CA1091557A - Method and apparatus for making an instantaneous thermochemical start - Google Patents

Abstract

ABSTRACT

Laser is used in conjunction with high-intensity oxygen jet to make instantaneous thermochemical start on the surface of workpiece.
Alternate embodiment does not require use of high-intensity jet.
Both embodiments can make flying starts use of piece, and machine in relative motion.

Description

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This invention relates, in general, to thermochemical removal o~ metal from the surface of a workpiece, commonly called scarfing. More particularly, it relates to the making of instantaneous or "flying starts" for scarfing operations.
A "flying start," as that terrn is used throughout the pre3ent specification and claims, means the virtually instantaneous ; starting of a thermochemical reaction on a workpiece which is moving relative to the scarfing machine at its normal scarfing speed, i.e., usually a speed of from about 6 to 45 me~ers per minute. The lower end of said range being used for scarfing cold workpieces and the upper end or scarfing hot workpieces.
It is well known in the art that a scaring reac-tion is started by preheating the metal workpiece to its - molten or ignition temperature -- normally by preheating flames directed onto a relatively small area -- before apply ing an obli~uely directed stream of scarfing oxygen at the molten puddle. The scarfing oxygen stream has a two-fold pur-pose, first to effect a thermochemical reaction with the metal, and secondly, to blow away the reacted metal thereby exposing fresh metal or the scarfing reaction.
Metal rods have long been used to ob~ain faster starts in hand scarfing operations, as shown for example by U.S~ Patent No. 2,205,890. Here the work must be station-ary and the operator, by his individual skill, must be able to manipulate both the timing of the scarfing oxygen stream, as well as the angle of the torch and rod. Starting of mechanized scarfing reactions with wire rods is likewise

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~O~ 5~7 known, as shown by Bucknam et al in U.S. Patent No. 2,309~096 Scarfing starts descrlbed therein are, however, likewise possible only on stationary workpieces.
Flying starts made with the aid of metal powder are disclosed by DeVries et al in U.S. Patent No. 3,216,867, and those made by use of an energized electrode are disclosed by Lobocso in U.S. Patent No. 2,513,4Z5 and by Svensson et al in U.S. Patent No. 3,658,599. Rapid wear of the powder con-veying equipment causes powder starts to be unreliable, and this fact plus the cost of the metal powder, render powder starts unsatisfactory. The problems associated with elec-trically powered starts are relatively complex.

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Transferred electric arcs wherein the work is part of the electrical circuit require electrical contact to ~he moving workpiece. Non-transferred electri~ arcs wherein the workpiece is not ;n the circuit require that the electrode be extremely close to the work surface in order to trans~er enough heat to bring the workpiece to ignition temperature.
This is impractical because of spatial limitations and because the extreme spatter of the scarfing reaction would destroy the arc torch. ~-Also, more recently it has been discovered, as described in U.S. Patents 3,966~503 and 3,991,985, that ~ `
flying starts may be made by contacting the me~al surface to be scared with a hot wire. The hot wire is brought to ~ `
ignition temperature by the heat of the scar~ing unit preheat flames or some external heat source. While this process has 9~SS~7 10617 - 1 proven to be succes9ful in situ~tions where ~ev~ral spot scsrI'ing operations are to ble performed, it i8 nece~5ary to provide a plur~lity of wire :Eeeding units corresponding to the number of scarfing uni~8 employed, Accordingly, up until now it has alway~ been re-~uired to u~e an ad~uvant mater~al such as metsl powder or wires to bring the ~orkpiece to ignition temperature.
For purposes of this dis~losure, high inten~ity jet means tha~ the oxygen flow rate through the spreader nozzle is greater than the oxygen flow rate through an equivalent width of a scarfing nozzle, Thi~ invention is pr~dicated on the di~covery that a high intensity laser beam can be focu~ed to ~ very small spot on a metal workpiece to be scarfed, which spot is already being impinged by an intense jet of oxygen or is simultaneously contacted by ~u~h a jet, and instant~ne- :
ously cause a thermochemical reaction ~o be initiated at ~uch very ~m~ pot and then ~pread out to a full ~pot scarfing p~g5 which is usually frc)m 5 to 25 centimeter~
wide. It was lulown that a la~er beam could bring a amall 9pot t.l ~o 1 mm dia, and 1 mm to .1 mm in depth) to it9 molten temperature instantaneou~ly~ However. it wa8 un-expectedly <liscovered that 8uch a' 8ma11 ~hallow spot of molten metal could be 8pread by a high intensity oxygen jet to a full width 8pot 8carfing ~ass, It wa~ thought that an oxygen jet of high inten~ity would blow ~uch a 8mall amount of molten metal away before the the~rmo-chemical reaction would be initi~ted or would cool the spo~ sufficAe~tly 4, , 9~ S S 7 ~o prevent the reaction from being started.
There are basically two different types of lasers, i.e., continuous wave lasers and pulsed lasers. Pulsed lasers, as the name implies, release their energy in very short high intensity bursts. The instantaneous starts of this invention, like the pulsed laserg are intermittent.
For this reason pulsed lasers are preferred in this invention.
It will be obvious however that continuous wave laser could be utilized in this invention by pulsing a continuous wave laser by means of a shutter or some other equivalent techni-que. A con~inuous wave laser is preferred or an alternate embodiment of this invention.
Accordingly, it is an object of this invention to provide a simple and reliable process and apparatus which is capable of making an instantaneous or flying start on a work-- piece without the use o any adjuvant material (e.g. powder ;~
or wire) or electric arc.
It is another object of this invention to provide a process capable of making an instantaneous, individual, fin-free spot scarfing cut on a metal workpiece wi~hout the use of adjuvcmt material or electric arcs.
It is still another object of this invention to pro-vide a process capable of making -- in a single pass over the surface of the workpiece -- a plurality of instantaneously started, ranclomly located, selective scarfing cuts on the surface of a workpiece moving at normal scarfing speed.

