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 refers to an arrangement of tools for the forming of spot joints that enables the implementation of a method of the forming of clinched spot joints with better strength parameters.
• US8615859 B2 discloses a method of improving the strength of joints that involves the placing of a first layer of material on a second material, wherein the first layer demonstrates lower ductility than the second layer.
• the first and second layers are installed between a forming punch and a double-action crimping punch.
• the crimping punch is pressed into a part of the surface of the first layer, thus creating an opening in the first layer.
• the forming punch is then pressed into the second layer in the direction opposite to the direction of the punch movement, thus forcing at least a part of the second layer into the opening and forming a ductile joint.
• a method of improving the strength of clinched joints is also disclosed in US application US9937548 B2 .
• the method described in this document consists in the clinching of metal sheets using ultrasound and is used especially with high-strength materials of low deformation characteristics, which are difficult to join via conventional clinching.
• the joint is made in at least two overlapping components, which are placed between a die and a punch that is present on both sides of a cylinder.
• the tool applies a compressive force to both objects, while ultrasound energy is applied continuously to at least one of the objects in the joint area.
• the use of ultrasound during deformation temporarily increases the ductility of at least one of the workpieces, therefore enabling the clinching of highly-durable or thick materials.
• a different method of increasing the durability of clinched joints is to use a self-piercing rivet fastener (Xing et al., 2015).
• the punch presses the rivet in the direction perpendicular to the top surface of the component, forcing it into the die.
• the force applied to the punch moves the rivet through the top sheet to the bottom sheet.
• Material from the lower sheet flows into the die and the rivet pin expands to create a mechanical interlock between the sheets.
• the use of an additional element for the joining of metal sheets increases their static shear strength, which has been experimentally proven on many occasions and using various materials (Chen et al., 2016; Liu et al., 2019).
• Another method of improving the strength of clinched joints is the process of reducing the joint height, i.e. the pressing of a finished joint between a convex die and flat die (Chen et al., 2017).
• a mechanically blocked height of the clinch allows more material to flow in the radial direction, thereby increasing the thickness of the generated neck and thus the shear strength of the joint.
• Another way of improving the strength of a clinched joint between two metal sheets is to use an adhesive between the bonded metal sheets.
• the surfaces of the joined parts must be first degreased and roughened, wherein an adhesive is applied in the form of a two-component acrylic glue. Following the completion of clinching, the applied adhesive is allowed to set and is left for about 24 hours at ambient temperature.
• the performed tests have demonstrated that the addition of an adhesive resulted in an increase in the maximum shear force and energy absorption of a joint consisting of two aluminium sheets (He et al., 2014) and deep-drawn steel and copper alloy sheets.
• a hybrid method of improving the durability of clinched joints involves the simultaneous use of an adhesive and a rivet, as described in application CN110116509 B .
• adhesive is first applied to the surface of one of the joined components and subsequently the components are clinched using a punch and die. Following the completion of the joint, the adhesive is allowed to set and in the next phase the rivet that penetrates the workpiece stack and the adhesive layer is installed.
• This method produces a high quality clinch joint and minimises the probability of its cracking, splitting or disintegration.
• WO 2006/047848 A1 discloses an arrangement of tools according to the preamble of appended claim 1.
• the purpose of the invention is to provide a simple method of the simultaneous improvement of both key strength parameters, i.e. the width of the undercut and the thickness of the neck.
• the aim is to develop a solution that is simple and cost-effective and does not require any additional energy for the heating of any one of the joined components.
• the invention relates to a an arrangement of tools for the forming of spot joints comprising a punch, a die and a press, wherein the punch of a specified diameter has at its upper end a widening of the width of between 0.1 and 2.0 of the punch diameter, wherein the angle between the punch axis and the outer surface of the widening is 20-70° and the widening has an upper curvature of the radius of 1-10 mm and a bottom curvature of the radius of 0.1-5 mm.
