Local multi-beam laser peening of connecting rods

Abstract

A vehicle link and a method of laser peening a link. A first end of the link defines a pin opening and a second end defines a cylindrical bore. A clear coating is applied on the first target surface and the second target surface of the connecting rod. Opposite first and second target surfaces are impinged with a plurality of pulses of a pulsed laser beam in a localized region between the pin opening and the cylindrical bore. After laser peening, a localized region between the pin opening and the cylindrical bore exhibits compressive residual stress at a depth of at most 0.75 mm.

Description

Technical Field

[0001] The invention relates to the field of vehicle connecting rods, and in particular to a method for laser peening a vehicle connecting rod and a cold processing method for a vehicle connecting rod. Background Art

[0002] Connecting rods are used in internal combustion and steam engines to convert the linear motion of the engine's piston into the rotational motion of the crankshaft. To facilitate the rotational motion, the connecting rod is usually connected to the piston at one end using a pin, which causes the connecting rod to rotate relative to the piston. During the internal combustion process, the piston moves up and down in the cylindrical bore. The other end of the connecting rod is connected to the crankshaft, which also causes the crankshaft to rotate relative to the connecting rod. The repetitive motion of the piston and the rotational motion of the crankshaft exert repetitive forces on the connecting rod, including shear, compression, and tension.

[0003] Connecting rods are typically made from steel, but other materials such as aluminum and titanium may also be used in applications. Additionally, connecting rods are typically machined from solid billets. They can also be formed through powder metallurgy and forging. To relieve some of the stresses applied during machining, connecting rods can be treated using a variety of heat treatment and surface treatment processes, including, for example, shot peening and austempering heat treatments.

[0004] While current connecting rods and surface treatments achieve their intended purpose, there is still room for advancement in surface treatments to improve connecting rod performance. Summary of the invention

[0005] According to various aspects, the present disclosure relates to a method for laser peening a vehicle connecting rod. A first end of the connecting rod is defined with a pin opening, and a second end is defined with a cylindrical hole. The method includes applying a transparent coating on a first target surface and a second target surface of the connecting rod. The method also includes striking the first target surface with a plurality of first pulses of a first pulsed laser beam in a local area between the pin opening and the cylindrical hole, and striking the second target surface with a plurality of second pulses of a second pulsed laser beam in a local area, wherein the second target surface is opposite to the first target surface, and the plurality of first pulses and the plurality of second pulses are emitted simultaneously. The method also includes applying compressive residual stress to the first target surface and the second target surface at a depth of at most 0.75 mm.

[0006] In the above embodiments, the method includes applying water as a clear coating.

[0007] In any of the above embodiments, the method includes applying a covering layer to the first target surface and the second target surface before applying the water. The covering layer is opaque to the first pulsed laser beam and the second pulsed laser beam. In other embodiments, the covering layer includes a black paint, and the method includes applying the black paint as the covering layer.

[0008] In any of the above embodiments, the method includes a first central axis of a first pulsed laser beam striking perpendicular to a first target surface, and a second central axis of a second pulsed laser beam striking perpendicular to a second target surface. In other embodiments, the first central axis and the second central axis are coaxial.

[0009] Alternatively, in embodiments, the first central axis and the second central axis are offset along the length of the connecting rod. Alternatively, in any of the above embodiments, the method includes striking the first central axis of the first pulsed laser beam at an angle greater than 0 degrees to 30 degrees from a direction perpendicular to the first target surface; striking the second central axis of the second pulsed laser beam at an angle greater than 0 degrees to 30 degrees from a direction perpendicular to the second target surface. In other embodiments, the first central axis and the second central axis are coaxial. In other alternative embodiments, the first central axis is at an angle of up to 10 degrees to the second central axis.

[0010] In any of the above embodiments, the pulses of the first pulsed laser beam present a first spot area on the first target surface, and the multiple first spot areas of the multiple pulses of the pulsed laser beam overlap in the range of 30% to 40% of the total spot area of ​​the multiple spots.

[0011] In any of the above embodiments, the method further includes striking the first target surface with a third pulsed laser beam; and striking the second target surface with a fourth pulsed laser beam.

