Patent Publication Number: US-3879974-A

Title: Forming of materials

Description:
United States Patent Biddell et al.  
 I Apr. 29, I975 FORMING OF MATERIALS [73] Assignee: National Research Development Corporation. London. England [22] Filed: Feb. 9. i973 Appl. No: 331.099  
 [52] US. Cl. 72/56: 72/350. 7Z/DIG. 20 [51] Int. Cl BZld 24/04 [58] Field of Search 72/56. DIG. 20. 347. 350  
 [56] References Cited UNITED STATES PATENTS 2.393.l3l l/l9-Jh Vang 72/56 3.201.967 8/[965 Balamuth et al 72/359 3.209.572 [(l/l965 Boyd et al 73/56 3.209.574 ill/I965 Boyd 72/56 3.233.012 2/l966 Bodine. Jr 72/56 3.354.688 ll/l967 Bodine. .lr 73/297 FOREIGN PATENTS OR APPLICATIONS 955.943 1/1957 Germany 72/DIG. 2U  
 Prinulry EJ&#39;lHHiHtF-RlCl&#39;lill&#39;d J. Herbst .-llmrm&#39; Agent. or Firm-Cushman. Darby 8. Cushman [57] ABSTRACT Apparatus including a die. for forming shapes from blanks. The blanks are drawn over a support surface upstream of the die with respect to the direction of travel of the particles which form the blank before they reach the die cavity and this surface is vibrated so that each point on it vibrates in a direction that passes through the drawing axis. The blank may he held against this surface by being sandwiched between it and a blank holder. the surface of which may vibrate in a similar direction. The invention includes special means of supporting the die unit in position during op eration in such a way that the dissipation of vibrational energy is minimised.  
 8 Claims. 5 Drawing Figures PATENTEU APR 2 93375 SHEET 10F 3 FORMING or MATERIALS This invention relates to a method and apparatus for forming materials, in particular for forming axisymmetric shapes such as cups from a metal blank by using a punch to force such blanks through or into a die cavity. It is known to excite the die so that the walls of the cavity vibrate. Various advantages have been claimed for this expedient, but publication of these advantages did not suggest the discovery upon which our invention is based, namely that similar vibrations. applied to the surfaces over which the blank is dragged before it reaches the cavity faces of the die during the forming operation, may significantly reduce the effect of friction and thus improve the efficiency of the process.  
  Our invention is defined by the claims at the end of this specification. and apparatus and methods according to it will now be described. by way ofexample. with reference to the accompanying drawings in which:  
  FIGS. l to 3 are perspective views of forms of vibrators suitable for use in carrying out our invention;  
  FIG. 4 is a diagrammatic section through apparatus using the vibrator of FIG. 1; and  
 FIG. 5 is a more detailed axial section through the punch and die of a deep drawing press using the vibrator of FIG. 3.  
  H0. 1 shows a vibrator comprising a solid ring 1 with top surface 2 and a central cavity 3 with cavity faces 4. At opposite ends of a diameter 5 are mounted vibrator units 6. It is possible by analysis to predict the radial rc sonnance that may be generated in such a ring; such an analysis is to be found in an article entitled Radial Mode Vibrators for Oscillatory Metal Forming&#34; by three of the present inventors in Applied Acoustics&#34; (3) (1970), pages 299 308. The fundamental resonant frequency or overtone modes can be predicted from a theoretically derived relationship between the inner and outer radii of the ring, and for the fundamental frequency the result is found to agree closely with the more simple approximate solution that radial resonance will exist if the mean circumference of the disc equals an integral number of wavelengths.  
  In the apparatus just described, it will be apparent that the top surface 2 of the vibrator lies at right angles to the cavity faces 4. Each particle on the faces 4 or on the top surface 2 will vibrate along a line passing at right angles through the axis of the cavity 3. If this vibrator is used as a die, faces 4 become the die cavity faces and top surface 2 will be the surface on which the blank is supported prior to drawing and over which it is drawn during a forming operation. If the vibrator is used to hold and support a conventional die, this will fit generally within cavity 3. in either case the vibrator either directly or indirectly vibrates the faces of the die cavity radially, and as drawing proceeds the blank will be drawn over top surface 2, each particle of which wiil be vibrating along a line passing through the axis of the ring 1.  
