GB845003A - Method and apparatus for producing a composite metal honeycomb structure - Google Patents

Abstract

845,003. Making sheet material; brazing. SOLAR, AIRCRAFT CO. Oct. 16, 1956 [Oct. 17, 1955], No. 31442/56. Classes 83 (2) and 83 (4). In producing a composite metal honeycomb structure comprising a honeycomb core bonded to at least one skin or sheet, the skin &c. is placed on the core with cohesive bonding material applied at one or both sides of the core at the core edges or at accessible points adjacent the cell wall joints, a substantially complete contact is made between the core edges and the skin &c., the temperature of the assembly is raised by creating relative movement between the assembly and a localized heat source to melt the bonding material which flows and cohesively diffuses into the core cell edges and contacting portions of the skin &c. and the temperature is allowed to decrease while maintaining the substantially complete contact. The core and skins may be cleaned by acid dip and brazing material, e.g. silver solder powder may be held in place in the open cells by sprayed acrylic resin or dilute polystyrene-methylchloride solution or a paste of acrylic resin and the powder may be used. A flux may be applied to the core and skin if a reducing atmospheric furnace is not used and the skin may be spot welded to the core edges before brazing. The assembly may be pressed between stainless steel, high alloy metal or ceramic dies. In an embodiment a core 33, Fig. 2, and a pair of skins 31 forming a sandwich are assembled between dies 35, which may be preheated to a temperature 50‹ F. above brazing temperature, with a resilient metallic or non- metallic sheet 36 or layer of asbestos or powdered ceramic between each skin and die to provide uniform pressure. Reinforcing channels 24, Fig. 7, may be provided at the ends of the core and brazing material held in perforations 26 melts during heating by a localized source of heat moved relatively to the sandwich to braze the channels to the skins. In a modification perforated plates provided with brazing material may be arranged between the skins and an unperforated channel. Alternatively the sandwich and die assembly is sealed in a stainless steel envelope 37, Fig. 3, which is partially evacuated before brazing and in a modification the dies may be omitted. In making a curved sandwich, the sandwich with core edge stiffeners spot welded to the core or skins is arranged between dies as shown in Fig. 10. Curved uniform thickness dies may be used. For use with a vacuum or pressure envelope a rigid die 35, Fig. 12, and a relatively flexible die 104 having metal squares 106 spot welded to a sheet 108 is employed. In order to attach fittings to the sandwich the core may be locally strengthened by using heavier core material or more closely spaced cells. In making a long narrow sandwich an electric tunnel furnace 150, Fig. 17, is moved along a track 152 by a motor 153 and the sandwich is enclosed in a metal bag 156 partially evacuated and held under tension. Asbestos sheets may be provided between the sandwich and bag and curved rollers may be provided on the furnace to shape the sandwich. The sandwich assemblies in dies (Fig. 10) or in vacuum bags (Fig. 3) may be held between tensioned sheets or positioned on a sheet with an upper tension sheet and moved relatively to a tunnel furnace. In a modification the sandwich may be arranged vertically when the furnace travels vertically up and down. In the continuous production of flat or curved sandwiches the skins 31, Fig. 25, are fed from rolls to engage a continuously fed core 33 which is supplied with brazing material and flux by rolls, brushes or by dipping. The assembly passes between positioning rolls 142, radiant gas heater heated rolls 144 and water-cooled rolls 146, 148. The rolls 142, 144 and 146 may alternatively be located inside a furnace. Specification 838,516 is referred to.