Ultrasonic excitation of segmented dies

Abstract

A method for reducing areas of friction within a forming die that includes identifying at least one region of interest in the forming die, wherein the at least one region of interest further includes a problematic aspect of a predetermined nature; designing a die segment corresponding to the at least one region of interest, wherein the die segment further includes at least one ultrasonic transducer embedded therein; modifying the forming die to receive the die segment; installing the die segment in the forming die and acoustically isolating the die segment from the remainder of the forming die; and energizing the ultrasonic transducer to provide ultrasonic energy to the die segment, wherein providing ultrasonic energy to the die segment addresses the problematic aspect of the at least one region of interest in the forming die.

Claims

1. A method for reducing areas of friction within a forming die, comprising: (a) providing a forming die, wherein the forming die is adapted for use in sheet metal forming processes, and wherein the forming die includes surfaces that contact sheet metal being formed by the forming die; (b) identifying at least one region of friction between the surfaces of the forming die and the sheet metal being formed by the forming die; (c) designing a die segment corresponding to the at least one region of friction, wherein the designed die segment includes at least one ultrasonic transducer embedded completely within the die segment, and wherein the at least one ultrasonic transducer is surrounded on all sides by the material of the designed die segment; (d) modifying the forming die to receive the designed die segment that includes the at least one ultrasonic transducer embedded completely within the designed die segment; (e) installing the designed die segment in the forming die and acoustically isolating the designed die segment from the remainder of the forming die; and (f) creating a three-dimensional, ultrasonically vibrating, acoustically resonating die segment by energizing the at least one ultrasonic transducer to provide ultrasonic energy to the installed designed die segment, wherein providing ultrasonic energy to the installed designed die segment reduces friction between the surfaces of the forming die and the sheet metal being formed by the forming die.

2. The method of claim 1, wherein the sheet metal is used for manufacturing automobile parts.

3. The method of claim 1, wherein acoustically isolating the designed die segment from the remainder of the forming die further includes placing low friction pads between the designed die segment and the forming die.

4. A forming die for use with sheet metal processes, comprising: (a) a forming die body, wherein the forming die body includes: (i) surfaces that contact sheet metal being formed by the forming die; and (ii) at least one opening created in the forming die body at a region of friction between the surfaces of the forming die body that contact the sheet metal and the sheet metal itself; (b) a designed die segment, wherein the designed die segment is inserted into the opening in forming die body, and wherein the designed die segment includes: (i) at least one ultrasonic transducer embedded completely within the die segment, (ii) wherein the at least one ultrasonic transducer is surrounded on all sides by the material of the designed die segment for creating a three-dimensional, ultrasonically vibrating, acoustically resonating die segment and directing ultrasonic vibrations into the die segment; and (c) at least one vibration-isolating device positioned between the designed die segment and the forming die body, wherein the at least one vibration isolating device prevents ultrasonic vibrations from the designed die segment from entering the forming die body.

5. The forming die of claim 4, wherein the at least one vibration-isolating device is a low friction pad.

6. The forming die of claim 4, wherein the sheet metal is used for manufacturing automobile parts.

7. The forming die of claim 4, wherein the at least one ultrasonic transducer includes piezoceramics, and wherein the piezoceramics have been pre-compressed prior to the at least one ultrasonic transducer being embedded in the designed die segment.

8. The forming die of claim 7, wherein the piezoceramics have been pre-compressed with a compression bolt.

9. The forming die of claim 7, wherein the piezoceramics have been pre-compressed with tapered shims.

Description

DESCRIPTION OF THE DRAWINGS

(1) The accompanying drawings, which are incorporated into and form a part of the specification, schematically illustrate one or more exemplary embodiments of the invention and, together with the general description given above and detailed description given below, serve to explain the principles of the invention, and wherein:

(2) FIG. 1A depicts an acoustically isolated die segment and FIG. 1B depicts an acoustically isolate blank holder segment;

(3) FIGS. 2A-C illustrate various shapes that may be subject to vibration analysis wherein FIG. 2A is a 3D block, FIG. 2B is a thin plate, and FIG. 2C is a thin rod;