  In contrast FIG. 2 shows a vibrator comprising an acoustic transformer 7 of cylindrical profile, with vibrator units 8 mounted at one end and with a flared mouth 9 at the other. The die cavity region 10, with cavity faces ll, lies close to the flared end 9, and the surface 12 of the flare even close to its extreme edge still lies at something less than a right angle to the punch axis 13. The reference just quoted also discusses the vibrations that this device will achieve; the faces 11 will vibrate parallel to axis 13. and the motion of any point in the surface l2 within the flare 9 will be tangential to the surface of the flare at that point and in a direction that intersects the axis 13. lf this vibrator is used in connection with a drawing operation. the surface 12 may constitute the surface over which the blank will be drawn while forming takes place.  
  In FIG. 3 the vibrator comprises a disc 14 with a central cavity IS, the faces ofwhieh are referenced l6. Radial slots [7 project inwards from the circumference of the disc but do not quite reach the cavity 15; they therefore divide the disc into eight near-sectors [8. The number of sectors is limited by the maximum circumferential wave path; that is to say that the apex angle of the sectors. measured in radians. must be less than VzA/Ro, where A is the wavelength of the vibrations within disc l4 and Re is the outer radius ofthe disc. Vibrators [9 are attached to the circumference of each sector. The reference already mentioned analyses also the vibrational mode of such a construction. suggesting that the radial slots in effect divide the disc into something similar to a series of axially vibrating wedges. each of which acts as a velocity transformer. A vibrator based on this design can sometimes produce greater radial amplitudes than might be achieved in a continuous ring. as shown in FIG. 1. Slots are more likely to be beneficial where the difference between the inner and outer radii of the disc is great rather than small.  
  FIG. 4 shows an application of a vibrator such as ring 1 of FIG. 1. Here the ring has a stepped central cavity 21 instead of the plain cylindrical one 3 as before. This cavity receives and supports a conventional die 20 with a flared entry or die radius 22. and with die face 25 defining the die cavity. Vibrators 26 are connected on the outer wall of the ring at opposite ends of a diameter by waveguides 27. The ring is mounted on an acoustically designed isolating sleeve 28 so as to avoid damping of the vibrations. A blank 29, to be formed into a cupshaped vessel, is held between a blank holder 30 and the top surface 24 of die 20. When a punch 31 descends. to form the blank into a shape corresponding on the inside to that of the punch and on the outside to that of the die face 25, the blank has to be dragged from the space between 24 and 30 against the resistance created by friction between the relatively moving surfaces of die and blank, and blank and blank holder. For certain applications the blank might also contact the top surface 23 of the ring, provided this surface is strong enough to withstand the necessary forces.  
  For the purposes of the vibrations that will now be discussed, the die 20 and the ring in which it is held are considered as integral. Vibrators 26 cause die face 25 to vibrate radially. i.e. each part of the face 25 vibrates in the direction normal to itself. This arrangement is already known and its alleged advantages have been published. According to our invention the surfaces 23, 24 that support the blank are caused to vibrate so that each part of them oscillates in a direction lying parallel to the surface and generally towards the punch axis 32. The essential effect of this vibration upon the friction between blank 29 and surfaces 23 and 24, as punch 31 descends. is that the oscillatory motion of the surfaces results in the effective reversal of the friction vector throughout that part of the vibration cycle during which the particle velocity that is to say the oscillatory velocity of any particle on the two surfaces 23 and 24, exceeds the mean drawing velocity. The net result of 3 this effect is to reduce the peak friction force opposing the motion of the blank, and thus the peak drawing force that the punch must exert and the blank must be able to withstand.  
  In order to achieve a beneficial effect the velocity ratio, that is to say the ratio of the drawing velocity to the maximum particle velocity, must be less than unity. For example. when this ratio is 0.] the friction force is reduced by approximately 90 percent. It is clear that the vibrators 26 should be designed so that they set up a standing wave in the appropriate parts when the apparatus is actually working. thus achieving maximum particle velocity. Particle velocity varies directly with both the frequency and the amplitude of the vibrations.  
