Anna Fellman

Visual measurement and tracking in laser hybrid welding

This paper presents a novel system for the automatic analysis of a hybrid welding process. High-speed imaging and laser illumination are used to measure the regularity of electric arc frequency and flight directions of filler metal droplets. A fuzzy c-means clustering method is used to detect arcs and segment the video sequences. The droplets are localized by combining principal component analysis and a support vector machine classifier. The flight of a droplet is tracked using Kalman filtering. Experiments indicate that the system is able to track the flights of droplets and to determine the regularity of the arc frequency with a high accuracy if the imaging conditions are stable.

The effect of shielding gas composition on welding performance and weld properties in hybrid CO2 laser–gas metal arc welding of carbon manganese steel

Metals industries producing large structures currently have a particular interest in hybrid laser welding processes, which possess advantages compared with conventional methods of welding. One major benefit is a reduction in deformation that enables the amount of postweld finishing work to be reduced. Assembly then also becomes simpler because of the greater accuracy that may be achieved. Larger joint tolerances may be accommodated compared with laser welding alone. By using appropriate filler metal, the weld metal composition may be controlled to meet metallurgical criteria. The hybrid CO2 laser–gas metal arc (GMA) welding process was investigated in this study; the aim being to clarify the effects of process gas composition on welding performance, weld cross section, quality, and mechanical properties, when welding carbon manganese steel. Helium, argon, and carbon dioxide were used in varying proportions as shielding gases for welding I-butt and T-butt joints. The composition of the shielding gas was fo...

Effect of laser and laser hybrid welding on the corrosion performance of a lean duplex stainless steel

Effect of laser and laser hybrid welding on the corrosion performance of a leanduplex stainless steel

Study of the phenomena of fiber laser-mag hybrid welding

Laser hybrid welding processes are gaining more interest in many sectors of metal industry. The process is already in successful use for example in automotive, ship building and construction industry. The laser hybrid welding processes are traditionally a combination of CO2 or Nd:YAG laser together with MIG/MAG or TIG welding. The arc welding source is chosen depending on whether there is also need for extra material. The use of high power fiber lasers in hybrid welding is increasing because of the small size, good beam quality and high powers available.The aim of this study was to study the characteristics of laser hybrid welding with fiber laser: How do the airgap, torch direction and distance between the processes affect the welding performance. The maximum power of fiber laser used is 5 kW. The arc process used was MIG/MAG welding. Material used was mild steel S355 of thickness 6 mm and joint type was butt joint. Welding process phenomena is photographed with CCD and CMOS cameras to see the welding appearance.It is obvious that the distance between the laser beam and arc welding process and torch direction play a big role in how wide airgaps can be tolerated. Leading torch tolerates longer distance between the processes than trailing torch, but trailing torch has better gap bridging ability.Laser hybrid welding processes are gaining more interest in many sectors of metal industry. The process is already in successful use for example in automotive, ship building and construction industry. The laser hybrid welding processes are traditionally a combination of CO2 or Nd:YAG laser together with MIG/MAG or TIG welding. The arc welding source is chosen depending on whether there is also need for extra material. The use of high power fiber lasers in hybrid welding is increasing because of the small size, good beam quality and high powers available.The aim of this study was to study the characteristics of laser hybrid welding with fiber laser: How do the airgap, torch direction and distance between the processes affect the welding performance. The maximum power of fiber laser used is 5 kW. The arc process used was MIG/MAG welding. Material used was mild steel S355 of thickness 6 mm and joint type was butt joint. Welding process phenomena is photographed with CCD and CMOS cameras to see the welding ap...

Observation of the phenomena of CO2 laser-mag hybrid welding

Laser hybrid welding combines laser and arc process to one process that has some advantages over both of the processes on their own. One advantage is the relief of the tolerances of laser welding. When this is combined with the advantages of laser welding, the hybrid welding process becomes an interesting solution for manufacturers of large products for improving their productivity.There have been many different assumptions made about the phenomena occurring during hybrid welding. This study utilizes special videographing system capable to provide a clear view of the hybrid welding process and the base material surrounding it. The pictures taken from CO2 laser-MAG hybrid welding process show that some of the earlier assumptions are correct. In the study some parameters were varied one at the time and the effects of the variations on the process were observed. The quality of the resulting welds was studied by visual and macrographic examination of the welds.It was seen clearly that when the processes are close enough to each other the arc is aimed towards the laser beam and keyhole and the processes are acting together. The airgap in the joint helps the interaction between the processes, since in such a case the arc turns more efficiently towards the laser beam and keyhole. It was also possible to see the changes in process stability and the formation of some of the weld defects.Laser hybrid welding combines laser and arc process to one process that has some advantages over both of the processes on their own. One advantage is the relief of the tolerances of laser welding. When this is combined with the advantages of laser welding, the hybrid welding process becomes an interesting solution for manufacturers of large products for improving their productivity.There have been many different assumptions made about the phenomena occurring during hybrid welding. This study utilizes special videographing system capable to provide a clear view of the hybrid welding process and the base material surrounding it. The pictures taken from CO2 laser-MAG hybrid welding process show that some of the earlier assumptions are correct. In the study some parameters were varied one at the time and the effects of the variations on the process were observed. The quality of the resulting welds was studied by visual and macrographic examination of the welds.It was seen clearly that when the processes are c...

