Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
  • B21D—WORKING OR PROCESSING OF SHEET METAL OR METAL TUBES, RODS OR PROFILES WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
  • B21D39/00—Application of procedures in order to connect objects or parts, e.g. coating with sheet metal otherwise than by plating; Tube expanders
  • B21D39/03—Application of procedures in order to connect objects or parts, e.g. coating with sheet metal otherwise than by plating; Tube expanders of sheet metal otherwise than by folding
  • B21D39/031—Joining superposed plates by locally deforming without slitting or piercing

Definitions

• the present invention relates generally to an apparatus for joining sheet material and specifically to a punch and a joint, each having a step therein.
• the conventional TOG-L-LOC* leakproof joints consist of two or more sheets of material having a button or joint formed therebetween by a uniformly cylindrical punch forcibly pushing a punch side sheet of material into interlocking engagement with a die side sheet of material.
• These conventional leakproof joints have seen tremendous commercial success for use in varied applications such as steel microwave ovens and aluminum automotive bodies. While these leakproof joints have proven reliable and inexpensive, it would be desirable to have an even stronger leakproof joint.
• an improved apparatus for joining sheet material provides a stepped punch.
• This stepped punch serves to strengthen a joint between two or more sheets of material by creating a stepped segment in at least one of these sheets of material.
• material is forcibly displaced toward another segment of material that is outwardly expanded to interlock with the adjacent sheet of material.
• the punch and joint of the present invention are advantageous over conventional punches and joints by achieving a surprisingly stronger leakproof joint. Furthermore, the joint of the present invention has improved wall thickness that is more resistant to fracture as compared to conventional leakproof joints. The punch, joint and method of the present invention thus reduce scrap during the joint forming process. Additional advantages and features of the present invention will become apparent from the following description and appended claims, taken in conjunction with the accompanying drawings.
• FIG. 1 is a side elevational view, partially in section, of a preferred embodiment apparatus for joining sheet material of the present invention, shown in its retracted position;
• FIG. 2 is a side elevational view, partially in section, of the preferred embodiment apparatus of the present invention of FIG. 1 , shown in its advanced position;
• FIG. 3 is an enlarged side elevational view, partially in section and taken from within circle 3-3 of FIG. 2, of the preferred embodiment apparatus of the present invention
• FIG. 4 is a graph comparing the shear strength of a joint in aluminum created by the preferred apparatus of the present invention of FIG. 3 as compared to a conventional leakproof joint without a step therein;
• FIG. 5 is a graph comparing the peel strength of a joint in aluminum created by the preferred apparatus of the present invention of FIG. 3 as compared to a conventional leakproof joint without a step therein;
• FIG. 6 is a graph comparing the shear strength of a joint in steel created by the preferred apparatus of the present invention of FIG. 3 as compared to a conventional leakproof joint without a step therein;
• FIG. 7 is a graph comparing the peel strength of a joint in steel created by the preferred embodiment of the present invention apparatus of FIG. 3 as compared to a conventional leakproof joint without a step therein;
• FIG. 8 is a graph optimizing the anvil depth of a joint created by the preferred embodiment of the present invention apparatus of FIG. 3;
• FIG. 9 is a graph optimizing the button diameter of a joint created by the preferred apparatus of the present invention of FIG. 3.
• a conventional interlocking leakproof joint is strong and inexpensively formed.
• Such a conventional leakproof joint is formed by using a substantially constant diameter punch to draw a punch side sheet of material downward into interlocking engagement with a die side sheet of material.
• the punch side sheet of material has a cylindrical recessed cup internally formed therein while the lower peripheral external section of the punch side sheet of material is outwardly expanded.
• This expanded section of the punch side sheet of material interlocks with the adjacent section of the die side material and serves to outwardly expand the adjacent section thereof thereby defining an external button or joint immediately adjacent the anvil.
• An increase of fracture resistance in the necking area of the side wall will lead to a reduction of pullout strength in the interlocking of the button and vice versa.
• a stepped punch of the present invention was developed.
• the idea to use the stepped punch of the present invention is to bring more material from somewhere in the sheet metal on the punch side to the joint element, and to increase simultaneously both thickness of the thinned side wall and locking volume in the interlocking expanded segment of the joint. Higher strengths for both shear and peel tests are expected if a stepped punch is appropriately designed.
