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News

Machining process removes burrs and flashing without affecting adjoining workpart surfaces

Kennametal : 26 April, 2011  (Technical Article)
The Thermal Energy Method (TEM) is a rapid, low cost, high production process that has the unique ability to remove burrs and flashing without affecting adjoining workpart surfaces. Depending on workpart size, a million or more parts can be processed a month in a single TEM machine.
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.

The patented Thermal Energy Method (TEM) uses intense heat for deburring and/or deflashing. Parts to be processed are sealed in a pressurized cylindrical bell chamber with a mixture of a combustible gas and oxygen. This mixture completely envelopes the workpart’s burrs and flash, regardless of their internal or external location. The gas mixture, ignited by a spark plug, creates an intense, rapid burst of heat. Burrs and flash, because of their high ratio of surface area to mass, quickly raise to a temperature well above their auto-ignition point and burst into flames.

Excess oxygen in the chamber combines with the vaporizing burrs to produce an oxide powder. As the oxidizing burr reaches the main body of the workpart, the temperature drops rapidly and stops the process. The oxidation is of very short duration; long enough to transform burrs and flash into oxide powder but not long enough to change workpart dimensions or metallurgy.

Oxidized powder from the burrs is redistributed over the workpart and containment chamber which can be cleaned away, if necessary, with virtually any Aqueous (water-based) cleaning solution.
In summary, TEM is a rapid, low cost, high production process that has the unique ability to remove burrs and flashing without affecting adjoining workpart surfaces. Depending on workpart size, a million or more parts can be processed a month in a single TEM machine.

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.

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 6,000F(3316C). The explosion lasts only milliseconds and the entire load-to-load cycle time is on the order of half a minute.

A problem that the inventors of the 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 gases.

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.
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