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Oil-in-water (O/W) emulsions are water-based lubricants and used as fire-resistant hydraulic fluids and metalworking fluids (MWFs) in industry. The (elasto-)hydrodynamic film-forming properties of O/W emulsions have been studied extensively in literature. Typical elastohydrodynamic lubrication (EHL) behaviors are revealed at low rolling speeds followed by a starved EHL regime at elevated speeds. These emulsions are self-prepared and mostly stable only for a limited time ranging from hours to several days. By contrast, the film-forming behavior of water-miscible commercial MWFs (long-term stable O/W emulsions) has rarely been reported. This restricts the understanding of the lubrication status of many tribological interfaces in manufacturing processes, e.g., the chip-tool contact in cutting. In this work, the (elasto-)hydrodynamic film-forming property of two commercial MWFs is investigated by measuring the film thickness on two ball-on-disc test rigs using different optical interferometry techniques. For comparison, two self-prepared simple O/W emulsions with known formulation have also been investigated. Experimental results from the two test rigs agree well and show that the two self-prepared emulsions have typical EHL behaviors as reported in literature. However, for the two commercial MWFs, there is almost no (elasto-)hydrodynamic film-forming ability over the whole range of speeds used in this study. This could be explained by the cleaning and re-emulsification effects of the MWFs. The lubrication mechanism of the two MWFs is mainly boundary lubrication rather than hydrodynamic lubrication. Graphical Abstract

In metal band sawing, higher cutting speeds increase frictional heat at sliding guide blocks. Recirculating water-miscible metalworking fluids (MWFs) often lack fine filtration and accumulate debris that can enter the guide–band interface. A 1 L coolant sample collected after 22.5 m2 of cutting contained a particle load of 0.438 g/L; optical sizing yielded a number-median maximum Feret diameter of 345 µm, with particles up to 1.5 mm. Compared with typical guide clearances (~0.1 mm), these sizes imply frequent ingress/bridging and three-body interactions. The coolant viscosity follows an Andrade relation and decreases by ~2% K−1 around 40 °C. HFRR tribometry indicates low steady-state friction (µ ≈ 0.12), comparable to cutting oil. Together, these results provide quantitative design inputs for next-generation guide clearances and targeted filtration/coolant-delivery concepts in high-speed band sawing.

This study investigates contaminants in metalworking fluids (MWFs) from an industrial band saw, focusing on microparticle classification and microbial quantification linked to fluid degradation. Most particles were under 50 µm, primarily aluminum and iron oxides from tool wear; oxygen- and sulfur-containing particles suggested corrosion. Microbiological analysis showed high contamination, with culturable microorganisms exceeding 1000 CFU/mL. A pathogenic strain associated with biodeterioration was identified, underscoring the need for microbial control. Filtration and ozonation have been used as decontamination methods to improve the purity and biological stability of the process fluid. Filtration enabled selective removal of metallic microparticles. Among six nanofiber filters, the Berry filter achieved the highest efficiency (70.8%) for particles ≥ 7.3 µm, while other filters were faster but less efficient. Ozonation proved highly effective for microbiological decontamination, reducing viable microorganisms by over 95%, improving visual clarity, and lowering pH from 9 to 8 while remaining within operational limits. Unlike filtration, ozonation significantly reduced microbial load. The combination of both methods is proposed as a sustainable strategy for maintaining process fluid quality under industrial conditions. These findings support integrated decontamination approaches to extend fluid life, reduce fresh MWF consumption and waste, and enhance workplace hygiene and safety in machining operations.

Micro end mills are characterized by high abrasive wear. To counteract this high abrasive wear, metalworking fluids can be applied. There are various methods to supply these fluids. One of these methods is the minimum quantity lubrication (MQL). The objective of this research is to investigate the influence of the supply direction and air pressure of a MQL system on the process result when micro milling. Micro milling tests were carried out using micro end mills made of cemented carbide with an effective diameter of 50 μm. When machining commercially pure titanium, the supply direction was varied at four levels relative to the feed direction (0∘, 90∘, 180∘ and 270∘) and the air pressure at three levels (0.1 MPa, 0.2 MPa and 0.3 MPa). At each air pressure, the spindle speed was varied at three levels (30,000 rpm, 60,000 rpm, 120,000 rpm). Tool wear, surface quality, burr formation, and manufacturing accuracy were analyzed. In terms of the supply direction, the best results were obtained with a supply direction of 180∘ (in feed direction) — the lowest roughness and the most uniform slot bottom structure were machined. Regarding the influence of the supply direction on tool wear and manufacturing accuracy, no significant differences could be found. With regard to the air pressure, no clear result could be achieved. The influence of the spindle speed on the process results was higher than the influence of the air pressure. However, it is possible to select a suitable air pressure depending on the spindle speed.