• the conventional joint has been surprisingly strengthened to a significant extent by forcibly deforming a step within the punch side sheet of material. This added step has provided a joint with tremendously improved strength while being relatively simple to create.
• the improved apparatus and joint is described hereinafter.
• a preferred embodiment of an apparatus of the present invention is comprised of a punch assembly 10 and a die 12.
• Punch assembly 10 and die 12 serve to form a joint or button 14 between a first sheet of material 16 and an adjacent second sheet of material 18.
• Punch assembly 10 has a punch holder 30, a stripper can 32, a stripper tip 34, a stripper spring 36 and a punch 38.
• punch 38 is defined by a distal drawing end 50, a cylindrical first drawing portion 52, a somewhat frusto-conical step 54, a cylindrical second drawing portion 56, a frusto-conical carrying portion 58 and a punch support shank 60.
• a longitudinal axis runs the length of punch 38.
• a first radius 70 is disposed on the peripheral edge of first drawing portion 52.
• First radius 70 is preferably 0.02 inches.
• a 0.01 inch radius defines a fillet 72 disposed at the theoretical intersection between first drawing portion 52 and step 54.
• First drawing portion 52 has a slight draft angle between radius 70 and fillet 72 in order to remove punch 38 from joint 14.
• a corner 74 is located on the peripheral edge of second drawing portion 56. Alternately, corner 74 may have a radius thereupon.
• the punch length and diameters are adjustable depending on the thickness of the sheet material employed for joint 14.
• first and second sheets of material, 16 and 18, respectively are each 2 mm thick aluminum
• the longitudinal length of first drawing portion 52 is 0.095 inches.
• First drawing portion 52, proximate to its theoretical intersection with distal drawing end 50, has a diameter of 0.19 inches.
• the constant diameter drawing portion of the conventional leakproof joint punch without a step is 0.18 inches.
• Second drawing portion 56 proximate to its theoretical intersection with step 54, has a diameter of 0.21 inches.
• dt J, + T 2 dt is defined as the total depth of punch between a surface of first sheet of material 16 immediately adjacent stripper tip 34 to distal drawing end 50;
• T is defined as the thickness of the first sheet of material 16.
• T 2 is defined as the thickness of the second sheet of material 18.
• die 12 has a substantially cylindrical anvil 90 surrounded by a set of die blades 92 which are laterally movable away from anvil 90 during formation of joint 14.
• Anvil 90 preferably has a flat face which mirrors the flat shape of distal punching end 50 of punch 38.
• Die blades 92 are retained to die 12 by an elastomeric band 98.
• Elastomeric band 98 is expandable to allow die blades 92 to pivot away from anvil 90 during formation of joint 14.
• Elastomeric band 98 then serves to move die blades 92 back toward anvil 90 upon removal of joint 14 from die 12.
• Elastomeric member 98 can alternately be replaced by a canted spring, compression spring, leaf spring or the like.
• joint 14 between first sheet of material 16 and second sheet of material 18 is defined by nominal segments 100, recessed or side wall segments 102, outwardly expanded segments 104, and bridging segments 106. Additionally, recessed segment 102 of first sheet of material 16 has an inside surface 120. A stepped segment 122 of first sheet of material 16 is located along inside surface 120 proximate with a bend 124 thereof.
• the leakproof joint of the present invention and the apparatus used to create the joint of the present invention provide surprisingly significant advantages over conventional joints.
• the stepped portion of the present invention punch acts to create a stepped segment within the joint, thereby moving otherwise unuseful material toward the expanded segment of the joint.
• the stepped punch 38 employs two different diameters acting on a particular region of the joint. This punch 38 brings two punch penetrations to the material sheets 16 and 18 in a single press stroke. It overcomes the problem that the side wall can be thickened only at the expense of a reduction in the interlocking.
• the first drawing portion 52 with a smaller diameter acts just like the regular punch, drawing material towards the die opening to form a joint.
• the second drawing portion 56 with a bigger diameter acts like a second punch that extrudes and pushes down some material in the side wall of the punch side so as to create a cup-shaped inner recess therein.
• the first drawing portion squeezes the sheet metal on the bottom of the cup (bridging segments 106 between the punch and die), and the second portion of punch 38 squeezes the material in the side wall of the cup.
• the final joint 14 is then removed from the die and punch.
• the action of the bigger second drawing portion is expected to obtain the following effects: increasing material volume in the joint element; thickening the cup-shaped wall in the joint; squeezing the material right below the cup-shaped wall outward to increase the interlocking; increasing the hardening of material in the thinned wall and interlocking by bringing more deformation to the material.
• the second effect will increase the fracture strength, while the third effect will result in a better resistance to a pullout failure.
