US3550417A - Process for the cold forming of metal - Google Patents

Description

Dec. 29, 1970 c. McMAsTER 3,550,417

PROCESS FOR THE cow FORMING OF METAL Filed March 14, 1968 3 Sheets-Sheet 1 YNVENTOR. ROBERT C. McMASTER QMQMW ATTORNEY Dec. 29, 1970 R. C. M MASTER PROCESS FOR THE COLD FORMING OF METAL Filed March 14, 1968 \Y \\W\ \\R ski ANDRAL SIZING DIE 3 Sheets-Sheet 2 DIE MANDRAL F! G. 2 d

INVENTOR C. MCMASTER *WAQM ATTORNEY ROBERT R. C. M MASTER PROCESS FOR THE COLD FORMING OF METAL Dec. 29, 1970 3 Sheets-Sheet 3 Filed March 14, 1968 INVENTOR. ROBERT C. McMASTER mmmmkw sssu1s United States Patent "ice PROCESS FOR THE COLD FORMING 0F METAL Robert C. McMaster, Columbus, Ohio, assignor to The Ohio State University, Columbus, Ohio, an institution of higher learning Filed Mar. 14, 1968, Ser. No. 713,036 Int. Cl. B21c 37/00 11.5. CI. 72--57 17 Claims ABSTRACT OF THE DISCLOSURE This invention is a system using sonic power to facilitate the cold rolling and deformation of metals. Sonic vibratory energy introduced into the work material is transmitted through the material causing dynamic stresses in the material. The dynamic stresses enable the material to be cold-formed at static loadings much lower than those necessary in conventional cold-forming operations.

CROSS REFERENCES There is disclosed in patent application, Ser. No. 571,490, now Pat. No. 3,396,285 for Electromechanical Transducer by H. M. Minchenko, a transducer capable of delivering extremely high power, i.e., measurable in horsepower (or kilowatts) at an acoustical frequency range. The principle underlying the high power output is in the structural arrangement of the components immediately associated with the piezoelectric driving elements. In theory and practice, the piezoelectric elements are under radial and axial pressure that assure that they do not operate in tension even under intense sonic action. Significantly, the structural design of this transducer, that permits the extraordinary power output from the driving elements, resides in the novel method of clamping the piezoelectric elements both radially and longitudinally (axially). In this way the acoustic stresses in the piezoelectric elements are always compressive, never tensile, even under maximum voltage excitation.

The transducer disclosed in the aforementioned patent application is intended, and therefore utilized, to deliver a steady-state vibratory power output signal. That is, the piezoelectric assembly is a component of a resonant structure that will produce a mechanical vibratory output at the frequency of the driving electrical signaland vice versa.

BACKGROUND In the sonic and ultransonic metal deformation systems disclosed in the prior art, sonic and ultransonic vibrations are introduced through the rolls, dies, press elements, pierces and other elements commonly used for application of static forces and pressures to the surface of the work materials. In general, such systems were not effective for purposes other than some reduction in friction at the interface with the work material. The effort to vibrate the masses of rolls, dies, and other force application elements required extremely high vibratory forces to overcome the inertial forces (F ma) of these elements. Very high levels of sonic power cannot be introduced into work materials by this means since the vibration lifts the forming element out of contact with the work material unless very high static forces (exceedingthe magnitude of the vibratory force) are superimposed. The latter condition eliminates the minor advantages of reduction of friction. Tools, dies, rolls, and other force application elements of this type tend to fail rapidly in fatigue.

Where longitudinal deformation is desired, and deforming force is applied transversely, as by rolls, dies, etc., the benefits of applying longitudinal vibratory force 3,550,417 Patented Dec. 29, 1970 directly to the work material in the region where deformation is occurring are lost.

SUMMARY OF INVENTION In the system of the present invention the vibratory energy is applied directly to the work material, and need not vibrate any elements of the forming machinery at all. Very high vibratory stress levels (approaching the elastic limit of the work material) can be applied effectively by this process, without any limitations related to the ability of the processing machinery to withstand vibratory forces or accelerations.

The cold rolling and forming systems of the present invention differ radically from prior art. This invention substitutes dynamic force from a sonic motor for a very large portion of the static forces normally required. The vibratory energy from the transducer produces dynamic stresses which approach the elastic limit of the material but do not exceed it. Static force is applied by the rolls whereby the elastic limit is exceeded locally and the material is deformed. In conventional processes metallic materials are deformed by static forces producing static stresses exceeding the elastic limits of the work materials. The role of the static force system in the present process is reduced to that of a control-signal system, and the basic work of metal deformation is done by means of the dynamic vibrational stress waves caused by one or more sonic power transducers. In consequence, it is estimated that the static force requirements could be reduced in ratios of 10:1 to :1 or more, as compared with conventional static force deformation systems.

