Review Reports

Round 1

Reviewer 1 Report

jmmp-1829062

Joining 30 mm thick shipbuilding steel plates EH36 using a process combination of hybrid laser arc welding and submerged arc welding

Review

 

1.           GENERAL COMMENTS

As outlined by the authors the subject of joining thick plates is of great economical and scientific interest. The introductions is very well written and easy to read.

The paper addresses the feasibility of combined laser and submerged arc welding. In the discussion, the authors insist on the scope of present work. This makes the paper easy to read.

2.           specific comments

As stated in the first section, the paper is well written and agreeable to read. Thus most requests concern details.

Page 2, lines 54-66

“The hybrid laser arc welding (HLAW) process is characterized by a higher penetration depth, a higher welding speed and a lower heat input and can thus be considered as an alternative high-performance welding process for joining thick-walled structures. Successful examples are known from the shipbuilding industry, where sheets with a thickness of up to 15 mm are joined using HLAW. There are first research results for single pass welding of up to 30 mm thick plates [6, 7] or for double side welding of up to 50 mm thick plates [8, 9]. However, an industrial breakthrough of high-power lasers for joining higher sheet thicknesses has not yet been achieved due to process-specific limitations. First, it was found that the stability of the process decreased at higher laser powers. A scaling of the penetration depth and the required laser power is not given above 20 kW laser power. Further limitations are droplet formation on the weld root, sensitivity to manufacturing 64 tolerances such as gaps or edge misalignment and deteriorated mechanical-technological properties, due to high cooling rates and inhomogeneous distribution of the filler metal over the entire weld depth.”

The following remarks are meant to increase the interest in present work. I am aware that the welding speed and heat input depend on the particular sheet thickness, metallurgy and others. However, could the authors give an indicative range of these values? The same holds for the high cooling rates. These are quite difficult to measure. But an indication of the order of magnitude would be appreciated.

Page 2, lines 68-69

“Droplet formation during single-pass HLAW of higher plate thicknesses takes place 68 due to the increasing hydrostatic pressure inside a keyhole.”

This needs to be supported by a reference.

Page 6, lines 177-178

“Leading electrode was supplied with direct current positive pole 177 (DC+) to achieve the maximum weld penetration depth.”

The Leading electrode was supplied with direct current positive pole 177 (DC+) to achieve the maximum weld penetration depth.

Figure 9. “Results of CVN impact test: (a) position of the CVN specimen in relation to the weld seam; 217 (b) CVN specimens after testing at -20 °C.

The fractured CVN specimens showed mainly a ductile fracture type while only one specimen indicated a mixed fracture. The mean value of the impact energy was 237.4±41 J”

 

The authors should discuss the rather large dispersion of the impact energy reaching from 173J to 274J. What are the main causes of this dispersion? (Local material variation observable on the fracture surface, variations in the test procedure?).

 

Author Response

Dear Reviewer,

thank you very much for the thoughtful review of our manuscript.

As a corresponding author, I have revised the manuscript taking into account all your comments and remarks. Please find below my responses to each comment:

Page 2, lines 54-66

“The hybrid laser arc welding (HLAW) process is characterized by a higher penetration depth, a higher welding speed and a lower heat input and can thus be considered as an alternative high-performance welding process for joining thick-walled structures. Successful examples are known from the shipbuilding industry, where sheets with a thickness of up to 15 mm are joined using HLAW. There are first research results for single pass welding of up to 30 mm thick plates [6, 7] or for double side welding of up to 50 mm thick plates [8, 9]. However, an industrial breakthrough of high-power lasers for joining higher sheet thicknesses has not yet been achieved due to process-specific limitations. First, it was found that the stability of the process decreased at higher laser powers. A scaling of the penetration depth and the required laser power is not given above 20 kW laser power. Further limitations are droplet formation on the weld root, sensitivity to manufacturing 64 tolerances such as gaps or edge misalignment and deteriorated mechanical-technological properties, due to high cooling rates and inhomogeneous distribution of the filler metal over the entire weld depth.”

