Gage R&R Methodology

Quick reference

• 00:04 Hi, I'm Ray Sheen.
• 00:06 Let's continue our discussion of Gage R&R by looking at the step by
• 00:10 step approach for planning and conducting a Gage R&R study.
• 00:16 I'll start with an overview of the three phases of a Gage R&R study.
• 00:20 The first phase is the planning phase.
• 00:23 The keys to this are to focus the study, create the plan and
• 00:27 then make your preparations.
• 00:29 While the third of these, sounds the simplest,
• 00:31 I actually find it the most difficult because of the work to create items for
• 00:35 measurement and lining up the resources.
• 00:38 Once you are ready, you can conduct the plan,
• 00:41 this involves measuring the items and recording the data.
• 00:44 Based upon the difficulty of the measurement system and
• 00:46 the ability to gain access to resources, this may take an hour or several weeks.
• 00:51 The third phase is the analysis, this is very different depending upon whether
• 00:55 the data was variable data or attribute data.
• 00:58 The calculations are complex enough, that we'll devote an entire
• 01:01 lessons to each of these but for now, let's dig a bit deeper into each phase.
• 01:06 Let's start with the creation of the Gage R&R study plan.
• 01:09 The first step is rather obvious.
• 01:11 Decide what measurement you're interested in.
• 01:14 We need to understand if it is a variable or attribute measurement.
• 01:17 While this step seems obvious,
• 01:18 it's not a trivial question on a Lean Six Sigma project.
• 01:22 It's easy to do a study on what is convenient to measure but
• 01:25 you need to ask what is important to measure and how will we measure that.
• 01:30 The next step is an obvious follow from the previous step.
• 01:33 Now that we know what we're measuring, the question becomes how it is measured.
• 01:37 What is the current measurement system in process?
• 01:40 Where is the measurement done?
• 01:42 What equipment or procedures are used?
• 01:44 Who does the measurement?
• 01:45 If there's no existing measurement process, you'll need to create one and
• 01:49 then your Gage R&R study becomes part of the validation process for
• 01:52 that measurement system.
• 01:54 These first two steps will focus our efforts.
• 01:57 Step 3 is to design the study.
• 01:59 That means deciding how many appraisers, items and trials.
• 02:03 There are some differences in the approach, depending upon,
• 02:05 whether it's variable measurements or an attribute measurement.
• 02:08 With variable studies, use 5 to 10 items.
• 02:11 With attribute studies, use 20 to 30 items.
• 02:15 The easiest way to see the study design is to see the data collection form.
• 02:20 That's where all of the design parameters are captured.
• 02:22 I’ll show these forms in the next few slides. Which takes us to step four.
• 02:27 With the study designed and
• 02:29 the forms ready, we need to communicate the plan to everyone involved.
• 02:33 Normally this is quite easy but depending upon what's involved,
• 02:37 you may need to do things like make special sample items for
• 02:41 inspection that are known to be out of specification.
• 02:44 So there may be some cost and time needed to create those items.
• 02:48 The coordination step is often combined with the previous step.
• 02:51 It is a coordination of the resources such as facilities equipment, parts for
• 02:55 inspection and the people needed to run the study.
• 02:58 When communicating the plan you may wanna start this coordination.
• 03:02 For instance, you may need to get access to the measurement equipment that
• 03:05 is being used as part of day to day business operations.
• 03:08 You'll need to coordinate them with the area supervisor.
• 03:11 Also, the operators who will be the appraisers need to be identified, so
• 03:14 that they're relieved from normal duties and available when you run the study.
• 03:19 Depending upon the complexity of the measurement system,
• 03:22 you may need support from other organizations.
• 03:24 This is especially true if you have to conduct the study outside of normal
• 03:27 business operations such as on a weekend.
• 03:30 Finally, you need to train the operators in the purpose and process of the study.
• 03:35 The individuals will need to understand that the study is not a performance
• 03:39 appraisal on them, it is an evaluation of the system.
• 03:43 Sometimes they get nervous about the study and
• 03:45 that creates special cause variation problems in the results.
• 03:49 Of course, if this is a brand new measurement system or
• 03:51 process, the appraisers will need to be trained on how to use the equipment.
• 03:56 Lets now look at the data collection form for variable data, Gage R&R study.
• 04:01 If using Minitab, a statistical software application commonly used
• 04:05 with Lean Six Sigma projects, this is easy.
• 04:08 You just enter your study parameters into the mini tab assistant setup form and
• 04:12 it generates a study plan complete with the data collection form.
• 04:16 I'll show you how to do this in a later lesson where I also show you how to use
• 04:20 Minitab to analyze the data.
• 04:23 The measurement results from each measurement are then entered right
• 04:25 into the Minitab form and you're ready for the analysis.
• 04:29 But if you don't have Minitab,
• 04:30 don't worry, you can do everything in the spreadsheet such as Excel.
• 04:34 You will need to create your own data collection form and
• 04:37 you'll need to put in the equations for your analysis.
• 04:40 Again, I'll show you how to do those on the variable data Gage R&R lessons.
• 04:44 As you can in this form, for this study we'll have three appraisers
• 04:48 who each will measure 10 items and do these three times.
• 04:52 One of the things that I have also put on this form is that we'll need to calculate
• 04:55 the averages or means for each appraiser and each part.
• 04:58 We'll use those in the calculations.
• 05:00 One caution when planning the study.
• 05:03 You need to do the measurements in a random order but
• 05:06 you need to record the data for the correct item.
• 05:08 So to prevent the appraiser knowing which item they're measuring and
• 05:11 their previous measurement value,
• 05:13 I always have someone else record the data who knows which item is which.
• 05:18 Well, that was for variable data studies.
• 05:20 The attribute data Gage R&R data collection looks a little bit different.
• 05:25 The Minitab approach is the same. Enter your study parameters and
• 05:28 Minitab will create the plan and the data collection form.
• 05:31 And I'll show you how to do that in the attribute data Gage R&R lesson.
• 05:36 And like with the variable data, we can do this analysis in a spreadsheet,
• 05:40 we just need to manually create the form and enter the equations.
• 05:44 As you can see, the form is different for attribute data.
• 05:47 We don't have numerical measurements.
• 05:49 Instead, we have pass-fail or good-bad ratings for each item.
• 05:53 Once again, I have three appraisers.
• 05:56 And this time, just two trials are repetitions.
• 05:59 But with the attribute data, you need more data points.
• 06:02 So my spreadsheet goes all the way down to data item number 30.
• 06:07 There are also columns for matches and match to the standard.
• 06:10 I will discuss those in the lesson on the Attribute Data Gage R&R calculation.
• 06:16 One of the things about Attribute Data Gage R&R analysis,
• 06:19 is that it can include an assessment of the effectiveness of the measure,
• 06:23 in addition to repeatability an reproducibility.
• 06:26 To do that, we need to know the true value of each item.
• 06:29 So, we have a column for
• 06:30 the actual condition of the item labeled standard that's either good or bad.
• 06:35 Once again, the items need to be randomized in the order of inspection.
• 06:39 But the correct value needs to be entered for each item.
• 06:42 So I have someone else recording the data.
• 06:46 The methodology for planning and executing a Gage R&R study is not difficult.
• 06:49 The key will be the creation of the data collection form which
• 06:54 captures the planning and sets us up for the data analysis.

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