Fast, effective case depth measurement of metal parts using physical surface preparation

Abstract

To provide a method for determining an effective case depth of a metal component.SOLUTION: The method includes conditioning a core surface by blasting or shot-peening an exposed surface of a metal component 10 with blast media. The exposed surface is a contiguous exposed surface of a case 14 and a core 16. The method includes measuring surface texture, compressive stresses, or another suitable characteristic of the conditioned core surface using a surface metrology sensor, and identifying a case-core boundary 18 using the measured characteristic. Identification of a case-core boundary 18 includes identifying a location at which a predetermined difference or gradient in the characteristic is present within the exposed surface. The method includes measuring the effective case depth DEC as a perpendicular distance between a reference surface 11R of the case and the case-core boundary 18.SELECTED DRAWING: Figure 1

Description

[Background technology]

[0001] Metallic components often undergo sliding contact along critical working surfaces, which over time can lead to component damage and failure. For this reason, it is beneficial to selectively harden critical working surfaces. For example, the interacting surfaces of rotating gear elements or rotating shafts can be selectively infused with application-suitable elements to produce a final product with desired mechanical properties. Such a process is referred to in the art as case hardening, and the hardened / infused layer(s) or case have increased surface hardness relative to the component's uninfused area, or core, along with increased wear and fatigue resistance. The softer core material is better suited to absorbing loads transmitted through the metallic component, which, in turn, is essential for the component's performance and long-term durability. Similar beneficial effects can be obtained by co-coating compatible hard and soft alloys as composite metallic materials.

[0002]

[0002] Although case hardening process parameters are closely controlled and monitored during part manufacturing, verification of the effective case depth of metal parts is still necessary. Hardness inspection techniques are relatively simple when applied to accessible surfaces of metal parts. In aerospace, transportation, and other industries where surface hardening techniques are utilized, the availability of case hardening data alone is insufficient. As a result, accurately and reproducibly measuring the effective case depth or comparable depth of other mechanical property-enhancing surfaces or layers typically requires the use of sacrificial test samples and extensive use of time-consuming processing steps such as ablating / cutting, mounting, and polishing the test samples, followed by hardness measurements and data processing.

[0003]

[0003] Indentation-based macroscopic hardness testing systems are typically used to measure the surface hardness of metal parts. Hardness generally refers to the resistance of a given metal part to plastic deformation under a calibrated load. Such hardness testing systems operate by pressing an indenter constructed from a baseline hard material, such as diamond or tungsten carbide, into a test surface at a single / discrete location under a specific load or set of loads, and then measuring the depth of penetration of the indenter into the test surface. When assessing the effective case depth of a case-hardened layer, a series of microscopically sized hardness indenters are positioned at specific distances from the surface of the part, and measurements are taken. The resulting hardness profile is used to determine the effective case depth, i.e., the vertical distance from the surface of the hardened case to the point where the hardness level equals a material-specific / application-specific value. As will be understood, "effective case depth" differs from "total case depth." The latter is the vertical distance from the surface of the case to the point at which differences in chemical or physical properties can no longer be distinguished in the microscopic structure of the metal part.

[0004]

[0004] In contrast to macroscopic hardness testing, hardness profiles can be generated using macroscopic hardness testing systems whose technical principles are nearly identical to those described above, except that instead of penetration depth, the size and shape of the resulting indentation are measured using dedicated software, which yields a hardness value. When the surface geometry of a metal part is relatively complex, verification of the effective case depth may be required at several discrete locations. As a result, hundreds or thousands of individual indentations may be required to verify the effective case depth in the required critical area.

[0005]

[0005] Due to the sensitivity of microscopic hardness testing, small tester or operator variations can affect the reported depth and hardness values. For example, calibration block, indentation spacing, microscope illumination, and traverse position / orientation. Similarly, visual techniques used to provide a rough estimate of hardness depth tend to rely on etching of the surface and, therefore, chemical exposure of the test sample. This introduces measurement variability due to factors such as the age of the etchant, etching time, and the uniformity of the microscopic structure of the surface being tested. Summary of the Invention

[0006]

[0006] Disclosed herein is a method and related system for quickly measuring the effective case depth or similar depth measurement of a metal part having a relatively hard layer disposed adjacent to a relatively softer layer. For consistency of description, and without limiting the present teachings specifically to case-hardened metals, the harder layer will be referred to herein as the case and the softer layer will be referred to as the core. That is, the present disclosure may also be applied to effective depth measurements of various layers of metal parts that have been substantially altered by the use of coatings and / or other layered material constructions, as well as metal parts having surfaces that are selectively hardened by heat treatment or other processes.

[0007]

[0007] The solution of the present disclosure can be used as an integral part of a quality inspection or quality assurance process, in place of or in conjunction with conventional indentation-based hardness testing methods of the type generally described above. The proposed solution allows users to bypass some of the most time-consuming steps of the conventional hardness testing process to quickly measure effective case depth over a sizable area. As a result, the extra time and variability typically associated with indentation-based hardness testing strategies are significantly reduced.

