Getting the Most Out of Aluminum CNC Machining

Aluminum is one of the most widely used metals for CNC machining. Its high strength-to-weight ratio, corrosion resistance, thermal and electrical conductivity, and relatively low cost make it an ideal material for a range of applications from aerospace components to consumer products. However, aluminum can also be tricky to machine correctly. This guide covers everything you need to know to get the best results when CNC machining aluminum.

What Makes Aluminum Good for CNC Machining?

There are several key properties that make aluminum such a popular choice for CNC machined parts:

• Strength – Aluminum alloys offer a high strength-to-weight ratio, meaning parts can be made lighter without sacrificing structural integrity. This makes aluminum suitable for aircraft, automotive, and other applications where reducing weight is a priority.
• Corrosion resistance – Pure aluminum naturally forms an oxide coating that protects it from corrosion. This makes it ideal for use in marine environments and other harsh conditions. Some alloys offer even better corrosion resistance.
• Thermal conductivity – Aluminum conducts heat efficiently, making it useful for heat sinks and other applications where heat dissipation is needed.
• Electrical conductivity – After copper, aluminum is the second-most electrically conductive metal. This makes it useful for electrical wiring, electronics enclosures, and other components that need conductivity.
• Machinability – Aluminum alloys are relatively soft and easy to cut. This allows faster machining times and lower tooling costs compared to metals like steel and titanium.
• Appearance – Aluminum can be brightly polished or anodized to create an attractive decorative finish for consumer products and architectural features.
• Cost – High abundance and recyclability make aluminum more affordable than other popular engineering metals. Scrap aluminum can even be profitably recycled.

With this versatile mix of properties, it’s easy to see why aluminum is used for everything from iPhone cases to aircraft wings. Next, let’s look at how to choose the right aluminum alloy for your application.

Choosing the Right Aluminum Alloy

There are many different aluminum alloys available, each optimized for specific properties. Choosing the right alloy for your project ensures you get optimal strength, machinability, corrosion resistance, and appearance.

Some of the most common alloys used for CNC machining include:

• 6061 – The most popular alloy for machined parts, offering a good all-round mix of strength, formability, and corrosion resistance. Used for structural frames, car/bike parts, camera bodies, valves, and more.
• 7075 – The highest strength aluminum alloy, but not very corrosion resistant. Best for high-stress aircraft and aerospace applications. Challenging to machine.
• 2024 – Another high-strength alloy with better fatigue resistance than 7075, but not very formable. Used for aircraft and aviation applications.
• 5052 – Excellent corrosion resistance and weldability make 5052 popular for marine applications, fuel tanks, and chemical equipment. Lower strength than 6061.
• 5005 – This medium-strength alloy offers good bending and welding properties. Used for chemical tanks and pressure vessels among other applications.
• 6063 – The most common choice for architectural extrusions due to excellent finishing characteristics. Also used for some consumer products. Not very high-strength.
• 7068 – A high-strength alloy with improved stress corrosion cracking resistance versus 7075, making it popular for aerospace applications.

Consider the required mechanical properties, corrosion resistance, weldability, and final appearance needs when selecting an alloy. Your aluminum supplier can help recommend the optimal grade.

Now let’s look at the aluminum stock forms used for CNC machining.

Common Aluminum Stock Forms for CNC Machining

Aluminum is available from suppliers in many different stock forms to suit various CNC machining needs:

• Bars – Solid aluminum cylinders available in different diameters. Allows machining complex 3D contours.
• Rods – Available in smaller diameters than bars for machining precision components.
• Plates – Flat sheets of aluminum in rectangular sizes. Well-suited for 2D profiling and flat parts.
• Blocks – Rectangular aluminum blocks for machining large robust components like machine bases and fixtures.
• Extrusions – Aluminum shaped into more complex profiles via extrusion. Allows creating intricate external shapes.
• Castings – Molten aluminum poured into a mold then machined to final shape. Used for complex geometries like engine parts.
• Forgings – Aluminum pressed/pounded into shape while hot then machined. Provides excellent strength.

Consider the shape and size of your final part when selecting the optimal stock form to start with. This minimizes wasted material and machining time.

Bars, plates, and extrusions are the most common starting forms for smaller aluminum CNC machined components. Now let’s examine aluminum CNC machining capabilities.