  It may be shown by analysis that the reduction in fric tion force may be related to the velocity ratio by the following expression: FO/F 17/2 Sin&#34; (V/M) where F and F are the friction forces under oscillatory and non-oscillatory conditions, V is the mean drawing velocity and M is the maximum particle velocity. Alternatively vibrators 26 may be connected, e.g., by waveguides 33, to blank holder 30, since it will be apparent that the benefits just discussed with relation to friction between blank 29 and surfaces 23, 24 can also apply to the contact between the blank and the blank holder 30. Yet further reductions in friction may be achieved by vibrating blank holder 30 simultaneously with surfaces 23, 24. Tests suggest that the greatest reductions will be achieved by vibrating these two parts substantially in antiphase, since this will ensure that only one of the two possible frictional contacts is operative at any one time. By avoiding any situation in which both could be working together, even if only for very short periods, some reduction of the peak drawing force is guaranteed.  
  It will be apparent also that the advantages of friction reduction apply not only to the contact between blank 29 and surfaces 23, 24 or the lower face of holder 30, but also to contact between the blank and the die radius 22.  
  FIG. shows, in detail, apparatus comprising a die 40, a vibratory support 41 and a punch 42. These correspond to the die 20, the ring and punch 31 of FIG. 4. ln PK]. 5 punch 42 carries a shoulder 43 which registers with a corresponding recess in a mounting plate 44. The edge of this plate is located in a groove formed by a cylindrical housing 45 and a lower adaptor plate 46, secured together by screws 47. Screws 48 secure plate 46 to upper adaptor plate 49, which is secured by screws 50 to the main stock 51 of the punch drive mechanism. The customary hydraulic power unit of this mechanism is not shown. The interior of housing 45 is fluid-tight and is connected by ports 52 to a source of pressure fluid (not shown), and a piston 53 carrying an annular seal 54 is free to slide up and down the drawing axis 55, relative to both punch 42 and housing 45, and seals the lower end of the interior of 45. The lower face 56 of piston 53 constitutes the blank holder.  
  Die 40 is located in a step recess 57 in the centre of ring vibrator 41, which at its periphery carries vibrator units 58 similar to units 19 of FIG. 3. Surface 56 of piston 53, and the upper surface 59 of die 40 constitute the opposed surfaces between which the blank will be sandwiched before drawing, and over which it must be dragged while drawing proceeds. ln a typical case, as just described, the blank at no time touches the upper surface 60 of ring 41&#39;, occasionally, however, such contact is desirable and the surface is finished accordingly. The blank also invariably contacts the die radius 590, and the vibration of this invention lessens the frictional drag of this contact.  
  The underside of ring 41 is formed with a ring-shaped recess 61 which receives a ring 62 secured by bolts 63 to an annular mounting member 64, itself secured by bolts 65 to a base member 66 forming part of the foundations of the whole apparatus. To reduce the dissipation of vibrational energy to a minimum, recess 61 is located at such a radius on ring 41 that it coincides with a displacement node of the vibrations generated by 58.  
  Ring 62 carries much of the weight of ring 41 and its attachments, and a proportion of the downward thrust that ring 41 has to withstand while drawing is taking place. However, constructions have been experimentally used in which ring 41 was 18&#34; in diameter, and larger sizes are clearly possible. In theory and as shown in FIG. 5, the supporting construction located by recess 6] lies a little closer to the periphery of ring 41 than to the centre; to resist the axial load on the die during drawing it is advantageous to provide an additional support in the vicinity of the die.  
  This comprises a sleeve 68 with a lower end flange 69 which is held against a spacer 70 by a collar 71 and bolts 72. Spacer 70 is secured to member 64 by bolts 73. The upper end of sleeve 68 abuts the lower surface of die 40, and is externally threaded to screw axially into the lower part of stepped recess 57, which is correspondingly threaded. Sleeve 68 also carries a collar 74 with an upper edge flange 75&#39;, when sleeve 68 is screwed into recess 57, so preventing the sleeve separating from ring 41 axially, flange 7S registers with a groove 76 cut in the underside of ring 41. The groove engages with both the radially inner and outer faces of flange 75, thus preventing relative radial movement between the sleeve and the ring. In the absence of such restraint, the considerable radial vibrations at the die would tend to disengage the screw threads.  
