Toshiaki Wakabayashi

Dry machining and minimum quantity lubrication

Modern machining processes face continuous cost pressures and high quality expectations. To remain competitive a company must continually identify cost reduction opportunities in production, exploit economic opportunities, and continuously improve production processes. A key technology that represents cost saving opportunities related to cooling lubrication, and simultaneously improves the overall performance of cutting operations, is dry machining. The elimination of, or significant reduction in, cooling lubricants affects all components of a production system. A detailed analysis and adaptation of cutting parameters, cutting tools, machine tools and the production environment is mandatory to ensure an efficient process and successfully enable dry machining.

Boron nitride as a lubricant additive

Hexagonal boron nitride (BN) has a graphite-like lamellar structure, but has been considered less effective than other solid lubricants except for high-temperature applications. The present paper describes a series of sliding experiments which show somewhat curious behavior of BN when added to lubricating oil, and discusses their results by comparing with the results of observation and analysis of sliding surfaces. In the case of sliding of bearing steel vs. itself, BN slightly increased the coefficient of friction, but dramatically decreased wear. Boron was found to remain on the surfaces, but the remnant was almost oxidized; it was some sort of oxide but not stoichiometric. If bearing steel was slid against cast iron, BN decreased the coefficient of friction, but the decrease in wear was less marked, and the remnant in this case was mostly BN. These results show that BN is effective in reducing wear if used as a lubricant additive.

A Synthetic Ester as an Optimal Cutting Fluid for Minimal Quantity Lubrication Machining

Abstract Significant progress has been made in dry and semidry machining recently, and minimal quantity lubrication (MQL) machining in particular has been accepted as a successful semidry application because of its environmentally friendly characteristics. A number of studies have shown that MQL machining can show satisfactory performance in practical machining operations. However, there has been little investigation of the cutting fluids to be used in MQL machining. In this study, several fluids, including vegetable and synthetic esters, are compared on the basis of the physical properties that would be suitable for MQL applications. The cutting performance of fluids is also evaluated using actual MQL operations. As a result, biodegradable synthetic esters are found to be optimal cutting fluids for MQL machining.

Tribological Characteristics and Cutting Performance of Lubricant Esters for Semi-dry Machining

Abstract In semi-dry machining, such as minimal quantity lubrication (MQL) machining, a very small amount of a lubricant plays an Important role to achieve a successful operation. This study investigates the tribological behavior of lubricants for semi-dry application in connection with their cutting performance. In MQL turning, synthetic biodegradable esters are superior to a vegetable oil and provide the satisfactory cutting performance compared with a conventional cutting fluid of flood supply. Their tribological action is further evaluated with the aid of tool surface analysis and the adsorption characteristics of a model ester are fundamentally examined using a controlled atmosphere machining apparatus.

TRIBOLOGICAL ACTION AND OPTIMAL PERFORMANCE: RESEARCH ACTIVITIES REGARDING MQL MACHINING FLUIDS

ABSTRACT As an optimal fluid for MQL machining, this paper introduces some synthetic polyol esters having the high biodegradability, excellent oxidation stability and satisfactory cutting performance. The fundamental investigation demonstrates synthetic esters possess the preferable adsorption ability on to the freshly cut metal surfaces and this ability can be enhanced by surrounding oxygen. This may result in effective lubricating film formation and is probably in close connection with their satisfactory MQL cutting performance. A multifunctional fluid, which is applicable to both machining and other lubricating parts of machine tools, is further developed based on the synthetic ester for MQL machining.

A Study on Tribology in Minimal Quantity Lubrication Cutting

Despite the fact that minimal quantity lubrication (MQL) machining produces almost similar cutting performance to conventional flood supply machining while using much less metal working fluid (MWF), it has not been fully utilized in industry due to lack of understanding of the fundamental process physics. To take full advantage of MQL machining and expand its applicability, an understanding of its tribological behavior is critical. Hence, in this study, the adsorption characteristics of MQL media during orthogonal cutting was investigated using two experimental setups; one in a high vacuum chamber with a mass spectrometer to observe mass changes of MQL media during cutting, and another setup in an atmospheric chamber where the supply of MQL media can be controlled. The former is mainly for analysis of the tribological behavior of MQL media, and the latter for cutting performance monitoring. It was found that the adsorption amount of MQL media was closely related to lubrication behavior. Oxygen in MQL supply plays a significant role in lubrication. Ultrasonic vibration cutting tests with MQL were conducted for further understanding of lubrication mechanism.

Multifunctional Application of a Synthetic Ester to Machine Tool Lubrication Based on MQL Machining Lubricants

Abstract Machine tools generally necessitate a variety of lubricants. Since some of those lubricants are often contaminated with cutting fluids and disposed without adequate separation treatments, it must certainly be convenient to prepare a multifunctional fluid applicable to both machining and other lubricating parts. In minimal quantity lubrication (MQL) machining, synthetic polyol esters are the successful cutting lubricant. This study therefore proposes a certain synthetic ester as a base candidate of environmentally friendly multifunctional fluids. Several cutting and lubrication tests have demonstrated the successful multifunctional lubrication performance of this ester with a very small quantity of a highly effective additive.

The Kinetics of Gas-Phase Lubrication in the Orthogonal Machining of an Aluminium Alloy:

Tetrachloromethane (carbon tetrachloride) has been used as a model gas-phase lubricant to investigate the kinetics of lubrication in the low-speed orthogonal machining of a precipitation-hardened aluminium alloy, in a controlled low-pressure environment. The dependence of cutting force on lubricant gas pressure, feed (that is depth of cut in these experiments), cutting speed and interfacial temperature was investigated. The results are not consistent with previous theories of vapour-phase lubrication in which transport of the lubricant molecules is assumed to control the reaction rate. A new model is proposed involving activated chemisorption of the lubricant at the tool-chip interface. The predictions of this model are in good agreement with the experimental observations and an activation energy of 18.4 kJ/mol has been derived for the relevant reaction.

The action of gaseous lubricants in the orthogonal machining of an aluminium alloy by titanium nitride coated tools

Abstract Specimens of an aluminium alloy have been machined at low speeds (up to 0.1 m s −1 ) with both conventional high speed steel and titanium nitride coated tools under controlled atmosphere. In the presence of CCl 4 vapour, TiN coated tools gave lower cutting forces and superior surface finishes. Although ethanol vapour also acted as an effective cutting lubricant, it produced little difference in behaviour between the two tool materials. Measurements of tool forces and observations on the degree of material transfer and pick-up suggest that the effectiveness of TiN coatings involves not only their direct frictional interaction with the material of the workpiece but also the interaction with any cutting lubricant: the coating may play a role by changing the wettability of the tool surface by reaction products formed at the interface between the chip and the tool.

Investigation of adsorption behaviour of lubricants in near-dry machining:

Abstract Near-dry machining (NDM) is a technology with many ecological and economic benefits that uses very small amounts of metal working fluid (MWF). In order to increase the applications of this technology, the tribological mechanism during this process needs to be better understood. To accomplish this, two experimental set-ups were configured. The first involved a vacuum chamber where changes of gas near the cutting area can be traced by a mass spectrometer. The second has an atmospheric chamber where practical cutting can be done for cutting-performance comparison. Three gases - argon, nitrogen, and oxygen - were used with and without an ester in a series of orthogonal cutting tests to understand their roles in lubrication. It was found that oxygen adsorbs best onto a newly generated work surface and plays a significant role in promoting adsorption of the ester and, in turn, creating a lubrication film. Therefore, it is important to supply an abundant amount of oxygen in NDM to provide good lubrication conditions.