[0008] The reliability of this approach is based on an identifiable correlation between hardness-related properties, such as, but not limited to, the surface texture or internal stress of a metal part and the corresponding surface hardness. Accordingly, a method according to one disclosed embodiment proceeds by physically conditioning the exposed surface of the metal part, thereby producing such properties. The term "physically conditioning" refers to the physical conditioning of a larger area of ​​the exposed surface in an embodiment of the present disclosure. The use of chemical etchants and other chemical surface treatment processes suitable for controlled plastic deformation is eliminated.

[0009]

[0009] Suitable physical surface conditioning within the scope of the present disclosure can be achieved by blasting or shot peening the exposed surface of a metal component with a blasting media appropriate for the application, for example, spherical beads and / or asymmetric pieces of glass, metal, or ceramic that collectively have a well-defined media hardness level. Each individual piece or bead of blasting media used in a given lot of blasting media need not have the exact same hardness level; the media hardness level of a collective lot of bulk media material or shot falls within a defined hardness tolerance or maximum-minimum hardness range, with the media hardness level typically being set by the manufacturer of a given lot. Thus, the media hardness level is a fixed parameter that can be selected as part of the methods of the present disclosure. After exposing the exposed surface to physical surface conditioning, a surface metrology sensor is used to measure and quantify the resulting properties.

[0010]

[0010] As described herein, using appropriately selected and applied control parameters, uniform physical conditioning of exposed surfaces, including the exposed continuous surfaces of the core and case, results in little or no surface deformation of the exposed case surface. In contrast to the case surface, the exposed core surface changes in a measurable and quantifiable manner to produce a conditioned core surface. The transition or boundary between the case and core, such boundary hereinafter referred to as the case-core boundary, may therefore be detected using a surface metrology sensor as part of the method, and then used to measure the effective case depth.

[0011] The proposed solution may therefore employ the use of a physical media blasting action using well-defined parameters, such as blast pressure, average and peak blast media hardness, media shape and size distribution, standoff distance, coverage, etc., all of which also help ensure process repeatability. Similarly, the proposed solution better lends itself to evaluating larger and more complex samples and multiple test locations simultaneously relative to existing indentation-based macroscopic hardness testing systems.

[0012] According to one exemplary embodiment, a method for determining the effective case depth of a metal component includes physically conditioning an exposed surface of the metal component, thereby forming a conditioned surface. It involves exposing continuous areas of the case and core of the metal component to a physical surface conditioning process. The conditioned surface includes a conditioned surface of the case and a conditioned surface of the core. In this case, such surfaces are continuous. The method according to this embodiment includes measuring a characteristic of the conditioned surface using a surface metrology sensor and then locating a case-core boundary using the measured characteristic. Locating the case-core boundary includes identifying a location on the conditioned surface where a predetermined difference or gradient in the measured characteristic indicative of the case-core boundary exists. The method also includes measuring the effective case depth as the perpendicular distance between a reference surface of the case and the case-core boundary.

[0013]

[0013] Physically conditioning the exposed surface may include blasting or shot peening the exposed surface using a blasting media. For example, when the metal component is optionally constructed from a carburized steel, such as 9310 steel, having a case hardness of about 50 HRC, the hardness level of the blasting media may be in the range of about 48 HRC to 52 HRC, and physically conditioning the exposed surface of the metal component may include blasting or shot peening the exposed surface from a standoff distance of about 6 inches, at a pressure of about 40 psig, and at a coverage level of about 200 percent.

[0014] In some embodiments, the measured property includes measured surface texture or surface roughness, and in such embodiments, the surface metrology sensor includes a profilometer. The profilometer may be configured as a non-contact profilometer, such as a laser profilometer, a scanning interferometer, or a reflectometer. Other configurations of metrology sensors include an X-ray diffractometer, and the measured property is the level of internal compressive stress.

[0015]

[0015] The metal parts may represent a certain stock quantity or lot. In such applications, the method optionally includes comparing the measured effective case depth to a threshold effective case depth, for example, from a view of the metal parts or another calibrated reference, and automatically performing quality assurance and / or control actions on the stock quantity or lot when the measured effective case depth is less than the threshold effective case depth.

[0016]

[0016] Some embodiments of the method may include cutting the metal part to form the exposed surface, such that the exposed surface is a cross-sectional area of ​​the metal part. Additionally, the present disclosure facilitates a retrofit design modification that allows for the cross-sectional area of ​​a continuous area of ​​the case and core, such as the end face of a gear, to be visible, allowing for measurement of the effective case depth without such cutting.

[0017] A system for determining the effective case depth of a metal part is also disclosed. One embodiment of such a system includes the surface metrology sensor described above, as well as an electronic control unit (ECU) and a measurement tool. The surface metrology sensor is configured to measure a characteristic of a prepared core surface of the metal part. The prepared core surface is a portion of the exposed surface of the metal part after the exposed surface, having a continuous case-core surface, has been uniformly exposed to a physical surface conditioning process. The ECU is configured to communicate with the surface metrology sensor and use the measured characteristic to identify a case-core boundary of the exposed surface. The case-core boundary includes a location on the exposed surface where a predetermined difference or gradient in the measured characteristic exists. The measurement tool, also in communication with the ECU, is configured to measure the effective case depth as the perpendicular distance between a reference surface of the case and the case-core boundary.

