Titanium extrusion - the master challenge for titanium crafters

Titanium extrusion is only one of the variety of metal-working processes, such as welding, casting, forging, fabricating, brake forming, rolling, by which complex metallic shapes have traditionally been produced.

It can be classified as traditional, as there were no significant modifications to the principles of the method since its first use. However, the manner in which it is applied today has greatly advanced with the development of powerful, automated extrusion tools and highly sophisticated control systems. Extrusion is favored amongst other processes since titanium shapes for extrusion are custom designed to achieve the final profile - within close tolerances - in relatively few operations, resulting in optimum material use, with less waste and less need to downstream machining. In addition, because of extrusion’s faster cycle times, lead times can be shorter, even for high volumes. On a second thought, retooling for titanium extrusion, although not cheap, is relatively inexpensive, compared to some other production processes, for instance, forging.

Complex shapes emerge from the titanium extrusion process with superior strength, dimensional control, and the specific titanium matte surface finish free of alpha case. The grades of titanium used in extrusion consists of pure and alloyed bar or billets in as required by the physical and mechanical properties needed for each particular designs.

Titanium is extruded at temperature range between 850 and 1150 degrees Celsius. Above 1000 degrees Celsius glass lubrication is necessary. The typical process starts with a solid round titanium bar, which is preliminarily precision-cut into shorter billets which are then subsequently induction heated to a specific extrusion temperature, dependent upon the alloy or the titanium grade. The heated billets are rolled down a conveyor chute and, as they roll towards the press, each billet is coated with a powdered glass compound that both lubricates and protects the surface of the material.

At the extrusion press, each billet is hydraulically pushed through a die at pressure of up to 2000 tons, forcing the metal to configure to the die’s profile. The press can be adjusted to operate at high speeds, making operation of each extrusion in periods of time ranging from 1.5 to 5 seconds. The key to close-tolerance extrusions is obviously the quality and of the die. Instant failure of the dies is not unheard of, especially when the glass film breaks at high extrusion speeds.

The intense heat and pressure that affect extrusion dies generate interior erosion, informally called “die wash” that can cause dimensional tolerances to shift. Usually, the tolerances are maintained by inserting a new die for each item. After the shapes are extruded, downstream operations vary with the material.

Titanium parts resulting from titanium extrusion processes require heat treating to refine their grain structure. Titanium extruded parts are hot stretch-straightened, using air cooled at tension in the stretcher.

Chemical treatment is employed after stretching by immersion in a chemical bath to remove any remains of the lubricant as well and titanium’s alpha case -a thin, but tough exterior layer formed during high-temperature heat treating. Removing the alpha case enhances machinability and prolongs tool life. Before the extruded parts are packaged and shipped, extensive metallurgical testing and dimensional inspection methods are employed to verify that the specified physical, metallurgical, and mechanical properties have been attained, and that the extrusion meets the performance and quality standards.

In the early days titanium extrusion was used almost exclusively for military aircraft components. They were a niche with in a niche. Today they are beginning to be largely used civilian airliners as well, in the form of titanium engine pylons or titanium tracks for cabin seats. Further development of titanium applications in industry with the possibility of standardized components is easily foreseeable.

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