Description:DESCRIPTION:
Field of the invention:
[0001] The present disclosure generally relates to the technical field of surface melting of components or products of ferrous materials such as steel, for example, shaft, roller, racer, construction rod, roller, spindle, sleeve, connecting rod, pin etc. by laser throughout its periphery or part there off. The present invention relates to setting up of an apparatus to modify surface of unhardened or prior-hardened (conventionally hardened) metallic materials at required region or throughout its outer or inner surface employing a laser workstation and a high speed rotary axis/spindle setup. Especially it relates to a processing methodology to alter the surface at desired region or regions of the metallic materials or components resulting in improvement of treated surface microstructure, tribological (wear, friction etc.,) and mechanical properties (hardness, strength, fatigue etc.,) and thereby envisaging life improvement. This is a novel method resulting in reduction of deleterious effects such as tempering or softening in overlapped regions in processing of cylindrical components and thereby enhancing engineering maneuverability and adaptability in industrial production lines. The invention provides vast advantages and adaptability for producing high strength and other properties enhanced cylindrical parts or components. The invented method entails uniform surface melting (thin) of the entire or part of peripheral surface (inside or outside) with ease of control in maintaining surface temperature (visibly melting surface) eliminating any adverse effects of inter-layer or inter-track softening or tempering enabling overall strength and or mechanical, tribological properties improvement as compared to untreated part.
Background of the invention:
[0002] Laser technology is used in industrial applications has experienced a major boost in recent years. Advantages such as high and uniform energy density, high heating and cooling rates, high productivity, low distortion, narrow heat affected zones and precise control of the treatable depth, make laser a viable processing tool to locally repair components, to repair parts over aged in service, to enhance life. Laser surface melting (LSM) have been successfully applied on metallic materials or components to achieve higher surface hardness as compared to that of other similar surfacing processes which involve longer interaction times that induce detrimental effects such as high distortion, large heat affected zone, unusual residual stresses.

[0003] Many a times, laser surface melting or transformation hardening has been in use in industry since its inception with applicability on components for more than five decades, there are still issues unresolved such as tempering or softening at inter-track overlapping regions, especially, when processing large area with economic viability, non-uniformity in treated layer affects etc. Due to the small size of the laser spot, when conducting large area laser surface hardening treatment, the laser beam can only be scanned over the object one by one, so there will inevitably be an overlapping zone between the two laser scanning tracks. To avoid the tempering or softening and mechanical degradation in the overlapping zone, there is an urgent need to invent a suitable method with apparatus to alter the surface at the desired region of the metallic materials or components resulting in improved microstructure, tribological (wear, friction etc.) and mechanical properties (hardness, strength etc.) and thereby life improvement without inducing any tempering effects in the overlapped regions of treated layers.

[0004] Another issue lies in controlling surface temperature within hardening range (without melting) with poor controllability as compared to that of surface melting. Thus, the present invention involves thin surface melting by dynamically produced quasi-stationery laser beam engulfing the periphery of part surface (either inner or outer) employing a tailored laser beam with requisite intensity profile and moderate to high-speed rotating spindle or axis holding the metallic part or component. Furthermore, laser surface melted part be subjected to post processing treatments such as grinding, polishing, tempering etc. to improve overall strength and other property of the treated component or part.

[0005] In existing technology, an innovative process for surface treatment of large cylindrical components based on a ring spot geometry is presented. The main concept of the proposed process consists of combining a fast rotation of the component with a linear displacement of the laser beam on the cylindrical surface, so that a ring-shaped “virtual” laser spot is achieved, promoting a very uniform heat distribution on the work piece. If the process is correctly set up, a very hard, deep and uniform melted layer is generated along the entire work piece surface without the formation of a tempered zone, even in the case of very large treated areas. The very high power density characteristic of the laser beam, together with the increased efficiency of modern laser sources, makes the proposed process even more attractive, especially from an energy saving point of view. Some of the related prior art patent or patent applications are discussed below by way of reference.

[0006] In US2002139453A1 discloses a method of Laser transformation hardening and coating for disc brake rotor braking surface with lesser rotary speeds to increase performance, reduce wear, corrosion, and reduce manufacturing costs.

[0007] In 102005005141B3 discloses a method for laser curing a plurality of surfaces of a plurality of necks of a crankshaft. This method is suitable for curing a plurality of very specific parts on the surface of the crankshaft but cures a plurality of general surfaces of a plurality of shafts and necks, this may not be appropriate and require improvised setups for generic surfaces.

