Aluminum Face Milling: The Impact of Coolant

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Aluminum Face Milling: The Impact of Coolant

Aluminum is milled in large quantities by manufacturers of automotive components such as engine blocks and cylinder heads.  Light passes are typically performed at the fastest speeds and feeds possible during these operations.  To achieve this, cutting speeds must be increased sufficiently to increase productivity without exceeding the force and power limitations of the cnc mill machining and cutting tools.  In order to be successful in this endeavor, it is necessary to have a thorough understanding of the interactions between cutting speed, tool edge wear, and required cutting power, as well as how the selected metalworking fluid formulation impacts all of these factors. 

Aluminum Face Milling: The Impact of Coolant

A series of aluminum face-milling tests can be carried out to determine the impact of various coolants on cutting power and tool edge wear.  Cutting forces generated at the same cutting speed with a new cutting tool were not significantly different when different coolants and cutting speeds were tested.  While machining with different fluid formulations, it becomes more difficult to achieve effective machining with a tool that has progressed further along in the cnc milling operation.

It is clear from these findings that:
Fresh, unworn inserts have little effect on the cutting power of the metalworking fluid.  In this case, the impact of two coolants on cutting power may not be noticeable until the tool edges begin to wear down and become worn down.
In addition, with a new, unworn cutting edge, the effect of speed on cutting power is negligible.
Cutting edge wear is a direct cause of power increase during aluminum milling.  Both the cutting speed and the metalworking fluid used have a direct impact on the rate of wear.
Relationships between these variables are linear (cutting speed increases in lockstep with increasing cutting edge wear and cutting power).  Manufacturers can potentially predict the condition of the cutting edge at any point in the milling routine, as well as the required power at other, untested cutting speeds, if they have this information at their fingertips.
Getting down to business in the laboratory.

This study focused on two fluids, one microemulsion and one macroemulsion.  Each fluid was diluted at a 5 percent concentration in water with a hardness of 100 parts per million and subjected to the same testing conditions.  The size of the suspended oil droplets is the most significant distinction between the two.  For the opaque macro-emulsion, these are larger than 0. 4 micron in diameter, and for the translucent micro-emulsion, they are much smaller in diameter.

Three-axis vertical milling machine (VMC) Bridgeport GX-710.  Copper (Cu), magnesium (Mg), zinc (Zn), and silicon (Si) were present in the workpiece, which measured 203. 2 by 228. 6 by 38. 1 mm and was cast and heat-treated in the process.  The cutter used was a shell mill with a 3-inch diameter and eight inserts with relief angles of 15 degrees and nose radii of 1. 2 millimeters.  It had an axial depth of 2 mm and a radial depth of 50. 8 mm when it was in operation. . Each coolant formulation was applied throughout 28 climb-milling passes at two different cutting speeds, 6,096 rpm (1,460 m/min. ) and 8,128 rpm (1,946 m/min.  ), resulting in a total material removal volume of 1,321. 6 cm3 for the entire test.  A total of 0. 5 millimeters per revolution (0. 0625 millimeters for each individual insert per revolution) was achieved at both speeds.

When cutting with a tool monitoring and adaptive control system, power measurements were taken for this investigation.  The charts in the slideshow at the top of this article depict the results of the tests.  Increased machining forces were expected to result from faster cutting speeds.  With a new, unworn insert at the start of a milling operation, however, as previously described, the differences in cutting power between two fluids were negligible.

At the beginning of the process, the properties of the workpiece material and the geometry of the cutting edge are the most important factors influencing the cutting power of the cutting edge.  Only after insert wear began to alter the cutting edge geometry did differences in metalworking fluid performance become apparent.  At any point during the milling operation, the choice of metalworking fluid had a direct impact on the rate at which this wear occurred and, as a result, the required cutting power.

This research has several implications, one of which is that a single test may not be sufficient to determine the full impact of switching to a different type of coolant.  Testing must be carried out until the inserts wear out to determine which formulation is capable of sustaining more aggressive cutting speeds for longer periods of time, assuming that both fluids perform at a certain baseline level.

The operational intelligence that can be gained by calculating the precise rate at which power increases with a particular cutting tool, coolant, and material combination (the slopes of the lines in Figure 2) is another implication of this technique.  Using the rate of power increase, for example, one can predict the state of the insert at any given point in the milling operation.  In a similar vein, power measurements taken at various cutting speeds can be used to calculate the required power at other, untested speeds.

The research indicates that a micro-emulsion performs better than a nano-emulsion when it comes to aluminum milling, even though the results cannot be extrapolated beyond this application.  The reason for this is that a tighter micro-emulsion with smaller-diameter oil droplets tends to remove heat more efficiently than a macro-emulsion with larger-diameter oil droplets.  A macro-emulsion and its comparatively greater lubricity, on the other hand, may be preferable in operations where cutting speeds are slower.