The following remarks are meant to increase the interest in present work. I am aware that the welding speed and heat input depend on the particular sheet thickness, metallurgy and others. However, could the authors give an indicative range of these values? The same holds for the high cooling rates. These are quite difficult to measure. But an indication of the order of magnitude would be appreciated.

DONE: The Introduction part has been revised. Appropriate information, including references, has been added. Please find the revision in Lines 57-77.

Page 2, lines 68-69

“Droplet formation during single-pass HLAW of higher plate thicknesses takes place 68 due to the increasing hydrostatic pressure inside a keyhole.”

This needs to be supported by a reference.

DONE: Corresponding references [21-24] have been added: Line 91.

Page 6, lines 177-178

“Leading electrode was supplied with direct current positive pole 177 (DC+) to achieve the maximum weld penetration depth.”

The Leading electrode was supplied with direct current positive pole 177 (DC+) to achieve the maximum weld penetration depth.

DONE: the correction has been made: Line 222

Figure 9. “Results of CVN impact test: (a) position of the CVN specimen in relation to the weld seam; 217 (b) CVN specimens after testing at -20 °C.

The fractured CVN specimens showed mainly a ductile fracture type while only one specimen indicated a mixed fracture. The mean value of the impact energy was 237.4±41 J”

The authors should discuss the rather large dispersion of the impact energy reaching from 173J to 274J. What are the main causes of this dispersion? (Local material variation observable on the fracture surface, variations in the test procedure?).

DONE: I agree with you that the impact test results are quite scattered. From our experience, this effect happens relatively often when testing laser and hybrid welds. One reason for this is that the fracture sometimes occurs directly through the center of the narrow fusion zone (mixed fracture mode), but sometimes propagates into the softer base material (ductile fracture mode). This phenomenon is known as fracture path deviation (FPD). An explanation of this is given in the discussion section of the manuscript: Lines 293-309

I would like to confirm that I have carefully considered your comments. I hope that my responses are in line with your comments and remarks.

Thank you very much for your support.

 

Yours sincerely

Sergej Gook

 

 

Author Response File: Author Response.pdf

Reviewer 2 Report

Please find enclosed the file with some remarks and suggestions.

Comments for author File: Comments.pdf

Author Response

Dear Reviewer,

thank you very much for the thoughtful review of our manuscript.

As a corresponding author, I have revised the manuscript taking into account all your comments and remarks.

Please find below my responses (in green color) to each comment:

2.1 materials: please add some more fundamental data, i.e. Ry and elongation; Please specify what you mean about “172 J impact absorbed energy at-40 °C” (CVN)?Moreover, check the temperature, in this point you wrote -40 in (row 210) you perform test at - 20°C (honestly in shipbuilding this second level of temperature is more typical)

DONE: the text has been revised. Table 2 with the mechanical properties of the base material has been added: Line 113

The values in the Table 2 were determined by our own tests.  The previously specified value "172 J impact absorbed energy at-40 °C" was the steel manufacturer's reference value.

Table1 please check the table format (now is split in two pages) and I think you miss a “0” in the content of “P” surely is 0.017 or less.

DONE: Yes, that was my mistake. The correction has been made.

(99) I understood it is a preliminary work but the dimension od the coupon is not in compliance with EN/ISO or IACS rules. Is true during the development of new process it is acceptable but I suggest you to add a justification sentence.

DONE: I agree with you that welding procedure tests should be performed on full-scale specimens according to the recognized standards. At the stage of preliminary tests, we use smaller specimens according to the laboratory capacities. A corresponding explanation has been included in the text: Lines 120-124.

(100-104) Sure is interesting to weld edge just cut by Plasma but plasma cut mean a lot of things. Please add the typical parameter of Plasma cut used in this work, possible a real profile of the edge and/ or the average roughness

DONE: Regarding this comment, I have the following explanation: the samples were prefabricated by the steel manufacturer using a CNC plasma cutting system. So, the real parameters of the plasma cutting process are unknown to us. However, we have made our own measurements of the edge surface morphology using a laser profile scanner. It was found that the cutting edge has a lateral inclination from the bottom to the top. Due to this inclination, a slight V-shaped groove is formed when the specimen halves are tacked together. For reference, results of the profile measurement are shown in Figure 2 and interpreted in Lines 140-144.

