Surface integrity after post processing of EDM processed Inconel 718 shaft

• Published in: International journal of advanced manufacturing technology Vol. 95; no. 5-8; pp. 2325 - 2337
• Main Authors: Holmberg, Jonas, Wretland, Anders, Berglund, Johan, Beno, Tomas
• Format: Journal Article
• Language: English
• Published: London Springer London 01.03.2018; Springer Nature B.V
• Subjects: Abrasive blasting; Abrasive water jet; Abrasives; Blasting; CAE) and Design; Compressive properties; Compressive residual stress; Computer-Aided Engineering (CAD; Crack initiation; Cracks; EDM; Electric discharge machining; Electric discharges; Electrical discharge machining; Engineering; Fatigue life; Fighter aircraft; Grit; Grit blasting; High-pressure water jets; Hydraulic jets; Inconel 718; Industrial and Production Engineering; Integrity; Jets; Manufacturing and materials engineering; Mechanical Engineering; Media Management; Microstructure; Nickel base alloys; Organic chemistry; Original Article; Production Technology; Produktions- och materialteknik; Produktionsteknik; Residual stress; Residual stresses; Roughening; Shot peening; Superalloys; Surface integrity; Surface integrity Inconel 718 Shot peening Abrasive water jet Grit blasting EDM; Surface roughness; Surface topography; Tensile residual stress; Surface integrity; Shot peening; Inconel 718; Abrasive water jet; Grit blasting; EDM
• ISSN: 0268-3768; 1433-3015; 1433-3015
• DOI: 10.1007/s00170-017-1342-6

Electrical discharge machining (EDM) is considered as an efficient alternative to conventional material removal concepts that allows for much higher material removal rates. However, EDM generates unwanted features such as re-cast layer (RCL), tensile residual stresses and a rough surface. In order to recover the surface integrity, different post processes has been compared: high-pressure water jet (HPWJ), grit blasting (GB) and shot peening (SP). Surface integrity has been evaluated regarding microstructure, residual stresses, chemical content and surface roughness. The results showed that a combination of two post processes is required in order to restore an EDM processed surface of discontinuous islands of RCL. HPWJ was superior for removing RCL closely followed by grit blasting. However, grit blasting showed embedded grit blasting abrasive into the surface. Regarding surface roughness, it was shown that both grit blasting and HPWJ caused a roughening of the surface topography while shot peening generates a comparably smoother surface. All three post processes showed compressive residual stresses in the surface where shot peening generated the highest amplitude and penetration depths. However, the microstructure close to the surface revealed that shot peening had generated cracks parallel to the surface. The results strongly state how important it is to evaluate the surface at each of the different subsequent process steps in order to avoid initiation of cracks.