OBJECTS The present invention has as its principal object a method for cold forming steels, aluminum alloys, titanium alloys, and all other materials possessing a stress-strain curve with an elastic region followed by a region of plastic deformation.

Another object of the invention is to provide a method of cold forming by which the cold forming of the material may be completed in one continuous operation eliminating the necessity for annealing.

Another object of the invention is to eliminate static shear-strain energy stored in the cold worked material so as to reduce or eliminate ruptures and fractures in the work material.

Another object of the invention is to facilitate the cold working of metals and alloys by eliminating the necessity for annealing to restore ductility of the material.

Another object of the invention is to provide a method for working materials not normally considered coldformable.

Another object of the invention is to reduce the weight, size, and cost of machinery required to perform a given forming operation.

Still another object of the invention is to increase the capabilities of existing cold-forming machinery to by ratios of 10:1 to 100:1 or more.

Other objects and features of the present invention will become aparent from a reading of the following detailed description when taken in conjunction with the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic View of a rolling mill for shaping or reducing the cross-section of metals, alloys, and other plastically-deformable materials by cold rolling utilizing dynamic stresses created by vibratory energy transmitted through the work material;

FIG. 2a is a sechematic view of a system for bending metal stook utilizing dynamic stresses created by vibratory-mechanical energy transmitted through the work material; I i w FIG. 2b is a schematic view of a system for piercing billets to make tubes utilizing dynamic stresses created by vibratory-mechanical energy transmitted through the work material;

FIG. 20 is a schematic view of a system for drawing Wire utilizing dynamic stresses created by vibratory-mechanical energy transmitted through the work material;

FIG. 2d is a sechematic view of a system for sizing material using a floating mandral and die in conjunction with dynamic stresses created by vibratory-mechanical energy transmitted through the work material;

FIG. 3a illustrates the sinusoidal dynamic stress wave created by the vibratory energy introduced into the material; the dynamic (sinusoidal) stress waves do not exceed the elastic limits of the material where the energy is efiiciently transmitted through the material;

FIG. 3b illustrates a dynamic (sinusoidal) stress superimposed on a static bias stress (tension) which causes the tension elastic limit to be exceeded once each cycle, causing incremental permanent deformations in the \work material;

FIG. 3c illustrates the same phenomenon illustrated in FIG. 3b except that the static loading here causes a negative (compressive) stress with the superimposed dynamic stress causing the negative elastic limit to be exceeded, causing incremental permanent deformations;

FIG. 4a illustrates a typical stress-strain curve for metals having regions of elastic deformation and plastic deformation; and

FIG. 4b illustrates the progression of incremental deformations with biased sonic stress applications.

DESCRIPTION OF PREFERRED EMBODIMENT In accordance with the general concepts of the present invention the sonic cold forming process of the present invention utilizes sonic stress waves directed longitudinally along the work material where elongation deformation of the work material is desired. Thus, this longitudinal vibratory stress acts to produce elongation deformation directly. More particularly, static forces or pressures applied through rolls, press 'dies, pieces, and other elements tend to be transverse to the elongation direction, but produce a component of force in the elongation direction. This component of the applied static force is a major factor in determining the directions, rate, and extent of elongation deformation in conventional processes. It is also this component of the transversely-applied static control-signal (bias) force that adds to the longitudinal dynamic force to guide elongation deformation in the sonic rolling and deformation system.

Referring now generally to FIGS. 1 and 2a, a sonic motor 1 or transducer 1' is coupled (directly by threads or clamps, or indirectly by means of impact either by the output shaft of the sonic motor or by means of an intermediate bouncing-mass element) to the work material to be rolled or deformed..The sonic vibratory power is introduced to the work material 2, such as metallic bar, tube, pipe, sheet, plate, slab, billet, round, ingot, or other length of material, at one end', by the sonic power transducer 1. Vibratory stress waves pass along this piece of work material from the transducer to the point of application of force or pressure by 'rneans'of rolls, hammers, mandrels, pierces, or other devices well-known in metal-working industries for the cold forming of metallic materials.

