Patent Application
20160298204
The present invention relates to self-attaching fasteners and, more specifically to clinch nuts and methods for installing them.
Self-attaching fasteners are used in many industries such as, for example, the automotive and appliance industries to secure various components to metal panels. When clinch nuts are attached to the metal panels, screws or bolts are threaded into the clinch nuts and tightened to prescribed torque values. During installation, the clinch nuts must have sufficient rotational resistance to keep them from rotating relative to the metal panels when the screws are inserted and tightened. During service, the clinch nuts must have sufficient pull-through resistance to keep them from pulling out of the metal panel when external forces such as, for example, vibration or other tensile forces are applied. A clinch nut typically includes a central pilot or punch portion which at least partially extends into an opening in a metal plate or panel. When the clinch nut is self-piercing, the central pilot portion cooperates with tooling to form the opening in the metal panel when attaching the clinch nut to the metal panel. The clinch nut is attached to the metal panel by a die member which forms a mechanical interlock between the clinch nut and the metal panel. The die member typically deforms the metal panel about the opening into an annular groove of the clinch nut which encircles the pilot portion and/or deforms the pilot portion of the clinch nut over the metal panel to entrap the metal panel.
The development of hot stamping has led to stronger, lighter and more complex geometries for structural components. Basically, the components are formed from a metallic substrate. The substrate enters a press in a heated condition that allows it to be formed into the desired shape. The press is designed to quickly form the desired shape and quickly cool the substrate.
As mentioned above, self-clinching fasteners are a popular way for providing fastening points for relatively thin structures. Unfortunately, hot stamped components are often too hard to use such fasteners. Both creating a hole for the fastener in such a component and clinching the fastener to the component present difficult problems.
The present invention addresses this problem by installing the fasteners in the components while they are still in the component forming die. The fasteners are installed after the substrate material is cool enough for the fastener to clinch properly, but not so hard that punching and clinching become problematic.
A method for installing a self-clinching fastener in a metal substrate includes receiving the substrate in a shape-forming press, the substrate being substantially hotter than the press; operating the press to shape the substrate, the substrate having a transitioning hardness while cooling in the press; and installing the fastener in the substrate during the transitioning.
Referring to
An aperture for attachment of the clinch nut to the substrate may be provided by other means, or in the case of the clinch nut 10, a punch portion 12 is used to punch through the substrate.
In general, clinch nuts have an annular indentation 14 into which a portion of the substrate is forced into thereby locking the clinch nut in place.
Referring to
Many possible substrates have abrupt changes in the rate at which they harden as they cool. It is desirable to install the fastener after the substrate has hardened enough to allow the fastener to be clinched in place, but before the substrate suddenly becomes too hard.
One example of such a substrate is some steels. When the proper cooling rate is used, the substrate changes from austenite to much harder martensite very rapidly when the temperature of the substrate reaches the martensite start temperature.
At cooling rates above the critical rate, the substrate is substantially austenite when entering the press and substantially martensite when exiting the press.
A preferable condition for when to install the fastener is when the installation occurs at a substrate temperature between +20% and −5% of the martensite start temperature. This provides a substrate firm enough to allow proper clinching of the clinch nut but not so hard as to prevent proper installation.
There are several ways of determining this condition. Some examples follow:
(a) Temperature sensors may be installed within the dies and used to trigger the installation tool at the desired temperature as measured by the sensors.
(b) The desired temperature is estimated by a control system that determines temperature based on the initial temperature of the substrate and the cooling rate of the press. The installation tool is then triggered at a time based on this estimate.
(c) The installation tool is triggered at a point in the hot press cycle that corresponds to said time.
It should be noted that the self-clinching fasteners may include without limitation fastener having a threaded bore, an un-threaded bore, a threaded stud, or an un-threaded stud.
It should be evident that this disclosure is by way of example and that various changes may be made by adding, modifying or eliminating details without departing from the fair scope of the teaching contained in this disclosure. The invention is therefore not limited to particular details of this disclosure except to the extent that the following claims are necessarily so limited.
| Number | Date | Country | |
|---|---|---|---|
| 62145870 | Apr 2015 | US |
