Recent research in dry (unlubricated) contacts reveals that the Archard’s coefficient K cannot accurately characterize wear when operating under transient conditions such as those encountered during running-in or when the system experiences variable loading or variable speed. In contrast, a so-called degradation coefficient B derived based on the entropic characterization of wear provides realistic results. This paper reports an investigation of the efficacy of extending the results to the boundary and mixed lubrication regimes. For this purpose, experiments were performed on a pin-on-disk test setup with different lubricants at a wide range of operating conditions that cover different lubrication regimes. From the obtained results a new formulation is offered for determining B in a lubricated condition that unitizes the Stribeck curve and the concept of load sharing. The proposed method is validated by comparing the predictions with results available in the existing literature. Further, the efficacy of the proposed method is demonstrated by considering disks made of different materials having different surface roughness values.

On the Degradation of Tribo-components in Boundary and Mixed Lubrication Regimes

Experimental and numerical analysis of industrial warm forming of stainless steel sheet

Lubricants are necessary to avoid adhesion, galling, and scratching in aluminum stamping processes. In this study, various lubricants, including dry lubes and wet lubes, were evaluated using cup drawing test (CDT) for stamping of Al 5182-O aluminum sheets. The effects of surface texturing, with electro-discharge texturing (EDT) and mill finish (MF), on the friction behavior were also investigated. Furthermore, the methodology to evaluate the performance of lubricants was established based on (a) maximum applicable blank holder force (BHF) and (b) draw-in length in flange or flange perimeter of formed cups. Finite element (FE) simulations were carried out to determine the coefficient of friction (CoF) at tool–workpiece interface during deep drawing under different lubrication conditions. Flow stress data of Al 5182-O material were obtained using viscous pressure bulge (VPB) and tensile tests. In this study, it was confirmed that, in forming Al 5182-O, dry film lubricants have better lubricity than wet lubricants. A better lubrication condition was found with EDT surface texture. [DOI: 10.1115/1.4030750]

Evaluation of Lubricants for Stamping of Al 5182-O Aluminum Sheet Using Cup Drawing Test

FRICTION AND LUBRICATION in sheet metal forming are influenced by such parameters as material properties, surface finish, temperature, sliding velocity, contact pressure, and lubricant characteristics. The parameters that affect friction and lubrication are schematically shown in Fig. 7.1. Depending on these parameters, the performance of a lubricant and the coefficient of friction (COF) vary. Material flow in the die cavity is influenced by frictional conditions at the die/work piece interface. Therefore, a good understanding of the parameters that affect friction is essential for selecting lubricants and producing good-quality sheet metal parts. In sheet metal forming, the magnitude and distribution of friction affect metal flow, part defects, and quality, as well as tool wear and production costs.

/pdf/friction-and-lubrication-2azfli1nw4.pdf

Friction and Lubrication

Friction plays a vital role in several micromanufacturing processes. Since the eighteenth century, the phenomenon of friction has been widely investigated, but it is still one of the least ...

Friction in micromanufacturing

There are various tribotests that are used to evaluate the performance of stamping lubricants.As these tests are performed under laboratory conditions, it is important that they emulate the conditions found in stamping plants. The tribotests widely used to evaluate lubricants include strip draw test (SDT), draw bead test, sliding test, and limited dome height test. Strip reduction test was introduced by Andreasen et al. [1] and was used to evaluate lubricants for galling of the tool while ironing stainless strips. Twist compression test was used by many investigators [2] in order to estimate the coefficient of friction (COF) of stamping lubricants. Many of the above tests fail to emulate real-world production conditions in terms of contact pressure, plastic deformation of the sheet material, temperature, and forming velocities. These factors influence the performance of the stamping lubricant and hence need to be considered while choosing a test to evaluate lubricants. The deep draw test (DDT) used in this study to evaluate the stamping lubricants represents very closely the conditions that exist in the production of sheet metal parts. Therefore, it was selected for this study. However, SDT was also used for prelimi

Evaluation of Stamping Lubricants in Forming Galvannealed Steels for Industrial Application

Materials for Sheet Forming

The major purpose of the present study is to evaluate the performance of various galvanized (GI) or galvannealed (GA) mild steels and AHSS in stamping applications. Finite Element Analysis (FEA) of selected stamping operations was conducted to estimate the critical pressure boundary conditions that exist in practice. Using this information, laboratory tribotests, e.g. Twist Compression (TCT), Deep Drawing (DDT) and Strip Drawing (SDT) Tests, were developed to evaluate the performance of selected lubricants and die materials/coatings in forming galvanized steels of interest. The sheet materials investigated included mild steels and AHSS (e.g. DP600 GI/GA, DP780 GI/GA, TRIP780 GA and DP980 GI/GA). Experimental results showed that galvanized material resulted in more galling, while galvannealed material showed more powdering and flaking. The surface roughness and chemical composition of galvanized sheet materials affected the severity of galling under the same testing conditions, i.e. lubricants and die materials/coatings. The results of this study helped to determine the critical interface pressure that initiates lubricant failure and galling in stamping selected galvanized sheet materials. Thus, to prevent or postpone the critical interface conditions, the results of this study can be used to select the optimum combination of galvanized sheet, die material, die coating and lubricant for forming structural automotive components.

Nimet Kardes

Papers

Friction and Lubrication

Evaluation of Stamping Lubricants in Forming Galvannealed Steels for Industrial Application

Materials for Sheet Forming

Investigation of Galling In Forming Galvanized Steel Sheet