Joining thermoplastic workpieces with induction heating

A method of joining workpieces, comprising the steps of:

• aligning protrusions of a first thermoplastic composite workpiece with receptacles of a second thermoplastic composite workpiece, each receptacle being sized to receive the respectively aligned protrusion;
• bringing the first and second workpieces together at a joint interface with the protrusions received by the receptacles;
• induction heating a susceptor material to thereby soften a thermoplastic material of each workpiece at the joint interface;
• and
• pressing the workpieces together while the thermoplastic materials are softened thereby reshaping the first workpiece where the thermoplastic material is softened, so that each protrusion is deformed while received in the respectively aligned protrusion to form a plurality of interlocks at which the workpieces are mechanically fastened together and at which a chemical bond is formed between the workpieces,
• wherein the first workpiece includes a sink mark along a side of the first workpiece opposite one of the protrusions before the step of bringing the workpieces together, the sink mark being at least partially removed by said reshaping of the first workpiece.

A method of joining workpieces, comprising the steps of:

• placing a first workpiece comprising a thermoplastic material together with a second workpiece between first and second portions of a heat staking tool so that a protrusion of the first workpiece extends through a receptacle of the second workpiece, wherein the first portion of the tool supports the first workpiece and includes a susceptor material in contact with a side of the first workpiece in which a sink mark is formed opposite the protrusion;
• induction heating the susceptor material to thereby soften the thermoplastic material;
• and
• moving at least one of the portions of the heat staking tool toward the other portion until the second portion of the tool contacts both the first workpiece and the second workpiece and presses the workpieces together,
• wherein the second portion of the tool includes a recess aligned with the protrusion and contacts the protrusion before contacting the second workpiece so that a head is formed at an end of the protrusion, and
• wherein said side of the first workpiece in which the sink mark is formed is reshaped when the first and second workpieces are pressed together while the thermoplastic material is softened to thereby at least partially remove the sink mark.