Objectives This report describes the extended follow-up (1941-2015) of a cohort of 38 549 automobile manufacturing workers with potential exposure to metalworking fluids (MWF). The outcomes of interest were mortality from cancers of the esophagus, stomach, intestine, rectum, bladder, liver, pancreas, larynx, lung, skin, prostate, brain, and female breast, as well as leukemia. This report includes 5472 deaths from cancer, more than ten times the numbers of deaths in our last summary report published 20 years ago. Methods Standardized mortality ratios were computed for the entire study period. Adjusted hazard ratios (HR) were estimated in Cox proportional hazard models with categorical variables for cumulative exposure to each type of MWF. Results Exposure-response patterns are consistent with prior mortality reports from this cohort. We found increased risk of skin and female breast cancer with straight fluids. For the first time, we found elevated risk of stomach cancer mortality. Overall, many of the exposure-response results did not suggest an association with MWF. Conclusions Mortality is a poor proxy for cancer diagnosis for treatable cancers and not the optimal outcome measure in etiological studies. Although the HR presented here handle bias from the healthy worker hire effect and left truncation, they do not handle bias from healthy worker survivor effect, which likely results in underestimates of the health impacts of MWF. Although this updated summary provides some information on the risk of cancer from MWF, targeted future analyses will help clarify associations.

Background Chronic kidney disease (CKD) carries a high public health burden yet little is known about the relationship between metalworking fluid (MWF) aerosols, occupational noise and CKD. We aimed to explore the relationship between occupational MWF aerosols, occupational noise and CKD. Methods A total of 2,738 machinists were sampled from three machining companies in Wuxi, China, in 2022. We used the National Institute for Occupational Safety and Health (NIOSH) method 5524 to collect individual samples for MWF aerosols exposure, and the Chinese national standard (GBZ/T 189.8–2007) method to test individual occupational noise exposure. The diagnostic criteria for CKD were urinary albumin/creatinine ratio (UACR) of ≥ 30 mg/g and reduced renal function (eGFR < 60 mL.min − 1 . 1.73 m − 2 ) lasting longer than 3 months. Smooth curve fitting was conducted to analyze the associations of MWF aerosols and occupational noise with CKD. A segmented regression model was used to analyze the threshold effects. Results Workers exposed to MWF aerosols (odds ratio [ OR ] = 2.03, 95% confidence interval [ CI ]: 1.21–3.41) and occupational noise ( OR  = 1.77, 95% CI : 1.06–2.96) had higher prevalence of CKD than nonexposed workers. A nonlinear and positive association was found between increasing MWF aerosols and occupational noise dose and the risk of CKD. When daily cumulative exposure dose of MWF aerosols exceeded 8.03 mg/m 3 , the OR was 1.24 (95% CI : 1.03–1.58), and when occupational noise exceeded 87.22 dB(A), the OR was 1.16 (95% CI : 1.04–1.20). In the interactive analysis between MWF aerosols and occupational noise, the workers exposed to both MWF aerosols (cumulative exposure ≥ 8.03 mg/m 3 -day) and occupational noise (L EX,8 h ≥ 87.22 dB(A)) had an increased prevalence of CKD ( OR  = 2.71, 95% CI : 1.48–4.96). MWF aerosols and occupational noise had a positive interaction in prevalence of CKD. Conclusions Occupational MWF aerosols and noise were positively and nonlinearly associated with CKD, and cumulative MWF aerosols and noise exposure showed a positive interaction with CKD. These findings emphasize the importance of assessing kidney function of workers exposed to MWF aerosols and occupational noise. Prospective and longitudinal cohort studies are necessary to elucidate the causality of these associations.

