In automotive manufacturing, polymeric composites are being used increasingly due to their favorable characteristics, including being lightweight, highly-conformable or shapeable, strong, and durable. Some composites are further colorable and can be finished to have most any desired texture.
The increased use in automobiles includes, for instance, in instrument and door panels, lamps, air ducts, steering wheels, upholstery, truck beds or other vehicle storage compartments, upholstery, external parts, and even engine components. Regarding engine components, and other under-the-hood (or, UTH) applications, for instance, polymers are configured, and being developed continuously, that can withstand a hot and/or chemically aggressive environment. Regarding external parts, such as fenders, polymers are being developed that are online paintability and have high heat and chemical resistance over longer periods of time. And many other potential usages in automotive applications are being considered continuously.
With this trend, finding ways to efficiently and effectively join polymer components is becoming progressively important. Compression molding and post-mold joining techniques—e.g., ultrasonic welding—are being used more commonly.
Traditional techniques have various shortcomings. With reference to the figures, and more particularly the first figure, FIG. 1 shows schematically a conventional ultrasonic welding arrangement 100 including a welding horn 102 and two workpieces 104, 106 prior to welding.
In the illustrated step, the horn 102 is lowered, as indicated by down arrow, toward contacting a top workpiece 104 of the two. Once in contact with the piece 104, an ultrasonic generator connected to the horn excites high-frequency ultrasonic vibrations, which are passed through the horn to the piece. At the interface heat is generated and the workpiece 104 begins to melt 200, as shown in FIG. 2.
FIG. 3 shows the arrangement 100 after it has been melted sufficiently for the molten material of the workpieces to connect the pieces 104, 106 at a joint 300.
The technique has shortcomings including the formation of unwanted excess, or squeeze-out, workpiece material 302 on the top surface of the proximate workpiece 104. The excess material develops at least in part because the workpiece material expands as it melts.
One option for handling this situation is to remove the excess material 302 from the now-welded workpiece arrangement. This cleaning is of course time consuming, eating up critical cycle time in the manufacturing process. Another shortcoming to this option is the energy—e.g., manpower or robotic resources, to perform the cleaning.
The cleaning can also add significant other cost, such as cost of purchase, customizing (programming, etc.), and maintenance of cutting machinery—e.g., blade-based, or light-based cutting tools.
Further challenges arise whether cleaning the excess 302 prior to or after the excess has cooled. Whether the excess has hardened by cooling, special care would need to be taken to ensure that the material 302 is removed without affecting the balance of the cooling or cooled material undesirably. Upsetting a surface portion of the cooling or cooled material could affect cosmetic quality of the resulting part. It is also contemplated that rough removal of the excess 302, such as by chipping at the material after hardening, could upset an integrity of the connection 300.
Another alternative is to use ultra-high-power ultrasonic energy. When more ultrasonic energy is used, the top workpiece, and eventually the bottom one, melts more quickly, and so the desired welding 300 is formed more quickly. In this way, less ancillary, lateral, workpiece material is melted, and so less excess material formed. This approach also is cost prohibitive, though. Moreover, excess material could still form.
Still another alternative is conventional mechanical fastening. The workpieces can be screwed together, or connected by nuts and bolts, for instance. These connections have shortcomings including unwanted added weight, unsightly exposed portions of the fasteners, and possibly less-robust joints.