The Influence of Material, Hardness, Roughness and Surface Treatment on the Frictional Characteristics of the Underhead Contact in Socket-Head Screws

Abstract

The present paper aims at determining the effect of several design and manufacturing parameters on the frictional response of the underhead contact in a bolted joint comprising a socket-head M6 class 12.9 screw. The rationale of the research moves from the need to understand the frictional behavior of screw joints used in machine tools as a means to join roller monoguides with the moving carriages of three-axis tooling units. The experimentation takes into account different underhead materials (Steel, Cast Iron, Aluminum), different roughness levels (Ra = 0.8, 1.6, 3.2), different surface treatments (No treatment, oxidised, DLC), as well as repeated tightening operations. The experimentation has been run by a specifically developed specimen, consisting of two parts: an instrumented sleeve, equipped with a double array of strain gauges capable of sampling both the axial preload and the underhead torque, and interchangeable underhead washers, with an anti-rotation device, whose material and surface treatment are suitably changed among the different sets. The tightening torque is recorded by a digital torque wrench. The collected data are processed by ANoVa tools, to investigate the significance of each factor, as well as related interactions. The friction coefficients associated with the different operating parameters are a useful tool to support the design task of bolted joints.

Research on the relationship between the tightening torque and the preload of composite bolted structures

“…Stefano et al 29 studied the effect of process parameters on the residual torque of the bolt, including the torsional stiffness of the bolt and the connected parts. Croccolo et al 30 studied the influence of design and manufacturing process parameters on the friction coefficient of the bolt bearing surface, including material composition, surface roughness grade, surface treatment process, and repeated tightening times. Croccolo et al 31 evaluated the influencing factors of key physical quantities on the elastic release of torque.…”

“…The fiber bending model is used to describe fiber compression failure in the LaRC05 criterion, as shown in equation (30):…”

Bolted joint preload decay and the effect of multiple reuse

“…Further experimental investigations which also include consideration of the impact of repeated tightening of threaded fasteners include. 26,27 Work by Hess 28 presents a novel approach to determining bolted joint preloads utilising only a torque wrench to measure installation and removal torque and knowledge of the bolt thread pitch and carried out experiments of repetitive uses as part of that work. Liu et al 29 as part of work looking at studies of bolted joints subjected to axial excitations, also identified that bolt preload is lost due to repetitive tightenings.…”

Wear behavior of electrodeposited nickel coating on ZP5 zinc alloy

“…Many studies on the wear behavior of metal coatings were run 15–18 ; however, few of them concern electroless nickel coatings, 19–28 and, to the best of the authors’ knowledge, none of them is focused on the wear behavior of electrodeposited nickel coating. 29 Therefore, the aim of this work is to determine the wear behavior of electrodeposited nickel coating on ZP5 zinc alloy, by assessing the influence of coating thickness and applied load.…”