CNC Machining Capabilities for Aluminum

Modern CNC machining centers can perform all kinds of cutting operations on aluminum:

• Milling – Using rotating end mills and drills to cut away material. Most common aluminum machining operation.
• Turning – Rotating the aluminum stock while cutting to create cylindrical forms and bores.
• Drilling – Machining holes and cavities with twist/specialty drill bits.
• Boring – Enlarging and smoothing pre-drilled holes for precise dimensions.
• Tapping – Cutting internal screw threads into holes to accept fasteners.
• Counterboring – Creating a flat-bottomed enlargement of a drilled hole to accept a bolt head.
• Countersinking – Beveling hole edges to allow flush mounting of bolts/screws.
• Profiling – Cutting external linear and contoured edges with a rotating cutter.
• Pocketing – Milling internal cavities and pockets into the aluminum surface.
• Surfacing – Smoothing/flattening surfaces with broad shallow cuts.
• Engraving – Using fine-tipped cutters to cut detailed patterns, lettering, and designs into the aluminum surface.

CNC enables performing all these operations in a fully automated sequence with extreme precision and repeatability. Complex 3D shapes can be produced directly from 3D CAD models. This allows custom aluminum components to be machined rapidly and accurately.

Best Practices for Machining Aluminum

To get the highest quality and most efficient results when CNC machining aluminum, follow these proven tips:

• Use rigid setups – Aluminum’s low density requires mass for vibration dampening. Clamp parts tightly to avoid chatter.
• Reduce deflection – Keep overhangs short and provide support near cutting edges to minimize tool deflection.
• Use high spindle speeds – Aluminum cuts best at high rpms. Typical speeds exceed 10,000 rpm.
• Select suitable tools – Carbide and diamond-coated cutters stay sharper. High helix angles and polished flutes help too.
• Keep tools sharp – Replace or resharpen end mills before they get dull to avoid poor surface finish and tool wear.
• Use proper feeds/speeds – Consult reference charts to find optimal feeds and speeds for your tooling and operations. Too slow melts and welds the aluminum.
• Use cooling lubricants – Aluminum chips can build up and gall without sufficient lubricoolant flow. Water-soluble oils or compressed air work well.
• Clear chips frequently – Long aluminum stringy chips can clog flutes and interfere with machining. Program periodic rapid moves to clear.
• Rough and finish – Rough out material with higher feeds/speeds then use light finishing passes to get final dimensions and surface finish.
• Deburr carefully – Aluminum is soft and burs easily. Use hand/mechanical deburring and break all sharp edges.

Following these guidelines helps avoid common issues like poor surface finish, rapid tool wear, and inaccurate dimensions when machining aluminum parts.

Design Tips for Machinable Aluminum Parts

Designing parts specifically for CNC machining allows taking full advantage of aluminum’s capabilities. Keep these tips in mind:

• Minimize tight internal radii – Use large inside corners whenever possible to allow cutting tool access.
• Avoid thin unsupported walls – Design thicker sections or ribs to add support against tool pressure and vibration.
• Allow sufficient stock – Leave adequate thickness to enable roughing/finishing passes and avoid tool crashes.
• Facilitate chip clearance – Include vertical chip slots and breaks in pockets to provide chip evacuation routes.
• Design for fixture simplicity – Include locating/clamping features to make workholding easier and more secure.
• Specify tight tolerances selectively – Apply tighter tolerances only to critical features to reduce machining time/cost.
• Consider edge treatments – Deburred, beveled, or rounded edges enhance aesthetics, safety, and functionality.
• Optimize part orientation – Position the part to enable shortest tool paths, adequate chip clearance, and maximum rigidity.
• Consolidate parts when possible – Combining assemblies into single machined components improves quality and reduces labor.

Following design-for-manufacturing guidelines ensures your parts can be CNC machined efficiently, accurately, and cost-effectively.

Useful Resources for Aluminum CNC Machining

Here are some helpful resources for further exploring aluminum CNC machining:

• Haas Tips of the Trade for Machining Aluminum – Collection of tips from Haas, a leading CNC machine tool manufacturer.
• Sandvik Coromant Machining Guide for Aluminum – In-depth aluminum machining data from cutting tooling expert Sandvik Coromant.
• In The Loupe – Your Guide to Machining Aluminum – Excellent primer on machining aluminum from Harvey Performance Company.
• ENGINEERING.com – CNC Aluminum Machining Guide – Overview of aluminum properties, alloys, and machining considerations from ENGINEERING.com.
• MakeItFrom.com – CNC Machining Aluminum – Helpful introduction to machining aluminum including design principles and tooling recommendations.

With the right knowledge, materials, tools, and techniques, you can machine aluminum parts that leverage the full potential of this versatile metal. CNC opens up vast possibilities for creating complex aluminum components accurately, rapidly, and cost-effectively.