Information of Tungsten Carbide End Mills and Its possible Failure Situations

Are end mills made from carbide?

Most end mills are manufactured from either cobalt steel alloys – referred to as HSS (High Speed Steel), or from tungsten carbide. The choice of material of your selected end mill will depend on the hardness of your workpiece and the maximum spindle speed of your machine.

What is the toughest end mill?

Carbide end mills.

Carbide end mills are one of the hardest cutting tools available. Next to diamond there are very few other materials harder than carbide. This makes carbide capable of machining almost any metal if done correctly. Tungsten Carbide falls between 8.5 and 9.0 on Moh's hardness scale, making it almost as hard as diamond.

What is the best end mill material for steel?

Primarily, carbide end mills work best for steel and its alloys because it has more thermal conductivity and works well for hard metals. Carbide also operates at higher speed, which means your cutter can withstand higher temperatures and can prevent excess wear and tear. When finishing stainless steel parts, a high flute count and/or high helix is required for the best results. Finishing end mills for stainless steel will have a helix angle over 40 degrees, and a flute count of 5 or more. For more aggressive finishing tool paths, flute count can range from 7 flutes to as high as 14.

Which is better，HSS or carbide end mills?

Solid Carbide provides better rigidity than high-speed steel (HSS). It is extremely heat resistant and used for high speed applications on cast iron, nonferrous materials, plastics and other tough-to-machine materials. Carbide end mills provide better rigidity and can be run 2-3X faster than HSS.

Why do end mills fail?

1. Running It Too Fast or Too Slow Can Impact Tool Life.

Running a tool too fast can cause suboptimal chip size or even catastrophic tool failure. Conversely, a low RPM can result in deflection, bad finish, or simply decreased metal removal rates.

2. Feeding It Too Little or Too Much.

Another critical aspect of speeds and feeds, the best feed rate for a job varies considerably by tool type and work piece material. If you run your tool with too slow of a feed rate, you run the risk of recutting chips and accelerating tool wear. If you run your tool with too fast of a feed rate, you can cause tool fracture. This is especially true with miniature tooling.

3. Using Traditional Roughing.

While traditional roughing is occasionally necessary or optimal, it is generally inferior to High Efficiency Milling (HEM). HEM is a roughing technique that uses a lower Radial Depth of Cut (RDOC) and a higher Axial Depth of Cut (ADOC). This spreads wear evenly across the cutting edge, dissipates heat, and reduces the chance of tool failure. Besides dramatically increasing tool life, HEM can also produce a better finish and higher metal removal rate, making it an all-around efficiency boost for your shop.

4. Using Improper Tool Holding and its Effect on Tool Life.

Proper running parameters have less of an impact in suboptimal tool holding situations. A poor machine-to-tool connection can cause tool runout, pullout, and scrapped parts. Generally speaking, the more points of contact a tool holder has with the too l’s shank, the more secure the connection. Hydraulic and shrink fit tool holders offer increased performance over mechanical tightening methods, as do certain shank modifications.

5. Not Using Variable Helix/Pitch Geometry.

A feature on a variety of high performance end mills, variable helix, or variable pitch, geometry is a subtle alteration to standard end mill geometry. This geometrical feature ensures that the time intervals between cutting edge contacts with the work piece are varied, rather than simultaneous with each tool rotation. This variation minimizes chatter by reducing harmonics, which increases tool life and produces superior results.

6. Choosing the Wrong Coating Can Wear on Tool Life.

Despite being marginally more expensive, a tool with a coating optimized for your workpiece material can make all the difference. Many coatings increase lubricity, slowing natural tool wear, while others increase hardness and abrasion resistance. However, not all coatings are suitable to all materials, and the difference is most apparent in ferrous and non-ferrous materials. For example, an Aluminum Titanium Nitride (AlTiN) coating increases hardness and temperature resistance in ferrous materials, but has a high affinity to aluminum, causing work piece adhesion to the cutting tool. A Titanium Diboride (TiB2) coating, on the other hand, has an extremely low affinity to aluminum, and prevents cutting edge build-up and chip packing, and extends tool life.

7. Using a Long Length of Cut.

While a long length of cut (LOC) is absolutely necessary for some jobs, especially in finishing operations, it reduces the rigidity and strength of the cutting tool. As a general rule, a tool’s LOC should be only as long as needed to ensure that the tool retains as much of its original substrate as possible. The longer a tool’s LOC the more susceptible to deflection it becomes, in turn decreasing its effective tool life and increasing the chance of fracture.

8. Choosing the Wrong Flute Count.

As simple as it seems, a tool’s flute count has a direct and notable impact on its performance and running parameters. A tool with a low flute count (2 to 3) has larger flute valleys and a smaller core. As with LOC, the less substrate remaining on a cutting tool, the weaker and less rigid it is. A tool with a high flute count (5 or higher) naturally has a larger core. However, high flute counts are not always better. Lower flute counts are typically used in aluminum and non-ferrous materials, partly because the softness of these materials allows more flexibility for increased metal removal rates, but also because of the properties of their chips. Non-ferrous materials usually produce longer, stringier chips and a lower flute count helps reduce chip recutting. Higher flute count tools are usually necessary for harder ferrous materials, both for their increased strength and because chip recutting is less of a concern since these materials often produce much smaller chips.

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