Friction related size-effect in microforming – a review

Abstract

This paper presents a thorough literature review of the size effects of friction in microforming. During miniaturization, the size effects of friction occur clearly. The paper first introduces experimental research progress on size effects of friction in both micro bulk and sheet forming. The effects of several parameters are discussed. Based on the experimental results, several approaches have been performed to develop a model or functions to analyse the mechanism of size effects of friction, and simulate the micro deep drawing process by integrating them into an FE program. Following this, surface modification, e.g. a DLC film and a micro structure/textured surface, as a method to reduce friction are presented. Finally, the outlook for the size effect of friction in the future is assessed, based on the understanding of the current research progress.

Influence of Test Stand and Contact Size Sensitivity on the Friction Coefficient in Sheet Metal Forming

“…Besides the effect of the test stand structural integrity, tribological effects could also be responsible for a change in the friction coefficient caused by a change in the contact area. According to Gou [13], the change in COF is mainly triggered by lubrication effects. To validate this theory, the lubricant distribution in the contact area must be non-uniform: close to the edges of the tool the lubricant must be squeezed out and therefore reduced locally.…”

“…Secondly, the contact area of each test stand was different. The effect of a significantly reduced contact area on the friction coefficient is already known for microforming [13]. Gou analyzed the size effect by comparing lubricated and non-lubricated specimens and determining the friction coefficient.…”

Effects of nano-particle lubrication on micro deep drawing of Mg-Li alloy

“…Yet, the mentioned and modified models are not capable of clarifying size effects expansively. Based on the open and close lubricant pockets, friction coefficient increases by decrease of specimen size, due to the increase of open to close lubricant pockets fraction consequently, commonly used lubricants in macroscale are unable to improve tribological characteristics in microscale [12,13] and lubricants overflow considerably at the open lubricant pocket regions without expected effects on the process [14,15]. However, in macroscale, lubricants are extensively utilised to enhance the product quality, to decline forming force and increase tools life-cycle.…”

Ultrasonic-Assisted Incremental Microforming of Thin Shell Pyramids of Metallic Foil

“…For this purpose, efficient microprocessing technologies with high accuracy and high surface quality are required to meet the demand for their production. Microcutting [ 1 ], micro-laser-machining [ 2 ], micro-electric discharge machining [ 3 , 4 ], and microforming [ 5 ] have been intensively studied, and recently, micro-additive-manufacturing combined with other microprocessing [ 6 ] is more and more important in tailor-made manufacturing or high-mix low-volume production of complex parts.…”