of the heat distribution and visualization techniques. © 2013 IOP Publishing Ltd.

Hypertherm Inc. | Date: 2010-08-10

Communications software for computer controlled plasma arc cutting or welding systems that facilitates the programming of computer numerical controls, cutting profiles, or shapes.

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