Mechanical joining of nitinol tubes
The present invention relates to mechanical joining of Nickel Titanium tubes, also known as Nitinol, to other tubular components. Such mechanical joining may be achieved by interpenetration of lobe features between the respective tubes by translating the tubes together on a longitudinal axis, a transverse axis, by a combination of translation and rotational motion or by a hinging motion. The Nitinol superelasticity is used to accommodate the lobe deformation required for assembly and to snap the lobe back into its original shape to complete the mechanical joint.
1. A method of forming a mechanical joint, comprising providing a first tube formed of nitinol wherein the first tube includes an end portion having a plurality of protruding first tube lobes and a plurality of first tube lobe recesses; providing a metallic second tubular component including an end portion having a plurality of protruding second tubular component lobes and a plurality of second tubular component lobe recesses; wherein each lobe of the second tubular component lobes has a same size and geometry with each lobe of the first tube lobes such that the mechanical joint is formable with more than one arrangement of the first tube and the second tubular component relative to one another; disposing one lobe of the plurality of first tube lobes in one lobe recess of the plurality of second tubular component lobe recesses, respectively; disposing one lobe of the plurality of second tubular component lobes in one lobe recess of the plurality of first tube recesses, respectively; mechanically engaging the first tube end portion having the plurality of first tube lobes with the second tubular component end portion having the plurality of second tubular component lobes by translating toward one another in an axial direction on a common longitudinal axis, wherein each lobe of the plurality of first tube lobes mechanically engages with two adjacent lobes of the plurality of second tubular component lobes and each lobe of the plurality of second tubular component lobes mechanically engages with two adjacent lobes of the plurality of first tube lobes, such that a mechanical joint is formed which interlocks the first tube and the second tubular component against axial separation on the longitudinal axis; wherein, during mechanically engaging the first tube end portion with the second tubular component end portion the nitinol of the first tube deforms, and elastically recovers when the mechanical joint is formed; wherein the first tube deformation includes moving the plurality of first tube lobes from an original position to an open position and holding the plurality of first tube lobes at the open position;
wherein the first tube elastic recovery includes releasing the plurality of first tube lobes from the open position such that they return to the original position;
wherein superelasticity of the nitinol accommodates deformation and elastic recovery of the first tube when the mechanical joint is formed, whereby the nitinol undergoes a phas e transformation between austenitic and martensitic phases; and
wherein the metallic second tubular component is formed of stainless steel, cobalt alloy or nickel alloy.
2. The method of claim 1 wherein the plurality of first tube lobes of the first tube comprise an initial minimum width (W1) and a length (L), wherein the length (L) to width (W1) aspect ratio of 0.33:1 to 10:1.
3. The method of claim 1 wherein the plurality of first tube lobes of the first tube comprises 2, 3, 4, 5 or 6 lobes.
4. The method of claim 1 wherein the first tube has an outer diameter (OD) of 0.010 inch to 0.625 inch.
5. The method of claim 1 wherein the first tube has a wall thickness of 0.002 inch to 0.065 inch.
6. The method of claim 1 wherein the outer diameter (OD) to wall thickness ratio is 5:1 to 30:1.
7. The method of claim 1 wherein each lobe of the plurality of first tube lobes and each lobe of the plurality of second tubular component lobes has a length (L) and a width at the end of the tube (W3) such that the length (L) to width (W3) ratio is in the range of 0.33:1 to 2:1.
8. The method of claim 1 wherein the mechanical engaging of the first tube end portion with the second tubular component end portion includes a strain on the plurality of first lobes of greater than 1.0% up to 8.0%.
9. The method of claim 1 wherein the mechanical joint has a torsional flexibility of 0.1 degree up to less than 1.0 degree.
10. The method of claim 1 wherein the mechanical joint has a torsional flexibility of 1.0 degree to 3.0 degrees.
11. The method of claim 1 wherein each lobe of the plurality of first tube lobes is disposable in any one lobe recess of all of the plurality of second tubular component lobe recesses, and each lobe of the plurality of second tubular component lobes is disposable in any one lobe recess of all of the plurality of first tube recesses.
12. The method of claim 1 wherein mechanical engaging the first tube end portion having the plurality of first tube lobes with the second tubular component end portion having the plurality of second tubular component lobes is performed by moving the first tube and/or the second tubular component towards one another along a common longitudinal axis of the first tube and the second tubular component.
13. The method of claim 1 wherein the mechanical joint interlocks the first tube and the second tubular component against separating along a common longitudinal axis of the first tube and the second tubular component via interference of the plurality of first tube lobes with the plurality of second tubular component.
14. A method of forming a mechanical joint, comprising: providing a first tube formed of nitinol wherein the first tube includes an end portion having a plurality of protruding first tube lobes and a plurality of first tube lobe recesses; providing a metallic second tubular component including an end portion having a plurality of protruding second tubular component lobes and a plurality of second tubular component lobe recesses; wherein each lobe of the second tubular component lobes has a same size and geometry with each lobe of the first tube lobes such that each lobe of the plurality of first tube lobes is disposable in more than one recess of the plurality of second tubular component lobe recesses, and each lobe of the plurality of second tubular component lobes is disposable in more than one recess of the plurality of first tube recesses; disposing one lobe of the plurality of first tube lobes in one lobe recess of the plurality of second tubular component lobe recesses, respectively; disposing one lobe of the plurality of second tubular component lobes in one lobe recess of the plurality of first tube recesses, respectively; mechanically engaging the first tube end portion having the plurality of first tube lobes with the second tubular component end portion having the plurality of second tubular component lobes by translating toward one another in an axial direction on a common longitudinal axis, wherein each lobe of the plurality of first tube lobes mechanically engages with two adjacent lobes of the plurality of second tubular component lobes and each lobe of the plurality of second tubular component lobes mechanically engages with two adjacent lobes of the plurality of first tube lobes, such that a mechanical joint is formed which interlocks the first tube and the second tubular component against axial separation on the longitudinal axis;
wherein, during mechanically engaging the first tube end portion with the second tubular component end portion the nitinol of the first tube deforms, and elastically recovers when the mechanical joint is formed; wherein the first tube deformation includes moving the plurality of first tube lobes from an original position to an open position and holding the plurality of first tube lobes at the open position; wherein the first tube elastic recovery includes releasing the plurality of first tube lobes from the open position such that they return to the original position;
wherein superelasticity of the nitinol accommodates deformation and elastic recovery of the first tube when the mechanical joint is formed, whereby the nitinol undergoes a phase transformation between austenitic and martensitic phases; and
wherein the metallic second tubular component is formed of stainless steel, cobalt alloy or nickel alloy.