Analysis of the tribological behaviour of polymer composite tool materials for sheet metal forming

Today's automotive industry shifts its focus on customised production, facing an increasing demand for medium and small batch production, where cost-effective manufacturability of sheet metal forming dies comes into the foreground. Filled polymers offer possibilities to fulfil such requirements in the ambit of prototype tools manufacturing or in small batch production of sheet metal components. This paper presents investigations dealing with tribological and tool design aspects of using polymeric materials for sheet metal forming purposes. Friction and wear behaviour of two polymer composites on sheet metal counterface materials have been investigated. A new testing method for wear evaluation of polymeric materials for sheet metal forming using a Strip Drawing Test facility is presented and discussed. A method to predict lifetime of polymeric stamping dies using the linear wear–distance relation W_l/s measured with the new testing method is also proposed. Significant improvements in friction and wear performance of polymer composites have been observed using sheet materials with structured surfaces. A theoretical model for abrasive friction and wear of polymer composites on sheet metal counterface material pairs has been developed, based on the results obtained by measurement of friction and wear.     

The Influence of Water Addition on High-Temperature Tribological Properties of Interstitial Free Steel Sliding against Different Counterparts

The influence of only water addition on the hot metal forming process has not yet been reported in regard to tribological performance. In the present study, simulation tests were carried out on a pin-on-disc tribometer to evaluate the effects of water lubrication on the wear and friction behaviors of interstitial free (IF) steel sliding against different countersurface materials at 800°C in comparison with those in dry sliding. The opposing materials were selected as GCr15 steel and ceramic-based compounds including ZrO₂, SiC, and Si₃N₄. It has been found that Si-based component–IF steel pairs exhibit the lowest wear losses despite achieving relatively high friction. Water addition adversely impairs the friction and wear characteristics on steel-steel tribopairs, whereas it shows insignificant effects on the pair involving ceramic-based components except ZrO₂. Varying tribological responses can be found among different mated surfaces under water lubrication. X-ray diffraction, scanning electron microscopy, and energy-dispersive spectroscopy were utilized to examine the worn surface. The acting mechanism of water addition for different rubbing pairs was further discussed from the aspects of oxide tribochemistry.     

Influence of solid lubricants and fibre reinforcement on wear behaviour of polyethersulphone

Polyethersulphone (PES), is an amorphous, brittle and high temperature engineering thermoplastic. Two composites of PES containing short glass fibres (GF) and solid lubricants viz. PTFE and MoS₂; and two composites containing short carbon fibre (CF) [30% and 40%] were selected for the present studies. Compositional analysis of selected materials was done with various techniques such as gravimetry, solvent extraction and thermal analysis viz. thermal gravimetric analysis (TGA) and differential scanning calorimetry (DSC). These materials were studied for adhesive and abrasive wear performance by sliding against a mild steel disc and silicon carbide abrasive paper respectively, under different loads. It was observed that GF reinforcement along with incorporation of solid lubricants (PTFE and MoS₂) enhanced the wear performance of PES by an order of two. In the case of solid lubricants, PTFE proved to be more beneficial than MoS₂. CF reinforcement, however, proved to be the most effective in enhancing wear performance of PES. PES reinforced with 40% CF exhibited a specific wear rate in the order of 10⁻¹⁶m³/Nm which is considered to be very good for the thermoplastic composite. In the case of abrasive wear behaviour, however, incorporation of fibres or solid lubricants deteriorated the performance of the neat matrix. SEM was employed to investigate the wear mechanisms.     

A study of the role of solid lubricant and fibrous reinforcement in modifying the wear performance of polyethersulphone

High‐temperature polymers are generally preferred for those tribology applications where cost is secondary and performance is the primary consideration. Since frictional heat dissipation limits the usefulness of polymers because of their poor thermal conductivity, high‐temperature polymers are preferred in applications which have harsh operating conditions. In this paper, a high‐temperature polymer, polyethersulphone (PES), was selected for some adhesive wear studies, along with two PES composites containing 18% glass‐fibre (GF) reinforcement and two solid lubricants, i.e., PTFE and MoS₂ (2% each). Adhesive wear studies of these materials on two pin‐on‐disc machines indicated that neat PES was not a good tribo‐material. However, incorporation of GF and solid lubricants enhanced the wear performance by an order of two. PTFE was found to behave better than MoS₂. However, after long sliding duration both the lubricants performed almost equally well. The topography of the surface of the pins and the disc was studied using SEM to investigate the wear mechanisms.     

