27-08-2014, 01:02 PM
Advanced Machining Processes
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Nontraditional Processes Defined
A group of processes that remove excess material by various techniques involving mechanical, thermal, electrical, or chemical energy (or combinations of these energies)
They do not use a sharp cutting tool in the conventional sense
Developed since World War II in response to new and unusual machining requirements that could not be satisfied by conventional methods
Importance of Nontraditional Processes
Need to machine newly developed metals and non‑metals with special properties that make them difficult or impossible to machine by conventional methods
Need for unusual and/or complex part geometries that cannot readily be accomplished by conventional machining
Need to avoid surface damage that often accompanies conventional machining
Ultrasonic Machining (USM)
Abrasives contained in a slurry are driven at high velocity against work by a tool vibrating at low amplitude and high frequency
Tool oscillation is perpendicular to work surface
Abrasives accomplish material removal
Tool is fed slowly into work
Shape of tool is formed into part
USM Applications
Hard, brittle work materials such as ceramics, glass, and carbides
Also successful on certain metals, such as stainless steel and titanium
Shapes include non-round holes, holes along a curved axis
“Coining operations” - pattern on tool is imparted to a flat work surface
WJC Advantages
No crushing or burning of work surface
Minimum material loss
No environmental pollution
Ease of automation
EDM Applications
Tooling for many mechanical processes: molds for plastic injection molding, extrusion dies, wire drawing dies, forging and heading dies, and sheetmetal stamping dies
Production parts: delicate parts not rigid enough to withstand conventional cutting forces, hole drilling where hole axis is at an acute angle to surface, and machining of hard and exotic metals
Air Carbon Arc Cutting
Arc is generated between a carbon electrode and metallic work, and high‑velocity air jet blows away melted portion of metal
Can be used to form a kerf to sever a piece, or to gouge a cavity to prepare edges of plates for welding
Work materials: cast iron, carbon steel, alloy steels, and various nonferrous alloys
Spattering of molten metal is a hazard and a disadvantage