Why Flute Count Matters

One of the most important considerations when choosing an end mill is determining which flute count is best for the job at hand. Both material and application play an important role in this critical part of the tool selection process. Understanding the effects of flute count on other tool properties, and how a tool will behave in different situations is an essential consideration in the tool selection process.

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Tool Geometry Basics

Generally, tools with more flutes have a larger core and smaller flute valleys than tools with fewer flutes.  More flutes with a larger core can provide both benefits and restrictions depending on the application.  Simply put, a larger core is directly proportional to tool strength; the larger the core, the stronger a tool will be.  In turn, a larger core also reduces the flute depth of a tool, restricting the amount of space for chips to exist.  This can cause issues with chip packing in applications requiring heavy material removal.  However, these considerations only lead us part way when making a decision on which tool to use, and when.

flute count core

Material Considerations

Traditionally, end mills came in either a 2 flute or 4 flute option.  The widely accepted rule of thumb was to use 2 flutes for machining aluminum and non-ferrous materials, and 4 flutes for machining steel and harder alloys.  As aluminum and non-ferrous alloys are typically much softer than steels, a tool’s strength is less of a concern, a tool can be fed faster, and larger material removal rates (MRR) is facilitated by the large flute valleys of 2 flute tools.  Ferrous materials are typically much harder, and require the strength of a larger core.  Feed rates are slower, resulting in smaller chips, and allowing for the smaller flute valleys of a larger core tool.  This also allows for more flutes to fit on the tool, which in turn increases productivity.

end mill flute count

Recently, with more advanced machines and toolpaths, higher flute count tools have become the norm in manufacturing.  Non-ferrous tooling has become largely centered on 3 flute tools, allowing greater productivity while still allowing proper chip evacuation.  Ferrous tooling has taken a step further and progressed not only to 5 and 6 flutes, but up to 7 flutes and more in some cases.  With a wider range of hardness, sometimes at the very top of the Rockwell hardness scale, many more flutes have allowed longer tool life, less tool wear, stronger tools, and less deflection.  All of this results in more specialized tools for more specific materials.  The end result is higher MRR and increased productivity.

Running Parameters

Just as material considerations will have an impact on the tool you choose, operation type and depth of cut requirements may also have a big impact on the ideal number of flutes for your application.  In roughing applications, lower flute counts may be desirable to evacuate large amounts of chips faster with larger flute valleys.  That said, there is a balance to find, as modern toolpaths such as High Efficiency Milling (HEM) can achieve extreme MRR with a very small step over, and a higher number of flutes.  In a more traditional sense, higher flute counts are great for finishing operations where very small amounts of material are being removed, and greater finish can be achieved with more flutes, not worrying as much about chip evacuation.

flute count

Flute count plays a big role in speeds and feeds calculation as well.  One common rule of thumb is “more flutes, more feed,” but this can be a very detrimental misconception.  Although true in some cases, this is not an infinitely scalable principle.  As stated previously, increasing the number of flutes on a tool limits the size that the flute valleys can be.  While adding a 5th flute to a 4 flute tool theoretically gives you 25% more material removal per revolution with an appropriately increased feed rate, feeding the tool that much faster may overload the tool.  The 25% increase in material removal is more likely closer to 10-15%, given the tool is exactly the same in all other specifications.  Higher flute count tools may require speeds and feeds to be backed off so much in some cases, that a lower flute count may be even more efficient.  Finding the right balance is key in modern milling practices.

Tackling Titanium: A Guide to Machining Titanium and Its Alloys

In today’s manufacturing industry, titanium and its alloys have become staples in aerospace, medical, automotive, and firearm applications. This popular metal is resistant to rust and chemicals, is recyclable, and is extremely strong for its weight. However, there are several challenges that must be considered when machining titanium and selecting the appropriate tools and parameters for the job.

Titanium Varieties

Titanium is available in many varieties, including nearly 40 ASTM grades, as well as several additional alloys. Grades 1 through 4 are considered commercially pure titanium with varying requirements on ultimate tensile strength. Grade 5 (Ti6Al4V or Ti 6-4) is the most common combination, alloyed with 6 percent aluminum and 4 percent vanadium. Although titanium and its alloys are often grouped together, there are some key differences between them that must be noted before determining the ideal machining approach.

Titanium 6AL4V

Helical Solutions’ HVTI End Mill is a great choice for high efficiency toolpaths in Titanium.

Titanium Concerns

Workholding

Although titanium may have more desirable material properties than your average steel, it also behaves more flexibly, and is often not as rigid as other metals. This requires a secure grip on titanium workpieces, and as rigid a machine setup as is possible. Other considerations include avoiding interrupted cuts, and keeping the tool in motion at all times of contact with the workpiece. Dwelling in a drilled hole or stopping a tool next to a profiled wall will cause the tool to rub – creating excess heat, work-hardening the material, and causing premature tool wear.

Heat Generation

Heat is a formidable enemy, and heat generation must be considered when selecting speeds and feeds. While commercially pure grades of titanium are softer and gummier than most of its alloys, the addition of alloying elements typically raises the hardness of titanium. This increases concerns regarding generated heat and tool wear. Maintaining a larger chipload and avoiding unnecessary rubbing aids with tool performance in the harder titanium alloys, and will minimize the amount of work hardening produced. Choosing a lower RPM, paired with a larger chipload, can provide a significant reduction in temperature when compared to higher speed options. Due to its low conduction properties, keeping temperatures to a minimum will put less stress on the tool and reduce wear. Using high-pressure coolant is also an effective method to reduce heat generation when machining titanium.

cutting tools for titanium

These camshaft covers were custom made in titanium for Mitsubishi Evos.
Photo courtesy of @RebootEng (Instagram)

Galling and Built-Up Edge

The next hurdle to consider is that titanium has a strong tendency to adhere to a cutting tool, creating built up edge. This is a tricky issue which can be reduced by using copious amounts of high pressure coolant aimed directly at the cutting surface. The goal is to remove chips as soon as possible to prevent chip re-cutting, and keep the flutes clean and clear of debris. Galling is a big concern in the commercially pure grades of titanium due to their “gummy” nature. This can be addressed using the strategies mentioned previously, such as continuing feed at all times of workpiece contact, and using plenty of high-pressure coolant.

Titanium Solutions

While the primary concerns when machining titanium and its alloys may shift, the methods for mitigating them remain somewhat constant. The main ideas are to avoid galling, heat generation, work hardening, and workpiece or tool deflection. Use a lot of coolant at high pressure, keep speeds down and feeds up, keep the tool in motion when in contact with the workpiece, and use as rigid of a setup as possible.

In addition, selecting a proper tool coating can help make your job a successful one. With the high heat being generated during titanium machining operations, having a coating that can adequately deal with the temperature is key to maintaining performance through an operation. The proper coating will also help to avoid galling and evacuate chips effectively. Coatings such as Harvey Tool’s Aluminum Titanium Nitride (AlTiN Nano) produce an oxide layer at high temperatures, and will increase lubricity of the tool.

Tooling Solutions

Helical Solutions offers the HVTI-6 line of tooling optimized for High Efficiency Milling (HEM) in Titanium and its alloys. Helical’s HVTI-6 features its Aplus coating which offers added lubricity and high temperature resistance for improved tool life and faster speeds and feeds.

As titanium and its many alloys continue to grow in use across various industries, more machinists will be tasked with cutting this difficult material. However, heat management and appropriate chip evacuation, when paired with the correct coating, will enable a successful run.

machining titanium