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Publications (10 of 26) Show all publications
Dewi, H. S., Fischer, A., Volpp, J., Niendorf, T. & Kaplan, A. F. .. (2020). Microstructure and mechanical properties of laser surface treated 44MnSiVS6 microalloyed steel. Optics and Laser Technology, 127, Article ID 106139.
Open this publication in new window or tab >>Microstructure and mechanical properties of laser surface treated 44MnSiVS6 microalloyed steel
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2020 (English)In: Optics and Laser Technology, ISSN 0030-3992, E-ISSN 1879-2545, Vol. 127, article id 106139Article in journal (Refereed) Published
Abstract [en]

Fatigue property improvement for automotive components such as crankshafts can be achieved through material selection and tailored surface design. Microalloyed steels are of high interest for automotive applications due to their balanced properties, excellent hardenability and good machinability. Lasers facilitate efficient and precise surface processing and understanding the laser-material-property interrelationships is the key to process optimisation. This work examines microstructural development during laser surface treatment of 44MnSiVS6 microalloyed steel and the resulting mechanical properties. Laser beam shaping techniques are employed to evaluate the impact of beam shaping on the process. It revealed that ferrite structures remain in the treated area surrounded by martensite due to insufficient heating and dwell time of carbon diffusion.

Place, publisher, year, edition, pages
Elsevier, 2020
Keywords
Laser surface treatment, 44MnSiVS6, Laser beam shaping, Microalloyed steel, Phase transformation
National Category
Manufacturing, Surface and Joining Technology
Research subject
Manufacturing Systems Engineering
Identifiers
urn:nbn:se:ltu:diva-77853 (URN)10.1016/j.optlastec.2020.106139 (DOI)
Available from: 2020-02-25 Created: 2020-02-25 Last updated: 2020-02-25
Volpp, J. (2019). Behavior of powder particles on melt pool surfaces. The International Journal of Advanced Manufacturing Technology, 102(5-8), 2201-2210
Open this publication in new window or tab >>Behavior of powder particles on melt pool surfaces
2019 (English)In: The International Journal of Advanced Manufacturing Technology, ISSN 0268-3768, E-ISSN 1433-3015, Vol. 102, no 5-8, p. 2201-2210Article in journal (Refereed) Published
Abstract [en]

Additive Manufacturing is in progress to change the production and manufacturing environments and possibilities; however, thecomplex processes taking place are not completely understood yet. A better understanding of the incorporation mechanism of theparticles into the melt pool during blown powder processes could lead to methods to increase the powder and energy efficiency.Therefore, the incorporation mechanism was investigated in experiments and simulation. High-speed images made it possible toobserve the behavior of single particles on the melt pool. A model based on the temperature-dependent surface tension/energydifference between the particle and the melt pool calculated the time until particle incorporation. It was shown that the surfacetension characteristics during particle heating can even lift the particle from the melt pool. The calculated wetting behavior incombination with high kinetic energies should lead to an immediate immersion of the particle into the melt pool. Since observationsdo not show this behavior, it is concluded that the surface tension plays a role in the incorporation mechanism, but othereffects like the occurrence of oxide layers or additional particle heating by the laser beam seem to lead to different mechanismsand heat conductions to support an earlier incorporation.

Place, publisher, year, edition, pages
London: Springer, 2019
Keywords
Laser additive manufacturing, Powder particle, Surface tension, Direct metal deposition
National Category
Other Engineering and Technologies not elsewhere specified Manufacturing, Surface and Joining Technology
Research subject
Manufacturing Systems Engineering
Identifiers
urn:nbn:se:ltu:diva-72697 (URN)10.1007/s00170-018-03261-1 (DOI)000469002200082 ()2-s2.0-85060679490 (Scopus ID)
Note

Validerad;2019;Nivå 2;2019-06-19 (johcin)

Available from: 2019-01-26 Created: 2019-01-26 Last updated: 2019-06-19Bibliographically approved
Volpp, J. & Vollertsen, F. (2019). Impact of multi-focus beam shaping on the process stability. Optics and Laser Technology, 112, 278-283
Open this publication in new window or tab >>Impact of multi-focus beam shaping on the process stability
2019 (English)In: Optics and Laser Technology, ISSN 0030-3992, E-ISSN 1879-2545, Vol. 112, p. 278-283Article in journal (Refereed) Published
Abstract [en]