The Use of D-optimal Design for Modeling and Analyzing the Tribological Characteristics of Journal Bearing Materials Lubricated by Nano-Based Biolubricants

Response surface methodology (RSM) based on a D-optimal design was employed to investigate the tribological characteristics of journal bearing materials such as brass, bronze, and copper lubricated by a biolubricant, chemically modified rapeseed oil (CMRO). The wear and friction performance were observed for the bearing materials tested with TiO₂, WS₂, and CuO nanoadditives dispersed in the CMRO. The tests were performed by selecting sliding speed and load as numerical factors and nano-based biolubricant/bearing materials as the categorical factor to evaluate the tribological characteristics such as the coefficient of friction (COF) and specific wear rate. The results showed that RSM based on a D-optimal design was instrumental in the selection of suitable journal bearing materials for a typical system, especially one lubricated by nano-based biolubricant. At a sliding speed of 2.0 m/s and load of 100 N, the bronze bearing material with CMRO containing CuO nanoparticles had the lowest COF and wear rate. In addition, scanning electron microscopy (SEM) examination of the worn bearing surfaces showed that the bronze bearing material lubricated with CMRO containing CuO nanoadditive is smoother than copper/brass bearing material.     

Dry Sliding Wear Behavior of Zircon Sand Reinforced Al–Si Alloy

The emerging demand of light weight alloys and composites for the engineering and structural applications leads to explore the possibility to develop new techniques to achieve materials of high performance. In the present study, Al–Si/zircon sand reinforced composite has been developed via spray forming technique. Dry sliding wear behavior of as cast Al–Si base alloy and spray formed Al–Si/zircon sand reinforced composite containing 8% V _f of zircon sand has been analyzed. An isotropic wear property of spray formed composite has been checked by selecting the spray formed preform in both horizontal and vertical sections of deposit. The wear tests which were carried out at loads of 14.7, 24.5, 34.3, 44.1, and 53.9 N have shown that spray formed composite is more wear resistant in comparison to the cast Al–Si alloy. Moreover, wear coefficient in case of composite is also found to be lower than base alloy. Optical and scanning electron microscopies have been carried out to furnish a suitable explanation for observed wear behavior of composite and alloy.     

Wear of commercially available plastic materials

This article reviews the data on the wear of commercially available plastic-based bearing materials. Much of these data were obtained during the course of a six-year project at NCT, using a purpose-built test facility. The wear performance of materials has been assessed in terms of the effect of bearing pressure and surface temperature rather than PV factors. Basic wear data are presented on a wide range of materials. The effect of bearing pressure on the wear rate of some composite materials is discussed and the influence of wear debris removal on the wear rate at high loads is also assessed. The wear performance of filled-ptfe composites and polyimides at elevated temperatures is compared. These tribological data are presented in a form which is intended to enable designers to select appropriate materials and to estimate bearing life under the conditions of a particular application     

Parametric study of solid-lubricant composites as ball-bearing cages

The performance of two polymer-based materials (polyimide/MoS₂ and ptfe/ glass fibre/MoS₂) as self-lubricating cages for ball bearings has been comprehensively evaluated. The two composites emerged as the most promising for operating at elevated temperatures during screening tests in a thrust-bearing geometry and were then tested in four sizes of 440C stainless steel single-row radial ball bearings at a range of loads, speeds and temperatures.Two regimes of operation were observed: the first with essentially zero steel wear when the lubricant transfer film is complete and bearing life is dictated by cage wear; the second with finite steel wear when the transfer film is only partially effective and bearing life is dictated by increase in internal clearance. The ball/raceway stress at which steel wear starts to occur is very low (< 1.2 × 10³ MN m^?2) compared to the stress implied by the catalogue load capacity of the bearings. The ball/raceway stress also has an important effect on both steel wear rate and cage wear rate.Overall, the ptfe-based composite gave lower steel and cage wear than did the polyimide-based composite, but the latter could be operated at higher temperatures (up to 360° C) and at slow speeds it gave a higher load capacity before the onset of steel wear.Using the wear results as a basis, a Bearing Performance Guide has been produced which provides a convenient means of approximately predicting the bearing life over a wide range of operating conditions     

