Laser cladding is a surface treatment method used to refurbish discs brake rotors, which have wide range of applications in road, rail and aviation. A new surface layer will be added on the regions of interest to refurbish the component during this treatment. Current recycling methodology used for recycling rotors is the remelting them with minimal amount disposed in landfills. Both these approach will produce considerable amount of CO2 emissions either way. The purpose of this study is to understand both the processes from sustainability and tribology point of view with focus on detailed life cycle study for both the processes of producing virgin grey cast iron brake rotors and refurbishing them by laser cladding. This study will help us understand the differences between both the processes from environmental stand point.
Grey cast iron discs are laser cladded using a 7kW fibre-coupled diode laser which has a high beam quality expressed as 44 mm*mrad. This allows the laser to be transported by a process fibre, which is as small as 400 µm. The metal powder is included in the process with the help of a coaxial powder nozzle, which allows a stand-off distance of 16-17 mm. The current combination of the process is setup in such a way that the heat transfer is minimum throughout the 6mm thick disc. It is also important to note that neither pre-heating nor annealing is performed on the discs. The surface of the discs is grinded with super abrasive grinding wheel until it reaches 55 HRC.
Certain pre-tests were conducted for both cladded and uncladded GCI discs to understand the tangential force, that is being applied on the discs due to the difference in their coefficients of friction. It is observed that the normal load applied on the cladded disc is 25% lower when compared to its counterpart. This is due to the difference in coefficient of friction, as cladded disc exhibits higher friction. Apart from this, a pin-on-disc test is also performed to understand the tribological properties of both the discs.
Fig1. Schematic diagram of pin-on-disc test
A life cycle assessment is also calculated for both these discs to understand their environmental impact. Goal and scope of the components, their inventory analysis and impact assessment are done as a part of this study. Material, manufacture, transport and disposal are the four different key points of the components in this assessment.
A typical curve between CoF (coefficient of friction) and time is observed for both Cast iron and Laser cladded discs. Apart from this, the wear marks for both the discs are also observed. The wear tracks observed for both the discs are relatively shallow and wide scars, which are due to plasticity dominated wear. Narrow and sharp scars are also observed, which might be due to abrasion. Apart from these observations, additional insights with microscopic images are included in the literature to achieve better understanding of the tribological behavior of both the discs.
Fig2. CoF vs Time graph
The main improvement of this study based on the observed results is at the manufacturing phase of the life cycle assessment. More than 50% savings are observed because of laser cladding in both energy consumption and emission departments. Main advantage of this process is that, by adding multiple layers are extending the life of the discs multiple times. It is also a hug advantage from an environmental stand point as we are eliminating the manufacture and transportation phase of the component.
The study pointed out that the difference in CO2 footprint for laser cladding method is almost 80 – 90% less when compared to manufacturing virgin brake rotors. It also puts emphasis on the fact that refurbished rotors exhibit higher friction when compared to its counterparts. The only downside is that the wear and particle emission is higher for laser cladded rotor than the original cast iron rotor. Though, this can be solved with the help of research advancements with focus on the surface finish of the discs. In conclusion, the proposal of this study to use laser cladding as an alternative to remelting brake disc rotors, is a realistic solution to achieve our carbon emission goals.
Laser Cladding Treatment for Refurbishing Disc Brake Rotors: Environmental and Tribological Analysis, Ulf Olofsson, Yezhe Lyu, Anna Hedlund Åström, Jens Wahlström, Senad Dizdar, Ana Paula Gomes Nogueira, Stefano Gialanella.
 Laser Cladding Treatment for Refurbishing Disc Brake Rotors: Environmental and Tribological Analysis, Ulf Olofsson, Yezhe Lyu, Anna Hedlund Åström, Jens Wahlström, Senad Dizdar, Ana Paula Gomes Nogueira, Stefano Gialanella.