By defining and comprehending carbide end mill wear, makers and users of cutting tools may improve the lifespan of carbide end mills. In addition, the modern coating technique for end mills, which incorporates the use of novel alloying elements, offers an efficient way of further prolonging the life of end mills and significantly boosting output.
The hardness of the tool is typically between 88 and 96 HRA degrees. With a surface coating, though, the difference becomes apparent. The most affordable approach to increasing an end mill’s performance is applying the proper layer. It may improve tool durability and performance.
The significance of end mill coating
The coating is a critical step that permits carbide end mills to withstand wear. Coatings help the cutting tool evacuate chips from the flutes quicker, removing the HOT chips from the ground surface of the end mill. Carbide is not a friend of heat. In the last ten years, the development of more heat- and wear-resistant coatings has boosted tool durability and productivity.
The performance of the cutting tool has a significant effect on cutting efficiency, precision, and surface quality. Unfortunately, there are perpetual inconsistencies between carbide tools’ two primary performance metrics, hardness, and strength. Materials with a high hardness have poor power, and a reduction in hardness is typically required to boost strength.
To resolve this contradiction in cemented carbide materials and increase the cutting performance of tools, it is more effective to coat one or more layers of hardness, high wear resistance material using different coating processes.
High surface hardness, excellent wear resistance, steady chemical performance, heat and oxidation resistance, a small friction coefficient, and low thermal conductivity are properties of coated tools. Compared to uncoated tools, cutting life may be enhanced three to five times with coated tools. In addition, the speed is increased by 20 to 70 percent, the machining precision is improved by 0.5 to 1 level, and the tool consumption cost is decreased by 20 to 50 percent.
The functions of coating include:
- Increase the difficulty.
- Enhance lubrication.
- Offer enhanced chip evacuation.
- Provide thermal insulation.
- Enhance the surface’s finish
- Decrease abrasive wear
- Extend the tool’s useful life.
The commercial acceptability of hard coatings for cutting tools is driven by demands on machining productivity, environmental regulations, and growth in the use of novel materials that are difficult to cut. In addition, enhanced cutting performance results from machine tool systems and cutting tool development synergy. The latter seeks an optimal tool material, hard coating, and cutting-edge geometry.
The initial method used was chemical vapor deposition (CVD), which proceeded from a single layer to the present multilayer varieties incorporating TiC, TiN, TiCN, and Al2O3.
After almost 35 years, it is clear that innovative physical vapor deposition (PVD) compositions have eclipsed the small number of current CVD coatings. The relative economics is controversial. However, it is acknowledged that the PVD technique is more environmentally friendly and has a longer life cycle. PVD hard coatings of successive generations, including TiCN, TiAlN, and AlCrN, are now commercially accessible and have proved performance in growing application areas.
Coated tools possess the following qualities:
- The surface coating has excellent wear resistance, high hardness, and temperature resistance.
- Coated cutting tools offer excellent overall performance, enhancing their adaptability and enabling them to be used in various applications.
- Coated tools’ oxidation resistance and high-temperature resistance will become more prominent, enable high-speed cutting, and enhance cutting efficiency due to the fast growth of science and technology.
Coatings, Grades, and Geometries for End Mills? Why are specific end mills so costly, and do they justify the additional cost?
Eventually, every machinist must have pondered this subject. Many build intense allegiances to the brand that has been successful for them. Manufacturer-recommended speeds and feeds vary according to the material and kind of cut. Different endmills function differently and are available at a variety of pricing points.
- Carbide Qualities and Grades
Let’s begin with the substance from which carbide end mills are constructed. Manufacturers of end mills commonly refer to their cutters as “solid carbide,” while the correct term is “cemented carbide.” I do not believe they are attempting to mislead people; marketing just cannot resist adding additional words, and you could just as well argue they use “solid” to refer to endmills that do not utilize inserts.
The substance is not solid metal but rather a tungsten carbide matrix (which consists of equal parts tungsten and carbon) bound together by a binder, often cobalt. In addition, a skinny coating may be applied to the end mill to improve performance further. More information regarding end mill coatings may be found below.
