Chapter 5: Warranty Analysis for Non-Repairable Items (WA-NRI) Module

In this module, the user can use a Nevada Chart to keep up with the products that are presenting failures in the client’s hands and being returned in warranty term. With shipped items and returned items information, it is possible to forecast warranty failures and detect manufacturing flaws.

Note: This module was developed to analyze non-repairable items.

5.1 WA-NRI Analysis List

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

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5.2 WA-NRI – Settings

Analogous to the other reliability modules in this tool, it is possible to set the Confidence Bounds.

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Important Note: Confidence Bounds settings are applied on the LDA tab of the WA-NRI Module, as the input spreadsheet (the Nevada Chart) on the Data tab must receive round values, as there is no logic in registering the warranty return of 1.5 items, for example. More on these tabs will be discussed in the next subchapters.

On the top side of the settings screen, there are fields to adjust how the user is treating the warranty return’s periods (in days, months, or years). It is also possible to set this field to simply “numbers”, to represent any desired time scale besides the standard three options.

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Mathematical Precision refers to how many decimal places the user wants to be considered on his results.

Note: these two options can be reconfigured on the analysis module’s tabs.

5.3 WA-NRI – Data tab

The WA-NRI Data tab is developed to receive the warranty returns data on a Nevada Chart, which contains on lines the period in which the items were manufactured, and on the columns the following periods of time in which the items were returned in warranty term. See below a 12-month chart resembling a 1-year production of an item with 1-year warranty term.

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On the left, there is the month of production/shipping and the quantity of items shipped in each period, and the warranty returns follow in the chart.

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The settings of a WA-NRI can be altered on the data tab during analysis, on the right side of the Nevada Chart:

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In this example, as the periods are measured in months, it is possible to see that the sales start in Jan/2019, and as the number of period is 12, there are inputs in the chart until Dec/2019, as the increment is 1 (no months are skipped). As for the returns, as they also have a period of 12 and increment of 1, they will start in Feb/2019.

Usually, if a sale is made and returned in the same month, it must be accounted as returned in the next month, unless the period is adjusted to show days, so a sale made on January first and returned on January third can be accounted for the same month using a period scale in days.

5.4 WA-NRI – LDA tab

Once the inputs are made in the Nevada Chart (Data tab), they will be automatically converted into an LDA format on the next tab (LDA).

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Note that this generated LDA tab is non editable, as it depends on the entries of the Nevada Chart.

The LDA tab inside the Warranty Analysis – Non-Repairable Items module works in a similar way to the Data tab of the LDA module (see chapter 2.4 LDA – Data tab for more details). The only difference is the absence of the Data Type button. This is because the data set generated by the WA-NRI always results the same data type format, including grouped data and failure and suspension (censored data) time.

5.5 WA-NRI – LDA Plot tab

After the Life Data Analysis over the Warranty Analysis – Non-Repairable Items is performed, the user can use the LDA Plot in the same way as on the Plot tab of the LDA module (see chapter 2.5 LDA – Plot tab for more details).

5.6 WA-NRI – Overlay Plot tab

This tab is linked to the LDA tab inside this module, and it’s functions are the same as the overlay plot tab inside the LDA tab. See chapter 2.6 LDA – Overlay Plot tab for more information and details.

5.7 WA-NRI – Report LDA tab

On the Report LDA tab, the user can visualize all the plotted graphs from the item previously selected on Sales / Return tab. The setting for each plot type presented in the Report will follow the setting the user made on the LDA Plot tab. The Report LDA tab is like the Report tab of the LDA module (see chapter 2.7 LDA – Report tab for more details).

5.8 WA-NRI – Forecast tab

The Forecast tab presents the warranty returns for future periods based on the items that are still working for each production period.

This WA-NRI 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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In this chart, the forecast for 2020, using the last example’s data, is made. It displays the expected warranty returned items in each period, referring to its sale/shipping time.

In the Period Increment fields, the chart is edited to show forecast returns for a few periods of time in advance, and, depending on the configuration of Future Sales, the forecast will display only a selected range of months. The forecast tab displays how many failures are expected for the considered period.

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.

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The example above is a forecast of a 12-month period. As this example follows a warranty analysis of a 12-month term and the Future Sales option on the data tab is marked to display only 12 months of future sales, the forecast cannot forecast over this period for this analysis.

The results configuration options will change the estimation methods used for the confidence bounds and can be set to show in the forecast table the median, lower, or upper values.

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5.9 WA-NRI – Forecast Plot tab

The Forecast Plot displays how the warranty returns evolve over time.

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This plot is linked to the settings on the Forecast tab, and it displays only information for Feb/2020 to Jul/2020 because the “Period to Forecast” on the “Warranty Forecast Settings” menu, shown in the picture before this one, is configured to display 6 periods of time, or in this example’s case, 6 months after the last month, even if there are 12 months in the Number of Period of Future Sales on the Data page.

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