| 1. |
- Ilar, Torbjörn, et al.
(författare)
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Modelling, simulation and analyses of systems with breakdown imposed scrapping
- 2009
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Ingår i: Journal of Simulation. - : Informa UK Limited. - 1747-7778 .- 1747-7786. ; 3:2, s. 107-113
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Tidskriftsartikel (refereegranskat)abstract
- This study shows that, for many manufacturing processes (such as welding and injection moulding), a machine breakdown will result in the scrapping of a component, and goes on to explain the effect that this can have on process simulation models. Breakdown-related scrapping events are ignored by commercially available process simulation packages and this reduces their usefulness in decision support. This paper explains the different types of breakdown/scrapping dynamic possible and clearly demonstrates the scrapping dynamics effect on one of the major performance measures in LEAN-based manufacturing systems, namely the Overall Equipment Effectiveness. The paper also demonstrates the effect on model accuracy of a miss interpretation of part scrap behaviour or none deliberately simplified modelling of part scrap. This uncertainty in model accuracy will reduce the usefulness of the simulation model as a decision support tool.
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| 2. |
- Ilar, Torbjörn, et al.
(författare)
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Root humping in laser welding : an investigation based on high speed imaging
- 2012
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Ingår i: Physics Procedia. - : Elsevier BV. - 1875-3892. ; 39, s. 27-32
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Tidskriftsartikel (refereegranskat)abstract
- Regular drop formation (humping) along the weld root during laser welding was studied by high speed imaging of the melt pool underneath the workpiece. The formation of droplets towards the rear of this weld pool was seen to be primarily caused by the pumping of melt from the bottom of the keyhole and the influence of gravity drawing melt into a sagging hump. This is a different process from the one which creates humps on the top surface of welds.
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| 3. |
- Ilar, Torbjörn, et al.
(författare)
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Simulation of production lines : The importance of breakdown statistics and the effect of machine position
- 2008
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Ingår i: International Journal of Simulation Modelling. - 1726-4529. ; 7:4, s. 176-185
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Tidskriftsartikel (refereegranskat)abstract
- This paper demonstrates the importance of choosing the correct values and statistical distributions for breakdown frequency and duration when simulating production line productivity. Statistical distributions with a wide range tend to reduce the productivity of the line but this trend can be disrupted by poor choice of mean values for the variables in question. Also, it is demonstrated that the productivity of a production line can be improved simply by re-arranging the order of unreliable machines in the line. If the line consists of similar or exchangeable machines, productivity can improved if the most unreliable machines are placed towards the end of the line. The paper also demonstrates the risks of reduction of the standard deviation to obtain a more deterministic model.
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| 4. |
- Ilar, Torbjörn, et al.
(författare)
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Simulation of production lines involving unreliable machines : the importance of machine position and breakdown statistics
- 2007
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Konferensbidrag (refereegranskat)abstract
- This paper demonstrates the importance of choosing the correct statistical distributions for breakdown frequency and duration when simulating production line productivity. Statistical distributions with a wide range tend to reduce the productivity of the line. Also, it is demonstrated that the productivity of a production line can be improved simply by re-arranging the order of unreliable machines in the line. If the line consists of similar or exchangeable machines, productivity can improved if the most unreliable machines are placed towards the end of the line.
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| 5. |
- Ilar, Torbjörn, et al.
(författare)
-
The effect of process interruption and scrap on production simulation models
- 2007
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Ingår i: CARV 2007. - : CARV. - 9780978318703
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Konferensbidrag (refereegranskat)abstract
- This study shows that, for many manufacturing processes (such as welding and injection moulding), a machine breakdown will result in the scrapping of a component, and goes on to explain the effect that this can have on process simulation models. Breakdown related scrapping events are ignored by commercially available process simulation packages and this reduces their usefulness in decision support. This paper explains the different types of breakdown/scrapping dynamic possible and provides equations which can be used to describe them in future generations of simulation software. This work clearly demonstrates the scrapping dynamics effect on one of the major performance measures in LEAN based manufacturing systems, namely the Overall Equipment Effectiveness.
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| 6. |
- Pocorni, Jetro Kenneth, et al.
(författare)
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Measuring the state-of-the-art in laser cut quality
- 2013
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Ingår i: 14th NOLAMP Conference: The 14th Nordic Laser Materials Processing Conference, August 26th – 28th 2013, Gothenburg, Sweden. - : Luleå University of Technology. - 9789174396881 - 9789174396898 ; , s. 101-108
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- This paper gives the current state of development of laser oxygen and inert gas cuttingfrom experimental results obtained in an industrial environment for a range of materials. The work considers cutting quality as a function of operating parameters. The keyquality parameters are the cut edge inclination, roughness and dross attachment, whilethe kerf width is also studied as an important feature. These parameters are studied asa function of three operating parameters; cutting speed, laser power and laser wavelength.
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| 7. |
- Pocorni, Jetro, et al.
(författare)
-
Measuring the State-of-the-Art in Laser Cut Quality
- 2013
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Ingår i: 14th NOLAMP Conference. - Luleå : Luleå tekniska universitet. - 9789174396881 - 9789174396898 ; , s. 101-108
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Konferensbidrag (refereegranskat)abstract
- This paper discusses the strategy appropriate to investigating the state of the art of laser cutting from an industrial point of view. The importance of creating the samples in a high quality industrial environment is emphasised and preliminary results are presented.
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| 8. |
- Powell, John, et al.
(författare)
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Weld root instabilities in fiber laser welding
- 2015
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Ingår i: Journal of laser applications. - : Laser Institute of America. - 1042-346X .- 1938-1387. ; 27:Suppl. 2
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Tidskriftsartikel (refereegranskat)abstract
- Fiber laser welding and fiber laser-arc hybrid welding have been developed into very useful industrial processes over the past few years. However, the use of fiber lasers can be associated with quality problems at the weld root such as intermittent penetration, melt ejection, and humping. This paper explains the mechanisms which create these instabilities and suggests a repair technique which would alleviate the problems in some cases. The main difference between fiber and CO2 laser welding is that during fiber laser welding there is a strong downward thrust on the melt in the keyhole.(This is not the case during CO2 laser welding.) The downward thrust on the melt is generated as a result of the fiber laser evaporating the top faces of bumps on the melt surface. The downward flow has two main effects;(a) the melt can achieve velocities which result in melt ejection from the root of the weld-which can result in intermittent penetration,(b) the supply of hot metal to the bottom of the weld makes the process much more thermally uniform at the top and bottom of the weld. This uniformity means that the melt is extended backward several millimeters on the top and bottom surfaces-which can result in melt humping in the weld root as well as on the top surface. This paper examines these weld root instabilities and also describes a technique of weld root remelting which has been shown to be effective in smoothing out the root of the weld to improve its tensile and fatigue properties
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