As expected, the tungsten carbide and not the binder are responsible for most of the cutting. Therefore, a significant proportion of the carbide’s quality is dependent on the ratio of tungsten carbide grains to the binder. Cheap carbide contains far more binder than high-quality carbide. This may be caused by the way the material is processed or the grain size.
Manufacturers characterize superior qualities using phrases such as “sub-micron” and “micrograin.” As tungsten carbide grains get more acceptable, more of them than the binder.
Consider a jar containing ball bearings. Suppose we fill one container with giant balls and another with more petite balls of the same size. Then, we fill each container with water until it is filled. Which container holds the most liquid? Therefore, the container with the more giant balls retains more moisture. Consider the ball bearings as tungsten carbide grains and water as the binder.
High vs. Low Helix End Mill
End mill performance is heavily influenced by geometry. Therefore there is much to discuss. Exotic geometries serve various purposes, and it would be impossible to cover all the possible variants in a single article. However, let’s examine a few of the most prevalent instances.
Let’s begin with the helix structure itself. High helix, low helix, roughing/finishing, and variable helixes are available. What does it all signify, and how does it benefit the machinist?
“high” and “low” refer to the endmill’s helix angle. Imagine the angle between the helix’s edge (the spiral flute) and the endmill’s flat bottom. A low helix endmill has an angle no more than 35 degrees, whereas a high helix endmill has an angle greater than 35 degrees. The helix angle of 38 degrees is an excellent balance between roughing and finishing with one cutter. The most significant feasible helix angle would be achieved with a straight flute cutter, such as certain CNC router bits. If you are acquainted with their drawbacks, you may be curious about the benefits and downsides of high vs. low helix cutters:
High Helix Benefits
– Cutting forces are directed more vertically and less horizontally, hence reducing deflection of the tool.
– Chips are expelled at a faster rate.
– Axial rake is more optimistic, resulting in improved shearing and reduced cutting forces.
Typically, this implies they can be fed more quickly. Reduced cutting forces result in reduced horsepower needs.
Due to the helix’s geometry, the tool’s core is thicker; consequently, the agency is more robust.
High Helix endmills are often used in more complex materials because of their superior wear resistance, although they may also be utilized in aluminum.
The most significant drawbacks of High Helix endmills are that they tend to chatter more and penetrate the material quite profoundly. With soft materials, it is more probable that they will fall out of the holder. The surface finish may also be compromised by a low-helix design.
Low Helix Benefits:
– Less likely to speak
– Perform often better with soft materials
Their downside is lower feed rates and, thus, poorer material removal rates for their target complex materials.
Variable Helix end mills are now regarded as state-of-the-art. The plan is to modify the helix in many ways over its length. It is possible that the flutes are not regularly distributed and that the helix angle varies over the distance. The variable helix is designed to combat buzz. Since chatter is a resonance effect, everything we can do to minimize the flutes’ resonant frequency against the workpiece would lessen chatter.
End Mill Coatings Carbon Coating Resembling Diamond A suitable coating is the cheapest approach to increasing an endmill.
Some end mill coatings are nothing short of miraculous performance effects. For example, the G-Wizard calculator’s default surface speed for a TiAlN-coated end mill is 20 percent greater than an uncoated carbide end mill, which is a conservative estimate. Today, TiAlN is quite commonplace, and there are many unusual coatings available, such as the Hydrogen-Free Diamond-Like Carbon coating seen to the right.
Coatings are often proprietary, and even identical chemical compositions may not provide the same outcomes. I do not want to engage in a lengthy debate on layers at this time. Since they are proprietary, the details are often not extensively documented. The coating is another approach to increase the performance and cost of a cutter.
Superior Quality Assurance
Suppose you decide to acquire an endmill of a particular brand and model. When they come, your diameters vary by two to three thousandths. Now you must measure each one and ensure that the machine is equipped with the correct offset to determine the diameter of each cutter.
Is Premium end mill coated Worth the Investment?
Consider the most costly grade of carbide and the unique shapes, the production of which requires complicated CNC grinding. Then, add a killer coating using the most advanced methods and equipment. Finally, examine each cutter to ensure its dimensions and performance are uniform and within close tolerances.