[0012] In any of the above embodiments, the method includes machining at least one of a side groove and a fastener thread in the connecting rod before striking the first target surface and the second target surface with the first pulsed laser beam and the second pulsed laser beam.

[0013] In any of the above embodiments, the method further includes modeling the connecting rod and performing a stress simulation to determine the local area to strike the connecting rod with a plurality of first pulses of the first pulsed laser beam and a plurality of second pulses of the second pulsed laser beam.

[0014] According to various additional embodiments, the present disclosure is directed to a method for cold working a vehicle connecting rod. A first end of the connecting rod defines a pin opening and a second end defines a cylindrical hole. The method includes emitting a plurality of first pulses of a first pulsed laser beam and a plurality of second pulses of a second pulsed laser beam from at least one laser source. The method also includes striking a first target surface in a localized area of ​​the connecting rod including a transparent coating with the plurality of first pulses. The localized area is located between the pin opening and the cylindrical hole. The method also includes striking a second target surface of the connecting rod including the transparent coating with the plurality of second pulses. The second target surface is opposite to the first target surface, and the pulses of the first pulsed laser beam and the second pulsed laser beam are emitted simultaneously. The method also includes evaporating a portion of the first target surface and generating a first plasma, and evaporating a portion of the second target surface and generating a second plasma; trapping the first plasma between the transparent coating and the first target surface, trapping the second plasma between the transparent coating and the second target surface; expanding the first plasma and generating a first shock wave, expanding the second plasma and generating a second shock wave; and forming a first compressive residual stress ranging from 500 megapascals (MPa) to 1000 MPa at the first target surface, and forming a second compressive residual stress ranging from 500 megapascals (MPa) to 1000 MPa at the second target surface. The depth of the first and second compressive residual stresses is at most 0.75 mm.

[0015] In the above embodiments, the clear coating layer includes a water layer.

[0016] In any of the above embodiments, evaporating a portion of the first target surface includes evaporating a portion of the covering layer on the first target surface, and evaporating a portion of the second target surface includes evaporating a portion of the covering layer on the second target surface. In other embodiments, the covering layer includes a black paint.

[0017] In any of the above embodiments, the first central axis of the first pulsed laser beam strikes the first target surface at an angle greater than 0 degrees to 30 degrees from the direction perpendicular to the first target surface, and the second central axis of the second pulsed laser beam strikes the second target surface at an angle greater than 0 degrees to 30 degrees from the direction perpendicular to the second target surface.

[0018] According to various other aspects, the present disclosure is directed to a vehicle connecting rod. A first end of the connecting rod defines a pin opening and a second end defines a cylindrical hole. The connecting rod includes a covering layer present on a surface of the connecting rod. In addition, the connecting rod includes a localized area between the pin opening and the cylindrical hole, wherein a portion of the covering layer is removed in the localized area, wherein the localized area exhibits a compressive residual stress in a range of 500 megapascals (MPa) to 1000 MPa at a depth of at most 0.75 mm. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] The drawings described herein are for illustration purposes only and are not intended to limit the scope of the present disclosure in any way.

[0020] Figure 1 An embodiment of a vehicle including a connecting rod according to an embodiment of the present disclosure is shown.

[0021] Figure 2 A process for laser peening a connecting rod according to an embodiment of the present disclosure is shown.

[0022] Figure 3A An embodiment of a connecting rod according to an embodiment of the present disclosure is shown.

[0023] Figure 3B An embodiment of a connecting rod including machined side grooves according to an embodiment of the present disclosure is shown.

[0024] Figure 4A A schematic diagram of a pulsed laser beam incident on a target surface of a connecting rod is shown according to an embodiment of the present disclosure.

[0025] Figure 4B A pulsed laser beam is shown incident on a target surface of a connecting rod according to an embodiment of the present disclosure.

[0026] Figure 5A A square laser beam pulse spot is shown according to an embodiment of the present disclosure.

[0027] Figure 5B A rectangular laser beam pulse spot is shown according to an embodiment of the present disclosure.

[0028] Figure 5C Overlapping laser beam pulse spots incident on a target surface are shown according to an embodiment of the present disclosure.

