Chapter 8:  Warranty Analysis – Repairable Items (WA-RI) Module

Although very similar to the Warranty Analysis – Non-Repairable Items (WA-NRI) module, this module is designed to store and treat claims’ data on repairable items. When a product or asset is made of several components, and customers start to send their complaints, it is possible to treat it as a system and apply Reliability Growth Analysis method.

8.1 WA-RI Analysis List

On the main page, the user can access the Warranty Analysis – Non-Repairable Items on the dashboard or by clicking on the main menu “WA-RI  My Analysis”. The dashboard also provides a graphical representation of the quantity of WA-RI performed in the user’s account in relation to other analyses’ types and how many items were created.

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As well as it is with other modules, on the analysis list it is possible to visualize and sort the previous created analysis made in this module, and to create new ones. Other functions of this list are shown below.

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On the bottom right it is possible to surf through the list’s pages. Above the list and on the right side of the search bar, there are four buttons, shown in the image below.

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As discussed in previous chapters, the functions of these buttons are, from left to right:

  1. Configure the list to show relevant information in the list, such as name, quantity of items or creation date.

  2. Copy the analysis list’s information so that the user can then paste it in another document of his choosing.

  3. Download a spreadsheet containing the list’s information.

  4. Generate a .pdf archive of the analysis list at hand.

8.2 WA-RI Settings

On the main menu, click on “WA-RI  Settings WA-RI” to adjust the estimation methods used in the Confidence Bounds and the General Settings.

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Note: These settings do not alter calculation or results, but instead they alter how the results are displayed.

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On the bottom right it is possible to surf through the list’s pages. Above the list and on the right side of the search bar, there are four buttons, shown in the image below.

Important Note: as discussed before, a Warranty Analysis for a repairable item, which has components and therefore cannot be treated as a lowest replaceable unit, does not use the LDA method, but instead the RGA, as this same item will keep running down with new components instead of being entirely replaced by a new, different item. So, the most adequate method here is RGA.

8.3 WA-RI – Ship/Claims tab

On the Ship/Claims tab, a Nevada Chart will be available for inputting the number of client’s claims per period, also considering the quantity of items released in each period.

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Note: the calculator is available on the RGA tab forward, after parameter estimation is defined.

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Important Note: analogous to the WA-NRI chart, the yellow cells are for representing upcoming production. The claims cannot be made for these cells, as the items are not yet released for field operation, and the only information regarding them is how much are expected to be released and sold. On the Forecast chart results, it is possible to observe an estimation of how many claims are expected for this future production, and when these claims are expected to happen, based on the input data entered on this tab.

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Note: it is mandatory to always hit the green buttons (which are for refreshing the chart) to update any changes made in these options.

Important Note: in contrast with a Warranty Analysis for non-repairable items, the Warranty Analysis for repairable items accepts more claims than the number of shipped items. For repairable items, the tool is requiring the number of complaints the item has, not if it has returned for warranty replacement, and as discussed before, repairable items are systems composed by many sorts of units and components. So, the same item can register multiple claims, which were triggered because different components failed, causing the same item to return for warranty inspection and maintenance multiple times.

8.4 WA-RI – RGA tab

As discussed before, repairable items are not entirely replaced for a brand-new item when they present failures in their systems. Instead, when clients report a claim for warranty inspection/maintenance, it is usual that only some components must be replaced or fixed, and so the item will be returned for the client and keep on running until it fails again.

In this scenario, the adequate reliability method is the Reliability Growth analysis, since interventions on components in these items will result in having components “as good as new” mixed in with other that still are degrading over usage since the item was delivered to the client’s hands. Therefore, this item will simultaneously present multiple life behaviors.

After data input on the Data tab, all other tabs in this module, besides the RGA tab, will not be accessible yet, since it is mandatory for the user to generate an RGA for parameter calculation first. Upon clicking on this tab, the RAG spreadsheet is generated using the input data already present on the Data tab, and therefore, it cannot be edited.

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Note: in this image, the column “Time in Service” is skipping 3 days intervals because this analysis was set to have an increment of 3 on the Ship/Claims tab, while the chosen unit of period was “Days”. The unit, however, cannot be altered on this tab, only on the Data tab.

