GB2259885A

GB2259885A - Friction weld orientation system

Info

Publication number: GB2259885A
Application number: GB9217556A
Authority: GB
Inventors: Francis C Peterson
Original assignee: Illinois Tool Works Inc
Current assignee: Illinois Tool Works Inc
Priority date: 1991-08-26
Filing date: 1992-08-18
Publication date: 1993-03-31
Also published as: JPH05254021A; GB9217556D0; BR9203406A; JPH0745183B2

Abstract

A friction weld orientation system 10 is provided for attaching and orienting precisely a series of thermoplastic fasteners 12 in substantially the same orientation relative to a substrate each time. The fastener 12 includes a base member 14 and a primary fastening element 16 formed integrally with the base member 14, which has a bottom surface adapted to be fused to the substrate by heat of friction induced by the application of rotative and axial forces applied to the fastener 12. A programmable DC servomotor 30 is provided for rotating the fastener 12 relative to the substrate and for automatically stopping rotation of the fastener 12 after a preset number of revolutions so that the primary fastening element 16 of the fastener 12 is precisely oriented in the same reference position each time in relationship to the substrate. <IMAGE>

Description

FRICTION WELD ORIENTATION SYSTEM This invention relates generally to friction or spin welding systems and more particularly to a friction weld orientation system for attaching and orienting precisely a series of thermoplastic fasteners in substantially the same orientation relative to a substrate each time.

Various types of friction welded fastener systems are generally known in the prior art as evidenced by the following U.S. Patent Nos.: 2,470,963 to Weyl; 3,438,825 to Fidler; 3,580,79 to Hewitt; 4,250,596 to Hara et al; 4,477,307 to Cearlock et al; 4,551,189 to Peterson; 4,636,124 to Gugle et al; and 4,824,304 to Shibayama et al.

The friction or spin welding techniques typically involve fusing of a thermoplastic fastener to a substrate by frictionally heating the interface between the fastener and the substrate through the application of rotative and axial forces therebetween. As a consequence, when a molten state has been achieved at the interface of the thermoplastic fastener and the substrate the rotation is stopped while the axial force is still maintained for a sufficient amount of time so as to form an adhesive bond therebetween. It should be noted that the thermoplastic fastener could also be a stud, post or any other design element which is desired to be fused to the substrate.

In U.S. Patent No. 4,477,307, there is disclosed a friction welded fastening system for fusing a thermoplastic fastener to a workpiece. The system includes a tool for rotating and applying pressure to the fastener and means for automatically stopping rotation of the fastener while maintaining contact pressure between the fastener and the workpiece. The means to automatically stop rotation includes at least one heat sensitive thermoplastic protrusion disposed adjacent the primary fastening surface and at least one projection formed on the tool so that when the protrusion reaches a predetermined minimum strength the projection causes the protrusion to yield and the fastener to stop rotating.

In U.S. Patent No. 4,551,189, there is disclosed a friction welding fastener system for fusing a thermoplastic material fastener to a substrate by heat of friction induced through the application of rotative and axial forces applied to the fastener. A cavity is formed inwardly of the bottom surface of the thermoplastic base member. A heat activated adhesive material having a bonding affinity for both the base material and the substrate material is inserted into the cavity to form a layer having a thickness equal to or greater than the thickness of the base member. The base member is rotated with sufficient rotative and axial forces to cause the heat activated adhesive layer to adhere to the substrate.

In U.S. Patent No. 4,824,304, there is described a rotary welding member made of resin which includes a post portion and a disk-shaped flange portion integrally mounted on one end of the post portion. The flange portion includes a plurality of radially extending ribs formed on its one surface for causing cooling air to flow thereacross so as to dissipate excessive heat generated. Thus, there is prevented deterioration of a substrate to be frictionally welded to the flange portion.

The major shortcoming common to all of the prior art spin welding systems, whether they used a heat activated adhesive in conjunction with the thermoplastic fastener or not, is that none of them had a way of providing a precise orientation of the thermoplastic element relative to the substrate to which the thermoplastic element is to be welded each time. For example, the thermoplastic element may include a hooked portion which must be aligned at the termination of the spin welding operation so that the hooked portion faces downwardly. This is necessary when the hooked portion is subsequently to be inserted into a co-mating aperture, such as when serving to attach a moulding strip to the exterior of an automotive body.

It would be desirable to provide an improved friction weld orientation system for attaching and orienting precisely a thermoplastic fastener in substantially the same position relative to a substrate each time.

