Method to reduce damage to backing plate

• US 6,303,901 B1
• Filed: 04/21/2000
• Issued: 10/16/2001
• Est. Priority Date: 05/20/1997
• Status: Expired due to Fees

• Current Assignee: Regents of the University of California (University of California)
• Original Assignee: Regents of the University of California (University of California)
• Inventors: Perry, Michael D., Banks, Paul S., Stuart, Brent C.
• Primary Examiner(s): Heinrich, Samuel M.
• Application Number:
  US09/558,144
• Time in Patent Office: 543 Days
• Field of Search: 219/121.7, 219/121.71, 219/121.67, 219/121.68, 219/121.69, 219/121.73, 219/121.74, 219/121.84
• US Class Current: 219/121.71
• CPC Class Codes: B23K 2103/04 Steel or steel alloys
• CPC Class Codes: B23K 2103/16 Composite materials , e.g. fibre reinforced
• CPC Class Codes: B23K 2103/30 Organic material
• CPC Class Codes: B23K 2103/32 Material from living organisms, e.g. skins
• CPC Class Codes: B23K 2103/36 Wood or similar materials
• CPC Class Codes: B23K 2103/50 Inorganic material, e.g. metals, not provided for in B23K2103/02 – B23K2103/26
• CPC Class Codes: B23K 26/0624 using ultrashort pulses, i.e. pulses of 1ns or less
• CPC Class Codes: B23K 26/12 in a special atmosphere, e.g. in an enclosure
• CPC Class Codes: B23K 26/123 in an atmosphere of particular gases
• CPC Class Codes: B23K 26/18 using absorbing layers on the workpiece, e.g. for marking or protecting purposes
• CPC Class Codes: B23K 26/382 by boring
• CPC Class Codes: B23K 26/389 of fluid openings, e.g. nozzles, jets laser machining of inkjet nozzles B41J2/1634
• CPC Class Codes: B23K 26/40 taking account of the properties of the material involved
• CPC Class Codes: C06B 21/0033 Shaping the mixture
• CPC Class Codes: F42B 33/008 Cutting explosive or propulsive charges
• CPC Class Codes: G02F 1/392 Parametric amplification

Abstract

The present invention is a method for penetrating a workpiece using an ultra-short pulse laser beam without causing damage to subsequent surfaces facing the laser. Several embodiments are shown which place holes in fuel injectors without damaging the back surface of the sack in which the fuel is ejected. In one embodiment, pulses from an ultra short pulse laser remove about 10 nm to 1000 nm of material per pulse. In one embodiment, a plasma source is attached to the fuel injector and initiated by common methods such as microwave energy. In another embodiment of the invention, the sack void is filled with a solid. In one other embodiment, a high viscosity liquid is placed within the sack. In general, high-viscosity liquids preferably used in this invention should have a high damage threshold and have a diffusing property.

Claims

1. A method for machining a workpiece that has a backing material, comprising:

providing a workpiece having a front piece and a backing material;

directing a series of laser pulses at said front piece, wherein each laser pulse of said series of laser pulses has a pulse duration of less than about 50 picoseconds, wherein each said laser pulse has an illumination fluence of less than about 10 joules/cm², wherein material is removed from said front piece by each said laser pulse.

2. The method of claim 1, wherein the step of providing a series of laser pulses includes providing laser pulses at less than about 10 joules/cm² until said front piece is penetrated.

3. The method of claim 1, further comprising trepanning said front piece with said series of laser pulses.

4. The method of claim 1, wherein said workpiece comprises a fuel injector.

5. The method of claim 1, wherein the step of providing a series of laser pulses includes propagating said series of laser pulses through a phase plate to flatten the intensity profile of each said laser pulse.

6. The method of claim 1, wherein the step of providing a series of laser pulses includes propagating said series of laser pulses through a deformable mirror to flatten the intensity profile of each said laser pulse.

7. The method of claim 1, wherein an intervening space exists between said front piece and said backing material, wherein said intervening space is filled with a gas that possesses a very large propensity to absorb photons from said at least one laser pulse.

8. The method of claim 7, wherein said gas comprises a low lying electronic state that is easily excited by absorption processes selected from a group consisting of a linear absorption process or a multiphoton absorption process.

9. The method of claim 8, wherein said gas absorbs a sufficient amount of the energy from said at least one laser pulse such that said laser pulse is at a level below the ablation threshold of said backing material prior to said laser pulse reaching said backing material.

10. The method of claim 8, wherein said gas absorbs enough energy to form a plasma of high enough density to shield said backing material from said at least one laser pulse.

11. The method of claim 7, wherein said gas is selected from a group consisting of CO₂, SF₆, NO₂, and N₂.

12. The method of claim 10, wherein said gas is a monatomic gas.

13. The method of claim 12, wherein said monatomic gas is selected from a group consisting of He, Ne, Kr and Ar.

14. The method of claim 7, wherein said gas is removed and replaces from said intervening space between the firing of each said laser pulse.

15. The method of claim 1, wherein an intervening space exists between said front piece and said backing material, wherein said intervening space is filled with a solid.

16. The method of claim 15, wherein said solid comprises a non-Newtonian solid.

17. The method of claim 16, further comprising applying a differential pressure between said from piece and said intervening space, wherein said non-Newtonian solid is drawn through said hole due to said differential pressure.

18. The method of claim 17, wherein said front piece is held at low pressure and said non-Newtonian solid is mechanically pressed with continuous pressure into said intervening space, wherein said non-Newtonian solid absorbs photons and is ablated if illuminated by each said laser pulse.

19. The method of claim 1, wherein an intervening space exists between said front piece and said backing material, the method further comprising filling said intervening space with a high viscosity liquid.

20. The method of claim 19, wherein said high viscosity liquid exhibits a high laser damage threshold and has a diffusing property.

21. The method of claim 20, wherein said high viscosity liquid comprises vacuum grease.