Method of additive manufacturing and tappet repaired by a process

Abstract

An additive manufacturing method includes: providing a substrate material at a position close to the surface of a part; and forming the substrate material into an additive layer on top of the surface by exposing the substrate material to a first laser beam having a first power level. After forming the additive layer on the part, the method includes cooling at least a portion of the additive layer from a first temperature reached when the forming step is completed to a second temperature. After cooling, the method includes exposing the additive layer to a second laser beam having a second power level, wherein the second power level is lower than the first power level.

Description

Technical Field

[0001] The present invention generally but not restrictively relates to methods for machining metal parts, and more particularly to performing a smoothing operation on laser cladding. Background Art

[0002] Materials can be added to existing parts using additive manufacturing processes. One such additive manufacturing process includes laser cladding. Laser cladding involves providing a base material to a location proximate to the surface of a part to which the base material will bond. The base material is generally powder metal. In combination with providing the base material to the surface of the part, a laser beam, also focused on the part, converts the base material into an additive layer that bonds to the surface of the part.

[0003] The above-described laser cladding process works well for parts that do not require machining of the laser cladding. However, laser cladding is difficult to machine, if not impossible, and thus cannot be used in many applications. Laser cladding produces materials with high hardness and irregular surfaces, which makes machining a challenge. In some cases, the machining blades used to machine the surface will immediately break and must be replaced. Due to these challenges, laser cladding cannot be used to add material to certain parts or to repair a part after a portion of it has worn due to use. An example of a part that is not suitable for laser cladding repair is a tappet, such as a tappet used in a fuel system. Since tappets have surface tolerance requirements that need to be machined, laser cladding is not a suitable additive manufacturing process for repairing tappets. In the absence of a suitable process for repairing tappets, they are typically scrapped at the end of their life rather than being repaired.

[0004] Accordingly, there is a need to improve the machinability of laser cladding surfaces, including parts repaired using laser cladding. There is also a particular need to improve the ability to repair tappets using additive manufacturing processes to restore material eroded from worn surfaces.

[0005] An attempt to address the problem of machining laser cladded components is described in U.S. Patent No. 10,067,494, issued to Chen et al. on September 4, 2018. The '494 patent describes a hybrid computer numerical control machining center for cutting, laser cladding, and surface heat treating a workpiece in a single machine such that the workpiece does not have to be moved between different machines. While the '494 patent reduces the need to move the workpiece between different types of machines, the '494 patent fails to improve the machinability of laser cladding surfaces and fails to improve the repairability of certain components such as tappets (e.g., tappets in a diesel fuel system).

[0006] Another attempt to address the problem of machining laser clad parts is described in U.S. Patent Publication No. 2017 / 0239751, issued to Luo et al. on August 24, 2017. The '751 publication describes a method for remanufacturing metal parts that combines the processes of laser cladding and large-area overlapping laser shot peening to repair grooves. However, the '751 publication failed to improve the machinability of the laser clad surface and failed to improve the repairability of certain parts such as lifters.

[0007] The present invention is directed to overcoming one or more of the above-identified disadvantages and / or other disadvantages in the art. Summary of the invention

[0008] In one aspect, the present invention relates to a method of additive manufacturing. The method may include providing a substrate material at a location proximate to a surface of a part, and forming the substrate material into an additive layer on top of the surface by exposing the substrate material to a first laser beam having a first power level. After forming the additive layer, the method may include cooling the additive layer from a first temperature reached when the forming step is completed to a second temperature. As the additive layer is lowered to the second temperature, the method may include exposing the additive layer to a second laser beam having a second power level. The second power level may be lower than the first power level.

[0009] In another aspect, the present invention relates to a method for repairing a lifter by a process that includes providing a base material proximate a surface of the lifter and forming the base material as an additive layer on top of the surface by exposing the base material to a first laser beam having a first power level. After forming the additive layer, the method may include cooling the additive layer from a first temperature reached when the forming step is completed to a second temperature. As the additive layer is lowered to the second temperature, the method may include exposing the additive layer to a second laser beam having a second power level. The second power level may be lower than the first power level.

[0010] In another aspect, the present invention relates to a method for smoothing a laser clad surface. The method may include providing, receiving or manufacturing a part having a laser clad portion, and exposing at least a portion of the laser clad portion to a laser beam configured to smooth a surface layer of the laser clad portion. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] In the accompanying drawings, which are not necessarily drawn to scale, the same number may describe similar components in different views. The same number with different letter suffixes may represent different instances of similar components. The accompanying drawings generally illustrate various examples discussed in this document by way of example and not limitation.

