DIFFERENTIAL WELD BEAD GEOMETRY

Abstract: The invention involves a method of vibration welding thermoplastic surfaces together by using specially formed weld beads. In a disclosed embodiment of this invention, a plastic surface has at least one weld bead (20) with an outermost portion (30) smaller than the base of the weld bead. Due to the smaller width of the outermost portion, greater pressure is brought to bear on the point of surface contact during vibration welding than by using uniform and conventional flat faced weld beads. Moreover, a smaller load of frictional heat is required to commence the welding process given the smaller point of contact.

Description: DIFFERENTIAL WELD BEAD GEOMETRY BACKGROUND OF THE INVENTION The present invention relates to weld beads and methods for vibration welding of thermoplastic joints through the use of weld beads. In the field of thermoplastics, vibration welding is frequently used to weld thermoplastic joints together. As known in the prior art, vibration welding is conducted by vibrating two thermoplastic parts under pressure along a common interface to generate frictional heat and to thereby melt and fuse their surfaces together. Vibration welding is a quick and inexpensive way to join irregularly shaped parts of various sizes. In the past, vibration welding has been used in low load-bearing applications. In automobile underhood applications such as air intake manifolds, resonators, air filter housings, the expanded use of engineered plastics is desirable to achieve savings and weight and cost. To facilitate the use of such plastics, improvements in the welding techniques are necessary. Welding results are extremely sensitive to significant changes in the weld process. Vibration welding parameters of pressure, frequency, amplitude, oscillation (welding) time, hold time, weld thickness, and surface contamination all affect tensile strength of welds. Weld beads assist in the welding process. Typically, a series of weld beads are formed on one or both of the abutting surfaces undergoing welding. However, before the present invention, weld beads were uniform and continuously flat faced. In a production setting, surface contamination on the weld beads (such as oil) inhibit the generation of frictional heat at the common interface whether the common interface is weld bead to weld bead or weld bead to weld face. Time-consuming efforts have been used to control the level of contamination at these surfaces. In addition, known weld bead designs are deficient for use in the vibration welding of the internal walls of plastic manifolds and plastic resonators. It has been difficult to bring pressure to bear at the common interface of an internal wall and a plastic shell body such as a plastic resonator or manifold body. Due to the dimensions of the plastic shell body, the vibration weld fixture is too distant from the joint to be welded. Accordingly, the vibration welding of internal walls required designers to core out the resonator or manifold body, or otherwise design the body to provide support at the common interface between the internal wall and plastic shell. As a consequence, design options were limited to accommodate this production concern. It is an object of the present invention to address the foregoing production problems. SUMMARY OF THE INVENTION The invention involves a method of vibration welding thermoplastic surfaces together by using specially formed weld beads. In a disclosed embodiment of this invention, a plastic surface has at least one weld bead with an outermost portion smaller than the base of the weld bead. Due to the smaller area of the outermost portion, initial pressure is brought to bear on the surface contact during vibration welding than by using larger, uniform and conventional flat faced weld beads. Moreover, a lower level frictional force is required to commence the welding process given the smaller area of contact. As the welding process proceeds, the outermost portion melts down to the base of the weld bead and is then at full weld joint width. In one embodiment of the invention, the outermost portion of the weld bead has a texture. This texture can take the form of a pattern such as a Crosshatch, knurl, or pebble pattern. Such a texture greatly improves the vibration welding of surfaces that have surface contamination such as oil. In another embodiment of the invention, the outermost contact area is a wedge. This embodiment is particularly useful in the welding of the internal walls of a plastic body such as an air intake manifold or a plastic resonator. Due to the reduced force created at the point of contact by the specially designed and formed welding bead and the decreased frictional load required to commence the welding process, internal walls can easily be welded to the plastic body without the need to core out the body to accommodate welding fixtures. Greater design opportunities for plastic bodies such as manifolds or resonators are thus available. In general, all of the inventive embodiments have weld beads with an outermost portion of a smaller outer cross-section contact area, and which increases as the bead is consumed. Some embodiments are wedge-shaped, while other embodiments are irregular surfaces. However, the embodiments all do include this feature. BRIEF DESCRIPTION OF THE DRAWINGS The various features and advantages of this invention will become apparent to those skilled in the art from the following detailed description of the currently preferred embodiment. The drawings that accompany the detailed description can be briefly described as follows: Figure 1 shows a cross-sectional view of a weld bead as known in the prior art. Figure 2 shows a weld bead in an embodiment of the present invention. Figure 3 shows a weld bead in an embodiment of the present invention and its application to a hollow plastic body. Figure 4 shows various embodiments of the present invention. Figure 5 shows an embodiment of the present invention, a weld bead with a Crosshatch pattern. Figure 6 shows an embodiment of the present invention, a weld bead with a knurl pattern. Figure 7 shows an embodiment of the present invention, a weld bead with a pebble pattern. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT Figure 1 shows weld bead 20 with a uniform and continuously flat face as known in the prior art. Typically, weld bead 20 has a height (shown here as 3.2 millimeters) and a base width (shown as 2.5 millimeters). Flash traps 22 surround weld bead 20 and provide an area for the melting of weld bead 20 and the displacement of any surface debris. Flash trap 22 is shown having a depth of 1.7 millimeters and a width of 1.0 millimeter. As known in the prior art, upper surface shell 26 is vibrated (at say 200 hertz) by a vibration welder, as commercially available. The lower shell 24 remains stationary. The vibration and consequent friction from the rubbing of weld bead 20 against upper shell 26 melts weld bead 20, welding upper surface 26 to lower surface 24. The crosshatched portion of weld bead 20 is consumed during the welding process. Shells 24 and 26 are most preferably part of an air intake system for vehicle engines. An inability to create sufficient pressure between lower surface 24 and upper surface 26 inhibits the melting of weld bead 20. The welding of hollow shells such as air resonators and air manifolds presents this problem as the welding fixture that supports the shells in the vibration welder is typically distant from interface 28 between weld bead 20 and surface 26. Figure 2 shows an embodiment of the present invention. Figure 2 illustrates the outermost portion of weld bead 120 in the shape of a wedge 30. The cross-section of weld bead 120 includes first cross-section 32 at an outermost portion smaller than second cross-section 34 spaced into the weld bead 22. Wedge 30 is shown with a height of 1.2 millimeters, a base width of 2 millimeters and a radius of 0.5 millimeters. Wedge 30 extends into flash trap 22 on lower shell 36. Of course, the location of weld bead 120 could also be on the lower shell 36. Trap 22 is shown with a width of 3.5 millimeters and a depth of 1.5 millimeters. Obviously, other configurations and sizes of both bead and trap can be used. During the vibration welding process, wedge 30 oscillates along the point of surface contact. The very low initial contact area generates lower friction forces at the onset of the welding process. Once friction temperature is created at the interface, molten plastic is produced, lowering vibration force loading. As the welding proceeds, the melting first cross-section 32 increases to the final meltdown distance, which is the design width 34 of the joint. The Figure illustrates a good portion of the wedge crosshatched. Again, the crosshatched portion shows the original shape of the weld bead 30. Wedge 30 is particularly useful in the vibration welding of the internal walls of hollow plastic bodies such as plastic manifolds and resonators. An internal wall weld joint needs less width than a structural wall weld joint. A smaller weld joint width provides sufficient sealing capability for an internal wall. The load at the end of the welding process is lower than that of conventional weld beads 20. Since the amount of meltdown material is considerably less than that of conventional (flat) weld beads, the space required for a flash trap may be less as well. Thus, relatively thin internal walls are possible without weld fixture support, allowing more design options and internal wall features. Figure 3 shows another application of the present invention. As shown in Figure 3 , plural wedges 40 have been used to connect a hollow plastic body such as tuning tube 42 of a resonator to upper shell 44. As in the above embodiments, the original shape of bead 40 is shown crosshatched after the bead has been consumed. Tuning tube 42 is typically molded with very thin wall sections. Wedges 40 allow for the vibration welding of tuning tube 16 to upper shell 44. The low initial weld load and minimized overall weld bead width reduces the likelihood of any collapse of tuning tube 16. Wedges 40, as shown, have a width of 1 millimeter at its base and a height of 1.5 millimeters. Here, wedges 40, spaced 0.67 millimeters apart, are shown. One wedge 40 may also accomplish the welding. Obviously, other configurations and sizes can be used. Figure 4 shows configurations 46 A, 46B, and 46C as differing wedge shapes. 46A is a wedge of an included angle (here 45 degrees). 