Flexible U-lock

1. A lock, comprising:

a shackle comprising a resilient flexible portion, the flexible portion comprising a cable slidably disposed within a coil spring, wherein the flexible portion further comprises a heat-treated coil spring that maintains the overall substantially U-shaped form, which, absent any external deformation forces, the flexible portion retains an overall substantially U-shaped form; and

a shackle-receiving portion comprising a locking mechanism operable to secure the shackle to the shackle-receiving portion.

2. The lock of claim 1 , wherein the substantially U-shaped form comprises substantially straight and parallel legs.

3. The lock of claim 1 , wherein the shackle further comprises a cable.

4. The lock of claim 3 , wherein the shackle further comprises a sleeve disposed over the cable.

5. The lock of claim 1 , wherein the shackle further comprises an external sleeve.

6. The lock of claim 1 , wherein at least a portion of the shackle is permanently affixed to the shackle-receiving portion.

7. A lock, comprising:

a shackle, the shackle further comprising:

a cable,

a flexible coil spring portion disposed around the cable,

a sleeve disposed between the flexible portion and the cable, and

an external sleeve disposed around the flexible portion and the cable; and

a shackle-receiving portion comprising a locking mechanism operable to secure the shackle to the shackle-receiving portion.

8. The lock of claim 7 , wherein the coil spring portion is resilient and heat-treated in order to maintain an overall substantially U-shaped form.

9. The lock of claim 8 , wherein, absent any external deformation forces, the coil spring portion retains an overall substantially U-shaped form.

10. The lock of claim 9 , wherein the substantially U-shaped form comprises substantially straight and parallel legs.

11. The lock of claim 7 , wherein at least a portion of the shackle is permanently affixed to the shackle-receiving portion.

12. The lock of claim 7 , wherein the flexible portion further comprises a flexible coil spring portion.

13. A method of making a lock, comprising:

manufacturing a shackle comprising a flexible coil spring portion, wherein manufacturing the shackle comprises heat-treating a coil spring to maintain an overall substantially U-shaped form, and wherein manufacturing the flexible coil spring portion comprises assembling a spring-cable assembly comprising a cable slidably disposed within the coil spring; and

manufacturing a shackle-receiving portion comprising a locking mechanism operable to secure the shackle to the shackle-receiving portion.

14. The method of claim 13 , wherein manufacturing the shackle and the shackle-receiving portion comprises manufacturing at least a portion of at least one of the shackle and the shackle-receiving portions using free-form fabrication.

15. The method of claim 13 , wherein manufacturing the shackle further comprises:

affixing a first lock plug to a first end of the spring-cable assembly;

affixing a second lock plug to a second end of the spring-cable assembly opposite the first end of the spring-cable assembly; and

permanently securing the first lock plug into the shackle-receiving portion, the locking mechanism being configured to releasably receive and lock the second lock plug.

16. The method of claim 13 , wherein manufacturing the shackle further comprises disposing a sleeve adjacent the coil spring.