Cutting Tools for High-Speed Aluminum Milling

High-speed milling (HSM) of aluminum and its alloys involves cutting speeds significantly higher than standard rates.
This approach ensures efficient material removal and excellent surface finish and accuracy. While there is no strict definition for what constitutes HSM speeds, it is generally accepted that they range from 1.5 to 4 times typical values.
Achieving HSM cutting speeds requires operating milling cutters at extremely high rotational velocities, often reaching 30000 RPM or more.

From a design perspective, cutting tools for high speed milling (HSM) of aluminum and its alloys (collectively, aluminum’) are typically classified into three types, as are general purpose milling cutters:

• Indexable tools
• Solid cutters, mostly solid carbide endmills
• (SCEM)assembled tools that mount replaceable, primarily tungsten carbide cutting heads (ISCAR's MULTI-MASTER products)

Machining at exceptionally high rotational velocity demands that milling tools withstand substantial centrifugal loads, maintain balancing quality, and ensure safety.
A key goal is to achieve, already at the design stage, a mass distribution that is theoretically symmetric about the tool axis, producing a “balanced-by-design” tool structure.
This engineered balance applies to the virtual model and, understandably, does not replace physical balancing of the finished tool.
However, this skillful design significantly reduces residual mass imbalance in the manufactured tool and makes subsequent physical balancing faster, easier, and more reliable.

Solid tools and replaceable solid cutting heads (designed on similar principles) are essentially monolithic.
This greatly simplifies achieving a balanced-by-design structure, especially when using 3D modelling in a modern CAD environment.
By contrast, for indexable milling cutters, which consist of multiple assembled elements, HSM requirements are particularly critical.

The design of indexable tools intended for high-speed milling of aluminum and its alloys focuses on addressing various specific challenging characteristics of HSM, such as:

• Preventing insert radial displacement caused by significant centrifugal forces.
• Reducing the mass of tool components to decrease centrifugal load.
• Ensuring soft, light cutting action, even in operations requiring a long-reach tool configuration.
• Optimizing the chip-gullet profile to maximize space for chip evacuation while maintaining the strength of the tool-body core.
• Shaping internal coolant channels for the most effective coolant supply and others.

The tools in the first group are general‑duty cutters that hold indexable inserts suitable for milling various materials, including those designed specifically for aluminum.
Principally, these cutters are used to mill a wide range of engineering materials and accept inserts that have the same basic shape and datum surfaces, which locate the insert in the pocket.
By mounting inserts with different rake and relief face geometries, the same cutters can be configured to machine specific material types.
The first group tools are typically operated at cutting speeds that do not exceed 1000 m/min (3280 SFM).

In HSM at exceptionally high rotational speeds, centrifugal forces become substantial.
To prevent radial displacement of the inserts caused by these forces, second group tools incorporate an insert retention mechanism.
As a result, cutting speeds increased significantly - for example, up to about 5000 m/min (16400 SFM) when radial engagement is small.

The third group of tools have been developed for applications requiring intensive ramp-down milling passes.
The aggressive cutting geometry of the inserts used in these tools enables cutting speeds of up to 2000 m/min (6560 SFM).

In high-speed milling of aluminum, elevated centrifugal forces impose significant loads on the insert's clamping screws.
To ensure high reliability, these screws should be replaced in accordance with tool-specific instructions.
As a general guideline, ISCAR recommends replacing a clamping screw after every ten insert replacements for the insert it secures.
In some HSM tool designs, inserts are supplied together with their clamping screws in combined packages.
The inserts and screws are selected within tight tolerances to meet the required balance grade of the assembled cutter. In such cases, the screws should be replaced whenever the inserts are replaced.

It is important to note that balancing requirements are not limited to the tool assembly comprising the tool body, inserts, and clamping elements such as screws.
The entire tooling system - including the tool assembly, the basic adaptor mounted in the machine tool spindle, and any intermediate elements (extensions or reducers) - must be balanced.
This rigorous requirement is emphasized also in the ISO 16084 standard.

What new tools for high-speed milling of aluminum does ISCAR offer customers? Which of the above-mentioned groups is the focus of the latest developments?

The group of general-duty indexable milling cutters has been expanded with various original designs.
For example, the range of tools carrying round inserts now includes new inserts intended for machining aluminum and other non-ferrous metals.
These inserts, which feature a polished top (rake) face to improve chip flow and eliminate built-up edge (BUE) formation, are produced in two geometries: one with a plain cutting edge and one with a serrated cutting edge.
Inserts with a plain edge are typically used for semi-finishing operations, while inserts with a serrated edge are primarily designed for roughing and for machining under unstable conditions, such as long-reach applications requiring high tool overhang and the machining of thin-walled workpieces (Fig. 1).

Recently introduced endmill heads with MULTI-MASTER and FLEXFIT threaded connection, available with a high-pressure coolant (HPC) option, provide another example (Fig. 2).
These heads accept ISCAR’s classic HELIALU inserts with a helical cutting edge.
The coolant delivery design was upgraded, using computational fluid dynamics (CFD) modeling, to maximize flow rate while minimizing pressure drop.
The screw-in configuration significantly broadens customization by enabling the use of MULTI-MASTER and FLEXFIT shanks, adapters, extensions, and reducers that are widely represented on the market.

Over the last years, ISCAR has emphasized a portfolio of indexable milling tools for aluminum designed for very high cutting speeds to boost metal removal rate (MRR).
These tools are engineered to prevent radial insert movement caused by strong centrifugal forces.
A dedicated anti-movement locking mechanism ensures reliable cutting during extended high-speed machining (HSM) operations. The latest development expands the portfolio’s performance with new tools that accept large inserts, enabling depths of cut up to 22 mm (Fig. 3).
This addition supports more effective utilization of modern, high-power machine tools with high-speed main drives.

The newest product, recently unveiled, is a 14 mm serrated insert designed to be mounted on existing HELIALU high-speed milling cutters.
The insert combines a polished rake face, super-positive cutting geometry, and sharp serrated cutting edges for chip-splitting action.
Breaking wide chips into small segments improves chip evacuation, reduces re-cutting, enhances the tool’s dynamic stability, and enables higher feed rates, thereby increasing productivity in rough milling operations (Fig. 4).

Naturally, solid carbide end mills (SCEM) and assembled tools with replaceable carbide heads are also undergoing continued development.
Recent innovations include several SCEM and heads with various profiles.
For example, a four-flute, 32 mm in diameter MULTI-MASTER head (Fig. 5) employs variable flute helix angles to improve dynamic stability, enabling consistent cutting across a wide range of operations from roughing to finishing.

Advances in machine tools have significantly expanded the limits of rotational velocity and feed rate, allowing higher cutting speeds.
Ultra-high-speed milling of aluminum is emerging as a guiding paradigm, which in turn places new demands on cutting-tool design.
How tool manufacturers will meet these challenges remains to be seen.