CNC Drilling in Aluminium and Steel: Key Differences

CNC (Computer Numerical Control) drilling has become one of the most reliable and widely used machining processes in modern manufacturing. Whether it’s for aerospace, automotive, construction, or consumer goods, drilling holes with high precision is essential. 

However, not all materials behave the same under machining. Two of the most common metals drilled in CNC operations are aluminium and steel, and they present very different challenges and considerations.

This article explores the key differences in CNC drilling between aluminium and steel, covering their physical properties, machining behaviour, tooling requirements, coolant strategies, surface finishes, and practical applications. By the end, you’ll have a clear understanding of how to approach CNC drilling projects involving these two vital materials.

Material Properties That Affect CNC Drilling

Aluminium

• Lightweight: Aluminium has about one-third the density of steel, making it ideal for weight-sensitive industries like aerospace and automotive.
• Softness & Malleability: It is relatively soft compared to steel, which makes it easier to cut but prone to issues like built-up edge (BUE).
• Thermal Conductivity: High thermal conductivity means heat dissipates quickly, reducing the risk of thermal deformation.
• Corrosion Resistance: Naturally resistant to rust, though certain alloys may still require protective coatings.

Steel

• Strength & Hardness: Steel is significantly harder and stronger than aluminium, making it better for load-bearing components.
• Density: Much denser than aluminium, which increases weight but enhances durability.
• Alloy Variability: Comes in a wide range of alloys (mild steel, stainless, carbon steel, tool steel), each with its own machining challenges.
• Thermal Conductivity: Lower than aluminium, so heat builds up faster during machining.

Cutting Forces and Machine Power For Both Materials

One of the most obvious differences in CNC drilling between aluminium and steel is the cutting force required.

• Aluminium: Because it is softer, aluminium requires lower cutting forces. Tools can operate at higher spindle speeds and feed rates, making drilling faster and more economical.
• Steel: Machining steel demands higher torque and cutting power. Feed rates must be carefully balanced to avoid excessive tool wear or part distortion. The harder the steel alloy, the greater the power requirement.

This difference directly affects machine tool selection. A lighter CNC setup may handle aluminium without issue, but drilling steel requires a rigid, vibration-resistant CNC machine capable of sustaining higher cutting loads. Learn in more detail about CNC drilling, its uses, applications and overall working.

Tooling Considerations for Aluminium and Steel

Tool choice is crucial in CNC drilling, as it affects hole quality, tool life, and efficiency. Since aluminium and steel behave differently, their tooling needs are not the same.

Tooling for Aluminium

• Material: HSS drills are common, but carbide tools are preferred for high-volume jobs. Coatings like TiN can help but aren’t always required.
• Geometry: Sharp cutting edges with high rake angles and wide flutes are ideal for chip removal.
• Chip Evacuation: Aluminium forms long chips that can clog flutes, so polished flutes and coolant help prevent re-cutting.

Tooling for Steel

• Material: Solid carbide drills are best due to steel’s hardness; HSS wears quickly.
• Coatings: TiAlN or TiCN coatings improve wear resistance and heat tolerance.
• Geometry: Stronger cutting edges with lower rake angles are needed to handle higher cutting forces.

If you’re exploring how CNC compares to other modern technologies, you may find our article on CNC machining vs 3D printing useful.

Cutting Speeds and Feeds Requirements

Cutting parameters differ widely between aluminium and steel, with aluminium allowing faster machining and steel requiring more control.

Aluminium

• Spindle Speeds: Can reach 3,000–10,000 RPM or more, depending on hole size.
• Feed Rates: Higher feeds are possible due to aluminium’s softness.
• Outcome: Faster cycle times and better productivity, but risk of chip welding if speeds are excessive.

Steel

• Spindle Speeds: Slower, usually 500–2,000 RPM, to avoid rapid tool wear.
• Feed Rates: Must be conservative; too high risks tool failure, too low may cause work hardening.
• Outcome: Slower but more precise drilling that preserves tool life.

For a broader understanding of machining basics, take a look at our beginner’s guide to CNC machining.

At Kirmell, our CNC drilling services are equipped with advanced machines that can efficiently handle both lightweight aluminium projects and heavy-duty steel components with precision. Contact us now with your project requirements to get a quote. 

Heat Management and Coolants

Both materials generate heat during drilling, but how they handle it is very different.

Aluminium

• Thermal Conductivity: Heat dissipates quickly, reducing the risk of distortion.
• Issues: Localised heat may still cause chip welding or galling.
• Coolant Use: Flood coolant, mist lubrication, or through-tool coolant improves chip evacuation and finish.

Steel

• Thermal Conductivity: Retains heat, leading to tool wear and dimensional changes.
• Need for Coolant: Essential to prevent overheating and work hardening.
• Coolant Strategies: High-pressure through-tool systems are ideal, especially in deep-hole drilling.

Cost Implications

Aluminium

Drilling aluminium is generally more cost-efficient because it allows faster cycle times, lower power consumption, and longer tool life. These advantages make it attractive for industries where speed and efficiency are priorities. However, aluminium does come with challenges such as chip welding, which can cause downtime if not managed with proper tooling and coolant strategies.

With Kirmell’s CNC drilling services, projects benefit from optimised coolant delivery systems and thermal control methods that reduce downtime and improve consistency.

Steel

CNC drilling in steel is comparatively more expensive due to slower machining rates, frequent tool changes, and higher energy demands. While it requires greater investment in time and resources, steel is indispensable in projects where strength and durability are critical. Its ability to withstand heavy loads and provide long-term reliability justifies the additional machining costs.

Safety Considerations

Aluminium

When drilling aluminium, chips can be sharp but are usually less hazardous compared to harder metals. The bigger concern lies in the fine dust generated during dry machining, which can pose fire risks if not managed with proper extraction and safety measures.

Steel

Drilling steel produces hot, sharp chips that present a higher risk of burns and injuries. To ensure operator safety, proper guarding, chip conveyors, and the use of protective gear are essential when working with steel.

CNC Drilling Services at Kirmell: Precision Solutions for Aluminium and Steel

Kirmell offers CNC drilling services designed to meet the diverse needs of modern manufacturing. With the ability to handle both aluminium and steel, the company focuses on delivering accurate hole placement, clean finishes, and consistent quality across projects of varying scale. 

Advanced tooling, optimised cutting parameters, and strict quality checks allow Kirmell to support industries ranging from construction and automotive to energy and aerospace. By combining decades of engineering experience with modern CNC technology, Kirmell ensures reliable results tailored to each client’s material and design requirements. Contact us for more information related to your project. 

Conclusion 

CNC drilling in aluminium and steel involves very different challenges. Aluminium is generally easier to machine, faster, and more cost-effective, though issues like chip welding and burr formation must be managed. Steel, on the other hand, requires slower speeds, tougher tools, and higher costs, but delivers exceptional strength and durability.

The key differences come down to cutting forces, tooling, speeds and feeds, coolant use, chip behaviour, and tool wear. Instead of asking which is better, manufacturers should match the material to the performance needs of the application, ensuring precision, cost control, and reliable results.

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