Formed core sandwich structure and method and system for making same

Abstract

A method and apparatus for producing a metal core sandwich structure that is lightweight and many times stiffer than regular sheet metal, and which is easily formable into curved structures as well as structures having compound curves. In one embodiment, a formed metal core includes a plurality of cells comprising alternating front and rear projections extending outwardly in front of and behind a median plane, with each projection having a bonding surface area or land configured to be brazed or bonded with corresponding external metal sheets on both sides of the formed metal core. A plurality of micro-abrasions or indentations are formed on the bonding lands, allowing stronger brazing or bonding joints to be formed between the metal core and the external metal sheets by facilitating improved capillary action by the metal core during the brazing or bonding process.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS [0001] The present application is a continuation-in-part of U.S. application Ser. No. 11 / 285,096, filed on Nov. 22, 2005, entitled “Formed Metal Core Sandwich Structure and Method and System for Making Same” and the disclosures of which are herein incorporated by reference in their entirety.BACKGROUND OF THE INVENTION [0002] 1. Technical Field [0003] The present invention relates to metal sandwich sheet structures and, more particularly, to formable metal core sandwich sheet structures and methods and systems for manufacturing same. [0004] 2. Description of Related Art [0005] Metal core sandwich structures are known in the art. For example, U.S. Pat. No. 3,525,663 to Hale and U.S. Pat. No. 4,035,536 to Morrison both disclose metal sandwich structures having a formed metal core brazed to two outer metal sheets. However, it is believed that the structures disclosed by Hale and Morrison, and other similar conventional formed metal core sandwich s...

AI Technical Summary

Benefits of technology

[0008] The invention addresses the above and other needs by providing an improved metal sandwich sheet structure that includes a formed metal core that is brazed or bonded to two outer flat metal sheets. This improved metal sandwich structure is capable of being formed into complex shapes while retaining its structural integrity. This improved metal sandwich structure is also easier and more economical to manufacture than prior honeycomb core sandwich structures, while providing similar strengths and characteristics as the honeycomb core structures.

[0009] In one embodiment of the invention, a method of producing a metal core sandwich structure includes providing a formed metal core that is lightweight and many times stiffer than regular sheet metal, and which is easily formable into curved structures as well as structures having compound curves that curve in two or more directions simultaneously, for example. In one embodiment, a metal core sheet is rolled, stamped or pressed into a corrugated shape having a plurality of cells comprising alternating front and rear projections extending outwardly in front of and behind a median plane, with each projection having a bonding surface area or land configured to be brazed or bonded with corresponding external metal sheets on both sides of the formed metal core sheet. A plurality of micro-abrasions or indentations are formed on the bonding lands, allowing stronger brazing joints to be formed between the metal core and the external metal sheets by facilitating improved capillary action by the metal core during the brazing process. The improved brazing joints provide better bonds so the resulting multi-layer sheet structure will not fracture or delaminate during forming. The resulting sandwich structure is easier to form into complex curves and shapes while maintaining its structural integrity. Thus, the improved metal sandwich structure is well suited for various applications where formability and structural integrity are important (e.g., automotive body applications).

[0010] In another embodiment of the invention, an apparatus for forming an improved core metal sheet is provided. The apparatus includes a press or mold that presses (via stretching and / or gathering) the core metal sheet to form a desired corrugated core structure. At desired locations on the surface of the press, micro-protrusions and / or micro-ridges and / or micro-lines (collectively referred to herein as “micro-protrusions”) extend outwardly from the press surfaces so that during forming of the core metal sheet, micro-abrasions and / or micro-grooves and / or micro-channels (collectively referred to herein as “micro-abrasions”) are formed to extend inwardly on desired surface areas of the formed metal core. These micro-abrasions allow for improved brazing between the formed metal core and the two outer metal sheets through improved capillary action by the metal core during brazing.

[0011] In a further embodiment, the outer layer sheets are electro-tacked to the formed core prior to brazing or bonding, which allows for improved subsequent brazing and an improved quality sandwich structure. In one embodiment, the invention provides a novel electro-tacking apparatus for tack welding the formed core to the outer metal sheets prior to brazing.

[0012] In various embodiments of the invention, various cell shapes and geometries such as hexagonal, square, octagonal or other shape may be formed in the core sheet as well as different cell sizes in accordance with desired formability, stiffness and crush characteristics. For example, it may be desirable for some zones of the sandwich structure to be more easily crushed (e.g., to provide “crush zones” in an automobile body frame) or to be more rigid or more flexible. For example, if crush zones are desired, the sandwich structure (or at least designated areas of the sandwich structure) can be designed to be more easily crushed which may help avoid automobile impact injuries while other areas of the automobile body (e.g., roofs) will be stiffer, allowing for more protection from metal crushing into passenger compartments.

Problems solved by technology

However, it is believed that the structures disclosed by Hale and Morrison, and other similar conventional formed metal core sandwich structures, cannot be easily formed into compound curves and other complex shapes without delaminating, wrinkling and / or otherwise losing its structural integrity.

Therefore, prior metal core sandwich structures are not well-suited for applications that require formation of compound curves, for example, without delaminating or wrinkling during the forming process.

Although this honeycomb core sandwich structure provides improved formability when compared to other metal core sandwich structures, it is relatively expensive to manufacture and, therefore, not well-suited for many commercial, cost-sensitive applications (e.g., automobile bodies).

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