An alternate embodiment o~ this invention 5. ' .

0~17-~L~391S57 ; provides ~ method and apparatus which is capable o making instantaneous or flying scarfi.ng cuts without the use of a high intensity jet of oxygen t:o spread the starting puddle.
: SUMMARY OF INVE'NTION
These and other objects which will become apparent -~ to those skilled in the art are achieved by the present inven-tion which consists in one aspect o a method or making an instantaneous thermochemical start on the surface of a ferrous metal workpiece, comprising the steps of:
(a) contacting a preselected spot on said surface where the reaction is to begin~ with a laser beam, (b) impinging a high intensity jet of oxygen gas on said surface at said spot, thereby causing an immediate scarfing reaction to begin and a molten puddle to form at said spot, and (c) continuing the impingement af a high inten-sity jet of oxygen on said paddle until said puddle has spread to the spot scarfing width desiredr In another aspect, the invention resides in appara-tus for making an instantaneous start comprising a scar~ing machine having a scarfing unit provided with means for dis- : :
charging a preheat 1ame and a scarfing oxygen stream toward a workpiece to be scared; an oxygen spreader nozzle moun~ed on the scarfing machine located in front of said scarfing unit and inclined at its discharge end so as to provide a high intensity jet of oxygen at an angle to the surace of the workpiece some predetermined distance ahead of the 6.

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scarfing oxygen stream and a laser provided on said scarfing machine having an optical syst:em associated therewith for focusing a laser beam on the surface of the workpiece.
After the molten pucidle has been spread to its pre-selected width, the instantaneous star~ has been completed The spreading oxygen jet may then be left on and used to carry out the scarfing reaction, or it may be ~urned off and another oxygen stream may be impinged on the spread puddle ~- at an acute angle to the work surface in order to "take over"
and carry out the scarfing reaction. The type o scarfing cut desired will determine the type of scarfing oxygen stream used to "take over" the scarfing reaction from the spreading jet.
An alternate embodiment of the present invention consists of a method for making an instantaneous scarfing cut .!
on the surface of a metal workpiece, comprising the steps of:
~ ~a) causing relative motion between the work-- piece and a stream of scarfing oxygen gas, and simultaneously therewith tl) impi~ging at least one laser beam on the work surface so as to produce a heated path o~ desired length across said surface relative ~o i~s direction of motion, said heated path being produced by the laser beam heating a series of .
points on said surface to their oxygen ignition ~emperature, and (2) implnging a stream of scarfing oxygen . . .. .

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onto said heated path, thereby causing an instantaneous sca~ing cut to begin along said path, and (b) continuing the flow of scarfing oxygen until the desired length of cut has been pro~uced.
Another aspect o this alternate embodiment o~ the - invention consists of scarfing apparatus, comprising in ~; combination:
(a) scar~ing nozzle means capable of dis-charging a controlled stream of scarfing oxygen onto thesurface of a workpiece to be scar~ed, ~ ) means for producing relative motion be-tween said nozzle means and said worlcpiece, and (c) laser means capable of impinging at least - one laser beam on the work sur~ace so as to produce a heated `.
path of desired length across said surface relative to i~s direction of motion, by having the laser beam heat a series of points on said surface to their oxygen ignition tempera-.:
.~ ture, said heated path being located proximate to the center~
line projection of said scarfing oxygen stream on the work surface.
When using this alternate embodiment, the preferred method of laser heating the surface of the workpiece to its oxygen ignition temperature is by traversing a continuous . wave laser beam such that the beam impinges a continuum o .: points across the surface of the workpiece.
The term "instantaneous'l as used with reference to 8.
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~O 9 ~S 57 making a thermochemical start, in the present specification and claims, is meant to include "flying starts~" as well as starts where there is no relative motion between the work-piece and the scaring apparatus until the instant the laser - beam contacts the preselected spot. At the instant of con-tact, however, normal scarfing speed is immediately co~menced (without waiting for puddlé formation as in the prior art) so that the starting process is carried out with relative motion between the workpiece and the scarfing apparatus. If motion 10 is not immediately commenced on contact of the laser beam, -the oxygen jet would gouge a hole in the workp~ece within a very short time. The relative motion may, of course, be caused by moving either the work surface relati~e to station-. ary scarfing apparatus, or vice versa.
- The term "stream of scarfing Qxygen" as used through-., ~
out the present specification and claims is intended ~o mean a stream of oxygen gas directed obliquely at the surface of the workpiece of sufficient intensity to thermochemically . . ~
remove a surface layer of metal, customarily to a depth of .
about 1 to 8 mm, and to make a scarfing cut at least 25 mm wide. Streams of scarfing oxygen are preerably sheet-like, ~ ,~
but may also be circular or of other shapes.
An individual, fin-free, spot scarfing cut can be made by discharging at the puddle, an oblique, sheet-like stream of scarfing oxygen gas whose intensity of flow is - gradual~y diminished towards the edges of the stream, reaching zero intensity at the lateral edges of the nozzle orifice ., , ~ .

1e~9~S~7 from which it is discharged, and which produces a cut which is narrower than the width of said orifice. Such a scarfing cut can be made with the nozzles described and claimed in copending Canadian Patent Application Serial No.258,959 filed August 12, 1976.
If selective spot scarfing of the entire surface of a workpiece is sought to be done in a single pass, the scarfing cuts must be made not only fin-free, but also in such manner that adjacent cuts will neither overlap nor leave excessively high ridges or deep grooves between them.
This requires the capability for discharging at the puddle ; abutting side by-side scarfing oxygen streams each of whose ., intensi~y of flow diminishes gradually towards its edges and each of which produces a scarfing cut which is at least as wide as its discharge orifice. Nozzles for making such scarfing cuts are described and claimed in U.S.Patent No.
4,013,486 issued March 22, 1977. As these scarfing units I ~-pass over the workpiece at normal scarfing speed, they can be turned on and off in a preselected manner to scarf out any random patte~ of defects located on the surface of the workpiece.
~ E a conventional scaring pass is sought - to be made this can be done by directing an oblique - sheet-like stream of scarfing oxygen at the puddle from a conventional rectangularly shaped nozzle whose intensity of flow is substantially uniform '`' ~. , .

