Titanium provides highly desirable mechanical properties to aircraft design and manufacturing such as relatively lightweight structure, with excellent rigidity, strength, heat and fatigue resistance. Effectively, titanium parts are stronger than their steel counterparts but weigh half as much.

Titanium components have twice the elasticity of steel parts which makes them ideal for applications that require flexible components that won’t crack or disintegrate under extreme forces. In addition, titanium components also resist corrosion better than those manufactured from stainless steels and 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 alloys – which include the addition of alumina, oxide and/or nitride and Beta alloys which feature the addition of molybdenum, ferrite, vanadium, chromium and/or magnesium. Many titanium alloys are a combination of the two.

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. It 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.

Thermal conductivity

When considering the thermal conductivity characteristics of titanium, it 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. The generated heat results in rapid tool wear – unless the cutting speed is lowered, which has a direct influence on productivity levels.

Modulus of Elasticity

Another important 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.
Work hardening tendency

Forged parts pose challenges with very hard, often non-homogeneous surfaces, resulting in high cutting pressures and excessive heat generation. In fact, a tool that can’t cut through the depth of hardened material will actually accelerate the hardening process. Instead of cutting, an incorrect tool will push against the material thereby straining it and as the material reaches a higher level of hardness, cutting speeds that were appropriate at the start of the cut become excessive resulting also in accelerated tool wear.

Machining solutions for Ti 5553

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 high speeds, feed rates and depths of cut. According to the company, the advantage of using its solution is higher productivity due to positive geometry, advanced coating technology and innovative chip former 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 completed 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 Iscar’s Helitang and Helido inserts. Conversely, the finishing operation removes small amounts of material with short, thin chip shapes.

For enhanced finishing performances, Iscar recommends its Finishred and Chatterfree tools which provide smooth machining operation of Ti5553 with the benefits of vibration reduction and shock absorption.

In line with the Ti5553 deficiency in terms of thermal conductivity characteristics, the newly developed Iscar tools utilise heat resistant, solid carbide inserts or endmill cutters coupled with effective internal coolant, or even high pressure coolant.

Furthermore, to combat the modulus of elasticity, Iscar’s solution relies heavily on precise 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 performance 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 that is said to further enhance the tool performance by lowering friction, enabling trouble free and smooth chip flow, and thus significantly reducing generated heat.

Iscar
www.iscaruk.co.uk