Analytic roughness prediction by deep rolling

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.

Several manufacturing processes are used to beneficially influence the surface and subsurface properties of manufactured parts. Different aspects such as the surface topography or resulting residual stresses are addressed using different manufacturing processes. This paper presents the first approach for pulsed mechanical surface treatment (PMST), a new manufacturing process aiming to combine the mechanics used in deep rolling and shot or hammer peening. The process can generate a defined surface topography while constantly impinging a mechanical impact on the workpiece. Two different tools (type 1 and type 2) have been designed to approach this new concept. Hardened carbide pins are used for type 1 to prove the concept using a simpler kinematic and resulting in a burnishing-like process. For type 2, hardened roller is used and results in an actual rolling process. Specimens made of S235 are processed in experiments with tool type 1 with varying pulse frequency and feeds. The resulting surface topography is described using optical measurement systems while micro-hardness measurements are used to describe the subsurface properties. The results in general show an increase of hardness in the surface and subsurface layer while the resulting surface topography can be directly controlled by the process parameters and therefore be designed for specific functional properties.

Mechanical surface treatment of EBM Ti6Al4V components: Effects of the resulting surface layer state on fatigue mechanisms and service life

In the current study, deep rolling treatment was applied to enhance low-cycle fatigue behavior of the AISI 304 stainless steel. Desirability function approach was applied to determine the process parameters offering the optimal surface roughness and hardness as these surface characteristics are supposed to control the fatigue cracks initiation and growth. The enhancement of the low-cycle fatigue behavior was investigated using strain-controlled fatigue tests applied to machined and deep rolled specimens associated to experimental evaluation of surface topography, microhardness, and residual stress. Findings of this work show that an increase of the fatigue lifetime of the AISI 304 components can be achieved by the application of deep rolling to machined surfaces. Moreover, the application of an intermittent deep rolling leads to a significant extension of service life especially when it is performed at low strain amplitudes. The improvement of the residual lifetime of deep rolled components is explained based on evaluations of the surface texture changes, residual stresses, cold work hardening, and strain-induced martensite transformation.

The Influence of Deep Rolling on the Surface Integrity of AISI 1060 High Carbon Steel

Abstract. The machine parts subjected to high wear are conventionally thermally hardened and/or hard coated to minimize surface erosion. The hard coating requires special arrangements and complex machining and finishing processes, which are time and labor-intensive. An alternative solution is work hardening of the surfaces, where hardening and surface finishing can be achieved within a single process step. The manganese steel X120Mn12 is known for its excellent work hardening and wear resistance, making it suitable for applications that require superior surface properties. The addition of 15 wt.% vanadium carbide (VC) enhances its abrasion resistance. Deep rolling (DR) processes have been found to affect microtopography, including surface roughness, increase hardness, and induce compressive residual stresses. Within the scope of this paper, a layer X120Mn12+VC is PTA (Plasma-transferred arc) welded onto a S235 steel substrate. The samples are then deep rolled under various combinations of influencing parameters such as rolling pressure, tool diameter, and feed. The main focus was to achieve maximum surface hardness, an optimal hardness depth profile, and reduced surface roughness. The combination of optimal deep rolling parameters achieved the surface hardness of 640 HV 1 while maintaining a relatively smooth surface. Additionally, an FE model was built, and the optimal DR process was simulated to study the development of residual stresses. The local distribution of equivalent plastic stresses corresponds well with the measured hardness distribution.

The most well known eSSect of mechanical surface treatments on metallic ~rlaterials is the improvement in fatigue properties. It is therefore not surprising that most of the archival literature on mechanical surface treatments, such as shot peening, deep rolling and laser shock peening, deals with the effect of near-surface properties on fatigue behavior. Most of these studies, however, are confined to room temperature fatigue behavior; in comparison, the effect of mechanical surface treatment on fatigue behavior at high temperatures has been rarely investigated [ I -51. The season for this disparity can be found in the popular belief that f~itigue strength irnprovement by mechanical surface treatments is mainly due to the presence of compressive residual stresses, and since such stsesses should anneal out at elevated tempesatures, mechanical surfice treatments for high temperature applications would appear questionable. However, this view may be over simplistic as there is always a possibility that the residual stresses may be at least partjally stable at elevated temperatures [6]; in addition, other factors may be involved, such as the nature of the near-surface microstructure. Accordingly, it is the objective of this study to examine the role of mechanical surface treatments on the high tcnlperature fatigue behavior of several metallic engineering materials. Moreover, it is the aim of this work to clarify what are the critical temperature thsesholds at which near-surface microstructures and residual stresses become unstable and whether this can explain the observed fatigue behavior.

