Unitary crank spindle assembly and method of fabrication
View Patent ↗A bicycle is provided having a unitary steering tube-crown member and a unitary crank arm-spindle member. A multistage aluminum 3D forging process is used to form the unitary members. This may allow the fabrication of components with substantially hollow interior areas to reduce weight, reduce part count while maintaining high strength and ductility. The multistage 3D forging process provided also allows the combination of multiple components into a single unitary part.
1. A method of fabricating an integrally formed unitary bicycle crank-arm spindle comprising:
forming a first elongated arm by three-dimensional (3D) forging, said first elongated arm having a solid pedal end portion and a first axial bore, said first axial bore having a first opening extending through a second end of said first elongated arm opposite said solid pedal end portion, said first axial bore having a closed end opposite the first opening, the closed end being adjacent the solid pedal end portion;
forming a first projection on said first elongated arm adjacent said second end and opposite said solid pedal end portion;
forming an elongated spindle from said first elongated arm by extending said first projection and forming a second axial bore in said first projection by 3D forging, the elongated spindle having an end opposite the first arm configured to couple to a second elongated arm, the second axial bore defining an axis of rotation of the first elongated arm when installed on a bicycle, said spindle being unitary and monolithic with said first elongated arm, wherein said second axial bore intersects and is contiguous with said first axial bore;
bending said first elongated arm, wherein said solid pedal end portion is substantially perpendicular to said first projection;
forming the second elongated arm by 3D forging, said second elongated arm having a third end and a third axial bore, said third axial bore having a second opening at a fourth end of said second elongated arm;
forming a second projection on said second elongated arm adjacent said third end; and,
forming a fourth axial bore in said second projection, wherein said fourth axial bore is sized to receive said spindle opposite said first elongated arm; and
inserting the spindle in the fourth axial bore to form a crank-arm spindle assembly.
2. The method of claim 1 further comprising:
inserting a first plug into said first opening, said first plug having third opening, said third opening being substantially co-axial with said second axial bore when the first plug is inserted into said first opening; and,
inserting a second plug into said second opening, said second plug having a fourth opening, said fourth opening being substantially co-axial with said second axial bore when said second plug is inserted into said second opening.
3. The method of claim 2 further comprising:
coupling said first plug to said first elongated arm by brazing; and,
coupling said second plug to said second elongated arm by brazing.
4. The method of claim 2 further comprising:
coupling said first plug to said first elongated arm by bonding; and,
coupling said second plug to said second elongated arm by bonding.