| 1. |
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| 2. |
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| 3. |
- Ring-Groth, Margareta, et al.
(author)
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Weldbonding of stainless steel : An introduction
- 1998
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In: Journal of Advanced Materials. - 1070-9789. ; 30:1, s. 36-39
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Journal article (peer-reviewed)abstract
- Weldbonding is a method which combines the best mechanical features of resistance spot welding and adhesive bonding. For adhesive users, the technique simplifies the curing stage since no fixtures are needed for the period when the adhesive develops handling strength, and for spot weld users, the technique gives a joint a better mechanical properties and a sealed joint line. The bonds created are similar to normal spot welds but the joint is constrained by the adhesive at the interface. The adhesive is not present in the area surrounding the spot weld, since the heat generated between the stainless steel sheets burns the adhesive in that area
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| 5. |
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| 6. |
- Joshi, Shrikant V., 1960-, et al.
(author)
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Lifetime determining factors during thermal cycling of zirconia based thermal barrier coatings
- 1995
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In: Surface Engineering. - : Informa UK Limited. - 0267-0844 .- 1743-2944. ; 11:3, s. 233-239
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Journal article (peer-reviewed)abstract
- Plasma sprayed yttria stabilised zirconia (YSZ) coatings were investigated to assess the factors influencing their durability during thermal cycling. For any given powder, the best performance was found to be achieved at an optimum plasma arc current, all other spray parameters being held constant. The YSZ overlayer thickness was found to be an important lifetime determining factor. Use of a NiCoCrAlY bond coat instead of Ni–Cr led to a substantial improvement in coating lifetime, with the enhancement provided by NiCoCr AlY becoming more pronounced with increasing porosity level of the ceramic overlayer. A post-coating heat treatment was also found to be beneficial to coating longevity. The relative ranking of magnesium zirconate and YSZ coatings was found to depend upon the thermal cycle adopted during testing, which has important implications in designing accelerated tests to evaluate coating performance.
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| 7. |
- Nilsson, Annika, et al.
(author)
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Finite-element simulation of V-die bending: A comparison with experimental results
- 1997
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In: Journal of Materials Processing Technology. - : Elsevier BV. - 0924-0136 .- 1873-4774. ; 65, s. 52-58
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Research review (peer-reviewed)abstract
- A major problem in sheet bending is to compensate for springback. Analytical descriptions are not sufficiently general to accommodate influences from the material and the geometry due to the simplifications that have to be made. Practical experiments are still needed to be able to compensate for springback. The aim of this work has been to test the finite-element method on its abilities to predict springback for free bending in a V-die. The work shows that the finite-element method can be used to predict springback off-line. The true stress-true strain curve from a tensile test is used as the material description. Springback has been studied for eight different materials of varying thickness. The process has been simulated with the code Nike2d and the results from the simulations compared with those from experiments, good correlation between the simulations and the experiments being achieved. © 1997 Elsevier Science S.A.
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| 8. |
- Nilsson, Annika, et al.
(author)
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Process development of aluminium ironing using finite element analysis
- 1999
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In: Modelling and Simulation in Materials Science and Engineering. - : IOP Publishing. - 0965-0393 .- 1361-651X. ; 7:6, s. 1005-1011
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Journal article (peer-reviewed)abstract
- In this paper, the use of finite-element simulation of an aluminum ironing process is presented. In this process friction, clearance distance between punch and die and punch radius must all be taken into consideration when designing products and processes. In practice, it is difficult to analyze individual parameters separately, but with computer simulation it is easy to see the effects of changing one specific parameter on the outcome of the process. This work has demonstrated the use of computational support in product development to gain an understanding of the effects of process and geometric parameters. The most important results were confirmation of the sensitivity of the process to clearance distance between punch and die and, also, frictional conditions, as well as the relative insensitivity of the process to change in punch nose radius
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| 9. |
- Bäckström, Mikael, et al.