[0008] “Laser Surface Hardening of a Crankshaft”, (SAE International), has a cured depth of more than 200 µm and a hardness of 500-600 HV at several different locations described. Discusses laser surface hardening of the crankshaft for this purpose. The document describes melting problems due to reduced heat sink effects at the boundaries and heat build-up around multiple holes. It has been stated that this problem can be addressed by reducing the preheating effect at the hole boundaries by selecting an appropriate starting position and changing several processing parameters within an acceptable range.

[0009] In US2015211083A1 discloses a further improved method and system for laser hardening of a surface of a cylindrical work piece was invented and showed improved and uniformity in hardness distribution across the treated layer.

[0010] In JP2016176542A developed a method for laser hardening of crank shaft including rotary axis speed and showed improvement in hardness and strength.

[0011] In another disclosure JP5771399B2 discloses a novel method of quenching crankshaft invented highlighting improvement in hardness with high rotational speeds.

[0012] In JP2023166471A, a novel method of heat treating the gear tooth profile by irradiating the work piece with a laser beam. The inventors proposed a laser hardening method in which the laser is irradiated so that a part of the first circumferential portion overlaps with the first circumferential portion. To prevent softening of the structure due to tempering when the starting and ending ends of laser irradiation overlap, the annular hardened surface of the work piece is heated so that it moves away from the center or approaches the center each time it goes around. The temperature of the irradiated region is heated to the A3 transformation point or higher by irradiating the laser in a spiral manner, and before the temperature of the first circulating section becomes below the martensitic transformation starting temperature, the second circulating section following the first circulating section is heated. However, even in the method according to patent, it is difficult to sufficiently solve the problem that the hardness of the work piece decreases due to tempering at the beginning or end of irradiation with the laser beam. There was a problem in that it was not always possible to ensure the strength of the steel according to the design specifications.

[0013] In another patented work DE102017004455A, similar process of laser heat treatment on gear tooth profile has been reported in which the component is subdivided into at least two sub regions overlapping one another in an overlapping region of the toothing with the laser radiation is acted upon and thereby hardened. The laser radiation is guided such that the overlap region comes to rest in a region, in which the component experiences a lower load during its operation relative to at least one part of the hardened partial regions which differs from the region. But the tempering effect in the overlapping region still exits which is avoided in the current patent due to rest part.

[0014] Few reports highlighting on high-speed laser processing setup to avoid tempering effects in overlapped tracks are available in literature. Guy Claus et al., reported laser surface hardening of shafts and holes using high speed rotation on shafts of 30 mm diameter of 42CrMo4V steel with elimination of deleterious overlapping induced softening effects. A fast rotating mirror with and a 6KW diode laser could effectively control the process. Luca Giorleo et al., utilized apparent spot (AS) technique to overcome the back tempering effects due to overlapping in laser surface hardening process and developed the analytical model for predicting the thermal cycles induced by AS technique. Fortunato et al. and Campana et al. proposed an optimal multi-pass laser process simulator and statistical method to optimize and control the process. The adopted method used to evaluate the uniformity in hardness distribution by varying laser processing conditions. In another report, Leonardo Orazi et al., proposed an interesting alternative to induction hardening process constituting high speed rotation with a ring spot geometry on AISI 1040 steel cylindrical work piece with two different diameters to overcome the tempering effects in the overlapped regions. The process simulation model developed help facilitated to predict the temperature field in the laser-work piece interaction zone and validated with the experimental results.

[0015] Recently, Sagar V. Telrandhe et al. optimized laser surface heat treatment process on rotating Ti6Al4V cylindrical specimens by adopting numerical modelling approach and correlated with experimental results. Optimization of input power with modification in simulated model approach (polynomial power variation) helped in achieving uniform distribution of heat penetration and case depth in treated layer with close agreement in predicting temperature profiles. In another study, Noureddine Barka et al., successfully adopted taguchi optimization analysis for optimizing laser hardening process on AISI 4340 cylindrical steel specimens to obtain uniform case depth with hardness distribution. Recently Rachid Fakir et al., analyzed the mechanical behavior in terms of static and dynamic fatigue strength of AISI 4340 laser treated steel specimens of cylindrical geometry employing high rotary axis speeds. Statistical analysis predicting the relationship of mechanical properties with laser processing parameters revealed that increase in fatigue endurance by 40% and average strain rate of about 0.30% could be achieved due to laser surface hardening. Notwithstanding these few reports on development of models to optimize laser surface treatment process on rotating parts with different methodologies and approaches, lack of knowledge in terms of understanding the physics and dynamics of the high speed laser processing still persists, difficulty to optimize with ease of process maneuverability without melting and also no proving out with properties evaluation and further studies needs to be undertaken to effectively implement in practical purposes.