[0012] Figure 1is a side perspective view of a tappet positioned close to a laser cladding head according to at least one example.

[0013] Figure 2 is of a tappet including an additive layer formed by laser cladding according to at least one example Figure 1 perspective view.

[0014] Figure 3 is a cross-section of a portion of a tappet taken along line 3-3 according to at least one example Figure 2 of the tappet.

[0015] Figure 4 is according to at least one example Figure 2 perspective view of the tappet after a laser smoothing operation.

[0016] Figure 5 is a cross-section of a portion of a tappet taken along line 5-5 according to at least one example Figure 4 of the tappet.

[0017] Figure 6 is according to at least one example Figure 4 perspective view of the tappet after a machining operation.

[0018] Figure 7 is a cross-section of a portion of a tappet taken along line 7-7 according to at least one example Figure 6 of the tappet.

[0019] Figure 8 is a flow chart showing a process for repairing a tappet according to at least one example. Detailed Description

[0020] Various examples of forming and repairing parts using laser cladding and performing a smoothing operation on the laser cladding will now be described. The examples described in the present invention improve the machinability of the laser cladding surface by performing a smoothing operation on the laser cladding surface. The addition of the smoothing operation allows components such as tappets to be repaired and reused, which are typically discarded at the end of their service life.

[0021] Reference will now be made in detail to embodiments of the invention, examples of which are illustrated in the accompanying drawings. Relative terms such as "substantially", "about" and "approximately" are used to denote possible variations of the stated values, e.g. ±10%. As defined herein, the use of the term "or" or "and" includes "or", "and" or "and / or".

[0022] Figure 1An example of an additive manufacturing process such as laser cladding performed on a part by a laser cladding machine 10 is shown. In this example, the part is shown as a tappet 100, where the tappet is held in a fixture 20. The tappet 100 can be of the type used in some fuel systems. The tappet 100 can include a cam engagement surface 102 for engaging a rotating cam. As is known in the art, when assembled into a fuel system, the cam engagement surface 102 of the tappet 100 is positioned to contact the rotating cam. When the cam rotates, the cam engagement surface 102 receives motion from the cam to linearly move the tappet 100. The movement of the tappet 100 aids in the timing of the fuel system. To achieve proper timing and movement, the cam engagement surface 102 of the tappet 100 needs to be machined to a surface with specific tolerances. However, over time, when the cam engagement surface 102 wears, the tappet 100 may no longer function as expected and must be repaired or replaced.

[0023] As Figure 1 The laser cladding process shown is used to add one material to the surface of another material in a controlled manner (e.g., an additive manufacturing). Laser cladding can be used for various reasons. Since laser cladding advantageously produces a strong bond with the part and provides a very hard surface, it can be used to repair worn or damaged parts. Laser cladding can be used to replace material that wears away on metal parts during use. However, laser cladding has limitations that restrict its use for repairing tappets (e.g., 100).

[0024] During laser cladding, a base material 12 such as powder is fed through a material delivery channel 14 to a laser beam 16, and the laser beam 16 scans across the surface on which the base material 12 is to be deposited. The laser beam 16 can be generated by a laser 18. In Figure 1 the example, this surface is the cam engagement surface 102 of the tappet 100. The laser cladding process leaves an additive layer 110 (e.g., a deposited coating) of the base material 104 on the cam engagement surface 102. Although the laser cladding process and smoothing operation for repairing the tappet 100 are described herein, the examples described herein can be applied to other parts. The methods, including portions of the methods, can be used to create, modify, or repair other parts.

[0025] Figure 2 An exemplary tappet 100 is shown that includes an additive layer 110 formed by a Figure 1 laser cladding process. The additive layer 110 replaces material that has worn during use, such that the tappet 100 can be repaired and reused. The tappet 100 is provided only as an example of a part for which depositing the additive layer 110 by laser cladding presents post-cladding machining challenges, and for which the challenges are addressed by the methods described herein.

[0026] During laser cladding, the laser 18 can be pulse - modulated at a first power level such that the laser 18 is turned on for a portion of time and then turned off for a portion of time in a very rapid and repetitive manner, thereby generating a first laser beam 16a. In one example, the first laser beam 16a can include a laser 18 pulse - modulated at a first power level of approximately 3000 watts, with the laser 18 alternating between being on for 1 millisecond and off for 8 milliseconds. The advantage of pulse - modulating the laser 18 rather than keeping the laser 18 continuously on is that it provides sufficient power for the laser cladding operation to occur, but interrupts the heat transferred to the part, thereby preventing the part from overheating. This is helpful in the case of the tappet 100, which is a small part that heats up quickly and would be at risk of melting if the laser were continuously on.