This research covers the development of novel metalworking fluids for machining of aluminium alloys which are based on renewable raw materials and do not contain mineral oil and conventional biocides. Glycerol/water and propanediol/water solutions were used as base fluids. The formulations were systematically optimized by the addition of performance enhancing additives. Thereby, the optimization steps were guided through laboratory investigations, like determinations of viscosities, corrosion protection properties, foaming characteristics, and microbiological stabilities. Furthermore, the fluids were investigated using tribological Brugger and tapping-torque tests. Finally, the metalworking fluids were applied in experiments on an industrial production machine with the processing routines deep drilling and thread forming. Two Al-alloys were used for the investigations: EN AW 6060 as a soft and EN AW 7075 as a hard alloy. For comparison purposes, a commercially available metalworking fluid for Al-machining, a mineral oil emulsion, was tested in parallel. As a result, a glycerol/water-based metalworking fluid was obtained that had a similar performance to the reference fluid. It is therefore already well suited for machining the Al-alloys. The propanediol/water-based metalworking fluid however was superior to the reference, especially concerning the surface qualities of the workpieces. No toxicological relevant emissions from the novel metalworking fluids were found by air samplings and measurements at the test machine. The concentrations of some identified carbonylic compounds were significantly below the occupational limit values, at least by a factor of 800.

Exposure assessments to metalworking fluids (MWF) is difficult considering the complex nature of MWF. This study describes a comprehensive exposure assessment to straight and water-based MWFs among workers from 20 workshops. Metal and organic carbon (OC) content in new and used MWF were determined. Full-shift air samples of inhalable particulate and gaseous fraction were collected and analysed gravimetrically and for metals, OC, and aldehydes. Exposure determinants were ascertained through observations and interviews with workers. Determinants associated with personal inhalable particulate and gaseous fractions were systematically identified using mixed models. Similar inhalable particle exposure was observed for straight and water-based MWFs (64–386 µg/m 3 ). The gaseous fraction was the most important contributor to the total mass fraction for both straight (322–2362 µg/m 3 ) and water-based MWFs (101–699 µg/m 3 ). The aerosolized particles exhibited low metal content irrespective of the MWF type; however, notable concentrations were observed in the sumps potentially reaching hazardous concentrations. Job activity clusters were important determinants for both exposure to particulate and gaseous fractions from straight MWF. Current machine enclosures remain an efficient determinant to reduce particulate MWF but were inefficient for the gaseous fraction. Properly managed water-based MWF meaning no recycling and no contamination from hydraulic fluids minimizes gaseous exposure. Workshop temperature also influenced the mass fractions. These findings suggest that exposures may be improved with control measures that reduce the gaseous fraction and proper management of MWF.

This paper presents the study of the finishing, repair, and maintenance turning operations of gamma titanium aluminide (γ-TiAl) parts from the aeronautic industry, with the aim to evaluate different sustainable lubrication/cooling environments, including a newly developed synthetic ester water-based metalworking fluid (EcoMWF) to replace mineral-based MWF (MWF). The systems considered in this work are dry, cold-compressed air, minimum quantity lubrication (MQL), cryogenic, and flood on turning of a new and relatively low explored titanium alloy, γ-TiAl. Therefore, the influence of machining parameters and insert type on tool wear, surface roughness, roundness, and cutting temperature have been investigated for each environment. Results detailed in this study showed a significant influence of the lubrication/cooling systems on the machinability of γ-TiAl. The study also revealed that the sustainability of turning γ-TiAl could be improved under the cryogenic system and the new EcoMWF, keeping the same machining performance as common mineral-based MWF. Graphical abstract

An understanding of the proper application of metalworking fluids (MWFs) is necessary for their implementation in efficient production processes. In addition, the knowledge of the process-related aspect of chip transport and the macroscopic cooling effect, the characteristics and properties of lubricant film formation, and the cooling conditions in the secondary shear zone on the chip surface, i.e., in the direct vicinity of the material separation, represent a combined fundamental scientific issue within production engineering. The aim is to transfer methods from the field of tribology of machine elements, which have already led to a considerable gain in knowledge in this discipline, to machining and to couple them with already established approaches to machining. In the case of roller bearings, the contact pressure is in the range as the pressure in the contact zone between the cutting insert and chip. Due to this, established methods might be transferred to the cutting process. In addition to classical pin-on-plate and pin-on-ring friction investigations, film thickness measurements were carried out and compared to machining tests. The coefficient of friction determined in the planing test rig is 0.48 for dry cutting, while it is 0.47 for wet cutting. These two values are much larger than the CoF with MWFs measured on the two tribometers. It is shown that the boundary friction of MWF especially influences the machining process. Thus, additives in MWF might have a high significance in machining.