According to one aspect of the present invention, a friction weld orientation system comprises: a thermoplastic fastener, as hereinafter defined, adapted to be fused to a substrate, said fastener having a base member and an upper element formed integrally with said base member; said base member having a bottom surface adapted to be fused to said substrate by heat of friction induced by the application of rotative and axial forces applied to said fastener; pressure means for applying the axial force to said fastener; and motor means for rotating said fastener relative to said substrate and for automatically stopping rotation of said fastener after a preset number of revolutions so that said upper element of said fastener is precisely oriented in a required reference position in relationship to said substrate.

Other aspects of the present invention include a fastener per se and methods for attaching and orienting precisely during a friction welding operation.

The advantages of the present invention will become more fully apparent from the following detailed description, when read in conjunction with the accompanying drawings wherein: Figure 1 is a perspective view of a thermoplastic fastener for use in conjunction with a friction weld orientation system of the present invention; Figure 2 is an enlarged front elevational view of the fastener of Figure 1; Figure 3 is an enlarged cross-sectional view of the fastener of Figure 1, taken along the line 3-3 of Figure 2; Figure 4 is a perspective view of a plurality of thermoplastic fasteners, each fused with an identical orientation to a substrate by using the friction weld system of the present invention; Figure 5 is a side view of a friction weld orientation system, constructed in accordance with the principles of the present invention;; Figure 6 is an end view of the friction weld orientation system of Figure 5; Figure 7 is front view, partly in section, of a holding tool for use with the friction weld orientation system of Figure 5; Figure 8 is a bottom end view of the holding tool of Figure 7; Figure 9 is a cross-sectional view, taken along the line 9-9 of Figure 4 and illustrating mechanical studs helping to join the fastener to the substrate; and Figure 10 is a motion profile of a positioning motor having a trapezoidal shape so as to produce the precise orientation of the fastener.

Referring now in detail to the drawings, there is shown in Figures 5 and 6 a friction weld orientation system 10 constructed in accordance with the principles of the present invention. The present friction weld system involves the use of a thermoplastic fastener 12 which may have the structure as illustrated in Figures 1 to 3. The friction weld orientation system 10 is used for attaching and orienting precisely the thermoplastic fastener 12 in substantially the same position relative to a substrate each time.

The thermoplastic fastener 12 is comprised of a discshaped base member 14 and a primary fastening element defined by a hooked portion 16 which is formed integrally with the base member. The base member 14 has a top or front surface 18 and a bottom or rear surface 20. The base member 14 includes a plurality of holes or openings 22 disposed adjacent its peripheral edge and extending from the top surface 18 to the bottom surface 20.

In the central part of the bottom surface 20, there is provided preferably a circular-shaped raised portion 24 which is adapted to firstly engage with the surface of the substrate to which the fastener is to be welded. The raised portion 24 serves to maintain the starting torque low since the bottom surface 20 is held away from the surface of the substrate initially. Thus, the heat will begin to build up first at the central raised portion 24 causing the same to melt to create subsequently a molten thermoplastic material between the bottom surface 20 of the fastener and the surface of the substrate. Then, the melting process will progress gradually toward the peripheral edge of the fastener.

At substantially the central portion of the top surface 18 of the base member 14, there is formed integrally the hooked portion 16 having a stem portion 17 and terminating in a downwardly projecting end or tip 26.

In order for the projecting tip 26 to perform its designed function, it is generally necessary to attach and orient precisely the fastener 12 in substantially the same position relative to the substrate each time. As previously pointed out, it may be desired that the hooked portion 16 of the fastener be aligned at the termination of the spin welding operation so that the projecting tip 26 thereof points downwardly. For instance, the projecting tip 26 may be required to be subsequently insertable into a co-operating aperture of a piece of moulding strip in order to retain the moulding strip.

The thermoplastic fastener 12 is preferably in the form of a single unitary body of a thermoplastic material.

Further, the fastener can be manufactured in any conventional process, such as by insert injection moulding.

It should be understood that the fastener described is only for the convenience of illustration and may take on various shapes and sizes. Moreover, the fastener could also be a stud, post or any other design element which is desired to be fused to the substrate by friction welding.

In Figure 4, there is depicted an example of four such thermoplastic fasteners 12a-12d in which all have been attached and oriented precisely in the same way each time relative to a substrate 28 by utilising the friction weld orientation system of the present invention. It should be noted in particular that each of the projecting tips 26 of the respective fasteners 12a-12d points downwardly in an identical manner. Thereafter, these projecting tips 26 can be received in corresponding aligned openings so as to perform their designed function.

