Austrian welding specialist Fronius International has collaborated with Linde Engineering, MIGAL.CO, and TÜV SÜD Industrie Service to qualify 3D printed pressure vessel components.
The project was completed as part of a working group under the German Institute for Standardization (DIN). It sought to assess and improve the use of additive manufacturing to produce pressure equipment. In particular, the group tested how well their new draft standard, prEN 13445-14, applies to unheated pressure vessel parts.
Each partner contributed expertise to conduct material qualification, design review, process validation, additive manufacturing, and component and pressure testing. After documenting the full process chain, they produced a binding additive manufacturing procedure specification (AMPS).
According to Linde’s Dr. Kati Schatz, the 3D printing standard includes all safety and quality requirements needed to meet European regulations for pressure vessels. Although the document requires further revision before it can be finalized, Schatz believes it already offers a useful guide for those 3D printing functional pressure equipment.
Fronius enhances wire-based 3D printing
With over 8,000 employees worldwide, Fronius is active in a range of sectors spanning photovoltaics, battery charging, welding, and metal 3D printing. The latter includes the company’s Cold Metal Transfer (CMT) process.
This metal-wire-based additive manufacturing process leverages a welding technique where the wire electrode is melted and deposited layer by layer to create a component. Combining features of conventional welding and 3D printing, CMT reportedly minimizes the heat input generated by its high deposition rates.
According to Fronius, CMT supports functions that are “perfect for metal 3D printing.” For instance, its “power correction” capabilities allow electrical power to be precisely adjusted to the process phase, while the deposition rate stays the same. This reportedly unlocks precise control over the height and width of the weld.
Designing and 3D printing pressure vessels
The team’s pressure vessel component featured a 3D printed pipe branch welded onto a conventionally manufactured base pipe. Aluminum was chosen as the material for this part due to its high strength and toughness at low temperatures down to -273°C.
Welding this alloy was reportedly challenging and required careful selection of the process and filler material. The latter needed to meet tight tolerances to diameter and chemical composition to minimize hydrogen inclusion. The welding wire also had to be free of defects and wound neatly onto a spool to avoid issues during 3D printing.
Robert Lahnsteiner, CEO of MIGAL.CO, noted that the materials used for this project were sustainable and possessed a low carbon footprint. The welding wire produced 3.8 kg of CO2 per kilogram, less than a quarter of the international average.
When designing the pressure vessel component, the team sought to optimize the flow and topology of the transition from the base pipe of the pressure vessel to the stub. They settled on three different wall thicknesses: 8mm for the base pipe, 14mm for the transition section, and 5mm for the 3D printed branch component.
Next, they determined how best to 3D print the pressure vessel component. Essential requirements included a high deposition rate, reduced heat to minimize cooling requirements and distortion, complete fusion in the connection to the base material, and no sensitivity to changes in distance between the welding torch and component. The team also required absolute reproducibility of material quality, and the ability to produce large components. Fronius’s CMT technology was selected to meet these needs
Advanced robotic welding technology was used to precisely plan the welding and 3D printing tool path. During fabrication, Fronius’s WireSense sensor scanned the component and made live adjustments to ensure accuracy and minimize geometric deviations. The company’s WeldCube welding data management software was also employed. This monitored the parameter limits specified in the AMPS, issuing a warning if they were exceeded.
An additional camera was used to record and monitor the build-up of layers. This reportedly allowed the team to analyze process deviations more accurately once 3D printing had finished.
Testing 3D printed pressure vessel components
Once 3D printed, the individual test pieces were subjected to non-destructive testing, including visual and dimensional tests, volume tests, and surface inspections. Destructive testing, including chemical analysis, tensile tests and bending assessments, was also employed to verify mechanical strength and integrity. Additionally, water pressure and bursting assessments were carried out.
In parallel with these tests, metallographic analyses were used to ensure the quality of the hybrid pressure vessel. This focused on areas where imperfections had already been detected and sections where conventionally manufactured and 3D printed materials were joined. The goal of the analyses was to verify the data collected from parameter monitoring and during the mechanical, technical, and non-destructive testing.
Ultimately, the parts passed the testing, evaluation, and final inspection phases. The 3D printed pressure vessel component was therefore confirmed to be compliant with the European Pressure Equipment Directive 2014/68/EU.
Looking ahead, the team hopes to promote the wider use of 3D printing in industries like plant and container construction by showing that it meets strict quality and safety standards. Manfred Schörghube, an R&D engineer at Fronius, believes the qualification process provides “compelling reasons to increase the use of metal 3D printing in plant and container construction.”
New 3D printing standards
Away from 3D printed pressure vessels, various new additive manufatcring standards have emerged for a range of applications and industries. Last year, the International Organization for Standardization (ISO) released ISO 5425:2023, a new standard for 3D printing PLA filament. This standard seeks to ensure consistent and quality-controlled utilization of PLA 3D printing.
The process leading to its publication began in 2019 when Shenzhen-based company, Esun Industrial Co., Ltd. and Beijing Technology and Business University introduced a new work item proposal (NWIP) at the ISO/TC 61 annual meeting. Once it was accepted, a dedicated working group featuring global experts convened to plan and develop the PLA standard.
The resulting document encompasses essential filament parameters including appearance, net mass and tolerance, diameter, ovality tolerance, volatile matter limits, line tensile load, and line elongation at break. It also provides a framework for rest methods, detection rules, marking, labeling, packaging, transportation, and storage.
2023 also saw the ISO publish a new standard for construction 3D printing. Titled ISO/ASTM 52939:2023, this aims to ensure quality, safety, and efficiency for construction applications. The document was prepared by the ISO’s Additive Manufacturing Technical Committee (ISO/TC 261), and ASTM International’s Additive Manufacturing Technologies Committee (F42).
The standard specifies quality assurance requirements for additive manufacturing in construction. It is independent of material, does not apply to metals, and applies to all additive manufacturing technologies used in construction.
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Featured image shows the additive manufacturing build-up of the pipe branch with weld layers. Image via Fronius.