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across its entire width. In such case the in~tantaneous scarfing start provides the benefit of being able to s~art the scarfing reaction on a wo.rkpiece as it comes into register with the scarfing units witho1lt having to slow down or stop either the workpiece or the units in order to start the scarf-ing reaction, as is required when using conventional preheat-ing flames. The instantaneous star~ permits the scarfing - operation to begin immediately upon contact o the apparatus -~ with the workpiece.
IN THE DRAWINGS
:~ Figure 1 is a side view illustrating the method and apparatus used for making an in~ividual, fin-free spot scarf-ing cut with an instantaneous st~rt in accordance with the present invention;
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Figure 2 is a front face view of the scarfing oxygen nozzle orifice taken slong line 2-2 of Figure l;
Figures 3, 4, 5 and 6 are schematic illustrations of the sequence of reactions, viewed from above along lines 3-3 o Figure 1, which takes place on the workpiece as an instant-aneous ~tart is made in accordance with the present invention;
Figure 7 shows, in perspective view, apparatus for carrying out the present invention, cantilever mounted or remote con~rol;
Figures 8 and 9 show modified versions of the appara-~tus shown in Figure 7;
Figure 10 illustrates in perspective view, another : preferred embodiment of the present invention, namely, a 11 ~

S~7 plurality of adjacent scarfing units for performing instant-aneously started selective, ~lti-cut, single pass, spot scarfing of the full width of a workpiece;
Figuxe 11 is a modified version o the laser arrange~
ment shown in Figure 10;
Figure 12 is a view of the front face of the scarf-: ing oxygen nozzle orifices used in the scarfing units sh~wn in Figure 10;
- Figure 13 is a top view of Figure 10 illustrating : 10 the manner in which the invention functions to produce a plurality of instantaneously started spot scarfing cuts in a single pass over the ~ull width of the workpiece; - ~:
Figure 14 is a side view illustrating an alternate .:
. embodiment of the method and apparatus that does not require a high-intensity oxygen jet;
Figure 15 is a front view (without the scaring unit) of Figure 14 illustrating a preferred arrangement for using a ~:
; laser to successively heat a series of points on the surface : of a workpiece to their oxygen ignition temperature; :~
Figure 16 shows an alternative arrangement for laser : :
heating the surface of the workpiece;
Figure 17 ~llustrates the shape of a scarfing cut.
made when the arrangement shown in Figure 16 is used to make a flying start.
- DETAILED DESCRIPTION OF TXE INVENTIO~
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In Figure 1 a laser unit 1, including a focusing lens 4 is mounted either on the scarfing machine or remotely .
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~9155 7 and arranged sv that a laser spot makes contact on the sur-face of the workpiece W at the point A, the point where the spot scarfing reaction, just ahead o the defective spot, is to begin. Oxygen spreader nozzle 2 may be a plain 1-5 cm round bore nozzle~ It will produce puddles having widths of from about 5 cm to 25 cm respectlvely. Noæzle 2 is inclined at its discharge end at an angle to work surface, such that the projected centerline o~ the oxygen jet (hereinafter referred to as the point of oxygen impingement) 30 discharged from the spreader nozæle will strike the work surface at - point B. Point A may be ahead of point B to as far behind - point B as point C. Poine C is the projection of the inside diameter of the spreader nozzle 2~ Scar~ing unit 3 is com-prised of conventional upper and lower preheat blocks 12 and -~ 13, respectively, which~may be provided with a row o either premixed or post-mixed pre-heat flame ports 14 and 15 respec-tively, and suitable gas passages therein. If post-mixed preheat flames are used, and these are preferred for greatest safety, then ports 14 and 15 will be used for discharging a fuel gas which will burn upon lgnition by admixture with a low velocity flow of oxygen, emanating from the scarfing oxygen nozzle slot 16 formed by the lower surface 17 of upper preheat block 12 and the upper surface 18 of the lower pre~
heat block 13. The slot oxygen nozzle 16 terminates within discharge orifice 19. In order to produce an individual, fin-free spot scaring cut, orifice 19 is shaped as shown in Figure 2. Oxygen and fuel gas are supplied to the scarfing :; ~
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unit 3 through feed pipes 20 and 21, respectively by means well known in the art.
The apparatus shown in Figure 1 functions as follows:
First, the preheat flames emanating ~rom scarfing unit 3 are ignited by actuating the flow o~ fuel gas from the rows of preheat ports 14 and 15, and a low flow of oxygen gas through orifice 19. These preheat flames, indicated by lines 22, strike the work surface and are deflected upward and backward.
When the defective area to be scarfed out of the moving work-piece W reaches a short distance before point B, a high inten-sity jet of oxygen is discharged from nozzle 2, to impinge on point B on the surface of the work~iece. When the de~ec-tive area reaches point A, the laser beam is pulsed, causing the spot to immediately reach ignition temperature thereby ;~
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starting an instantaneous scaring reaction. The oxygen jet from nozzle 2 causes the small puddle formed by ~he laser pulse to spread to its full width very rapidly, a~ which time it is shut off and the scarfing oxygen stream from ori~ice 19 which is aimed at point D on the work surface is increased to its scarfing flow rate, to take over ~he reaction from the spreader nozzle. The scarfing oxygen flow is kept on for as long as the scarfing cut is desired.
The steps foLlowing ignition of the preheat flames discharged from scarfing unit 3 may be automa~ed to operate ~or example through a series of sequenced timers, relays and solenoid valves so that an operator or other appropriate signal will initiate and automatically carry out the sequence 14.