(4) FIG. 3 illustrates three dimensional (left) and one dimensional (right) vibrational modes;

(5) FIGS. 4A-B illustrate an acoustically resonant shape having an internal ultrasonic vibration source, wherein FIG. 4A depicts a 3D block with section AA marked thereon, and wherein FIG. 4B depicts section AA of the 3D block, and wherein the ultrasonic vibration source is visible therein;

(6) FIG. 5 depicts a bolted 3D resonant die, wherein an ultrasonic vibration source is visible therein;

(7) FIGS. 6A-B depict alternate means for pre-compressing the piezoceramics included in an ultrasonic transducer, wherein FIG. 6A depicts the use of a center bolt for compression, and wherein FIG. 6B depicts pre-compression by means of tapered shims;

(8) FIGS. 7A-B depict an ultrasonic die insert in a die structure, wherein FIG. 7A depicts a monolithic die with an ultrasonic die insert, and wherein FIG. 7B depicts the ultrasonic die insert removed from the die; and

(9) FIG. 8 depicts a set screw method of holding ultrasonic containment plate that is modified for an ultrasonic die.

DETAILED DESCRIPTION OF THE INVENTION

(10) Exemplary embodiments of the present invention are now described with reference to the Figures. Although the following detailed description contains many specifics for purposes of illustration, a person of ordinary skill in the art will appreciate that many variations and alterations to the following details are within the scope of the invention. Accordingly, the following embodiments of the invention are set forth without any loss of generality to, and without imposing limitations upon, the claimed invention.

(11) The purpose of the present invention is to apply ultrasonic vibrations to one or more regions of a large stamping die in order to reduce friction between the sheet metal being formed and the surface of the die, thereby improving the formability of the metal at critical shape locations, as well as reducing galling, tearing and cracking of the sheet metal. This desired effect is accomplished by acoustically isolating a segment (or segments) of the die and embedding within the die, an ultrasonic vibration source (i.e., an ultrasonic transducer) that creates resonant vibrations of the die, of varying magnitudes, at its several surfaces thereby creating an ultrasonic friction reduction effect having various benefits. Thus, the present invention typically includes the steps of: (i) identifying a critical region (or regions) of a die where friction reduction would have greatest effect (or effects); (ii) acoustically isolating a segment (or segments) of the die, from the critical region (or regions) into a manageable mass (or masses) that is capable of being ultrasonically excited; and (iii) incorporating within that mass a source of ultrasonic excitation, i.e., an ultrasonic transducer system. The ultrasonic excitation of the die segment by an internal source versus transmitting vibrations from an external source to the die segment along with the specific means of its acoustic isolation, are among the novel features of the invention.

(12) With reference now to the Figures, FIGS. 1A-B illustrate the application of ultrasonic vibration to a segmented die by external means, wherein FIG. 1A depicts an acoustically isolated die segment and wherein FIG. 1B depicts an acoustically isolated blank holder segment. These illustrations share two common features: (a) a segment of die is shown to be isolated, by means of low friction pads, from the balance of the die mass; and (b) ultrasonic vibration is transmitted to the die segment from an external transducer by means of an ultrasonic transmission line connection. Low friction pads are one, but not the only, means of acoustic die isolation. However, the requirement of an external means of both generating ultrasonic vibrations (the transducer) and a direct, robust mechanical connection between the transducer and a die segment (by a transmission line that may be several inches in length, e.g. at least 10 inches for systems operating at 20 kHz) can be a significant disadvantage to a die vibration technology dependent on such means. For this reason, the present invention replaces this means of die excitation with other means of die excitation.

(13) With regard to three-dimensional (3D) vibration, in general, a fundamental aspect of the present invention is that of creating ultrasonic resonant vibrations in a 3D mass of arbitrary mass and shape. While all objects are 3D, in the present context it means that the general L, W and H dimensions of the object are of the same order of magnitude, i.e. WLH as shown in FIG. 2A for the case of a rectangular block. For possible later reference, the cases of a thin plate, WL>>H and a thin rod, L>>W, H are shown in FIGS. 2B-C. Determining the vibration characteristics of a 3D shape typically requires use of the equations of elasticity and FEA methods, whereas analysis of plate and rod shapes can often involve simpler governing equations and analysis methods. While the 3D block of FIG. 2A is not an arbitrary shape it is generally illustrative with regard to this invention.