[0016] These works envisage a method for treating large cylindrical components with higher rotational speeds with complete elimination of softening in the overlapped regions with uniform hardness distribution across the treated layer and improved mechanical and tribological properties of the treated layer with retention of the bulk properties using laser surface melting. Also, advantage in laser surface melting method to easily monitor melting temperature (ease of identifying melting surface) and control the process which entails uniform case profile with well-defined depth and hardness of treated subsurface.

[0017] Although few of the above reported works categorically proved the adoption of high-speed laser surface transformation hardening of steel parts or components, no study or report is available on thin-surface melting with control in surface temperature to entail uniform hardening case profile and hardness (with complete elimination of any tempering or softening effects). Apparently, there are no reports or works that entail uniform hardening profile with surface melting and prove out of improvement in strength and properties of cylindrical parts or components processed.
Objectives of the invention:
[0018] The primary objective of the invention is to provide an improved processing method to obtain a homogeneous thin surface melting on the whole or part of the perimeter of the cylindrical steel part or similar component by fast rotation under laser heating.

[0019] Another objective of the invention is to provide a method significance a continuous thin melted surface that entails removal of deleterious back-tempering effects with effective overlapping of laser tracks with the generation of a dynamically changing quasi-stationery laser beam utilizing a high-speed rotary axis or spindle.

[0020] The other objective of the invention is to provide an external heat sink setup such as liquid nitrogen which facilities efficient heat dissipation during the surface treatment of the shaft.

[0021] The other objective of the invention is to provide the external heat sink includes improvement of the microstructure, tribological (wear, friction etc.) and mechanical properties (hardness, strength etc.) and thereby life improvement of the shaft.

[0022] The other objective of the invention is to modifies surface of a metallic material using laser based surface processing apparatus using high speed spindle at desired localized regions leading to improvement in various characteristics and properties such as hardness, strength, wear resistance, and compressive residual stress level at treated surface.

[0023] The other objective of the invention is to modified surface of a metallic material that enhance fatigue life with retention of core hardness and bulk properties without inducing any softening effects in the overlapped regions.

[0024] The other objective of the invention is to provide a method that facilitates liquid nitrogen on the surface of steel to be laser treated, with a continuum with definite flow being maintained to act as heat sink and enhance heat transfer co-efficient along with a significant reduction in softening or back-tempering effects associated with overlapping.

[0025] Yet another objective of the invention is to provide a method that enhance life as compared to that of usual conventional hardening techniques by improving mechanical and tribological properties.

[0026] Further objective of the invention is to provide a method that adaptability to process difficult-to-harden low hardenability metallic materials, thin-sectioned and or complicate component designs such as shafts, rollers, construction rods, sleeves, connecting rods etc.
Summary of the invention:
[0027] The present disclosure proposes a process to improve strength and other properties of cylindrical metallic parts and components for engineering applications. The following presents a simplified summary in order to provide a basic understanding of some aspects of the claimed subject matter. This summary is not an extensive overview. It is not intended to identify key/critical elements or to delineate the scope of the claimed subject matter. Its sole purpose is to present some concepts in a simplified form as a prelude to the more detailed description that is presented later.

[0028] In order to overcome the above deficiencies of the prior art, the present disclosure is to solve the technical problem to provide a novel method of surface strengthening cylindrical metallic rods or parts or components which are melted (thin surface) to overcome softening effects in the overlapping of subsequent tracks to achieve uniform hardened case (harder than core) with improved strength and fatigue properties utilizing a diode laser integrated to a robotic workstation.

[0029] According to an aspect, the invention provides a system with methodology for treating surface of cylindrical metallic components for example, shafts, rollers, construction rods, sleeves, bearings, connecting rods spindles, pins, etc. The system comprises a high-speed rotary axis unit and a laser source. The laser source is configured to generate a laser beam that is configured to focus the generated laser beam on the surface of the cylindrical component to perform surface melting treatment.

[0030] In another embodiment, an optical unit includes at least one collimating lens, at least one homogenizing lens, a focusing lens, a protection lens or any combination thereof.

[0031] In the embodiment, the system includes the optical unit that is configured to receive the laser beam generated by laser source. The optical unit is configured to transform it into a user-defined profiled laser beam. Further, the optical unit is configured to focus the profiled laser beam on the surface of a cylindrical metallic part or sample, thereby performing surface melting covering part or the entire periphery depending on requirement. In an embodiment, the shape of the profiled laser beam is selected from the group consisting of a square, a rectangle, a triangle, a circle, a trapezoid, and any geometrical or non-symmetric geometrical shape. Similarly, the laser beam source is configured to produce a laser beam of specific wavelength and having a pre-defined intensity profile.

