Quaker Chemical Corporation has developed new metalworking fluid technology which extends cutting tool life beyond that currently obtained in production CGI machining operations, while also offering a sustainable, mineral oil- and boron-free solution.
Recent studies in CGI machining have focused on continuous cutting conditions which occur during high speed cylinder boring. Boring of engine cylinders is one of the more critical operations in engine production, requiring high quality surfaces to be produced at relatively high cutting speeds. It is at such elevated cutting speeds (200-250 m/min), where the machinability of CGI presents significant challenges with regard to obtaining acceptable cutting tool life.
New metalworking fluid technology developed within the past few years specifically for CGI machining, has been shown to yield a 20 -- 30 percent increase in tool life relative to that obtained using more conventional ferrous machining fluids. To continue to advance productivity in CGI machining, further improvements in fluid technology, along with developing a deeper understanding of the effects of cutting speeds on machining performance, are needed.
In addition to minimizing tool wear, there is also a need in industry for sustainable, mineral oil- and boron-free metalworking fluids. Such attributes are highly desirable with regard to resource conservation and fluid longevity.
To meet these objectives, a new mineral oil-free, sustainable metalworking fluid was developed and tested in the high speed continuous cutting of compacted graphite iron. Machinability was assessed by measurement of flank wear occurring on the cutting insert. Using wear rates measured at three cutting speeds, the C and n constants for the Taylor Tool Life Expectancy equation were determined, This equation enables the prediction of tool life at different speeds, and can be used for optimizing the operation with regard to cutting speed and tool life.
To evaluate the performance of new CGI metalworking fluid technology, machining tests were performed on a Haas SL-30 Turning Center where multiple turning passes were made on test cylinders of Grade 450 CGI supplied by SinterCast. Machining was performed using coated carbide inserts at cutting speeds of 190, 250, and 310 m/min, at a feed rate of 0.3 mm/rev and a radial depth of cut of 0.2 mm.
In this process, abrasive wear on the flank face of the cutting insert develops and progresses rapidly with continued machining. For the testing conducted, and for determination of the C and n constants in the Taylor equation, 0.2 mm flank wear length was used as the failure point for the tool.
The insert wear measured at the three cutting speeds, using two different metalworking fluids, one a current state of the art CGI machining fluid, and the second being a new fluid developed for enhanced CGI machinability and fluid sustainability, are shown in the chart on the right. With higher wear rates typically experienced in CGI machining, a tool life improvement obtained from use of a new metalworking fluid, can offer significant benefit with regard to the quality and economics of the machining operation. In looking at the insert wear measured for the two fluids, at the three cutting speeds, the new mineral oil-free fluid machines with lower wear rates and thus offers the potential for both economic and productivity improvements in current industrial CGI machining operations.
Taylor Tool Life Expectancy Equation
The Taylor Tool Life Expectancy equation which provides a prediction of the tool life to be expected at various cutting speeds, offers a useful means for optimizing a machining process. When the tool life values obtained at the three cutting speeds are plotted on a natural log-log graph of cutting speed versus tool life, the resulting relationship is a straight line expressed in the Taylor Tool Life Equation, VTn = C, where V = cutting speed, T = Tool Life, and n (slope) and C (y-intercept) are constants whose values depend upon cutting conditions, workpiece and tool materials as well as tool geometry.
Once determined experimentally, the n and C constants can be used to calculate and predict the tool life to be expected at various cutting speeds. The n and C constants determined for the two metalworking fluids tested are shown in the graph on the right.
Use of the Taylor equation can assist greatly in a decision making process regarding cutting fluids and speeds to be used, and their subsequent impact on tool life and productivity. For example, if in a given operation, the current CGI machining fluid technology is used at 190 m/min and giving an average tool life of 134 minutes, a change to the new sustainable fluid would be expected to increase tool life to 181.35 minutes, representing a 35 percent tool life improvement.
However in this same operation, if increasing cutting speed was the primary objective, then a change to the new CGI fluid would be expected to enable an increase in cutting speed from 190 m/min to 201.22 m/min, with no change in the cutting tool life currently obtained.
Summary & Conclusions
Extending tool life can have a significant impact on the productivity and costs associated with a CGI machining operation. Metalworking fluids designed to enhance CGI machinability and extend tool life have been developed. In addition, newer technology has been developed which can further enhance CGI machinability as well as offer a mineral oil- and boron-free fluid.
Using tool life measured at the three cutting speeds, the n and C factors for the Taylor Tool Life Expectancy Equation were calculated for the two fluids tested. This allows for the prediction of tool life to be expected at varying cutting speeds for both fluids, and provides a useful tool for optimizing conditions in a CGI machining operation.
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