US3535159A - Method and apparatus for applying ultrasonic energy to a workpiece - Google Patents

Description

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METHOD AND APPARATUS FOR APPLYING ULTRASONIC ENERGY TO A WORKPIECE Filed Dec. '7. 1967 GENE TRANSDUCER FIG.

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BENJAMIN P- SHIRO BY W a W AT'KORNEYSV a 535,159 METHOD AND APPARATUS FOR APPLYING ULTRASONiC ENERGY TO A WORKPIECE Benjamin P. Sliiro, Pittstord, N.Y., assignor, by mesne ABSTRACT OF THE DISCLOSURE High intensity electric pulses, rather than waves, are applied to a pulse-responsive transducer to propagate positive displacements in liquid containing a workpiece. The pulses are at an ultrasonic rate and each pulse is equal to or less than one-half the interval between commencement of pulses. Such pulse displacements in'the liquid environment of the workpiece are effective at both cleaning and removing metal burrs and can be aided by burr-embrittling material or abrasive material in the liquid. Deburring is accomplished in a plastic container immersed in water, and pulse displacements propagated in the water pass through the plastic wall of the container to the liquid environment of the workpiece.

This invention relates to a method and apparatus for applying ultrasonic energy to a workpiece for deburring, cleaning, polishing, separating parts, etc.

Prior art ultrasonic operations in liquids have used transducers resonant at the desired ultrasonic frequency, and have applied a wave form to such'transducers to produce wave-form displacements in the liquid. Such displacements were usually both positive and negative to produce cavitation which was sought for its effectiveness in cleaning. Abrasives and cleaning solvents have been included in the liquid environment, and such prior-art methods have been fairly effective at many cleaning tasks. However, stubborn cleaning jobs and deburring of metal parts have resisted such methods.

The objects of this invention include, without limitation:

(a)" Deburring metal parts ultrasonically;

(b) Accomplishing stubborn cleaning tasks ultrasonically;

(c) Separating parts ultrasonically;

(d) Polishing and finishing workpieces ultrasonically; and

(e) Accomplishing cleaning, deburring, polishing, find ishing, and part separation more rapidly, efiiciently, and effectively than by prior art methods.

These and other objects of the invention will be apparent hereinafter from the specification which describes the invention, its uses, operation, and preferred embodiments, from the drawings, which constitute a part of the disclosure, and from the subject matter claimed.

Generally, the inventive method comprises switching a source of DC potential to generate high-intensity electric pulses at a rate of 20,000 or more pulses per second with the duty time for each pulse being equal to or less than one-half the pulse period, and applying such pulses to a pulse-responsive transducer in communications with a liquid material containing the workpiece to propagate high intensity, positive displacements in the liquid in the region of the workpiece. Burr-embrittling material, wetting agents, detergents, and abrasives can be added to the liquid material, the workpiece can be tumbled in the liquid material, and the total time for subjecting the workpiece to the energization is preferably limited. The inventive apparatus generally comprises a container for holding a workpiece and liquid material, a pulse generator, and a States Patent "ice 3,535,159 Patented Oct. 20, 1970 pulse-responsive transducer having a substantially flat response throughout a broad ultrasonic range and arranged in communication with the container for propagating highintensity positive displacements in the liquid material. Preferably the container is plastic walled and immersed in liquid in a tank with the transducer communicating with the tank liquid to transmit the displacements through the plastic wall to the liquid material in the container.

In the drawings:

FIG. 1 is a partially schematic elevational view of apparatus according to the invention; and

FIG. 2 is a schematic diagram of electric pulses used in the inventive method and apparatus.

Generator 10. shown schematically in FIG. 1, produces electrical output pulses such as shown in FIG. 2. Essentially, generator 10 comprises a device for switching a high-voltage DC on and off rapidly to produce pulses. Several known devices can accomplish such switching, and they include blocking oscillators, multiv-ibrators, flip-flops, tunnel-diodes, and others. A suitable switching device must act rapidly and switch completely and substantially instantly to produce substantially square pulses. Preferably, the switching device in generator 10 can adjust the pulse rate and the pulse duration or pulse duty time as desired. A blocking oscillator is preferred for the invention.