(author)
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Development of a multi-tooth approach to tool condition monitoring in milling
- 1998
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In: Insight. - 1354-2575 .- 1754-4904. ; 40:8, s. 548-552
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Journal article (peer-reviewed)abstract
- The need to develop reliable, adequate and cost-efficient methods for tool condition monitoring in milling has been emphasized by industry for a long time. The development of such methods has to deal with many difficulties such as complex machining conditions and a large number of available process variables. The paper presents the development of a multi-tooth approach to tool condition monitoring applied to milling where the inherent methods have been evaluated in experimental studies. Non-traditional methods such as multivariate techniques have been used to handle the large amount of process information that become accessible during machining. The developed methods are applied on different aspects of tool condition monitoring where the results obtained create opportunities for future research.
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| 10. |
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| 11. |
- Bäckström, Mikael, 1963-
(author)
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On Monitoring and Control of Machining Processes
- 1999
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Doctoral thesis (other academic/artistic)abstract
- The thesis presents several aspects related to the industrial and academic activities associated with monitoring and control of the machining process and machine tools A survey of the industrial situation identified some key factors for a successful implementation of monitoring and control techniques. Applicable, relatively simple, systems for cutting-process monitoring and adaptive control are available on the commercial market today but the degree of industrial utilisation of the technique is low because the systems are experienced as hard to operate and use, and are at the same time considered unreliable. In order to promote a higher degree of industrial utilisation more work has to be devoted raising the performance of the system solutions. An Integrated Supervisory Process Control (ISPC) concept is presented as an approach dealing with multi-purpose control requirements utilising the individual advantages of several sensors and modelling techniques. The ISPC system is supposed to operate as a conceptual integration of sensors, process models and different control modules. Two prototype systems, based on five-axis machining centres, for real-time control of the machining process are outlined. Different strategies for monitoring and control are developed, implemented and experimentally tried out, and the studies conducted demonstrate results that encourage further research work devoted to verification of the proposed control concept. The results obtained in the initial experiments utilising methods for process control and monitoring, such as double exponential smoothing technique (DES), multivariate monitoring applied to signal tracking and artificial neural networks applied to cutting torque control, reveal that the different techniques have potential to improve the performance of monitoring and control tasks, thus contributing to the creation of more sophisticated and reliable solutions in the ISPC concept.
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| 12. |
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| 13. |
- Andersson, Roger
(author)
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Effects of composition and the production process on formability of austenitic stainless steels
- 1999
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Licentiate thesis (other academic/artistic)abstract
- Formability of austenitic stainless steels is strongly influenced by the chemical composition, the internal texture and the deformation conditions. The purpose of this study is to determine how small variations in chemical composition and minor variations in the production process are influencing the formability of type 304 and 316 austenitic stainless steels. In this study, the formability of ten sub-grades of type 316 austenitic stainless steel and four sub-grades of type 304 austenitic stainless steel were investigated. These investigations are expected to have significant impact for both stainless steel producers and users. If the influence of the chemistry on the formability and the influence of different paths in the cold-rolling plant on the anisotropy are better understood, then manufacturers will be able to design processes which optimise the limiting strains.
