Patent Application
20060168792
The present invention relates generally to joining sheet material and more specifically, to an apparatus and method that includes using ultrasonic vibrations in combination with a clinching operation to facilitate forming a joint.
Ultrasonic metal welding is a solid-state welding process that produces coalescence through the simultaneous application of localized high-frequency vibratory energy and moderate clamping forces. Ultrasonic welding of various materials is known and can be used to join dissimilar metals and can weld both thin sections and thin to thick sections. It can weld through most oxides and surface oils and creates negligible odor and fumes. Ultrasonic welding requires no welding consumables and is typically cost efficient. Energy consumption is low relative to resistance spot welding and variable costs are significantly lower than for self-pierce rivets.
Ultrasonic welding normally involves vibrating overlapping or adjacent workpieces clamped between a sonotrode and an anvil. Frictional forces occurring between the vibrating workpieces create a bond or weld that occurs at the interface between the workpieces, effectively joining them to one another.
Clinching is a low-cost, mechanical fastening process that can be used to join both similar and dissimilar materials of varying thickness. Clinching involves clamping the sheets in a die and using a punch to squeeze the sheets between the punch and the die causing sideways movement of the material to form an interlock or joint between the sheets. The process does not result in a heat-affected zone, requires no joining consumables, is characterized by long tool life and low maintenance requirements and does not require high current electrical systems. Clinching operations, however, employ large clamping forces, thereby requiring heavy equipment frames that can impose access limitations. In addition, clinch joints are characterized by lower peel and shear strengths than resistance spot welds and self-pierce riveted joints.
In addition, the clinching operation may require substantial deformation of the sheet material to be joined in order to form a proper bond. In some cases, the deformation can be particularly difficult, specifically when joining high-strength metal sheets, which tend to be more brittle and thus may develop cracks or stress in the joint area.
Therefore, there is a need in the art to provide an apparatus for joining two members or workpieces that utilizes or takes advantage of the benefits of both clinching and ultrasonic welding. Combining the use of ultrasonic energy with clinching overcomes limitations associated with traditional clinching operations and enhances ultrasonic metal welding capability. Accordingly, the combination of clinching and ultrasonic welding can reduce clamping force requirements, promote material flow and deformation and result in increased joint strength.
Accordingly, the present invention is a method and apparatus for joining adjacent members, including multiple layers of material, that combines a mechanical bonding process or operation with imparting vibrational energy to the members to reduce clamping force requirements, promote material flow and deformation and increase joint strength.
In one embodiment, the present invention provides a method for joining a plurality of adjacent members or multiple layers of materials including a clinching process. The method includes several steps operating alone or in combination, including the step of placing the members in an overlapping relationship and clamping the members between a die and a blank holder; performing a clinching operation wherein the clinching operation uses a punch to deform the members and create at least a partial bond between the members; and imparting a level of vibrational energy to at least one of the plurality of members before, during or after the clinching operation is performed to assist in the clinching process and in some cases, create an ultrasonic weld between the members.
Further, the present invention provides an apparatus for joining a plurality of overlapping members. The apparatus includes a punch and a die wherein the members are positioned between the punch and the die. The punch cooperates with the die to deform and form an interlock between the members. A transducer connected to either the punch or the die operates to vibrate either the punch or the die, or possibly both, and impart vibrational energy to at least one of the members either before, during or after the members are deformed by the punch and die.
In a further embodiment, the apparatus includes a sonotrode and an anvil. The plurality of overlapping members or multiple layers of material is positioned between the sonotrode and the anvil. The respective sonotrode and anvil having contact surfaces configured such that the clamping pressure exerted on the members by the sonotrode and anvil coupled with vibrational energy imparted by a transducer causes deformation of the members and creates at least a partial bond between the members.
The apparatus 10 includes a base 16, a press support and column 18 and a head 20 connected to the press support and column 18. A punch assembly 22 is mounted to the head 20 for reciprocal movement in the direction of the arrow 24. The punch assembly 22 includes a punch 26; see
The apparatus 10 also includes a die assembly 32 secured to the base 16. The die assembly 32 includes a cylindrically shaped die 34. The cylindrically shaped die 34 includes an anvil 38. A plurality of die segments 36 surrounds the circumference of the anvil 38. The die segments 36 cooperate with the anvil 38 to form a generally annular wall defining a cavity 40. Typically, an elastic band, spring or other mechanical restraint 42 surrounds the die segments 36 to retain the die segments 36 in position about the anvil 38. While the die assembly 32 is disclosed herein as including a plurality of moveable die segments 36, this is for illustration purposes. The invention is also suitable for use with a die assembly 32 utilizing a fixed die; i.e., a die having a shaped cavity wherein the punch forces the overlapped sheets of material 12, 14 into the shaped cavity, causing the material to deform to fill the cavity.
Accordingly, the apparatus 10 is capable of performing a clinching operation to achieve at least a partial mechanical bond between the first and second sheets of material 12, 14. In accordance with a typical clinching operation, the punch 26 cooperates with the die 34 as follows: the punch 26 forces the sheets 12, 14 down into the cavity 40. The punch 26 and anvil 38 squeeze the sheets 12, 14 between them causing sideways movement of the material of the sheets 12, 14 to form an interlocking button 44, see
As shown in
In the present embodiment, the transducer 46 is an ultrasonic transducer of the type utilized for ultrasonic welding. Thus, the transducer 46 operates in a known manner to impart vibrational energy along the longitudinal axis 30 or axis of punch translation. Further, in accordance with the present invention, the vibrational energy can be imparted to the first or second members or sheets of material 12, 14 at various times or stages during the bonding or fastening sequence. In addition, the vibrational energy may be imparted to the first or second members 12, 14 more than once. Specifically, the vibrational energy may be imparted at the start of the clinching operation, during the middle of the clinching operation or at the end of the clinching operation. Thus, depending upon the material being joined, the application of the vibrational energy can be varied to provide assistance with a conventional clinching operation.