The pulses ll output from generator 10 are each substantially square as illustrated in FIG. 2 with a sharp rise 12 from zero voltage to a slight ovcrtravcl peak 13 above a high and intense voltage level E, a sharp drop or fall 14 to zero voltage (with a slight overtravel), and quiescense until the next rise 12. The interval or duty-time T of each pulse is equal to or less than one-half the period P between the commencement or rise 12 of each successive pulse. Thus the pulse duty time is equal to or less than one-half the total output time.

Relatively high voltages are preferred for pulses 11,'

depending upon the work to be accomplished. Lower voltages can accomplish some cleaning tasks, but deburring, stubborn dirt, or other more difficult work requires higher voltages. In prior art ultrasonic wave methods, voltages were practically limited to the power required to produce optimum cavitation which was relied upon to do the work. However, in the inventive method, cavitation is avoided, and substantially higher voltages are used. Thus, operating voltages between 600 and 2,500 volts are customarily used, in the inventive method, and voltages near the upper end of such a range are practical and feasible.

Pulses 11 are preferably produced at a rate of 20,000 or more pulses per second so as to stay above the audio range. Prior art wavc-produced-cavitation methods rarely used higher frequencies, but extremely high pulse rates, even above 100,000 pulses per second, are possible and useful in the inventive method.

Pulses 11 are applied to transducer 15 which moves mechanically in rcsponse to the pulses. Several generally known devices can be made pulse-responsive to serve as transducer 15, and these include crystals, piezoelectrics, electrostrictive and magnetostrictive devices, and others. Transducer 15 must move rapidly in substantial correlation with pulses ii for a sharp mechanical motion in one direction on rise 12 and a quick return to a rest position of fall 14.

Transducers that are wave responsive for prior art ultrasonic equipment are tuned to resonate at an ultrasonic frequency at which the equipment is designed to operate. This produces maximum movement for a wave signal applied at the resonant frequency. The more intense pulses 11 according to the invention are used to drive transducer 15 at a rate differing from its resonant frequency. Preferably transducer 15 is constructed to resonate at a pulse-per-sccond rate substantially below 3 the pulse rate at which the equipment is intended to operate, and transducer is tuned for a flat response throughout a pulse range in which it is to be driven. For example, transducer 15 can be tuned for a fiat response throughout an operating range of 20,000 pulses per second to 40,000 pulses per second, and with such tuning might resonate to pulses near rates of 10,000 to 12,000 pulses per second. Such a transducer would not be driven near its resonant period but would be operated over its flat response range according to the invention. Of course, transducers can be tuned for flat responses in other ranges such. as 40,000 pulses per second to 60,000 pulses per second, 60,000 pulses per second to 100,000 pulses per second, or any other desired range, depending upon the work to be done by the pulses.

Transducer 15 is in communication with liquid 17 in tank 16, and as shown in FIG. 1, transducer 15 is arranged on the bottom of tank 16. Transducer 15 can also be arranged on the sides of tank 16, or can be a portable unit immersed in tank 16 in any convenient position. Transducer 15 is arranged to move toward liquid 17 with the rise 12 of each pulse 11 to produce successive, intense, positive displacements in liquid 17. Thus, transducer 15 gives liquid 17 rapid, hammerlike blows in response to pulses 11, and such displacements are propagated rapidly through liquid 17.

Some work can be accomplished directly in liquid 17. For example, for some cleaning operations, preferably a wetting agent and a cleaning agent can be added to liquid 17 and workpieces can be disposed in liquid 17 to receive the displacements produced by transducer 15. An open basket or tumbling device can contain a number of workpieces for such operations. For another example, the separation of stuck together parts, such as lenses adhered to a lens block, can be accomplished directly in liquid 17.