• the angle between the punch axis and the outer surface of the widening in the forming tool arrangement according to the invention is 35-55°.
• This range of values is the most effective in preventing a radial outflow of the material of the top element during the pressing phase and produces the most geometrically favourable joint, i.e. having the thickest neck and widest undercut.
• the invention also relates to a method for the forming of clinched spot joints having better strength parameters, wherein the method comprises the joining of at least two elements: a top element and a bottom element, characterised in that it comprises the following steps:
• the method according to the invention preferably involves an intermediate element that during step a) has a yield strength of between 5% and 50% of the yield strength of the top element, preferably this yield strength is between 15% and 40%.
• This yield strength is between 15% and 40%.
• the top element and bottom element are made of metal sheets, especially steel sheets.
• the use of steel generates the greatest increase in the strength of joints produced according to the described forming method, in comparison to joints produced using traditional methods.
• the advantage of the solution according to the invention is that it provides a method of forming joints that simultaneously increases the shear strength and the transverse tensile (pull-out) strength of clinched joints under simple and complex load conditions.
• Shear strength is directly proportional to the thickness of the neck (S), as can be observed during the shearing process, where the fracture of the top element (BG) occurs at the location of the smallest cross-section. Its lower part remains pressed into the bottom element (BD), while its upper part, together with the opening created by the fracture, is subject to unrestricted displacement.
• Transverse tensile strength meanwhile, is directly proportional to the width of the undercut (P).
• the process of the formation of a joint can be divided into several phases. Once the bottom element (BD) rests on the upper surface of the die (MA) and the position of the top element (BG) relative to the bottom element (BD) is fixed, the punch (ST) moves towards the material. The applied pressure deforms the material and creates an embossing. The process continues, until the bottom sheet comes into contact with the die surface. As a result of the further application of force by the punch (ST), the bottom of the created joint thins out and the material flows out radially. This process is known as pressing.
• This joint forming process therefore provides a simple way of increasing the width of the undercut (P) by reducing the thickness of the bottom of the joint, but this always takes place at the cost of reducing the thickness of the neck (S).
• the method of improving the strength parameters of clinched spot joints comprises the clinching of top element BG and bottom element BD made of 1.2 mm thick DP600 steel by increasing the key geometrical dimensions of the joint, especially of the thickness of neck S and the width of undercut P.
• top element BG and bottom element BD are aligned axially against each other and their position is fixed by pressing them against the retaining surface of die MA using pressing tool DO, as shown in fig. 1 .
• intermediate element PR made of plastic PLA characterised by yield strength R e of 60 MPa, thickness G P1 of 0.4 mm and diameter ⁇ D P of 4.4 mm, is placed above top element BG.
• Intermediate element PR is then formed together with top plate BG and bottom plate BD using a specially shaped punch of the diameter ⁇ D S of 4 mm and a die with an internal diameter of 6 mm.
• the punch as shown in fig. 2 , has an additional widening of the width W of 8 mm, formed at an angle ⁇ of 20°, which is curved with an upper radius R of 1 mm and a bottom radius F of 0.1 mm.
• the forming process is continued until intermediate element PR has the thickness G P2 of 0.08 mm.
• intermediate element PR has the thickness G P1 of 5 mm and the diameter ⁇ D P of 2,4 mm and is formed using a specially shaped punch of the diameter ⁇ D S of 4 mm that has an additional widening of the width W of 0.4 mm, formed at an angle ⁇ of 70°, which is curved with an upper radius R of 10 mm and a bottom radius F of 5 mm.
• the forming process is continued until intermediate element PR has the thickness G P2 of 3.5 mm.
• intermediate element PR is made of temper T4 aluminium alloy 2024 with the yield strength R e of 40 MPa.

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• Engineering & Computer Science (AREA)
• Mechanical Engineering (AREA)
• Insertion Pins And Rivets (AREA)
• Non-Disconnectible Joints And Screw-Threaded Joints (AREA)

Priority Applications (2)

Applications Claiming Priority (1)

Publications (3)

Family

ID=89853621

Family Applications (1)

Country Status (2)

Family Cites Families (6)

• 2023
  • 2023-12-19 EP EP23461696.9A patent/EP4574296B1/en active Active
  • 2023-12-19 PL PL23461696.9T patent/PL4574296T3/pl unknown

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