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Adaptive Milling with plastics and easy flammable materials

Siemens Phenom Siemens Phenom
Siemens Phenom
Hi all,
I would like to react to a question, raised through  in this Blog from :
Proper Feeds and Speeds with Adaptive Milling in NX 12
Question from Michiel:

Let me share my thoughts and experiences with these materials:
Careful with plastics and "easy flamable materials" in general
With plastics, the heat is not being evacuated through the chips or the part (maybe just a bit, depending on which plastic is being worked on). Plastics are bad heat conductors. So most of the heat goes into the tool, which could be a problem itself, because at a certain point it can melt the plastic and you get built-up edge. So what is really necessary is the right coolant. Some plastics don't like fluid coolant, so air is nearly the only left option here.
So even if it seems very tempting to run with extrem high feeds and speeds in plastics because of low tensile forces, you should check from case to case. I had very good experience on using extreme sharp HSS tools with special coating and only two or three flutes.
If you are running too fast and dry, you can watch your tool break real quick - experienced first hand Smiley Very Happy
For easy flammable materials it is not that easy to make recommendations. It depends on a lot of factors. In general, I would take more conservative feedrates.
Magnesium for example can only take 650°C (1202° Fahrenheit) until it ignites. Going to aggressive, this limit can easily be reached with any kind of toolpath. Especially with the chips, there is a danger of igniting. And if one magnesium chip get's fire, then better run.
For the modern, efficient processing, one often uses amine-free, water-based coolants that achieve better cooling, enable higher cutting speeds, plus the surface and dimensional accuracy improve. The risk of chips igniting is reduced. And I don't wish anyone Magnesium fire Smiley Wink
Magnesium reacts at the surface with water to magnesium hydroxide and hydrogen. The higher the pH, the lower the temperatures and the smaller the surface, the lower the hydrogen formation and thus the risk of explosive hydrogen-air-mixtures.
I hope I could make clear, that you should be very careful working with these materials.
I would be more than happy, if you can share your thoughts and experiences on this topic as well.
Lead Product Manager - Mold & Die

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