Page 62 - MTW NOVEMBER 2021 - Digital Magazine_Neat

TECH INNOVATION

recommend end mills with two or three will help minimize heat and deformation. traditional one-side machining, is one
flutes. Three flutes will provide a balance Regularly inspecting tools for wear will way to reduce deformation produced by
of tool strength and chip clearance. Two prevent dull or worn tools from being residual stresses during the machining
fluted end mills will be slightly weaker but used. process, especially when working with
provide slightly more clearance. Anything If chip evacuation is a concern, using thin-walled parts or light alloys. With
with more than three flutes will provide an endmill with a chip breaker design symmetrical machining, a part is attacked
additional strength you don’t need while may help. These end mills feature a from multiple sides or angles, rather than
also limiting chip evacuation. profile with notches that improve chip just one face.
For the most part, the choice between evacuation. For example, imagine milling an
two and three flutes will come down to aluminum plate to a desired thickness.
personal preference and the tooling you 2. Choose Materials and Pre-Heat Milling exclusively one side of the plate
have on hand. So long as you don’t use to Minimize Deformation Risk will concentrate heat, increasing the risk
an end mill with four or more flutes, the The choice of material can influence of thermal deformation. Milling both sides
end mill should work well. deformation during machining. While to reach the desired plate thickness will
heat treating is traditionally done after spread this heat out.
Helix Angle rough machining and before finishing This process change is not complex,
Helix angle choice will help to minimize machining, choosing an aluminum alloy but it can make it much easier to manage
chatter while improving material that has been pre-heat-treated for the heat that is generated by processing
removal speed. Typically, machinists strength and ductility can help prevent a part.
will recommend angles of 35, 40, or 45 deformation. Vibration and cryogenic
degrees for machining aluminum. 35- and treatments to eliminate internal stress Running Parameters
40-degree angled tools will work well for may be an option. Choice of cutting parameters can also
roughing. A tool with a 45-degree helix The use of salvaged components that affect how easy aluminum is to work with
angle will work better for finishing. have been pre-treated may reduce risks and how likely the material is to deform.
The lower angle helps to keep the of deformation. Using the components Commonly recommended surface
tool — and the aluminum — cooler could also mean significant savings. Some footages for aluminum typically fall
than it would be otherwise. The faster machinists say it’s possible to save as around 400 to 1,000 SFM. Wrought
processing that a wider angle enables much as 60% on material costs by using aluminum alloys may require a higher
will also help with the thermal regulation salvaged components and materials. surface footage than cast aluminum,
of both the end mill and the part being In some areas, the material choice will possibly between 800 and 1,500 SFM.
milled. While the angle will result in a not have an impact, however. The thermal You can use this formula to calculate tool
rougher surface finish, you’re likely going coefficient of aluminum can vary between RPM from your chosen SFM:
to return with another tool for a finishing alloys, but only somewhat — meaning RPM = SFM ÷ tool diameter (in inches)
pass — meaning it shouldn’t be a major heat will always be a challenge when × 3.82
issue. working with aluminum, no matter the
A 45-degree helix angle is better for alloy or material source. Machining Strategies That Can
finishing as it produces smoother cuts. Prevent Aluminum Deformation
While a tool with this angle will produce 3. Make Process Changes to Aluminum can deform easily during
more heat, it should be less of a problem Minimize Deformation machining due to its softness and high
when making the light cuts you need to Your approach and strategy for organizing thermal coefficient. Working carefully
finish a part. the machining process can also have a with the right tools can help you minimize
Higher angles could be possible if the major impact on part deformation. Along the risk of deformation.
45-degree angle tool does not produce with strategies that improve the efficiency Tools with the right material, flute
the desired finish. However, higher helix of your machining, these strategies can count, and helix angle can encourage chip
angles will produce more heat, which will help you better manage aluminum’s evacuation and more effectively manage
make deformation more likely. thermal properties and softness. heat. The right process changes can also
help you to distribute thermal energy and
Other Considerations Symmetrical Machining balance efficient machining with effective
Keeping your tools as sharp as possible Symmetric machining, rather than heat management.

56 MACHINE TOOLS WORLD NOVEMBER 2021 www.mtwmag.com