10617-l ~IOS'~ e~S7 of steps described above. A second signal is required to end the cut by shutting off or decreasing the scarfing oxygen flow to an amount just sufficient to maintain the preheat flames on. In this state the apparatus is ready to immediately spot-scarf again.
An alternative way to carry out the above steps in the process is to turn the scarfing oxygen stream on at the same time as the spreader nozzle jet. The latter, having much more impact will control the course of the thermochemical operation, i.e., will cause the molten spot to spread. Then, as the spreader nozzle oxygen jet is `~ shut off, the scarfing oxygen flow will "take over" the reaction in a very gradual and even, though rapid, manner.
Figure 2 shows the scarfing nozzle orifice 19 used in the scarfing unit of Figure 1 for producing an individual, fin-free scarfing cut. Other types of scar-ing nozzles useful in the present invention are described in detail in my above-mentioned copending application Serial No. 258,959 filed August 12, 1976. It is im- ;
portant to note that a critical parameter of such a nozzle is that the cut it produces is narrower than the width of `-~
the nozzle itself. This is necessary in order to obtain ~ -; a fin-ree spot-scarfing cut. This fact, however, prevents such nozzles from being used side-by-side with another such nozzle, because the parallel cuts which - they produce would leave an unscarfed surface between the cuts. Hence, such nozzles are useful only for making in-dividual fin-free cuts. Figure 2 which is a view of Figure 1 , 15.
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5~7 along llne 2-2 shows the upper and lower ~reheat blocks 12 ~nd 13, containing the rows of upper nnd lower preheat fuel g~9 ports 14 and lS respectively, The oxygen nozzle orifice 19 contains triangular inserts 25 at each end of orifice 19, thereby causing the edges of the oxygen ~tream eman~ting from the orifice 19 to be gradually less intense, i.e., to have less impact on the work surface, It is to be noted that while in Fi~ure 1 point A
is behind point B. this distance may vary so th~t point A
may be from about 10 cm ahead to a distance behind point B, which ls determined by the projection of the inside di~eter of nozzle 2, see point C. Accordingly, point C
; is determined by the size and shape of nozzle 2. Preferably ::~
the distance between A and B is such that point A is about ~.
1 cm in fron~ of point B. The optimum range of the d~tance ~ between points A and B depends upon the sngle~C at which - the oxygen jet is directed at the work surfaee and the Bize of the jet nozzle. The ~ngle c~ may vary from about 30- to 80-; the ~referred angle is between 50- and 60-. If the an~l~
c~ of the nozzle i8 30- and a t.wo c~ntimeter inside di~et~r round nozzle is used, the range of distance between A and B
should be 0 to 8 cm, If the same size nozzle is used and the angle'~ is 80, the range is 0 to 3 cm. Polnt C which is the intersectlon of the projection of the back side of the spreader nozzle 2 and the ~teel ~urface. i8 the limit on the distance behind point B that point A may be and still make a flying startO
` Flgure 3-6 are ~ketches illustrating how.
ins tantaneous i 16, .