The operation illustrated in FIG. 1 is the deburring of metal parts, and this is an important achievement of the inventive method. For deburring, a container 18 preferably formed of relatively hard plastic material is immersed in liquid 17. Container 18 holds liquid material 19 and workpieces 20 which schematically illustrate metal parts that have been machined or worked so as to produce burrs requiring removal. Ultrasonic removal of such burrs has been sought for years with prior art equipment, but with relatively little success. Burrs are readily removed from workpieces 20 by the inventive method, however.

High intensity positive displacements produced in liquid 17 by transducer 15 are readily transmitted through plastic wall 18 and through liquid material 19 to impinge on workpieces 20.

Both liquid 17 and liquid material 19 preferably contain a wetting agent for better contact and coupling respectively with container 18 and workpieces 20. This facilitates transmission of pulse displacement energy from transducer 15 to workpieces 20.

Plastic container 18 ispreferred for deburring operations which would eventually erode a metal container. Since pulse displacements effectively pass through the walls of container 18, transducer 15 can be located outside container 18 and coupled to container 18 through liquid 17.

All the physical effects of the inventive liquid pulse displacements on burrs on workpieces 20 are not fully understood, but it is known that such displacements are effective at removing burrs that resist all known prior art ultrasonic methods. The following is a partial explanation of the believed effects of liquid pulse displacements on metal burrs, but the invention is not limited to such explanation.

The liquid pulse displacements cause sharp and intense pressures in liquid material 19, and are believed to flex slightly the burrs on workpieces 20 until such burrs are fatigued and snap off. Rath g r than cavitation relied on in ultrasonic cleaning by prior art standing wave equipment pulse displacements according to the inventive method impinge upon the burrs of workpieces 20 directly through an unbroken liquid coupling to exert a large and effective force on such burrs. Also, the inventive liquid pulse displacements are believed to heat the burrs considerably. Such pulses generally warm the liquid in which they are generated so that cooling must be used to maintain desired operating temperatures in continued operation. Pulse displacements also heat workpieces 20 on which they impinge. The main bodies of workpieces 20 dissipate such heat evenly throughout their masses, but burrs, which are thin metal shavings having thin connections to the main bodies of workpieces 20, cannot so well dissipate the heat received from pulse displacements and grow quite hot. Such heating combined with flexing force from the mechanical impingement of pulse displacements on the burrs of workpieces 20 operates to fatigue and break away such burrs.

Deburring operations using the inventive method can be enhanced or speeded up; by adding an embrittling material, an abrasive, or both to liquid material 19.

A variety of materials are known to embrittle various metals. Embrittlement is generally accomplished by atoms of foreign material entering the crystal lattice structure of the metal. For ferrous metals, hydrogen atoms readily effect embrittlement, and for aluminum and copper base metals, oxygen atoms readily effect embrittlement. Thus, embrittling material for ferrous metals preferably produces hydrogen atoms in liquid material 19 near the metal, and embrittling material for aluminum or copper base metals preferably produces oxygen atoms in liquid material 19 near the metal.

An example of embrittling material suitable for ferrous workpieces is a one-to-ten percent slurry of acid embrittling agent in water with the embrittling agent formed of nitric acid, hydrochloric acid and phosphoric acid. Such a slurry also preferably includes a wetting agent, a detergent, and an oxidation inhibitor in small proportions. Aluminum workpieces are preferably embrittled in a one-to-ten percent slurry of acid embrittling agent in water with the embrittling agent formed of hydrofloric acid, phosphoric acid, and glacial acetic acid. Such a slurry also preferably includes a detergent, and a wetting agent. Copper-base burrs are preferably embrittled in a one-to-ten percent slurry of sulfur dioxide and water, with trisodium phosphate preferred as the wetting agent and chromic acid preferably added in a small proportion.

Many other embrittling slurries are usable in the inventive method, and embrittling slurries are preferably adjusted to the particular alloy of workpieces 20. Those skilled in the metallurgical arts will be able to select a suitable embrittlement slurry for any particular workpiece Without undo experimentation.

