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What’s Hot in Titanium Machining
With the demand for titanium aerospace components expected to exceed current manufacturing capacity, it should come as no surprise that interest in titanium machining is rapidly growing.
However, there are several attributes of titanium that contribute to the challenge of titanium machining conditions, which make profitable titanium part production a balance of both processing speed and maximizing tool life.
Heat generation, a natural occurrence within all machining processes, typically disperses through the part material, tool and surrounding environment.
Due to titanium’s low thermal conductivity, a higher level of heat is concentrated directly onto the cutting edge of the tool, causing rapid degradation and deformation of the cutting tool. In many cases, tools are worn down so quickly that the cost of tooling alone negates sizeable profit margins.
“Titanium possesses several unique characteristics that contribute to extreme heat generation within the cutting zone,” says Brian List, titanium process engineer at Makino. “By understanding these characteristics and how they impact all aspects of the titanium machining process, we can better understand the source of the heat, why it develops and how we can manage the heat for a more efficient and profitable titanium machining process.”
Three Tests to Examine Cutting Forces
In order to properly manage the thermal conditions present in titanium machining, it’s critical to first understand how and why heat is generated in the cutting zone. To do so, calculations can be derived using force models within two distinct areas: the primary deformation zone, where energy is input into the system and material is forced upward, and the secondary deformation zone, which produces frictional heat as the chip curls along the cutter edge.
The following series of experiments were conducted at Makino’s titanium research and development facility using a Kistler dynamometer to measure cutting tool forces along the X, Y and Z axes. By mounting a workpiece to the Kistler dynamometer and performing a variety of test cuts, verification of the force model and cutting parameters–surface speed, depth of cut, chip loadâ€”were achieved. This information was then used to generate a ranking of how cutting parameters impact forces in the cutting zone.
1. Cutting Tool Forces vs Axial Depth of Cut
The first experiment compared cutting tool forces with axial depth cut. Adjustments were made to the depth of cut incrementally at 2mm, 4mm, 6mm, 8mm and 10mm. The results revealed a linear relationship between increases in the depth of cut and forces experienced by the tool.
2. Cutting Forces vs Cutting Speed
In the next case, cutting tool forces were measured against various cutting speeds. While there was a measurable difference in forces experienced by the tool as cutting speeds varied, the overall deviation had a minimal impact on the cutting performance. From these findings, an optimal cutting speed of 70 meters per minute was determined. At this speed, heat levels rose to titanium’s softening point of 550 degrees Celsius (1,022 degrees Fahrenheit), reducing the cutting tool forces for improved efficiency.
3. Cutting Forces vs Feed Rates
The third experiment evaluated the relationship between cutting tool forces and feed rates. Similar to the test observing axial depth of cut, the cutting tool forces adjusted proportionally to incremental changes in feed rates between 60 microns and 140 microns.
By combining results from each test in a Design of Experiment (DOE) study, parameter rankings were revealed: Axial depth and radial engagement had the greatest impact on cutting tool forces, followed by chip load, cooling methods and finally surface speed. It was determined that by reducing radial engagement, a larger axial depth using full flute of a cutter can be used while minimising the force energy applied to the work zone.
What’s hot and what’s not in Titanium Machining
Click here to watch the full Makino webinar. For more on Makino’s research and development in titanium machining, visit www.TiMachining.com
Sections of this article originally appeared in Radical Departures, the publication from Makino that serves the aerospace industry exclusively.