Donna J. Michalek

Examining the role of cutting fluids in machining and efforts to address associated environmental/health concerns

ABSTRACT Cutting fluids have seen extensive use and have commonly been viewed as a required addition to high productivity and high quality machining operations. Cutting fluid related costs and health concerns associated with exposure to cutting fluid mist and a growing desire to achieve environmental sustainability in manufacturing have caused industry and academia to re-examine the role of these fluids and quantify their benefits. This work summarizes the traditional purposes of cutting fluids and reports on recent analytical and experimental research to critically examine these functions. To minimize or even eliminate the concerns associated with cutting fluid usage, several recent and novel approaches have been proposed and are examined.

Infusing sustainability principles into manufacturing/mechanical engineering curricula

Sustainability issues are increasingly important among governments, consumers, and corporations around the world. Many companies are directing their resources to reduce the environmental impact of their products and services. To remain competitive in the global economy, these companies must recruit employees who understand the impact of their decisions on the environment and society, while at the same time influencing the companys bottom line. It is the mission of universities to prepare these future employees to meet this need. A group of faculty and students in the Dept. of Mechanical Engineering-Engineering Mechanics at Michigan Technological University is working to address this growing demand. This paper assesses the current undergraduate mechanical engineering curriculum at Michigan Tech with regard to sustainability and identifies barriers to incorporating sustainability throughout the curriculum. A benchmarking study, progress made at Michigan Tech, and a vision for the future of the mechanical engineering curriculum are presented.

Character and Behavior of Mist Generated by Application of Cutting Fluid to a Rotating Cylindrical Workpiece, Part 1: Model Development

Increasing attention is being devoted to the airborne emissions resulting from a variety of manufacturing processes because of health, safety, and environmental concerns. In this two-part paper, a model is presented for the amount of cutting fluid mist produced by the interaction of the fluid with the rotating cylindrical workpiece during a turning operation. This model is based on relationships that describe cutting fluid atomization, droplet settling, and droplet evaporation. Experiments are performed to validate the model. In Part 1 of the paper, the emphasis is on model development. In the model, thin film theory is used to determine the maximum fluid load that can be supported by a rotating cylindrical workpiece; rotating disk atomization theory is applied to the turning process to predict the mean size of the droplets generated by atomization; and expressions for both the evaporation and settling behavior are established. Droplet size distribution and mass concentration predictions are used to characterize the fluid mist. Model predictions indicate that the droplet mean diameter is affected by both fluid properties and operating conditions, with cutting speed having the most significant affect. Model predictions and experimental results show that the number distribution of droplets within the control volume is dominated by small droplets because of the settling and evaporation phenomena. In Part 2 of the paper, the cutting fluid mist behavior model is validated using the results obtained from a series of experiments. @DOI: 10.1115/1.1765150#

Experimental and analytical efforts to characterize cutting fluid mist formation and behavior in machining.

The use of cutting fluids in machining operations is being carefully scrutinized by industry for several reasons, including its overall cost in the manufacturing process and its impact on worker health. Given the concerns associated with the use of cutting fluids, a number of experimental and analytical research efforts are being conducted to gain an understanding of the role of these fluids in various machining processes. The knowledge gained by this research will aid in the development and implementation of strategies to reduce or eliminate the negative effects of cutting fluids, while maintaining their beneficial role. This article presents the results of designed experiments focused on determining the significant variables that influence air quality during turning operations, as well as characterize the aerosol emissions associated with wet and dry turning. Air quality is characterized by measuring the mass concentration and particle size distribution of the dust and mist created during a set of machining experiments. The relative importance of vaporization/condensation and atomization as mist-generating mechanisms is also explored. The experiments revealed that spindle speed has a dominating effect on both mist mass concentration and aerodynamic particle size. Analytical models are presented that predict the average droplet size of the mist generated by atomization and are used to investigate droplet size trends for various cutting fluids and machining parameters. The results predicted by the models are consistent with the expected trends.