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| 14. |
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| 15. |
- Bengtsson, Per
(author)
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Microstructural, Residual Stress, and Thermal Shock Studies of Plasma Sprayed ZrO2-Based Thermal Barrier Coatings
- 1997
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Doctoral thesis (other academic/artistic)abstract
- Thermal barrier coatings (TBCs), with a thickness of 0.4 mm, are today extensively used on the hot parts of both stationary and flying jet engines. The purpose of the TBC is to protect the underlying material from high temperatures and severe thennal shock. To increase the efficiency of a jet engine, higher turbine inlet temperatures and higher pressure ratios are sought. Consequently, materials with increased insulating properties will be required and a way to achieve this is to use thicker coatings. However, standard production procedures of thick TBCs (> 1 mm) result in coatings with an insufficient thernal shock life. The aim of this work is to develop a thick thermal barrier coating withan acceptable thernal shock life.In the present thesis, parts of the microstructure, the residual stress state, and their correlation to process parameters in thick thermal barrier coatings are described. Further, an optimised coating structure is developed to increase the thermal shock resistance of a burner can, coated with a 1.8 mm thick TBC. The studied thermal barrier coatings, plasma sprayed onto a nickel-based substrate material, consist of a bond coating and a top coating. The bond coating material is an MCrAlY alloy and the top coating material is made of Zr02, partially stabilised with 8 wt.% Y203. The spraying of the coatings is perforned at Volvo Aero Corporation. Residual stresses in the samples were measured with a layer removal technique and the stresses were compared to modelled stresses from a finite element model.Tensile stresses in the order of 150 MPa were measured in the bond coating, after the bond coating deposition. These stresses remained after the spraying of the top coating, where low stresses varying from -15 to 10 MPa were found, dependent on spraying conditions. The low stresses were a result of stress relaxation by microcrack formation. The compressive top coating stresses were found in samples where the substrate temperature was high at the end of the topcoating spraying. This gave a large temperature difference when cooling to room temperature, and due to different thermal expansion coefficients between the substrate and the top coating, more compressive stresses resulted. Good agreement between modelled and measured residual stresses was obtained. Columnar grains were found in the solidified droplets (splats) of the top coating. Between the splats, horizontally oriented delaminations were found. Top coatings sprayed at a high substrate temperature or a high passage thickness showed the columnar grains to extend through the thickness of each lamella. This decreased the density of horizontal delaminations. The density of vertical microcracks was also found to decrease as the substrate temperature increased. This was confirmed from the modelling, where the top coating inelastic strain showed the same behaviour.Also, a segmentation crack network was found in top coatings sprayed with a high substrate temperature or a high passage thickness. The thermal shock performance of a burner can containing a 1.8 mm thick segmented top coating was compared to a can sprayed according to standard procedures. Within 35 thernal shock cycles, the standard burner can contained cracks which were considered to be unsafe for the integrity of the can. No such cracks were found in the segmented structure after 1000 cycles.The study shows that thick thermal barrier coatings on real components can be used in jet engines provided that the correct structure is chosen.
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| 16. |
- Bostanjoglo, Georg, et al.
(author)
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Processing of Ni-based aero engine components with repetitively Q-switched Nd:YAG lasers
- 1996
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In: High-Power Lasers. - : SPIE. ; , s. 145-157
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Conference paper (peer-reviewed)abstract
- Aircraft engine industry uses free running high power Nd:YAG lasers for drilling cooling holes into nickel base alloy turbine components. A cw-pumped, Q-switched, high beam quality laser system with 400W laser power is presented. The laser is used to trepan drilling of 1.6mm. Hastelloy X sheets and ceramic coated combustion chamber tubes of the same metal. Cylindrical shape, uniformity, and reproducibility are achieved with a trepan-like drilling setup. The heat load of the workpiece as well as the process time is considerably decreased by employing high-repetition Q-switched lasers.
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| 17. |
- Bylesjö, Hans, et al.
(author)
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Holistic design of manufacturing systems
- 1995
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In: Colloquium / Institution of Electrical Engineers. - : IEE. - 0963-3308. ; :238, s. 4/1-4/5
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Journal article (peer-reviewed)abstract
- To design, implement and operate an efficient manufacturing organizations today, a systems view is necessary; this picture is further complicated as manufacturing systems are also dynamic in nature. Holistic design of manufacturing systems, that is using dynamic systems thinking based on business strategy, can help to optimize technical, organizational and human factors in new system implementation. During the last decade numerous packages for the simulation of manufacturing systems have been developed as a support for the analysis and design of these systems. Simulation has traditionally concentrated on details, which is important at the design stage, but many of the total system aspects such as machine, organization and human aspects are lost. This paper presents the concept of a virtual arena as a means of approaching the holistic design of manufacturing systems; the literature relating to this concept is also presented in outline. Special interest is placed upon work relating to the total or holistic view of manufacturing organizations. Current research initiatives in Scandinavia are also presented.