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or fLying star~s, made in accordance with this invention, take place. It is important t:o bear in mind that the sequence of steps illustrated in Figures 3-6 represent the reactions which take place in about 1 second.
Figure 3 shows the t:ime when the laser beam has made contact with point A, the point where the spot-scarfing pass is to begin. The arrow indicates the direction in which the workpiece W is travelling at a speed of about 15 meters/min.
Simultaneously, oxygen from spreader nozzle 2 causes ignition of the surface of the workpiece. This in turn melts the area 23 surrounding point Ao The instantaneous start has begun.
Figure 4 shows the same area about one-quarter second later than Figure 3. As the steel workplece continues to move in the direction of the arrow, the molten puddle 24 begins to be spread by the action of the spreader noz~le oxygen jet in a fan-like shape.
Figure 5 represents the defective area approximately one-half second later than Figure 3. Area 25 shows the molten puddle which has been spread on the moving workpiece W by the continuou~ discharge of oxygen from the spreader noz21e 2.
With the puddle having been spread to its maximum width of about 25 cm, the oxygen rom nozzle 2 is now shut off, and -the scarfing oxygen flow rate from scarfing unit 3 is increased to "take over" the scarfing reaction. The scarfing oxygen stream having picked up the puddle, continues the scarfing cu~
in the area 26. Area 26 contains both molten metal and slag on top of unscarfed steel and is clearly distinguishable from lSS7 10617-l ~he all-molten puddle area 25, The manner in which the reaction proceeds can be seen from Figure 6, which represent the reaction about 1 second later than Figure 3, Area 27 ha~ been sc~rfed, area 28 i9 molten but metal removal hs3 not yet taken place, and area 39 contains a mixture of slag and molt~n met~l on top of un~Qcarfed steel. As the 8urface of the metal moves by under the scarfing a~para~us, it goes through ~hree clearly distingu~shable stages, ~he first being &n area of molten metal and slag on top of un~carfed steel, the sec~nd molten metal alone, and ~hf rd scarfed, At the time shown in Figure 6, the 6preader oxygen flow h~ been shu~ off and a full width scarfing cut i6 being made by the ~e~rfing unit 3, It is important to note th~t the width of the cut rom ~carfing nozzle i~ the 8ame a~ the width to which the ~preader nozzle 2 has spread the puddle. This iB i~portant in order to prevent fin formation.
Figure 7 shows a perspectiv~ view of the appara~u~ --of F~gure 1, cantilever mounted for pur~oses of m~king the :
scarfing apparatu~ movable both laterally ~cro~s ~he width o~ the workpieee W, as well as longitudinally along ~t~
length. Horizont~l for~ member 31 i8 fixedly attached to a rail mounte~d operators pulpit 32, Pulpit 32 con~ain~
the controls for operation of ~he apparatus, including ; `
the 12ser controls, the oxygen discharged from the 8pread~
. . , er nozzle 2, aQ well as the o~ygen and fuel gases which ~ ;~
are ~upplied to scarfing uni~ 3 through feed ~ipe~ 20 and 21, respectively. Pulpi~ 32 ~ mobile la~er~lly . along the workpiece W on ra~.ls 33. A rack 34, : -~ .
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l0617-1 1~ 9~57 fixedly attached to one of thle rails, is engaged by a motor driven pinion (not shown) mounted under pulpit 32, permitting the entire cantilever mounted scarfing assembly and pulpit to be controllably moved along tracks 33. The scarfing assembly consisting of the scarfing unit 3, nozzle 2, a~d laser assembly 5 are all fixedly attached to carriage member 37 which rides up and down on plate 38 which in turn is fix-edly attached to housing 40. Motor 39 is used to controllably raise and lower the scarfing assembly by a rack and pinion arrangement (not shown) with the rack fixedly attached to ; plate 38~
The scarfing assembly and housing 40 is also capable o~ being mechanically moved across the width of the workpiece W, by motor driven pinion 35 which engages rack 36, fixedly attached to frame 31.
The apparatus shown in Figure 7 may be used to selectively spot scar~ randomly located defects on the sur~
face of the workpiece by being moved in line with the deect and then travelling longitudinally over the de~ective area.
Area 41 illustrates a typical spot scarfing cut made by the apparatus shown.
Figure 8 illustrates an alternative positioning of laser head 5. In the figure parts similar to those in Figure 7 bear the same reference characters. The laser itself is remotely lccated. Through the use of an cptical arrange-` men.t, in this case a 90 degree prism, the laser beam is directed at point B from the right side of the workpiece~ In the arrangement-shown in Figure 9, nozzle 2 is directed at 19.
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i~ 9 ~ ~5~ 10617_ point B from the right side o~ the workpiece W, causing the puddle to be projected toward the left side of the workpiece in front of the scarfing unit 3. This arrange-ment permits one to spread the starting puddle more rapidly over a wider area, enabling a wider scarfing cut to bP made, ; than with the same sized nozzle arrangement as shown in Figures 7 and 8. Nozzle 2 can, of course, also be located on the left side or anywhere in between. A combination using two such nozzles could also be used; the arrangements of Figure 7 or 8 to start the arrangement of Figure 9 to spread the puddle.
Figure 10 illustrates, in perspective, a plurality of scarfing units provided with nozzles for performing selec-tive, multi-cut, spot scarfing with instantaneous or flying ,~
starts of an e~tire width of a workpiece W in a single pass.
The plurality of scarfing uni~s 51, a laser head 52 with a plurality of optical arrangements and spreader nozzle 53 are all fixedly mounted upon a mobile carriage 54 which rides - upon rails 55 and 56, respectively by rack and pinion motive means. Rails 55 and 56 are fixedly mounted upon rail support members 57. The laser assembly 52 may include a housing H
purged with nitrogen or other gas. Mounted in the housing H
at predetermined intervals are 90 par~ial transmitting and partial reflecting prism P. The prisms permit the energy of the laser beam to be split and distribu~ed to a plurality of spots on the workpiece surface. Alternately 90 degree mirrors may be used which are selected in or out of ~he beam path to direct the beam to the spot desired. Accordingly, any optical ZO .

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system using either beam splitting and beam selecting can be used. The entire assembly of adjacent flying start scarfing units is able to pass over the full length of the workpi4ce W, whereby the entire width can be selectively scarfed at normal scarfing speed by the selective operation o~ each of the scarf-ing assemblies separately. Although in the apparatus illustrat-ed in Figure 10 the workpiece is stationary and the scar~ing apparatus moves over it, it is possible and in some cases preferable to do the reverse; namely, to have a stationary scarfing apparatus under which the workpieces pass on rollers . .
~- driven at normal scarfing speed.
Figure 11 shows another alternative to the apparatus shown in Figure 10. In this embodiment one mirror M would - direct the laser beam from laserhead L to a plurality fixed mirrors (F) mounted so as to direct the beam received by such - mirrors to the worksurfac`e W through a ~ocusing lens G.
When performing multi-cut selective spot scarfing with apparatus such as disclosed in Figures lO and ll, wherein two or more cuts of overlapping duration may be made, and .
-- 20 which may be started at different times but in which the speed of both are determined by the relative motion between -~ the workpiece and the scarfing assembly, no pause or slow down in scarfing speed can be tolerated, ~rom the ins~ant a first cut is begun until the last has been completed. The reason for this is that a pause would uncontr~llably affect a cut in progress by an adjacent unit. In other words, if the assembly has to be slowed down, for example, for preheating 21.

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lV9~S7 purposes as in the prior art, an adjoining assembly in which the scarfing oxygen is on would gouge a deep hole in the work~
piece. Hence, it should be apparent why no slow down may be tolerated in a multi-pass, selective, spot scarfing operation, and why the instantaneous or flying start is of such crucial importance to the proper functioning of this process.
In addition, it is essential that this process not cause scarfing cuts which either overlap the area to be scarfed by an adjacent unit, or cause excessive fins or ridges between adjacent scarfing cuts. This requirement is satisfied - by providing the l'gang pass'' scarfing oxygen noæzles, i.e., plurality of adjacent scarfing units with no~zles such as shown in Figure 12.
Figure 12 illustrates the front ~ace of the scarfing units employed in the "gang pass'i scarfing nozzles of Figure 10. These nozzles each contain a row of upper and lower post-mixed fuel gas ports 61 and 62, respectively above and below the scarfing oxygen discharge orifice 63. Orifice 63 is typically about 0~6 cm high and 20 cm wide. Its edges are partially closed by the end wall members 64. These are typically about 3 cm along the bottom edge, 0.4 cm high (at ` lts maximum height) and contain an inclined cut having an internal angle of about 10. Such end wall members 64 are provided at each end of each scaring o~ygen orifice 63 in order to gradually diminish the flow of oxygen towards the edges of each unit, but without totally closing off the edge of the unit, as is done in the case of the orifice shown in 22 .

