Aluminium CNC Machining

Choosing the alloy for machining

6061-T6 and its European twin 6082-T6 are the default: good strength (yield 240 to 260 MPa), excellent machinability, weldable, anodisable and available as plate up to 150 mm and bar up to 300 mm. 7075-T6 nearly doubles the strength (yield 460 to 500 MPa) for aerospace-style brackets and tooling, but it is not weldable, anodises with a slight yellow tone and costs roughly 60 to 100% more than 6061. 5083-H111 is the marine grade for parts on boats and coastal installations; it machines with more burr and is softer, so tolerances open up. 2024-T3 is used where fatigue strength matters but corrodes in salt air unless coated. Cast plate (for example 5083 cast tooling plate) is stress-relieved and stays flat after heavy pocketing, which matters for large fixture plates.

Tolerances and surface finish

Aluminium machines fast and cleanly, so standard tolerance is ISO 2768-m (±0.1 mm for 6 to 30 mm, ±0.2 mm for 30 to 120 mm), with ±0.05 mm on called-out features at no significant extra cost and ±0.01 to ±0.02 mm on bores and datums when specified. Thermal expansion is 23 µm per metre per °C, about twice steel; a 500 mm part measured at 35 °C in a Dubai workshop is 0.17 mm longer than at 20 °C, so critical parts are inspected in an air-conditioned room. Surface finish as milled is Ra 1.6 to 3.2 µm; a finishing pass gives Ra 0.8 µm; bead blasting then anodising gives a uniform matt look that hides tool marks.

Machine capacity in the network

Vertical 3-axis machining centres with tables of 500 x 400 mm to 1500 x 800 mm cover most housings and plates. 4-axis machines add rotary indexing for parts with features on several faces, and 5-axis simultaneous milling handles impellers, angled ports and complex brackets in one setup. CNC lathes with bar feeders turn round parts from 5 to 65 mm bar automatically, and chucking lathes reach 400 mm diameter. Parts larger than 1500 mm are possible on a small number of gantry machines in the region; ask before designing.

• 3-axis milling: parts up to 1500 x 800 x 500 mm, most economical
• 4-axis: rotary indexing for multi-face parts up to 300 mm diameter
• 5-axis: single-setup complex geometry, best accuracy between features
• Turning: bar work 5 to 65 mm, chucking up to 400 mm diameter, live tooling for cross-holes
• Batch sizes: 1 to 5000 pieces, fixture plates built for repeat orders

Finishing for the Gulf and Egypt

Bare 6061 develops a dull grey oxide and, in coastal Jeddah or Abu Dhabi air, white pitting within months. Type II sulphuric anodising at 10 to 25 µm is the standard protective finish, in clear, black or colours; it adds 5 to 12 µm per face, so machine tight fits to allow for it. Type III hard anodising at 25 to 50 µm gives a 400 HV surface for sliding parts and wear areas. Chromate or trivalent conversion coating (Alodine) keeps electrical conductivity for RF and earthing housings. Powder coating at 60 to 120 µm suits outdoor enclosures and hides machining marks. Sand abrasion in desert sites favours hard anodising over decorative anodising.

Design for lower machining cost

Machining time is the main cost. Deep pockets with small corner radii force small cutters and slow cuts; a 3 mm corner radius in a 40 mm deep pocket needs a 6 mm end mill at 7 times its diameter in depth, which is slow and chatters. Use radii of at least one third of pocket depth, or 8 mm where the design allows, and keep pocket depth under 4 times the cutter diameter. Avoid walls below 1 mm and floors below 1.5 mm. Standardise on metric drill sizes and thread sizes, and use through-holes rather than blind where possible. Ask for stock-size thickness (6, 8, 10, 12, 15, 20, 25 mm plate) so the top and bottom faces need only a light skim.

Applications

Pricing and lead time

Three factors dominate the price: machining time (set by the volume of material removed, the smallest corner radius and the number of setups), tolerance and finish class (each ±0.01 mm feature and each Ra 0.8 µm surface adds inspection and finishing passes), and quantity, since programming and setup are spread over the batch so that 50 pieces typically cost 40 to 60% less per piece than a single prototype. 7075 adds roughly 60 to 100% to material cost over 6061, and anodising adds 10 to 20% to the part price. Lead time is 3 to 7 working days for simple milled parts, 7 to 12 working days for 5-axis or anodised parts, and 10 to 15 working days for batches above 500 pieces.

Frequently asked questions