[0029] Figure 6 A system for laser peening a connecting rod according to an embodiment of the present disclosure is shown. DETAILED DESCRIPTION

[0030] The following description is merely exemplary in nature and is not intended to limit the present disclosure, application or use. In addition, there is no intention to be bound by any express or implied theory presented in the foregoing background technology, summary of the invention or the following detailed description. It should be understood that throughout the drawings, corresponding reference numerals indicate similar or corresponding parts and features.

[0031] In the claims and the specification, certain elements are designated as "first", "second", "third", "fourth", "fifth", "sixth" and "seventh". These are arbitrary designations and are intended to be consistent only in the parts where they appear (i.e., the specification or claims or the invention summary), and are not necessarily consistent between the specification, the claims and the invention summary. In this sense, they are not intended to limit the elements in any way, and the element marked as "second" in the claims may or may not refer to the element marked as "second" in the specification. Instead, these elements can be distinguished by their configuration, description, connection and function.

[0032] The term "vehicle" as used herein is not limited to automobiles. Although the present technology is described herein primarily in conjunction with connecting rods used in conjunction with internal combustion engines and vehicles. These concepts can be used in a variety of applications, such as applications related to components used in motorcycles, mopeds, locomotives, aircraft, ships and other vehicles, as well as other applications in conjunction with hydrogen fuel cells and applications in conjunction with electric motors. Applications include, for example, industrial machinery and motor components, agricultural equipment, compressors, defense equipment, HVAC (heating, ventilation and air conditioning) systems, residential and commercial generators and pumps.

[0033] Reference will now be made in detail to several examples of the present disclosure illustrated in the accompanying drawings. Whenever possible, the same or similar reference numerals are used in the drawings and description to represent the same or similar components or steps. The drawings are in simplified form and not drawn to exact scale.

[0034] The present disclosure relates to a method for surface treatment of a connecting rod using localized multi-beam laser peening. The laser peening produces a compressive residual stress of 500 megapascals (MPa) to 1100 MPa (including all values ​​and ranges therein) at a depth of up to 0.75 mm from the laser peened surface. As previously described and with reference to Figure 1 , the connecting rod 102 is used in an internal combustion engine 104 of the vehicle 100 to convert the linear reciprocating motion 108 of the engine piston 112 within the combustion chamber 114 into the rotational motion 110 of the crankshaft 116. To facilitate the rotational motion, each connecting rod 102 is generally connected to the piston 112 by a pin opening 120 defined at a first end 122 of the connecting rod 102, and a pin 121 is inserted into the pin opening 120, thereby allowing the connecting rod 102 to rotate relative to the piston 112. The other end 124 of the connecting rod 102 includes a cylindrical hole 126, into which the crankshaft 116 is inserted, which also allows the crankshaft 116 to rotate relative to the connecting rod 102. The repeated motion of the piston 112 and the rotational motion of the crankshaft 116 exert repeated forces on the connecting rod 102, including shear, compression, and tension.

[0035] Figure 2 shows the laser peening Figure 3A102 is a method 200 for forming a connecting rod 102. At block 202, the connecting rod 102 is formed. In an embodiment, the connecting rod 102 is forged from steel, such as SAE 1050 or 1075 steel, microalloyed steel including manganese, silicon, vanadium and sulfur alloying elements, such as 46MnSiVS 4, 5, 6 series, and the steel includes carbon in a range of 0.42 wt% to 0.48 wt% and sulfur in a range of 0.04 wt% to 0.06 wt%. In an alternative embodiment, the connecting rod 102 is formed from cast steel or iron, such as austempered ductile iron (ADI), titanium, aluminum or metal matrix composite (MMC), and can alternatively be machined from solid billet, forged, powdered metal, or formed using any of the above materials by an additive manufacturing process such as direct metal laser sintering or directed energy deposition. Metal matrix composites are understood to be composite materials including fibers or particles dispersed in a metal matrix such as copper, aluminum or steel. The fibers or particles may be ceramics (eg, alumina or silicon carbide), or other metals. The connecting rod 102 may also be surface treated, such as by carburizing and hardening, austempering, and converting ductile iron into austempered ductile iron.

