D. Nespor

Repairing parts from nickel base material alloy by laser cladding and ball end milling

Due to rising costs of raw material, companies of the aerospace industry increasingly seek to repair components of aircraft engines instead of replacing them. Particularly the clad repair of turbine blades made of high strength nickel-base alloys with directionally solidified or single crystalline structure is a difficult issue, especially due to high requirements regarding the conditions of the final part surface. The present work deals with the question whether the prediction of surface and subsurface conditions, e.g. surface topography and residual stresses, is possible after repairing the inhomogeneous nickel-base alloy Rene 80. For this purpose, laser deposition cladding is applied for the polycrystalline Rene 80, using the filler material Rene 142. In the following re-contouring process, the claddings are milled with a ball end mill cutter. The influence of the inhomogeneous base material and the shape of the clad on the cutting forces as well as the final part surface are experimentally investigated. Superficial residual stresses are measured and evaluated. The cutting forces and the final surface reveal characteristic variations in the area of the material deposition and the dendrites. A geometric process simulation shows that the prediction of cutting forces and surface conditions for the polycrystalline material is only possible to some extent.

Chip formation and modeling of dynamic force behavior in machining polycrystalline iron–aluminum

Intermetallic iron–aluminum (FeAl) has an excellent resistance against corrosion and abrasion, a low density as well as high specific strength compared to conventional steel. In addition, the raw materials and manufacturing costs of FeAl-alloys are relatively low. The machinability is challenging. Economical machining of FeAl-alloys is currently not possible because of high tool wear. The chip formation mechanisms in machining FeAl-alloys are currently unknown. This study focuses on the influence of the material grain size on the thermomechanical processes during chip formation. A simultaneous measuring system for the determination of process forces, temperatures and chip formation in planing and orthogonal turning is presented. The chip formation mechanisms change with the grain transition and grain size. Decreasing grain sizes lead to the higher ductility in material separation by favorable thermomechanical loads and reduced crack initiation. By using force data from monocrystalline machining a model is introduced, which predicts the force dynamics in machining of polycrystals.