Characterization of machinability of sintered steel foams having different porosities during drilling operations

Abstract

Steel foams are a new class of engineering materials with exceptional structure and properties. Foams produced by powder metallurgy generally have a near-net shape, however, sometimes machining operations may be required. The presence of porosity in steel foams significantly affects the cutting process and causes poor machinability. This study deals with the evaluation of the machinability of Cu-Ni-Mo-based steel foams having different porosity produced by powder metallurgy. High speed steel and carbide-tipped drills were used for the drilling. All tests were performed in dry condition with drill diameter of 3 mm. The drilling characteristics were evaluated in terms of the surface roughness, chip formation, drilling force, tool wear, microstructure and hardness change after drilling. The machinability was also evaluated by measuring average width of breakout and skewness values of the hole drilled. The results indicated that the increase of porosity negatively affected the drilling quality of high porous steels. Both drills broke the chips in powder form and produced discontinuous chips. High porous parts exhibited higher hardness change as compared to lower ones. The carbide drill showed acceptable drilling forces and surface quality. HSS drill is not suitable for drilling due to poor hole quality and high drill wear.

Highlights

• Steel foams exhibit poor machinability due to highly porous structure.

• Porosity and tool type significantly affect the surface integrity of steel foams.

• Surface roughness and drill wear increased with increasing porosity; however, feed force decreased.

• Intense presence of pores decreases the tool life remarkably.

• The skewness values of hole are positive in all porosities.

• Carbide-tipped drill produced the finest hole quality.

• The larger damage was observed at the exit of the drilled holes with HSS drill.

Keywords:

• Drill life
• drill type
• drilling
• hole quality
• porosity
• steel foam

Disclosure statement

No potential conflict of interest was reported by the author.

Funding

This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors.

Additional information

Notes on contributors

Nuray Bekoz Ullen

Assistant professor Dr. Nuray BEKOZ ULLEN is currently working in the Department of Metallurgical and Materials Engineering, Istanbul University-Cerrahpaşa (IUC), Turkey. She obtained her BSc, MSc and PhD degree at Department of Metallurgical and Materials Engineering from Istanbul University, Turkey in 2003, 2006 and 2011, respectively. Her main research interest includes powder metallurgy, metal foams, coating technology, surface treatments, material characterizations, machinability and welding. In recent years, she has focused on improving the surface properties of dense porous materials. She has collaborated actively with researchers in several other disciplines of mechanical, chemistry and physics. She has taught on engineering materials and deformation mechanisms, highly porous material production techniques and characterization, failure of materials. She had role as a consultant in master theses in the fields of material characterization. She has published several research articles on material production, characterization and processing.