[0036] At block 204, the connecting rod 102 is optionally cleaned using shot peening, wherein the shot is formed of, for example, steel, iron, ceramic, or sand. In addition, a solvent or detergent may be used to remove oil and grease before or after the shot peening. At block 206, the connecting rod 102 is optionally at least partially machined to form various features, including, for example, Figure 3B At least one of the side grooves 130 and the mechanical fastener threads 132 is shown. In an embodiment, block 204 may be omitted entirely and the flow may be moved from block 202 to block 206 so that processing may be more easily performed at block 206.

[0037] At block 208, again refer to Figure 3A , laser peening of the connecting rod 102 is performed in a local area 400 using at least two pulsed laser beams impinging on opposing surfaces 402, 404 of the connecting rod 102. Opposing surfaces are understood to be surfaces on the connecting rod 102 that are opposed to each other relative to the connecting rod 102 as a whole or features of the connecting rod 102. For example, 402 and 404 are opposing surfaces, and 402 and 403 are also opposing surfaces of the slot wall 405. The local area includes the target surfaces 402, 404 between the pin opening 120 and the cylindrical hole 126. In an embodiment, laser peening is performed only in a local area to prevent the need to mask features that have been machined into the connecting rod 102.

[0038] Laser peening, also known as laser shock peening, is understood to be a cold working process that applies compressive residual stresses in the surface of a workpiece (i.e., the connecting rod 102). Furthermore, a cold working process is understood to be any metalworking process in which a metal undergoes plastic deformation below its recrystallization temperature. It should be understood that the localized area 400 of the connecting rod 102 to which the laser peening is applied may have been previously identified through computer modeling and stress simulation as an area that exhibits relatively high stresses during use. In other embodiments, the laser peening may be varied in the localized area determined by computer modeling simulations of the highest stress or relatively high stress applied to the connecting rod during use compared to other stresses applied to the connecting rod during use. In an embodiment, for the connecting rod 102, this is limited to Figure 3A The rod area / I-beam area shown in FIG. In addition, during the laser peening process, other areas of the connecting rod 102 do not need to be masked, so the laser peening process is performed without masking.

[0039] Back again Figure 2 At frame 210, the connecting rod 102 may be inspected for defects or other manufacturing problems. At frame 212, finishing is performed to form any remaining threads, holes or other features. In addition, polishing may also be performed to smooth the surface of the connecting rod 102.

[0040] Reference now Figure 4A , Figure 4A Pulses from each of a pair of pulsed laser beams 422, 424 impinging on opposing target surfaces 402, 404 of the connecting rod 102 are shown. Figure 2 In the laser peening process at box 208, the target surface 402, 404, i.e., the surface to be laser peened, is covered with a transparent coating 406, 408, such as a layer of water. The water can be delivered by a water jet fixed to the laser source 420 (see Figure 4B ). The water layer 406, 408 may have a thickness 410 in the range of 1 mm to 100 mm, including all values ​​and ranges therein. In alternative embodiments, other transparent coatings may be used, such as a transparent polymer coating or glass coating, or a transparent tape. The transparent coating 406, 408 is transparent to the pulses of the pulsed laser beam 422, 424, so that the laser source 420 (see Figure 4B ) at least 50% (including all values ​​and ranges from 50% to 100%) of the incident electromagnetic energy emitted passes through the water or other transparent coating.

[0041] Furthermore, in other embodiments, the target surfaces 402, 404 are covered by a cover layer 412, 414 that is opaque to the pulses of the pulsed laser beam 422, 424. The cover layer 412, 414 is understood to absorb the laser source 420 (see Figure 4B ) of the target surface 402, 404. In an embodiment, the cover layer 412, 414 includes at least one of black paint, black tape, aluminum tape, or other absorptive coatings. In other embodiments, the target surface 402, 404 can be surface treated with a black oxide coating.

