Patent Description:
The invention relates to a method for inspecting an assembly including at least two components joined by a rivet, and a system for inspecting the assembly including at least two components joined by the rivet.

Inspection of a joint between metal components is oftentimes required to determine the quality of the joint. For example, automotive vehicle components joined by self-piercing rivets (SPR) are typically inspected for quality control. The method used to inspect the joint typically includes cutting through the joint, polishing the cut joint so that a cross-section of the joint is visible, and then taking images of the joint at a high resolution for analysis. Improved inspection techniques which require less time and expense are desired. Thomas Schromm et al, DOI: <NUM>/<NUM>, is entitled and describes "an attempt to detect anomalies in CT-data of car body parts using machine learning algorithms". <NPL>, is entitled and describes "high resolution computed tomography".

This section provides a general summary of the inventive concepts associated with this disclosure and is not intended to be interpreted as a complete and comprehensive listing of all of its aspects, objectives, features, and advantages.

It is an aspect of the subject invention to provide a method of inspecting an assembly as set out in claim <NUM>.

Another aspect of the invention provides a system for inspecting an assembly as set out in claim <NUM>.

The system and method of the present invention are able to provide for improved quality control at a relatively low cost. An advantage over other inspection methods is that the assembly to be inspected does not need to be destroyed or modified prior to inspection. Thus, the system and method of the present invention create less scrap, which saves energy and costs, and provides for more accurate inspection of each assembly produced.

The drawings described herein are for illustrative purposes only of selected embodiments and are not intended to limit the scope of the present disclosure. The inventive concepts associated with the present disclosure will be more readily understood by reference to the following description in combination with the accompanying drawings wherein:.

However, the example embodiments are only provided so that this disclosure will be thorough, and will fully convey the scope to those who are skilled in the art.

The invention provides a system and method for inspecting an assembly <NUM> including at least two components 12a, 12b joined by at least one self-piercing rivet <NUM> by performing a computerized tomography (CT) scan of the joint. An example of a riveting process that can be used to form the assembly <NUM> to be inspected is shown in <FIG>. In this case, the assembly <NUM> includes two of the components 12a, 12b which are sheets of metal, and the self-piercing rivets <NUM> joining the two components 12a, 12b. A top one of the components 12a is formed of steel, a bottom one of the components 12b is formed of aluminum, and the rivet <NUM> is formed of steel. However, the components 12a, 12b and rivets <NUM> could be formed of different materials, and the assembly <NUM> could alternatively include three or more components 12a, 12b formed of various different materials and/or dimensions. Various different types of assemblies <NUM> can be inspected using the method described herein; the designs, dimensions, and materials can vary. According to an example embodiment, the first component 12a is a cast front shock tower formed of an aluminum alloy, for example Aural <NUM> at T7 temper or Aural <NUM> in either F Temper or T81 (after paint bake); the second component 12b is a front rail formed of steel, for example DP <NUM>; and the rivet <NUM> is also formed of steel.

As shown in <FIG> and <FIG>, the rivet <NUM> includes a head <NUM> and a tubular-shaped base <NUM>, also referred to as legs, depending from the head <NUM>, but the design and dimensions of the rivet <NUM> can change. <FIG> illustrates the rivet <NUM> before the rivet <NUM> is inserted into the components 12a, 12b, and <FIG> illustrates the rivet <NUM> after the rivet <NUM> joins the components 12a, 12b. Also, the components 12a, 12b can be joined by a single rivet <NUM>, but typically the components 12a, 12b are joined by multiple rivets <NUM>.

The example process of <FIG> includes disposing the components 12a, 12b to be joined on a die <NUM>. The die <NUM> includes a slot for receiving the rivet <NUM> and at least a portion of the components 12a, 12b. The system used to pierce the components 12a, 12b further includes a blank holder <NUM> disposed above the components 12a, 12b to be joined. The blank holder <NUM> includes a slot receiving a punch <NUM> and the rivet <NUM>. During operation, the blank holder <NUM> rests on the components 12a, 12b to be joined, and the punch <NUM> presses the rivet <NUM> into the components 12a, 12b. The rivet <NUM> pierces the first component 12a and pierces through a portion of the second component 12b, but does not pierce entirely through the second component 12b. The base (legs) <NUM> of the rivet <NUM> should not be visible by inspecting the exterior of the components 12a, 12b forming the assembly <NUM> with the naked eye.