[0018]

[0018] According to another embodiment, a method can be used to identify the effective case depth of a carburized steel component having a case and a core. The case hardness level is greater than about 50 HRC. The core hardness level is less than about 48 HRC. The method includes forming a prepared core surface by uniformly blasting or shot peening the exposed surface of the metal component with a blasting media having a medium hardness level within a range of about 50 HRC to 52 HRC. The exposed surface of the metal component is a continuous surface of the case and core. The method also includes measuring the surface texture of the prepared core surface using a profilometer and then identifying the case-core boundary using the surface texture. Identifying the case-core boundary includes identifying a location where a predetermined difference or gradient in surface texture exists across the exposed surface. The predetermined difference or gradient is indicative of the case-core boundary.

[0019]

[0019] Further, in this embodiment, the method includes measuring the effective case depth as the perpendicular distance between a reference surface of the case and the case-core boundary. Forming the prepared core surface includes blasting or shot peening the exposed surface of the carburized steel component with blast media or shot at about 40 psig and about 200% coverage.

[0020]

[0020] The foregoing summary is not intended to represent all embodiments or all aspects of the present disclosure. Rather, the foregoing summary provides only an illustration of some of the novel concepts and features described herein. The above-mentioned features and advantages, as well as other features and advantages, will become readily apparent from the following detailed description of exemplary embodiments and representative modes for carrying out the present disclosure when taken in conjunction with the accompanying drawings and appended claims. Moreover, the present disclosure expressly includes any and all combinations and subcombinations of the elements and features described above and below. [Brief explanation of the drawings]

[0021] [Figure 1]

[0021] FIG. 1 is a schematic diagram of a typical metal part having a relatively hard layer or case whose effective depth can be measured using the present metrology. [Figure 2]

[0022] FIG. 1 is a schematic flow diagram illustrating an exemplary method for determining an effective case depth of a metal part. [Figure 3]

[0023] FIG. 3 is a schematic diagram of a blasting media / shot peening process that can be used to physically condition one or more surfaces of a metal part as part of the method shown in FIG. 2. [Figure 4]

[0024] FIG. 1 is a schematic diagram of a system for measuring surface texture and effective case depth as part of the present method. [Figure 5]

[0025] Each is a representative plot of surface hardness (on the horizontal axis) versus surface roughness (on the vertical plane). DETAILED DESCRIPTION OF THE INVENTION

[0022]

[0026] The present disclosure may extend to modifications and alternatives using the exemplary embodiments shown by way of example in the drawings and described in detail below. The inventive aspects of the present disclosure are not limited to the disclosed embodiments. Rather, the present disclosure is intended to cover modifications, equivalents, combinations, and alternatives that fall within the scope of the present disclosure as defined by the appended claims.

[0023]

[0027] The present disclosure is susceptible to embodiments in many different forms. Representative embodiments of the present disclosure are shown in the drawings and will be described in detail herein. It should be understood that these embodiments are provided as an illustration of the principles of the present disclosure and do not limit the scope of the aspects of the present disclosure. To that extent, examples and limitations described, for example, in the Abstract, Background, Summary, and Detailed Description sections, but not explicitly set forth in the claims, should not be incorporated into the claims, singly or collectively, by implication, inference, or otherwise.

[0024]

[0028] For purposes of this detailed description, unless specifically excluded, the singular includes the plural and vice versa, for example, "a" means "at least one" or "one or more," the terms "and" and "or" may be both conjunctive and disjunctive, the terms "any" and "all" may mean "any and all," and terms such as "comprise," "include," "comprise," "have," etc. each mean "including without limitation." Furthermore, approximating terms such as "about," "almost," "substantially," "approximate," "approximately," "generally," etc. may be used herein to mean "in, near, or approximately near," "within 0-5% of," "within acceptable manufacturing tolerances of," or any logical combination thereof.

[0025]

[0029] Referring to the drawings, wherein like reference numerals refer to like features throughout the several views, a simplified embodiment of a metal component 10 is depicted generally in FIG. 1. For illustrative simplicity, the metal component 10 is depicted as an axial end view of a non-limiting, exemplary rotating shaft 10R having an outer diameter surface 11 and a central longitudinal axis 12. However, the present teachings are extendable to countless other embodiments of the metal component 10, such as gear elements, panels, beams, turbine blades, etc., and therefore the simplified embodiment of FIG. 1 is intended to be illustrative and non-limiting.

