# US 5,705,796 A · Reinforced composites formed using induction thermoplastic welding

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- Number: US 5,705,796 A
- Document ID: US5705796A
- Status: Granted
- Kind: A
- Application number: 08/608,454
- Filed: 1996-02-28
- Granted: 1998-01-06
- Earliest claimed: 1991-10-18
- Assignees: The Boeing Company
- Inventors: Karl A. Hansen, deceased; C. David Lunden
- Web page: https://patentgrep.com/patent/US5705796A

## CPC

- H05B 6/44: having more than one coil or coil segment
- B29C 65/364: {being a woven or non-woven fabric or being a mesh}
- B29C 65/3644: {being a ribbon, band or strip}
- B29C 65/3656: {being a layer of a multilayer part to be joined, e.g. for joining plastic-metal laminates}
- B29C 65/368: {with a polymer coating}
- B29C 66/1122: {Single lap to lap joints, i.e. overlap joints (B29C66/45, B29C66/472, B29C66/52272 take precedence)}
- B29C 66/3472: {in the plane of the joint, e.g. along the joint line in the plane of the joint or perpendicular to the joint line in the plane of the joint}
- B29C 66/43421: {with a right angle, e.g. for making L-shaped pieces}
- B29C 66/474: {said single elements being substantially non-flat}
- B29C 66/721: {Fibre-reinforced materials (B29C66/729 takes precedence)}
- B29C 66/72321: {consisting of metals or their alloys}
- B29C 66/73921: {characterised by the materials of both parts being thermoplastics}
- B29C 66/80: {General aspects of machine operations or constructions and parts thereof}
- B29C 66/81811: {of the welding jaws}
- B29C 66/836: {Moving relative to and tangentially to the parts to be joined, e.g. transversely to the displacement of the parts to be joined, e.g. using a X-Y table (B29C66/65 takes precedence)}
- B29C 65/3668: {characterised by the means for supplying heat to said heated elements which remain in the join, e.g. special induction coils}
- B29C 66/71: {characterised by the composition of the plastics material of the parts to be joined (welding bar compositions B29C65/125)}
- B29C 66/7212: {characterised by the composition of the fibres}
- B29K 2071/00: Use of polyethers {, e.g. PEEK, i.e. polyether-etherketone or PEK, i.e. polyetherketone or derivatives thereof}, as moulding material
- B29K 2105/06: containing reinforcements, fillers or inserts
- B29L 2031/3076: {Aircrafts (blades, propellers B29L2031/08)}
- H05B: ELECTRIC HEATING; ELECTRIC LIGHT SOURCES NOT OTHERWISE PROVIDED FOR; CIRCUIT ARRANGEMENTS FOR ELECTRIC LIGHT SOURCES, IN GENERAL
- B29C: SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING (making preforms B29B11/00; making laminated products by combining previously unconnected layers which become one product whose layers will remain together B32B37/00 - B32B41/00)
- B29K: INDEXING SCHEME ASSOCIATED WITH SUBCLASSES B29B, B29C OR B29D, RELATING TO MOULDING MATERIALS OR TO MATERIALS FOR {MOULDS, } REINFORCEMENTS, FILLERS OR PREFORMED PARTS, e.g. INSERTS
- B29L: INDEXING SCHEME ASSOCIATED WITH SUBCLASS B29C, RELATING TO PARTICULAR ARTICLES

## Abstract

We form welded reinforced composites by heating a susceptor along the bond line with a time-varying magnetic field produced with a moving induction coil. To obtain more uniform heating across the susceptor when welding composite parts using induction heating, edge regions of lower absolute impedance or a lower longitudinal impedance than the transverse impedance counterbalance the higher current density and current that occurs near the edges. The susceptor has lower impedance at the edges by altering the aspect ratio (length/width) of openings in the susceptor, by folding the susceptor over onto itself, or both. Uniform heating is important to obtaining a uniform, consistent weld on which aerospace designers can rely.

## Claims

### Claim 1

A welded reinforced composite, comprising:
(a) a plurality of fiber reinforced composite parts arranged to define a bond line;
(b) a susceptor disposed between the parts at the bond line for receiving induced currents from an induction heater to peak heating at the bond line, wherein the susceptor has higher electrical conductivity than fibers in the parts; and
(c) a thermoplastic fusion bond at the bond line embedding the susceptor and joining the parts.

### Claim 2 (depends on 1)

The welded reinforced composite of claim 1 wherein the fibers are carbon or graphite.

### Claim 3 (depends on 2)

The welded reinforced composite of claim 2 wherein the composite is a polyimide resin.

### Claim 4 (depends on 1)

The composite of claim 1 wherein the susceptor is metal.

### Claim 5

An assembly for welding composite parts, comprising:
(a) a plurality of fiber reinforced composite parts arranged to define a bond line;
(b) a susceptor disposed between the parts at the bond line for receiving induced currents from an induction heater during a thermoplastic welding operation to peak heating at the bond line, wherein the susceptor has higher electrical conductivity than fibers in the parts.

### Claim 6 (depends on 5)

The assembly of claim 5 further comprising thermoplastic resin encasing the susceptor.

### Claim 7

A method for creating a thermoplastic fusion bond at a bond line between a plurality of fiber reinforced composite parts, comprising the steps of:
(a) assembling a plurality of fiber reinforced composite parts to define a bond line between the parts where the parts will be joined with a thermoplastic fusion bond;
(b) disposing a susceptor along the bond line to peak heating at the bond line, the susceptor being susceptible to induction heating and having a higher electrical conductivity than fibers in the parts; and
(c) inducing currents in the susceptor to melt resin at the bond line in the parts and to form a thermoplastic fusion bond between the parts at the bond line.

### Claim 8 (depends on 7)

The method of claim 7 further comprising the step of:
tailoring the susceptor to achieve a substantially uniform temperature along the bond line when melting the resin to form the fusion bond.

### Claim 9 (depends on 7)

The method of claim 7 wherein the susceptor is a metal mesh encased in thermoplastic resin and wherein the composite have a resin matrix of the same material as the thermoplastic resin.