Unwanted process defects occur during laser deep penetration welding. The formation mechanisms of the main process defects like spatters and pores are not completely identified yet. Several methods like beam oscillation or laser power modulation are known to help reducing the occurrence of defects. These methods change the temporal energy input. It can be assumed that also beam shaping influences the energy input into the keyhole and has the potential to influence process defects as well. Due to the adapted energy input keyhole instabilities, that are assumed to influence the formation of the defects, can be avoided. A newly developed multi-focus beam shaping optic that creates multiple beam waists in axial direction is used in this work. The additional areas with increased intensities are used to modify the energy input in the keyhole in order to explain the mechanism of spatter formation and evaluate the potential of the axial beam shaping for defect suppression during laser deep penetration welding. It is found that the number of spatters can be reduced when the middle sections of the keyhole are illuminated with a high intensity. It can be concluded that spatters can be reduced when a keyhole collapse is avoided and a high enough energy input is guaranteed in the upper keyhole sections.

Place, publisher, year, edition, pages
Elsevier, 2019
Keywords
Laser deep penetration welding, Pore and spatter formation, Axial beam shaping, Multi-focus optic
National Category
Manufacturing, Surface and Joining Technology
Research subject
Manufacturing Systems Engineering
Identifiers
urn:nbn:se:ltu:diva-71900 (URN)10.1016/j.optlastec.2018.11.032 (DOI)000458941800035 ()2-s2.0-85057245489 (Scopus ID)
Note

Validerad;2019;Nivå 2;2018-12-05 (svasva)

Available from: 2018-12-05 Created: 2018-12-05 Last updated: 2019-03-11Bibliographically approved
Frostevarg, J., Volpp, J., Thompson, C., Prasad, H. S., Fedina, T. & Brückner, F. (2019). Influence of the vapour channel on processing in laser powder bed fusion. Paper presented at 17th Nordic Laser Materials Processing Conference (NOLAMP17), 27-29 August, 2019, Trondheim, Norway. Procedia Manufacturing, 36, 80-87
Open this publication in new window or tab >>Influence of the vapour channel on processing in laser powder bed fusion
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2019 (English)In: Procedia Manufacturing, E-ISSN 2351-9789, Vol. 36, p. 80-87Article in journal (Refereed) Published
Abstract [en]

Additive Manufacturing provides many opportunities to design and manufacture parts that are difficult or not possible to produce with conventional methods. In Selective Laser Melting (SLM) in powder bed fusion (PBF), melt pool dynamics and stability is dependent on a large number of factors, e.g. laser power output, power density, travel speed, reflectivity of powder bed, rapid heating and vaporization. Since travel speeds are often very fast and the laser interaction zone is small, the physical events become difficult to predict but also to observe. This work aims to describe the formation and geometrical characteristics of the vaporization zone during processing. Using a combination of theoretical descriptions, resulting material structures and a comprehensive analysis of high-speed images of the processing zone for different heat inputs and travel speeds, explanations for the dynamic melt pool behaviour are derived. The melting and pressures from processing involved moves powder particles next to it, changing the conditions for neighbouring tracks due to lack of material. These findings can provide a basis for creating more efficient and stable SLM processing, with fewer imperfections.

Place, publisher, year, edition, pages
Elsevier, 2019
Keywords
High speed imaging, SLMPowder movement, Pressure
National Category
Manufacturing, Surface and Joining Technology
Research subject
Manufacturing Systems Engineering
Identifiers
urn:nbn:se:ltu:diva-75755 (URN)10.1016/j.promfg.2019.08.012 (DOI)
Conference
17th Nordic Laser Materials Processing Conference (NOLAMP17), 27-29 August, 2019, Trondheim, Norway
Note

Konferensartikel i tidskrift

Available from: 2019-08-29 Created: 2019-08-29 Last updated: 2019-08-29Bibliographically approved
Kaplan, A. F. ., Robertson, S. M., Frostevarg, J., Volpp, J., Ramasamy, A. & Kalfsbeek, B. (2019). Microstructure morphology characterization of welding consumables studied by pulse-shaped laser heating. Paper presented at 17th Nordic Laser Materials Processing Conference (NOLAMP17), 27-29 August, 2019, Trondheim, Norway. Procedia Manufacturing, 36, 184-191
Open this publication in new window or tab >>Microstructure morphology characterization of welding consumables studied by pulse-shaped laser heating
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2019 (English)In: Procedia Manufacturing, E-ISSN 2351-9789, Vol. 36, p. 184-191Article in journal (Refereed) Published
Abstract [en]

