The process used to carry out a thermal deburr is unique. It utilises the extreme difference in mass between the main bulk of the com¬ponent and its burrs, and the inability of small parts to dissipate heat quickly. This in the case of burrs drives their temperature up past their ignition point when they oxidise completely.
The majority of the oxide (gas) is extracted, but a substantial part of the oxide powder (dependant on the mass of burr removed) is deposited on the surface of the component. This can be subsequently removed with a simple washing process. To wash workpieces either a cleaning procedure with a special neutral cleaning agent and supporting ultra-sonic process can be used or e. g. steel workpieces could be washed in a 20% phosphoric acid solution or aluminium parts could be washed in an agent which is usually required for preparing part for the anodi¬zing procedure.
To find out more about the thermal deburr process offered by the Deburring and Finishing Group read on or contact us now.
A thermal deburr is essentially a chemical reaction aided by heat. The heat is generated by combusting fuel gas and oxygen under pressure inside a sealed chamber. The size of the deburring chamber is depending on the type of thermal deburring machine that is used and might have a size Ø250mm and 300mm height. This blast lasts only 20 milliseconds with temperatures reaching between 2,500 and 3,500°C (4532 - 6332°F). The bulk of the heat hitting the surfaces is safely dissipated throughout the component's mass. Aluminium will typically reach 55-60°C (131 – 140°F) whilst steels reach around 150°C (302°F) (due to being fired twice). By the very nature of using a gas as the deburring 'media', no surfaces are scratched; no hole is too small; no burr inaccessible; and, more importantly, no burr, debris or contaminant missed.
Historically the thermal deburr process was first utilised by the hydraulics and die cast industries. Hydraulics liked the focus on - and guarantee of - removing the smallest, most awkward burrs, and those most likely to come off in service. 'If it didn’t come off in the explosion it won’t come off in service' was the thought.
The amount of burr removed is influenced by the amount of heat, the material, and the shape of the burr. Milled burrs from using sharp tools tend to produce an even thickness, thin burr. The process will then oxidise them neatly back to the sharp edge of the component. Burrs resulting from blunt tools result in a certain amount of pushed up displaced material before pro¬ducing the burrs. This shape of burr extends the distance over which the temperature drops. In these cases the thermal deburr process still oxidises the potential loose parts. It then melts back the next section and, depending on its geometry, could possibly leave a raised edge at the root of the burr where the heat safely dissipates into the bulk of the components.
Trials is the easiest way of ascertaining the best heat setting, the optimum component preparations, and the suitable range of burr variation that will be acceptable and repeatedly deburred. Although quite sizeable burrs can be removed, by increasing the heat - eventually the thermal deburr process will start to 'deburr' the largest burrs. They can then melt and fuse to the body; or even explode and splatter (especially aluminium). For this reason any swarf compacted in holes is best removed. And if sizeable flaps are knocked off with a nylon brush, a better, more even, finished result is obtained. Also oil needs to be removed. Excessive oil can cause pre-ignition of the thermal deburr machines. It also has a tendency to utilise the heat when vaporising, causes a black carbon deposit and subsequently reduces the deburring effect.
The heat could also find the ‘weakest’ part of the component. This is usually the thinnest section, which could start to melt back. Cavities and porosity in castings can be revealed. Threads will normally be left intact (unless they are smaller than the burrs!) as there is a mass of material behind the points. The thin lead-in to the thread, however, will be burnt back along with any whiskers on the threads.
Metallurgical effects are minimal. In most cases they are nonexistent. Negligible dimensional change is usually expe¬rienced. Some burr roots could experience hardening to a depth of a few micron, and very thin walled shapes, i.e. tubes or boxes, could distort with the heat and blast. Fixturing eliminates any bounce damage. Heat sinks can also be used to protect delicate features.
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