[0026]

[0030] A metal component 10 according to the present disclosure includes one or more layers of a relatively hard metallic material. Such layers are collectively referred to hereinafter as the case 14, and one or more additional layers of a relatively soft metallic material are collectively referred to hereinafter as the core 16. While both the case 14 and the core 16 are constructed from metal and are therefore "hard" in the standard sense, the case 14, unlike the core 16, may be subjected to a hardening process or constructed via a coating of a harder metal. In either embodiment, the hardness level of the case 14 exceeds the hardness level of the core 16, as will be understood by those skilled in the art. Due to this case-core hardness difference, a case-core interface 18 exists between the case 14 and the core 16. The vertical distance between the reference plane 11R of the case 14 and the case-core interface 18 is referred to as the effective case depth (D EC In the various case-hardened examples provided herein, i.e., without including coatings or other alternative scenarios, the hardness will decrease as a function of depth until it matches the hardness of the core.

[0027]

[0031] In the exemplary embodiment shown, outer diameter surface 11 serves as reference surface 11R. However, other embodiments may be envisioned having complex exterior and / or interior geometries, and thus the identity of reference surface 11R will vary based on the application or end use. Similarly, while for simplicity and clarity, case 14 and core 16 are represented in FIG. 1 as distinct, uniform areas separated from one another by case-core boundary 18, in actual embodiments, the hardness level of case 14 may gradually decrease until it ultimately matches the hardness level of core 16, as described above. In one such embodiment, case-core boundary 18 is located somewhere below surface 11. The hardness at that location is equal to or below a particular threshold hardness level, for example, from a blueprint of metal part 10 or another calibrated, part-specific / application-specific standard.

[0028]

[0032] The effective case depth (D) of a hardened metal part, such as the exemplary metal part 10 depicted in FIG. EC) can be quickly identified using the present method 100, one exemplary embodiment of which is described below with reference to FIG. 2. As a basic aspect of method 100, exposed surface 20 of metal component 10 is physically prepared, such as by using a well-controlled media blasting or shot peening process. The particular media used in this preliminary step of physical surface preparation should have a hardness level that substantially matches the hardness of case-core interface 18, i.e., within a small acceptable tolerance, as described below.

[0029]

[0033] By way of example and not limitation, using a core 16 having a threshold hardness level of approximately 50 HRC on the Rockwell hardness C scale (HRC) and a core hardness level of less than approximately 48 HRC, the particular blasting media or shot used to physically surface condition the metal component 10, as shown at 30 in FIG. 3, should have a hardness level of approximately 50 HRC, and thus match or equal the threshold hardness level of this example. However, in one exemplary embodiment, a blasting media 30 having a slightly higher hardness level, such as approximately 102% to 105% of the case-core interface 18, or approximately 51-52 HRC, can be used. Such a hardness level can reveal the case-core interface 18 less effectively than would be possible using a blasting media 30 having a hardness level that exactly matches the threshold hardness level. In other words, the hardness level of the blasting media 30 need not exactly match the threshold hardness level within the scope of the present disclosure. This is provided that the blasting media 30 can exceed the hardness level of the core 16 by a sufficient margin to plastically deform the exposed surface of the core 16 without also plastically deforming the exposed surface of the case 14.

[0030]

[0034] The exposed surface 20 of the metal component 10 may be an exterior surface, as shown in FIG. 1 , or in various embodiments may be a cross-section, and thus physically tailored to change the properties of the core 16, such as its surface texture or internal stress, in a detectable manner. As discussed above, by selecting a blasting media 30 whose hardness level sufficiently matches that of the case-core interface 18 or a threshold interface hardness level, the core 16 is physically deformed to a controlled extent without altering the surface of the case 14. The resulting differences in surface texture, internal stress, or other properties between the case 14 and the core 16 are therefore amenable to automated detection, quantification, and interpretation within the scope of this disclosure. Such an approach, in turn, allows the location of the case-core interface 18 to be precisely determined and subsequently used to determine the effective case depth (D EC ) can be used to measure the

[0031]

[0035] 2, one embodiment of method 100 begins at block B102 ("physical surface conditioning") with controlled surface conditioning of exposed surface 20 (see FIG. 3) of metal part 10. Block B102 may optionally perform a sample preparation step. For example, a sample preparation step may be performed on the interior surface of metal part 10 to a depth of effective case (D EC ), block B102 may entail cutting the metal part 10 using, for example, a bland saw or laser cutting device, so that the exposed surface 20 is a cross-sectional area of ​​the metal part 10. In other approaches, such as having the exposed end faces of FIG. 1, the case 14 and core 16 may already be fully exposed, which may reduce or eliminate the need to section or cut the metal part 10.

[0032]

[0036] Providing information for Block B102, a set of baseline data can be identified that correlates a given texture or other characteristic of the metal part 10 to its surface hardness after surface preparation. Such data can be used to determine its effective case depth (D EC) is specific to the particular material that is ultimately identified using method 100. A non-limiting example of such a hardness correlation is depicted in FIG.

[0033]

[0037] Referring briefly to FIG. 5, hardness on the Rockwell C scale (HRC) is plotted on the horizontal axis. A non-limiting example characteristic is plotted on the vertical axis, a surface texture characteristic, in this case in the form of average surface roughness (Ra) in microinches, but which in another embodiment can be embodied as internal compressive residual stress. As shown by the series of data points 55 and the line of best fit 55L, a correlation exists between surface roughness and hardness, with higher levels of surface roughness being closely correlated with softer materials. Thus, unlike the softer material of core 16 shown schematically in FIG. 1, the harder material of case 14 should have a higher resistance to plastic deformation during a carefully planned and executed media blasting process. Correlations of the type depicted in FIG. 5 may therefore be used as described herein to help set useful control parameters for executing block B102.

