Target Reliability Tool

Deciding on a reliability goal/target involves trade-offs. This is because higher reliability typically correlates with higher production costs, lower warranty costs and higher market share. With Weibull++'s Target Reliability tool, you can generate plots that help you visualize and estimate a target reliability that will minimize cost, maximize profit and/or maximize your return on an investment in improving the product’s reliability. The ReliaWiki resource portal has more information on the Target Reliability tool at: http://www.reliawiki.org/index.php/Target_Reliability_Tool.

The Target Reliability tool is divided into a target estimation sheet and control panel. The top part of the sheet is the Target Estimation Inputs area, where you provide the best, most likely and worst case estimates for various factors involved in the production and sale of the product. The bottom part of the sheet contains the plot that you select to generate from your inputs.

The control panel contains settings for the type of plot that will be displayed, as well as other plot settings and icons. It also contains an input field for the product's maximum market potential and, when the R3OI vs. reliability plot is selected, an input field for the expected initial investment.

Generating a Plot

Follow the steps outlined below to generate a plot.

  • Open the tool by choosing Home > Insert > Target Reliability.

  • In the Target Estimation Inputs area, enter the estimated best, worst and most likely scenarios. Each scenario includes all of the following factors.

Note: A better scenario involves an improvement in both reliability and ROI. Thus the production costs in the best case scenario must be higher than that of the worst case scenario. This is because improving reliability requires increasing spending on factors such as facilities, higher quality materials, etc.

    • Expected failures/returns per period (as % of sales). The number of failures or returns that are expected in a given period, given as a percentage of sales. For example, if the best case scenario is one where 1% of the sold units are expected to fail or be returned within a year, then you would enter 1 under the Best heading for this factor.
    • % of market share that you expect to capture. The percentage of the market share that you expect to capture with your product. For example, if the worst case scenario is one where you expect to capture 40% of the market, then you would enter 40 under the Worst heading for this factor.
    • Average unit sales price. The average sales price per unit. For example, if the most likely scenario is one where the average sales price per unit is $20, then you would enter 20 under the Most Likely heading for this factor.
    • Average cost per unit to produce. The average cost of producing a single unit. For example, if the best case scenario is one where it costs, on average, $2 to produce a single unit, then you would enter 2 under the Best heading for this factor.
    • Other costs per failure (in addition to replacement cost). The average failure cost per unit, ignoring the cost of replacing a returned unit. For example, if the worst case scenario involves a cost of $5 per failed unit, $3 of which are due to the cost of replacing the failed unit, then you would enter 2 (the remaining cost) under the Worst heading for this factor.
  • Select the kind of plot you want to generate in the Plot Settings area of the control panel:
    • Cost vs. Reliability displays total cost as a function of target reliability. The total cost is the sum of the production cost, which is the cost involved in manufacturing the product to achieve a target reliability, and the unreliability cost, which is the cost incurred as a result of failures/returns and lost sales. By default, the plot displays curves for the production and unreliability costs and displays a vertical line marking the lowest point of the total cost curve.
    • Profit vs. Reliability displays profit as a function of target reliability. Profit is calculated by subtracting the production cost, warranty cost and other failure-related costs from the estimated total sales revenue. By default, the plot displays a vertical line marking the highest point of the profit curve.
    • R3OI vs. Reliability uses ReliaSoft's Reliability Return on Investment (R3OI) equation to calculate expected returns on an initial investment that will affect reliability. The R3OI is calculated by subtracting the initial investment from the expected increase in sales revenue and dividing the result by the initial investment. This plot displays the return on investment as a function of the reliability achieved through that investment. By default, the plot displays a vertical line marking the highest point of the R3OI curve.

      If you choose R3OI vs. Reliability, then you must enter your expected initial investment in the Initial Investment field at the bottom of the control panel.
  • Near the bottom of the control panel, enter the maximum number of units that could be sold in a given period in the Max. Market Potential (Units) field.
  • The Show Plot Items area will display a list of curves and vertical lines that can be displayed for the plot you selected in the Plot Settingsarea. To remove a line/curve from the current plot display, clear the associated check box.
  • Click the Plot icon on the control panel to generate the plot.

Tip: You can hide the Target Estimation Inputs area and expand the plot to fill the entire sheet by double-clicking the plot. To show the area and shrink the plot to its original size, simply double-click the plot again. See the descriptions below for other plot commands that are available in this control panel.

Control Panel

The Target Reliability Tool control panel contains the following options:
  • The Analysis Details (...) button displays the equations that are used to generate the plots. The values of A and B for each equation are calculated from the inputs provided in the Target Estimation Inputs area of the target estimation sheet.
  • In the Plot Settings area:
    • Keep Aspect Ratio maintains the ratio of the horizontal size of the plot graphic to the vertical size when you resize the plot.
    • Only Show Positive Values will include only positive values for the y-axis when that axis has a minimum value of at least zero.
  • In the Scaling area:
    • The X and Y boxes show the minimum and maximum values for the x- and y-axes. To change these values, clear the check box beside the value range. If it is selected, the application will automatically choose appropriate values for the range.
  • The Plot Setup icon opens the Plot Setup window, which allows you to customize most aspects of the plot including the titles, line styles and point styles.
  • The RS Draw icon launches ReliaSoft Draw, which allows you to annotate your plot and view your plot in greater detail.
  • The Export Plot icon opens the Save As window, which allows you to save the current plot graphic in *.jpg, *.gif, *.png or *.wmf format.

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