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l(JY~lSS7 Figure 2. While orifices of the type shown in Figure 2 create a scarfing cut on the workpiece, which is narrower than the width of the orifice from which the oxygen is dis-charged, the "gang pass" orifice 63 of Figure 12 produces a cut, which though flared toward it~ outer edges, is of at least ~he same width as the orifice 63 itsel~.
Figure 13 is a top view illustrating the manner i~
which the apparatus shown in Figures 10 and 11 function to produce selective, multi-cut, spot scar~ing with flying starts on a workpiece. Re~erence ko Figure 10 will show a plurality of adjacent scar~ing units 51, each of which contains an oxygen -` spreader nozzle 53 and an optical system including pri3ms P
and a focusing lens in tube T, and each of which is provided ` . with oxygen and fuel gas to the scarfing unit.
`. The areas containing defects on the ~urface of work-, piece W to be spot scarfed out are designated 81, 82, 83, 84 : and 85. As the moving gang of adjacent scarfing units ~now - identified by reference characters 71, 72, 73, 74 and 75) comes into contact with the workpiece W, a flying start must 20 be made by unit 74 ag it reaches the front end 86 of area 84 : and must remain in operation until it reaches the back end . 87 of area 84, at which time unit 74 is shut off, and units - 71 and 72 are started on the fly. As the gang of scarfing .
units passes over the workpiece, unit 72 will remain on until it reaches the back end of defective area 82, at which time ;. it will be shut off either by an operator or a mechanical or electrical signal, while unit 71 renains on~ Uni~ 74 would :

~3.

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- ~ 9 i~ 10617-1 be turned on ag~in to begin ~pot ~carfing the area desig-nated 85. As the beginning of area 83 ia approached by the gang of scArfing units, unit 73 iB turned on, unit 74 i3 . turned off as the en~ of area 85 is re~ched, ~nd unit 71 :- ~ 5 turned off as ~he end of area 81 i~ reached. I)uring the entire spot scarfing p~s~, unit 75 rem~ined off, ~lnce no de~ects were contained in the zone of the workpiece over which this particular unit ~a~sedO
Figures 14 to 17 illustrate an altern~te embodi-ment of the invention that does not require u~e of a ; high-intensity ~et of oxygen ~nd spreader nozzle. ~ ~.
In Figure 14z a laser unit 1, i~cluding a focus-ing lens 4, i~ mounted on the ~carfing machine fr~me (not shown) - it could be moun~ed remotely - and arranged ~ so that the laser beam R impinges on ~he ~urface of the `~ workpiece W at point A, the point where the sc~rfing cut :~ is to begin. Scarfing unit 3 i8 typically comprised of conventional upper and lower ~reheat blocks 12 ~nd 13, respectively, which may be provided with rows of either premixed or p~st-m1xed prehe~t portæ 14 and 15, ~nd su~tsble gas passage~ ~herein. The scarfing oxy~en no~zle 810t 16 iS formed by the lower surface 17 of the upper preheat block l2 and ~he upper ~urface 18 of the lo~er ~reheat block 13, The ~lot-like oxygen nozzle 16 termin-~ ate8 with a discharge orifice lg, In order to start the ~ ~:
thermoch~mical reaction, point A may be ~ligh~ly 8head of or coincide with ~he area enclo9ed by the straight line projections of surfaces 17 and 18 onto the work .. surface, ~xygen ~nd fuel ~ ~ .
j 24, .. . . . .

109~LS5~

gas are supplied to the scarfing unit 3 through feed pipes 20 and 21, respectively by means well known in the art.
The apparatus shown in Figure 14 functions as follows. First, the preheat flames emanating from scarfing unit 3 are ignited by actuating the flow of fuel gas from the xows of preheat ports 14 and 15, and a low flow of oxygen gas through orifice 19. The preheat flames are indicated by lines 22. Relative motion is taking place between the scarfing apparatus and the workpiece. Just before the defective area to be scarfed on the surface o workpiece W reaches point A, the stream of oxygen ~rom orifice 19 is turned up to the scarfing oxygen rate. Simultaneously therewith, or shortly thereafter, the laser beam R is turned on, causing point A to immediately reach oxygen ignition temperature, causing ~n instantaneous scarfing cut to begin at point A. The laser beam is then directed across the surface of ~he workpiece relative to its direction of travel, causing the scarfing reaction to spread to the desired width by foLlowing the laser heated path. The stream o~ scarfing oxygen is kep~ on for as long as the scarfing cut is desired. The laser beam may be shut off as soon as the scarfing cut has reached i~s desired width.
Relative motion may be started after a scarfing reaction of desired width has been initiated, in those cases where a flying start is not desired. A flying start is one which takes place wlth the workpiece moving rela~ive to the scarfing apparatus at normal scarfing speeds.

, 25 .

. ~
, 10617-~

~ 9 ~S ~7 Figures 15 and 16 illustrate two ways in which a laser may be used ~o heat a path of desired length on ~he work surface to its oxygen igrlition temperature. Figure 15 is a front view of Figure 14 along line 2-2 with the scarfing uni~ not shown. The laser 1 and its optical system is turned ; on and rotated through the angle ~ , causing the laser beam :
R to heat a continuous series of points, formi~g a path on the metal work surface between points ~ and B to be beated to their oxygen ignition temperature. Instead of rotating the laser, the beam R may be optically directed to traverse the path between points A and B.
An alternative technique ~or heating a path on the -work surface is illustrated in Figure 16, where the laser - beam is directed between points A and B by moving ~y means ~` not shown) reflecting mirror M and lens 4, respectively ~ :.
across the path of the desired scarfing cut to position M' and 4'.
: ~ The laser used in Figures 15 and 16 is preferably ~.
of the continuous wave type. However, a pulsed laser may be used, in which case a.series of closely-spaced spots between . , points A and B are brought to their oxygen ignition tempera-~ure. The individual spots will flow together as the oxygen is turned on. Of course, other optical arrangements may be used to achieve the same result, including use o~ more than . one laser.
Figure 17 shows the shape of a scar~ing cut made when a flying start is made in ac:cordance with this invention, 26.