[0042] When the laser source 420 emits multiple pulses forming the pulsed laser beams 422, 424, electromagnetic energy of a given wavelength or wavelengths passes through the transparent coating 406, 408 and strikes the cover layer 412, 414, or if no cover layer is present, strikes the bare target surface 402, 404. Each pulse causes a portion of the cover layer 412, 414 or bare target surface 402, 404 to vaporize. The vapor is then trapped between the transparent coating 406, 408 and the target surface 402, 404. Successive pulses of the laser beams 422, 424 cause additional vaporization and ionization of the vapor, thereby generating an expanding plasma 426, 428. The plasma 426, 428 generates shock waves 430, 432 in the connecting rod 102 as the pulses expand, resulting in the formation of compressive residual stresses at the target surface 402, 404 and at a depth of up to 0.75 millimeters (mm) below the target surface 402, 404. Compressive residual stress can be determined by calculating compressive residual stress measured by X-ray diffraction (as determined by ASTM E915) or by Almenstrip testing (as determined by SAE J433).

[0043] In an implementation scheme, Figure 4A and Figure 4B The one or more laser sources 420 shown emit electromagnetic energy exhibiting one or more wavelengths in the range of 532 nanometers (nm) to 1054 nm, including all values ​​and ranges therein. In other embodiments, the laser source 420 comprises a neodymium-doped glass laser, such as a neodymium-doped yttrium aluminum garnet laser. The laser source 420 transmits multiple pulses of each laser beam 422, 424. In an embodiment, each pulsed laser beam 422, 424 has a power of 2 gigawatts per square centimeter (GW / cm 2 ) to 5GW / cm 2 The power density is in the range of 500 ns to 200 ns, including all values ​​and ranges therein. In addition, the duration of each pulse is in the range of 5 nanoseconds (ns) to 20 nanoseconds, including all values ​​and ranges therein. The pulse frequency is in the range of 0.6 kilohertz (kHz) to 1.5 kHz, including all values ​​and ranges therein. The pulses are generally emitted simultaneously from the laser source 420 of the relative pulsed laser beams 422, 424, so that at least a portion of a given pulse of each pulsed laser beam 422, 424 overlaps.

[0044] like Figure 5A and Figure 5B As shown, in an embodiment, the pulses of the pulsed laser beams 422, 424, 436, 438 incident on the target surfaces 402, 404 present a spot 502 when they hit the target surfaces 402, 404. The area of ​​the pulsed spot 502 of the pulsed laser beams 422, 424 incident on the target surfaces 402, 404 presents a height 510 in the range of 1 mm to 2.5 mm (including all values ​​and ranges therein), and a width 512 in the range of 1 mm to 2.5 mm (including all values ​​and ranges therein). Figure 5A and 5B As shown, the shape of the spot 502 and the spot area defined by the spot 502 is rectangular or square. It should be understood that other shapes, such as circular, elliptical, etc., can also be used. In addition, the pulse density of the pulsed laser beams 422 and 424 is 700 pulses per square centimeter (pulse / cm 2 ) to 1000 pulses / cm 2 is within the range of , including all values ​​and ranges therein. Figure 5C As shown, the spot 502 of the multiple pulses from each pulsed laser beam 422, 424 may exhibit an overlap 514 of 30% to 40% of the total spot area of ​​the multiple spots 502. The pulses forming the pulsed laser beams 422, 424 apply compressive residual stress in the target surface 402, 404 and at a depth of 0.20 millimeters to 0.75 millimeters (mm) from the target surface 402, 404, including all values ​​and ranges therein. In addition, for example, in 1050 or 1075 steel, the compressive residual stress may be in the range of 500 megapascals (MPa) to 1100 MPa, including all values ​​and ranges therein, wherein relatively high compressive residual stress exists near the steel surface.

[0045] Referring again to 4A and 4B, multi-beam laser peening utilizes at least a pair of opposing pulsed laser beams 422, 424, such as Figure 4A Without being bound by any particular theory, the use of opposing pulsed laser beams 422, 424, 435, 436, 437, 438 is understood to help prevent deformation of the connecting rod 102 during the laser peening process. Figure 4BAs shown, two pairs of opposing pulsed laser beams 435, 436, 437, 438 are incident on opposing target surfaces 402, 404 of the connecting rod 102. For example, a first pair of opposing pulsed laser beams may include a first pulsed laser beam 435 impinging on the first target surface 402, which is opposite to a second pulsed laser beam 437 impinging on the second target surface 404. A second pair of opposing pulsed laser beams may include a third pulsed laser beam 436 impinging on the first target surface 402, which is opposite to a second pulsed laser beam 438 impinging on the second target surface 404. As shown, the pulsed laser beams 435, 436, 437, 438 are emitted by a single laser source 420. However, it will be appreciated that when a light guide is utilized, pulses from a plurality of pulsed laser beams 435, 436, 437, 438 may be generated by a single laser source 420, and in other embodiments, all of the pulsed laser beams 422, 424, 436, 438 may be emitted by a single light source 420. The angles of incidence and the degree of offset between the axes of the pulsed laser beams 435, 436, 437, 438 are selected to provide relatively uniform temperature and to minimize tensile residual stresses beneath the connecting rod surface that could cause deformation of the connecting rod.