At the rolls 4, 4a, the pointof application of static forces or pressures, the sonic vibratory stresses thus created are added to the longitudinal components of stress provided by therolls, forging hammer, or other means of applying static forces to createstatic stresses in the work material. Referringto FIGS. 3b and 3c, the sum of the static force (which itself will be of much smaller magnitude than the force required for deformation in processes using only static force) and the dynamic vibratory force passing longitudinally along the work material 2 exceeds the elastic limit of the work material. With total stresses exceeding the elastic limit of the material, plastic deformation occurs and the metallic material is readily changed in shape or dimensions. This action occurs only in the region where the static force applied by the rolls 4, 4a and the dynamic forces create stresses which, when superimposed, exceed the elastic limit of the material.

FIG. 1 illustrates a sonic transducer I mounted at the node 5 to a bracket 5a, coupled to work material 2 at the end of the output shaft 3 by one of several possible methods mentioned hereinabove. Sonic vibratory power introduced into the work material 2, which may assume any given geometry (bar, tube, pipe, sheet, plate, slab, billet, round, ingot, etc.), causes vibratory stress waves to pass along the work material 2 from the point of transducer 3 to the point of application of force by the work rolls 4 or other devices used for metal working (hammers, pierces, mandrels, etc.). The application of static force F at the node 5 of the transducer feeds the work material 2 into the working devices 4 in direction 8 where the static bias force F in FIG. 1 or the combination of static forces F F and F on the rolls 4a in FIG. 2a causes the material to deform. The static forces required to deform the work material 2 which has been excited by vibratory-mechanical energy are less by a factor of 10 to 100 than the static forces required to deform work material 2 which has not been excited by vibratory-mechanical energy.

FIG. 2a illustrates the work material 2 being stressed in compression at 6 and in tension at 7. Whether the stress introduced into the work material 2 is tensile or compressive the static force required to deform the material is reduced by a factor of 10 to 100. FIG. 3a illustrates the stress-time or stress distance relation 9 resulting from the sonic vibratory-mechanical energy introduced into the work material 2. The dynamic stresses introduced into the work material 2 by the sonic vibratory energy from the sonic transducer 1 may not exceed the elastic limits 10, 11 of the work material 12 into which they are introduced if the vibratory-mechanical energy is to be efiiciently transmitted. FIG. 3b illustrates the effect of a static bias force applied to the material through the work rolls 4, 4a resulting in a corresponding static bias tensile stress 0 to which the dynamic stress 9 introduced by the sonic transducer 1 is additive. The cross-hatched areas 12 of FIG. 3b indicate the periods of time which the work material 2 experiences total stress (from the sum of the static 0' and the dynamic stress 9) in excess of its elastic limit 10 in the tensile direction. During each period in which the elastic limit 10 is exceeded by the sum of the static bias incremental deformation adds to the total permanent deformation or set 20. As time of application of vibratory'and static stressing continues, the work material follows the static stress-strain curve, FIG. 4b, curve through its plastic deformation region 16 until any desired level of cold deformation (within the capabilities of the work material) have been achieved. Thus, it is essential for this process (as for all other cold forming processes) that the material have a plastic range 16 (a curved portion of the stress-strain curve between the elastic limit and the ultimate tensile-strength at which the material fails or ruptures).

Where the static bias load causes a compressive static stress to be introduced into the work material 2, the sum of this compressive stress and the dynamic stresses introduced by the transducer 1 will produce incremental deformations 19 in a manner analogous to that described hereinabove in conjunction with FIG. 3b. FIG. 3c is the graphical illustration of how a' compressive static stress 1 combines with the dynamic stress to exceed the elastic limit 11 in the negative direction to produce incremental deformation. This compressive deformation 13 occurs in a manner analogous to that described hereinabove for the tensile stress in FIG. 3b.

The dynamic stresses 9 combine with tensile or compressive 0' stresses wherever they maybe found in the work material 2. FIG. 2a illustrates the bending of the work material 2' for which a combination of static loading producing tensile stresses at point 6 and compressive stresses at point 7 within the work material 2 must be used. The dynamic stresses 9 introduced by transducer 1 effectively combine with the stresses at points 6 and 7 to exceed the respective elastic limits 10, 11, of the work material 2 producing incremental deformation 12, 13, 19 when the tensile and compressive at points 6 and 7, respectively, are exceeded.