During welding, wire consumables can essentially contribute to the resulting microstructures and mechanical properties. In order to maintain high toughness even for high strength steel, certain microstructures are desirable, particularly acicular ferrite. An efficient, controllable test method was developed during which the wire is molten and experiences a thermal cycle by a shaped laser pulse, or a sequence of pulses, which shall resemble continuous laser-arc hybrid welding or narrow gap multi-layer laser welding. Different thermal cycles and wire chemistries have led to manifold microstructures. The morphology of the microstructures can become complex. Therefore, more detailed characterization of essential morphology aspects was carried out, to distinguish different results. The thermal cycles from quenching have led to shorter, thicker laths with more random orientation. The latter can be favourable for high toughness. Short reheating cycles by about 200 K/s caused finer, longer and more parallel laths, as for bainite, in varying size of blocks. Other aspects considered were grain boundary ferrite and non-metallic inclusions. Systematic variation of the thermal cycle by the testing method along with systematic description of microstructure morphology in more detail is a promising method to identify and optimize favoured routes for wire chemistry and welding techniques.

Place, publisher, year, edition, pages
Elsevier, 2019
Keywords
weld, steel, microstructure, categorization, morphology, geometry, shape, systematics
National Category
Manufacturing, Surface and Joining Technology
Research subject
Manufacturing Systems Engineering
Identifiers
urn:nbn:se:ltu:diva-75730 (URN)10.1016/j.promfg.2019.08.024 (DOI)
Conference
17th Nordic Laser Materials Processing Conference (NOLAMP17), 27-29 August, 2019, Trondheim, Norway
Note

Konferensartikel i tidskrift

Available from: 2019-08-28 Created: 2019-08-28 Last updated: 2019-08-28Bibliographically approved
Moradi, M., Khorram, A., Fallah, M. & Volpp, J. (2019). Nd:YAG Laser Welding of Ti6-Al-4V: Mechanical and Metallurgical Properties. Lasers in engineering (Print), 43(1-2), 21-33
Open this publication in new window or tab >>Nd:YAG Laser Welding of Ti6-Al-4V: Mechanical and Metallurgical Properties
2019 (English)In: Lasers in engineering (Print), ISSN 0898-1507, E-ISSN 1029-029X, Vol. 43, no 1-2, p. 21-33Article in journal (Refereed) Published
Abstract [en]

Titanium and their alloys have high strength to weight ratio, good corrosion resistance and high melting point temperature lead to their application in engineering. Ti-6Al-4V alloy has been widely used in medical, chemistry and aerospace industries. In this research, laser welding of Ti-6Al-4V sheet with the thickness of 1.7 mm performed using a 400 W pulsed Nd:YAG laser. The effects of laser peak power, pulse duration and laser pulse energy on the weld bead profile, weld microhardness, tensile strength and microstructure were studied. Results showed that by increasing laser peak power, decreasing pulse duration and increasing laser pulse energy, the weld penetration increases. Metallurgical observations revealed that welded zone comprises of acicular αˊ phase within prior coarse β grains. Microhardness distribution is more uniform in welded zone. The microhardness value in the welded zone is the highest which is attributed to high martensitic phase content in the welded zone. The ultimate tensile strength (UTS) values show the variation from 649 to 998 MPa in the Nd:YAG laser welded samples.

