The application of wire arc additive manufacturing technology for fabricating the arc torch mounting bracket to the manipulator robot flange.

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Introduction

Additive manufacturing (AM) is a technology enabling the creation of complex-shaped objects by sequentially depositing layers of material [1, 2, 3]. One promising direction in this field is Direct Energy Deposition - Arc (DED-Arc or WAAM - Wire Arc Additive Manufacturing). DED-Arc is an additive manufacturing technology that uses an electric arc as the energy source to melt the filler material [4]. Welding wire of various cross-sections and diameters is typically used as the filler, achieving a high material utilization rate. Another significant advantage of this technology is its high deposition rate and the low cost of wire feedstock [5]. The application of bionic design and topology optimization leads to a reduction in the mass of the preform, which can subsequently improve the operational properties of the final product. Therefore, integrating DED-Arc technology into the production cycle of components can significantly reduce material and time costs [6].

For example, S7 Airlines has long used WAAM to create large-scale components for the aerospace industry. Their work presents a section of a fuel tank bottom, 850 mm in diameter, fabricated from an aluminum alloy [7]. Furthermore, to identify an efficient production method, a comparison was made between different technologies for manufacturing a tank bottom ring: milling versus DED-Arc. The results showed that DED-Arc significantly reduces waste, greatly increasing the material utilization coefficient. Thus, it can be concluded that DED-Arc technology offers significant advantages over traditional manufacturing methods.

Another company developing DED-Arc technology is Relativity Space. Their primary focus is promoting commercial space flight [8]. To this end, they have designed and manufactured their own launch vehicles at their production facilities, with some components made from aluminum alloys using DED-Arc technology. In March 2023, the first launch of the "Terran-1" vehicle took place. During the flight, it crossed the Kármán line (100 km above sea level), making "Terran-1" the first additively manufactured rocket to reach space.

Another example utilizing DED-Arc technology is the company MetalWorm [9]. They are leading manufacturers specializing in high-pressure vessels. The manufacturer fabricated a vessel 300 mm in diameter and 495 mm high using ER 5356 wire as the filler material. MetalWorm specialists believe that implementing WAAM technology has brought several key advantages to their pressure vessel production process. By eliminating the need for numerous tools and minimizing machining requirements, production lead times can be significantly reduced. The time to fabricate the entire vessel was 8.5 hours, optimizing project timelines. Moreover, the reduction in material waste and the efficiency of the DED-Arc process resulted in substantial cost savings.

The company MX3D is also actively advancing DED-Arc technology [10]. This company not only develops the technology but also manufactures its own systems for its implementation. One of the company's most renowned projects is a bridge fabricated using DED-Arc technology and installed over a canal in Amsterdam. Additionally, specialists from this company manufactured an aluminum alloy bicycle frame.

Thus, it can be concluded that modern mechanical engineering has seen a significant increase in demand for DED-Arc technology, leading to a growing number of companies producing equipment for its implementation. Technological complexes typically include a welding power source and a motion system for the working tool and workpiece. Portal systems or various industrial robots combined with positioners can be used as manipulators.

Industrial robots are devices that move along a predetermined trajectory during the production process. Their primary purpose is to perform specific operations under operator control or autonomously. Industrial robots are classified by purpose into several types: universal (performing various operations) and specialized (designed for a single type of activity such as assembly, cutting, welding, etc.).

The operating principle of a welding robot depends on its design type. Generally, these mechanisms feature a movable arm with a welding torch at the end. Special tooling is used to connect the torch to the robot flange. This tooling is primarily made from aluminum alloys to ensure rigidity without exceeding the maximum permissible load. Creating tooling using additive technologies is becoming widespread in modern mechanical engineering.

Thus, this work achieved the goal of developing and manufacturing a torch mounting bracket for a robot flange using DED-Arc technology.

1 Equipment and Materials

AMg5 aluminum alloy wire was used to fabricate the mounting bracket components. A 10 mm thick sheet was used as the substrate. The chemical composition of the wire is given in Table 1.

Table 1 – Chemical composition of SvAMg5 wire according to GOST 7871-2019 [11]

High-purity argon (HP) according to GOST 10157-2016 [12] was used for shielding the work zone.

Fabrication of individual bracket components was carried out on a DED-Arc testbed. The testbed's appearance is shown in Figure 1.

Figure 1 – Appearance of the DED-Arc testbed

The list of equipment included in the testbed is presented in Table 2.

Table 2 – List of equipment in the DED-Arc testbed.

