Tooling tackles titanium

Titanium provides unmatched mechanical properties to aircraft design and manufacturing, such as relatively light weight structure, with a remarkable stiffness, strength, heat and fatigue resistance.

Titanium components have twice the elasticity as steel parts, which make them ideal for applications that require flexible components that won't crack or disintegrate under extreme forces. Titanium components also resist corrosion better than those manufactured from stainless steels. In addition, like steel, titanium offers manufacturing flexibility due to its ability to be cast or forged into various shapes.

Titanium alloy types are structured as: Alpha alloy – addition of alumina, oxide and/or nitride; Beta alloys - addition of molybdenum, ferrite, vanadium, chromium and/or magnesium for a combination of α + β alloys – the majority of titanium alloys including Ti-6Al-4V and Ti5553.

The titanium alloy 5553 (Ti-5Al-5V-5Mo-3Cr) is a near-beta alloy developed with the intention to replace the popular standard Ti-6Al-4V, particularly for highly loaded forged parts such as flap tracks and pylon or landing gear applications.

The Ti5553 exhibits excellent hardenability characteristics with superior strength, combined with high fracture toughness and excellent high cycle fatigue behaviour properties when compared to the standard Ti-6Al-4V.

Titanium is clearly identified as a poor heat conductor, where only 25% of the heat is transferred to the chip (a third of the amount compared to steel), thus creating a greater heat concentration on the cutting edge of the tool interfacing with the workpiece. Another issue is the low modulus of elasticity exhibited by the titanium, which leads to a ‘springiness' characteristic whereby titanium parts may move under the force of the cutting edge, and then spring back. This condition can lead to excess heat generation and tool chipping.

Iscar, in association with a European aerospace manufacturer of large structural parts has developed a family of tools specifically designed as a solution for machining Ti5553 applications, running at competitive speeds, feed rates and depths of cut. Iscar claims that the advantage of using its solution is expressed in terms of higher productivity due to positive geometry, advanced coating technology and novel chipformer design. The helix design and radial geometry produces the most suitable sheering mechanism for this material, leading to a reduction in cutting forces, pressure and generated heat.

Based on this technology, roughing operations can be performed using large diameter fine pitch configuration milling cutters, removing large volumes of material in the form of thick and narrow chips. This can be achieved by using specially designed extended flute milling cutters, equipped with HELITANG and HELIDO inserts. Conversely, the finishing operation removes small amounts of material with short thin chip shapes.

For enhanced finishing performances, Iscar recommends the FINISHRED and the CHATTERFREE, which provide smooth machining operation of Ti5553 with the benefits of vibration reduction and shock absorption.

In line with the Ti5553 deficiency, as far as the thermal conductivity nature is concerned, the newly developed Iscar tools utilise heat resistant solid carbide inserts or end mill cutters, coupled with effective internal coolant, or even high pressure coolant.

Furthermore, to combat the modulus of elasticity, Iscar's solution relies heavily on proper tool geometry, with an emphasis on primary and secondary relief angles and helix angle, as well as special designed edge preparation.

Finally, Iscar PVD coating technology plays a significant role when machining Ti5553, by adding adequate wear resistant and low friction characteristics to the cutting process, but most of all enhancing the performances of cutting tools by using the coating as a heat barrier and thus providing thermal stability.

An additional advantage of the coating results from the SUMOTEC coating process which further enhances the tool performance by lowering friction, enabling trouble-free and smooth chip flow, and significantly reducing the generated heat.

www.iscar.co.uk