Due to the welding and bending processes involved with the manufacturing of high performance exhausts, residual stresses can be created, these stresses along with surface changes or defects, such as the edge of a weld, can lead to micro-cracks in the surface of the metal and cause the exhausts to crack and in some instances early failures.
We can offer some finishing processes, in house and externally supplied, to reduce these stresses and therefore substantially improve the life of our products.
Controlled Shot Peening
Shot-peening is a controlled cold working process used to mechanically modify the properties of metals, increasing the fatigue life of exhaust components.
The process is carried out by impacting the component with a spherical media to modify the surface of a component, each particle acts like a miniature ball-peen hammer meaning no surface material is removed during the process. A variety of media can be used including:
- Metallic
- Glass
- Ceramic
This creates an even compressive layer across the component reducing any tensile stresses that may have been created during the manufacturing process. Therefore, reducing the chance of micro cracks in the surface and lengthening the life of the exhaust component.
The intensity of shot-peening is a key factor of the process. This is controlled and calibrated for each component with the use of an ‘Almen strip’, this metallic strip is shot-peened and doing so causing the Almen strip to deform, the percentage of deformation is then measured and adjusted to reach the desired intensity of the blast stream.
Every Almen strip is filed and stored for inspection and accountability purposes.
Whilst we have an in house shot-peening service and capable of low-volume and service requirements, we also have a long-term relationship with one of our partners, Sandwell UK, for all major shot-peening requirements and high quantities.
Heat Treatment
Heat treatment is a stress relieving process where metals such Inconel and Titanium are heated and cooled in a fully controlled environment, the process is intended to reduce the residual stress present in exhaust component and a result of welding and fabrication.
If these residual stresses are not removed from components before they go into service, the result can be early failures, which in the case of exhaust manufacturing could result in power loss or even early retirement from a race.
Components that have not been stress relieved can also, after heating up during their first use, move out of tolerance, causing poor fitment and transfer stress to other parts.
The high temperature super alloys used in exhausts are usually heated up to temperatures as high as 1000°C at a steady rate, held for a set amount of time depending on the alloy and then gas cooled using pressurised nitrogen.
Exhausts parts can be heat treated in heavy duty temperature resistant jigs if necessary, to stop them from going out of shape and moving out of tolerance during the process.