Chemical Reactivity Factor for Metallic Sulfide Lubricants

Wear data for molybdenum lubricated with various metallic sulfides have been analyzed. It is found that wear life in the Falex Lubricant Tester depends greatly upon chemical reactions, which apparently form MoS₂ in situ. With the possible exception of WS₂, none of the metal sulfides except MoS₂ are lubricants per se. Water solubility as an index of reactivity shows that compounds exhibiting pronounced water solubility function as more effective lubricants for molybdenum than less soluble compounds. There is also some evidence that wear life of alloy pins in the Falex wear test correlate with performance characteristics of ball bearings in high-speed bearing tests for several different alloy retainer materials.     

Tribological characterisation of a‐C:H coatings at room temperature: Effect of counterbody material

Metal‐free amorphous carbon (a‐C:H) coatings with 15% hydrogen were deposited on bearing steel surfaces. The friction and wear performance of these specimens was characterised in oscillating sliding tests with a ball‐on‐flat geometry. Balls of four ceramic and four metallic materials were investigated in tests at room temperature. Special attention was paid to the effect of moisture by testing in dry, normal, and moist air. The effect of water vapour on the friction and wear of the a‐C:H coatings was quite different for the different counterbody materials. The wear was in all cases very low, with a coefficient of wear below 10⁻⁷ mm³/N m for most cases. The coefficient of friction was also very low, between 0.04 and 0.12 for most of the tests. The smallest wear and friction coefficients were found for oxide ceramics, while during tests against SiC and Si₃N₄ the coating was worn through during the test. The effects of counterbody material and the humidity of the surrounding air are discussed in terms of friction and wear mechanisms.     

Effect of temperature and load on three-body abrasion of cermets and steel

The effect of temperature and load on three-body abrasion resistance has been examined for stainless steel, Cr₃C₂-Ni cermet, plain WC-Co hardmetal and yttria stabilized zirconia doped WC-based composites. Series of tests at various tribo-conditions were performed on a recently developed device. Coefficient of friction and materials response to abrasive actions have been analyzed and positive effect of zirconia addition on materials wear resistance has been shown. The low wear rates of ZrO₂ containing cermets are due to lower susceptibility of zirconia to transgranular crack propagation, smaller mean free path between ceramic grains and formation of lubricating glazed silica-rich layer.     

A Proof‐of‐Concept Study of the Use of Complex Borides for Disassembly of Decommissioned Nuclear Reactor Containment Vessels

Tool specimens of hot pressed AlMgB₁₄ were employed in lathe turning tests cutting exterior surface material from 6061 aluminum, 304 stainless steel, Inconel, and concrete at various cutting rates. Performance was measured via analysis of mass change (removal rate), wear mechanisms, surface chemistry (reactivity), and fracture mechanisms. Preliminary results indicate that this new family of ultra‐hard materials exhibits good cutting performance against all four workpiece materials, while combining favorable toughness with an unusual absence of tool heating, leading to minimal wear and anticipation of long life in application for sectioning of ferrous‐based metals and structures such as reinforced concrete containing such metals. The potential value of these new materials for use in disassembly of decommissioned nuclear reactor pressure vessels is discussed.     

