Influence of Process Parameters on Surface Hardening in Hammer Peening and Deep Rolling

Abstract

This paper focusses on the statistical evaluation of process parameters in the mechanical surface treatments deep rolling (DR) and machine hammer peening (MHP) on the hardness increase. In MHP process a spherical hard metal tool is repeatedly accelerated onto the material surface. Just as the shot peening process MHP is an impact treatment although in MHP the impact area can be controlled, leading to the desired impact density. In DR the contact between spherical tool and work piece is quite different to MHP as the spherical is in sliding contact as it is moved along the surface. Although the material loading of both surface treatments vary, the resulting surface structure is the same. Both lead to a cold worked, smooth surface including compressive residual. Technically DR and MHP parameters have been part of researches but there still is a lack of statistical validation of every single process parameter leading to a hardened surface. This paper tries to close this gap. DR and MHP are conducted on different materials, containing tool steel 1.2379 and grey cast iron EN-JS-2070. Using a fractional factorial test design an experimental matrix was created able to examine the influence of every single process parameter. Which were for DR: rolling pressure, line spacing between hammer traces, diameter of roller ball and the travelling speed. For MHP the influence of the following process parameters was investigated: angle between hammering direction and surface normal, line spacing between hammering traces, diameter of hammering ball, hammering energy, travelling speed and hammering frequency. On every single sample ten Brinell hardness indents are made which give the statistical coverage needed to calculate the effect of every single process parameter within a confidence interval of at least 95 %. For all mentioned materials the effect of every single process parameter has been calculated with respect to hardening. It could be shown that especially the loading of the cast iron is quiet complex as a high amount of impact energy (MHP) or contact pressure (DR) can lead to overloading of the material leading to a degradation of the surface. At least an explanatory approach which describes the different influence of the tool diameter on the surface hardness is given using FEM simulations. These FEM simulations contain an advanced material model in which the Bauschinger-effect of 1.2379 is implemented. It can be clearly shown that a larger tool diameter in DR produces a higher amount of cold working in the material surface leading to harder surfaces compared to the smaller tool diameter. In contrast to DR the contact pressure in MHP is determined by the Hertzian pressure distribution. Here smaller tool diameters create larger Hertzian pressure and therefore a higher amount of cold working.

Influence of Hammer-Peened Surface Textures on Friction Behavior

“…An increase in surface hardness by more than 30 % can be observed. Depending on the set of parameters, the hardness increase is realized more or less pronounced [16].…”

Research on Mechanical Properties of 210Cr12 Shaft Surface Processed with Rolling

“…Coatings 2019, 9, x FOR PEER REVIEW 3 of 11 phenomenon can be produced [21,22], and residual compressive stress can be introduced on the workpiece surface [23], which can prevent the occurrence of fatigue failure and improve the fatigue strength and fatigue life of the workpiece [24,25].…”

“…Coatings 2020, 10, 611 3 of 11 the same time, subgrains of the rolling layer are refined to form gradient nanocrystalline layer [17][18][19]. After rolling, the roughness of the workpiece surface can be reduced [20], the work hardening phenomenon can be produced [21,22], and residual compressive stress can be introduced on the workpiece surface [23], which can prevent the occurrence of fatigue failure and improve the fatigue strength and fatigue life of the workpiece [24,25].…”

Analysis of the Velocity Distribution of an Elliptic Surface Structure Manufactured by Machine Hammer Peening

“…Due to high-frequency impacts of a spherical MHP head [1], surface asperities during forming are smoothed [2], while compressive residual stresses [3] and strain hardening [4] are induced into the surface layer. For the generation of high-frequency impacts, there exist pneumatic [5], piezoelectric [6] and electrodynamic [1] technologies.…”