Place, publisher, year, edition, pages
Old City Publishing, 2019
Keywords
Nd:YAG laser, Ti-6Al-4V alloy, laser welding, pulsed, welding parameters, microstructure, mechanical properties
National Category
Manufacturing, Surface and Joining Technology
Research subject
Manufacturing Systems Engineering
Identifiers
urn:nbn:se:ltu:diva-75179 (URN)000470835800003 ()
Note

Validerad;2019;Nivå 2;2019-07-01 (johcin)

Available from: 2019-07-01 Created: 2019-07-01 Last updated: 2019-07-01Bibliographically approved
Volpp, J. (2019). Powder particle movement during Powder Bed Fusion. Paper presented at 17th Nordic Laser Materials Processing Conference (NOLAMP17), 27-29 August, 2019, Trondheim, Norway. Procedia Manufacturing, 36, 26-32
Open this publication in new window or tab >>Powder particle movement during Powder Bed Fusion
2019 (English)In: Procedia Manufacturing, E-ISSN 2351-9789, Vol. 36, p. 26-32Article in journal (Refereed) Published
Abstract [en]

Powder Bed Fusion is a widely used technique to produce complex parts with different materials. In principle, a pre-placed powder layer is locally melted by a laser beam and thereby fused to the previous tracks and layers. This technique offers high flexibility at fast processing speeds. High-speed laser scanning enables, on the one hand, the fast processing but induces heat, forces and pressure in and around the processing zone on the other hand. The behavior of the single particles on the powder bed around the processing zone is hard to observe and therefore not sufficiently investigated. High-speed-imaging was used in this work to track the movement of the powder particles of the powder bed during Powder Bed Fusion in order to observe and explain their behaviour. It could be observed that powder particles move towards the melt pool affecting a large area around the melt pool, which changes the powder distribution of the powder bed. This indicates that a strong gas flow is constantly present during processing, which is thought to be due to the metal vapour induced by laser evaporation but can be also induced when no vapour is present due to the temperature and pressure increase around the processing zone.

Keywords
Selective laser melting, particle tracking, denudation, particle movement, vapor flow
National Category
Manufacturing, Surface and Joining Technology
Research subject
Manufacturing Systems Engineering
Identifiers
urn:nbn:se:ltu:diva-75728 (URN)10.1016/j.promfg.2019.08.005 (DOI)
Conference
17th Nordic Laser Materials Processing Conference (NOLAMP17), 27-29 August, 2019, Trondheim, Norway
Note

Konferensartikel i tidskrift

Available from: 2019-08-28 Created: 2019-08-28 Last updated: 2019-08-28Bibliographically approved
Volpp, J., Brueckner, F. & Kaplan, A. (2019). Track geometry variations in selective laser melting processes. Journal of laser applications, 31(2), Article ID 022310.
Open this publication in new window or tab >>Track geometry variations in selective laser melting processes
2019 (English)In: Journal of laser applications, ISSN 1042-346X, E-ISSN 1938-1387, Vol. 31, no 2, article id 022310Article in journal (Refereed) Published
Abstract [en]

Selective laser melting processes are widely used for many industrial applications using a laser beam to melt preplaced powder materiallayer by layer to create technical parts. The building process of those structures requires remelting of adjacent tracks and layers in order toavoid cavities and achieve the joining of the new track to the previous track and layer. In order to achieve a sufficient overlap and minimizecavities, usually conservative processing parameters are chosen. A higher energy and powder usage efficiency would be achieved if knowingabout the formation process of the single tracks and their geometrical dimensions depending on the available powder. In this work, it isshown that the cross-sectional track geometry significantly varies within one layer. A simple model is developed describing the influence ofthe available powder for each track within one layer. Depending on the hatch distance, different variation patterns are observed andmodeled showing that the track variations are inherent phenomena of the process. It can be concluded that the variations of powder avail-ability can cause the geometric variations of the tracks.

Place, publisher, year, edition, pages
American Institute of Physics (AIP), 2019
Keywords
laser additive manufacturing, selective laser melting, laser metal fusion, track geometry, powder availability
National Category
Manufacturing, Surface and Joining Technology
Research subject
Manufacturing Systems Engineering
Identifiers
urn:nbn:se:ltu:diva-73778 (URN)10.2351/1.5096107 (DOI)000484435200040 ()2-s2.0-85065612393 (Scopus ID)
Note

Validerad;2019;Nivå 2;2019-05-29 (oliekm)

