Introduction
In modern engineering and fabrication, environmental aspects are often as much of a consideration as technical and economic drivers. The European Commission is developing legislation regulating the environmental impact all industry, from the producer to the consumer. The main goal is to develop a green economy, which is not only sustainable but circular, and with a zero-waste objective. Energy consumption is a prime topic.
As part of this objective, the EuP (Energy-using Products) Directive was adopted in 2005 (EuP 2005a) and transposed into national law in member states in August 2007. This directive concerns producers of energy-using products other than transport. The environmental impact of all products must be taken into account during their design and manufacture, including the choice of joining technology used for fabrication. The EuP Directive is a major part of European legislation and has the potential to be imposed on any aspect of a product’s design to reduce its environmental impact. For welding equipment, a study has been carried out by Fraunhofer-Institut für Zuverlässigkeit und Mikrointegration (IZM) and Fraunhofer-Institut für Produktionsanlagen und Konstruktionstechnik (IPK) (EuP 2005a).
It has been estimated that welding and joining processes, including resistance polymer and arc welding, represent 4.5 per cent of the European Union’s gross energy consumption (EPTA, 2007). A better choice of process or an increased understanding of this consumption can lead to energy saving.
This job knowledge article is focused only on power supplies and major arc welding processes and is based on a TWI report (Pike S, 2010).
Approach
A welding process is primarily selected for its performance and secondarily for its cost. The environmental factor is not generally considered, though this may be required in the future.
To effectively compare the environmental impact of different joining techniques it is necessary to use a quantifiable value. Multiplying power consumption in kilowatts (kW) by time in operation gives the energy consumption of a process in kilowatt-hours (kWh). This value can then be transformed into equivalent kilograms of CO2, a measure of the process’s environmental impact.
Comparison
Arc welding power sources operate at high efficiency levels, typically 65 per cent for conventional transformer and 90 per cent for inverter equipment. The inverters operate at higher frequencies (10kHz) compared to power frequency (50/60Hz), leading to reduced losses and higher efficiency. However, this improved efficiency can be decreased by additional ancillary functions (such as square wave capability).
In every case, process efficiency is increased when the power source is used near its maximum output. As an example, using a 500A arc welding power source for a weld at 200A will be more detrimental to the environment than using a 200A arc welding power source.
Figure 1 presents the environmental impact of joining techniques depending on the CO2 emission in grams per second. The SAW (submerged arc welding) process, with direct current, three phases and a transformer power source, has the greatest impact on the environment, with 18.63 grams of CO2 produced per second. At the opposite end of the scale, the process with the lowest impact on the environment is PAW (plasma arc welding) with a direct-current, single-phase inverter power source. It produces 1.49 grams of CO2 per second.
It is necessary to keep in mind that process comparison can only be complete when the time to perform a specific weld is known. For example, the SAW process has a greater impact on the environment but has a much higher deposition rate, so joint completion time (and resulting energy usage) may be lower than MMA (manual metal arc).
Another consideration is standby or idle losses. These vary depending on the power source design and process and may have a noticeable impact on energy consumption. The cost of leaving an arc process on standby is generally low (three pence per hour) in comparison with laser-welding equipment such as a 4kW Nd:YAG laser (£1 per hour).
It is also possible to assess welding technology in terms of environmental lifecycle. For example, Chang et al. 2015 compared MMA with manual and mechanised MAG (metal active gas), and determined that MMA has a greater potential environmental impact as a result of the greater consumption of resources (energy, filler metal and coating on electrodes) per one metre of welding seam.
Other studies (Maak et al. 1993) taking into account standby and arc-on period also demonstrate that significant energy savings may be obtained by changing the power supply for a more efficient one, with less energy consumption during standby, or changing the process for a less energy-intensive alternative.
Recommendations
Manufacturers should be aware of the EuP Directive and its potential impact within their business.
The environmental impact of joining techniques and arc welding processes is significant and should be taken into account when designing and manufacturing.
An audit of equipment usage should be made by manufacturers to evaluate their impact and assess how to reduce electricity consumption and CO2 emission and potentially lower costs.
For more information about environmentally conscious design you can refer to our best practice guide ( Best practice guide 2011 ) or contact us.
References
Best practice guide 2011: Environmentally conscious design
Chang 2015 ‘Environmental and social life cycle assessment of welding technologies’, 12th Global Conference on Sustainable Manufacturing, Procedia CIRP 26 293-298
EPTA 2007: ‘Study for preparing the first working plan of the EcoDesign Directive’. Report for tender No. ENTR/06/026
EuP 2005 a: www.eup-network.de
EuP 2005 b: www.eup-network.de
Maak 1993: ‘Energy efficiency studies for arc welding equipment and processes’, The Environment and the Joining Industry – Product Manufacture, Pollution Prevention, and Safety and Health. Proceedings, 9th Annual North American Welding Research Conference, Columbus, OH.
Pike S 2010, ‘Environmentally Conscious Design and Manufacture: Efficiency Measurements of Welding and Joining Equipment’, TWI Industrial Member Report Summary 944/2010