[0034]

[0038] Briefly referring to FIG. 3 , a simplified illustration of a media blasting process 150 that may be used as part of block B102 is provided. The exposed surface 20 of the metal component 10 is positioned relative to a blast nozzle 22. The blast nozzle 22 is supplied with air pressure (arrow AA) from a compressor (not shown) and also with a supply of blast media 30, e.g., spherical and / or asymmetric media, which is discharged under pressure from the end 24 of the blast nozzle 22, as shown by arrow A. When the discharged blast media 30 strikes a portion of the exposed surface 20 having a surface hardness less than that of the incident blast media 30, the blast media 30 plastically deforms those portions of the exposed surface 20 corresponding to the softer core 16, in this manner forming a conditioned core surface 20-CORE. Surface irregularities 25 are created within the conditioned core surface 20-CORE. Such surface irregularities 25 are collectively detectable over a large area of ​​exposed surface 20 as surface texture, surface roughness, or another detectable characteristic such as subsurface / internal stress.

[0035]

[0039] At the same time, the blasting media 30, by virtue of its construction, will not plastically deform the portion of the exposed surface 20 corresponding to the harder case 14, i.e., the conditioned case surface 20-CASE, as shown in FIG. 3. Thus, the exposed surface 20 is uniformly conditioned throughout, but the conditioned case surface 20-CASE is unaffected, at least to an extent deemed significant for purposes of performing the present method 100. In other words, a material of construction having a known surface hardness will plastically deform in a detectable and quantifiable manner in response to being maintained in contact with the harder blasting media 30. The parameters used in performing block B102 of FIG. 2 are therefore selected and controlled to ensure such a result.

[0036]

[0040] To ensure optimal repeatability and sufficient uniformity of plastic deformation of the core 16 of Figure 1 (particularly of the material of the core 16) across the exposed surface 20 of Figure 3, an application-specific set of surface conditioning control parameters is established for a given build of the metal part 10. Such parameters may include any or all of the composition, shape, and hardness of the blasting media 30, the nozzle pressure at which such blasting media 30 is discharged toward the exposed surface 20, the standoff distance between the nozzle end 24 and the exposed surface 20, the coverage rate, etc. Because a given lot or supply of blasting media 30 may vary, at least to some extent, in hardness, size, and shape, the parameters used to select the appropriate blasting media 30 may be averages and / or maximum / minimum ranges.

[0037]

[0041] By way of representative example and not limitation, metal component 10 may be constructed from carburized steel, such as 9310 carburized steel, and blasting media 30 may be embodied as #13 glass beads having a hardness level of 48-52 HRC in accordance with AM2431 / 6. In one such embodiment, a nozzle pressure of approximately 40 psig, at a standoff distance of approximately 6 inches, and a blast duration sufficient to ensure at least 200% coverage may be used to create conditioned core surface 20-CORE of FIG. 3. Note that although the entire exposed surface 20 is conditioned using the same media blasting conditions, case 14 is not subjected to such exposure with similarly discernible deformation effects, as only the softer portions of exposed surface 20 are plastically deformed and / or have compressive stresses imparted thereto.

[0038]

[0042] As will be understood by those skilled in the art, "coverage" or "coverage rate" refers to the percentage of a surface area that receives shot-induced indentations, dents, or depressions, with higher coverage rates ultimately resulting in uniform indentations or depressions in the resulting surface. 100% coverage is defined as uniform indentations within the entire surface when viewed with the naked eye, i.e., without device-assisted magnification. When viewed under magnification (e.g., up to 30x), individual unpeened islands are acceptable only if such islands are randomly distributed and the width of any single unpeened island is less than the diameter of a typical indentation. Coverage greater than 100% is defined as a multiple of the exposure time of 100% shot blasting. Thus, a typical 200% in this non-limiting example would require twice the media blasting / shot peening time required to achieve full coverage. An approximately perpendicular blasting angle, e.g., 80-100 degrees, may be used in this particular embodiment. Those skilled in the art will understand that the defined parameters used in block B102 may differ in other embodiments, and therefore the above example is merely one possible approach for implementing method 100.

[0039]

[0043] 2 and 4, the method 100 proceeds to block B104 once the exposed surface 20 has been physically conditioned. Block B104 of FIG. 2 (“Measure Surface Texture Characteristics”) includes measuring one or more surface texture characteristics or other properties of the conditioned core surface 20-CORE, for example, using a surface metrology sensor 32, as depicted generally in FIG. 4. The surface texture characteristics in some embodiments may include the surface roughness of the conditioned core surface 20-CORE. In one such embodiment, the surface metrology sensor 32 may be embodied as a profilometer 32P. As will be appreciated by those skilled in the art, a profilometer 32P is an instrument for measuring surface irregularities as a way of determining surface roughness. In some embodiments, a stylus or other contact-based gauge may be used to measure the surface roughness.

