Thermal Energy Deburring
Thermal energy deburring is a commercial process which was
developed to offer industry an alternative to hand deburring.
In the past, hand deburring has cost 10% and sometimes more of
total manufacturing costs. Currently, thermal energy deburring
is the fastest deburring method in existence. The actual deburring
time using the thermal energy method is only a few milliseconds.
The process itself consists of placing manufactured parts
in a thick walled chamber which is sealed and pressurized with
oxygen and natural gas. A common oxygen to natural gas mixture
ratio is 2.5:1. After the chamber is closed, it is sealed with
a toggle mechanism which exerts a force of 250 tons. The combustible
mixture of gas and oxygen then fills the chamber, and is ignited.
The ignitor used in this process is similar to that of a spark
plug, an it produces a 30,000 volt spark. The combustion creates
a temperature climb to over 6000°F in the chamber, and pressures
in excess of 6000psi.
Because metals are all relatively good thermal conductors,
much of the heat wave can be absorbed by the part. Thermal energy
deburring is effective because of the location and geometry of
most burrs found on metal parts. The small mass in comparison
to surface area of burrs slows the conduction of the heat in the
burrs into the part. Because burrs are located on the surface
of the part, they reach very high temperatures, closest to those
of the combustion chamber. These two factors cause the burr to
burst into flames. Thus, the burr becomes a source of fuel, and
will continue to vaporize until the heat moves into the part itself.
This reduction in heat due to conduction into the part will cause
the flame to extinguish itself. By this time, all the burrs which
existed on the part have been vaporized.
During the process of vaporizing, the burrs become oxides.
The type of oxide which forms is dependent on the type of the
material being deburred. The oxide formed settles on the parts
as a loose powdery residue, which causes discoloration of the
parts. However, the surfaces of the parts have not been oxidized,
and the residue can be removed with a suitable cleaner. This cleaning
step can be avoided however, if the parts need to be heat treated
or plated upon completion of the thermal energy deburring. For
those cases when cleaning may be necessary, cleaning equipment
is available from most manufacturers of thermal energy deburring
systems.
One of the best improvements the thermal energy deburring
system has made is the use of gas as the deburring media. Other
deburring processes generally use small abrasive particles which
flow through and around the parts. This process can not guarantee
that all burrs will be removed, especially in hard to reach locations.
On the other hand, the gaseous mixture used in thermal energy
deburring completely encloses the parts, reaching into all confined
areas. Using thermal energy deburring, it is virtually impossible
to miss burrs.
Because thermal energy deburring uses instantaneous and very
intense heat energy, some parts require fixtures to support them
against the shock. If the parts are rather thin, for example,
more mass is needed to absorb the heat energy. If thin parts are
not fixed, deformation due to the intense heat could result. Depending
on the size of the parts, some smaller dense parts can often be
batch processed. When parts must remain scratch free, or if die
cast parts which are not heavily ribbed are being processed, those
parts should be held or supported.
When fixtures are used where needed, thermal energy deburring
will not affect any dimensions, surface finishes, or any physical
properties of the part. This is true, because the actual part
will rarely reach a temperature greater than a few hundred degrees
when the extreme heat is created for only a few milliseconds.
Additionally, threads are also unaffected by the heat because
their wide roots transfer heat quickly.
Thermal energy deburring is effective on most engineering
materials, although it is more suitable for some than others.
As previously mentioned, the burr must absorb heat, reaching a
temperature which is high enough to oxidize it. For materials
with extra high heat transfer coefficients thermal energy deburring
may work, but not without increased difficulty.
Thermal energy deburring is currently being used by a variety
of industries. The die cast industry have been able to use the
thermal energy system not only for deburring, but also for blasting
core sand out of parts, leaving them with a smooth surface. Also,
thermal energy deburring has been used to decore sand castings.
Thermal energy deburring is able to melt binders out of foundry
sand which allows sand to be easily poured out of intricate castings.
Lastly, a form of thermal energy deburring has recently been used
in the plastic industry, and has a bright future.
The cost for thermal energy deburring equipment is high, however
the operational costs are not. The total cost for cycle and maintenance
has been estimated to be about ten cents for one cycle. Therefore,
the operational costs are inexpensive, and if a company wisely
utilizes the use and maintains meaningful operation, the thermal
energy deburring equipment will be profitable.
From a manufacturing perspective, thermal energy deburring
is very attractive because of the many benefits it provides. The
process ensures fixed manufacturing costs with no variances. For
many companies this would help eliminate the costly and time consuming
manual deburring. Above all, thermal energy deburring provides
assurance that all burrs are consistently removed, which provides
increased quality levels and reliability. These are the types
of features that are extremely important in the manufacturing
world.
Sources
Processes and Materials of Manufacture, Second Edition, by
Ron A Lindberg; Allyn and Bacon, Inc. 1977.
Modern Manufacturing Processes, First Edition, by James Brown;
Industrial Press Inc. 1991.