Mechanical Fabrication

  1. Milling : Milling machines for fabrication of aluminum have larger teeth pitches than equivalent tools for steel and therefore a more spacious groove for chips. As with other sawing, a high cutting speed is required for a good result. A high quality surface demands high power and stability in the tool and feed mechanism.

    Drilling : As with most machining, drilling should be carried out at a high speed. When using standard bits, they should be sharpened so as to reduce the pressure required and obtain a better result. Special bits for aluminum are only required for deep holes or soft alloys. It is important to note that the hole will be considerably larger than the bit diameter when drilling in aluminum, especially when drilling in soft alloys.

    Turning : Aluminum can be turned in standard, special and automatic lathes and should be carried out at high speeds of rotation. Parts to be turned should therefore be fitted securely to avoid vibration. Spacers between the part and the mounting prevent marks on the metal and deformation.

    Tapping : Internal and external threads can be made using all available machining methods as well as through plastic deformation. Heat treatable alloys give especially high quality results. Taps for steel can be used for threads under 6 mm but special taps should be used for larger diameters.

    Shearing/pressing : Press work is normally carried out in eccentric presses with a cutting (shearing) tool. The press tools for aluminum are slightly different from those designed for other metals. Punch and die of hardened tool steel are recommended. Burrs are avoided by regularly sharpening the punch and die.

    Insulation : Aluminum's high coefficient of thermal conductivity is not so desirable in applications where low heat transfer is wanted such as in windows. There are many ways of insulating, two techniques that greatly reduce the ability to conduct are commonly used. In the first the extrusion is pressed in one piece and a closed space in the extrusion is filled with polyurethane. When the polyurethane has set, the extrusion is divided into two parts held together by the polyurethane. In this way the thermal bridge is interrupted (fill and mill).
    In the other method two extrusions are joined using polypropylene or polyamide strips. These are rolled into position. This way of insulating makes it possible to use different colors on the inside and outside of the window.

    Plastic Forming : Aluminum extrusions can be bent using the same equipment as for other metals. Bending can take place with the hardened metal for larger radii but smaller ones usually require soft annealed or T4 (half-hardened) metal. It is possible to harden to full strength after bending. Bending should be carried out before anodizing if a complete anodized layer without cracks is required.

    Bending : High shaping accuracy. The extrusion is held tightly at both ends and the shaping takes place by the tool moving.

    Stretch forming : With or without internal and external supports. The extrusion is held tightly and rotates with the tool. This method is suitable for small radii and can be repeatedly carried out.

    Roller bending : Used to bend extrusions with large radii. The extrusion is rolled between three wheels of which one is adjustable. It is possible to vary the radius on the same component using CNC-controlled machines.

    Press bending : Suitable for simpler operations in large batches. The parts are shaped in a two-part tool in, for example, an eccentric or hydraulic press or other simple equipment.

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