[0040]

[0044] In other embodiments, block B104 may be performed using a non-contact profilometer, such as a laser profilometer, a scanning interferometer, an optical surface profiler, a 3D optical microscope, and / or other suitable non-contact profilometer, which directs a beam LL of electromagnetic energy within an applicable wavelength or range toward the prepared core surface 20-CORE. In yet another embodiment, the surface metrology sensor 32 of FIG. 4 may also be embodied as a reflectometer 32R, such as a radar, lidar, particle beam, ultrasound, or other incident electromagnetic energy beam. In such an embodiment, the surface texture characteristic includes the level of reflectivity of the prepared core surface 20-CORE. Once the measurement of the surface texture characteristic or other characteristic is complete, the method 100 proceeds to block B106 of FIG. 2.

[0041]

[0045] As mentioned above, other types of surface metrology sensors 32 can be used as possible alternatives to the contact and non-contact profilometers 32P, in which case characteristics other than surface texture are used to detect the case-core boundary 18. For example, an X-ray diffractometer 32X can be used to measure internal compressive stresses using X-ray diffraction from the prepared core surface 20-CORE when such core surface 20-CORE is illuminated by an incident X-ray or neutron beam embodiment of light beam LL. As will be appreciated, X-ray diffraction can be used to measure atomic-level lattice spacings, and therefore, X-ray diffraction can be beneficial when applied to this task of quantifying measurable characteristics of the prepared core surface 20-CORE. Such an approach relies on internal compression of the subsurface microstructure rather than surface roughness, with a similar end effect.

[0042]

[0046] 2, the method 100 includes outputting and / or recording the measured surface texture characteristic or other measured characteristic as a data file ("output STC data"). Such a data file may be variously embodied as a digital output signal and / or a physical file, such as a printout or displayed result. Once the STC data has been generated and recorded, the method 100 proceeds to block B108.

[0043]

[0047] Block B108 involves analyzing the data file from Block B106, e.g., surface texture characterization data ("STC analysis") or other characteristic data, to thereby locate the case-core boundary 18 (see FIG. 1). Block B108 involves identifying where a threshold difference or gradient in the surface texture characterization or other characteristic used in a given embodiment exists across a contiguous area of ​​the now-conditioned case 14 and core 16. Such a threshold difference then indicates the presence of the case-core boundary 18. Because the physical surface conditioning process performed in Block B102 is configured so as not to alter or plastically deform the exposed case surface 20-CASE (see FIG. 3), the location of the case-core boundary 18 can be readily identified by detecting the transition from a plastically deformed surface area (or compressive stress) indicative of the softer core 16 to an unaffected or relatively unaffected surface indicative of the harder case 14. Once the coordinates of the case-core boundary 18 are known, for example using a caliper, gauge, or other optical measurement tool, the method 100 proceeds to block B110.

[0044]

[0048] Block B110 ("Effective Case Depth") calculates the effective case depth (D EC ) as the linear vertical distance between the case-core boundary 18 and the reference plane 11R of the case 14. In the embodiment of FIG. 1, for example, the effective case depth (D EC) can be measured as the perpendicular distance between the outer diameter surface 11 of the case 14 and the case-core interface 18, such as by using a gauge, caliper, or optical measuring tool similar to that used in block B108. Once measured, the effective case depth (D EC ) may be used in a myriad of automated or manual processes, including, but not limited to, quality assurance and / or end-of-line quality inspection processes.

[0045]

[0049] As an example, the effective case depth (D EC The metal component 10 whose effective case depth (D ) is determined according to method 100 may itself be representative of a particular stock or lot. By way of example, a manufacturer of case-hardened pinion gears may select a sample pinion gear from a lot and perform method 100 on the sample pinion gear to determine its effective case depth (D ). EC ) and then calculate the measured effective case depth (D EC ) is compared to a threshold effective case depth, which may be, for example, from a part and / or application specific blueprint, table, chart, or other calibrated standard or requirement; one example of such a threshold effective case depth is approximately 2 mm. The effective case depth (D EC Wherever the effective case depth (D) is less than the threshold case depth, quality assurance or other control actions may be taken on that stock or lot. In this particular exemplary embodiment, EC ) is less than 2 mm, appropriate action ranges from testing additional sample pinions to rejecting the stockpile or lot.

[0046]

[0050] 4, and as will be appreciated by those skilled in the art, the various blocks of method 100 may be performed automatically with and / or with the assistance of a host computing device or electronic control unit (ECU) 50 equipped with the requisite hardware and software associated with the described blocks. ECThe system 60 for determining the effective case depth (D ) may include the surface metrology sensor 32 in any or all of the embodiments described above, including, but not limited to, a profilometer 32P, an X-ray diffractometer 32X, and / or a reflectometer 32R. The system 60 further includes one or more ECUs 50 configured to determine the case-core boundary 18 using the surface texture characteristic(s) described above. The system 60 may also include one or more ECUs 50 configured to determine the effective case depth (D ) illustrated in FIG. EC ) as a linear straight-line distance between the reference surface 11R of the case 14 and the case-core boundary 18.

