Gear Repair using Laser Metal Deposition

Abstract

The urge for more sustainable and cost-efficient repair methods for damaged parts is growing every day. On the other hand, laser metal deposition (LMD) is gaining momentum. This flexible technique, where material is added in a layer-by-layer fashion with a minimal heat input offers solutions for a wide range of production and repair purposes. Especially restoration or replacement of large and complex high-performance parts with long production times could profit from these developments. Industrial gears are certainly such type of parts. Occasionally, unforeseen tooth breakage of gears occurs, often leading to the replacement of the parts. No reliable repair techniques have emerged yet, due to the desired material properties and the uneven distributed hardness seen in carburized gears. This study was initiated to examine the feasibility of LMD for the repair of industrial gears with the goal to reduce both material waste and down time while retaining or exceeding the required mechanical performance. The initial part of the research is focused on finding the best suitable material and deposition parameters to ensure the desired mechanical properties of the core and a good bonding of the structure to the gear. Multiple deposition parameters are varied followed by destructive and non-destructive testing. It was found that the mechanical properties of deposited structures Inconel 718 and its bonding to a carburized substrate can be adjusted by accurately selecting the deposition parameters. Large differences in outcome were obtained by changing the deposition direction between each layer and tuning of the shielding gas flow rate. In further investigation the effects on the mechanical behavior of a deposited tooth structure were studied by altering the thermal cycle during and after deposition. The tests are performed on a specially developed static load testing setup. The results show a negative correlation between the interpass temperature and both the yield and ultimate tensile strength. This effect is attributed to a lower cooling rate during solidification at higher interpass temperatures. Ultimately, the results of a deposited tooth with hard flanks and built on a case hardened base were compared to a case hardened gear tooth that was manufactured according to the regular production method. It is found that the deposited structure exhibits significantly lower yield strength. Nonetheless, the superior ductility of the newly deposited tooth structure in the presented work is considered as a promising method for future gear repair.