[0046] Return to reference Figure 4A , Figure 4A A first pair of opposing pulsed laser beams 422, 424 are shown impinging on a first target surface 402 and a second target surface 404. The central axes 440a, 440b of the pulsed laser beams 422, 424 are coaxial, wherein the central axes 440a, 440b overlap. The central axis of each pulsed laser beam can be understood as an optical axis, which is an imaginary line that defines the path of propagation of the emitted electromagnetic energy and is the average center point or geometric center within the physical perimeter of the pulsed laser beam (spot). For a cylindrical laser beam, the central axis is the center of the cylinder. For a square laser beam, the central axis is the center of the square. Or, as Figure 4B As shown, the central axes 444a, 444b of the pulsed laser beams 435, 437 can be along the length 452 of the connecting rod 102 (see Figure 3A ) are offset and parallel to each other. In other alternative embodiments, the central axes 442a, 442b may deviate from the coaxial angle 443 of up to 10 degrees, including all values ​​and ranges greater than 0 degrees to 10 degrees. Figure 4A The central axes 440a, 440b of the pulsed laser beams 422, 424 are shown as well as Figure 4BThe central axes 444a, 444b of the pulsed laser beams 435, 437 are shown to be perpendicular (i.e., 90 degrees) to the target surfaces 402, 404. In other or alternative embodiments, only one central axis, i.e., the first central axis, can be perpendicular, while the other central axis, i.e., the second central axis, can be arranged at an angle of up to 10 degrees relative to the first central axis. In other or alternative embodiments, Figure 4B The central axes 442a, 442b of the pulsed laser beams 436, 438 shown may be offset at an angle 445 in the range of 0.1 degrees to 30 degrees (including all values ​​and ranges therein) from the direction perpendicular to the target surfaces 402, 404. Accordingly, the pulsed laser beams 436, 438 may be arranged at an angle 446 in the range of 0.1 degrees to 70 degrees (including all values ​​and ranges therein) from the target surfaces 402, 404. As with the pulsed laser beams 422, 424, 435, 437 perpendicular to the target surfaces 402, 404, the pulsed laser beams 436, 438 at a certain angle to the direction perpendicular to the target surfaces 402, 404 have coaxial axes 442a, 442b that may be offset from the coaxial direction by 10 degrees. Although Figure 4B Two pairs of pulsed laser beams 435, 436, 437, 438 are shown in FIG. 4 , but there may be more than two pairs of pulsed laser beams, for example, up to 10 pairs. In other embodiments, pulses of the pulsed laser beam may be incident around the entire perimeter of the connecting rod 102 at a given position 450 along the length 452 of the target surface 402, 404, such as Figure 3A shown.

[0047] Figure 6 A system 600 for laser peening a connecting rod 102 is shown. The system 600 generally includes a fixture 602 for fixing the connecting rod 102. The system 600 also includes at least one laser source 420. In addition, for each laser source 420, the system includes a water supply 604 for applying a layer of water on the surface of the connecting rod. As shown, in an embodiment, the water supply 604 can be fixed to the laser source 420 or can be a separate component from the laser source 420. In addition, a power supply 606 is provided for each laser source 420 to transmit a pulsed laser beam. The system can also include a milling head 610 controlled by a computer numerical control for machining features on the connecting rod.

