Magnet cap

One or more method(s), system(s), and/or device(s) produces an assembly for securing a product to a dissimilar material, such as a magnet to plastic. A magnet assembly may include a plastic cap having one or more wings extending laterally from a side surface of the plastic cap. A plastic holder defines a product cavity and has one or more grooves formed to integrally fit with the one or more wings of the plastic cap. A magnet is positioned within the product cavity. The plastic cap is joined to the plastic holder, such as through staking or welding, to capture the magnet within the product cavity.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This description generally relates to securing magnets within or to plastic parts, and more particularly to one or more methods, devices, and/or systems for attaching a magnet or other non-plastic part to a plastic part in a variety of manufacturing applications.

2. Description of the Related Art

The staking of plastic materials is one technique for joining materials, such as thermoplastic materials. There are four common methods of staking, including cold staking, heat staking, thermo staking, and ultrasonic staking or welding. The choice of the joining process is often dependent upon the materials to be joined, the loads to which the assembly will be subjected and/or the required cosmetic appearance.

In each case, accurate alignment of the components is important to the quality of the joint. The common design parameters may include stud diameter, stud height and stud geometry. Due to the deformation of previously formed parts, effective staking is often restricted to thermoplastic materials. For example, in heat staking, a probe is heated so that less pressure is required to form a head on a stud. This widens the application of staking to a broader spectrum of thermoplastic materials than is possible with cold staking, including glass-filled materials. The quality of the joint is dependent on control of the processing parameters: temperature, pressure and time—a typical cycle time might be between 1 to 5 seconds.

Heat staking has the advantage that parts can be disassembled. It also has the flexibility to allow the simultaneous formation of a large number of studs and to accommodate a variety of stud head designs.

SUMMARY OF THE INVENTION

The present inventors have determined that the use of staking processes to join dissimilar materials, such as in the manufacture of telecommunications devices may produce inconsistent results. For example, heat-staking a magnet directly to a plastic part within a mass-produced telephony device may produce inconsistent results in high volume manufacturing, e.g., inconsistency in location and dimensional tolerances from telephony device to telephony device.

Alternatively or in addition, a magnet secured in a conventional housing or recess with heat staking may be easily broken loose from the plastic part, e.g., even when the magnet is held in place properly the difference between the coefficients of expansion of the magnet and the plastic results in the magnet not being held securely in place, such that the magnet may rattle within the telephone enclosure.

The present invention allows the use of several joining processes, including staking processes to securely, accurately, and consistently join a magnet or other material to a plastic part.

In one general aspect, a method for securing a product having a dissimilar material to a plastic part includes positioning the product within a recess of a bucket having stepped grooves. A cap is positioned over the bucket, wherein one or more wings of the cap integrally fit within the grooves of the bucket. The cap is joined to the bucket to form an assembly. The product is encapsulated within the bucket and the cap by one or more ribs extending away from the cap or bucket.

Implementations of this aspect may include one or more of the following features. For example, the cap may be joined to the bucket by heat staking the cap to the bucket. The cap may be joined to the bucket by ultrasonic welding. The cap and bucket may comprise thermoplastic, such as acrylonitrile butadiene styrene (ABS) thermoplastic. The product may include a magnet, such as a cylindrically shaped magnet formed to fit with an interference fit within the bucket.

In another general aspect, a magnet assembly includes a magnet cap having one or more wings extending laterally from a side surface of the magnet cap, a magnet bucket defining a product cavity and having one or more grooves formed to integrally fit with the one or more wings of the magnet cap, and a magnet positioned within the product cavity, wherein the magnet cap is joined to the magnet bucket to encapsulate the magnet within the product cavity.