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using a single laser and the arrangement shown in Figures 15 or ~. The start of the cut begins at point A and continues to point B due to relative motion between ~he scarfing appara-tus and the workpiece W. Area 101 represents the scarfing cut.
This alternàte embodiment of the invention may be used for the same purposes as that requirlng a high intensity jet of oxygen. Such uses include, bu~ are not limited to making conventional scarfing cuts with a sheet-like stream of oxygen, i.e. desurfacing the entire surface; making indivi-dual fin-ree spot scarfing cuts whose width is narrower, as wide as or wider than the width of the scarfing nozzle, and making wide spot scarfing cuts by mounting several scarf-ing units together for spot scarfing in a gang-pass arrange-` ment.
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EXAMPLE
The amount of laser energy necessary to practicethis invention will vary depending on such variables as scarfing speed, workpiece composition and temperature, oxygen flow and purity, etc. However, in order to illus~rate the principle of the inve~tion to tho~e skilled in the art, the following example of one mode of practicing the invention is now provided.
;' Equipment such as shown in Figure 1 was used. The width of the scarfing unit was 15 cm. Oxygen 10w ~hrough the orifice 19 was 570 standard cubic meters per hour (SCMH).
The fuel gas flow was 40 SCMX. The speed of the workpiece relative to the scarfing unit was 14 meters per minute. The 27.

~9~57 oxygen spreader noæzle had a circular cross-section and had a 2 cm inside diameter. The nozzle angle to steel was 50 - degrees. Oxygen flow from the spreader nozzle was 850 SCMH.
The laser was a solid state Nd-YAG pulsed laser. Beilm dia-meter out of the laser was l cm. Beam divergence was 5 milli-radians. The laser pulse width was 11.0 microseconds. The laser energy was 50 joules. The laser spot s~ze was 2.0 mm diameter and the laser spot ~A) was 1 cm ahead o the projec- -- tion (B) of the center line of the spread nozzle. A 50 cm foeal length lens was used to focus the beam to a spot.
j In operation the scarfing Ullit flame was ignited and relative motion was started between the scarfing unit and the . . .
- workpiece. A signal to begin spot scarfing star~ed flow from the spreader nozæle and when full flow was reached the laser ~-, . .
was pulsed orming a molten spot in the steel and instant-aneously starting the thermochemical reaction. Approximately 1/2 second after the laser pulse the oxygen flow from the spreader nozzle was gradually turned off so that 3/4 of a : ~:
. ~
-~ second after the pulse the spreader nozzle flow was zero.
, The scaring 1OW was turned on so that at least 50% o~ full flow was reached when the laser pulsed. The scarfing oxygen then sustained the scarfing pass unti1 the pass was terminated by a predetermined signal. The width of the pass created was 15 cm, the depth was 3 mm. The temperature of the s~eel was 20 degrees centigrade. The composition was low carbon steel and the fuel gas was natural gas.
The process of this invention can be carried out by 28.

- . : - . .. . . .

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igniting the scaring uni~ flame from the molten puddle formed by the laser and spreader nozzle, i desired.
While the invention has been described with reference to certain preferred embodiments, it should be understood that modiications may be made to the arrangement of parts or ~he sequencing of steps without depar~ ng from the splri~ and scope of this inventionO For example, it is Rossible to use a continuous laser beam because the line made by such beam would be scarfed out as the scarfing reaction progresses.
Also two or more jets of oxygen rom two or more nozzles of various shapes and sizes can be used to spread the molten spot produced by a laser to any desired spot scarfing width.
Further, two or more laser-heads may be used if deemed necessary or desirable. Also, while the invention has been described with reference to thermochemical scar~ing of ferrous metal bodies, it should be understood tha~ the inven-tion includes any metal body which is amenable to thermo~
chemical scarfing using oxygen.
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Claims (35)

WHAT IS CLAIMED IS:

1. A method for making an instantaneous thermo-chemical start on the surface of a metal workpiece to be scarfed comprising the steps of:
(a) contacting a preselected spot on said sur-face where the scarfing reaction is to begin with a laser beam to bring such spot to its ignition temperature;
(b) impinging a high intensity jet of oxygen gas on said surface at said spot, thereby causing an instantane-ous scarfing reaction to begin and a molten puddle to form at said spot; and (c) continuing the impingement of a high inten-sity jet of oxygen on said puddle until said puddle has spread to a preselected width.

2. Method according to claim 1 wherein the metal workpiece is ferrous metal.

3. The method of claim 1 wherein relative motion between the workpiece and the means for producing said steps is caused to take place at normal scarfing speed prior to and throughout said steps without interruption, thereby pro-ducing a flying start.

4. The method of claim 1 wherein relative motion between said workpiece and the means for producing said steps is caused to commence at normal scarfing speed upon contact of said laser beam with said spot.

30.

5. Method according to claim 1 wherein said laser beam is a single pulse of laser power.

6. Method according to claim 3 wherein said laser beam contacts the workpiece surface at a point behind the point of impingement of the high intensity oxygen stream up to 10 cm ahead of said point.

7. Method according to claim 6 wherein the point of impingement behind the point of oxygen impingement is deter-mined by the projection of the inside diameter of the nozzle from which the oxygen stream emanates.

8. The method of claim 3 wherein the high intensity oxygen jet defined by step (b) is directed at said point from a position such that the included angle formed by the central axis of said jet and the line of travel on the work surface is between 30° and 80°, and such that the puddle is spread parallel to the direction of relative motion.

