DSQR Training Destructive Testing GR&R HEATING, COOLING & WATER HEATING PRODUCTS DSQR Training Destructive Testing GR&R Fred Nunez Corporate Quality

Key Assumption Parts can be selected from a single batch or lot that are very similar to one another Homogeneous: composed of parts or elements that are all of the same kind; of the same kind or nature; essentially alike. having a common property throughout If the particular process of interest does not satisfy this assumption, this method will not work.

Secondary Assumption Different batches can be found that will produce parts that are different from the parts in other batches: Batch 1 parts are very similar to one another Batch 2 parts are very similar to one another Batch 2 parts are different than the parts from Batch 1 Within batch variation is much smaller than batch-to-batch variation (at least for the batches chosen for the GRR study)

Selecting the Parts Select the parts within a batch (that make up a psuedo-part) to be as similar as possible GIVE IT SOME THOUGHT Select the batches to be as different from one another as possible

Selecting the Parts We will call the collection of parts selected within each batch a “pseudo-part”. Each “pseudo-part” will be treated similar to an individual part in a standard GRR Standard GRR – 10 parts, 3 operators, 3 replicates Destructive GRR: 10 parts = 10 pseudo-parts = 10 batches 3 operators x 3 replicates = 9 parts within each batch 90 total parts to be destroyed

CASE STUDY from David Benham, DaimlerChrysler Corporation A stamped part goes through a critical weld assembly process which must be destructively tested on an ongoing basis. The process has an inhouse progressive stamping die which produces the steel stampings. This process is followed by robotic MIG welding (attaching an outside purchased steel rod to the stamping) in one of 24 different weld stations. Each weld fixture is assigned a letter designation, A through X. This process has been in production long enough that it has been studied and analyzed for stability and capability. Each of the 24 weld stations is providing a stable and capable process, however some are better than others. For process control, for a sample of parts, the rods are pull tested off the stamping for a pulloff force, destroying the part. In an effort to improve the overall process, the measurement system would be analyzed using this non-replicable MSA methodology.

Study Format This study used the 10-2-3 format – 10 parts, 2 appraisers, 3 – thus requiring 60 parts total for the study. Given the complexity of the process, it was felt that the 10-2-3 would be more manageable than a 10- 3-3. Although there are 24 weld fixtures, only 10 of them were used for this study and they were chosen using previously gathered data to represent the full range of the process. There was enough early confidence in the measurement system to make this judgment. Similarity (homogeneity) within each row was created by taking 6 consecutively produced stampings (6 is chosen to meet the 2 appraisers x 3 trials requirement), then welding those 6 parts consecutively through the same weld fixture. Dissimilarity (heterogeneity) between rows was created by taking groups of 6 consecutive stampings from different coils of steel at a time separated by a few hours, then running them consecutively through a different weld fixture at a different time. The rod component which is welded to the stamping is received in bulk and has already been determined to not play a major role in pull test variation. Therefore, in this study there was no effort made to maintain similarity and dissimilarity issues with the rod component.

Study Format Previous studies using common problem solving tools had shown that a manual positioning and clamping system used on the testing machine was appraiser dependent, so a new and better positioning system with hydraulic clamps was installed. Parts are located into the machine with positive locators and hydraulic clamps. A hook on the testing machine grabs the rod and mechanically pulls on the rod to destruction. A digital readout on the machine displays the peak pulloff force in pounds and reads to one decimal place. Although the appraiser dependency was assumed to be resolved, this study still used two appraisers to verify that assumption. A total of 60 parts were required to do this study. There were 10 groups of similar parts, 2 appraisers and 3 trials; 10 x 2 x 3 = 60. Parts were first gathered off the stamping operation, carefully numbered and quarantined until all 60 parts had been collected. These 10 groups of parts were selected at 3 hour intervals, over 3 days of production, in order to force some difference between each group of parts. Then, each similar stamped group of parts was run through a different weld fixture. Parts introduced to each weld fixture were presented in random order within each group of 6.

The Data Each batch of steel will only go through one unique welder, so the welder # will represent the pseudo-part ID For Minitab we will only need: Parts = Welder Operators = Operator Measurement = Force

Minitab Open the file: Destructive GRR.mtw Create a Gage Run Chart Stat>>Quality Tools>>Gage Study>>Gage Run Chart Run a Gage R&R (Nested) Stat>>Quality Tools>>Gage Study>>Gage R&R (Nested) Comment on Results

Gage Run Chart

Gage R&R Study (Nested)

Gage R&R Study (Nested) Gage R&R (Nested) for Force Source DF SS MS F P Operator 1 6304 6304 0.0087 0.927 Welder (Operator) 18 13089851 727214 13.9399 0.000 Repeatability 40 2086717 52168 Total 59 15182871 Gage R&R %Contribution Source VarComp (of VarComp) Total Gage R&R 52168 18.82 Repeatability 52168 18.82 Reproducibility 0 0.00 Part-To-Part 225015 81.18 Total Variation 277183 100.00

Gage R&R Study (Nested) Gage R&R (Nested) for Force Lower process tolerance limit = 5000 Study Var %Study Var %Tolerance Source StdDev (SD) (6 * SD) (%SV) (SV/Toler) Total Gage R&R 228.403 1370.42 43.38 16.40 Repeatability 228.403 1370.42 43.38 16.40 Reproducibility 0.000 0.00 0.00 0.00 Part-To-Part 474.358 2846.15 90.10 34.06 Total Variation 526.482 3158.89 100.00 37.81 Number of Distinct Categories = 2

Final Notes The data in any non-replicable study such as this will necessarily include SOME process variation (even within batch). So some portion of the GRR% is actually process variation. It is impossible to separate all process variation from measurement system variation with this scheme. The better the Key Assumption is met… Parts can be selected from a single batch or lot that are very similar to one another. the better will be the results.