[0047]

[0051] The ECU 50 of FIG. 4 may encompass a single standalone or multiple networked physical computing devices, each of which has one or more processors (P) and associated non-transitory memory (M), such as read-only memory, programmable read-only memory, random access memory, optical memory, or magnetic memory. Non-transitory memory as contemplated herein may be used for software and / or firmware programs, as well as host input / output circuits and devices for interacting with peripherals, including contactless / optical embodiments of the surface metrology sensor and case depth measurement device. Such an ECU 50 may also include the necessary signal conditioning and buffering circuitry, as well as other hardware components that may be accessed to provide the described functionality of the present method 100. Electronic control signals (arrows CC) may be included in the ECU 50. 32 and CC 70 ) may be transmitted to and from the metrology sensor(s) 32 and the measurement tool 70, respectively, as part of the method 100.

[0048]

[0052] Benefits resulting from the presently disclosed method 100 and its possible hardware implementations will be readily appreciated by those skilled in the art. For example, the present teachings are intended to significantly simplify and expedite sample preparation and reduce the person-to-person or machine-to-machine test variability typically associated with indentation-based macroscopic hardness traverse testing systems. Furthermore, uniform surface preparation across the exposed surface, as described herein, does not equally affect the surface texture of different prepared materials, allowing more cases to be evaluated relative to existing methods. Correspondingly, the effective case depth (D EC ), reduced consumables are required to evaluate the case depth data, and less time is required to collect the case depth data. Conventional macroscopic and microscopic hardness testing processes rely on precise size / depth measurements of indentations at multiple discrete locations, and therefore rely on greater plastic deformation of softer materials relative to harder materials. By extension, as enabled by the present disclosure, uniform surface preparation of exposed surface 20 results in plastic deformation of a larger area of ​​core 16, allowing other appropriate properties, such as surface texture or subsurface stress, to be used over a larger area, with the resulting benefits described above. These and other benefits will be readily apparent to those skilled in the art upon review of the foregoing disclosure.

[0049] Article 1. 1. A method for determining an effective case depth of a metal component having a relatively hard layer, or case, and a relatively soft layer, or core, comprising: physically conditioning an exposed surface of the metal component to form a prepared surface, the method comprising exposing continuous areas of the case and the core to a physical surface conditioning process; measuring a characteristic of the prepared surface using a surface metrology sensor as a measured characteristic; locating a case-core boundary using the measured characteristic, the locating a case-core boundary including identifying a location on the prepared surface where a predetermined difference or gradient in the measured characteristic indicative of the case-core boundary exists; and determining the effective case depth as the measured depth, the method comprising measuring the perpendicular distance between a reference plane of the case and the case-core boundary. Article 2. 10. The method of claim 1, wherein physically conditioning the exposed surface of the metal component comprises blasting or shot peening the exposed surface with a blasting media. Article 3. 3. The method of claim 2, wherein the metal component is constructed from carburized steel, the blasting media has a hardness level within a range of 48 HRC to 52 HRC, and physically conditioning the exposed surface of the metal component comprises blasting or shot peening the exposed surface of the metal component from a standoff distance of about 6 inches, at a pressure of about 40 psig, and at a coverage level of about 200 percent. Article 4. 3. The method of claim 2, wherein the measured property comprises measured surface texture or surface roughness and the surface metrology sensor comprises a profilometer. Article 5. 5. The method of claim 4, wherein the profilometer comprises a non-contact profilometer. Article 6. 6. The method of clause 5, wherein the non-contact profilometer comprises a laser profilometer or a scanning interferometer. Article 7. 6. The method of clause 5, wherein the non-contact profilometer comprises a reflectometer. Article 8. 10. The method of claim 1, wherein the surface metrology sensor includes an X-ray diffractometer and the characteristic is a level of internal compressive stress in the metal component. Article 9. 2. The method of claim 1, wherein the metal parts represent a certain stock or lot, and the method further includes comparing the measured depth with a predetermined threshold depth, and automatically performing quality assurance or control actions on the stock or lot when the measured depth is less than the predetermined threshold depth. Article 10. 10. The method of claim 1, further comprising cutting the metal component such that the exposed surface is a cross-sectional area of ​​the metal component, thereby forming the exposed surface of the metal component. Article 11. 1. A system for determining an effective case depth of a metal part having a relatively hard layer, or case, including a reference surface, and a relatively soft layer, or core, the system comprising: a surface metrology sensor configured to measure a characteristic of a prepared core surface of the metal part as a measured characteristic, the prepared core surface being a portion of the exposed surface of the metal part after the exposed surface has been uniformly exposed to a physical surface conditioning process; an electronic control unit (ECU) in communication with the surface metrology sensor and configured to use the measured characteristic to identify a case-core boundary of the exposed surface, the case-core boundary including a location on the exposed surface where a predetermined difference or gradient in the measured characteristic exists; and a measurement tool in communication with the ECU, configured to measure the effective case depth as a perpendicular distance between the reference surface of the case and the case-core boundary. Article 12. 12. The system of clause 11, wherein the measured property includes a surface roughness or surface texture of the conditioned core surface, and the surface metrology sensor includes a profilometer. Article 13. 13. The system of claim 12, wherein the profilometer is a non-contact profilometer. Article 14. 14. The system of clause 13, wherein the non-contact profilometer comprises a laser profilometer or a scanning interferometer. Article 15. 14. The system of claim 13, wherein the non-contact profilometer is a reflectometer and the surface texture characteristic comprises a reflectivity level of the uniformly conditioned core surface. Article 16. 12. The system of claim 11, wherein the surface metrology sensor is an X-ray diffractometer and the measured property includes a measured level of internal compressive stress. Article 17. 1. A method for determining an effective case depth of a carburized steel component having a case and a core, wherein the case has a case hardness level greater than 50 HRC and the core has a core hardness level less than 48 HRC, the method comprising: forming a prepared core surface, the prepared core surface being a continuous surface between the case and the core, by uniformly blasting or shot peening an exposed surface of the carburized steel component with a blasting media having a medium hardness level within a range of approximately 50 HRC to 52 HRC; measuring a surface texture of the prepared core using a profilometer; and identifying a case-core boundary using the surface texture; locating a location across the exposed surface where a predetermined difference or gradient in the surface texture exists, the predetermined difference or gradient indicative of the case-core boundary; identifying a case-core boundary using the surface texture; and determining the effective case depth as a measured depth, the measured depth being the perpendicular distance between a reference plane of the case and the case-core boundary; and forming the adjusted core surface includes blasting or shot peening the exposed surface of the carburized steel component with blasting media or shot at approximately 40 psig and approximately 200 percent coverage. Article 18. 18. The method of clause 17, wherein the profilometer is a non-contact laser profilometer or a scanning interferometer. Article 19. 18. The method of claim 17, wherein the steel parts represent a stock or lot, the method further comprising comparing the measured depth to a predetermined threshold depth, and automatically performing a quality assurance or control action on the stock or lot when the measured depth is less than the predetermined threshold depth. Article 20. 18. The method of clause 17, further comprising cutting the carburized steel component such that the exposed surface is a cross-sectional area of ​​the carburized steel component, thereby forming the exposed surface of the carburized steel component.