With attention directed again to Figures 5 and 6 of the drawings, the friction weld orientation system 10 includes a precision positioning motor 30, such as a stepper motor or a programmable DC servomotor, which can be controlled accurately to stop automatically, after a preset number of total revolutions has been completed, in the same position or reference at which it was started. In other words, the motor can be positioned in relationship to a defined zero reference position after a predetermined distance has been travelled (i.e. 10,000 motor steps which is equal to one revolution). The positioning motor 30 is preferably of the type which is commercially available from Compumotor Division of Parker Hannifin Corp. sold under their part Nos. CPL57-120, CPL83-150, CPH83-150 and CPH106210.

In Figure 10, there is illustrated a motion profile of the positioning motor 30 having a trapezoidal shape so as to stop the fastener in an exact predetermined orientation.

As can be seen the positioning motor has a very rapid acceleration time ta where the velocity is increased from zero to its maximum speed, i.e. 3600 revolutions per minute. Then, the velocity is maintained at a constant speed for tc which is sufficient to melt the thermoplastic material.

The positioning motor is programmed to have a deceleration time td which occurs after the time tc has been completed. In this manner, the motor is decelerated for a brief definite period of time prior to stopping in which the velocity is decreased very rapidly from its maximum speed to zero. By controlling the deceleration time td, the fastener can be stopped in a precise orientation after melting of the thermoplastic material at the interface with the substrate.

To this end, there are provided thumbwheel switches 31 which are used to preset the total number of desired revolutions to be made by the motor 30. Of course, the number of total revolutions is selected to frictionally heat the bottom surface 20 of the fastener 12 in order to sufficiently create a puddle of molten thermoplastic material between the fastener 12 and the substrate 28. It should be understood that the number of revolutions to achieve this molten interface must be determined empirically and is dependent upon a variety of factors such as the fastener material, the substrate material, the size and configuration of the interface, the amount of contact pressure, the rotational speed of the motor, and a number of other indeterminate factors.

The positioning motor 30 has a shaft 32 having its free end connected to one end of a chuck (not shown). The other end of the chuck is adapted to be connected to a first end of a holding tool 34. The second end of the holding tool 34 is engageable with a top surface of the fastener part or element 12a (Figure 4) which is to be welded to the substrate. The holding tool is used to place initially the fastener part in a starting reference position in relationship to the substrate. The substrate 28 is supported on a locator fixture 36 which is disposed underneath the holding tool and above a bottom frame member 38.

A pneumatic or hydraulic cylinder 40 is provided for reciprocating the motor 30 and the holding tool 34 having the fastener part 12a joined thereto so as to press the raised portion 24 of the fastener 12a against the top surface of the substrate 28 (as indicated in the direction of arrow 42 in Figure 6). A typical pressure applied is in the range of approximately 6.8-68kg (15-150 lbs) load which is dependent upon a variety of factors, such as the size and configuration of the fastener part. When the pressure reaches the predetermined amount, the motor is turned on by depressing a pushbutton switch 43.The motor will be rotated rapidly at a high speed (i.e. approximately 3600 rpm) so as to reach the total number of preset revolution counts, as set by the thumbwheel switches 31, and then will automatically stop in precisely the same position in relationship to the starting reference position (i.e. zero reference). In practice, it has been encountered that time required for fusing the fastener and the substrate together is approximately 2-3 seconds.

In this manner, the projecting tip 26 of the hooked portion 16 will always be aligned or oriented precisely in the desired position with respect to the substrate 28 to provide the structure shown in Figure 4. with the fastener remaining in this desired orientation, the molten plastic will cool and set, thereby fusing the fastener to the substrate. Finally, the cylinder 40 is retracted so as to leave the fastener 12a welded to the substrate 28. Now, these operations can be successively repeated for the fasteners 12b-12d (Figure 4) so as to provide the aligned row of fasteners with the projecting tips thereof all pointing in the same direction relative to the substrate 28.

An enlarged view of the holding tool 34 for use in the friction welding orientation system of the present invention is illustrated in Figures 7 and 8. As can be seen, the first end 33 of the holding tool is adapted to be received in the chuck (not shown) and the second end 35 thereof is adapted to engage the top surface of the fastener. The holding tool includes an interior recess 44 having a generally designed contour matching the profile of the stem portion 17 of the fastener to be welded. In order to increase the frictional properties between the holding tool and the fastener to be welded, over the friction existing between the fastener and the substrate, the bottom drive face of the holding tool has a roughened surface 46 so as to facilitate driving of the fastener.The roughened surface 46 can be made in any suitable manner such as by sandblasting, cross-hatching or knurling and the like.