Generally, it is preferred that the main bodies of workpieces 20 not be embrittled during dcburring operations. Since-embrittlement depends upon the concentration of embrittling material and the temperatures of the metal and the liquid environment, these parameters are kept low enough undcr operating conditions to insure that workpiece body surfaces are not generally embrittled. Thus, liquid material 19 is preferably maintained in it relatively low temperature range between and 200 F., and the concentration of embrittling material is made insufficient to embrittle the body surfaces of workpieces 20 at such temperatures. Furthermore, the temperature of liquid material 19 and the concentration of embrittling material are kept low enough so that the body surfaces of workpieces 20 are not embrittled even when heated somewhat under the attack of pulse displacements. However, as previously described, thin burrs extending from the bodies of workpieces 20 are hcatcd to higher tcmperalures by the pulse displacements. and at such elevated temperatures are substantially embrittled by the embrittling material and are more easily broken off by the pulse displacements. Thus, higher burr temperatures allow burr embrittlement while the main body surfaces of workpieces 20 are spared any embrittlement.

Suitable abrasive materials can also be added to liquid material 19, and such materials include ground, powdered, or beaded glass, diamond dust, carborundum, aluminum oxide, and other known abrasives. Fine particles of such abrasive materials are suspended in liquid material 19 and are driven against workpiece 20 by the inventive pulse displacements. Abrasives generally attack all the body surfaces of workpieces 20 and would erode such surfaces if the process were continued for too long a time. At the same time, such abrasives attack the relatively weak connection of the burr to the main body of workpieces 20 and facilitate the breaking off of the burrs.

Abrasive materials in liquid material 19 also aid in cleaning and polishing of workpieces 20, and when used in proper proportion for an operation that is properly timcdfwill polish. clean. and finish workpieces 20 while they facilitate burr removal.

Generally, since burr removal by the inventive method constitutes a relatively strong attack on workpieces 20, it must be carefully timed and cannot be continued indefinitely like prior art ultrasonic cleaning operations. Each deburring operation according to the invention requires some experimentation to reach an optimum balance of parameters. Thus, the temperature of liquid material 19 can be raised for a generally faster operation, the height and rate of the pulse displacements can be increased depending on the metal of the workpieces and the speeds desired, abrasive concentration can be reduced or increased and abrasive particle size changed, the pulse duty time can be varied, and the process can be continued for different lengths of time. Since overall time is generally of greater commercial significance than the other parameters, and optimum deburring operation is preferably adjusted to accomplish deburring in three to five minutes by adjusting the other parameters. Faster deburring is possible with the inventive method, but small errors in timing become more costly as speed is in-, creased.

Continuous and automated deburring operations can be accomplished faster than those requiring an operator's manual intervention, and such automatic processes are possible within the spirit of the invention. Driven and timed equipment can be arranged for introducing workpieces 20 after deburring. The temperature of liquid material 19 can be easily maintained automatically, and the concentration of embrittling material and abrasive material can also be monitored and adjusted by known equipment.

The inventive method also preferably includes ultrasonic cleaning and rinsing of workpieces 20. before and after deburring. Also, tumbling or stirring of workpieces 20 facilitates their cleaning and deburring and can be incorporated into any stage of the method.

Apparatus according to the invention has been generally described above in reference to the inventive method. In addition, tank 16 is formed of any convenient size, shape, and material, and preferably of steel. Liquid 17 is preferably water including a wetting agent. Also, tem perature control to keep liquid material 19 at the desired operating temperature is preferably accomplished through liquid 17. Plastic container 18 is preferably formed of a relatively hard and dense plastic material. Such materials successfully transmit pulse displacements to liquid material 19 and do not substantially erode during deburring or other operations.

Tumbling and other workpiece-holding devices are generally well known and can be employed as desired at any stage of the inventive method. A variety of transducer materials can be used to construct transducer 15, provided such materials are tuned for a flat response to pulses as described above. Also, those skilled in the electric pulse 6 art can build generator 10 in a variety of ways to provide the pulses ll]. shown in FIG. 2.