8.5 WA-RI – RGA Plot tab

On this tab, it is possible to plot the Reliability curves obtained by the Reliability Growth Analysis.

Important Note: this function is the same as in the RGA Plot present in the RGA module itself.

For a RGA, there are 5 types of plot:

  • Cumulative Number of Failures

  • Instantaneous MTBF vs. Time

  • Cumulative MTBF vs. Time

  • Instantaneous Failure Intensity vs. Time

  • Cumulative Failure Intensity vs. Time

Follows an example of a Cumulative Failure Intensity vs. Time:

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The Confidence Bounds button also lets the user customize how the bound curves are calculated, in the same way as in the LDA Plot, but with different methods.

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8.6 WA-RI – Overlay Plot tab

An Overlay Plot has the same plot types previously presented in the 8.5 subchapter, but it can plot all the analysis’ items in the same graphs, for comparison and reading of the RGA curves of different items.

The Overlay Plot tab allows users to see more than one item in the same plot. As the RGA Overlay Plot tab works in a similar way to the LDA Overlay Plot tab, there is no need to show them again here. If more information is needed, please see chapter 2.6 (LDA – Overlay Plot tab).

8.7 WA-RI – Report RGA tab

On the Report tab, the user can visualize all the plotted graphs from the item previously selected on the Data page, just like in the LDA Report. As the graphs were all shown in the Plot chapter, there is no need to show them again here. If more information is needed, please see chapter 2.7 (LDA – Report tab).

8.8 WA-RI – Forecast tab

The Forecast tab displays the predicted warranty claims values expected for the desired future period, and this estimation is calculated given the inputted data on the Ship/Claims tab.

This WA-RI module applies the conditional probability of failure to determine the number of items that may fail for each production period. The system multiplies the conditional probability of failure by the number of units that are still working in a determined period and then the number of warranty returns will be calculated.

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Note: If Round Values is selected, have in mind that the sum on the line “Total” will still be made considering all the decimal places in the cells above, so it may diverge from the sum of the rounded values shown in the cells when this option is selected.

8.9 WA-RI – Forecast Plot tab

The Forecast Plot tab can be accessed after obtaining the results in the Forecast tab. If the previous tab was not yet accessed, a message reading “Before displaying the graph, perform the forecast calculation” will appear. Once Forecast tab is selected, the Forecast Plot will be available.

Important Note: notice how there is an order when working through the WA-RI module’s tabs: first input warranty data on Ships/Claims tab, then access the RGA tab to obtain analyzed system’s parameters and to be able to plot graphs in subsequent tabs, then surf to the Forecast tab to see results of estimated number of warranty claims for future periods before going to the Forecast Plot tab. For convenience, the tabs already follow this logical sequency.

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Note: this Forecast Plot cannot exceed the Future Sales interval time, but it can be below it, as discussed before.

8.10 WA-RI – RGA Calculator

This calculator follows the same rules and applications of the RGA calculator, present on the 3.6 subchapter. 

The RGA Calculator has different options from the LDA Calculator, and it can be accessed just like its pair, by selecting the calculator icon on the top side of the page, right above the tabs. The calculator will be available for use after the calculation of the Data has been made.

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The icons on the left are the parameters which can be determined on a specific value for the systems. The acronyms on the buttons indicate which buttons calculate each parameter:

  • IMTBF (T): Instantaneous MTBF vs. Time

  • CMTBF (T): Cumulative MTBF vs. Time

  • IFI (T): Instantaneous Failure Intensity vs. Time

  • CFI (T): Cumulative Failure Intensity vs. Time

  • T (IMTBF): Inverse of IMTBF

  • T (CMTBF): Inverse of CMTBF

  • T (IFI): Inverse of IFI

  • T (CFI): Inverse of CFI

  • NOF (T): Number of Failures vs. Time

  • T (NOF): Inverse of NOF

  • Optimum Overhaul Time

The Inverse functions are for finding a time value that corresponds with a desired parameter value.

While calculating the parameters in the corresponding plots, the Confidence Bounds can be reconfigured to be shown with the calculation results. To maintain intuitive review, they follow the same pattern as in the LDA Calculator: the top bound is shown above the value calculated and the bottom bound under it.

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