[0032] In an embodiment, the system includes plurality of optical fibers are configured to receive the laser beam from the laser source. Further, the plurality of optical fibers are configured to carry and transmit the laser beam towards the optical unit.

[0033] Further, the optical unit comprises at least one collimating lens, at least one homogenized lens, and focusing lens or a combination of them. Further, the profiled laser beam is directed towards the focusing lens and protection lens. The focusing lens, upon receiving the profiled laser beam, is configured to focus the profiled laser beam on cylindrical component. The protection lens is configured to prevent the entrance of any foreign particle or spatter during processing within the optical unit.

[0034] In an embodiment, the system includes a first conduit and a second conduit. The first conduit and second conduit are configured to supply shielding gas and liquid nitrogen respectively on the surface of the cylindrical component. The supply of shielding gas such as nitrogen, argon etc., to prevent spatter as well as protection form atmospheric contamination and the supply of any fluid such as liquid nitrogen etc., facilitating fast heat dissipation during the surface treatment of the cylindrical components.

[0035] In another embodiment, the system includes an additional conduit to supply gas such as nitrogen to diffuse into the melted region during laser surface melting treatment process.

[0036] In another embodiment, the disclosure a process for treating a surface of cylindrical components by melting or melting with diffusion of nitrogen. The process comprises the following steps include generating a laser beam by a laser source and focusing, the generated laser beam on the surface of cylindrical metallic part or component or sample, rotating the cylindrical component at high-speed utilizing d spindle or rotary axis, thereby performing laser surface melting treatment.

[0037] The process is configured to setup enables homogeneous temperature on part or whole perimeter of the cylindrical component by fast rotation and consequently, a continuous thin melting zone engulfing the periphery entails elimination of deleterious back-tempering effects with effective overlapping of laser tracks. The setup enables complete elimination of softening inevitable due to the overlap of subsequent tracks when processed with low rotating job adopted in conventional helical laser processing setup.

[0038] The process setup includes adoption of post-process machining or treatment for laser surface melted cylindrical part or component by machining, grinding, tempering at designated temperature (depending on material) or combination of them using same laser setup or by conventional furnace methods or otherwise.

[0039] Further, objects and advantages of the present invention will be apparent from a study of the following portion of the specification, the claims, and the attached drawings.
Detailed description of drawings:
[0040] The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate an embodiment of the invention, and, together with the description, explain the principles of the invention.

[0041] FIG. 1 illustrates a schematic view of an integrated laser processing system constituting a fiber-coupled diode laser, an optical module to tailor the laser beam into a fine spot, a temperature monitoring device for measuring temperature during processing and a moderate-to-high speed rotary axis to melt the cylindrical components, in accordance to an exemplary embodiment of the invention.

[0042] FIG. 2 illustrate a flowchart of a high-speed laser surface melting methodology on metallic cylindrical components or parts followed by post-process machining and treatment by process optimization with analysis of case-depth, and then testing and evaluation, in accordance to an exemplary embodiment of the invention.

[0043] FIG. 3 illustrates a cross sectional view of a macrograph of LSM cylindrical component with various zones, namely, melted zone, hardened zone, heat-affected or transition zone and unaffected substrate after completion of laser melting process, in accordance to an exemplary embodiment of the invention.

[0044] FIG. 4 illustrates a cross sectional view of contour graphs illustrating micro- hardness distribution across the longitudinal section of LSM cylindrical component, in accordance to an exemplary embodiment of the invention.

[0045] FIG. 5 illustrates a graphical representation of stress-strain tensile of a typical LSM cylindrical component compared with that of untreated substrate, in accordance to an exemplary embodiment of the invention.

[0046] FIG. 6 illustrates a schematic view of a long shaft subjected to LSM processing methodology, in accordance to an exemplary embodiment of the invention.
Detailed invention disclosure:
[0047] Various embodiments of the present invention will be described in reference to the accompanying drawings. Wherever possible, same or similar reference numerals are used in the drawings and the description to refer to the same or like parts or steps.

[0048] The present disclosure has been made with a view towards solving the problem with the prior art described above, and it is an object of the present invention to provide a novel method of surface strengthening cylindrical metallic rods or parts or components which are melted (thin surface) to overcome softening effects in the overlapping of subsequent tracks to achieve uniform hardened case (harder than core) with improved strength and fatigue properties utilizing a diode laser integrated to a robotic workstation.

