The surface enlargement process mostly used in the manufacturing of automotive parts like crankshaft, different types of bearings, and axles is termed as burnishing. To increase the roughness, roundness, integrity, and residual stress of surface of mechanical component, the process used is called ball-burning, it provides the super-finished final product. In this method, we get the expected models that has surface residual stress depending on the data obtained from experiment and outcome of ball-burnishing on the contour of residual stress (compressive nature) of AISI 8620 stainless steel. When surface was prepared by turning, different burnishing parameters (speed, feed and pressure) were studied to understand the impact on residual stress profiles in axial direction. Among studied parameters, pressure has important role in compressive residual stresses, whereas speed and feed have less influence on residual stress profiles.

Introduction:

The modifications and treatments of surface are very crucial in improving the service life of various components being used in engineering and structural functions. The surface engineering methodology includes use of thermal treatment, mechanical treatment, chemical treatment, coatings (hard and soft). Burnishing process is the most proficient method for the engineering of surface. Burnishing technique is a non-chip process that involve the working at low temperatures to getaflat hardened surface with the principle of plastic deformation whereas other used processes like grinding, polishing, honing and lapping of the surface [1].

Burnishing is a final process of on the mechanical component that has been done by putting a layer of polish and then allow the hard ball to roll against the surface of metal under the influence of pressure, this provide us the surface that is smooth and have more hardness and good corrosion resistance [2,3].

Burnishing is defined as a finishing process that is performed by applying an extremely polished ball (hard) to roll on thesurface of pressure under the influence of pressure, it results in smoothening of the surface and increase in the corrosion resistance and hardness.

In the processes of machining and finishing, surface and subsurface of the mechanical component pop up the extreme thermomechanical loadings, residual stresses, and surface hardness. The parameters mentioned above generally included in the nomenclaturegiven by Griffiths known as the ‘surface integrity’. Afterwards, Rech et al modified this definition [5] by adding the concept of long life of component and better performance during the life span.

The operation of the cold forming is necessarily done on low scale during which strain (change in dimensions) plays an influential role to enhance the hardness and strength of surface that results in the crystal-clear surface smoothing and advantageous leftover stresses (compressive) in the surface and inner-surface layer finally results in the reliability of the component [6].

Burnishing modifies the features of surface through plastic deformation of different layers of surface. Furthermore, burnishing process induces residualstresses that are compressive in nature as compared to theresidual stresses of tensile nature at surface incited by conventional methods.

Now the ball burnishing process is more frequently used for post-machining and metal finishing [1]. The burnishing process is distinguished by incitation of advantageous and balancedresidual stress of compressive nature, surface hardening, distinctive combination of elements, reducing surface hardness as well as micro notches. This process also has more advantages as it requires less skilled labor, can be done in conventional machine shops, thus it proves to be economical. It reduces surface defects and modifies surfaces being already machined[1, 7].

Burnishing process enhances the reliability of the mechanical component under the influence of dynamic load and high wearing resistance [2,7,8].

The crankshafts, different types of bearings, and axles of the automotive industry are the applications of the burnishing process [9,10].

Brinksmeier [11] et al proposed a recent state of art. Novovic et al [12], Sasahara [13]and several scientific works, state that those surface treatments that provides low roughness of surface related to the severe residual stresses of compressive nature have commendatory effects on the life span of fatigue and resistance to corrosion as compared to the component on which no process has done. The treatments of mechanical surfaces like burnishing [14,15] are very effective techniques to get the high surface integrity of material and according to some authors that these techniques also affect the roughness of surface, leftover stresses, and fine structure of various mechanical components.

The technique of ball-burnishing comprises of the rolling of hard ball on the surface of mechanical component, that results in the plastic deformation of the peaks crests of roughness and shifts the component to the troughs profile. This include the four key criteria of the surface integrity that involve the parameters i.e. roughness of surface, residual stresses of compressive nature, microstructure, and surface hardness.

The process of burnishing doesn’t use chip and applies suitable force that is above the range of yield strength of material to deform the surface layer of material plastically, a roller or ball press the surface material from crests and shifts to troughs to eliminate the irregularities and get a smoothen surface. This technique improves the surface integrity’s parameters of the material like finishing and hardness of mechanical component [6].

It is common that residual stresses of compressive nature considerably alter the reliability and surface smoothness is necessary because of the involvement of properties like wear resistance and fatigue life of workpiece [16].

The results of ball-burnishing parameters on the integrity of surface has been highlighted by various studies such as roughness of surface, hardness of component, and leftover stresses of compressive nature as shown in the literature review [17]. But unfortunately, many of the papers only discussed the outcomes of burnishing process for some parameters of process [15,18].

It has been found that most of the papers discuss the results of burnishing on a single parameter i.e. roughness of surface. For example, Loh et al [19] gave the descriptive literature survey related to the surface roughness of cylindrical parts. Afterwards, Lopez de Lacalle et all [20], discussed the burnishing process for the complex parts of the milling machines. As compare to the evolution of the microstructure, the research conducted is limited.

Almost all the researches conducted on the affects of burnishing process, residual stresses induced are of compressive nature. The tensile stresses present in the surface zone of mechanical component are converted to the compressive stresses after the burnishing takes place. This conversion of tensile residual stresses to the residual stresses of compressive nature of work-piece during the burnishing process increases the reliability of mechanical component [2,3].

Empirical model is commonly applied method to determine the characteristics of surface of work-piece [27]. Sagbas [28] presented regression technique of second-order for roughness of aluminum alloy’s surface by employing the technique of surface analysis in corporation with fundamental design of composite. The model presented was compatible with the results obtained from experimentation relying on the parameters that are force applied, speed of operation, feed given, and number of cycles. Generally, the residual stresses of compressive nature are significant in the simulation of finite element model as residual stress have influence on the fatigue life of the mechanical component.

Rodriguez et al [29] manifested the 2D finite element model that base on the distribution of residual stresses acting in the axial and tangential directions and have qualitative relation with the results obtained from the experimentation.

Yen et al [30] provided a thorough study on burnishing in which we used hard ball on the work-piece i.e. hardened steel. This study gathered the 2D and 3D finite element FE models of the work-piece to get the surface geometry and profile of tangential residual stresses.

Thus, this study is focusedon:

• Acquiring empirical models on residual stresses.
• Analyzing the parameters of burnishing that are sped, feed, and pressure of burnishing. The impact of the parameters of burnishing on the responses we get in the form of outputs that are roughness, roundness, and residual stresses of surface is also provided in this study.