Heat is a natural byproduct with any cutting tool application, but it’s important that you know how to minimize it, as it will improve the life of your tool. Heat isn’t always bad and doesn’t need to totally be avoided, although, controlling heat will help prolong your tool life. Taking every precaution possible to redirect heat will prolong your tool’s usable life, avoid scrapped parts, and save you money.
HEM Tool Paths to Reduce Heat Generation
High-Efficiency Milling (HEM) is one way a machinist should explore to manage heat generation during machining. HEM is a roughing technique that uses the theory of chip thinning by applying a smaller radial depth of cut (RDOC) and a larger axial depth of cut (ADOC). HEM uses RDOC and ADOC similar to finishing operations but increases speeds and feeds, resulting in greater material removal rates (MRR). This technique is usually used for removing large amounts of material in roughing and pocketing applications. Using HEM will evenly spread heat across the whole cutting edge of your tool, instead of building heat along one small portion, reducing the possibility of tool failure and breakage.
Chip Thinning Awareness
Chip thinning occurs when tool paths include varying radial depths of cut, and relates to chip thickness and feed per tooth. When performing HEM, you effectively reduce your stepover and increase your speeds and feeds to run your machine at high rates. But if your machine isn’t capable of running high enough speeds and feeds, or you do not adjust accordingly to your reduced stepover, trouble will occur in the form of friction between the material and tool. This can create mass amounts of heat which can cause your material to deform and your tool to overheat.
When milling, there are two ways to cut materials: conventional milling and climb milling. The difference between the two is the relationship of the rotation of the cutter to the direction of feed. In conventional milling, the cutter rotates against the direction of the feed. During climb milling, the cutter rotates with the feed.
When conventional milling, chips start at theoretical zero and increase in size, causing rubbing and potentially work hardening.
In climb milling, the chip starts at maximum width and decreases, causing the heat generated to transfer into the chip instead of the tool or workpiece. When going from max-width to theoretical zero, heat will be transferred to the chip and pushed away from the workpiece, reducing the possibility of damage to the workpiece.
Utilize Proper Coolant Methods
If used properly, coolant can be an extremely effective way to keep your tool from overheating. Coolant can be compressed air, water-based, straight oil-based, soluble oil-based, synthetic or semi-synthetic.
Using coolant will allow those chips to slide out of your toolpath easily, avoiding the chance of re-cutting and causing tool failure. Coolant can be expensive and wasteful if not necessary for the application, so it’s important to always make sure you know the proper ways to use coolant before starting a job.