Embeddability behaviour of some Pb-free engine bearing materials in the presence of abrasive particles in engine oil

One of the tribological requirements on engine bearing material is its ability to safely embed contaminant particles onto its surface and minimise damage to both the bearing and crankshaft surfaces. In this work, a journal bearing test rig that operates under constant load has been employed to investigate the embeddability behaviour of selected multi-layered Pb-free engine bearing materials at three different rotational speeds using engine oil contaminated with SiC particles. Experimental results have shown that third-body abrasive wear is influenced by the lubricant film thickness. There was also difference in embeddability of the different materials. Bismuth-based overlay and MoS₂ containing polyamide-imide-based overlay-coated materials show higher wear compared to tin-based overlay and a polyamide-imide-based composite overlay-coated material. Steel counter surfaces sliding against bismuth-based overlay and MoS₂ containing polyamide-imide-based overlay exhibited higher wear than those sliding against tin-based overlay and polyamide-imide-based composite overlay.     

Comparative evaluation of machinability characteristics of Nimonic C-263 using CVD and PVD coated tools

Machining of Nimonic C-263 has always been a challenging task owing to its hot strength, low thermal conductivity, tendency to work harden and affinity towards tool materials. Although coated tools have been used to overcome some of these challenges, selection of coated tool with appropriate deposition technique is of immense significance. The current study attempts to comparatively evaluate various performance measures in machining of Nimonic C-263 such as surface roughness, cutting force, cutting temperature, chip characteristics, and tool wear with particular emphasis on different modes of tool failure for commercially available inserts with multi-component coating deposited using chemical vapour deposition (CVD) and physical vapour deposition (PVD) techniques. Influence of cutting speed (V_c) and machining duration (t) has also been investigated using both coated tools. The study demonstrated remarkable decrease in surface roughness (74.3%), cutting force (6.3%), temperature (13.4%) and chip reduction coefficient (22%) with PVD coated tool consisting of alternate layers of TiN and TiAlN over its CVD coated counterpart with TiCN/Al₂O₃ coating in bilayer configuration. Severe plastic deformation and chipping of cutting edge and nose, abrasive nose and flank wear along with formation of built-up-layer (BUL) were identified as possible mechanisms of tool failure. PVD coated tool successfully restricted different modes of tool wear for the entire range of cutting speed. Superior performance can be attributed to the hardness and wear resistance properties, thermal stability due to presence of TiAlN phase and excellent toughness owing to PVD technique and multilayer architecture.     

Evaluation of the performance of coated carbide tools in face milling TC6 alloy under dry condition

Titanium and its alloys are well known as the typical different-to-cut materials because of their low thermal conductivity, high chemical reactivity, and low modulus of elasticity. During machining of titanium alloy, advanced high-speed, high-efficiency processing technologies are adopted to improve the production efficiency and reduce the production costs. The main goal of this work is to compare the performance of physical vapor deposition (PVD)-coated (TiN/TiAlN) and chemical vapor deposition (CVD)-coated (TiN/Al₂O₃/TiCN) carbide inserts in face milling TC6 alloy. To this end, the present paper reviewed the main works on the application of PVD- and CVD-coated tools in machining titanium alloys and the material performance of TC6 alloy, especially the machinability in machining process. Several tool life tests and tool wear experiments were carried out on a milling center with a five-axis spindle drive. Cutting forces were measured with a Kistler dynamometer. The failure modes and chip morphology were observed. Surface roughness and tool wear evolution were determined. The wear mechanism was discussed to compare the performance of PVD and CVD-coated tools. The main conclusions of this work were that the cutting tools made with PVD coating (TiN/TiAlN) had the excellent tooling quality and the main wear mechanisms were spalling and adhesion. PVD-TiN/TiAlN insert was more suitable to milling TC6 alloy than CVD-TiN/Al₂O₃/TiCN insert.     

Effect of nanosilica additive particles on both friction and wear performance of mild steel/CuSn/SnBi multimaterial system

This paper presents an experimental study of the tribological behaviour of a multimaterial system using conventional powder metallurgy process with SiO₂ nanoparticles. Four configurations were studied with and without SiO₂. The tribological properties of the sintered materials were analysed by wear experiments at lubricated conditions on a ball disc wear test rig. The results are compared with those of conventional material for journal bearing. These show less variation of the friction coefficient and less wear rate for the materials with SiO₂ compared to the ones without SiO₂ and to those of the reference material. The dominant wear mechanism is adhesive wear, accompanied by mild abrasive wear.     