Thus, it can be seen that the inventive method and apparatus accomplishes the above-described objects in providing a more eiiicient and more effective means for applying ultrasonic energy to a workpiece. Such improvement allows effective deburring of metal parts that has eluded prior art methods. Other features, advantages andother specific embodiments of this invention will be apparent to those exercising ordinary skill in the pertinent art after considering the foregoing disclosure. In this regard, while specific preferred embodiments have been described in detail, such disclosure is intended as illustrative, rather than limiting, and other embodiments, variations, and modifications can be effected within the spirit and scope of the invention as disclosed and claimed. Furthermore, the following claimed subject matter is intended to cover fully all the aspects of the disclosed invention that are unobvious over prior art, including all equivalent embodiments.

I claim:

1. A method of applying ultrasonic energy to a workpiece immersed in liquid material, said method comprising:

(a) switching a DC potential to generate high intensity electric pulses;

(1) said pulses being at a rate of 20,000 or more pulses per second; and (2) the duration of each pulse being equal to or less than one-half the interval between commencernent of successive pulses;

(b) applying said pulses to a transducer that moves in substantial correlation with said pulses; and

(c) arranging said transducer in communication with said liquid material to produce high intensity positive displacements in said liquid material in the region 0 said workpiece.

2. The method of claim 1 including limiting the total time for subjecting said workpiece to said displacements.

3. The method of claim ll including tumbling said workpiece in said liquid material.

t. The method of claim ll wherein said liquid material includes a wetting agent.

5. The method of claim ll wherein said liquid material includcs a detergent.

6. The method of claim 1 including holding said workpiece and said liquid material in a container formed of plastic material.

7. The method of claim 6 including immersing said container in water, and arranging said transducer in communication with said water to produce said high intensity, positive displacements in said water for transmission through said plastic material and said liquid material.

8. The method of claim 7 wherein said water includes a wetting agent. i

9. The method of claim 1 wherein said workpiece comprises a metal part having a burr, said liquid material includes means for embrittling said burr, and including limiting the total time for subjecting said workpiece to said displacements.

10. The method of claim 9 including holding said work- I piece and said liquid material in a container formed of plastic material, immersing said container in water, and arranging said transducer in communication with said water to produce said high intensity, positive displacements in said water for transmission through said plastic material and said liquid material.

ll. The method of claim 10 wherein said liquid mate rial and said water each include a wetting agent.

12. The method of claim 10 wherein said liquid material includes abrasive material.

13. The method of claim 10 including ultrasonically cleaning said workpiece.

l4. Themethod of claim 10 including maintaining said liquid material between and 200 F., and tumbling said workpiece in said liquid material.

15. The method of claim 1 wherein said workpiece comprises a metal part having a burr.

16. The method of claim 15 wherein said liquid material includes abrasive material.

17. The method of claim 15 including ultrasonically cleaning said workpiece.

18. The method of claim 15 wherein said liquid material includes material for embrittling said burr.

19. The method of claim 18 including maintaining said liquid material between 100 and 200 F.

20. The method of claim 18 wherein said embrittling material etfects hydrogen embrittling of said burr.

21. The'method of claim 18 wherein said embrittling material effects oxygen embrittling of said burr.

References Cited UNITED STATES PATENTS MORRIS O. WOLK, Primary Examiner D. G. MILLMAN, Assistant Examiner US. Cl. X.R.

Disclaimer and Dedication 3,535,159.--Benjamin P. Shim, Pittsford, NY. METHOD AND APPARA- TUS FOR APPLYING ULTRASONIC ENERGY TO A WORK- PIECE. Patent dated Oct. 20, 1970. Disclaimer and dedication filed Nov. 30, 1973, by the assignee, Bramon Instruments, Incowporated. Hereby disclaims and dedicates to the Public the remaining term of said patent.

[Official Gazette M arch 12, 1 974.]

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