Friction Surfacing (FS) is a solid state process used to produce fine grained coatings with superior surface and corrosion properties; eliminate subsurface voids and cracks. Bulk melting does not occur, allowing us to join dissimilar metals. Key advantages of FS include high energy efficiency and low environmental impact compared to other technologies. One of the applications of this process include repair of damaged surfaces by deposition of material over the affected area. Studies are also being performed on effectiveness of the process to improve surface properties on parts and tools.
Figure 1 shows the process setup. The rod plunges into the substrate at a high rotational speed (around 2000 RPM). A traverse feed is also provided to the rod, so it moves along the surface of the plate. This causes a layer of the rod material to be deposited on the substrate.
| Figure 1: Process setup for friction surfacing (Gandra et. al. 2013) |
The process can be divided into two steps:
- Pre-heating step (material frictional softening step): The process starts with an initial deformation period, as the rotating rod is pressed against the substrate.
- Deposition step: When a viscoplastic layer is developed, the consumable rod starts to travel. The main heat source shifts from interfacial friction to plastic deformation.
Both the pre-heating and the deposition steps can be controlled by either force/pressure or rod feed rate.
Figure 2 shows the thermo-chemical events in the FS of high speed steels.
| Figure 2: Cross sectional view of thermo chemical events in FS of HSS (Bedford et. al. 2001) |
The video below shows the process in real time.
Project Procedure
We shall be using a 3-axis CNC milling machine: the HAAS Model TM-1 “Tool Room Mill” available at the Laser-assisted Multi-scale Manufacturing Laboratory. The spindle motor’s maximum rating is 5.6kW, the maximum spindle torque 45Nm, and the maximum spindle speed is 4500 RPM.
The material we have chosen to perform tests on is Stainless Steel 304. The reason for choice of this material is that studies using this material for the consumable rod and substrate material have not been performed before. Stainless steel 304 is used in various industrial applications such as the food processing industry, pipes and architectural, heat exchangers etc. As mentioned before, FS is used for repairing surfaces that are damaged. In most cases, the damage occurs due to SCC, or Stress Corrosion Cracking. Stainless Steel 304 is appropriate for this process as it has good corrosion resistance to slightly acidic and caustic media and is known for excellent strength and toughness at high temperatures.
We intend to perform tests on the material to find a good process window where the material deposits appropriately. We will be using a feed control setup (i.e. constant feed rate). We would also investigate the effect of the process parameters on the bonding of the deposited material and substrate. We would then analyze the microstructures of the cross-sections in terms of bond strength and layer thickness.
Project Goals
- Design of experiment to test the various parameters that affect the quality of single deposition.
- Force analysis of the process to draw the relationship of different forces with deposition quality.
References:
Gandra, J., H. Krohn, R. M. Miranda, P. Vilaça, L. Quintino, and J. F. Dos Santos. “Friction surfacing—A review.” Journal of Materials Processing Technology 214, no. 5 (2014): 1062-1093.
Bedford, G. M., V. I. Vitanov, and I. I. Voutchkov. “On the thermo-mechanical events during friction surfacing of high speed steels.” Surface and Coatings Technology 141, no. 1 (2001): 34-39.