• the last effect will benefit both fracture and pullout strengths. /03232 PCIYUS94/08413
• the cup shaped recessed wall is thicker and the material in the interlocking expanded segment, especially in the gap between die blades, moves outward more than in conventional joints. They contribute to the increase of both fracture and pullout resistance. That is why a higher load carrying ability is observed for the present invention joint made by a stepped punch.
• FIG. 8 discloses peel test forces versus anvil depth for two sheets of material made from steel grade A366. Each sheet of steel had a thickness of 0.060 inches while the punch diameter was 0.190 inches and the button diameter (BD) measured 0.285 inches.
• Curve 200 schematically charts the failure by pullout test results while curve 202 schematically depicts the failure by fracture test results. The intersection of 204 of these two curves provides the optimum anvil depth for the present invention joint.
• buttons diameter (BD) based on peel strength and failure mode employs two sheets of steel, grade A366, each having a thickness of 0.060 inches.
• the punch used for this test had a first drawing portion diameter of 0.190 inches while the anvil depth (AD) measured 0.040 inches.
• Curve 250 depicts the pullout failure results while curve 252 depicts the side wall fracture failure results.
• the intersection 254 between curves 250 and 252 demonstrates the optimum button diameter.
• additional trial and error may be required to adjust the various punch and anvil dimensions based upon individual sheet material batch thicknesses and differing material types.
• FIG. 4 graphically represents a sheer strength test comparing conventional leakproof joints 140, without a step, to the present invention leakproof joints 142 having a stepped segment therein. Both joints were formed using 0.190 inch diameter first /03232 PCIYUS94/08413
• FIG. 4 graphically depicts a peel strength test comparing the present invention leakproof joint 144 to a conventional leakproof joint 146 without a step. Again, two tests were conducted for each type of joint. It will be noted that the present invention joint 144, having a step therein, has significantly improved peel strength over the conventional joint 146.
• Aluminum grade 5754 having a thickness of 2 mm, was used for each material sheet for the above shear and peel strength tests.
• the button had a diameter of 0.298 inches (BD) while the present invention joint had a button diameter of 0.323 inches.
• the anvil depth (AD) of joint was 0.040 inches for the conventional joint and 0.045 inches for the present invention joint.
• Shear strength testing results for two steel sheets of material are shown in FIG. 6. Fourteen gauge, grade A366 steel was used.
• the stepped punch had an anvil depth (AD) of 0.050 inches and created a button diameter (BD) of 0.320 inches while the conventional punch had an anvil depth (AD) of 0.045 inches and created a button diameter (BD) of 0.305 inches.
• the results for the stepped punch are shown with the solid lines 300 and the results for the conventional joint, without a step therein, are shown with the dashed lines 302.
• the stepped present invention joint 300 test was repeated twice while the conventional joint 302 test were repeated three times.
• FIG. 7 graphically represents the peel strength test results for the same sized steel, punch apparatus and joint as that of FIG.6.
• the stepped joint of the present invention is shown by the solid lines 350. The test was repeated five times for the present invention joint 350 and twice for the conventional joint 352.
• the punch of the present invention may have multiple stepped portions thereof between three or more differing diameter drawing portions.
• these drawing portions may alternately have ovular, starred, polygonal or other shapes thereto.
• the distal drawing end of the punch or the anvil face of the die may also take on a variety of curved, slotted or angular configurations.
• alternate die constructions may be provided in combination with the present invention punch or joint. Either of the sheets of material can be metallic vinyl, polymeric, composite, or any other deformable material.
• the stepped configuration of the present invention can also be used in a TOX® joint wherein a die blade is fixed around and partially extends above an anvil with a trough therebetween.
• the TOX ® joint is defined by a die-side second material sheet forced to expand downwardly into the trough when a first punch side material sheet is outwardly expanded to interlock with the second material sheet.

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• Engineering & Computer Science (AREA)
• Mechanical Engineering (AREA)
• Shaping Metal By Deep-Drawing, Or The Like (AREA)
• Punching Or Piercing (AREA)

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• 1994
  • 1994-07-22 JP JP8505700A patent/JPH10503427A/ja active Pending
  • 1994-07-22 AU AU75147/94A patent/AU7514794A/en not_active Abandoned
  • 1994-07-22 DE DE69431490T patent/DE69431490T2/de not_active Expired - Fee Related
  • 1994-07-22 EP EP94925111A patent/EP0783384B1/de not_active Expired - Lifetime
  • 1994-07-22 WO PCT/US1994/008413 patent/WO1996003232A1/en active IP Right Grant

Patent Citations (4)

Non-Patent Citations (2)

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