Effects of Minimum Quantity Lubrication - Mql Technique in Machining Under Various Conditions

Introduction

Traditionally high temperature in cutting zone has been controlled by using cutting fluid. The cutting fluid helps to improve the surface finish as well as to facilitate chip flushing. It performs both coolant and lubricant function simultaneously. The coolant effect reduces temperature in cutting zone and the lubrication action decreases cutting forces. Thus the friction coefficient between the tool and chip becomes lower in comparison to dry machining. Minimizing the friction between the cutting edge of the tool and workpiece, corrosion control, chip ejection and washing are the functions of the cutting fluid in machining.

The beginning of metal cutting can be traced to the middle ages. It was not until the middle of the 18th century, that the major developments in metal cutting were found. Historically, until the 19th century, water was used for centuries as a cooling medium to assist various metalworking operations. [Taylor, 1907] was probably the first to prove the practical value of using liquids to aid in metal cutting. The turning lathe, milling machine, shaper, saw and other machines were developed to fulfill industry’s need for mass production at low cost and high accuracy. Now days metal cutting has become a very large segment of our industry and indispensable to modern man. Wherever metal is used in any manmade object, one can be sure that it must have reached its final stage through processing with machine tools.

Mineral oils were developed at this time as they had much higher lubricity. However, their lower cooling ability and high costs restricted their use to low cutting speed machining operations. Finally, between 1910 and 1920 soluble oils were initially developed to improve the cooling properties and fire resistance of straight oils [Childers, 1994]. Other substances were also added to these to control problems such as foaming, bacteria and fungi. Oils as lubricants for machining were also developed by adding extreme-pressure (EP) additives. Today, these two types of cutting fluids (coolants) are known as water emulsifiable oils and straight cutting oils. Additionally, semi- synthetic and synthetic Cutting fluids were developed to improve the performance of many machining operations [Mariani, 1990].

Today, cutting fluids play a significant role in manufacturing processes, supporting their high productivity and efficiency. Today many kinds of metal cutting fluids used are such as oils, oil-water emulsions, pastes, gels, aerosols (mists), and air or other gases.

The objective of the present work is to examine the effects of minimum quantity lubrication on the cutting performance of medium carbon steel at different cutting velocities and feeds in terms of main cutting force and feed force, average chip-tool interface temperature, tool wear and surface finish.

Irani et al. (2005) studied that heat generation is the limiting factor in the grinding Process due to the thermal damage associated with it. To combat this energy transfer, a cutting fluid is often applied to the operation. These cutting fluids obstruct the amount of energy transferred to the job through debris flushing, lubrication and the cooling effects of the liquid. This paper reviews some of the common as well as some of the more obscure cutting fluid systems that have been employed in recent years with an emphasis on creep-feed applications. Tawakoli et al. (2009) conducted an experimental investigation of the effects of job and grinding parameters on minimum quantity lubrication-MQL grinding coolant is a term generally used to describe grinding fluids used for cooling and lubricating in grinding process.

The main purposes of a grinding fluid can be categorized into lubrication, cooling, transportation of chips, cleaning of the grinding wheel and minimizing the corrosion. On the other hand, grinding fluids have negative influences on the working environment in terms of the health of the machine operator, pollution and the possibility of explosion (for oil). Barczak et al. (2010) studied the plane surface grinding under minimum quantity lubrication (MQL) conditions. Abrasive material removal processes can be very challenging due to high power requirements and resulting high temperatures. Effective lubrication and cooling is necessary to ensure temperature levels do not become excessive. This study aims to understand the effectiveness of MQL in the fine grinding plane surface grinding regime. This paper presents a comparative study of three cooling methods: conventional flood cooling, dry grinding and grinding with MQL. Common steels EN8, M2 and EN31 were ground with a general purpose alumina wheel.

Importance of the proposed project in the context of the current status.

MQL can provide significant savings and improved performance in the right applications. Here are some important considerations when looking at this technology.

Reduction of tool costs:

• Reduce tool wear, tools last longer
• Increased speed of production:
• Reduce heat and friction so higher cutting speeds.
• Reduction of labor costs:
• Tools last longer and require less regrinding, lessdowntime, reducing cost per part.
• Reduction of power costs:
• Friction reduced so less power required by machining.

A detailed literature review on cutting fluids and types of cooling methods was performed to explain the background. The literature survey was undertaken from various resources such as journals, conference articles, online sources, and reference books. All relevant information was analyzed to construct a precise summary of background information. All research work is described in a very brief manner in the form of thesis methodology.

Conclusion

MQL results in more effectively are reducing the temperature at cutting zone than Flood and Dry cutting. The results can be determined in terms of better surface finish and low tool wear under MQL. The cutting performance of MQL machining is much better than that of dry and conventional flood machining taking into consideration tool wear. Surface finishes is also better for MQL machining. This is improved mainly due to reduction of wear and damage at the tool tip by the application of MQL. The other intangible by product of the study are reduction in the ecology and health related problems, reduce the cost of machining by reducing the cutting fluid consumption rate and cost related to the carrying and disposal of cutting fluid, Increase the production rate by reducing the time taken in house keeping the machine, shop floor and handling of wet chips.