(14) With regard to using a 3D vibrating die segment, in nearly all ultrasonic transducer and tooling developments, the effort is continually one of one-dimensionalizing the geometry in order to avoid energy absorbing 3D vibrational modes. Thus, it is desirable to confine the major vibration direction to a single dimension along a vibration axis, such as shown by the thin rod in the FIG. 2C. The present invention seeks to increase the lateral dimension to comparable sizes and to deliberately seek achieving a 3D vibrational situation, versus a 1D mode, as illustrated in FIG. 3. Thus, the 3D block is made into an ultrasonically vibrating, acoustically resonant shape by embedding, completely within the block, an ultrasonic vibration source that is connected to the external system simply by an electrical connection, and possibly an air cooling connection. A simplistic version this system is shown in FIGS. 4A-B, which provide perspective and cutaway views, respectively.

(15) Embedding the vibration source within the block typically involves sectioning the block and FIG. 5 illustrates a bolted, sectioned arrangement. In FIG. 5, the electrical connection has been redirected to exit the end of the block. For use in the present invention, the piezoceramics in an ultrasonic transducer are pre-compressed to prevent tensile fracture. In standard transducers, this is usually accomplished by a compression bolt, as shown in FIG. 6A. However, the assembly method for the die may not allow for the careful control of precompression that the standard transducer construction provides and other means may be necessary. One such alternate means includes the use of tapered shims, as shown in FIG. 6B.

(16) Maintaining the thickness of the block walls is important for exerting significant forces while undergoing vibration. Because of the 3D shape, and the varied shapes that may be used for different dies, the frequency spectrum of the die will likely be complex, possibly having a number of adjacent frequencies. Finite element analysis (FEA) may be used to arrive at an optimum frequency giving the desired vibration modes. This may not be at the usual standard 20 kHz, but may vary from case to case and may involve a more flexible power supply than currently used that is able to match to a wider range of frequencies.

(17) With regard to holding the ultrasonic die segment, it is important to acoustically isolate the ultrasonic die segment from the surrounding die structure, while at the same time securing it in a fixed location so that it seamlessly merges into the overall die. Two approaches, which may be used alone or in combination with one another include: (i) low friction pads, wherein the pads include a Frelon coating or are made from a metallic bearing material such as bronze or cast iron; and (ii) a setscrew engagement. The first of these is illustrated in FIG. 7A. Although the surrounding die structure is shown as monolithic, it should be capable of some disassembly in order to insert the ultrasonic die as well as to provide access for the electrical (and possibly air) connections to the die insert. The low friction pads may be screw-in inserts and the dark gray circles on the die in FIG. 7B are the locations where the inserts on the opposite die wall (hidden in the view) touch the ultrasonic die. While the inserts may be sufficient to secure the die, a set screw method shown in FIG. 8, may be modified for this purpose.

(18) The present invention has been described herein in reference to forming dies. A typical stamping/forming operation consists of the forming die, a blank holder and a punch, each of which may have large mass and dimensions (as noted earlier for a die). The concept of the present invention, i.e., an ultrasonically activated, embedded die insert may be applied to blank holders or punches, as well. By means of this invention it is possible to create ultrasonic vibrations in a critical segment or segments of a large die that would otherwise be impossible to ultrasonically excite to any significant vibration level, and in so doing, to reduce friction forces between sheet metal being formed and the forming die at one or more critical forming locations on the die.

(19) While the present invention has been illustrated by the description of exemplary embodiments thereof, and while the embodiments have been described in certain detail, it is not the intention of the Applicant to restrict or in any way limit the scope of the appended claims to such detail. Additional advantages and modifications will readily appear to those skilled in the art. Therefore, the invention in its broader aspects is not limited to any of the specific details, representative devices and methods, and/or illustrative examples shown and described. Accordingly, departures may be made from such details without departing from the spirit or scope of the applicant's general inventive concept.