The fracturing ahead of the tool, and the occassional jamming of material under the tool, and the waviness of the generated surface are concepts to keep in mind when you try to understand why you are getting the finish on the surface that you get.
Also, a good way to visualize how the material is being workhardened by “rubbing” where the material is not separating easily ahead of the tool.
Built Up Edge (BUE) is the accumulation of workpiece material onto the rake face of the tool. This material welds under pressure, and is separate from the chip.
In school we were taught that this is because the first material to contact the tool workhardens, and we did hardness tests to confirm this.
Because BUE changes the effective geometry of the tool, it can have either positive or negative effects. Positive effects
Less tool wear
Lower power requirements
Less contact of the workpiece with the tool (It contacts the BUE instead)
Better surface finish and improved process capability
These effects are only beneficial if the BUE is thin and stable. Machining additives such as sulfur combine with manganese to form manganese sulfides. Manganese sulfide helps to control BUE because of its anti weld properties. On resulfurized steels, BUE is usually stable and not a problem. Negative effects
Poor tool life
Poor and variable surface finish ( As the BUE sloughs off the tool, it can weld to the workpiece)
Loss of statistical capability on dimensional control
Loss of uptime trying to troubleshoot the process
I have found that BUE is more likely on alloys that work harden. In order to get BUE under control, the steps that you take depend on the tool material. For Carbide
Decrease the feed. (Pressure welding usually is the culprit)
Increase the speed
Increase the rake angle or “hook”
Get a better metalworking fluid (including get the fines out of your existing MWF!)
Get a different coating
For High Speed Steel (HSS)
If the tool is High Speed Steel (HSS) you may think you are in oppositeland when you discover that slowing down the speed reduces the build up. I have found on HSS that as speed (heat increases) so does the tendency to form BUE. Graphic.