For instance, upon initial contact of the punch 26 with the first member or sheet 12, ultrasonic vibrational energy may be applied or imparted to the first or second members or sheets 12, 14. The ultrasonic vibrational energy acts to reduce interfacial friction and assist in material deformation. In addition, during the clinching process ultrasonic vibrational energy may be applied or imparted to the first or second members or sheets 12, 14 since ultrasonic vibrations promote material flow and deformation and thereby reduce the risk of developing cracks in the joint area. Finally, after the clinching operation ultrasonic vibrational energy may be applied to take advantage of metal to metal solid-state joining of the first and second members or sheets 12, 14 through an ultrasonic welding process.
In the current embodiment, the punch 26 is shown separate from the blank holder 28. Thus, the transducer 46 transmits the vibrational energy directly to the first and second members or sheets of material 12, 14 rather than being dampened by a spring member used to hold the blank holder 28 against the first sheet of material 12.
As shown in
As shown in
Accordingly, imparting vibrational energy along the longitudinal axis 30 of the punch 26 increases the relative motion between the sidewalls 82, 84 of the first and second members or sheets of material 12, 14 formed in the generally cylindrical cup like shape 50 shown in
In addition to connecting the transducer 46 to the punch 26, the transducer 46 may be connected to the die assembly 32 and in particular the anvil 38. In this manner, the vibrational energy may be imparted to the second member or sheet 14 through contact with the die assembly 32 or through contact with the anvil 38. It should be understood that the geometry, material, temperature and surface pattern of the punch assembly 22, including the punch 26, and the die assembly 32, including the anvil 38, will impact the effectiveness of energy transmission, and in particular ultrasonic energy transmission and impartation thereof to the first or second members or sheets 12, 14 and should be optimized for minimal sticking, adhesion to the first and second members, useful life and cost. In addition, these factors should also be considered when determining whether the vibrational energy should be imparted to the first or second members or sheets 12, 14 through either the punch assembly 22 or die assembly 32.
Accordingly, the joint strength from combining the clinching and ultrasonic welding processes is considerably higher since the mechanical interlock formed by clinching is combined with the metal-to-metal solid-state joining of ultrasonic welding.
Turning now to
With a typical ultrasonic welding apparatus, both the sonotrode and the anvil have a contact surface, that is, the surface of the sonotrode or anvil that contacts either the first or second member or sheet of material 12, 14. As shown in
Accordingly, the clamping force applied in the direction of the arrow 64 along with the vibration of the sonotrode 60 causes deformation or material flow of the material of the first and second members or sheets of material 12, 14. In particular, as shown in
The apparatus of the present invention utilizes an anvil to support the first and second members or sheets of material 12, 14 during the joining operation. In some circumstances, however, the mass and stiffness of one of the first or second members 12, 14 is adequate to allow it to act as the anvil thereby eliminating the need for a separate anvil. For instance, when joining a small or thin member to any portion of a large member or frame, the mass and stiffness of the large member or frame may be sufficient such that only the sonotrode or punch need be used. That is, no anvil is required where the mass of the larger member is sufficient to resist the clamping force of the sonotrode or punch. In addition, the clamping force of the sonotrode or punch is sufficient to locally deform both the thin member and the large member to create both an ultrasonic weld and a partial mechanical bond. Accordingly, this eliminates the need for an anvil.
In addition to applying a gripping pattern to the contact surfaces 72, 74 of the sonotrode tip 70 and anvil 66, as is typical in ultrasonic metal welding, a gripping pattern can also be applied about the periphery or perimeter of the contact surfaces 72, 74. Specifically, the surface extending along the longitudinal or clamping/punch motion axis and contacting one of the first or second members or sheets of material 12, 14. This facilitates an increase in the relative motion between the first and second members or sheets of material 12, 14 to promote the formation of a stronger ultrasonic weld.
In addition, unidirectional vibrational input may result in axial variations in clinch-weld mechanical properties. Introduction of torsional ultrasonic vibrations to the punch and/or die or the use of torsional ultrasonic metal welding systems would result in more axially symmetric clinch weld properties, with the formation of a stronger ultrasonic weld not only across the bottom of the joint button but along its sidewalls. Again, the addition of a gripping pattern about the perimeter or peripheral surface of the tool extending along the longitudinal or clamping axis, promotes an increase in relative motion between the members or sheets of material to be joined and thus facilitates the formation of an ultrasonic weld. As set forth previously, the vibrational energy can be introduced or applied more than once during the clinching operation. For example, the vibrational energy can be applied initially in a direction transverse to the longitudinal axis of the punch and may then be applied in a torsional manner whereby the punch rotates about its longitudinal axis. Further, the punch may be repositioned before applying the vibrational energy a second time.
The combination of clinching and welding processes is not limited, as set forth above, to ultrasonic vibrational frequencies. Clinching and welding processes can also be combined such that they exploit lower frequency vibrations, which are characterized by higher power, energy and amplitude levels. Additionally, the vibrational energy can be applied at multiple times and in multiple directions depending upon the particular materials being joined.
It will thus be seen that the objects of the invention have been fully and effectively accomplished. It will be realized, however, that the foregoing specific embodiments have been shown and described for the purposes of illustrating the functional and structural principles of the invention and are subject to change without departure from such principles. Therefore, this invention includes all modifications encompassed within the scope of the following claims.