46B is a wedge of an included angle (here 120 degrees). For successful welding, the included angle may range from approximately 45 degrees to about 120 degrees. Additionally, the wedge may have a crown as shown in 46C. Conventional weld bead 20 is shown as well. Figure 5 shows the first cross-section 48 in the form of texture on weld beads 220. Optimally, such texture has a depth ranging from approximately 0.0635 millimeters to about 0.254 millimeters with an included angle from approximately 4 degrees to about 10 degrees. In Figure 5, the texture consists of a Crosshatch pattern on weld bead 220 with a depth ranging from approximately 0.2 millimeters to about 0.5 millimeters. The angle of the Crosshatch ranges from approximately 30 degrees to about 80 degrees in relation to the direction of vibration of weld bead 220. Here, Crosshatch pattern 48 is shown applied against weld bead 222. Figure 6 shows the first cross-section 50A and 50B in the form of a knurl pattern on two opposing weld beads 52 and 54. The pattern has a depth ranging from approximately 0.2 millimeters to about 0.5 millimeters. The angle of the knurl ranges from approximately 30 degrees to 80 degrees in relation to the direction of vibration of weld beads. Here, weld bead 52 is applied against weld bead 54 and therefore pattern 50A is applied against pattern 50B. Finally, Figure 7 shows the first cross-section 56 in the form of a pebble pattern on weld beads 58. The pattern has a depth ranging from approximately 0.2 millimeters to about 0.5 millimeters. Pattern 56 is applied against pattern 56. The embodiments of Figures 5, 6 and 7 are useful to reduce the affect of surface contamination such as oil on weld beads 20, 220, 52, 54, and 58. Specifically, the area of contamination is reduced to the initial contact areas of patterns 48, 50A, 50B and 56. Surface contamination is also displaced to the depths of the texture or pattern during the vibration welding process. Moreover, less frictional force is required to commence the welding process. The heat generated even burns off the contamination. The Figures show some of configurations applied against well beads. Any of the configurations could be used against another bead or a flash trap. In general, all of the inventive embodiments have weld beads with an outermost portion of a smaller cross-section contact area, and which increases as the bead is consumed. Some embodiments are wedge-shaped, while Figure 5-7 embodiments are irregular surfaces. However, the embodiments all do include this feature. The aforementioned description is exemplary rather then limiting. Many modifications and variations of the present invention are possible in light of the above teachings. The preferred embodiments of this invention have been disclosed. However, one of ordinary skill in the art would recognize that certain modifications would come within the scope of this invention. Hence, within the scope of the appended claims, the invention may be practiced otherwise than as specifically described. For this reason the following claims should be studied to determine the true scope and content of this invention.

Claims: CLAIMS 1. A plastic body to be vibration welded comprising: a surface; and at least one weld bead of a cross-section that provides a first cross- section at an outermost portion smaller than a second cross-section spaced into said weld bead. 2. The plastic body of claim 1 , wherein said first cross-section is a texture. 3. The plastic body of claim 2, wherein said texture is raised pebbles. 4. The plastic body of claim 2, wherein said texture is knurls. 5. The plastic body of claim 2, wherein said texture is crosshatches. 6. The plastic body of claim 2, wherein said texture has a depth ranging from approximately 0.0635 millimeters to about 0.254 millimeters with an included angle from approximately 4 degrees to about 10 degrees. 7. The plastic body of claim 1 , wherein said weld bead is a wedge. 8. The plastic body of claim 7, wherein said wedge has an included angle from approximately 45 degrees to about 120 degrees. 9. The plastic body of claim 1 , wherein said surface has a plurality of weld beads. 10. A method for vibration welding comprising the steps of: providing a surface with at least one weld bead for vibration welding to another surface; forming at least one weld bead of a cross-section that provides a first cross-section at an outermost portion smaller than a second cross-section spaced into said weld bead; pressing the surfaces together; and vibrating the surfaces together to thereby form a weld between the surfaces. 11. The method of claim 10, wherein a texture is formed on the weld bead. 12. The method of claim 10, wherein a wedge is formed on the weld bead. 13. The method of claim 10, wherein a plurality of weld beads are formed on at least one surface. 14. The method of claim 10, wherein at least one weld bead is vibrated against a flash trap. 15. The method of claim 10, wherein at least one weld bead is vibrated against another weld bead. 16. The method of claim 10, wherein at least one of said surfaces is an internal wall of a plastic body. 17. A vibration welded article produced by a method comprising the steps of: providing a surface with weld beads for vibration welding to another surface; forming at least one weld bead of a cross-section that provides a first cross-section at an outermost portion smaller than a second cross-section spaced into said weld bead; pressing the surfaces together; and vibrating the surfaces together to thereby form a weld between the surfaces. 18. The vibration welded article of claim 17, wherein a plurality of weld beads are formed on at least one surface. 19. The vibration welded article of claim 17, wherein said surfaces are used in a vehicle air supply system.

Inventors: BLOOMER STEPHEN FRANCIS, BROOKS MICHAEL ANTHONY, MORRISON DOUG, SCHWARZPECH KARL ROBERT, BLOOMER, STEPHEN, FRANCIS, BROOKS, MICHAEL, ANTHONY, MORRISON, DOUG, SCHWARZPECH, KARL, ROBERT
Applicants: SIEMENS CANADA LTD, SIEMENS CANADA LIMITED
Application year: 2000
Main classification: B29C65
IPC codes: B29C65