Voila! You’ve just developed a formula for a contemporary super cutter.
You should now understand why this endmill is superior in performance and costs more to manufacture. Those imported end mill sets from the discount bin have none of these advantages. Do you need a super end mill in your workshop?
Lean forward, and let’s examine this subject in-depth since the answer is not evident unless you run the figures.
First, purchasing quality endmills is likely not worthwhile if you are a hobbyist. You’re not attempting to earn money, and your machine lacks the power and rigidity to handle the performance these endmills can provide. You do not want inexpensive endmills since they will make your life more difficult. You want respectable bargain endmills that lack most premium features listed before.
What is the difference between end mill coatings?
The carbide end mill is also known as a carbide end mill with cement. The hardness of the tool is typically between 88 and 96 HRA degrees. With a surface coating, though, the difference becomes apparent. The most affordable approach to increasing an end mill’s performance is applying the proper layer. It may improve tool durability and performance.
Some of the basic coatings of end mills
|TiN||Titanium Nitride||Yellowish||Excellent wear resistance, thermal stability, and low coefficient of friction||Steel, stainless steel, cast iron, general use|
|TiCN||Titanium Carbo Nitride||Bluish-grey||Good adhesion, toughness, and resistance to chipping||Stainless steel, aluminum, copper, cast iron, high-silicon alloys, and other abrasive materials|
|AlTiN||Aluminum Titanium Nitride||Dark purple||Good heat resistance, high hardness at high temperatures||Titanium, tool steel, alloy steel, mild steel, stainless steel, nickel alloys, cast iron, and other high-temperature materials|
|TiAlN||Titanium Aluminum Nitride||Violet bronze||Low electrical and thermal conductivity, high hardness||High strength steels, hard die steels, and high-temperature alloys, including nickel base & titanium|
For example, HRC45 end mills, HRC50 degree end mills, HRC60 end mills, HRC65 end mills, and HRC70 end mills are often referred to based on the hardness of the treated material.
The degree after the number indicates the material’s hardness before processing. The unit is HRC, which denotes the maximum hardness that may be treated.
For instance, an HRC55 milling cutter can process steel with an HRC55 degree, including S136 die steel.
|HRC45 end mill||can process ~ HRC45
Carbon steel, Alloy steel, Cast iron
|HRC55 end mill||can process ~ HRC55
Titanium alloy, High-temperature alloy, Hardened steel
|HRC65 end mill||can process ~ HRC65
Carbon steel, Alloy steel, Cast iron, Hardened steel
Currently, the quality of cemented carbide end mills on the market varies. As a result, some sales will accommodate the purchasers’ desired hardness range, while others may provide incorrect information. This necessitates more testing, careful selection, and identifying end mill providers with superior quality.
Benefits of Coating for End Mills
- PVD TiN coatings are the most common coating for end mills, although TiCN and TiAlN are gaining popularity. When and at what speeds these advanced coatings should be operated are common concerns for milling applications.
- TiCN is tougher than TiN and has excellent abrasion resistance. As a result, it is exceptional for milling steels, stainless steels, and non-ferrous materials. TiCN-coated end mills should be run at speeds up to 50 percent faster than their uncoated counterparts.
- TiAlN is a high-performance coating applicable to all sorts of materials. It has about the same hardness as TiCN but retains that hardness at far greater temperatures. This makes TiAlN very successful in applications involving high-temperature alloys, high-speed machining, and dry milling. TiAlN-coated end mills must be run at speeds up to one hundred percent faster than uncoated end mills.
Categories and Utilizations
The features of the most prevalent end mill coating types are listed below. However, this list is not comprehensive. More specialized items are available for bespoke applications.
The tip of Ball Nose End Mills is rounded. They are mainly used for 3D milling of contoured surfaces, groove rounding, pocketing, and other contouring operations. In addition, it can serve as the last trimmer for “finishing touches.”
