Robust High-Speed Melt Pool Measurements for Laser Welding with Sputter Detection Capability

2007 ◽  
pp. 476-485 ◽  
Author(s):  
Nicolaj C. Stache ◽  
Henrik Zimmer ◽  
Jens Gedicke ◽  
Alexander Olowinsky ◽  
Til Aach
Keyword(s):  
Laser Welding ◽  
High Speed ◽  
Detection Capability ◽  
Melt Pool

scholarly journals Multi-Output Monitoring of High-Speed Laser Welding State Based on Deep Learning

Sensors ◽  
2021 ◽  
Vol 21 (5) ◽  
pp. 1626
Author(s):  
Boce Xue ◽  
Baohua Chang ◽  
Dong Du
Keyword(s):  
Deep Learning ◽  
Laser Welding ◽  
High Speed ◽  
Production Quality ◽  
Monitoring Methods ◽  
State Monitoring ◽  
High Speed Imaging ◽  
Melt Pool ◽  
Multiple State ◽  
Output Monitoring

In order to ensure the production quality of high-speed laser welding, it is necessary to simultaneously monitor multiple state properties. Monitoring methods combining vision sensing and deep learning models are popular but most models used can only make predictions on single welding state property. In this contribution, we propose a multi-output model based on a lightweight convolutional neural network (CNN) architecture and introduce the particle swarm optimization (PSO) technique to optimize the loss function of the model, to simultaneously monitor multiple state properties of high-speed laser welding of AISI 304 austenitic stainless steel. High-speed imaging is performed to capture images of the melt pool and the dataset is built. Test results of different models show that the proposed model can achieve monitoring of multiple welding state properties accurately and efficiently. In addition, we make an interpretation and discussion on the prediction of the model through a visualization method, which can help to deepen our understanding of the relationship between the melt pool appearance and welding state. The proposed method can not only be applied to the monitoring of high-speed laser welding but also has the potential to be used in other procedures of welding state monitoring.

scholarly journals An Experimental Approach for the Direct Measurement of Temperatures in the Vicinity of the Keyhole Front Wall during Deep-Penetration Laser Welding

2020 ◽  
Vol 10 (11) ◽  
pp. 3951
Author(s):  
Ronald Pordzik ◽  
Peer Woizeschke
Keyword(s):  
Laser Welding ◽  
Boiling Point ◽  
High Speed ◽  
Pure Aluminum ◽  
Welding Process ◽  
Deep Penetration ◽  
Front Wall ◽  
Melt Pool ◽  
Direct Laser ◽  
Welding Processes

The formation of defects such as pores during deep-penetration laser welding processes is governed by the melt pool dynamics and the stability of the vapor capillary, also referred to as the keyhole. In order to gain an insight into the dynamics of the keyhole, the temperature in the transition region from the liquid to the gaseous phase, i.e., near the keyhole wall, is a physical value of fundamental importance. In this paper, a novel method is presented for directly measuring temperatures in the close vicinity of the keyhole front wall during deep-penetration laser welding. The weld samples consist of pure aluminum with a boiling point of 2743 K. The measurement is performed using high-speed pyrometry with a refractory tantalum probe capable of detecting temperatures that significantly exceed the boiling point of the sample material. Temperature curves are recorded from the beginning of the welding process until the moment the probe is finally destroyed through direct laser-tantalum interaction. With an effective spatial resolution up to 0.3 µm in the welding direction, a detailed investigation into the temperature ranging from the prerunning melt pool front to the keyhole center is possible, exhibiting temperatures of up to 3300 K in the vicinity of the keyhole front wall.

scholarly journals Process characterization and analysis of ceramic powder bed fusion

2021 ◽  
Author(s):  
Kevin Florio ◽  
Dario Puccio ◽  
Giorgio Viganò ◽  
Stefan Pfeiffer ◽  
Fabrizio Verga ◽  
...  
Keyword(s):  
High Speed ◽  
Ceramic Powder ◽  
Integrating Sphere ◽  
Alumina Powder ◽  
Powder Bed Fusion ◽  
Single Track ◽  
Ceramic Powders ◽  
Pure Alumina ◽  
Powder Bed ◽  
Melt Pool

AbstractPowder bed fusion (PBF) of ceramics is often limited because of the low absorptance of ceramic powders and lack of process understanding. These challenges have been addressed through a co-development of customized ceramic powders and laser process capabilities. The starting powder is made of a mix of pure alumina powder and alumina granules, to which a metal oxide dopant is added to increase absorptance. The performance of different granules and process parameters depends on a large number of influencing factors. In this study, two methods for characterizing and analyzing the PBF process are presented and used to assess which dopant is the most suitable for the process. The first method allows one to analyze the absorptance of the laser during the melting of a single track using an integrating sphere. The second one relies on in-situ video imaging using a high-speed camera and an external laser illumination. The absorption behavior of the laser power during the melting of both single tracks and full layers is proven to be a non-linear and extremely dynamic process. While for a single track, the manganese oxide doped powder delivers higher and more stable absorptance. When a full layer is analyzed, iron oxide-doped powder is leading to higher absorptance and a larger melt pool. Both dopants allow the generation of a stable melt-pool, which would be impossible with granules made of pure alumina. In addition, the present study sheds light on several phenomena related to powder and melt-pool dynamics, such as the change of melt-pool shape and dimension over time and powder denudation effects.