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| 19. |
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| 20. |
- Ducharme, R., et al.
(author)
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Effects of different shielding gas compositions on the process of cw CO2 laser welding in the hyperbaric range
- 1996
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In: XI International Symposium on Gas Flow and Chemical Lasers and High-Power Laser Conference. - Bellingham, Wash : SPIE - International Society for Optical Engineering. ; , s. 530-533
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Conference paper (peer-reviewed)abstract
- A continuous carbon-dioxide laser of 1.35 kW has been used to study the welding of 5 mm thick stainless steel for pressures ranging from 0.1 to 0.8 MPa in increments of 0.1 MPa. Experimental data, including penetration depths, weld widths, and in some cases weld pool profiles, has been obtained for each value of the pressure using different mixtures of argon and helium shielding gases. In a previous paper it has been reported that keyhole welding could not be carried out for pressures significantly in excess of atmospheric pressure using pure argon and nitrogen shielding gases, but that the process was possible at pressures up to 0.8 MPa using helium. In the present paper the critical pressure for keyhole welding is determined as a function of the mixed shielding gas composition. The laser material interaction is analyzed by solving the heat conduction equation with line and point heat sources representing the keyhole and plume respectively. The line source strength is itself calculated from consideration of the inverse bremsstrahlung and Fresnel absorption processes in the keyhole. It is concluded that successful laser welding in the hyperbaric range crucially hinges on good plume control through the effective delivery of an appropriate shielding gas mixture.
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| 23. |
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| 24. |
- Engström, Hans
(author)
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Laser welding catalytic converters : a complete success for AP Torsmaskiner AB, Sweden
- 1999
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In: Svetsaren. - 0039-7083. ; 54:1-2, s. 26-28
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Journal article (other academic/artistic)abstract
- AP Torsmaskiner AB (Smaland, Sweden) is using an LMI laser welding machine equipped with a Trumpf 6 kW CO2 turbolaser and a helium shielding gas for welding car catalytic converters. The LMI system has three axes with two welding stations, with the laser being switched between stations via a moving indexing mirror. The silencer/catalytic converter is produced from W-1.4512 ferritic stainless steel using lap joints. Commissioning problems, including porosity due to dry oil from pressing steel plates, are discussed. Potential system design improvements are mentioned.
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| 25. |
- Engström, Hans
(author)
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"Racer" : a new laser and water jet R&D programme in Sweden
- 1999
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In: 7th NOLAMP Conference. - Lappeenranta : Lappeenrannan teknillinen korkeakoulu. - 9517643500 ; , s. 48-50
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Conference paper (peer-reviewed)abstract
- A new research and development programme, called Racer, for the promotion of laser and water jet technologies in mechanical engineering industries in Sweden is described. The programme is financed mainly by NUTEK, the Swedish National Board for Technical and Industrial Development. The programme is supported by more than 20 Swedish companies with Lulea University of Technology acting as programme manager. The sub-projects are: development of laser welding techniques for components of thick engineering materials; automation and laser welding by industrial robots; development of process technology and production equipment for laser surface treatment; laser surface hardening by Nd:YAG and diode lasers; and the development of alternative process technology for abrasive water jet cutting.
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| 29. |
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| 30. |
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| 31. |
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| 32. |
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| 33. |
- Forsman, Tomas, et al.