[0027] Unfortunately, while pulse - modulating the laser 18 prevents the part from melting, the pulse - modulation process also creates a rough outer surface 112a that is very difficult to machine( Figure 3 ). As described herein, the tappet 100 needs to be machined to a smooth surface with specific tolerances in order to engage with other parts such as cams in a fuel system. Therefore, laser cladding is not a suitable method for repairing certain parts, including but not limited to the tappet 100.

[0028] The rough outer surface 112a produced by the laser cladding process can be described as an interrupted surface. As Figure 2 and 3 shown, these interruptions 114 along the outer surface 112a repeat along the path of the laser 18 as it travels to form the additive layer 110. Each time the laser 18 goes from on to off or from off to on, an interruption 114 is formed. Attempting to machine this rough outer surface 112a can lead to damage to the cutting tool (e.g., the cutting blade of a lathe). This damage is caused by the shock induced in the cutting tool when the blade hits the interruption 114 and because the microstructure of the laser - clad surface (e.g., the additive layer 110) being cut has a high hardness value. The hardness value of the additive layer 110 can be higher than the hardness of the tappet 100 or other parts to be repaired.

[0029] Figure 3 Shows a cross - section of a portion of the tappet taken along line 3 - 3 Figure 2 This cross - section shows the tappet 100, which includes a worn surface 120 and an additive layer 110 formed on the worn surface 120 by laser cladding. As shown in the cross - section, laser cladding gives the additive layer a rough outer surface 112a, which includes interruptions 114 created when the laser 18 is pulse - modulated on and off.

[0030] Figure 4 Shows Figure 2An example of a laser cladded tappet 100, but after it has undergone a laser smoothing operation. After performing the laser cladding operation, but before performing the laser smoothing operation, cool the laser cladded tappet 100. Cooling can be deliberately provided, such as by exposing the tappet 100 to a cooling source, or by allowing the tappet 100 to simply cool due to the ambient room temperature being lower than the temperature of the tappet 100. The tappet 100 can be cooled until the additive layer 110 (e.g., at least a portion of the additive layer) reaches a second temperature that is lower than the first temperature reached at the completion of the laser cladding step. In some examples, the first temperature can be in the range between 100 - 120 degrees Celsius, and the second temperature can be in the range between 5 - 25 degrees Celsius. In a potentially preferred example, the second temperature can be approximately 20 degrees Celsius. Depending on the application, a variety of first and second temperature combinations are possible. In some examples, the second temperature can be in the range of 70 - 75% lower than the first temperature. In a potentially preferred example and for a particular part that can include the tappet 100, the first temperature can be in the range between 90 - 100 degrees Celsius and the second temperature can be in the range between 5 - 15 degrees Celsius. In a potentially preferred example, the second temperature can be approximately 10 degrees Celsius.

[0031] In the case where the tappet 100 is at the second temperature range, the laser smoothing operation can be performed by exposing the additive layer 110 to a second laser beam 16b having a second power level that is lower than the first power level (e.g., Figure 1 ). In some examples, the first and second laser beams (16a, 16b) can be provided by the same laser 18 ( Figure 1 ). For example, the tappet 100 can be laser cladded by Figure 1 's laser cladding machine, and the tappet 100 can be removed from the laser cladding machine 10. Then, the tappet 100 can be cooled to the second temperature. In some examples, while the tappet 100 is cooling, the laser cladding machine 10 can be used to laser clad another tappet 100 (or another part). After the tappet 100 has reached the second temperature, the tappet 100 can be reinserted into the laser cladding machine 10 to perform the smoothing operation. However, during the smoothing operation, and in contrast to the cladding operation, the tappet 100 is at the second power level (e.g., Figure 1A second laser beam 16b) is exposed to the laser 18 without providing any substrate material 12. In some examples, the second laser beam 16b is a continuous (e.g., substantially continuous, mostly continuous, more continuous) laser beam having a lower power than the first laser beam 16a. In some examples, the first power level can be in a range between 750-2000 watts. In some examples, such as for the exemplary push rod 100, the second power level can be in a range between 900-1100 watts. In some examples, the second power level can be in a range of 70-75% lower than the first power level, or in a potentially preferred example, about 70% lower. In some examples, the second laser beam 16b may not be a continuous laser beam, but may be a lower power level and pulsed at a lower pulse rate than the first laser beam 16a during the laser cladding operation.

