Deformed parts can be a costly waste of both material and time. Preventing deformations during machining is critical, but many materials — like aluminum, with its low hardness and high thermal expansion coefficient — are more prone to deforming than others.
Simple changes to machining equipment and practices can help machinists prevent the deformation of aluminum, aluminum alloys, and similar materials.
The tool used for machining the aluminum will have a major impact on cutting force and heat, which can cause the deformation of aluminum.
Typically, it’s best to avoid general-purpose tools when working with aluminum. These tools may work, but their characteristics typically make them a bad fit for machining aluminum.
Material, flute count, and helix angle of your tool will all significantly affect tool performance while machining aluminum.
Coated carbide end mills are essential for working with aluminum. While carbide is more brittle than other material options, its hardness means it stays sharper for longer. The softness of aluminum also means that carbide’s brittleness likely won’t be an issue while machining.
Aluminum’s softness also makes coatings important. Aluminum chips can easily clog the flutes of your end mills, especially when your cuts are particularly deep. Coatings keep chips moving, helping you to avoid some of the “stickiness” that aluminum chips can have.
Most experienced metalworkers will recommend end mills with two or three flutes. Three flutes will provide a balance of tool strength and chip clearance. Two fluted end mills will be slightly weaker but provide slightly more clearance. Anything with more than three flutes will provide additional strength you don’t need while also limiting chip evacuation.
For the most part, the choice between two and three flutes will come down to personal preference and the tooling you have on hand. So long as you don’t use an end mill with four or more flutes, the end mill should work well.
Helix angle choice will help to minimize chatter while improving material removal speed. Typically, machinists will recommend angles of 35, 40, or 45 degrees for machining aluminum. 35- and 40-degree angled tools will work well for roughing. A tool with a 45-degree helix angle will work better for finishing.
The lower angle helps to keep the tool — and the aluminum — cooler than it would be otherwise. The faster processing that a wider angle enables will also help with the thermal regulation of both the end mill and the part being milled. While the angle will result in a rougher surface finish, you’re likely going to return with another tool for a finishing pass — meaning it shouldn’t be a major issue.
A 45-degree helix angle is better for finishing as it produces smoother cuts. While a tool with this angle will produce more heat, it should be less of a problem when making the light cuts you need to finish a part.
Higher angles could be possible if the 45-degree angle tool does not produce the desired finish. However, higher helix angles will produce more heat, which will make deformation more likely.
Keeping your tools as sharp as possible will help minimize heat and deformation. Regularly inspecting tools for wear will prevent dull or worn tools from being used.
If chip evacuation is a concern, using an endmill with a chip breaker design may help. These end mills feature a profile with notches that improve chip evacuation.
The choice of material can influence deformation during machining. While heat treating is traditionally done after rough machining and before finishing machining, choosing an aluminum alloy that has been pre-heat-treated for strength and ductility can help prevent deformation. Vibration and cryogenic treatments to eliminate internal stress may be an option.
The use of salvaged components that have been pre-treated may reduce risks of deformation. Using the components could also mean significant savings. Some machinists say it’s possible to save as much as 60% on material costs by using salvaged components and materials.
In some areas, the material choice will not have an impact, however. The thermal coefficient of aluminum can vary between alloys, but only somewhat — meaning heat will always be a challenge when working with aluminum, no matter the alloy or material source.
Your approach and strategy for organizing the machining process can also have a major impact on part deformation. Along with strategies that improve the efficiency of your machining, these strategies can help you better manage aluminum’s thermal properties and softness.
Symmetric machining, rather than traditional one-side machining, is one way to reduce deformation produced by residual stresses during the machining process, especially when working with thin-walled parts or light alloys. With symmetrical machining, a part is attacked from multiple sides or angles, rather than just one face.
For example, imagine milling an aluminum plate to a desired thickness. Milling exclusively one side of the plate will concentrate heat, increasing the risk of thermal deformation. Milling both sides to reach the desired plate thickness will spread this heat out.
This process change is not complex, but it can make it much easier to manage the heat that is generated by processing a part.
Choice of cutting parameters can also affect how easy aluminum is to work with and how likely the material is to deform.
Commonly recommended surface footages for aluminum typically fall around 400 to 1,000 SFM. Wrought aluminum alloys may require a higher surface footage than cast aluminum, possibly between 800 and 1,500 SFM. You can use this formula to calculate tool RPM from your chosen SFM:
RPM = SFM ÷ tool diameter (in inches) × 3.82
Aluminum can deform easily during machining due to its softness and high thermal coefficient. Working carefully with the right tools can help you minimize the risk of deformation.
Tools with the right material, flute count, and helix angle can encourage chip evacuation and more effectively manage heat. The right process changes can also help you to distribute thermal energy and balance efficient machining with effective heat management.
Emily Newton is the Editor-in-Chief of Revolutionized. She has over four years experience covering the industrial sector.
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