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Advanced Materials Always on the Edge

 Ellen Kehoe

 

 

 

 

 

 

By Ellen Kehoe
Senior Editor

As materials discoveries have advanced, techniques have evolved “to accelerate the transition from materials processing in a laboratory environment to fabrication techniques in a full scale production environment” and to show how “the advent of new materials and advances in the design of mechanical and electrical components are inextricably linked.” The paper stating this describes a knowledge-based approach to hot isostatic pressing.

The more well-known so-called advanced materials are titanium, tungsten and magnesium and their alloys, but there are many more elements represented in the rich lode of knowledge contained in the SME Tech Paper library. We’ll discuss the above “big three” in this article, and then pick up other tantalizing topics (such as tantalum, beryllium or—everyone’s spelling stumble—molybdenum) in another item.

 

Titanium

In the early 1950s, none other than Kennametal Inc.’s chief engineer describes the promising titanium carbide compositions suitable for use in “rocket and jet engine components for ever increasing operating temperatures” as well as for cutting tools, dies, jigs and fixtures. Another paper explains what is known about machining titanium: the physical characteristics of titanium place it in a category of its own, and “the procedures and techniques for common metals are not applicable to titanium.”

Underscoring the importance of titanium to the aerospace industry’s growth, two 1960s papers by Lockheed authors, including 1981-82 SME president Robert L. Vaughn, cover high-speed milling and electrochemical machining of Ti alloys. McDonnell Douglas authors discuss a unique manufacturing system used on high-reliability flight-weight titanium alloy pressure vessels. Later, several papers from Edward F. Rossman of The Boeing Company present parameters for machining difficult features in titanium for the F-22 Raptor, collected thoughts on high-speed machining and breakthroughs in rough machining of Ti.

The never-ending challenge of improving material removal processes for titanium is addressed in many papers from SME’s grinding and manufacturing research conferences. In the results of one paper, medium-tough diamond-type abrasives are found to grind titanium alloys more efficiently than CBN or silicon carbide. Machining performance is investigated during milling of titanium alloy using directed through-spindle coolant, and infrared-based measurements and analysis of cutting tool temperatures are performed for orthogonal cutting of alloyed titanium.

As composite materials have emerged, the machining characteristics of titanium metal matrix composite and titanium/graphite hybrid composite are examined. Drawing of titanium is discussed through case histories of hot deep drawing, hot rubber pad work, hot spinning and hot stretch forming. Extrusion of titanium alloys and steel by the glass process provides the means to produce previously difficult metallic forms and shapes.

 

Tops for Tools

Cemented titanium carbide and titanium carbide coated cutting tools are compared, reviewed and analyzed in great detail in multiple papers. “Most claims have been borne out in tests and production operations” for turning, milling, threading and grooving, and the materials have “become an important commercial factor.” A series of tests on the performance of various tungsten and titanium carbide cutting tools on several grades of steel is explained in charts of speeds, feeds, materials and tool angles.


Tungsten

The Sandvik ejector drill helped the utilization of tungsten carbide in drilling tools for even more efficiency and economy than obtained with cemented carbide tools. Micrograin tungsten carbides proved to have extraordinary long tool life at lower cutting speeds.

The effect of cryogenic treatments on tungsten carbide tool life is analyzed through microstructural alterations within the eta, gamma and alpha phases. Four turning tool types are studied for tool life as well as the combined influence of the phases.

 

Difficult Machining

Processing brittle tungsten carbide itself, for applications in automotive, electronics and aerospace, has challenges. Early attempts at electrochemical machining of sintered tungsten carbide alloys with DC in NaCl solutions caused tungsten carbide to change to tungsten oxide, stopping the material removal process.

Investigations such as nanometer scale ductile cutting and the effect of tool inclination on machining helped reveal important new technologies to meet industry demands. Ductile cutting at very small depth of cut characterized the process in the context of machining forces, machined surfaces and tool wear. Analysis of actual cutting time and cutting areas on the edges during rotation of a ball end mill showed that cutting time decreased with inclination angle.


Magnesium

The earth’s third most plentiful metal, magnesium, has desirable characteristics of light weight, dimensional stability, stiffness, machinability and weldability. One company that used magnesium extensively for many years for radar components recognized its economy for tooling, saying “we use it like lumber.” The lightness of magnesium is attributed to lessen worker fatigue and production accidents, “permit women employees to handle many more tools” and eliminate the use of mechanical devices to store tools.

German researchers present new processing technologies for magnesium superlight alloys, such as magnesium-lithium powder, for precision die forging. These alloys “assume a conspicuous position” in meeting demands for extremely light metal alloys with high specific strengths.

With magnesium’s tendency for built-up edges due to adhesion between the tool and material during dry machining at high cutting speeds, other German researchers examine the success and safety of using tools that are polycrystalline diamond coated by chemical vapor deposition. A successful case study using the Thixomolding (Thixoforming; Longmont, CO) magnesium injection molding process overviews the basic design process, functional requirements, dimensional tolerances and considerations for corrosion resistance and secondary operations.


SME Technical Papers

More than 16,000 papers and presentations make SME’s collection of manufacturing knowledge the largest of its kind. Find papers on best practices, advancements and industry trends. Add your insights to help others Learn More & Do More.


Published Date : 11/19/2014

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