We had an opportunity to perform a GR&R (Gage Repeatability and Reproducibility) test that compared VTube-LASER measurements (using a 7-axis RA8 HEXAGON scan arm) to a customer's current infrared 6-axis tube-probe system. The differences between the results of the two systems were significantly greater than we expected.It proved that VTube-LASER, when used properly, can better protect the operator from taking measurements that cause repeatability and reproducibility issues.
Gage REPEATABILITY is defined as the variation in measurements usingone operatorwith one measuring center measuring the same attributes on several parts. For example, one operator will measure 10 tubes and then compare the repeatability of measured end points of a batch of 10 tubes of the same shape.
Gage REPRODUCIBILITY is defined as the variation in measurements usingmultiple operatorswith the same measuring center while measuring the same attributes on several parts.
We used a HEXAGON RA8325 arm with an RS5 scanner.
We mounted it to a 5000 lb metal table for stability.
We used a magnetic-base mount to attach the arm to the table.
The table was in a standard factory with other machines running. It was not temperature controlled or in a metrology lab.
We used three operators to measure10 tubes in what is called a Crossed GR&R study. This means that each part was measured three times by each operator for a total of 90 measurements.
Each tube had 3 bends. One bend has a large angle of 120 degrees. One bend has a shallow angle of 3 degrees. (See the image on the right.)
One VTube-LASER operator had never handled an arm and had never used a VTube-LASER before the day of the test.
VTube-LASER output data to Excel spreadsheets. The data was then imported into Minitab 19.
Using Minitab, we calculated and compared the GR&R values for the XYZ 3D deviations of all 5 centerline points. (These values were compared to the other measuring system.)
We calculated the GR&R values for the second LRA bender data values. These values were not collected from the other measuring system.
We calculated the GR&R of the AB-Length deviation (End to End). This value was not collected from the other measuring system.
VTube-LASER - Shallow Bend Data
It's essential to compare the correct values in the report to understand the significance of the comparison. The Total Gage R&R Variance Components (VarComp) is one of the most revealing. In the report below, you can see that the variation caused by all three operators plus the measuring center with this value. We chose the XYZ point 4 deviation in this test because it is the intersection point of the shallow 3-degree bend. This kind of measuring is the most difficult in the industry because of the math involved. The total deviation caused by the measuring center and operators in this test was only 0.17870 millimeters - even though the total changes due to part shape change between parts was 3.04 millimeters. (See the Total Gage R&R VarComp below.)
Comparison Chart of Total Gage R&R Values
Compare the actual "Total Gage R&R" deviations calculated on both systems in this chart:
Note 1 - Point 4 is the center of the 3-degree bend. Shallow bends are more complicated to measure well. The competing system struggled to calculate the intersection point of this bend accurately. VTube-LASER measurements were 40 times better for this point. Note 2 - Point 2 is the center of the 30-degree bend. This bend is not complicated to measure or calculate. We were surprised that VTube-LASER's measurement result was 34 times better than the competing system.
Competing System - Shallow Bend Data
When we compare the same Gage R&R values measured using the customer tube-probe system, the same calculation shows that the deviation caused by the measuring center and operators was 7.16108 millimeters. (See the Total Gage R&R VarComp value below.)
The calculated results showed stunning Gage R&R results forVTube-LASER. These are conclusions that we believe this test proved:
With the right equipment and setup, VTube-LASER is very repeatable and reproducible compared to legacy tube-probe systems.
The difference in GR&R performance between the two systems is especially pronounced when measuring shallow bends.
VTube-LASER is easy to use accurately even by novice operators after a few minutes of training.
Even the less expensive HEXAGON RS5 (red laser) scanner is suitable for measuring most tubes accurately.
Download the full GR&R report below. (To protect proprietary information contained in this test, the customer asked us to agree to not share their name. They also asked us to remove images and prints of the part from the report. Only solid models and numeric data are included.)