Refurbishment of small diameter nitrided spindles with laser based direct energy deposition

Laser based direct energy deposition is a process that is commonly used to refurbish worn components in the power generation sector. In this work the potential for refurbishment of nitrided spindles manufactured from AISI 420 SS, with a small diameter (20 mm), is evaluated. Firstly, the required material removal from the nitrided surface was established. Secondly, the distortion of the shaft was measured as a function of the length of the refurbished section, and the thickness of the added material. It was found that the shaft must be pre-machined to a depth of 0.4 mm to ensure a pore-free weld on AISI 420 SS subjected to a typical gas nitriding cycle. Furthermore, it was shown that the distortion of a 20 mm diameter shaft, with a length of 1000 mm, can be 0.12 mm, if a 200 mm long section of the shaft is repaired. Reasons for the distortion are discussed, and possible mitigation measures are proposed.