A manual Fronius 400I PM CMT welding torch was used as the working tool (Figure 2). This device is not intended for DED-Arc as it is designed for manual welding. However, due to the lack of alternatives like purchasing a robotic welding torch, it became necessary to create a mounting bracket for the available equipment. The welding torch also features the Cold Metal Transfer (CMT) function. The main principle of this technology involves the forced detachment of the droplet through the reciprocating motion of the filler wire.

Figure 2 – Fronius 400I PM CMT welding torch.

2 Process Development

2.1 Selection of Deposition Parameters and Metallographic Testing

During the investigation of the DED-Arc process, a stable deposition window was established, bounded by two regimes (with low and high heat input). Parameter selection was performed by varying the welding current while the travel speed remained constant at 15 mm/s.

As part of the parameter selection experiment, single beads 100 mm long were deposited. The starting point was a welding current of 20 A (Figure 3). This parameter was then increased in 20 A increments. After deposition, a visual assessment of the beads was performed, along with measurements of width and height. The measurement results are presented in Table 3.

Figure 3 – Single beads: a – 20 A, b – 40 A, c – 60 A, d – 80 A, e – 100 A, f – 120 A, g – 140 A

Table 3 – Measurement results of single beads

Due to low heat input, beads deposited at 20 A and 40 A exhibited unstable formation.

Subsequently, for deposition regime selection, walls 100 mm long and 10 layers high were deposited. The welding current was varied in the same sequence as for the single beads. Based on the results, it was determined that the best formation is achieved within a welding current range of 60 A to 120 A. Higher values cause molten material to sag, resulting in overlaps on the side surface of the sample. Lower heat input values are insufficient for stable bead formation. Figure 4 shows the appearance of the deposited walls.

Figure 4 – Appearance of the obtained samples: a – 40 A, b – 60 A, c – 80 A, d – 100 A, e – 120 A, f – 140 A

For fabricating large-scale components, a high heat input regime is necessary to maintain the required interpass temperature. This can be achieved by increasing the welding current to 120 A. Deposition was performed with multiple beads per layer and an overlap factor of 35%. As a result of the experimental work, stable formation with high side surface quality was achieved. The appearance of the obtained sample is shown in Figure 5.

Figure 5 – Appearance of the obtained sample

Metallographic testing was performed on the obtained samples to examine their macrostructure (Figure 6). The image shows that the selected deposition parameters yield an almost defect-free structure. Porosity in both samples did not exceed 0.5% of the cross-sectional area.

Figure 6 – Macrostructure of the obtained samples: a – Regime I=100 A, V=15 mm/s, b – Regime I=120 A, V=15 mm/s

2.2 Selection of Deposition Strategy and Mechanical Testing

To prevent potential anisotropy, a specific deposition strategy was used (Figure 7).

Figure 7 – Deposition strategy

The strategy involves using the "Wave" function. Its essence is as follows: while the working tool moves along the programmed path, it performs oscillatory movements with a specific amplitude and oscillation frequency. During the selection of these parameters, defects in the form of lack-of-fusion occurred (Figure 8).

Figure 8 – Defects occurring during Wave function parameter selection

This problem was solved by decreasing the oscillation frequency and increasing the welding current. The selected amplitude and frequency values were 13 mm and 2 Hz, respectively.

Using this strategy, specimens for mechanical testing were fabricated (Figure 9).

Figure 9 – Specimen for mechanical testing

Based on the obtained results, it was established that the yield strength and ultimate tensile strength values in the Z-direction are lower than the standard values for wrought material presented in GOST 17232-99 [13]. In the X-direction, the mechanical properties exceed those in the standard.

This material behavior is associated with the formation of an anisotropic structure, typical for the WAAM process. The inhomogeneities are related to varying grain sizes and the formation of columnar structures at the bead boundaries, leading to reduced strength properties. Phase inhomogeneity is also observed in the specimens: bead boundaries are enriched with large needle-like intermetallics compared to the bead centers. The mechanical testing results are presented in Table 4.

Table 4 – Mechanical Testing Results

All mounting bracket components were fabricated using the Wave function, except the "Bracket" element (Figure 10).

Figure 10 – Deposition strategy for the bracket

This choice was due to the robot's amplitude limitation of 15 mm when the Wave function is activated. In this case, the width of the manufactured component exceeded this value. Prior to its fabrication, the offset between the contour bead and the infill beads was optimized. This was necessary because, with a standard offset of half the single bead width (2.1 mm for 100 A current), defects in the form of lack-of-fusion appeared (Figure 11). It should be noted that this defect only appeared at the start point of the deposition.

