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Tuesday, July 29, 2014

Innovative Techniques for Titanium Aerospace Applications

EBDM

Sciaky’s additive manufacturing technique, electron beam direct manufacturing (EBDM), deposits titanium and other metals and alloys layer by layer to create components. Credit: Sciaky

Commercial and defense aerospace manufacturers are facing market challenges but continuing to develop innovative production methods and technology. The increasing demand for fuel-efficient aircraft and innovations in sensitive communications and surveillance technology like unmanned drones have provoked the development of such techniques that meet the technical needs of these markets.

Defense spending is down in the United States, following a White House reshuffle of defense priorities and the ongoing fallout from sequestration. According to Deloitte, 2013 will mark the third consecutive year of aerospace and defense spending cuts. Amid tighter budgets and cost control, now is a good time for a wide variety of cutting-edge techniques to drive efficiency in aerospace manufacturing. From additive techniques to new twists on subtractive methods, a common denominator is the manipulation of titanium, the hard, corrosion-resistant metal with a high strength-to-weight ratio ideally suited for many aerospace vehicle applications.

Chicago-based Sciaky has developed a version of electron beam direct manufacturing (EBDM), a method of focusing an electron beam on a metal or alloy wire to melt it into a controlled shape. The wire is melted layer by layer within a vacuum chamber with a build volume of 19 by 4 by ft, which is one of the biggest additive manufacturing volumes available. The EBDM process can print complex shapes like 3-D printers, but it works with metal media, including titanium and tantalum and alloys like stainless steel and Inconel, and is suited for large parts.

The technology, which was developed over the course of a decade, cuts die costs and reduces finishing costs. Scott Stecker, chief engineer of direct manufacturing for Sciaky, told IMT Machining Journal that the cost and time savings vary on a part-by-part basis, but some of the reductions via EBDM can be dramatic. “Customers have told me that it can take a year to 18 months to get a forging, while we can set up the titanium plate and wire and turn around a part in six weeks,” Stecker says.

In the video below, Sciaky demonstrates EBDM in producing aerospace components.

 

Machine tool manufacturer MAG, which recently announced the sale of its Americas division to French conglomerate Fives, has developed cryogenic machining techniques for several years to help prolong tool life and avoid issues related to tool coolants. Once coolant fluids have been used, they can be cleaned and recycled a limited number of times, requiring the manufacturer to invest in a new stock of fluid as well as properly and safely dispose of the used coolant, both of which can be expensive. Additionally, coolant cannot consistently reduce thermal wear, which results in tools wearing out faster.

Cryogenic machining replaces the need for coolant fluid with a nozzle of liquid nitrogen spray directed at the tool area. The liquid nitrogen, which is about -321°F, can dramatically cool the tool during operation, extending its life by as much as 80 percent compared to other forms of cooling, according to Aerospace Manufacturing and Design. The liquid nitrogen is superior to other cooling media that may be flammable or cause environmental concerns due to their chemical properties.

MAG Vice President of Cryogenic Business Development Michael Judge highlighted the cost savings and green elements of cryogenic machining during the 2011 imX show in Las Vegas for the Society of Manufacturing Engineers. Said Judge: “In addition to the increases it brings in metal removal rates and tool life, low-flow cryogenic machining is a green manufacturing process that will produce a cascade of additional cost reductions by eliminating, or vastly minimizing, the use of liquid coolants. Liquid nitrogen is a non-greenhouse gas, so it is harmless to the environment, too.”

Because cryo-cooling methods can work with titanium machining, cryogenic machining has been popular in aerospace manufacturing, including for the production of defense aircraft like Lockheed Martin’s F-35 Lightning II stealth fighter, which is roughly 25 percent titanium.

The video below shows cryogenic machining in action.

Trochoidal milling is a method of machining hard metals that “peels” layers of material away using a coated carbide tool that spins on a standard spindle while the entire toolpath is rotated in a circle (see the video below for an illustration of this movement). This way, the tool is only briefly in contact with the workpiece, and the tool approaches in an arc.

This circular motion, or trochoid, presents many benefits in machining hard metals like titanium. Because of the tool’s arc approach, there is less pressure on the tool than during a direct approach, which in turn generates less heat. Both of these factors reduce the strain on a tool, preserving its life over time. Additionally, trochoidal milling can handle high feed rates and is particularly suited for machining deep, low-width cuts.

Also known as “spiral” or “peel” milling, trochoidal milling is capable of machining titanium for aerospace parts, but because of its relative novelty and specialization, not all conventional CNC software is capable of running it.

Brian Lane

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