| 181. |
- Powell, John, et al.
(author)
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Laser casting and laser clad-casting : new processes for rapid prototyping
- 2002
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In: Congress proceedings. - Orlando, Fla : Laser institute of America. - 912035730
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Conference paper (peer-reviewed)abstract
- This paper presents preliminary experimental results from two new processes: Laser casting involves a process similar to blown powder laser cladding but the final product is not joined to the substrate. The substrate surface therefore acts as a mould in a laser casting process and the eventual casting retains the topological features of the substrate. Laser clad-casting involves the production of clad tracks which are welded as usual to a substrate but which are laid down between machined copper blocks. The eventual clad track therefore has its cross sectional profile determined by the blocks which are removed after completion of the cladding process. In this way clad tracks with large depth to width ratios can be achieved with pre determinated cross sections
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| 182. |
- Powell, John, et al.
(author)
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Laser cutting : from first principle to the state of art
- 2004
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In: Peer reviewed conference proceedings. - Orlando, Fla : Laser institute of America. - 0912035765
-
Conference paper (peer-reviewed)abstract
- This paper presents an overview of the subject of laser cutting. Subjects covered include; Laser-materials interactions, different laser types, the technical and commercial growth of laser cutting and the state of the art.
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| 183. |
- Powell, John, et al.
(author)
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LASER CUTTING OF STEELS: A physical and chemical analysis of the particles ejected during cutting : Part II
- 1993
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In: Journal of laser applications. - : Laser Institute of America. - 1042-346X .- 1938-1387. ; 5:1, s. 25-31
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Journal article (peer-reviewed)abstract
- This paper is a continuation of work published in an earlier edition of this journal[1]. Both papers deal with the results of a detailed analysis of the particles ejected from the cut zone during laser cutting of mild and stainless steels. The earlier paper presented the thermochemical data and discussion generated by the experimental investigation. This paper concentrates on the physical characteristics and metallography of the particles. Analysis techniques used included: scanning electron microscopy, optical microscopy, metallography and particle sizing. The results from this extensive analysis have enabled the authors to postulate oxidation histories for the particles. In addition to this, it has been possible to explain the variation in particle size for various material thicknesses.
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| 184. |
- Powell, John, et al.
(author)
-
Laser cutting stainless steel with dual focus lenses
- 2000
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In: Journal of laser applications. - : Laser Institute of America. - 1042-346X .- 1938-1387. ; 12:6, s. 224-231
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Journal article (peer-reviewed)abstract
- In this article the performance of a new type of lens is compared with traditional meniscus lenses for CO sub 2 laser cutting of medium ( > 5 mm) section stainless steel. Dual Focus lenses produce two focus spots, one above the other. This type of optic was found to be capable of higher cutting speeds and better quality cuts. A phenomenological model is presented which explains the superior performance of Dual Focus lenses. The model concentrates upon the fact that during high speed cutting of medium section metals, the laser does not irradiate the lower portion of the cut zone. This lower part of the cut is heated by the melt flowing over it, which has been previously heated by the laser. This melt preheating involves narrower kerfs and higher cut speeds if a dual focus lens is used.
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| 185. |
- Powell, John, et al.
(author)
-
Laser cutting technology - a commercial perspective : Fiber or CO2 laser – which one to buy next?
- 2012
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In: Laser Technik Journal. - : Wiley. - 1613-7728. ; 9:2, s. 39-41
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Journal article (peer-reviewed)abstract
- Since the advent of commercial fibre and disk laser cutting machines there has been a lot of controversy about the performance of these devices – particularly in comparison to their more established CO2 counterparts. In the early days the sales staff promoting fibre technology would often declare that the new lasers would completely take over from CO2 technology very quickly – but this has not happened. Even taking into account the entrenched position of the older technology, fibre and disk lasers have not been as widely accepted as was predicted, although they have been proven to outperform CO2 lasers in certain important areas.This article presents a discussion of the advantages and disadvantages of both types of cutting technology from a commercial point of view – written from the perspective of a laser cutting jobshop owner trying to decide between buying a fibre or CO2 laser cutting machine
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| 186. |
- Powell, John, et al.
(author)
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Laser–oxygen cutting of mild steel: the thermodynamics of the oxidation reaction
- 2009
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In: Journal of Physics D. - : IOP Publishing. - 0022-3727 .- 1361-6463. ; 42:1
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Journal article (peer-reviewed)abstract
- In a considerable proportion of the published work on the subject of laser-oxygen cutting of mild steel, the details of the oxidation reaction are overlooked or confused. For example, it is not uncommon for the oxidized material to be attributed with the physical characteristics of iron rather than iron oxide. Also, the fact that the oxidation reaction cannot take place above a certain temperature limit is usually overlooked. This paper presents, for the first time, an in-depth analysis of the Iron to FeO oxidation reaction in the context of laser-oxygen cutting of mild steel. The paper concludes by presenting a number of guidelines for future theoretical models.
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| 187. |
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| 188. |
- Powell, John, et al.
(author)
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Role of oxygen purity in laser cutting of mild steel
- 1992
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In: Proceedings of the laser materials processing symposium, ICALEO '92. - Orlando, fla : Laser institute of America. - 0912035498 ; , s. 433-442
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Conference paper (peer-reviewed)abstract
- This paper begins by describing the thermal inputs to the cut zone when cutting mild steel with oxygen as the assist gas. The investigation concentrates on the chemical thermo-dynamics in the cut zone and pays particular attention to the influence of oxygen dilution. A detailed experimental program has allowed the authors to theoretically clarify why the process is highly sensitive to small levels of contamination of the oxygen jet.
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| 189. |
- Powell, John, et al.
(author)
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Self organised criticality in abrasive water jet cutting
- 1997
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In: International Journal of Water Jet Technology. - 1180-0402. ; 2:3, s. 181-186
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Journal article (peer-reviewed)abstract
- This paper demonstrates that the material removal processes employed during abrasive water jet (AWJ) cutting show evidence of Self Organised Criticality (S.O.C.). This means that the overall erosion process consists of a large number of events which are identical except for their size. The relative frequency of these self-similar events is related to their magnitude by a power law, for example an erosion event of relative magnitude 100 may be accompanied by 10 exp 3 of magnitude 10 and 10 exp 8 of magnitude 1. As the mechanism of step formation and localised erosion has been establish in earlier work (4, 5, 6), it is reasonable to postulate that the numerous self similar erosion events are of this type. It is demonstrated that for ductile material (such as metals) and brittle material (such as glass) the abrasive water jet cutting mechanism obeys the laws of self organized criticality
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| 190. |
- Powell, John, et al.
(author)
-
The energy generated by the oxidation reaction during laser-oxygen cutting of mild steel
- 2008
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In: Congress proceedings. - Orlando, Fla : Laser institute of America. - 9780912035123 ; , s. 628-636
-
Conference paper (peer-reviewed)abstract
- This paper presents an in-depth analysis of the Iron to FeO oxidation reaction in the context of laser-oxygen cutting of mild steel. The paper concludes by presenting a number of guidelines for future theoretical models of laser-oxygen cutting.
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