[0049] According to an exemplary embodiment of the invention, FIG. 1 refers to a schematic view of an integrated laser processing system constituting a fiber-coupled diode laser, an optical module to tailor the laser beam into a fine spot, a temperature monitoring device for measuring temperature during processing and a moderate-to-high speed rotary axis to melt the cylindrical components. In one embodiment herein, the method for surface processing a cylindrical metallic material leading to improvement in mechanical strength and tribological properties. The processing methodology enhances the properties of the surface at which it is laser surface Melting (LSM) with complete elimination of deleterious inter-pass tempering effects in overlapped regions.

[0050] In another embodiment herein, the method provides apparatus constituting a laser, robotic workstation, optical head and a moderate-to-high speed rotary axis for LSM treatment for simple cylindrical metallic materials to a complex component for accomplishing the task. A further embodiment of the invention is the utilization of the method to impart LSM treatment for complex large shaft components.

[0051] The process a simple cylindrical rod or a shaft but for any cylindrical hardenable metallic material component of any thickness or design requiring laser surface melting treatment at single or multiple locations with different profiles.

[0052] The setup facilitates to obtain laser-melted track across the peripheral surface of the cylindrical rod due to variation in process dynamics. In high-speed rotational process (depending on the diameter and section-thickness), the laser spot rotates multiple times within the circumferential periphery resulting in virtual ring shaped laser beam termed as quasi-stationery beam spot that envelops the diameter of the cylindrical rod. The fast moving laser spot (moderate to high rotational speed) entails sufficient thermal diffusion within critical temperature range at the surface with promotion of self-quenching from cool bulk with an effect vital for melting of the thin surface to a depth of few microns determined by the power density and laser beam profile intensity.

[0053] As the thermal interaction in between rotations is so small, in millisecond level, enveloping the entire circumferential periphery of the rod, the question of reduction in temperature below thin surface melting (TM – 1350°C) does not arise. Thus, softening of subsequent tracks avoided completely and the obtained hardness profile will not have reduced hardness along the treated circumferential track when laser beam traverses. Figure 1 is an overall conceptual diagram showing laser processing apparatus with spindle or rotary axis or lathe for a metallic (1.0%C Steel) cylindrical work piece subjected to LSM treatment. A laser [oscillating] source emitting a continuous-wave laser beam for surface treatment to enter through an optical fiber (101a) and carried to an optical head to tailor the beam into a requisite size and shape as per the requirement. The source of the laser can be an Nd:YAG, Fiber, Diode or any laser delivered through the optical fiber or any beam delivery system.

[0054] The laser beam passing through the fiber is collimated and homogenized through the collimating optics 101b and homogenizing optics 101c, which can be made of one or more array of lenses or mirrors, and then focused through a focusing optic 101d and passed through a protection lens 101e to produce a laser beam of desired spot 101f, rectangular or square or circular to impinge onto the surface of the work piece, a cylindrical steel rod 101j of thickness 1-mm or higher. The work piece material can be a hardenable carbon steel or any other hardenable metallic material, clamped on a high speed spindle or rotary axis or mini lathe constituting a chuck 101k with tailstock end 101l secured to a working table or bench 101m. The laser beam spot is scanned at a predetermined scanning speed and rotary speed to result in a thin melted layer at the interaction region to a depth of few tens of micrometers. The laser beam is scanned using several combinations of process variables to attain a definite surface temperature leading to melting in the metallic material.

[0055] The laser beam spot is scanned over the surface of cylindrical work piece using a 6-axis Robot with the movement of beam occurring along the slow or fast axis of the square beam or a circular beam with optical head being fixed to the sixth arm of the Robot. The movement of the laser beam is programmed and controlled through the Robotic Controller. Necessary air-supply 101g and shielding-gas/liquid nitrogen supply 101i conduits are provided during laser melting processing for purposes such as effective heat dissipation, spatter protection and shielding from atmospheric contamination(as shown in FIG. 1).

[0056] Thus, the desired rapid cooling rates are achieved and result in melting of surface and subsurface with few tens of microns depth with and hardened phase transformation further below the surface in hundreds of micrometers without inducing any softening tempering effects in the overlapped tracks due to higher rotary speed ranging from 500 to 2000 rpm. Thus, the hardness achieved on surface through a depth of hundreds of microns can be superior to that of core hardness without affecting the microstructure of the bulk. The temperature monitoring during processing be conducted by using pyrometer or a high speed camera 101h.