CO2-GMA hybrid welding of carbon steel – The effect of shielding gas composition

Metal industry producing large structures is nowadays very interested in hybrid welding processes. That isn’t a surprise, as the process has many advantages compared to the conventional welding methods. One of the major benefits is the reduction in deformations. That reduces the post-work needed and makes the assembly easier since the hybrid welded parts are more accurate. Another advantage of hybrid welding is that it allows much wider groove tolerances compared to laser welding. In addition, with filler metal the composition can be balanced, if metallurgical factors are critical.In this study CO2-GMA hybrid welding process was used. The aim was to clarify the effects of shielding gas composition on welding performance, weld profile and quality in hybrid welding of carbon steel. Shielding gases used consisted of helium, argon and carbon dioxide. Joint types used were butt and T-butt joints.The research revealed that the composition of shielding gas affects welding performance, weld quality and penetration profile in CO2-GMA hybrid welding of carbon steel. Hybrid welds of a good quality can be produced with many different shielding gas compositions, but if the productivity, low gas costs, reliability of the process and high quality are desired, the shielding gas composition does make a difference in hybrid welding of carbon steel.Metal industry producing large structures is nowadays very interested in hybrid welding processes. That isn’t a surprise, as the process has many advantages compared to the conventional welding methods. One of the major benefits is the reduction in deformations. That reduces the post-work needed and makes the assembly easier since the hybrid welded parts are more accurate. Another advantage of hybrid welding is that it allows much wider groove tolerances compared to laser welding. In addition, with filler metal the composition can be balanced, if metallurgical factors are critical.In this study CO2-GMA hybrid welding process was used. The aim was to clarify the effects of shielding gas composition on welding performance, weld profile and quality in hybrid welding of carbon steel. Shielding gases used consisted of helium, argon and carbon dioxide. Joint types used were butt and T-butt joints.The research revealed that the composition of shielding gas affects welding performance, weld quality and penetratio...

Effect of joint configuration on high-power diode laser welding of steel

High power diode laser was the first semiconductor laser used for materials processing. It has found some areas of applications in production. The most promising applications of HPDL in mechanical engineering are in thin steel sheet welding and hardening. The HDPL welding process is at this moment usually performed as conduction limited welding process. In this study the effect of joint configuration and beam properties on the efficiency of welding with HPDL were examined. Joint types tested were bead on plate and butt joint with different joint manufacture. The laser parameters tested were beam intensity, welding speed, incidence angle of laser beam and focal spot size. The tested parameters had an effect on the weld quality and the welding speed. The higher the beam intensity is the higher the welding speed can be achieved. The reliable welding parameters can be established for the welding of various industrial products.

The effect of laser and welding parameters on keyhole and melt pool behavior during fiber laser welding

The laser welding process is gaining ever growing part in the field of manufacturing. The advantages of laser welding are based on the utilization of keyhole, which is a vapor channel generated to base material. The energy of laser beam is brought to the material via keyhole. With new generation lasers, like fiber laser the keyhole diameter thus resulting weld cross section are narrow. At the moment, the validation of the keyhole behavior according to change in the parameters is lacking. It is commonly accepted idea that the stability of the keyhole plays a major role when considering the ability of the laser welding process to produce high quality welds.This study utilizes a photography system and concentrates on the visual evaluation of the keyhole behavior, stability and effects of welding parameters on it and the weld cross section. The material used was low alloyed steel S355 of thickness 6 mm. The laser used in the experiments was fiber laser of 5 kW power. The effects of focal point position, weldi...

The effect of parameter changes in CO2 laser welding on spectra

The use of laser welding is evermore increased in metal industry. Due to its high process speed, the bottleneck of the production is usually the quality inspection of the weld. A solution to this is the use of automatic monitoring equipment. The monitoring systems are able to identify the changes in the process and weld defects generated but are not always able to identify different weld defects. The monitoring systems usually measure the intensity value of the electromagnetic spectra in quite a wide wavelength range, which may be the reason for the poor ability to identification of detects.Reliable weld defect identification would make it possible to develop a closed-loop control and adjustment of the process. Since with the current systems the weld defects can not be identified reliably enough, it is reasonable to study if there could be certain narrow areas in spectrum which can indicate a creation of a specific weld defect. Therefore, we started to study the spectral output from the welding.In this study on-line spectroscopy was used to measure the effects of parameter changes in CO2 laser welding process. The material welded was mild steel of thickness 6 mm and the joint type was butt joint. The analysis of spectra is very promising: the variations in welding parameters and groove preparation affect the spectra, changing its level and the intensity distribution of it.The use of laser welding is evermore increased in metal industry. Due to its high process speed, the bottleneck of the production is usually the quality inspection of the weld. A solution to this is the use of automatic monitoring equipment. The monitoring systems are able to identify the changes in the process and weld defects generated but are not always able to identify different weld defects. The monitoring systems usually measure the intensity value of the electromagnetic spectra in quite a wide wavelength range, which may be the reason for the poor ability to identification of detects.Reliable weld defect identification would make it possible to develop a closed-loop control and adjustment of the process. Since with the current systems the weld defects can not be identified reliably enough, it is reasonable to study if there could be certain narrow areas in spectrum which can indicate a creation of a specific weld defect. Therefore, we started to study the spectral output from the welding.In this st...

The effect of welding parameters on keyhole behavior in CO2-laser welding

The advantages of laser welding are based on the utilization of keyhole, which is a vapor channel generated to base material. The energy of laser beam is brought to the material via the keyhole. There are various mathematical models created explaining the shape and behavior of keyhole during welding. However, the validation of the keyhole behavior against the models is lacking. It is commonly accepted idea that the stability of the keyhole plays a major role when considering the ability of the laser welding process to produce high quality welds.This study utilizes a photography system and concentrates on the visual evaluation of the keyhole behavior, stability and effects of welding parameters on them. The material used was austenitic stainless steels of thickness 3 mm. The effects of different airgap, welding speed, laser beam power and alignment were tested and their effects on keyhole behavior were observed by visually examining the pictures made by the photography system. The welds were evaluated by v...