Current machining technology has developed to make just about every conceivable object. Yet, there are still some things that, though they can be made, are difficult to finish. For example: removing burrs at the intersection of two cross-drilled holes. A technology to overcome this machining problem was first conceived in the 1960s. The idea was to use a contained explosion to deburr the parts.
Today the process is known as Thermal Energy Machining, or simply TEM, because despite all of the magnificent machinery available to us, nothing, absolutely nothing, is as cool as an explosion.
TEM is often deployed for parts with complex internal passages where conventional deburring techniques would be difficult or impractical. Some small engine blocks and fluid or gas manifolds are common examples. TEM also has undergone many developments in its 50-year life. The most recent of these developments is a new patent issued April 12, 2011 for a "Gas Regulator for Thermal Energy Machining," which is assigned to Kennametal Inc., the tungsten-carbide cutting tool experts.
Kennametal’s patent describes TEM eloquently:
"The concept behind TEM is elegantly simple: instead of mechanically abrading off burrs and flashing, the burrs and flashing are simply burned away in a fraction of a second. This simple concept is applied in an exciting way: one or more metal or plastic parts requiring deburring or deflashing are sealed inside a combustion chamber and surrounded with a highly pressurized explosive gas mixture which is then ignited by an electric spark. The resulting explosion produces a thermal shock wave that literally burns away (oxidizes) the burrs and flashings from the parts while the relatively great thermal mass of the parts prevents the parts themselves from being damaged by the thermal shock wave. The explosive flame temperature can reach over 6,000°F. (3,316°C.). The explosion lasts only milliseconds and the entire load-to-load cycle time is on the order of half a minute."
Now when I observed nothing is cooler than an explosion it is implied that the explosion is controlled and expected. A problem that the inventors of the new Gas Regulator patent identified was that bringing pressurized fuel-gas like hydrogen and pure oxygen into close proximity to an electrically operated valve that could potentially spark is inherently dangerous. The improvement to this sort of machinery then covered in the patent is a fluid-controlled pressure regulation subsystem.
The pressure regulator's diaphragm that controls the gas-flow valve is mechanically operated by a pneumatic or hydraulic cylinder. It employs a pressure transducer and a digital controller in combination to adjust the feed pressure of the pneumatic or hydraulic cylinder. This eliminates any possibility of an accidental electric spark from unintentionally detonating the gasses.
While it is arguable that this improves safety, the actual likelihood of an inadvertent detonation being a real threat is statistically almost zero. However, an undiscovered problem causing consistent premature detonations within the chamber could result in parts that are not properly finished, resulting in rejections from QC or poor quality parts escaping into production. So, notwithstanding safety, the hydraulic or pneumatically operated system for gas delivery has the inherent additional benefit of a more reliable TEM machine with less maintenance and consistently better finishing results.
Depending on the configuration of a specific TEM machine, gas delivery can be achieved in a couple of different ways. The new pressure regulator system can deliver the active gasses either directly to the combustion chamber or to a mixing block, or indirectly to either of these by way of a fixed-volume dosing device.
Throughput efficiency in a TEM machine is accomplished with a multi-station carousel. This allows an operator to be loading a part in one station while successive stations are closing, filling, detonating, and then opening. Operations take place such that the carousel stops for a few seconds between each indexing of the machine.
Perhaps the next step forward in the evolution of TEM technology will be a continuously moving carousel without indexing stops that will dramatically increase throughput? Only time will tell, but if Buckminster Fuller's concept of ephemeralization (the ability of technology to accomplish “more and more with less and less”) holds true, then logically it is the next evolutionary horizon.
Paul DQ Campbell is an author and technology freelance writer. For more information or to contact Paul visit www.pdqcampbell.com