[0057] The laser beam spot is scanned over the top surface of steel cylindrical work piece used in either continuous or modulated pulsed mode using a 6-axis Robot with 1 – 6 KW Power range, a pre-determined speed of 8 – 15 mm/s and rotary axis speed 500 - 4000 rpm chosen based on the dimensions of the cylindrical rod. Temperature measurement has been performed using a pyrometer or a high speed camera for continuous monitoring during processing.

[0058] The continuous shielding gas supply or liquid nitrogen flow dissipates heat quicker and thereby boosting higher heat transfer rates. Thus, the desired rapid cooling rates are achieved and result in melting or hardening of surface and subsurface with few hundreds of micrometres depth with melted and hardened phase transformation without inducing softening effects in the overlapped tracks. After, the laser surface melting process, selected specimens shall also be subjected to post-process machining and the coupons shall be subjected to metallographic analysis, tensile and hardness distribution analysis.

[0059] The LSM treated surface such as macrostructures, hardness distribution in the treated case and tensile stress condition (as shown in FIGs. 3-5). A 12.5 mm thick 1.0 %C Steel cylindrical rod was taken and subjected to LSM treatment with through-thickness (core) hardness ranging between 240 – 250 HV. A 4 X 4 mm square spot diode laser beam was scanned along the surface of the steel specimen rod at a predetermined speed of 8 – 15 mm/s to produce a melted case to a depth of few tens of micrometers. The LSM treatment was carried out with shielding gas supply/liquid nitrogen contact on the surface of the cylindrical steel work piece.

[0060] Additionally, laser power was varied in the range of 1 – 6 KW with shielding gas to protect atmospheric contamination during processing. Other optimized processing conditions used with the apparatus described in the method are not limited to type of shielding gas supply/liquid nitrogen flow condition, focusing position of the laser beam, speed of the rotary axis ranging from 500 - 4000 rpm. All these variables can be selected with respect to the desired depth of melted layer and hardness level to be produced on the treated surface layer without inducing any deleterious softening effects in the overlapped regions. Thus, we now describe overall improvement in various characteristics and properties of the LSM processed cylindrical steel work piece such as macrostructure, hardness, and yield strength referring to Figs 3-5. The results described are not limited to the 1.0%C Steel rod used in the investigation and can be any hardenable metallic material of thickness and any prior-treatment condition.

[0061] According to another exemplary embodiment of the invention, FIG. 3 refers to a cross sectional view of a macrograph of LSM cylindrical component with various zones, namely, melted zone, hardened zone, heat-affected or transition zone and unaffected substrate after completion of laser melting process. According to another exemplary embodiment of the invention, FIG. 4 refers to a cross sectional view of contour graphs illustrating micro- hardness distribution across the longitudinal section of LSM cylindrical component. The hardness distribution across their depth of LSM treated layers of optimized processing condition. Further, to decipher the evolution of melted case profile across different depths for a representative case (as depicted in Fig. 3) the surface temperature to nearly 1450-1480°C was evident from the peak temperature analysis using pyrometer throughout the length of the rod. Thus, the surface temperature could be maintained in within solidus temperature (Tm) throughout its periphery across and along its track width. As the temperature range maintained was well within 900–1480°C, elimination of softening effects is completely possible. Indeed, the experimental result depicting case depth profile along and across its radial and lateral directions.

[0062] The melted case depth of 50 µm, hardened case below melted case in the range of 0.5 to 1 mm or higher with heat affected zone of 0.9 to 1 mm thickness with a laser beam having a power, ranging from 1000 - 6000 W, a scanning speed of 8 - 15 mm/s and rotating axis speed of lathe ranging from 500 to 4000 rpm with continuous-wave or pulsed-wave mode of processing to a depth of few hundreds of micrometers with hardness being greater than that of core. A further embodiment of the invention is enhancement in surface hardness of 780-830 HV (as depicted in Fig. 4) when treated using high speed processing whose core hardness is 240-250 HV as depicted in the microhardness distribution contour plot of LSM sample.

[0063] According to another exemplary embodiment of the invention, FIG. 5 refers to a graphical representation of stress-strain tensile of a typical LSM cylindrical component compared with that of untreated substrate. In one embodiment herein, the yield and tensile strength evaluated for LSM treated 12.5 mm thick cylindrical 1.0%C Steel rod or sample processed employing high speed rotary axis described and various conditions. The results presented are not limited to the 12.5 mm thick 1.0%C steel and extendable to any hardenable metallic material of any thickness. The hardened case depth of about 0.4 mm was produced after the removal of melted layer by surface grinding (machining) due to LSM treatment but not limited. The room-temperature static tensile testing was carried out as per ASTM A370-15 standards with LSM treatment being carried out on both laser treated under optimum processing conditions and untreated samples. The laser melted and post-machined sample 501a exhibited 600 – 630 MPa of yield strength, 800 – 820 MPa of ultimate tensile strength and 18 – 20% of elongation when compared to that of untreated base material 501b whose yield strength was 360 – 390 MPa, ultimate tensile strength 630 – 650 MPa and elongation 20 – 25%. LSM treatment showed maximum improvement in yield and tensile strength (10 - 30%) possibly due to formation of high strength martensitic structure.