Figure 11 – Defects during bracket fabrication

To solve this problem, a new offset was selected, amounting to 25% of the single bead width, equaling 1 mm. After changing this parameter, no defects were observed.

3 BRACKET DESIGN

3.1 Initial Data for Defining Tooling Design Criteria

The bracket design was created considering the specific shape of the welding torch, the robot flange, and their relative positioning. The initial stage of bracket design involved measuring the welding torch and the robot flange.

The structure of the Fanuc M-710iC/50 robot does not allow attaching a standard robotic welding torch due to the absence of a hollow flange. The designed bracket must: account for the mass characteristics of the welding torch; be of sufficient height to prevent kinking of the hose package in bent positions; have a length of at least 150 mm to prevent the hose package from rubbing against the robot flange during operation. It is also necessary to integrate a collision sensor into the design to ensure safe movement of the working tool.

Based on the established criteria, it was decided that the bracket assembly must:

• Have a length of at least 150 mm from the robot flange axis;

• Have a height of at least 170 mm from the robot flange;

• Utilize lightweight alloys with high strength characteristics.

After considering all criteria, the following bracket assembly was developed, the 3D model of which is presented in Figure 12.

Figure 12 – Bracket assembly diagram with labeled positions

The bracket components are listed in Table 5.

Table 5 – Bracket Components

The adapter flange serves to connect the entire bracket assembly to the robot. The bracket ensures the length criteria are met and connects the collision sensor to the plate. The plate is intended for mounting the welding torch. Connection rigidity is ensured by the clamping plate.

The stiffness of the bracket was verified using the SOLIDWORKS Simulation function within SolidWorks, which allows checking geometry deviation under external loads. The analysis showed that a load of 7 kg (equal to the weight of the welding torch) causes a maximum deviation of 0.046 mm for this material and configuration, which is considered insignificant and meets the established criteria (Figure 13).

Figure 13 – Bracket stiffness verification

4 Fabrication

4.1 Fabrication of Bracket Components

Following the design stage, all bracket components were fabricated. The adapter flange was fabricated in 2 stages: Stage 1 involved depositing a large cylinder; Stage 2 involved fabricating a small cylinder. The welding current was 100 A, and the travel speed was 15 mm/s. Figure 14 shows an image of the fabricated flange.

Figure 14 – Fabricated flange: a – Fabricating large cylinder, b – Fabricating small cylinder

The next stage in manufacturing the bracket assembly was fabricating the bracket itself (Figure 15). The welding current for the contour bead was 120 A, and for the infill beads, 100 A; the travel speed remained constant at 15 mm/s.

Figure 15 – Fabricated bracket

Next, plates for securing the welding torch were fabricated (Figure 16). The welding current and travel speed were the same as for the adapter flange.

Figure 16 – Fabricated plates: a – Plate, b – Clamping plate

4.2 Bracket Assembly

After manufacturing all bracket components, the assembly stage commenced. Figure 17 shows the fully assembled tooling.

Figure 17 – Assembled bracket assembly

Conclusion

This article presents the results of applying DED-Arc technology to manufacture a bracket assembly for mounting an arc welding torch to a robot flange.

The following tasks were accomplished during the work:

1. Analysis of literature sources was conducted.

2. Deposition parameters were selected and metallographic testing ensuring high quality of the deposited material was performed.

3. A deposition strategy was selected and mechanical testing was conducted.

4. Initial data for tooling design were analyzed.

5. Bracket components were designed.

6. Control programs were created.

7. The bracket assembly was manufactured and assembled.

About the authors

Nikita Roschin

Санкт-Петербургский Государственный Морской Технический Университет

Author for correspondence.
Email: n.d.roschin@gmail.com
ORCID iD: 0009-0004-2167-5303
Russian Federation

Konstantin Nasonovskiy

Saint Petersburg State Marine Technical University

Email: nasonovskiy.konstantin@gmail.com
Russian Federation

Darya Volosevich

Saint Petersburg State Marine Technical University

Email: dasha.volosevich@mail.ru
Russian Federation

Rudolf S. Korsmik

Saint Petersburg State Marine Technical University

Email: rudak27@yandex.ru
ORCID iD: 0000-0003-1591-1942
SPIN-code: 6726-2629

Cand. Sci. (Engineering)

Russian Federation, Saint Petersburg

References

Supplementary files