<FIG> illustrates a cross-section of the rivet <NUM> of the assembly <NUM> which can be inspected by the method disclosed herein. The inspection method can be used to determine various dimensions and features of the assembly <NUM>. The method can be used to identify the location of the components 12a, 12b, the base <NUM> and the head <NUM> of the rivet <NUM>, a diameter D of the head of the rivet <NUM>, a slug <NUM> formed by the bottom component 12b. According to one embodiment, the method can be used to measure an interlock SH and minimum thickness Tmin, which are identified in the example of <FIG>. The interlock SH is a radial distance between a top end of the base <NUM> and the outermost portion of the base <NUM> of the rivet <NUM>. The minimum thickness Tmin is the distance between the bottom end of the lowermost surface of the rivet <NUM> and the exterior surface of the lowest component 12b joined by the rivet <NUM>. The method can also be used to measure a height of a button, referred to as a button height H, which is present in the finished assembly <NUM>, as shown in <FIG>. The button height H is the distance between a bottom flat surface of the bottom component 12b (which is located radially outward of the rivet <NUM>) and a lowermost surface the bottom component 12b (which is located directly beneath the river <NUM>). Destruction of the assembly <NUM>, for example to obtain a cross-section of the assembly <NUM>, which occurs in other methods and previously occurred to obtain the cross-section of <FIG>, is not required according to the method of the present invention.

A system which can perform the method, including a computerized tomography (CT) scan, is shown in <FIG>. The system generally includes a source of x-rays <NUM>, a mounting unit <NUM> for holding the assembly <NUM> including the joint (object to be inspected) which is subject to the x-rays, and an x-ray detector <NUM> disposed opposite the source <NUM> for detecting the x-rays from a tungsten film. The mounting unit <NUM> is located between the source of x-rays <NUM> and the x-ray detector <NUM>. The x-rays are emitted at a high energy level of at least <NUM> kV, for example <NUM> kV to <NUM> kV, with a current of at least <NUM> microamp (µA), in order to generate high resolution images of the assembly <NUM>. The images typically have a resolution of at least <NUM> micrometers (µm), for example <NUM> to <NUM>, or at least <NUM>.

