Extend End Mill Life
End mill breakage and premature wear are not only costly, but they also put a crimp in productivity. The first 4 are a summary of what Regal Cutting Tools offers as considerations for making your end mills last as long as possible.
Feeds & Speeds
The correct speed and feed will determine chip load. For every work material and end mill design, there is a narrow niche for running at optimal speed to maximize efficiency. Even if you run at the perfect spindle speed, feeding too quickly will break the mill. In the same way, the correct feed rate doesn't matter if the spindle speed is not dialed in.
Coatings give mills a hard shell to protects cutting edges and allows them to withstand high temperatures. Made from Titanium nitride (TiN), coatings offer general purpose protection against wear of high-speed steel (HSS) and carbide end mills. Coatings that also contain carbon (TiCN) allow carbide end mills to be run nearly twice as fast as end mills that are not coated.
Deflection causes the mill to bend. Constant flexing and relaxing along the mill flutes weakens them. When the mill bows while it is inside the cut, the flutes can dig too deeply into the work piece. The resulting chip load can break the mill or cause build up and/or re-cutting of chips too big to evacuate effectively that leads to premature wear.
Removing chips from the cutting area is the main concern for productivity, surface finish, and reducing tool wear. Chips absorb a lot of heat during the cutting process, and heat is an end mill’s worst enemy. Heat also helps bind and adhere some materials – aluminum in particular – to the end mill. As aluminum chips “weld” themselves to tool edges, a broken end mill is only a matter of time.
Length of Cut (LOC)
A tool's Length of Cut (LOC) should only be as long as necessary. This allows the tool to retain more of the original substrate. Sometimes, longer lengths are needed, but the tools are also more susceptible to deflection.
Flute Count has a direct impact on tool performance. Lower flute counts are normally used in aluminum and non-ferrous materials, whereas higher flute counts are used for harder materials because of the strength.
High Efficiency Milling (HEM)
High Efficiency Milling is a roughing technique that uses a lower Radial Depth of Cut (RDOC) and a higher Axial Depth of Cut (ADOC). Using this technique spreads out the wear and heat more evenly. Overall, using HEM can increase tool life, give you a better finish with a higher metal removal rate, and increase shop efficiency.
The more secure the connection, the better. Without this, tools can runout and pullout resulting in scrapped parts. Hydraulic and shrink fit tool holders give better performance over mechanical tightening methods.
High-speed Machining (HSM)
Use Dedicated Tools
You can't expect one tool to hold up during a roughing operation and then use that same tool to finish. It won't maintain the tight tolerance. There are tools that combine roughing and finishing, but varying cutting edges for each step help the tool to perform better. Use a tool for the process it was designed for.
Depending on the geometry of the insert, different thicknesses of coating may be required. A thinner coating is usually better at resisting heat, whereas a thicker coating will have more thermal expansion. However, it does not expand and contract as completely as a thin coat. If the coating has a very low coefficient of friction, operations like tapping probably won't create enough heat to break the chip correctly. The low heat level can cause the chip to not break. Chips will stock up in the hole and break the tap. If the coating cannot handle the heat, it will break down and expose the tool substrate, leading to poor tool life.
At high RPMs, tool balance is important. Most common tool designs with tool holders will work without a problem at speeds less than 8,000 RPM. Over that speed, there may be run out problems causing decreased tool life. This makes the tool holding decision critical. Not all clamping systems will hold their grip at a high rotational speed. During high-speed machining, there is not a lot of cutting pressure because you take a light radial and axial depth of cut. For this reason, not many one-flute tools are used in HSM because they are naturally unbalanced.
High tool loads bring out a system’s weaknesses such as poor rigid setup, a weak tool, or a loose vibrating bolt. HSM is straining to tools because they are being pushed to their limits, Because of this, the fixtures and tools have to be rigid to withstand the loads. The longer flute length is not as rigid as a short length, making those tools a less ideal option. Material and length-to-diameter ratio affects HSM success. In general, carbide tools are better for HSM applications requiring a longer reach. Dampened steel tools are able to cut even further because they absorb vibrations at the cutting end. Tool manufacturers are also adding tapered necks to carbide tools, so you have a stronger tool for a longer reach and the tool will not rub the side walls of the mold cavity.
HSM quickly produces a lot of chips. Whether it is dry, using air, oil, mist, or coolant, removing these chips is critical. You can use air or oil to do the jobs sometimes, especially in hard milling. Other times coolant can be very effective, just make sure you use the correct delivery such as axial coolant lines or coolant channels out of the cutting edge. Ensure that you use clean and quality coolant that has the proper oil concentration. Moral of the story, get those chips out of there.
Speeds, feeds, depth of cut and checking the setup for rigidity can reduce the possibility of fracturing. Coolant usage can also help to avoid hot spots in material. These spots can dull a cutting edge and cause a fracture. HEM (High Efficiency Milling) tool paths prevent fracture because of the consistent load. Shock loading is lessened, reducing the stress put on a tool.
To prevent this, ensure the operation is free of chatter and vibration. Speeds and feeds adjustment may help as well. Interrupted cuts and repeated part entry can have a negative impact on a tool. Lowering feed rates when this happens can lessen this risk.
This is caused by the temperature drastically fluctuation during milling. The correct coating on an end mill helps to provide heat resistance and reduced abrasion. HEM tool paths spread the heat across the cutting edge of the tool, reducing the overall temperature and preventing heat fluctuations.
The wear land is a pattern of uniform abrasion on the cutting edge of a tool. This dulls the cutting edge of a tool and can alter dimensions like the diameter. If the wear land becomes excessive or the tool is failing, reducing the cutting speed and using coolant can help. HEM tool paths help reduce wear by spreading the work over its entire length of cut. This mitigates uniform wear and lengthens tool life because the entire cutting edge is being used.
- Use the cutting wheel at a 90-degree angle, perpendicular to the work surface.
- Apply the proper amount of pressure, allowing the tool to do the work. Always avoid pushing too hard on the wheel, which can cause the grinder to stall or you to slip.
- Choose a grinder with the highest torque or amperage available for the application. RPMs stay the same, but the tool will provide more torque to cut into the metal.
- Choose a tool and consumables that offer quick, consistent cutting, which typically provides the most efficient performance.
- The thinner the cutting wheel, the more susceptible it can be to side loading, which is when the wheel bends while moving side to side in the cut. This can turn dangerous if you lean too hard on a wheel, which can cause the wheel to break or jam in the cut.
- Store the wheel in a clean, dry environment and avoid placing it in moisture.
- Inspect the wheel and consumable before each use to check for damage. Cutting wheels are typically harder to control as they wear.