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Advancements in the metalworking industry have led to new, innovative ways of increasing productivity. One of the most popular ways of doing so (creating many new buzzwords in the process) has been the discovery of new, high-productivity toolpaths. Terms like trochoidal milling, high speed machining, adaptive milling, feed milling, and High Efficiency Milling are a handful of the names given to these cutting-edge techniques.
With multiple techniques being described with somewhat similar terms, there is some confusion as to what each is referring to. High Efficiency Milling (HEM) and High Speed Machining (HSM) are two commonly used terms and techniques that can often be confused with one another. Both describe techniques that lead to increased material removal rates and boosted productivity. However, the similarities largely stop there.
High speed machining is often used as an umbrella term for all high productivity machining methods including HEM. However, HEM and HSM are unique, separate machining styles. HSM encompasses a technique that results in higher production rates while using a much different approach to depth of cut and speeds and feeds. While certain HEM parameters are constantly changing, HSM uses constant values for the key parameters. A very high spindle speed paired with much lighter axial depths of cut results in a much higher allowable feed rate. This is also often referred to as feed milling. Depths of cut involve a very low axial and high radial components. The method in general is often thought of as z-axis slice machining, where the tool will step down a fixed amount, machine all it can, then step down the next fixed amount and continue the cycle.
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High speed machining techniques can also be applied to contoured surfaces using a ball profile or corner radius tool. In these situations, the tool is not used in one plane at a time, and will follow the 3 dimensional curved surfaces of a part. This is extremely effective for using one tool to bring a block of material down to a final (or close to final) shape using high resultant material removal rates paired with the ability to create virtually any shape.
High speed machining is usually associated with any spindle speed above 15k rpm, but it is much more than just a faster spindle. The whole machine must be considered when selecting a good candidate machine for HSM. Thermal compensation, overall machine rigidity and construction, positional feedback, the motion control system, tool retention, and many other characteristics must be looked at, in detail, before determining that a particular machine is suitable for the task.
For a More In Depth Look at HSM: What is High Speed Machining?
HEM has evolved from a philosophy that takes advantage of the maximum amount of work that a tool can perform. Considerations for chip thinning and feed rate adjustment are used so that each cutting edge of a tool takes a consistent chip thickness with each rotation, even at varying radial depths of cut and while interpolating around curves. This allows machinists the opportunity to utilize a radial depth of cut that more effectively uses the full potential of a given tool. Utilizing the entire available length of cut allows tool wear to be spread over a greater area, prolonging tool life and lowering production costs.
Effectively, HEM uses the depths associated with a traditional finishing operation but boosts speeds and feeds, resulting in much higher material removal rates (MRR). This technique is typically used for hogging out large volumes of material in roughing and pocketing applications.
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MORE INFO: GF Machining Solutions Mikron MILL E U High-Efficiency Machining Centers |
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High Efficiency Milling (HEM) is a strategy that continues to gain popularity in the metalworking industry, and most CAM packages now offer modules to generate HEM toolpaths, each with their own proprietary name. In these packages, HEM can also be known as Dynamic Milling or High Efficiency Machining, among others.
HEM can result in:
High performance end mills designed to achieve higher speeds and feeds will help machinists to reap the full benefits of this popular machining method. |
HEM vs HSM
| HEM is somewhat similar to an accelerated finishing operation in regards to depth of cut, while HSM is more of a high feed contouring operation. Both can achieve increased MRR and higher productivity when compared to traditional methods. While HSM can be seen as an umbrella term for all high efficiency paths, HEM has grown in popularity to a point where it can be classified on its own. Classifying each separately takes a bit of clarification, showing they each have power in certain situations. |
HEM is a milling technique for roughing that utilizes 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.
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This strategy differs from traditional or conventional milling, which typically calls for a higher RDOC and lower ADOC. Traditional milling causes heat concentrations in one small portion of the cutting tool, expediting the tool wear process. Further, while Traditional Milling call for more axial passes, HEM toolpaths use more passes radially.
Machining technology has been advancing with the development of faster, more powerful machines. In order to keep up, many CAM applications have developed built-in features for HEM toolpaths, including Trochoidal Milling, a method of machining used to create a slot wider than the cutting tool’s cutting diameter.
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| High Efficiency Milling Strategy - Trochoidal Machining |
HEM is largely based on the theory surrounding Radial Chip Thinning, or the phenomenon that occurs with varying RDOC, and relates to the chip thickness and feed per tooth. HEM adjusts parameters to maintain a constant load on the tool through the entire roughing operation, resulting in more aggressive material removal rates (MRR). In this way, HEM differs from other high performance toolpaths, which involve different methods for achieving significant MRR.
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Virtually any CNC machine can perform HEM – the key is a fast CNC controller. When converting from a regular program to HEM, about 20 lines of HEM code will be written for every line of regular code. A fast processor is needed to look ahead for the code, and keep up with the operation. In addition, advanced CAM software that intelligently manages tool load by adjusting the IPT and RDOC is also needed.
Generally speaking, HEM is a matter of running the tool – not the tool itself. Virtually every tool can perform HEM, but using tooling built to withstand the rigors of HEM will result in greater success. While you can run a marathon in any type of shoes, you’d likely get the best results and performance from running shoes.
HEM is often regarded as a machining method for larger diameter tooling because of the aggressive MRR of the operation and the fragility of tooling under 1/8” in size. However, miniature tooling can be used to achieve HEM, too.
Using miniature tooling for HEM can create additional challenges that must be understood prior to beginning your operation.
Best Tools for HEM:
- High flute count for increased MRR.
- Large core diameter for added strength.
- Tool coating optimized for the workpiece material for increased lubricity.
- Variable Pitch/Variable Helix design for reduced harmonics.
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Mikron DNA |
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DNA
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User Benefit
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| Integrated Chuck | Improved Accuracy - Less Stack Error - Reach your tolerances faster | |
| Direct Rotary Torque Table | Ultra Dynamic, High Precision, Less Wear - Ensures repeatable accuracy for the life of the machine - Made in GF Machining Solutions factory since 2001 | |
| Step-Tec Spindle | High-RPM, High Power to size ratio, Designed to run full power around the clock, Dependable - Long service life, extreme precision | |
| Integrated Pallet Changer System | Unattended Machine Uptime - Industry leading affordability, FAST ROI | |
| Heidenhain CNC | Fully Loaded - Best in Class for High Speed 5-axis Machining - Take advantage of Mikron Smart Machining Modules | |
| Polymergranite Construction | Thermostability, Vibration Dampening, Heavy - Same Material Used On CMM - Handles high acceleration - Better surface finish - better accuracy control | |
| High Acceleration | Key to Fast Cycle Times & Long Tool Life - reduce heat build up in tool and workpiece material | |
| Symmetrical Design | High Accuracy, Ergonomics, Stability throughout the day | |
| Automation in Mind | Designed to be Modular & Scalable - Ergonomic - No operator obstruction | |