<FIG> lists imaging geometry and parameters of the system performing the CT scan according to an example embodiment. However, the imaging geometry and parameters can vary. In the example embodiment, the x-rays are provided at an energy level of <NUM> kV. However, the energy level of the example embodiment could vary by +/-<NUM> %; for example, the energy level could range from <NUM> kV to <NUM> kV. The current of the x-rays is provided at <NUM>µA. However, the current of the example embodiment could vary by +/- <NUM>%; for example, the current could range from <NUM>µA to <NUM>µA. The system of the example embodiment has a focal spot size of <NUM>. However, the focal spot size of the example embodiment could vary by +/- <NUM> %; for example, the focal spot size could range from <NUM> to <NUM>. The images generated by the system of the example embodiment have a resolution of <NUM>. However, the maximum achievable resolution of the example embodiment could vary by +/- <NUM> %; for example, the voxel size resolution could range from <NUM> to <NUM>. The active area of the example system, which is defined as the total area of the assembly <NUM> imaged, is <NUM> inches x <NUM> inches. However, the active area of the example embodiment could vary by +/- <NUM> %; for example, the active area could range from <NUM> to <NUM>. The magnification of the example embodiment is <NUM>. However, the magnification of the example embodiment could vary by +/- <NUM>%; for example, the magnification could range from 2x to 10x. The integration time of the example embodiment, which is defined as the total scan time for performing a scan must take into consideration the additional image reconstruction time when determining how quickly the image(s) may be viewed, is <NUM> second. However, the integration time of the example embodiment could vary by +/- <NUM>%; for example, the integration time could range from <NUM> second to <NUM> seconds. The frame average of the example embodiment, which is defined as a method to balance the exposure time and signal to noise ratio (SNR), is <NUM>. However, the frame average of the example embodiment could vary by +/- <NUM>%; for example, the frame average could range from <NUM> to <NUM>. The example system does not includes a copper (Cu) prefilter. However, a copper prefilter could be used. The CT scan of the example embodiment includes <NUM> projections. However, the number of projections could vary by +/- <NUM>%; for example, the number of projections could range from <NUM> to <NUM>. In the example system, the distance from the assembly <NUM> to the detector <NUM> is <NUM>. However, the distance from the assembly <NUM> to the detector <NUM> could vary by +/- <NUM>%; for example <NUM> to <NUM>. In the example system, the distance from the source <NUM> to the detector <NUM> is <NUM>. However, the distance from the source <NUM> to the detector <NUM> could vary by +/- <NUM>%; for example <NUM> to <NUM>. In the example system, the distance from the source <NUM> to the assembly <NUM> is <NUM>. However, the distance from the source <NUM> to the assembly <NUM> could vary by +/- <NUM>%; for example, <NUM> to <NUM>. Features as small as <NUM> or less, <NUM> or less, or <NUM> or less can be identified in the images obtained by the system of the example embodiment. A computer stitches or combines the images together to form reconstructive images which show details of the assembly <NUM> with the joint to be inspected. A reconstructive image can be referred to as a combined image which has a resolution of at least <NUM>, or at least <NUM>.

<FIG> are x-ray images of the assembly <NUM> including the components <NUM> joined by the self-piercing rivet <NUM> which were obtained by the system and method according to example embodiments. An advantage of the system and method disclosed herein is that the assembly <NUM> does not need to be destroyed or modified, for example to obtain a cross-section of the assembly <NUM>, prior to inspection. Thus, the system and method creates less scrap, which saves energy and costs, and provides for more accurate inspection of each assembly <NUM> produced.

The presence of cracks, if any, the interlock SH, the minimum thickness Tmin, and the overall structure of the assembly <NUM> can be determined based on the x-ray images of the assembly <NUM> generated by the system and method. In other words, the resolution of images generated by the method is great enough to determine the presence of cracks, if any, the interlock SH, the minimum thickness Tmin, and the overall structure of the assembly <NUM>. For example, the cross-sectional views of the assembly <NUM> shown in <FIG> are obtained by the high energy x-rays, without having to cut the assembly <NUM>. In <FIG>, the interlock SH, minimum thickness Tmin, the button height H, the slug <NUM>, the head <NUM> and base (leg) <NUM> of the rivet <NUM>, the diameter D of the head <NUM>, the top component 12a, and the bottom component 12b can be identified. The values for the interlock SH, minimum thickness Tmin, and the button height H can be obtained based on the diameter D of the head <NUM> of the rivet <NUM>, which is a known value determined prior to joining the components 12a, 12b.

Claim 1:
A method of inspecting an assembly (<NUM>) including at least a first component (12a) and a second component (12b) joined by a rivet (<NUM>) by a computerized tomography (CT) scan of the joint, the method comprising:
scanning a portion of the assembly (<NUM>) which includes the rivet (<NUM>) joining the first component (12a) to the second component (12b) with computerized tomography (CT); and
generating a plurality of X-ray images (<NUM>) of the portion of the assembly (<NUM>) which includes the rivet (<NUM>), and combining the X-ray images (<NUM>) together to form a combined image using a computer,
wherein the scanning step includes emitting X-rays (<NUM>) at an energy level of at least 200kV, and wherein the emitting step includes emitting the X-rays (<NUM>) with a current of at least <NUM> microamp; and
characterized in that the method includes identifying the presence of cracks in the portion of the assembly (<NUM>) which includes the rivet (<NUM>) based on the combined image.