HREM vs HEM: Titanium Milling Test Results

Harvey Performance Company’s Don Grandt Employs a Novel “Heavy Radial Efficiency Milling” or “HREM” Technique to Boost Tool Life and Minimize Heat Generation in Titanium

For all the characteristics that make Titanium ideal for extreme conditions, such as its high strength, low density, and corrosion resistant properties, it also makes it very difficult to machine. A modern approach to machining, High Efficiency Milling (HEM), helps. It involves using the theory of chip thinning by applying a smaller Radial Depth of Cut (RDOC), and a larger Axial Depth of Cut (ADOC). This method puts the vast majority of an end mill’s cutting edge to work, evenly distributing heat throughout it. An HEM toolpath works by taking more radial passes with a lower RDOC.

But from experience, Harvey Performance Company National Applications Engineer and “Cutting Tool Counselor,” Don Grandt, has found that there’s a better way to machine titanium. Rather than HEM, Don employs a strategy he calls “Heavy Radial Efficiency Milling (HREM)”, something he’s developed over time with a tried and true “Theory, Science, Experience (TSE) Triple Knowledge Approach” to machining.

The Theory:

In switching from a regular toolpath to a standard HEM toolpath, machinists are permitted to increase the surface foot and boost material removal rates because there is less heat generated at the cutting edge due to the lighter radial depth of cut being utilized.

In titanium, specifically, recommended parameters for HEM are often in the ballpark of 400-500 SFM and 121-152 M/Min, with a radial step over of 6% of the cutting diameter. This allows you to increase the speed to achieve higher feed rates.

However, Don has noticed that most of the heat is coming from the SFM or M/Min when machining titanium, and not the RDOC, thus prematurely fatiguing the cutting edge of the tool in HEM toolpaths. He uses the “MRR Triangle” to compensate for this.

In a 2022 episode of In the Loupe TV, a collection of videos Don creates to educate the machining industry on popular machining methods, tips, tricks, and more, he dives into the Material Removal Rate Triangle, explaining that it’s a representation of how IPM, ADOC, and RDOC interact.

“Each one of these things…contributes to your MRR, material removal rate. I know I don’t want to change that, I don’t want to stop it, and I don’t want to slow the customer down. So what do I do?

Three things (IPM, ADOC, and RDOC) are bringing in the heat. Which one’s causing the most heat? That’s what I want to find out. Because guess what? If I find out which one’s causing the most heat, and I can bring that down, then I can bring one of my other things over, adjust it, keep my MRR, and stay productive.”

In this case, Don opts to increase the RDOC while running the tool at lower SFM-M/MIN, the backbone of the “HREM” toolpath. An illustration of this toolpath, compared to a traditional and standard HEM toolpath, is below.

The Science:

While Don’s strategy can be utilized using any End Mill for Titanium, including Harvey Tool’s offering of Variable Pitch End Mills for Titanium Alloys, the below comparison of HEM vs. HREM toolpaths showcases a 6 Flute Helical Solutions End Mill for Titanium.

HEM vs. HREM Parameters Comparison (3.51 Cubes of Material)

The change in parameters, utilizing the MRR Triangle as a model, generates consistent results in both time and MRR output, so what’s the benefit of making the change? Tool life. And again, it boils down to heat generation.

Toolpath Results

Traditional HEM Strategy

“HREM” Strategy

The Experience:

From the example above, where the same Helical Solutions End Mill for Titanium was utilized, you can see that by simply increasing the RDOC and slowing down the feed, while accommodating the chip with more flutes, the MRR remains consistent but the cutting edge of the tool faired much better. 

Toolpath Results

HEM Example

HREM Example

Before Utilizing an HREM Strategy

While HREM can be beneficial in extending the life of your cutting tool when machining titanium, there are several things that machinists must be mindful of before beginning. Notably, an HREM strategy will add more tangential force to your setup, meaning that fixturing, horsepower, and bending force must be properly accounted for.

In addition, the longer the tool’s length of cut, the less radial there is to be had. This means that if a tool’s length of cut is 2x the diameter, the maximum RDOC will be 27%. With 2.5x length of cut, the maximum radial will only be 20%. As the length of cut increases, the radial decreases, meaning that machinists must make adjustments accordingly to reduce the SFM and, in turn, reduce heat generation and built-up edge (BUE).

Harvey Performance Company Brand Tooling Best Suited for HREM

Leading cutting tool brands Helical Solutions and Harvey Tool offer several cutting tool options specifically designed for the machining of Titanium Alloys. Helical’s offering is extensive, with options ranging from roughers to 5, 6, 7, and multi-flute finishers. Included in this range of fully stocked product is the popular HVTI-6 line, which is optimized specifically for advanced machining toolpaths, such as HEM and HREM, in Titanium.

Harvey Tool’s Material Specific End Mill offering includes options for Titanium Alloys, as well. Featuring variable pitch geometry, options include both square and corner radius profiles. A new Variable Pitch End Mills for Titanium Alloys – Ball offering is set to be released in August 2025.

In Conclusion

By rethinking conventional titanium machining strategies, Don’s “Heavy Radial Efficiency Milling” (HREM) approach challenges the standard High Efficiency Milling (HEM) model with proven results. Through his “Theory, Science, Experience” methodology, Don demonstrates that increasing radial engagement while reducing surface speed can significantly lower tool temperatures and extend tool life, all without sacrificing productivity. Backed by data and real-world trials, HREM offers a compelling alternative for shops looking to optimize titanium machining performance in the most demanding applications.

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