Basically, sonic forming of metals (in particular, cold rolling) may be carried out on any metal possessing stressstrain characteristics including a non-linear region of any type; a typical stress-strain curve is illustrated in FIG. 4a. Such stress-strain curves are characterized by a linear region 17 (denoting elastic deformation) terminating at the elastic limit 14 and 15 of the material. Beyond the elastic limit 14 and 15, the stress-strain curve is deflected; in this area called the plastic region 16, plastic deformation occurs. Plastic deformation is essential to cold forming because the work material 2 once plastically deformed, retains a permanent deformation or set. A .workmaterial 2 stressed to a value not exceeding the elastic limit 14 and 15, returns to its original geometry once the stress is removed.

FIG. 4b illustrates how fully-reversed or sinusoidal stresses cause small plastic deformations 19 or incremental movements along the plastic deformation region 16 of the stress-strain curve. (Note, however, that a sinusoidal wave shape is not the only feasible shape. All other wave shapes with peak values high enough can be used.) A small deformation occurs with each cycle of vibratory energy introduced into the work material 2 by the transducer 1. The cross-hatched areas 12and 13 of FIGS.'3b and 3c illustrate the cyclic nature (described hereinabove) of the deformations19 which follow the plastic range 16 of the stress-strain curve in FIG. 4b. The lines parallel to the elastic range 17 of the stress-strain curve indicate each incremental deformation. 19 produced by the-sum of the dynamic sonic stresses 9 (introduced during each cycle of sonic vibratory energy) and "static stresses 0' and 0' The incremental deformations 19 are separated by intervals of released stress (typically reversed to a level not exceeding the opposite elastic limit 15). The reversed stress has the desirable effect of relieving shear strain energy and preventing static shear strain energy from being built up and stored in the work material .2 as the successive small deformations add up to a large total or composite deformation. In fact, the total energy stored or remaining in the material after working is equal to the cross-hatched area 18 of FIG. 4b. Energy equal to the entire area under the stress-strain curve, above the abscissa, and bounded by and including increment 18 of FIG. 4b remains in a material when the material is worked by conventional metal-working processes employing only static forces to deform the work material 2.

Static shear strain energy is not stored in the workpiece. Such storage of static shear strain energy in work materials deformed continuously by static forces (which are maintained by friction with tools, rolls, dies, etc.) can lead to ruptures and fractures of the work material, if

the deformation is carried to high levels. Such ruptures and fractures do not appear to occur in the sonic cold forming process. Thus, much greater total deformations can be performed without fracture of the work materials in the vibratory-mechanical energy or sonic cold working process. The result is that materials not normally considered cold-formable can be formed by the sonic technique. (This effect was demonstrated, for example, in the cold-heading of titanium alloy rivets, in a recent project.)

The basic sonic cold forming process is equally applicable to rolling and shaping of ingots, billets, bars, tubes, pipe, rails, beams, and all other longitudinal shapes produced in primary steel manufacture. In addition, the process can be applied to rolling of sheets, plates, bars and other shapes; the process can be used in later finishing, bending, forming, and manufacturing processes by customers of primary steel producing plants. Stress in a material is defined as applied force over cross-sectional area (F /A). To deform a material the stress which must be exceeded is the elastic limit of the material (L For each application, the sonic power input must meet the requirement of providing dynamic longitudinal stresses approaching the elastic limit for the cross-sections and material characteristics involved. To a first approximation, the vibratory force required (F) would be nearly equal to the product of the material cross-section involved (A) and the elastic limit (L of the workpiece because the required stress to match the elastic limit (L is thus, the required dynamic force would approximate F=AL to provide maximum reduction in the static guiding forces required to control the deformation processes. High-power sonic transducers, or several lower-power transducers, might be used to excite the work material, when large cross-section work pieces are to be formed.

In bending of shapes, such as bars, rails, plate, sheets, etc., the outer fibers are elongated by tension deformation, and the inner radius fibers are subject to compression. Fortunately, the alternating stresses produced by the sonic vibration can aid both deformation processes to occur simultaneously, as shown in FIGS. 3b and 30.

In present cold rolling and deformation processing, it is frequently necessary to remove work materials from the process after certain levels of deformation, and to anneal or otherwise remove the effects of cold Working before further processing. This is done because materials are Work-hardened, and build up high levels of internal shear strain energy. Annealing restores ductility to the work material so that it can be further deformed without producing cracks and fractures. In the sonic process, a degree of stress relief occurs due to the rapidly-reversed stresses to which the material is subject (beyond and after the deformation). This, in turn, aids in retaining the ductile characteristics of the work material, and permtis greater deformations to occur without achieving high levels of work hardening.