[0050]

[0053] Aspects of the present disclosure have been described in detail with reference to exemplary embodiments. However, those skilled in the art will understand that certain modifications can be made to the structure and / or methods of the present disclosure without departing from the scope of the present disclosure. The present disclosure is also not limited to the exact constructions and compositions disclosed herein. Modifications apparent from the foregoing description are within the scope of the present disclosure, as defined by the appended claims. Furthermore, the present concepts expressly include combinations and subcombinations of the elements and features described above.

Claims

1. 1. A method for determining an effective case depth of a metal component having a relatively hard layer or case and a relatively soft layer or core, comprising: physically conditioning the exposed surface of the metal component to form a prepared surface, the physical conditioning comprising exposing a continuous area of ​​the case and the core to a physical surface conditioning process; measuring a property of the prepared surface as a measured property using a surface metrology sensor; locating a case-core boundary using the measured characteristic, including identifying a location on the prepared surface where a predetermined difference or gradient in the measured characteristic indicative of the case-core boundary exists; and determining the effective case depth as a measured depth, the determining the effective case depth as a measured depth including measuring a vertical distance between a reference plane of the case and the case-core boundary; physically conditioning the exposed surface of the metal component includes blasting or shot peening the exposed surface with a blasting media; method.

2. 10. The method of claim 1, wherein the metal component is constructed from carburized steel, the blasting media has a hardness level within a range of 48 HRC to 52 HRC, and physically conditioning the exposed surface of the metal component comprises blasting or shot peening the exposed surface of the metal component from a standoff distance of about 6 inches, at a pressure of about 40 psig, and at a coverage level of about 200 percent.

3. The method of claim 1 , wherein the measured property comprises a measured surface texture or surface roughness, and the surface metrology sensor comprises a profilometer.

4. The method of claim 3 , wherein the profilometer comprises a non-contact profilometer.

5. The method of claim 4 , wherein the non-contact profilometer comprises a laser profilometer or a scanning interferometer.

6. The method of claim 4 , wherein the non-contact profilometer comprises a reflectometer.

7. The method of claim 1 , wherein the surface metrology sensor comprises an X-ray diffractometer and the property is a level of internal compressive stress in the metal component.

8. The metal parts represent a stock or lot, and the method comprises: comparing the measured depth to a predetermined threshold depth; and The method of claim 1 , further comprising automatically performing a quality assurance or control action on the stockpile or the lot when the measured depth is less than the predetermined threshold depth.

9. The method of claim 1 , further comprising cutting the metal component such that the exposed surface is a cross-sectional area of ​​the metal component, thereby forming the exposed surface of the metal component.

Images