Electric heating – Metal heating – By arc
Reexamination Certificate
2000-04-21
2001-10-16
Heinrich, Samuel M. (Department: 1725)
Electric heating
Metal heating
By arc
C219S121710, C219S121840
Reexamination Certificate
active
06303901
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to ultrashort pulse laser machining, and more specifically, it relates to techniques for machining layered materials and articles without affecting other than the first layer.
2. Description of Related Art
In many materials processing applications it is important to penetrate the work item frontal piece using some form of energy, laser beams or electron beams being examples, without causing damage to subsequent surfaces facing the laser or electron beam. One example of this is the need to place holes in fuel injectors without damaging the back surface of the sack in which the fuel is combusted. Damage to this back surface severely reduces the reliability of the overall fuel injector as its subsequent exposure to extremely high temperatures and pressures requires that the fuel injector be of very high integrity.
The mechanical structure of fuel injectors (or other components requiring that portions of the piece be machined without causing damage to the remainder of the piece) usually severely limits the strategies for machining. In the case of fuel injectors the back or subsequent surface encountered by the machining laser or electron beam is typically only some millimeters away from the machined surface. Therefore, a laser beam that is of high enough intensity to cut or drill the frontal piece remains high enough in intensity at the subsequent surface to damage it. One strategy that has been tried is to insert a flowing, absorbent liquid between the frontal piece and the back surface (fill the “sack”). Unfortunately, the severe constriction of the sack region does not allow the liquid to be flowed fast enough to avoid bleaching of the dye by high energy pulses from high repetition rate machining lasers. Another strategy has been to plug the sack region with a non-flowing absorbent solid. However, the energy absorbed by the absorbing solid is so great that it in turn heats up and damages the surrounding surfaces in the sack.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide techniques for forming holes in a frontal piece of a workpiece without affecting a backing material.
It is another object of the present invention to provide techniques for forming holes in fuel injectors without affecting the second wall.
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 combusted.
In one embodiment, pulses from an ultra short pulse laser remove about 10 nm to 1000 nm of material per pulse. This occurs when the illumination fluence is near or below approximately 500-1000 milli-joules/cm
2
at the work piece. The injector may be trepanned and a diagnostic used to lower the laser illumination fluence to this level either as soon as the frontal piece is penetrated or just slightly before the frontal piece is penetrated.
In another embodiment, the intervening void (or sack) between the initial surface and the subsequent surface is filled with a gas that possesses a very large propensity to absorb photons from the short pulse laser. These gases would either absorb a majority of the energy from the laser beam prior to the beam reaching the back surface or would absorb enough energy to form a plasma of high enough density to shield the back surface. Similarly a simple monatomic or molecular gas could be used to absorb photons, forming a high density plasma, to shield the back surface.
In one embodiment, a plasma source is attached to the fuel injector and initiated by common methods such as microwave energy. The plasma so formed could be in contact with the sack region of the injector but would only flow into the sack region once an injector hole first penetrates the frontal piece, allowing the gas contained in the sack to diffuse through the penetration, drawing the plasma into the penetrated area.
In another embodiment of the invention, the sack void is filled with a solid. Once the injector hole penetration is made, the substance is drawn toward the penetration and through it due to the differential pressure existing on the material. The material absorbs photons and is ablated if subsequently illuminated by the machining laser beam. The result is that the machinist could choose to machine fuel injector holes by trepanning.
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. This liquid would absorb photons during the “clean-up” of the hole, thereby preventing damage to the sack.
REFERENCES:
patent: 5720894 (1998-02-01), Neev et al.
patent: 5948172 (1999-09-01), Neiheisel
patent: 6020988 (2000-02-01), Deliwala et al.
patent: 6156030 (2000-12-01), Neev
patent: 6156461 (2000-12-01), Grenon et al.
patent: 6208458 (2001-03-01), Galvanauskas et al.
Banks Paul S.
Perry Michael D.
Stuart Brent C.
Heinrich Samuel M.
The Regents of the University of California
Thompson Alan H.
Wooldridge John P.
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