[0064] In one embodiment herein, the results presented indicates vast improvement in various microstructural characteristics and mechanical or tribological properties of any hardenable metallic rod materials (without inducing any softening effects in the overlapped regions and with retention of core strength) when subjected to LSM treatment under optimum laser processing conditions and setups. Furthermore, the invention envisages application of the process for any structural and engineering cylindrical components of varied dimension and prior-treatment conditions and thereby enhancing strength and life. Additionally, the present invention facilitates melting of virtually all hardenable metallic materials like steels, cast irons, super-alloys etc., applicable in various industrial sectors.

[0065] In another embodiment herein, the applicability of the developed LSM treatment method on an engineering component, i.e. Steel tapered Shaft. The proposed invention is not limited to a tapered Shaft and can be applied to any other component (of any design and section-thickness) made of any hardenable metallic material). Figure 6 depicts the LSM treatment methodology imparted on steel tapered shaft to enhance mechanical and tribological properties at required contact surfaces without inducing any softening effects in the overlapped regions, thereby, leading to improvement in life. A further embodiment is adopting appropriate setup ensuring liquid nitrogen contact on the laser scanning region with optimum processing parameters in which high-speed rotary axis speed is the crucial one. A further embodiment is the sequencing of laser scanning directions with appropriate rotary axis speed to eliminate softening effects in the overlapped regions of the treated layers. Enabling appropriate liquid nitrogen contact on the laser scanning region every time until processing of all steel tapered shaft facilitates higher heat transfer rates and retention of core hardness/strength. Thus, the developed method produces improved strength and properties with complete elimination of softening (back tempering) effects in the overlapped regions and bulk properties retention as compared to that of base metal.

[0066] Numerous advantages of the present disclosure may be apparent from the discussion above. In accordance with the present disclosure, invention provide the improved processing method to obtain a homogeneous thin surface melting on the whole or part of the perimeter of the cylindrical steel part or similar component by fast rotation under laser heating. The proposed method significance a continuous thin melted surface that entails removal of deleterious back-tempering effects with effective overlapping of laser tracks with the generation of a dynamically changing quasi-stationery laser beam utilizing a high-speed rotary axis or spindle.

[0067] The proposed method provide an external heat sink setup such as liquid nitrogen which facilities efficient heat dissipation during the surface treatment of the shaft. The proposed external heat sink includes improvement of the microstructure, tribological (wear, friction etc.) and mechanical properties (hardness, strength etc.) and thereby life improvement of the shaft. The proposed surface of a metallic material using laser based surface processing apparatus using high speed spindle at desired localized regions leading to improvement in various characteristics and properties such as hardness, strength, wear resistance, and compressive residual stress level at treated surface.

[0068] The proposed modified surface of a metallic material that enhance fatigue life with retention of core hardness and bulk properties without inducing any softening effects in the overlapped regions. The proposed method that facilitates liquid nitrogen on the surface of steel to be laser treated, with a continuum with definite flow being maintained to act as heat sink and enhance heat transfer co-efficient along with a significant reduction in softening or back-tempering effects associated with overlapping. The proposed method that adaptability to process difficult-to-harden low hardenability metallic materials, thin-sectioned and or complicate component designs such as shafts, rollers, construction rods, sleeves, connecting rods etc.