Implementations of this aspect may include one or more of the following features. For example, the magnet cap and/or magnet bucket may comprise thermoplastic, such as ABS thermoplastic. The magnet cap may comprise two, three, or more wings. The magnet bucket may comprise two or three, or more, stepped grooves shaped to integrally secure a portion of the two or three, or more, respective wings of the magnet cap therein. The magnet cap may be joined to the magnet bucket through staking, such as heat staking or ultrasonic staking (welding). The magnet cap may include one or more ribs extending from an underside of the magnet cap into the product cavity to securely engage the magnet therein. The magnet cap may include one or more stepped edges on an upper side thereof, the stepped edges being formed to integrally fit with one or more attachment ribs on the magnet bucket which define the one or more grooves of the magnet bucket. The magnet cap may include a substantially round body portion and the one or more wings may extend generally laterally away from a center of the round body portion. The magnet bucket may comprise a substantially cylindrical body portion which defines the product cavity. The cylindrical body portion may further include the one or more ribs of the magnet bucket which define the one or more grooves of the magnet bucket. The magnet may be a substantially cylindrically shaped magnet which fits with an interference fit within the product cavity when encapsulated by the joined magnet cap and magnet bucket.

Implementations of this aspect may include one or more of the following features. For example, the magnet cap may include multiple wings, e.g., two, three, four-winged configurations, for securing to a bucket. The magnet may be secured to the magnet cap or to the magnet bucket prior to joining the magnet cap to the magnet bucket. The magnet cap may be removed for access to the magnet held within the magnet bucket for inspection and/or replacement, e.g., if a heat staking joining process is utilized.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1is a perspective view of a top of a plastic cap11, in accordance with the present invention. In one embodiment, the plastic cap11is formed of a thermoplastic, such as acrylonitrile butadiene styrene (ABS) thermoplastic. The plastic cap11includes a substantially round midsection13. One or more wings15extend laterally from a side surface of the plastic cap11. In the illustration ofFIG. 1, three wings15-1,15-2and15-3extend away from a center of the midsection13. Stepped edges17may optionally be provided between the wings15. In the illustration ofFIG. 1, three stepped edges17-1,17-2and17-3exist between the three wings15-1,15-2and15-3.

FIG. 2is a perspective view of a bottom of the plastic cap11ofFIG. 1.FIG. 2illustrates the presence of at least one ramp-shaped rib21extending away from the plane of the midsection13in a direction substantially perpendicular to the lateral extension of the wings15. In the illustration ofFIG. 2, three ramp-shaped ribs21-1,21-2and21-3exist on the bottom of the plastic cap11. Each rib21tapers from a base attached to the plastic cap11to a relatively narrower free end.

FIG. 3is an exploded view illustrating an assembly of the plastic cap11ofFIGS. 1 and 2and a non-plastic part23and a plastic holder25, such as a plastic bucket. In one embodiment, the non-plastic part23is a disc-shaped magnet. Although a magnet has been illustrated, the non-plastic part23could be formed of other materials dissimilar to plastic, such as metal, wood, glass or ceramic.

The plastic holder25forms a recess or product cavity27. In one embodiment, the product cavity27is cylindrical in shape, such that the non-plastic part23can fit therein. Typically, the plastic holder25is attached to, or integrally formed with, a plastic base35, which forms a floor for the product cavity27. In one embodiment, the plastic holder25is formed of a thermoplastic, such as acrylonitrile butadiene styrene (ABS) thermoplastic.

A rim defining an opening to the product cavity27includes at least one groove29formed therein. In the illustration ofFIG. 3, three grooves29-1,29-2and29-3exist along the rim of the product cavity27. The three grooves29-1,29-2and29-3are sized to accept, in a close fitting relationship, the three wings15-1,15-2and15-3of the plastic cap11. Attachment ribs31may optionally be provided on the plastic holder25on the upstanding portions33defining the grooves29. In the illustration ofFIG. 3, three rounded attachment ribs31-1,31-2and31-3face inwardly from three upstanding portions33-1,33-2and33-3along the periphery of the product cavity27.

Now, with reference toFIGS. 3-6, a method for securing the non-plastic part23to the plastic holder25will be described. First, the non-plastic part23is positioned within the product cavity27of the plastic holder25. Next, the plastic cap11is superimposed or positioned over the plastic holder25. The one or more wings15of the plastic cap11are fitted within the corresponding one or more grooves29of the plastic holder25.

