Machining aluminum for lighter components and a recyclable future

Car and aircraft manufacturers are facing a big transformation. New environmental legislations and the expectations from more environmentally conscious consumers are pushing the manufacturers for new low- and zero-emission vehicles.

Aluminum can be one answer to the component challenges the manufacturing industry is facing. Aluminum is one of the lightest metals in the world, almost three times lighter than iron but very strong and corrosion resistant. Also, aluminum can be reused over and over again. It can be melted down and reused without any harm or change done to its mechanical properties. Thanks to effective recycling, approximately 75% of all aluminum ever produced, is still in use today which is great for a more sustainable future.

Machining aluminum alloys in automotive industry

Video: Milling cutters for automotive aluminum machining

Although electric vehicles are on the rise, it will take time until the internal combustion engine leaves the stage. In the current effort to use cleaner energy, the application of lightweight materials in internal combustion engines becomes imperative as it results in greater fuel efficiency and thus reduces pollution. The power train of a European passenger car typically contains around 80 kilograms of aluminum, which means these parts – the engine, gear box, suspension parts, housings – are an obvious area of interest for light weighting measures. By replacing the conventional cast iron with aluminum alloys can reduce the weight of the engine block by up to 40–55%, even accounting for the lower strength of aluminum compared to grey cast iron. Several transmission components, particularly gear box housings, electrification devices/components, suspension arms and rear axle, are prime examples of driveline applications where aluminum is a favored material.

Dedicated tooling solutions for the automotive manufacturing industry as well as for machine tool builders (MTMs) lead to more productive machine operations. The complete series of M5 milling cutters offers everything from first stage machining to super finishing - for optimized quality and cost per part.

M5 milling cutters for ISO N materials:

• The M5Q90 cleans the surfaces of newly casted aluminum cylinder heads and engine blocks in one smooth operation, without burring. The milling tool performs reliably and provides a long tool life.
• The M5R90 is the first choice for roughing to semi-finishing in shoulder milling operations of automotive aluminum components such as cylinder blocks, cylinder heads, transmission housings.
• The M5B90 face milling concept offers a highly effective tool for super finishing cylinder heads, blocks, covers, and other components with wide cutting engagements. The M5B90 prevents uneven tool wear and leads to a much superior tool life, even at high feed rates.
• The M5C90 concept is based on M5B90 and likewise offers smooth burr-free cutting process, scratches and breakages with indexable inserts in a stepped configuration. What sets the M5C90 face mills apart, is their extra row of roughing inserts positioned tangentially on the outer diameter.
• The M5F90 is a dedicated face milling cutter for machining thin-walled aluminum components in a single operation but it can also be used for spot facing and operations with wide material engagements.

ISO N materials

Non-ferrous materials includes not only aluminum, but also magnesium, copper and zinc based alloys. The machinability differs primarily depending on the Si-content. Hypo-euthectic aluminum is the most common type, with a Si-content below 13%.

For many years, the engine block has been manufactured using cast iron alloys due to its strength, low cost and wear resistance. But as engines become more complicated, new materials have been taken in use to reduce its weight as well as to increase strength and wear resistance. Today´s most common materials for passenger car engines are aluminum alloys, because of their reduced weight and excellent casting properties.

Tools for cylinder boring operations in cast iron and in aluminum with integrated cast iron liners or sleeves:

• B685 for stable and productive cylinder boring, from roughing to semi-finishing
• B687 for stable and productive finishing cylinder boring
• B681 for stable and productive roughing cylinder boring
• B683 for stable and productive semi finishing cylinder boring

Automotive parts are typically mass produced parts with high density of complex hole geometries – an application that often justifies the use of optimized drilling tools to achieve maximum productivity and long tool life for high productivity, and ultimately, low cost per hole.

Drilling tools / solid round tools for aluminum machining:

• CoroDrill® 400 is a straight flute drill designed for complex multi-step, chamfer and radius forms as well as large step ratios over diameters ranging between 3 and 25 mm (0.118–0.984 inch). These drills excel in easy chip removal, hole straightness and surface finish.
  
• CoroDrill® 430 is a 3-flute spiral solid carbide drill for core drilling, in other words opening out existing holes. These offer excellent hole size control and straightness in challenging conditions.
  
• Thread forming is the favoured threading solution for aluminum engine components and the CoroTap® 400 selection of chip-free forming taps is the first choice for this application.
  

Drilling aluminum tips

1. Burr formation and chip evacuation can be a problem. Poor tool life can also be present due to adhesion. Recommendations: For best chip formation, use low feed and high-speed machining.
2. In order to avoid poor tool life it may be necessary to test different coatings, minimizing adhesion. These coatings could include diamond coatings or certain cases (depending on the substrate) not using any coating at all.
3. Other: Use emulsion or mist coolant at high pressure.

Machining aluminum alloys in aerospace

When machining aluminum in aerospace, a key factor is to combine a stable and reliable machining process with high speed and high metal removal rates. A vital element of good machinability is to achieve low cutting forces, which allows for low power consumption, less vibration tendencies and a good quality surface finish.

Image: RAL90 aluminum cutter and wing rib

There are several types of aluminum components on an aeroplane such as spars, skins, and ribs. The wing rib as an example shows some of the machining challenges such as thin walls/bases, 2D pockets and the importance of balanced tools. Sandvik Coromant offers a wide range of tools dedicated for cost effective and high-quality machining of wing rib.

Thin wall machining

The machining strategy for thin wall sections should vary depending on the height and thickness of the wall. The number of passes will be determined by the wall dimensions and axial depth of cut.

Use of high speed techniques, i.e small ap/ae and high vc facilitates milling of thin walls, as they reduce the time of tool engagement and consequently the impulse and deflection. Step support machining the wall in overlapping passes is used when wall thickness vs height are 15:1 to 30:1.

Pocketing with high speed router RAL 90

The RAL90 aluminum milling cutter is designed for extremely high metal removal rates. The extra robust cutter body with optimized insert seats sets the standard for a new level of process stability in high speed milling - ideal for heavy roughing to semi-finishing pocketing of aerospace frames in aluminum alloys.

In applications requiring even higher metal removal rates, the new RAL90 Super MRR milling cutter can reach extra high spindle rotation, e.g. up to 33000 RPM for DC 50 mm compared to 23500 RPM for RAL90. This means a 40% productivity increase.

Milling aluminum with solid carbide tools

When smaller diameters are required, solid carbide tools is the solution. With a geometry and grade optimized for milling aluminum, the CoroMill® Plura end mill and CoroMill® 316 end mill with exchangeable cutting head deliver long tool life at high metal removal rates.

The flutes are designed with a large chip space for great chip evacuation. Furthermore, the specific cylindrical land reduces tool vibration in milling machine and minimizes chipping problems, leading to an excellent surface finish.

Machinability of aluminum

• Polymer Long-chipping material
• Relatively easy chip control, if alloyed
• Pure Al is sticky and requires sharp cutting edges and high vc
• Specific cutting force: 350–700 N/mm
• Cutting forces, and thus the power required to machine them, are low
• The material can be machined with fine-grained, uncoated carbide grades when the Si content is below 7-8%, and with PCD tipped grades for aluminum with higher Si content
• Over eutectic Al with higher Si content > 12% is very abrasive