Laser cutting method

1. A laser beam cutting method for cutting a first plate made of a first material, having a first melting point and having a first thickness, and for cutting a second plate made of a second material, having a second melting point and having a second thickness, the second melting point not being the same as the first melting point, the second thickness not being the same as the first thickness, by irradiating the plates with a laser beam, the laser beam cutting method comprising:

a plate material placement process for placing the first and second plates side by side so that the laser beam can only irradiate one plate at a time and out of the first and second plates, an opposite surface of a laser beam irradiated surface of the plate material with a lower melting point extends further from the laser irradiated surface than an opposite surface of the laser beam irradiated surface of the plate with a higher melting point;

a focus adjustment process for aligning a focus length of the laser beam with the opposite surface of the laser beam irradiated surface of the plate with the higher melting point of the first and second plates; and

a plate material cutting process for cutting the first and second plates through irradiation with the laser beam according to a series of operations while maintaining constant the focus length of the laser beam such that when the laser beam irradiates the plate with the higher melting point it is focused at the opposite surface of the laser beam irradiated surface of the plate with the higher melting point.

2. The laser cutting method according to claim 1 , wherein out of the first and second plates, a maximum value of a plate thickness of the plate with the lower melting point is set according to a tolerance of the focus length of the plate with the higher melting point and a maximum value of thickness of the plate with the lower melting point is made smaller as the tolerance of the focus length of the plate with a higher melting point becomes narrower.

3. The laser beam cutting method according to claim 2 , wherein:

out of the first and second plates, the plate with a material having the lower melting point is an aluminum plate and the plate with a material having the higher melting point is a copper plate; and

the maximum value of the thickness of the plate with the material having the lower melting point is set to 3.3 times the plate thickness of the plate having a material with the higher melting point.

4. The laser beam cutting method according to claim 1 , wherein

the plate material placement process places the first and second plates side by side so that the laser irradiated surfaces thereof are flush with each other before the focus adjustment process.

5. The laser beam cutting method according to claim 1 , further comprising

a gas blowing process for blowing an assist gas to the first and second plates along with irradiation with the laser in order to assist cutting by the laser, and

the first and second plates are cut continuously while supplying the assist gas.

6. The laser beam cutting method according to claim 5 , wherein the first and second plates are cut continuously while sustaining conditions to supply the assist gas.

7. The laser beam cutting method according to claim 1 , wherein

out of the first and second plates, the plate with the lower melting point is a positive electrode tab of a laminated battery and the plate with the higher melting point is the negative electrode tab of the laminated battery; and

the positive electrode tab and the negative electrode tab are formed to be thicker than a collector foil for use in formation of electrodes of the laminated battery.

8. A laser beam cutting method for cutting a first plate made of a first material, having a first melting point and having a first thickness, and for cutting a second plate made of a second material, having a second melting point and having a second thickness, the second melting point not being the same as the first melting point, the second thickness not being the same as the first thickness, by irradiating the plates with a laser beam, the laser beam cutting method comprising:

a plate material placement process for placing the first and second plates side by side so that the laser beam can only irradiate one plate at a time and out of the first and second plates, an opposite surface of a laser beam irradiated surface of the plate material with a lower melting point extends further from the laser beam irradiated surface than an opposite surface of the laser beam irradiated surface of the plate with a higher melting point;

a focus adjustment process for aligning a focus length of the laser beam with the opposite surface of the laser beam irradiated surface of the plate with the higher melting point of the first and second plates; and

a plate material cutting process for cutting the first and second plates through irradiation with the laser beam according to a series of operations while maintaining constant the focus length of the laser beam such that when the laser beam irradiates the plate with the higher melting point it is focused at the opposite surface of the laser beam irradiated surface of the plate with the higher melting point,

wherein out of the first and second plates, the plate with the lower melting point is a positive electrode tab of a laminated battery and the plate with the higher melting point is the negative electrode tab of the laminated battery; and

the positive electrode tab and the negative electrode tab are formed to be thicker than a collector foil for use in formation of electrodes of the laminated battery.