As an additional comment, I would like to say that this V-shape of the plasma-cut edge is not a "desired" edge preparation. It is rather an artifact of the cutting process. In the paper, we only want to show that such a weld edge quality is also weldable with the laser hybrid process.

(113-118) please add a scheme (an image explains better than 1000 words), in the text I do not retrieve the information about the side where was performed the HLAW, I image on the side where the gap is “0” (142-143)

DONE:  The schematic illustration of the process configuration and the position of the welding process with respect to the V-opening is shown in Figure 3a and b. The welding process is performed directly into V-opening. This V-opening is relatively small at the top and there is a technical zero gap to the bottom of the plate. So, the laser beam does not fall through the gap. The edges of the plate are melted and the weld is formed.

a fundamental data is missing: which is the feed ratio speed of the wire for the two experiments? You wrote exactly the same value for the two experiment of the arc parameter but in my experience when change the laser parameters, the standard GMAW machines even if the imposed parameters are set the same, changing the externa characteristic of the arc, change ( this is true for synergic or standard GMAW generators because there is the “autostability of the arc” (intersection of external characteristic that was influenced of laser parameters and the internal characteristic of the generator) so please if your equipment allow to control precisely the U an I of the arc whatever are the external condition let me know Specify that the condition of weld is Spray arc DC or other.

DONE: the wire feed rate (v_f) for the GMAW process has been given in Figure 4. The indicated values of welding current and voltage are the preset values. The actual values may differ due to the process control realized by the welding machine.

Yes, correct. We use welding machines with programmed synergetic curves. When welding GMAW, the “internal” or “ΔI-control” with constant voltage is used.  The wire feed speed with "ΔI-control" remains constant. By adjusting the welding current, arc length can be changed without external action. See schematic in PDF (unfortunately, I have it only in German).

For SAW with thicker electrodes, the "ΔU-control" with constant current or "outer control" is used. The current source has the falling characteristic. The arc voltage is coupled with anchor voltage of the wire feed motor. Changes in the arc voltage lead to proportional changes in the motor speed, the wire feed speed is adjusted. In attached PDF is the circuit diagram and mode of operation of the ΔU-control.

GMAW was performed with direct current of positive polarity (DC+). The relatively high current and voltage values of the GMAW process ensured that an arc with spray transfer mode was set. The wire feed speed (v_f) was automatically adjusted according to the synergy curve programmed in the welding machine: Lines 151-154

(159) even for the SAW are missed the wires feed speeds.

DONE: The wire feed rates for SAW have been given in Table 3.

(168) check the image of the Figure 5. Probably “a & b” are exchanged.

DONE: Yes, thank you, that was my oversight.

(196) reference is standard ISO and it is OK, I suggest you to take in account moreover some specification of shipbuilding i.e. IACS. In The discussion you correctly wrote that this paper report preliminary result, in the abstract you mention Destructive ( HV, Charpy and Bending) OK and NDT. In the Paper if exclude a visual examination, that is non clearly described, the NDT like PT, UT o XR are missing. So, add something about NDT ore change the Abstract.

DONE: I agree with you. The reference to welding procedure qualification according to shipbuilding standards / requirements of classification societies such as Bureau Veritas, Lloyd's Register or Det Norske Veritas (DNVGL) has been added: Line 124 - 128.

Because the NDT (X-Ray) was performed only for a few selected samples (i.e. no statistical data are available at the time of publication), I decided to remove these data from the manuscript. The abstract has been adapted accordingly.

 

I would like to confirm that I have carefully considered your comments. I hope that my responses are in line with your comments and remarks.

Thank you very much for your support.

 

Yours sincerely

Sergej Gook

 

Author Response File: Author Response.pdf

Round 2

Reviewer 2 Report

Thanks for understanding my comments and for updating the paper with more detail that I am sure will improve the interst in the readers. 

Beste regards.