Ultrasonics – Deburring – Fact or Fantasy?

Over the years I have had many hundred people approach me with potential applications for ultrasonic deburring.  There are many references to ultrasonic deburring in the literature going back decades in time so it’s not unlikely for the question to be asked.  In fact, ultrasonic deburring may have limited application but requires certain very special circumstances in order to have even a hope of success.  To my knowledge there are only a handful of successful, (purely ultrasonic) applications for deburring in regular use today.

A “burr” is usually defined as a thin sliver of metal or other malleable material that has been partially but not completely separated from a parent piece of metal by a cutting process utilizing a lathe, milling machine, drill, router, or any number of other machining operations.  The fact is that if the burr is completely removed by the cutting process it is not known as a burr.  A piece that is fully removed is a “chip” which is quite a different thing.  A burr, therefore, is defined as an unwanted piece of material that is partially but not totally severed from the parent workpiece.  The success of any deburring process is dependent on just how robust the remaining attachment is.

The removal of any burr requires that the remaining attachment between it and the parent material be somehow broken or removed.  Some burrs, notably those of materials that are susceptible to fatigue fracture, can be removed by repeatedly bending the connecting link to the parent until it fractures due to fatigue.  The rational for the possibility of success for ultrasonic deburring is usually based on the fact that the implosion of cavitation bubbles will cause repleted bending until the burr breaks free.  In fact, this would only be a haphazard occurrence and, although it could happen, is not something that can be relied on in the real world.  Sort of like if the stars are properly aligned and . . . . . . . (you know what I mean).

The one hope for the application of ultrasonic energy to a deburring process would be as an assist to a chemical deburring process.  In chemical deburring, a chemical is used that will dissolve the parent metal.  The assumption is that if the dissolution process is uniform on all surfaces, any thin piece of parent metal (like that holding a burr in place) will be totally dissolved before significant dissolution is present over the entire surface area of the remaining part.  Ultrasonics may and will in many instances speed up the process of the dissolving chemistry by constantly agitating the chemistry in contact with the bridge holding the burr in place.  The foible in this plan, of course, is where does deburring stop and part damage begin.  If all burrs were uniform and all connecting bridges were of the same physical dimensions it would be very simple to expose the part being deburred to the combination of chemistry and ultrasonic energy that had been pre-determined to dissolve the connecting bridge.  Unfortunately, this is not the real world.  Burrs are, if for no other reason than the fact that they are in a sense “accidents” anyway, not predictably uniform.

Are there successful applications of deburring using ultrasonics to assist a chemical? Yes, there are! Most are done on a very small parts. Stents (small devices implanted in human blood vessels to prevent them from collapsing) are typically cleaned and “deburred” using ultrasonics in combination with a chemical. In this application, a strict inspection protocol is applied both during and after deburring.

In summary, the application of ultrasonics to deburring should be approached very carefully and with adequate testing to verify that the desired result will be achieved.  Also, any study of deburring using chemistry and ultrasonics is extremely difficult to scale from the laboratory test bench to something of practical size.  Tests using full sized loads should be performed before any conclusions are drawn.  This is not a process that can be successfully applied by simply controlling process parameters like time, temperature and chemistry.

–  FJF  –