Character and Behavior of Mist Generated by Application of Cutting Fluid to a Rotating Cylindrical Workpiece, Part 2: Experimental Validation

Summary and Conclusions This two-part paper has developed and experimentally vali-dated a model for cutting fluid mist formation that describes theinteraction of the fluid with the rotating cylindrical workpieceduring a turning operation. Part 1 of this paper focused on themodel development, incorporating the following components:• Thin film and rotating disk atomization theory to predictmean droplet size.• A lognormal distribution to characterize the droplets that aregenerated.• Relations for both droplet generation and settling rates.• Relations to describe the droplet evaporation.• An expression for mass concentration as a function of thedroplet size distribution.Part 2 of this paper has been devoted to the experimental vali-dation of the model developed in Part 1. The work presented inPart 2 may be summarized as follows:• The experimental setup and capabilities were described.• The mean generated droplet diameter and maximum cuttingfluid flow rate are validated.• The standard deviation was empirically determined using ex-perimental data.• The mist behavior component of the complete model wasvalidated with data collected on both time varying dropletsize distributions and dynamic changes in the mass concen-tration.• The complete model was validated using mass concentrationand size distribution data.Both the model predictions and the measured data point to theimportance of cutting speed as a significant parameter for dropletgeneration and the maximum flow rate. Cutting speed is alsofound to be the dominant variable in terms of mass concentration,with increasing cutting speed producing smaller droplets andhigher PM10 mass concentration levels.Based on the model and the validation effort described in thistwo-part paper, the following conclusions may be drawn:• The complete model accurately predicts the droplet size dis-tribution and the mass concentration behavior.• For the conditions examined, during fluid application themass concentration increases over time because the rate ofdroplet generation exceeds the settling/evaporation rate.• Once the fluid application is discontinued, the mass concen-tration decays exponentially.• The assumption that the droplets within the control volumefollow a lognormal distribution appears to be valid.• Regardless of the droplet mean diameter associated with theatomization mechanism, the distribution of droplets withinthe control volume will be dominated by small droplets be-cause of the settling and evaporation phenomenon.With the present model established, the model may now be usedto judge the effects of processing conditions, fluid applicationvariables, and fluid type on the resulting droplet size distributionand mass concentration.

An Education Program in Support of a Sustainable Future

The historical evolution and current status of sustainability education at Michigan Technological University is described. The history considers the last 15 years, during which, the faculty of Michigan Tech have been collaborating on the development of environmental curricula and courses. This development effort initially focused on specialized offerings for the environmental/chemical engineering programs. With time, recognition of the importance of environmental issues (wastes, natural resources, energy, etc.) to other disciplines across the campus grew. For example, chemists, biologists, foresters, etc. each have a role in characterizing the behavior of ecological systems. Engineering disciplines that are focused on the design of products, processes, or systems influence long term societal sustainability. Social scientists must understand the relationship/linkages between the environment, industry, citizens, and government. Greener products, environmentally responsible processes, life cycle thinking, and environmental stewardship need to become part of the modern lexicon of globally aware students. Faculty from diverse disciplines across the campus are now collaborating to develop courses and modify curricula to educate students with respect to the triple bottom line (i.e., sustainable economic, societal, and environmental future). Problems associated with the traditional education paradigm are discussed. A new education model aimed at training students to create a sustainable future is proposed.Copyright

Development of an Imaging System and Its Application in the Study of Cutting Fluid Atomization in a Turning Process

Airborne inhalable particulates in the workplace can represent a significant health hazard, and one of the primary sources of particles is mist produced through the application of cutting fluids in machining operations. One of the principal mechanisms associated with cutting fluid mist formation is atomization. Atomization is studied by applying cutting fluid to a rotating workpiece such as found in a turning process. In order to properly study the atomization mechanism, an imaging system was developed. This system extends the size measurement range typically achievable with aerosol sampling devices to include larger particles. Experimental observations reveal that workpiece rotation speed and cutting fluid flow rate have significant effects on the size of the droplets produced by the atomization mechanism. With respect to atomization, the technical literature describes models for fluid interaction with the rotating workpiece and droplet formation via drop, ligament, and film formation modes. Experimental measurements are compared with model predictions. For a range of rotation speeds and fluid application flow rates, the experimental data are seen to compare favorably with the model predictions.