[0032] In some examples, the first and second laser beams 16a, 16b may be provided by the same laser 18 on the same machine 10. In some examples, the first and second laser beams 16a, 16b may be provided by different lasers, or even by different machines.

[0033] The second laser beam 16b may be configured to process Figure 2 The additive layer 110 produced by the laser cladding operation is formed into a smoother, more machinable layer, such as Figure 4 112b is shown in the example of the smooth outer surface 112b.

[0034] Figure 5 A cross-sectional view taken along line 5-5 is shown. Figure 4 1 is a cross section of a portion of a lifter 100, the cross section showing the lifter 100 including a wear surface 120 and an additive layer 110 formed by laser cladding, but the rough outer surface 112b of the additive layer 110 is smoothed by a smoothing operation. The smoothing operation may result in a change in the microstructure of the outer layer 116 of the additive layer 110, while leaving the remaining layers below unchanged or less changed.

[0035] One benefit of smooth operation is that it results in the tappet 100 having a Figure 2 The remaining layer 118 provides a smoother outer layer 116 than the original laser clad surface. This smoother outer layer 116 can be machined away more easily than the rough original laser clad surface. The remaining layer 118 provides a beneficial durable cam engagement surface 102 for the tappet 100, which can be machined to a specified tolerance for engagement with a cam in the fuel system.

[0036] In some examples, the smoothing operation substantially does not affect the hardness of the outer layer 116 of the additive layer 110. For example, before exposing the additive layer 110 to the second laser beam 16b, the additive layer 110 may include an outer layer 116 having a first hardness in the range of 64 - 66 HRC and a first surface roughness including interruptions created by laser cladding. After exposing the additive layer 110 to the second laser beam 16b, the outer layer 116 may include a second hardness in the range of 64 - 66 HRC and a second surface roughness having fewer protruding interruptions. In other words, the second surface roughness may be less abrasive than the first surface roughness.

[0037] The exemplary smoothing operations described herein for the smoothing tappet 100 can also be used to smooth other laser - clad surfaces or parts. Examples of other parts that can employ the methods described herein include, but are not limited to, camshafts, crankshafts, water pump shafts, fuel injector housings, and pistons. In some examples, the smoothing operation can be performed completely separately from the laser - cladding operation, on a different machine, at a different facility, and at a different time.

[0038] Figure 6 An example of the tappet 100 is shown, which has a machined outer surface 130 after having undergone the laser - cladding operations described with respect to Figure 2 and Figure 3 and the laser - smoothing operations described with respect to Figure 4 and Figure 5 and a machining operation to remove at least a portion of the additive layer. Figure 7 A cross - section of a portion of the tappet 100 taken along line 7 - 7 is shown. The cross - section shows the worn surface 120 and the additive layer 110 formed by laser cladding, but with the smoothed outer surface 112b of the additive layer 110 removed by machining. Figure 6

[0039] Suitable machining processes for machining away a portion of the additive layer 110 of the tappet 100 can include using a lathe or other machines, such as a grinder or a milling machine. Any other suitable machining operations can be performed depending on the size, geometry, and tolerance requirements of the part.

[0040] Industrial Applicability

[0041] Generally, the foregoing disclosure can be used in various industrial applications, such as repairing tappets. The method of smoothing laser - clad surfaces herein can provide improved machinability of the laser - clad surfaces, such that tappets and other components can be repaired and reused at the end of their life rather than being scrapped.

[0042] Figure 8 ​illustrates a method 800 for laser smoothing a laser cladded part. One such part on which method 800 can be performed includes a tappet 100 as previously shown and described with respect to Figure 1-7 For example, over time and with use, parts of a fuel system such as tappet 100 may become worn or damaged and may need to be replaced or repaired. When tappet 100 is worn, typically the cam engagement surface 102 of tappet 100 is worn away. The worn-away portion of tappet 100 can be added back through a process of laser cladding and laser smoothing rather than scrapping tappet 100.

[0043] Method 800 allows parts such as tappet 100 that were previously discarded to be recycled, repaired, and reused, thereby reducing costs.

[0044] Through an additive manufacturing process, such as laser cladding, method 800 can include, in step 802, providing a base material 12 proximate to a worn surface 120 of the tappet 100 to be laser cladded. The base material 12 can include a powder suitable for bonding and forming a metal layer on a metal tappet.