As best seen in the cross sectional view ofFIG. 6, as the plastic cap11is pressed onto the plastic holder25, the ramp-shaped ribs21engage a side surface of the non-plastic part23to wedge the non-plastic part23within the product cavity27with an interference fit. If the optional stepped edges17-1,17-2and17-3are provided on the plastic cap11and the optional attachment ribs31-1,31-2and31-3are provided on the plastic holder25, these features may snap past each other to hold the plastic cap11on the plastic holder25.

Finally, while the plastic cap11is fully seated onto the plastic holder25, the plastic cap11and plastic holder25are joined by a fixed joint to capture the non-plastic part23in the product cavity27and form an assembly37. The fixed joining of the plastic cap11and the plastic holder25can be accomplish by cold staking, heat staking, thermo staking, ultrasonic staking or welding, or any other known means of joining two like plastic parts.FIG. 5is a perspective view of the assembly37of the plastic cap11joined to the plastic holder25by heat staking. As seen inFIG. 5, the assembly37is substantially uniform in shape, as the individual elements of the plastic holder25and the plastic cap11have become joined together and substantially indistinct from each other during the heat staking process.

FIGS. 7 and 8illustrate a modified cap41in accordance with an alternative embodiment of the present invention.FIG. 7is a perspective view of a top of the modified cap41.FIG. 8is a perspective view of a bottom of the modified cap41ofFIG. 7. Like elements to the plastic cap11ofFIGS. 1 and 2have been labeled with the same reference numerals.

A primary distinction between the modified cap41and the plastic cap11ofFIGS. 1 and 2is that the third wing15-3′ is greatly shortened so that it substantially follows the outer circular periphery of the midsection13of the modified cap41.

As best illustrated inFIG. 9, when the plastic holder25is located on a portion of the plastic base35which is immediately adjacent to an obstruction51, like the protruding channel, the modified cap41can be employed to avoid interference with the obstruction51. As illustrated inFIG. 9, the short wing15-3′ is placed in the groove29-3between the upstanding portions33-2and33-3. By this arrangement, the modified cap41will not contact the obstruction51, whereas the plastic cap11ofFIG. 1could not have been employed with the plastic holder25ofFIG. 9, because the third wing15-3would have interfered with the obstruction51and not fully seated onto the plastic holder25.

Another distinction of the modified cap41is that the modified cap41has only two ramp-shaped ribs21-1and21-2. The primary purpose of the ramp-shaped ribs21is to hold the non-plastic part23within the product cavity27with an interference fit so that the non-plastic part23will not rattle within the product cavity27. This may be accomplished with two ramp-shaped ribs21(as illustrated inFIG. 8) or even one ramp-shaped rib21.

AlthoughFIGS. 2,6and8illustrated the ramp-shaped ribs21as being attached to the plastic cap11/14it would be possible to have the ramp-shaped members21attached to the floor of the product cavity27. Under either circumstance, the ramp-shaped ribs21would engage the side edges of the non-plastic part23to hold the non-plastic part23in the product cavity27with an interference fit, which prevents the non-plastic part23from rattling within the product cavity27.

The caps11and41and holder25have been described as being formed of acrylonitrile butadiene styrene (ABS) thermoplastic. ABS is a copolymer derived from acrylonitrile, butadiene, and styrene. The advantage of ABS is that this material combines the strength and rigidity of the acrylonitrile and styrene polymers with the toughness of the polybutadiene rubber, producing a tough, impact and heat resistant product. In addition, ABS plastics have desirable electrical properties. However, it should be appreciated that other materials may be employed in the present invention to achieve one or more of these recognized advantages to differing degrees.

The caps11and41and holder25of the present invention provide greater dimensional consistency in high-volume manufacturing. They also provide a much stronger attachment of a magnet or other non-plastic part23, thus extending the life-expectancy of the ultimate product. One application of the present invention is to use the plastic cap11/41and plastic holder25in a telephone set, such as an Avaya desktop telephone, to attach a magnet within the telephone base.