Straight End/Square End
The most often used types of end mills are square or flat. Profiling, slotting, side and face milling, and plunging are just a few of the many applications these tools excel in. Flat End Mills provide precise 90-degree corner cuts on the workpiece. Depending on the workpiece, they may be appropriate for roughing and finishing tasks.
Router / Tail of the Fish
If one end of an end mill bit is much thinner than the other, it is likely a fishtail or router end mill. Due to the tiny cutter form, this design can penetrate the material and create a flat surface without breaking out. They may also be used for pocketing, routing, and contouring.
Bull-nose end mills are pretty similar to square end mills, except that their rounded edges assist disperse the cutting power uniformly. Excellent for grooves with flat bottoms and rounded inner corners. Feature slightly rounded edges that aid inappropriately distributing cutting forces to minimize blade damage and prolong its life. They can make flat-bottomed grooves with slightly rounded inner corners and are often used in mold milling.
Abrasive End Mills
As its name indicates, Roughing end mills rapidly remove a great deal of workpiece material, particularly during heavy cutting stages. They provide a rapid, rough finish with slight vibration, later refined by a separate cutter.
V-bits get their name from the v-shaped cut produced by their narrow angles and tips. These end mill cutters are used for engraving, precise cuts, lines, and even signage. There are two sorts of V-bits: 60 degrees and 90 degrees.
Carbide or HSS Mills?
Carbide mills are more costly than High-Speed Steel End Mills. However, they are appropriate for many materials, including many metals and, of course, cannabis. In addition, you can anticipate using them for an extended period before having to resharpen them because of their high resistance to wear. HSS is the preferred cutter for the majority of typical procedures. However, the whole tool life is shorter, and there are additional constraints on speed and performance.
Solid carbide end mills provide superior stiffness, heat resistance, and cutting speeds to their HSS counterparts. This increases your productivity and makes you miss various (harder) materials. In addition, Carbide end mills are often used for finishing.
How do I choose the proper end mill?
Numerous distributors and manufacturers, including Harvey, Niagara, Jan, Avvupro, Guhring, and Mcmaster-Carr, provide their milling cutters online. However, regardless of whatever brand or vendor you choose to purchase your end mills from, there is no one-size-fits-all option.
We advise you to ask yourself the following questions before making a decision:
- What kind of material will you be cutting?
- How precisely do you want to make the characteristics of your workpiece?
- How deeply do you intend to slice?
- How critical are feed, cutting speed, and performance?
Once these and other questions have been addressed, you will better know the end mill required for your applications.
The correct coating may result in significant time and cost savings, but only if your machine is capable of reaching the high speeds necessary by that coating.
Carbide End Mills Wear Principle
The heat and friction produced during metal cutting processes manifest energy. Extremely demanding machining conditions are created for carbide end mills by the heat and friction caused by the high surface load and the fast speed of the chip sliding over the front face.
The magnitude of the cutting rate fluctuates primarily based on the various machining circumstances (e.g., the presence of complex components in the workpiece material or interrupted cutting). Therefore, for carbide end mills to keep their strength at high cutting temperatures, they must possess fundamental qualities such as high hardness and wear resistance.
Although the cutting temperature at the carbide end mill/workpiece interface is crucial in determining the wear rate of almost all carbide end mill materials, it may be challenging to establish the parameter values necessary to compute the cutting temperature. Nonetheless, the measurement findings of the cutting test may serve as a foundation for specific empirical methodologies.
Select the proper coating
Additionally, the coating enhances the cutting performance of carbide end mills. Current coating technologies include the following:
- Titanium Nitride (TiN) Coating:This coating enhances the hardness and oxidation temperature of carbide end mills.
- Titanium Carbide (TiCN) Coating: The coating’s hardness and surface finish are enhanced by adding carbon to TiN.
- Nitro-aluminum titanium (TiAlN) and nitro-aluminum titanium (AlTiN) coatings:the application of an alumina (Al2O3) layer in conjunction with these coatings increases the durability of carbide end mills for high-temperature cutting.
- AlTiN coatings have a more excellent aluminum content and better surface hardness than TiAlN coatings with a higher titanium content, making them ideal for dry and near-dry cutting. Typically, AlTiN coatings are used for high-speed machining.