Measurement of the Melt Pool Length During Single Scan Tracks in a Commercial Laser Powder Bed Fusion Process

2017 ◽  
Author(s):  
J. C. Heigel ◽  
B. M. Lane
Keyword(s):  
Laser Power ◽  
High Speed ◽  
Infrared Camera ◽  
Powder Bed Fusion ◽  
Single Track ◽  
Laser Powder Bed Fusion ◽  
Powder Bed ◽  
Melt Pool ◽  
Significant Difference ◽  
Scan Speed

This work presents high speed thermographic measurements of the melt pool length during single track laser scans on nickel alloy 625 substrates. Scans are made using a commercial laser powder bed fusion machine while measurements of the radiation from the surface are made using a high speed (1800 frames per second) infrared camera. The melt pool length measurement is based on the detection of the liquidus-solidus transition that is evident in the temperature profile. Seven different combinations of programmed laser power (49 W to 195 W) and scan speed (200 mm/s to 800 mm/s) are investigated and numerous replications using a variety of scan lengths (4 mm to 12 mm) are performed. Results show that the melt pool length reaches steady state within 2 mm of the start of each scan. Melt pool length increases with laser power, but its relationship with scan speed is less obvious because there is no significant difference between cases performed at the highest laser power of 195 W. Although keyholing appears to affect the anticipated trends in melt pool length, further research is required.

Analysis of Image Characteristics of Plume and Spatter of High Power Disk Laser Welding Based on K-L Transform

2012 ◽  
Vol 532-533 ◽  
pp. 330-334
Author(s):  
Qian Wen ◽  
Xiang Dong Gao
Keyword(s):  
Laser Welding ◽  
High Power ◽  
High Speed ◽  
Metal Vapor ◽  
Mean Value ◽  
Gray Level ◽  
Characteristic Parameters ◽  
Transform Method ◽  
Disk Laser ◽  
Vapor Plume

Metal vapor plume and spatters are the important phenomena in the process of high power disk laser welding, and there exists a close relationship with the welding stability. The images of metal vapor plume and spatters which captured by a high speed camera during high power disk laser welding were analyzed in this experiment. Image processing techniques such as median filtering, Wiener filtering, gray level threshold and lightness transform were used to process the images so that the image characteristic parameters such as the area and number of spatters in an image, the average gray, mean value, variance and entropy of a spatter gray level image and the coordinate ratio of the centriod of plume and the welding point can be extracted. To reflect the actual welding results obviously by those characteristic parameters, K-L transform method was used to get a new set of characteristic parameters. Experimental results showed that this new set of characteristic parameters could reflect the actual welding effectively.

A Study on Laser Welding of Titanium and Stainless Steel

2018 ◽  
Author(s):  
Angshuman Chattopadhyay ◽  
Gopinath Muvvala ◽  
Vikranth Racherla ◽  
Ashish Kumar Nath
Keyword(s):  
Stainless Steel ◽  
Laser Welding ◽  
Weld Joint ◽  
Welding Speed ◽  
Fusion Process ◽  
Longitudinal Stress ◽  
Transverse Cracks ◽  
Cooling Rates ◽  
Melt Pool ◽  
Longitudinal Cracks

Joining of dissimilar metals and alloys has been envisioned since a long time with specific high end applications in various fields. One such combination is austenitic stainless steel grade SS304 and commercial grade titanium, which is very difficult to join under conventional fusion process due to extensive cracking and failure caused by mismatch in structural and thermal properties as well as formation of the extremely brittle and hard intermetallic compounds. One of the methods proposed in literature to control the formation of intermetallics is by fast cooling fusion process like laser beam welding. The present study has been done on laser welding of titanium and stainless steel AISI 304 to understand the interaction of these materials during laser welding at different laser power and welding speed which could yield different cooling rates. Two types of cracks were observed in the weld joint, namely longitudinal cracks and transverse cracks with respect to the weld direction. Longitudinal cracks could be completely eliminated at faster welding speeds, but transverse cracks were found little influenced by the welding speed. The thermal history, i.e. melt pool lifetime and cooling rate of the molten pool during laser welding was monitored and a relation between thermo-cycle with occurrence of cracks was established. It is inferred that the longitudinal cracks are mainly due to the formation of various brittle intermetallic phases of Fe and Ti, which could be minimized by providing relatively less melt pool lifetime at high welding speeds. The reason of the transverse cracks could be the generation of longitudinal stress in weld joint due to the large difference in the thermal expansion coefficient of steel and titanium. In order to mitigate the longitudinal stress laser welding was carried out with a novel experimental arrangement which ensured different cooling rates of these two metals during laser welding. With this the tendency of transverse cracks also could be minimized significantly.

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