[0048] The methods and connecting rods formed herein have many advantages. These advantages include reducing debris and contaminants generated during the shot peening process. These advantages also include reducing shot peening particles that may become embedded in the connecting rod and entrained in the engine lubricating oil if the connecting rod is shot peened before laser peening. These advantages also include applying compressive residual stresses at specific locations and greater depths in the connecting rod compared to processes such as shot peening, which is beneficial for improving fatigue performance. Such compressive residual stresses are relatively higher than those that can be achieved using shot peening. These advantages also include the ability to laser peen localized areas, reducing the need to mask features that do not need to be treated. These advantages also include the ability to machine formed threads before laser peening without the need for masking during the laser peening process.

[0049] The description of the present disclosure is merely exemplary in nature, and variations that do not depart from the gist of the present disclosure are intended to fall within the scope of the present disclosure. These variations should not be regarded as departing from the spirit and scope of the present disclosure.

Claims

1. A method for laser peening a vehicle connecting rod, comprising: applying a clear coating on a first target surface and a second target surface of a connecting rod, wherein a first end of the connecting rod defines a pin opening and a second end defines a cylindrical bore; impinging the first target surface with a plurality of first pulses of a first pulsed laser beam in a localized area between the pin opening and the cylindrical bore; impinging the second target surface with a plurality of second pulses of a second pulsed laser beam in the local area, wherein the second target surface is opposite to the first target surface, the plurality of first pulses and the plurality of second pulses being emitted simultaneously; and Compressive residual stress is formed on the first target surface and the second target surface at a depth of at most 0.75 mm.

2. The method according to claim 1, further comprising: Water was applied as the clear coat.

3. The method according to claim 2, further comprising: Prior to applying the water, a cover layer is applied to the first target surface and the second target surface, wherein the cover layer is opaque to the first pulsed laser beam and the second pulsed laser beam.

4. The method according to claim 3, wherein: Applying the covering layer includes applying a black paint.

5. The method of claim 3, further comprising striking a first central axis of the first pulsed laser beam perpendicular to the first target surface; and striking a second central axis of the second pulsed laser beam perpendicular to the second target surface.

6. The method according to claim 5, wherein: The first central axis is coaxial with the second central axis.

7. The method according to claim 6, wherein: The first central axis and the second central axis are offset along a length of the connecting rod.

8. The method of claim 3, further comprising striking a first central axis of the first pulsed laser beam at an angle greater than 0 degrees to 30 degrees from a direction perpendicular to the first target surface; and striking a second central axis of the second pulsed laser beam at an angle greater than 0 degrees to 30 degrees from a direction perpendicular to the second target surface.

9. A method for cold working a vehicle connecting rod, comprising: emitting from at least one laser source a plurality of first pulses of a first pulsed laser beam and a plurality of second pulses of a second pulsed laser beam; impacting a first target surface in a localized region of a connecting rod including a transparent coating with the plurality of first pulses, wherein a first end of the connecting rod defines a pin opening and a second end defines a cylindrical hole, the localized region being located between the pin opening and the cylindrical hole; impacting a second target surface of the connecting rod including the transparent coating with the plurality of second pulses, wherein the second target surface is opposite to the first target surface, and pulses of the first pulsed laser beam and the second pulsed laser beam are emitted simultaneously; vaporizing a portion of the first target surface and generating a first plasma, vaporizing a portion of the second target surface and generating a second plasma; trapping the first plasma between the clear coating and the first target surface, and trapping the second plasma between the clear coating and the second target surface; causing the first plasma to expand and generate a first shock wave, causing the second plasma to expand and generate a second shock wave; and A first compressive residual stress ranging from 500 MPa to 1000 MPa is formed at the first target surface, and a second compressive residual stress ranging from 500 MPa to 1000 MPa is formed at the second target surface, wherein the depths of the first compressive residual stress and the second compressive residual stress are at most 0.75 mm.

10. A vehicle connecting rod, comprising: a connecting rod having a first end defining a pin opening and a second end defining a cylindrical bore; a covering layer present on a surface of the connecting rod; as well as A localized area is located between the pin opening and the cylindrical hole, wherein a portion of the cover layer is removed in the localized area, wherein the localized area exhibits a compressive residual stress in the range of 500 megapascals (MPa) to 1000 MPa at a depth of at most 0.75 mm.

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