LASER HEAT TREATMENT
A method of heat treating a surface with a laser, successive passes of the laser over the surface having a large overlap with each individual pass applying insufficient energy to obtain the desired effect on the surface but the overlapping passes applying sufficient energy. Various patterns of laser movement may be used.
This application claims the benefit of U.S. Provisional Application No. 61/846,584, filed Jul. 15, 2013, which is herein incorporated by reference in its entirety.
TECHNICAL FIELDLaser heat treatment.
BACKGROUNDLasers are commonly used to heat treat the surfaces of metal objects. Typically, it is not desired to melt the surface. A laser is used to bring the surface to a temperature below the melting point of the metal but sufficient to cause hardening when the surface is cooled. Cooling occurs quickly when laser energy is no longer applied due to conduction into the bulk of the material. The laser energy is applied by a laser which follows a path over the material guided by a computer. Conventionally, the laser supplies sufficient energy to adequately treat the surface at least at the center of the path in a single pass. The path zigzags to cover the whole surface to be heat treated. The surface at the center of the beam is heated more than the edges, causing an uneven effect of the treatment over the surface. It is known to overlap the path to some extent but the overlap is generally small, as too great an overlap would cause overtreatment of the overlapped area. The paper “Predictive Modeling of Multi-Track Laser Hardening of AISI 4140 Steel” discloses simulations of overlaps of up to 50% but teaches away from 50% overlap as it finds 5/12 overlap to be preferable. When a percentage or fraction is used to indicate a degree of overlap, the percentage or fraction is used to indicate the width of the overlap of the beam in successive passes as a percentage or fraction of the width of the laser beam in a single pass.
Lasers are also used in treatment applications which melt the surface. The paper “Three body abrasive wear of X12CrNiMo martensitic stainless steel laser alloyed with TiC” discloses 75% overlap when melting the surface of steel to alloy the steel with TiC grains. The surface is melted even with a single pass. This degree of overlap is not conventionally applied when not intending to melt the surface.
SUMMARYThere is disclosed a method of heat treating a surface with a laser to obtain a change in the structure of the surface without melting the surface by directing a laser beam onto the surface, the laser beam illuminating at a point in time a portion of the surface, and moving the laser beam to illuminate at successive points in time successive portions of the surface, the portion of the surface and the successive portions of the surface forming a path, the path overlapping itself to pass over each point in an area of the surface to be treated more than once, the laser beam supplying insufficient energy to obtain the change in structure of the surface in a single pass.
In various embodiments, there may be included any one or more of the following features: the width of the overlap of the path between successive passes may be greater than 50% of the width of the path in a single pass, at least 75% of the width of the path in a single pass, or greater than 75% of the width of the path in a single pass.
There is also disclosed a method of heat treating a surface with a laser to obtain a change in the structure of the surface without melting the surface by directing a laser beam onto the surface, the laser beam illuminating at a point in time a portion of the surface, and moving the laser beam to illuminate at successive points in time successive portions of the surface, the portion of the surface and the successive portions of the surface forming a path, the path overlapping itself to pass over each point in an area of the surface to be treated more than once, the width of the overlap of the path between successive passes being greater than 50% of the width of the path.
In various embodiments, there may be included any one or more of the following features: the width of the overlap between successive passes may be at least 75% of the width of the path, or greater than 75% of the width of the path. The surface to be treated may be steel. The change in the structure of the surface may be the formation of a martensitic grain structure. The path may follow a zig-zag route, a route with stacked line passes, a looping route, or a route with S-pattern motion.
These and other aspects of the device and method are set out in the claims, which are incorporated here by reference.
Embodiments will now be described with reference to the figures, in which like reference characters denote like elements, by way of example, and in which:
In standard laser heat treating a laser is used with a small amount of overlap 12 between successive passes 14, as shown in
Our process can work with various laser motion controls, be it zig-zag, stacked line passes, looping motions, or S-pattern motion. Each consecutive pass provides a pre-heat for the next pass.