9. The method of claim 3 wherein the high intensity oxygen Jet defined by step (b) is directed at said spot from a position such that the included angle formed by the central axis of said jet and the surface of the workpiece is between 30° and 80°, and such that the puddle is spread perpendicular to the direction of relative motion.

10. The method of claim 1 which in addition contains 31.

the step of (d) scarfing said surface by impinging a sheet-like stream of scarfing oxygen on the molten puddle directed at an acute angle to said surface.

11. The method of claim 10 wherein said sheet-like stream of scarfing oxygen is gradually diminished in inten-sity towards the edges of said stream, reaching zero inten-sity at the lateral edges of the orifice from which it is discharged, thereby producing an individual, fin-free spot scarfing cut whose width is less than the width of said dis-charge orifice.

12. The method of claim 10 wherein said sheet-like stream of scarfing oxygen is gradually diminished in intensity towards the edges of said stream, but remaining greater than zero intensity at the lateral edges of the orifice from which it is discharged, thereby producing a fin-free spot scarfing cut which will not leave excessively high ridges or deep grooves between adjacent cuts made simultaneously and in like manner, said cut having a width equal to the width of said discharge orifice.

13. The method of claim 10 wherein said sheet-like stream of scarfing oxygen is substantially uniform in inten-sity across the entire width of the orifice from which it is discharged, thereby producing a conventional scarfing cut.

32.

14. The method of claim 11 wherein the width of said cut produced is equal to or greater than the width of the started puddle.

15. The method of claim 12 wherein the width of said cut produced is equal to or greater than the width of the started puddle.

16. The method of claim 13 wherein the width of said cut produced is equal to or greater than the width of the started puddle.

17. Apparatus for initiating a thermochemical reac-tion on the surface of a metal workpiece comprising in combine tion a scarfing machine having a scarfing unit provided with means for discharging a pre-heat flame and a scarfing oxygen stream toward a workpiece to be scarfed;
an oxygen spreader nozzle mounted on such scarfing machine and located in front of such scarfing unit inclined at its discharge end so as to provide a high inten-sity jet of oxygen at an angle to the surface of the workpiece some pre-determined distance ahead of the scarfing oxygen stream; and a laser provided on such scarfing machine and having an optical system associated therewith for focusing a laser beam on the surface of the workpiece.

18. Apparatus according to claim 17 wherein means is provided for causing relative motion between said scarfing 33.

machine and said workpiece.

19. Apparatus according to claim 17 wherein said laser is a pulsed laser.

20. Apparatus according to claim 17 wherein said laser is a solid state laser.

21. Apparatus according to claim 17 wherein said laser is a Nd-YAG crystal.

22. Apparatus for initiating a thermochemical reac-tion on the surface of a ferrous workpiece, comprising in combination a scarfing machine having a plurality of scarfing units provided with means for discharging a preheat flame and a scarfing oxygen stream toward a workpiece to be scarfed;
a plurality of oxygen spreader nozzles mounted on said scarfing machine, each of said oxygen spreader nozzles being located in front of a scarfing unit and inclined at its discharge end so as to provide a high intensity jet of oxygen at all angle to the surface of the workpiece some pre-determined distance ahead of the scarfing oxygen stream;
at least one laser provided on said scarfing machine and having associated therewith an optical system capable of providing a plurality of focused laser spots on the workpiece.

34.

23. Apparatus according to claim 22 wherein said laser optical system includes a plurality of partial trans-mitting and partial reflecting means mounted in a laser housing at predetermined intervals so that the energy of laser beam may be split and distributed to a plurality of spots on the workpiece surface.

24. Apparatus according to claim 22 wherein said laser optical system includes a plurality of mirrors mounted in a laser housing at predetermined intervals so that the mirror may be selectively positioned in or out of the laser beam path to direct such beam at a preselected spot on the workpiece surface.

25. Apparatus according to claim 22 wherein a plurality of lasers are provided on said scarfing machine and having associated therewith an optical system capable of pro-viding a plurality of laser spots on the workpiece.

26. A method for making an instantaneous scarfing cut on the surface of a metal workpiece, comprising the steps of:
(a) causing relative motion between the work-piece and a stream of scarfing oxygen gas, and simultaneously therewith (1) impinging at least one laser beam on the work surface so as to produce a heated path of desired length across said surface, relative 35.

to its direction of motion, said heated path being produced by the laser beam heating a series of points on said surface to their oxygen ignition temperature, and (2) impinging a stream of scarfing oxygen onto said heated path, thereby causing an instantaneous scarfing cut to beging along said path, and (b) continuing the flow of scarfing oxygen until the desired length of cut has been produced.

27. The method of claim 26 wherein the heated path is produced by rotating a continuous wave laser beam across the work surface.

28. The method of claim 26 wherein the heated path is produced by rotating a pulsed laser beam across the work surface.

29. The method of claim 26 wherein the stream of scarfing oxygen is sheet-like.

30. The method of claim 26 wherein the heated path is produced by moving a reflecting mirror and beam focusing lens across the work surface.

31. Scarfing apparatus comprising in combina-tion:
(a) scarfing nozzle means capable of dis-charging a controlled stream of scarfing oxygen onto the 36.

surface of a workpiece to be scarfed, (b) means for producing relative motion between said nozzle means and said workpiece, and (c) laser means capable of impinging at least one laser beam on the work surface to produce a heated path of desired length across said surface relative to its direc-tion of motion, by heating a series of points on said surface to their oxygen ignition temperature, said heated path being located proximate to the centerline projection of said scarfing oxygen stream on the work surface.

32. The apparatus of claim 31 wherein the laser means is a continuous wave laser.

33. The apparatus of claim 31 wherein said laser means is a pulsed laser.

34. The apparatus of claim 31 including means for rotating said laser beam along said path.

37.

35. The apparatus o? claim 31 including means for optically moving said laser beam along said path.

38.