[0045] Step 804 can include forming the base material 12 into an additive layer 110 by exposing the base material 12 to a first laser beam 16a. In some examples, the first laser beam 16a is a pulsed laser beam having a first power level, which, along with beneficially forming the additive layer 110, creates machining challenges due to the hard interruptions 114 left on the rough outer surface 112a of the additive layer 110. These interruptions 114 are difficult to machine.

[0046] Step 806 can include cooling the additive layer 110 to reduce the additive layer 110 from a first temperature reached upon completion of forming step 804 to a second temperature lower than the first temperature. In some examples, cooling of the additive layer 110 can be achieved by allowing the tappet 100 to cool while exposed to ambient temperature (e.g., removed from the laser cladding machine 10 and left to cool outside the machine 10). The additive layer 110 can be cooled to ambient temperature, or to a value between the first temperature and ambient temperature, or to a temperature below ambient temperature. In some examples, rather than simply allowing the tappet 100 to cool at room temperature, techniques can be employed to cool the additive layer 110, such as by using convection, conduction, or radiation. In some examples, a cooling chamber, a fan, or quenching the tappet 100 in a fluid can be used to more rapidly reduce the temperature. The tappet 100 can be cooled without being removed from the laser cladding fixture 20, or it can be removed during cooling such that the fixture 20 can be used to, for example, laser clad other tappets or other parts while the additive layer is cooling.

[0047] Step 808 can include performing a smoothing operation by exposing the additive layer 110 to a second laser beam 16b. In some examples, the second laser beam 16b is a substantially continuous laser beam having a second power level that is lower than the first power level.

[0048] Step 810 can include removing a portion of the additive layer 110. The portion of the additive layer 110 to be removed can include the smoothed outer surface 112b, leaving a remaining layer 118 that serves as a new cam engagement surface 102 of the tappet 100. Step 810 can include using a machining process that can produce a specific roughness and tolerance to remove a portion of the additive layer 110.

[0049] It will be apparent to those skilled in the art that various modifications and variations can be made to the disclosed laser smoothing operations. Considering the specification and the practice of the disclosed processes, other embodiments will be apparent to those skilled in the art. The specification and examples are considered to be exemplary only, and the true scope is indicated by the claims and their equivalents.

Claims

1. A method (800) of additive manufacturing, the method (800) comprising: Providing a base material (12) at a position close to the surface (102) of a part; Wherein the part is a fuel system tappet (100); Forming step: By exposing the base material (12) to a first pulsed laser beam (16a) having a first power level, forming the base material (12) into an additive layer (110) on top of the surface (102); Cooling the additive layer (110) from a first temperature reached when the forming step is completed to a second temperature; And Exposing the additive layer (110) to a second laser beam (16b) having a second power level, wherein the second power level is lower than the first power level; wherein the method further comprises removing a portion of the additive layer (110) in a machining process to form a surface that engages with a cam.

2. The method (800) according to claim 1, wherein exposing the additive layer (110) to the second laser beam (16b) comprises exposing the additive layer (110) to a substantially continuous second laser beam (16b) having a power in the range between 900 - 1100 watts.

3. The method (800) according to claim 1, wherein the second power level is in the range of 70 - 75% lower than the first power level.

4. The method (800) according to claim 1, wherein the second temperature is in the range of 60 - 65% lower than the first temperature.

5. The method (800) according to claim 1, wherein the step of exposing the additive layer (110) to the second laser beam (16b) does not include adding the base material (12).

6. The method (800) according to claim 1, wherein before exposing the additive layer (110) to the second laser beam (16b), the additive layer (110) includes an outer layer (116) having a first hardness in the range between 64 - 66 HRC and having a first surface roughness including interruptions generated by laser cladding, and wherein after exposing the additive layer to the second laser beam (16b), the outer layer (116) has a second hardness in the range between 64 - 66 HRC and has a second surface roughness with less prominent interruptions, and wherein the second surface roughness is less abrasive than the first surface roughness.

7. A fuel system tappet having an additive layer formed by the method (800) according to claim 1.

8. A tappet (100) repaired by a process, the process comprising: Providing a base material (12) at a position close to the surface (102) of the tappet (100); And Forming step: By exposing the base material (12) to a first pulsed laser beam (16a) having a first power level, forming the base material (12) into an additive layer (110) on top of the surface (102); Cool the additive layer (110) from a first temperature reached upon completion of the forming step to a second temperature; Expose the additive layer (110) to a second laser beam (16b) having a second power level, wherein the second power level is lower than the first power level; And Remove a portion of the additive layer (110) in a machining process to form a surface that engages with the cam.

Images