  To allow sleeve 68 to vibrate radially with ring 41 to which it is attached, the top end of the sleeve is axially slotted at 77 to reduce radial stiffness. The total length of sleeve 68 is chosen so that the maximum amount of vibratory energy that it receives from disc 41 is reflected back; in theory, this requires that the axial length of the sleeve should be an odd whole number of quarter-wavelengths of the vibration in the material of the sleeve.  
  Connection of ports 52 to a regulated source of pressure fluid ensures that blank holder surface 56 can be brought into contact with the blank at the required force as punch 42 descends, and can then be maintained at a desired contact force as the punch descends further to carry out the forming operation.  
  It will be apparent that the oscillatory motion of either the blank holder or die will be transmitted to the blank, imparting to it a cyclic motion. This may result in an additional reduction in friction force between the blank and the die, provided the maximum oscillatory particle velocity exceeds the mean blank velocity.  
  It will also be apparent to those skilled in the art that an oscillatory force, related to the oscillatory motion of die 40, ring 41 and blank holder surface 56, may be generated in the blank. This force may be added to the non-oscillatory force of punch 42 in such a way as to reduce further the forces required to draw the blank.  
  Although the invention has been described with reference to a punch-type machine in which metal is forced through a die from behind. it is also of course applicable to apparatus for drawing operations in which the metal is pulled through the die.  
 We claim:  
  1. Apparatus for forming shaped products from blanks comprising:  
 a die defining a die cavity into which a blank is forced during forming. said die cavity defining an axis about which the product forms.  
 a support structure defining a support surface upstream of said die.  
 means for drawing the blank over said support surface during forming.  
 means for vibrating said structure in a radial resonant mode during drawing, wherein said support surface vibrates so that each point of said surface moves tangentially to said surface. and generally in a line directed towards said axis, and  
 a blank holder, said blank holder being located in confronting relation to said support surface. wherein said blank is sandwiched between said support surface and said blank holder as it is drawn towards said die. said holder being vibrated by induced vibration from said vibrating support structure in a radial mode about said axis. wherein each point on the surface of said holder in contact with said blank is in vibratory movement in a direction tangential to said surface and along a line directed generally towards said axis.  
  2. Apparatus according to claim 1 in which said support structure includes a supporting ring for said die, and in which the support surface includes the top face of said die and said ring.  
  3. Apparatus according to claim 1 in which the means for vibrating the support structure comprise at least two vibrators, said vibrators being disposed on said structure at positions having symmetry with respect to at least one plane which includes the said axis.  
  4. The apparatus of claim I further comprising means for exciting said blank holder into vibration in a radial mode during drawing.  
  5. Apparatus according to claim 4 in which the means for vibrating said holder comprise at least two vibrators disposed on said holder at positions having symmetry with respect to at least one plane including said axis.  
 6. Apparatus according to claim 4 wherein said means for vibrating said holder comprise at least two vibrators disposed on said holder at positions having symmetry with respect to at least one plane including said axis said vibrators generating vibrations in the holder which are substantially out-of-phase with those of said support surface.  
 7. In an apparatus for forming shaped products including:  
 a die having a cavity therein, said die cavity defining an axis about which the product forms, support structure defining a support surface upstream of said die.  
 a blank supported on said support surface and a blank holder located in confronting relation to said support surface, wherein said blank is sandwiched between said support surface and said blank holder, said support structure and said blank holder being resonant in a radial mode about said axis. the method of forming a shaped product comprising the steps of drawing said blank over said support surface as said product is being formed, vibrating said support structure in a radial resonant mode during said drawing step wherein each point of said surface moves tangentially to said surface and generally in a line directed toward said axis and vibrating said blank holder in a resonant radial mode during drawing, wherein each point on the surface of said holder in contact with said blank is in vibratory motion in a direction tangential to said surface and along a line directed toward said axis.  
 8. Apparatus for forming shaped products from blanks comprising:  
 a die defining a die cavity into which a blank is forced during forming, said die cavity defining an axis about which the product forms,  
 a support structure defining a support surface upstream of said die.  
 means for vibrating said structure in a radial resonant mode during drawing, wherein said support surface vibrates so that each point of said surface moves tangentially to said surface. and generally in a line directed towards said axis. and  
 a blank holder, said blank holder being located in confronting relation to said support surface, wherein said blank is sandwiched between said support surface and said blank holder as it is drawn towards said die.