The tremendous economic advantage of sonic cold forming lies in the enormous potential reduction in the size, weight, costs, and slowness of operation of massive machines which produce cold deformation entirely by application of static forces. Generically, the required static forces can be reduced by ratios of 10:1 up to :1 or more. Since the size and weight (and cost) of machines are proportional to the static forces they must withstand, sonic excitation can reduce these factors by comparable ratios (greatly reducing the capital and amortization costs of such equipment in industry). Alternatively, the capacities (work cross-sections which can be handled) of exist ing sizes of cold forming and rolling machines might be increased by comparable ratios. With smaller machines to do the work, higher operating speeds could also be attained, with additional economic advantages.

What is claimed is:

1. A process for the cold-forming elongation of metals, alloys, and other plastically-deformable materials comprising the steps of applying vibratory-mechanical energy to the work material in a direction parallel to the direction of elongation of said work material and applying static force to said work material at a point other than the point of application of said vibratory-mechanical energy.

2. A process as described in claim 1 further including transmitting reversed dynamic stresses through the work material by applying said vibratory-mechanical energy to said work material.

3. A process as described in claim 2 wherein said process further includes maintaining the amplitude of said reversed dynamic stresses at a value less than the elastic limit of said work material between the point of application of said vibratory-mechanical energy and said static force thereby permitting the efiicient transmission of said reversed dynamic stresses between said point of application of said vibratory-mechanical energy and said static force.

4. A process as described in claim 2 wherein said process further comprises combining said reversed dynamic stresses with the static stresses in said work material thereby creating static stresses by applying said static force to said work material.

5. A process as described in claim 4 wherein said process further comprises varying said static force thereby creating varying static stresses in said work material.

6. A process as described in claim 4 wherein said process further comprises cold-forming said work material when said reversed dynamic stresses in said work material in combination with said static stresses exceed the elastic limit of said work material.

7. A process as described in claim 6 wherein said process further comprises cold-forming said work material incrementally once each cycle of said reversed dynamic stress during the period when said combination of said static stresses with said reversed dynamic stresses exceed said elastic limit of said work material.

8. A process as described in claim 7 wherein said process further comprises combining said reversed dynamic stresses with tensile static stresses thereby coldforming said work material incrementally by periodically exceeding the tensile elastic limit.

9. A process as described in claim 7 wherein said process further comprises combining said reversed dynamic stresses with compressive static stresses thereby cold-forming said work material incrementally by periodically exceeding the compressive elastic limit.

10. A process as described in claim 7 wherein said process further comprises combining said reversed dynamic stresses with tensile static stresses and compressive static stresses, respectively, wherever said tensile stresses and compressive stresses exist in said work material there by cold-forming said work material incrementally by periodically exceeding said tensile and compressive elastic limits, respectively.

11. A process as described in claim 2 wherein said process further comprises stress relieving said work material a said work material is incrementally cold-formed wherein the rapidity with which said reversed dynamic stress occurs creates intervals of released stress thereby relieving shear strain energy, preventing said shear strain energy from being stored in said work material as the incremental deformations add up to the total deformation.

12. A process as described in claim 4 wherein said process furthercomprises cold-forming said work material by applying static forces more than 10 times less than those required without the assisatnce of said vibratory-mechanical energy.

13. A process as described in claim 4 wherein said process further comprises stress relieving said cold-formed work material by said reversed dynamic stresses created by said vibratory-mechanical energy remaining in said work material after said work material has been coldformed by said combination of reversed dynamic stresses and said static stresses.

14. A combination for the cold-forming elongation of metal comprising: means for applying static forces to deform the work material, means for supporting and guiding said work material through said deforming forces, a source of electromechanical energy and means for coupling said source of electromechanical energy to said work material at a point parallel to the direction of elongation of said work material prior to said deforming means.

15. A combination as set forth in claim 14 wherein said source of electromechanical energy is high power electromechanical sonic transducer.

16. A combination as-set forth in claim 14 wherein said means for coupling and said source of electromechanical energy further comprises an electromechanical transducer threaded at its tip and said work material threaded at one end, said threaded portions being joined.

17. A combination as set forth in claim 16 wherein said means for coupling said work material to said electromechanical transducer further includes intermittent contact means.

I References Cited UNITED STATES PATENTS

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