(author)
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Nd:YAG laser lap welding of coated aluminum alloys
- 1997
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In: Proceedings of the Laser Materials Processing Conference. - Orlando, Fla : Laser institute of America. - 0912035560 ; , s. G113-G120
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Conference paper (peer-reviewed)abstract
- This experimental program investigated the production of lap welds between 1 mm thick sheets of aluminium alloys 5182 and 6016 which had previously been coated with Drylube. (Drylube is a polymer based coating approx1 mu m thick which improves the formability of the aluminium alloy sheet). Successful welds were produced using a 2.5 kW Nd:YAG laser in conjunction with a 0.6 mm optical fibre. It was discovered that there is an optimum gap width between the two sheets which gives the best weld quality and strength. Pulsed and CW laser welds were produced and compared with respect to porosity and surface profile, etc
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| 34. |
- Forsman, Tomas, et al.
(author)
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Nd:YAG laser welding of aluminium : factors affecting absorptivity
- 1999
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In: Lasers in engineering (Print). - 0898-1507 .- 1029-029X. ; 8:4, s. 295-309
-
Journal article (peer-reviewed)abstract
- This paper investigates the factors affecting the absorptivity during Nd:YAG laser keyhole welding of a 6xxx aluminum alloy. The influence of surface condition on absorption is shown to be negligible. Experimental absorption measurements by calorimetry are compared to analytical absorption values using a simple model based on Fresnel absorption during multiple reflections in the keyhole.
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| 35. |
- Forsman, Tomas, et al.
(author)
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Nd:YAG laser welding of coated aluminium sheet with a new dry lubricant film
- 1998
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In: Svetsen. - 0039-7091. ; 57:3, s. 10-12
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Journal article (peer-reviewed)abstract
- Trials are reported of the Nd:YAG laser welding of sheet of thickness about 1 mm in two aluminium alloys (AA-5182 (Al, 4.0-5.0%Mg) and AA-6016 (Al, 0.3-0.6%Mg, 1.0-1.5%Si)) coated with "Drylube" dry lubricant (some with zinc passivation first). Effects were investigated of welding conditions (constant or pulsed operation, gap of 0.0-0.3 mm) on porosity, penetration, and microcracking at the fusion boundary. Weld cross-sections are presented. Results are given also of hardness and tensile tests.
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| 36. |
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| 37. |
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| 39. |
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| 40. |
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| 41. |
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| 42. |
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| 43. |
- Ivarson, Anders, et al.
(author)
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Laser oxygen cutting of stainless steel with powder injection or metal tape feed
- 1997
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In: Lasers in engineering (Print). - 0898-1507 .- 1029-029X. ; 6:3, s. 235-245
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Journal article (peer-reviewed)abstract
- This paper investigates the development and automation of an idea originally published by Arata et al.. If a layer of mild steel is placed over a stainless steel sheet during laser cutting, the cut edge quality of the stainless steel will be greatly improved. This present work demonstrates that similar cut edge improvements are possible by passing a mild steel tape through the laser beam above the stainless steel work piece during cutting.
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| 44. |
- Ivarson, A., et al.
(author)
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Reflection phenomena in Co2 laser cutting
- 1997
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In: Proceedings of the 6th Nordic Laser Material Processing Conference, Luleå, Sweden, August 27-29, 1997. - Luleå : Luleå tekniska universitet. ; , s. 16-24
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Conference paper (peer-reviewed)
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| 45. |
- Ivarson, Anders, et al.
(author)
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Role of oxygen pressure in laser cutting mild steels
- 1996
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In: Journal of laser applications. - : Laser Institute of America. - 1042-346X .- 1938-1387. ; 8:4, s. 191-196
-
Journal article (peer-reviewed)abstract
- This paper presents the results of an experimental program investigating the effects of using high pressure oxygen as assist gas in combination with a pulsed laser while cutting medium thick mild steel plates. It was discovered that if the pulse conditions are optimized, the maximum cutting speed for a set average laser power could be increased by up to 10% compared to low oxygen pressure continuous wave (CW) laser cutting. The assist gas was found to have two optimum pressure ranges between which the material suffered from burning on the cut edge. The paper presents a phenomenological model to explain the changes in cut front dynamics as the oxygen pressure is increased and the role of pulsing in suppressing edge burning
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