Application of an Imaging System to Study Machining Mist Formation via an Atomization Mechanism

Airborne inhalable particulate in the workplace represents a significant health hazard. One of the primary sources of this particulate is mist produced through the application of cutting fluids in machining operations. One of the important mechanisms for the production of cutting fluid mist is the atomization mechanism. In this paper, atomization is studied by applying cutting fluid to a rotating workpiece such as found in turning. An imaging system is presented for the study of the atomization mechanism. The imaging system extends the size measurement range typically achievable with aerosol sampling devices to consider larger particles. Experimental observations from the imaging system reveal that workpiece rotation speed and cutting fluid flow rate have significant effects on the size of the droplets produced by the atomization mechanism. With respect to atomization, the technical literature describes models for fluid interaction with the rotating workpiece and droplet formation via drop and ligament formation modes. Experimental measurements are compared with model predictions. For a range of rotation speeds and fluid application flow rates, the experimental data is seen to compare favorably with the model predictions.Copyright

Experimental and Numerical Investigation of Vapor Formation in a Fuel Rail

Recently, additional scrutiny is being placed on all vapor releases to the environment from the fuel system of an automobile. In an effort to lower the overall release of fuel vapor, a preliminary study of the vapor formation processes that occur in a low pressure supply fuel rail was undertaken. The first objective of this work was to determine the means by which fuel vapor is generated within the fuel rail, particularly during hot soak conditions. Then, using this information, the next task was to develop a computational fluid dynamics (CFD) code which would model the vapor formation in the rail. An investigation of the fuel rail material and design revealed that the probable mechanism for vapor formation is nucleate boiling from cavities in the fuel rail surface and at the o-ring connections with the fuel injectors. Therefore, an experiment was constructed to investigate the vapor formation from artificial cavities on a metallic surface and at an o-ring interface. The data collected from the experiment included the departure diameter of the vapor bubbles, the bubble frequency, and the bubble rise velocity. These values, which are used to determine the vapor generation rate, were compared to the results predicted by various correlations available in the literature. Subsequently, a CFD model was constructed of the fuel rail, using Star-CD, by incorporating the appropriate vapor generation correlations as user-defined subroutines. The experimental observations clearly demonstrated that a large amount of vapor was generated at the o-ring interface and, to a lesser degree, from the cavities in the metallic surface. A CFD model was constructed to predict the vapor generated in a fuel rail from these cavities. Existing correlations that describe nucleate boiling adequately model this generation mechanism in the fuel rail. This CFD code can be used to determine the amount of vapor formed under various hot soak conditions. An analytical means of predicting the vapor formation at the o-ring interface will have to be developed in order to complete the CFD model.© 2002 ASME

Development of a Transient CFD Model of an SI Fuel Injector

As the use of fuel injection in spark ignition engines has increased, continuous refinements in the design of fuel injectors are needed in order to obtain lower engine emissions and increased performance. In this endeavor, computational fluid dynamics (CFD) has been used as a means of gaining an understanding of the flow through the injector, and also as a valuable tool in the design process. Most CFD models constructed to study injector flow utilize the standard k-e turbulence model and perform steady state calculations with the fuel injector needle held in a fixed position. The objectives of this research were to determine the appropriate turbulence model for this flow situation and the accuracy of using a steady state analysis to simulate the transient flow in an operational fuel injector. An evaluation of three turbulence models was performed. The standard k-e, along with the Renormalisation Group (RNG) and the Chen modifications of the k-e scheme were used to obtain steady state flow results for a fuel injector in the fully open position. Star-CD was used to perform the simulations of two fuel injectors containing Ford compound nozzles, which are specifically designed to generate turbulent flow just upstream of the injector exit. This comparison resulted in the determination of an appropriate turbulence model, which was then used in a transient CFD simulation of the injector. In addition to the transient simulation, which modeled the opening and closing processes, four steady state simulations were performed at different needle lift positions. The results obtained from these steady state simulations were compared to those from the transient simulation at the same needle lift positions. In all cases, the flow properties used for the comparisons were the fluid velocity, the turbulent kinetic energy, and the turbulent dissipation in the nozzle exit plane. This location was chosen because of its influence on the spray dispersion and droplet size distribution produced by the injector. From the turbulence model study it was determined that the Renormalisation group and Chen’s modifications schemes were preferred over the standard k-e scheme for predicting the turbulent flow properties. Comparisons between the transient and steady state simulation results clearly illustrated that the rapid movement of the pintle needle during the opening and closing processes greatly influences the flow at the injector exit. From these observations, it was determined that a fuel injector can operate entirely within the transient mode. Therefore, it was concluded that a transient simulation is the preferred method to use for injector analysis.Copyright