Influence of the Erodent Shape on the Erosion Behavior of Ductile and Brittle Materials

Solid particle erosion is identified as a major wear process occurring in numerous industrial applications. A number of test parameters influence the behavior of the materials during this wear process. Particle shape is one of the key factors, which is often discussed for ductile or brittle materials in the literature, but a comparative study of ductile and brittle materials showing an effect of particle shape has not been addressed in detail until now. The present work discusses the influence of erodent shape on the wear behavior of a ductile (Ti-6Al-4 V alloy) and a brittle (TiN coating) material during the erosion process. Investigations are performed in an erosion test rig where the ductile and brittle materials are charged with spherical and angular SiO₂ particles at normal impact. Results show an inverse erosion behavior of ductile and brittle materials with the variation in particle shape. Ductile materials show low material removal with spherical particles, whereas brittle materials show low material removal rates with angular ones. This work also provides an analysis of the material removal phenomenon to understand the effect of particle shape on tested materials. Since materials removal phenomenon in ductile materials is often reported in the literature, this work addresses the material removal behavior especially in ceramic coatings.     

Studies on the Tribological Properties and Structure of Antifrictional Iron-Containing Aluminum Alloys

Experimental aluminum alloys with the addition of iron (about 1%) have been considered in order to simulate alloys obtained from secondary raw materials (wastes of domestic manufacture, scrap, etc.). In particular, the alloys have been studied using sclerometric tests according to a criterion of relative shear strength (τ/σ_mc). The tribological testing of the alloys has been also carried out according to the block-pad and ball–plane schemes of loading. A mathematical model of the wear process has been used to process the results of wear testing for the ball-plane scheme of friction contact. As a result, the wear law parameter K_w has been determined for all of the experimental alloys. The results of testing have confirmed that, in general, it is possible to use aluminum alloys that contain iron for manufacturing monometallic plain bearings. The structure and chemical composition of the surface have been studied for both the initial samples and the samples after testing.     

The Sliding Friction of Hybrid Composite Journal Bearing Under Various Test Conditions

The friction and wear behaviour of SiC, Si₃N₄ and SiC/Si₃N₄ composite ceramics were investigated with oscillating sliding (gross slip fretting) at room temperature. The influence of counter body material and the humidity of the surrounding air was studied with a ball-on-disc configuration with different ball materials (1000Cr6, Al₂O₃ SiC and Si₃N₄). The effect of RH on friction is marginal with exception of SiC (low friction) as counter body material. The wear behaviour, however, is strongly affected by humidity, showing inverse trends for different counter body materials. Consequently, the wear behaviour of a tribo couple can be improved by selecting an adequate mating material. The results reveal the necessity to control RH in tribological tests. For estimation of the performance of tribo couples under varying environmental conditions, a variation of RH is required. In tribo couples with single phase SiC, either as ball or disc, the tribological behaviour of the system is dominated by SiC. The friction behaviour of the composite material is in between the behaviour of the two single phase materials, Si₃N₄ and SiC, whereas the wear behaviour is very similar to that of single phase Si₃N₄.     

Sliding wear behaviour of ion implanted ultra high molecular weight polyethylene against a surface modified titanium alloy Ti-6Al-4V

A study has been made of the sliding wear behaviour of untreated and ion implanted ultra high molecular weight polyethylene (UHMWPE) against a surface modified titanium alloy (Ti-6Al-4V) using a pin on disc apparatus. It was found that the presence of water lubrication and a very smooth counterface was necessary to maintain low wear rates of the UHMWPE. A ‘zero wear’ effect was observed when nitrogen implanted UHMWPE was tested against very smooth counterfaces (R_a ≈ 0.03 μm) of either surface oxidized or nitrogen implanted Ti-6Al-4V under water lubrication. The enhanced mechanical and physical properties of the surface treated materials are believed to be responsible for the improved wear performance.