Available from: 2019-04-29 Created: 2019-04-29 Last updated: 2019-10-01Bibliographically approved
Laskin, A., Volpp, J., Laskin, V. A. & Ostrun, A. B. (2018). Beam shaping of focused radiation of multimode lasers. In: Kaierle S.,Heinemann S.W. (Ed.), High-Power Laser Materials Processing: Applications, Diagnostics, and Systems VII 2018. Paper presented at SPIE LASE, San Francisco, United States, 31 January - 1 February 2018. SPIE - International Society for Optical Engineering, 10525, Article ID 1052507.
Open this publication in new window or tab >>Beam shaping of focused radiation of multimode lasers
2018 (English)In: High-Power Laser Materials Processing: Applications, Diagnostics, and Systems VII 2018 / [ed] Kaierle S.,Heinemann S.W., SPIE - International Society for Optical Engineering, 2018, Vol. 10525, article id 1052507Conference paper, Published paper (Refereed)
Abstract [en]

Performance of various laser technologies like welding, metal sheet cutting based on the use of powerful multimode fiber lasers, fiber-coupled solid-state and diode lasers can be improved by manipulation of energy distribution perpendicular and along optical axis. Welding, cladding with 0.5-2 mm size working spots benefit from "inverse-Gauss" intensity profiles, and doubled or tripled spots perpendicular to axis are good solutions to provide more uniform temperature profiles on a workpiece. Thick metal sheet cutting, some types of welding get benefits from distributing the laser energy along the optical axis resulting in more efficient usage of laser energy, higher and more stable cutting edge quality, faster processing. Since the radiation of multimode lasers is of low spatial coherence, characterized by big Beam Parameter Products (BPP) or M2 values, it is difficult to control the intensity distribution by methods other than imaging of a fiber end using a collimator and focusing objective. A promising suggested solution is combining of imaging the fiber end and geometrical separation of focused spots either perpendicular to or along the optical axis using dedicated optical components. Thus, energy of high power lasers is distributed among multiple foci. To provide reliable operation with multi-kW lasers and avoid damages the multi-focus optical devices are designed as refractive elements with smooth optical surfaces. The paper presents descriptions of multi-focus optics as well as examples of intensity profile measurements of beam caustics and application results

Place, publisher, year, edition, pages
SPIE - International Society for Optical Engineering, 2018
Series
Proceedings of SPIE--the International Society for Optical Engineering, ISSN 0277-786X, E-ISSN 1996-756X ; 10525
Keywords
multi-focus, beam shaping, high power laser, multimode laser, welding, sheet metal cutting, cladding
National Category
Manufacturing, Surface and Joining Technology
Research subject
Manufacturing Systems Engineering
Identifiers
urn:nbn:se:ltu:diva-69306 (URN)10.1117/12.2287980 (DOI)000449776000006 ()2-s2.0-85047847165 (Scopus ID)978-1-5106-1536-6 (ISBN)
Conference
SPIE LASE, San Francisco, United States, 31 January - 1 February 2018
Available from: 2018-06-11 Created: 2018-06-11 Last updated: 2019-09-13Bibliographically approved
Volpp, J. (2017). Dynamik und Stabilität der Dampfkapillare beim Laserstrahltiefschweißen. (Doctoral dissertation). Bremen: Bias Verlag
Open this publication in new window or tab >>Dynamik und Stabilität der Dampfkapillare beim Laserstrahltiefschweißen
2017 (German)Doctoral thesis, monograph (Other academic)
Abstract [en]

The keyhole which is typical for laser deep penetration welding is responsible for the highly dynamic process behavior, which results in unwanted pore and spatter formation. This work aims to better understand the dynamic keyhole properties and occurrence of process defects. Therefore, a semi-analytical model is developed and validated by optical emission analysis. Spatter characteristics are evaluated in high speed videos and porosity in x-ray analysis. Correlations between keyhole behavior and spatter and pore characteristics could show that pores can form due to a keyhole collapse and spatter detachment requires more than the momentum from keyhole wall fluctuations. Dynamic behavior and process defects are influenced by the spatial laser intensity distribution.

Place, publisher, year, edition, pages
Bremen: Bias Verlag, 2017. p. 116
Keywords
Laser deep penetration welding, keyhole dynamics, pore and spatter formation mechanisms
National Category
Other Mechanical Engineering
Identifiers
urn:nbn:se:ltu:diva-72390 (URN)978-3-933762-57-3 (ISBN)
Available from: 2018-12-30 Created: 2018-12-30 Last updated: 2019-01-17Bibliographically approved
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ORCID iD: ORCID iD iconorcid.org/0000-0003-0194-9018

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