[0069] It will readily be apparent that numerous modifications and alterations can be made to the processes described in the foregoing examples without departing from the principles underlying the invention, and all such modifications and alterations are intended to be embraced by this application.
, Claims:CLAIMS:
I / We Claim:
1. The high-speed rotation process enables a quasi-stationary beam of a virtual ring-shaped laser spot that traverses completely throughout its circumferential periphery of the cylindrical rod or part.
2. The setup enables the complete elimination of softening inevitable due to the overlap of subsequent tracks when processed with low rotating job adopted in conventional helical laser surface hardening or melting setup.
3. In case of high-speed rotational process, the laser spot rotates multiple times within the circumferential periphery resulting in virtual ring-shaped laser beam termed as quasi-stationery beam spot that envelops the diameter of the cylindrical rod.
4. The fast moving laser spot (high rotational speed) entails sufficient self-quenching of the bulk and thereby promoting self-quenching effect vital for melting and austenitization of the surface to a depth of hundreds of microns determined by the power density and laser beam profile intensity.
5. As the thermal interaction in between rotations is so small, in millisecond level, enveloping the entire circumferential periphery of the rod, the question of reduction in temperature below austenitization level (Ac1 – 735°C) does not arise. Thus, softening or tempering of subsequent tracks is completely avoided and the obtained hardness profile will not have reduced hardness along the treated track when laser beam is traversed.
6. A laser-based surface processing apparatus for treating metallic materials components, comprising:
a laser source (101a);
an optical head to tailor the laser beam to a specific size and shape comprising of collimating optics (101b), homogenizing optics (101c), which is made of one or more array of lenses or mirrors and integrating, and focusing optic (101d) and a protection lens (101e) to produce a laser beam of desired spot; and
a fixturing setup to which the workpiece (101j) is held to the high-speed rotating spindle or rotary axis or mini lathe constituting a self-centering chuck with tailstock enabled the holding of cylindrical solid steel rod to rotate in a straight horizontal axis of rotation with almost negligible runout.
7. The laser-based surface processing apparatus as claimed in claim 6, wherein the laser source is selected from an Nd:YAG, Fiber, Diode or any laser delivered through the optical fiber or any beam delivery system and the laser beam emitted from the source (101a) is capable of being modulated in different modes either in continuous-wave mode or pulsed-wave mode.
8. The laser-based surface processing apparatus as claimed in claim 6, wherein the movement of laser beam occurring along the slow or fast axis of the rectangular or square beam with optical head being fixed to the sixth arm of the robot.
9. The laser-based surface processing apparatus as claimed in claim 6, wherein the IR pyrometer temperature measurement enabled the uniformity in surface temperature measurement along the length of the rod.
10. The laser-based surface processing apparatus as claimed in claim 1, wherein the high-speed rotating rotary axis or spindle or mini lathe holds the work piece, a cylindrical steel rod specimen of thickness 3-mm or higher and hardenable carbon steel or any other hardenable metallic material.
11. The laser-based surface processing apparatus as claimed in claim 6, wherein said laser source is selected from solid state laser, fiber laser, diode laser or any other laser in continuous or pulsed mode with power density in the range of 103 to 108 W/cm2 and the laser beam is delivered through the beam delivery system.
12. The laser-based method of surface treating or processing as claimed in claim 1, wherein laser surface melting with stationary square beam on solid cylindrical steel rod, is carried out for processing across its length by traversing the beam with robot manipulation with pre-determined linear speed and rotary axis speed.
13. The laser-based surface processing apparatus as claimed in claim 6, wherein setup can also constitute liquid nitrogen environment that enables fast dissipation of heat from the contacting surface and surrounding areas of the steel.
14. The laser-based method of surface treating or processing as claimed in claim 1, wherein the surface melts up to 50 µm, hardens 0.5 to 1 mm or higher with heat affected zone of 0.9 to 1 mm thickness with a laser beam having a power, ranging from 1000 - 6000 W, a scanning speed of 8 - 15 mm/s and rotating axis speed of lathe ranging from 500 to 4000 rpm with continuous-wave or pulsed-wave mode of processing to a depth of few hundreds of micrometres with hardness being greater than that of core.
15. The laser-based method of surface treating or processing as claimed in claim 1, wherein the process is designed to cater to various variables selected from laser power, scanning speed, rotary axis speed, beam spot size, metallic material chemistry, material thickness and component design, for enhancing hardness and strength in the treated layer of predetermined depth with complete elimination of softening effects associated with induced temperatures and thermal diffusion effects of overlapping spiral tracks during high-speed processing and retention of bulk hardness.
16. The laser-based method of surface treating or processing as claimed in claim 1, wherein it induces high hardness of 780-850 HV0.5 when treated using continuous mode of processing whose core hardness is 240-250 HV.
17. The laser-based method of surface treating or processing as claimed in claim 1, wherein imparting laser surface melting treatment leading to improvement in yield strength by 25-30%, ultimate tensile strength by 10-20% and hardness by 250-300% to that of base metal counterpart.
18. The laser-based method of surface treating or processing as claimed in claim 1, wherein Laser surface melting treatment imparted on the required cylindrical surface of metallic material in a component shape of varied section-thickness selected from bearing racer, roller, shaft, sleeve, pin, and similar workpiece of any design, shape and section-thickness enhance life as compared to that of the base material by improving mechanical and tribological properties.