This roughened surface 46 also serves to distribute the torque substantially across the entire top surface of the fastener and thus reduces the torque around the central stem portion 17 of the fastener.

In order to further increase the necessary interfrictional relationship between the holding tool and the fastener, the top face 18 of the fastener 12 may also have a roughened surface 18a as depicted in Figure 1. By virtue of the plurality of holes 22 formed in the disc-shaped base member 14 of the fastener 12, the molten plastic can flow into the holes during the rotational welding process so as to form mechanical studs 48 (two of which are shown in Figure 9) so as to enhance fusing of the base member 14 of the fastener 12 and the substrate 28. In Figure 9, the mechanical studs 48 are formed in the openings 22 to facilitate a permanent securement of the fastener part 12 with the substrate part 28 to which the fastener part is to be welded.

From the foregoing detailed description, it can thus be seen that the present invention provides an improved friction weld orientation system for attaching and orienting precisely a thermoplastic fastener in substantially the same position relative to a substrate each time. The orientation system includes a thermoplastic fastener adapted to be fused to a substrate, and a programmable DC servomotor for rotating the fastener relative to the substrate and for automatically stopping rotation of the fastener after a predetermined number of revolutions so that the fastener is precisely aligned in the same reference position each time in relationship to the substrate.

Claims

1. A friction weld orientation system, comprising: a thermoplastic fastener, as hereinbefore defined, adapted to be fused to a substrate, said fastener having a base member and an upper element formed integrally with said base member; said base member having a bottom surface adapted to be fused to said substrate by heat of friction induced by the application of rotative and axial forces applied to said fastener; pressure means for applying the axial force to said fastener; and motor means for rotating said fastener relative to said substrate and for automatically stopping rotation of said fastener after a preset number of revolutions so that said upper element of said fastener is precisely oriented in a required reference position in relationship to said substrate.

2. A friction weld orientation system according to claim 1, wherein said motor means comprises a programmable DC servomotor which is controllable accurately to stop, after the preset number of revolutions has been completed, in the same reference position at which it was started.

3. A friction weld orientation system according to claim 2, wherein said programmable DC servomotor has a predetermined deceleration time after melting of said fastener at its interface with said substrate so as to stop said fastener in a precise orientation.

4. A friction weld orientation system according to any preceding claim, wherein a holding tool is operatively connected to said motor means for engaging a top surface of said base member, said holding tool having a roughened bottom face engageable with the top surface of said base member so as to increase the frictional properties between said holding tool and said fastener.

5. A friction weld orientation system according to claim 4, wherein the top surface of said base member is also roughened to further increase the interfrictional relationship between said holding tool and said fastener.

6. A friction weld orientation system according to any preceding claim, wherein said base member includes a plurality of holes for receiving therein molten plastic so as to form mechanical studs in order to enhance the connection of said fastener to said substrate.

7. A friction weld orientation system according to any preceding claim, wherein said upper element of said fastener is an asymmetrical fastening element.

8. A friction weld orientation system substantially as hereinbefore described with reference to the accompanying drawings.

9. A fastener, as hereinbefore defined, formed integrally of a thermoplastic material and adapted to be friction welded to a substrate, comprising: a base member having a top surface and a bottom surface, the bottom surface of said base member being adapted to be fused to said substrate by heat of friction induced by the application of rotative and axial forces applied to said fastener; a primary fastening element being formed integrally with the top surface of said base member; and the top surface of said base member having a roughened face engageable with a bottom face of a holding tool mounted on a high-speed rotating tool so as to increase the frictional properties between said holding tool and said fastener.

10. A fastener according to claim 9, wherein said base member includes a plurality of holes for receiving therein molten plastic so as to form mechanical studs in order to enhance connection of said fastener to said substrate.

11. A method for attaching and orienting precisely during a friction welding operation, comprising: providing a thermoplastic fastener, as hereinbefore defined, adapted to be fused to a substrate; rotating said fastener against said substrate; and stopping rotation of said fastener after a predetermined deceleration time, sufficient to have allowed melting of said fastener at its interface with said substrate to have already occurred, so that said fastener is precisely oriented in a required reference position in relationship to said substrate.

12. A method for attaching and orienting precisely during a friction welding operation, comprising: providing a thermoplastic fastener, as hereinbefore defined, adapted to be fused to a substrate; rotating said fastener, by use of a motor, against said substrate; and stopping rotation of said fastener after a predetermined number of revolutions of said motor, sufficient to have allowed melting of said fastener at its interface with said substrate to have already occurred, so that said fastener is precisely oriented in a required reference position in relationship to said substrate.