The process disclosed uses a higher travel speed or lower laser energy output (or a combination of both) than is used in standard laser heat treatment. By increasing the speed or lowering the laser power output we are enabling ourselves to use a greater overlap than is possible in conventional laser heat treatment. By using a greater overlap we are able to insure that the areas we heat treat do not have areas of shallow hardening.
Referring to
Referring to
The process can be used for heat treatment of metal products in any industry, including but not limited to, for example, oilfield equipment or automotive parts.
As the heat from each laser pass dissipates over time, it is preferred that each pass over a point in the surface occur within a relatively short time frame. For a sufficiently large surface, there may not be enough time for the laser to traverse the full width of the surface before the heat from a pass dissipates, and so the width of the surface can be divided into strips 30, the path of the laser traversing the width of a strip in each pass and each strip being treated in turn.
Immaterial modifications may be made to the embodiments described here without departing from what is covered by the claims.
In the claims, the word “comprising” is used in its inclusive sense and does not exclude other elements being present. The indefinite articles “a” and “an” before a claim feature do not exclude more than one of the feature being present. Each one of the individual features described here may be used in one or more embodiments and is not, by virtue only of being described here, to be construed as essential to all embodiments as defined by the claims.
Claims
1. A method of heat treating a surface with one or more lasers to obtain a change in the structure of the surface without melting the surface, the method comprising:
- directing a beam of a laser of the one or more lasers onto the surface, the beam illuminating at a point in time a portion of the surface, and illuminating at successive points in time further portions of the surface, the portion of the surface and the further portions of the surface defining a path, the path overlapping itself or the path of another laser of the one or more lasers to pass over each point in an area of the surface to be treated more than once, each laser of the one or more lasers supplying insufficient energy to obtain the change in structure of the surface in a single pass.
2. The method of claim 1 in which the width of the overlap between successive passes is greater than 50% of the width of each of the successive passes.
3. The method of claim 1 in which the width of the overlap between successive passes is at least 75% of the width of each of the successive passes.
4. The method of claim 1 in which the width of the overlap between successive passes is greater than 75% of the width of each of the successive passes.
5. A method of heat treating a surface with one or more lasers to obtain a change in the structure of the surface without melting the surface, the method comprising:
- directing a beam of a laser of the one or more lasers onto the surface, the beam illuminating at a point in time a portion of the surface, and illuminating at successive points in time further portions of the surface, the portion of the surface and the further portions of the surface defining a path, the path overlapping itself or the path of another laser of the one or more lasers to pass over each point in an area of the surface to be treated more than once, the width of the overlap of the path between successive passes being greater than 50% of the width of the path.
6. The method of claim 5 in which the width of the overlap between successive passes is at least 75% of the width of each of the successive passes.
7. The method of claim 5 in which the width of the overlap between successive passes is greater than 75% of the width of each of the successive passes.
8. The method of claim 1 in which the surface to be treated is steel.
9. The method of claim 8 in which the change in the structure of the surface is the formation of a martensitic grain structure.
10. The method of claim 1 in which the surface is divided into strips, each pass of the laser traversing the width of a respective strip, and successive passes traversing a strip overlapping within the strip.
11. The method of claim 10 in which neighbouring strips overlap each other.
12. The method of claim 1 in which the path follows a zig-zag route.
13. The method of claim 1 in which the path follows a route with stacked line passes.
14. The method of claim 1 in which the path follows a looping route.
15. The method of claim 1 in which the path follows a route with S-pattern motion.
16. The method of claim 1 in which the surface is divided into segments, each segment having at least two passes with substantially 100% overlap.
17. The method of claim 16 in which neighbouring segments overlap each other.
Type: Application
Filed: Jul 17, 2013
Publication Date: Jan 15, 2015
Inventors: Curt Bergeson (Beaumont), Konrad Feigel (Edmonton)
Application Number: 13/944,744
International Classification: C21D 1/34 (20060101);