Multi-response optimization of the turn-assisted deep cold rolling process parameters for enhanced surface characteristics and residual stress of AISI 4140 steel shafts

Because of the general problem of the welding workpiece such as fatigue fracture caused by tensile residual stress lead to initial and propagation crack in the fusion zone. Thus, the mechanical surface treatment of deep rolling on Gas Tungsten Arc Welded (GTAW) surfaces of AISI 316L was studied. Deep rolling (DR) is a cold working process to induce compressive residual stress in the surface layer of the workpiece resulting in hardening deformation which increased surface hardness, and smooth surface that inhibit crack growth and improve fracture strength of materials. The present study focuses on compressive residual stress at the surface of stainless steel AISI 316L butt welded joint of GTAW. The three parameters of DR process were used; pressure 150 bar, rolling speed 400 mm/min, and step over 1.0 mm. The residual stresses analysis by X-ray diffraction with sin2Ψ method at 0, 5, 10, and 20 mm from the center of the welded bead. The results showed that the DR process on the welded of GTAW induce the minimum compressive residual stress-408.6 MPa and maximum-498.1 MPa in longitudinal direction. The results of transverse residual stress in minimum and maximum are 43.7 MPa and-34.8 MPa respectively. The FWHM of DR both longitudinal and transverse direction were increased in the same trend. Furthermore, the microhardness after DR treatment on workpiece surface layer higher than GTAW average 0.4 times.

Enhancing surface integrity in friction stir welding through deep rolling and post-weld heat treatment

Deep rolling process is a mechanical surface treatment that provides several advantages, such as low friction on the interface between the tool and workpiece in the process, controlled profile of induced compressive residual stress to enhance the HCF and LCF strength, enhancement of the stability of the near-surface structure at high temperature, and improvement of surface finish after the process. This paper investigates the deep rolling process under lubricated condition for a complex deep rolling path. A three-dimensional finite element model incorporating the strain hardening and strain rate effects on the material responses is developed to sequentially simulate the continuous multi-axis roller motion in the process. This model can capture the horizontal and normal forces acting on the roller so that a time-varying apparent coefficient of friction can be obtained. In addition, due to the complex roller path, the model also predicts a complex residual stress distribution in the near-surface material.

Deep rolling (DR) is an effective mechanical surface treatment method to improve the fatigue properties of engineering components. In this method, the surface of the component was rolled using a roller with a predetermined force to obtain reduced roughness, hardness increases and compressive residual stresses in the surface region. These alterations allow for increasing the fatigue lives of the components in industrial applications. In the current study, DR was applied in tangential and longitudinal directions on specimens that were manufactured using EN-AW 6082-T6 aluminum. The resulting roughness, hardness and residual stresses were determined experimentally. Fatigue tests were carried out to determine the improvements in fatigue properties after DR. It was found that DR-induced compressive residual stresses depend on DR direction considerably. Due to this reason, fatigue strength improvements were found to be different for different DR direction applications. Longitudinal rolling resulted in a 23% fatigue strength increase compared to a 7% increase for tangential rolling. For both DR direction applications, fatigue cracks were shown to initiate at the sub-surface region, whereas the as-turned specimens exhibited surface crack initiation.

The mechanical surface treatment by deep rolling and burnishing is a widely used process in many industrial applications to optimize surface characteristics such as roughness, hardness and the residual stress state. Multiple process parameters (contact pressure, feed rate, tool diameter) need to be adapted to achieve an optimal treatment result, requiring major experimental efforts for the optimization process. Therefore, an approach was developed to simplify the optimization. The single target parameter for optimization in this approach is the overlap factor. This overlap factor can be simply determined experimentally from the width of single tracks, theoretically by Finite Element Analysis (FEA) or analytically by assuming linear elastic contact (Hertzian contact). The overlap factor was correlated with the surface condition after treatment (roughness, residual stress state) and an optimum value was proposed based on the treated material. For verification, the new approach was applied to Laser Bed Powder Fusion (LBPF) manufactured materials made of AlSi10Mg and 316L. To avoid overtreatment, i.e. an extensive plastic deformation of the surface during the process, an overlap factor of max. 90% was recommended based on former results. The predicted process parameters show the highest surface quality in this investigation.

Mechanical and thermal stability of mechanically induced near-surface nanostructures

High-strength w r o ~ ~ g h t magnesium alloys are considered as potential candidates for application as suspension parts in future automobiles due to their high strength to weight ratio 11-31, For this application, good HCF performance of notched components is one of the most demanding requirements. While previous work on magnesium alloys has demonstrated to what extent mechanical surface treatments such as shot peening and roller-burnishing can increase the HCF strength of smooth specimens compared to an electropolishecl reference [4-7 1 , corresponding results on notched specimens are not available yet. From earlier work on titanium and a l ~ ~ m i n u n ~ alloys 18101, it is known that particularly notched components beneficially react to mechanical surface trcatments such as shot peening or deep rolling. This result was explained by the interaction of the notch root stress field with the process-induced resitlual conlpressive stresses affecting nxiinly microcrack growth. In addition, the triaxial stress statc at the notch roo1 was thought to result in resitlual stresses bcing more stable during cyclic loading co~nparecl to those in the surface layer of smooth specimens.