The terms “First Time Through (FTT)” /” First Time Yield (FTY)” often appear or are requested as a quality metric – however, there may also be different definitions or calculation in use for those terms…
For the following and to review graphics and reporting options in qs-STAT - Process Capability Analysis module. In this context, the following definition was applied:
First Time Through (FTT) / First Time Yield (FTY):
- Seen as the ratio of the number of good “units” coming out of the process to the number of “units” going in.
Below are some examples of summary report or graphic options by measured part where the evaluation takes place across all characteristics measured, for the same part or produced “unit”.
The main focus of the graphics / output options below is on different aspect of “out of tolerance” measurements compared to available measurements.
1 Defective part Summaries – by characteristic
1.1 “Defects/no. of non-conforming units” Graphics
The Error proportion (as “DPMO” – “Defects per million Opportunities” or %) per characteristic is available e.g. as a graphic called “Defects/no. of non-conforming units (summary)”, for example on the “Results” or “Assessment” tab:
With “Graphical settings” additional display options can be turned on, for example a label for the number of out of tolerance values:
With the “Graphical settings > bar label” function, you can switch to % or “DPMO” / “%” or absolute value as scale
There are also prepared bar graphics available from the same menu that would break down the percentages by a machine, cavity, gages etc., assuming this information has been recorded: For example: break-down by gages:
For the “breakdown” graphics, the “Graphical settings” and “Allocate for additional data” function was used.
As an additional function, there is an option to “Merge all characteristics” into one percentage.
Merging the characteristics here would give you an “accumulated” percentage. So if the same measured part with e.g. the same serial number was out of tolerance for 2 characteristics, this part would count double in the overall percentage for a more “measured pert” specific kind of view.
From here, and if a part serial number is recorded as additional data field, it is now easy to switch the view above to a “unit” / measured part based view,
Using the “Allocate for additional data” function by field containing the part serial number and
“Merge all characteristics” option afterwards.
2 Defective part Summaries – by measured part (“serial number”)
For a yield that is based on how many measured parts out of all measured parts were OK for all characteristics, versus those measured parts that had one or more characteristics were out of tolerance, a few additional settings / graphic settings are required.
2.1 Preconditions
- Sorting data by measured part when “Reading from the database”
- A “complete” data set including all characteristics for the data set has to be loaded
- Evaluation strategy: measured part based evaluation has to be turned on in the evaluation strategy:
“Requirements variable characteristics”
2.2 Standard Report
The standard “1060_Part_Evaluation” report from the standard reports folder displays “measured part” based evaluation and counts per characteristic class:
2.3 On-screen Graphics
2.3.1 “Graphical points rating” Graphic:
Displays information per measured part (= row in the values mask): % of characteristic out of Tolerance
2.3.2 “Tabular points rating” Graphic
Displays information per measured part (= row in the values mask): % of characteristic out of Tolerance as bar graph, considering the weighting by class
2.4 Output points, e.g. for Form Designer
Output points are available as well for good/bad measured part counts, that can be used in Form Designer for example.
Output points 10000 – 14999:
Per measured part (= row in the values mask): number of parts / “trials” in tolerance (all characteristics) or out of tolerance (at least for one characteristic).
Other terms used for this evaluation: “First pass report” / “Part throughput yield”
2.5 Another “part measurement related” report example
The below shows another example report that was created using Form Designer and the graphics and output points and graphics above :
