Trend Analysis in GOM Software for Quality Control

How To Do Trend Analysis in GOM Software for Quality Control

In manufacturing, having multiple stages requiring the same features to be inspected is quite common – but it doesn’t have to be. If the current method you use does not allow for the same features to be inspected at different times, or maybe you just don’t have a method, learning to analyze trends in GOM Inspect Professional software provides a simple solution. Keep reading to learn more about trend analysis, and how you can incorporate it into your processes to cut down on iterations and increase your productivity.

One successful example of trend analysis application comes from a mold iteration for a manufacturing company. They just started a new product line and had developed a brand-new mold for their part. Through the iterative process of making a part, scanning it, and then inspecting the trends, they were able to adjust the mold to ensure the attainment of a perfect part.

Simply, an operator can pull a part from the manufacturing floor about once every ten runs per machine. This process is called batch sampling.

After you take five individual batch samples and scan each of those parts with your scanner, you will then be able to have the measurement data for those five individual parts, providing what is commonly referred to in GOM software as “Stages.”


To begin learning how to use trend analysis in GOM Inspect Professional software, open the program window, then retrieve the CAD file by clicking on the CAD and dragging and dropping it directly into your workspace window.

Once releasing the click button, three options will appear. Select the first available option labeled “New Part.” This option introduces your CAD file as a new part. Then, the CAD model will populate into the software. Select OK and accept the default settings, and the CAD file will be inside the project.

Next, retrieve your scan file by going back to your set of data, taking the first scan, and dragging and dropping it directly into the workspace window. Ensure you add it to the already existing part container so that your mesh, or scan, is relative to the CAD.

You can ensure this by checking your part container and making sure that your CAD and your mesh are all relative to the same parts, which is important for moving forward with your alignment phase. You’ll notice the CAD model and the scan data are not aligned in space, so open the “Operations” drop-down menu, select “Alignment,” then “Initial alignment,” and finally, select “Prealignment.” By establishing a prealignment, the scan data is pulled to the CAD utilizing the overall best-fit.

Select OK to accept the changes.

Next, you will move forward with inspecting the part. When inspecting a part, or creating any primitive elements, such as cylinders, your CAD model must be exclusive, so click on the CAD file and drag and drop it directly into the workspace.

You’ll see “Show Elements Exclusively” appear, and by releasing the click button, your CAD model will be the only thing visible within the software. This step is vital because your cylinders must be created on the nominal file, in this case, on the CAD.

Create your cylinders by opening the “Construct” drop-down, select “Cylinder,” then “Auto Cylinder.” So, by holding CTRL and clicking anywhere on this curve surface, you will have created a cylinder. Use this method to create two cylinders.

Next, we will utilize measuring principles. In GOM software, measuring principles dictate how you want to measure a specific feature. In this case, access your measuring principles in the I-Inspect wheel.

The I-Inspect wheel is also retrieved by holding the CTRL button and right-clicking anywhere on the workspace window. The “T” in the top of the I-Inspect wheel brings out your measuring principles.

Select “Fitting Elements” for the two cylinders, then accept the default settings of “Gaussian best-fit” with three sigma. By selecting OK, you have established your actual cylinders based on these nominal cylinders through the measurement principle of fitting element.

Once given a measurement principle, go into “Check Diameter,” and measure the diameter of the cylinder. You can then adjust your tolerances accordingly and accept the changes by hitting OK. You’ll see a check in the table displaying the nominal value expressing the diameter of the CAD file, the actual value expressing the value of the scan data, and the deviation is the subtraction between the two values.

Next, import the remaining meshes by going into the files, and retrieving the remainder of the scan files by highlighting them and dragging and dropping them directly into the workspace window. This time do not select “New Part.” Instead, select “New Stage.”

Once imported into the software, the timeline will appear at the bottom. First, select “Recalculate All Elements in All Stages” within your timeline. Making this selection will measure the same dimension across the stages. Using that prealignment will establish the same alignment for all five stages. By alternating between your stages, you can visualize the results between stages.

A better way to do this is to change the visualization of these checks to utilize your trend analysis features. Hold CTRL and highlight the green box around your dimensions, then go back into your I-Inspect wheel and select “Choose Visualization,” then “Trend.” By clicking on “Trend,” you will then have the option to visualize diameters across the five stages graphically through what the table reflects.

Some additional elements to be observed are statistical process controls like Pp and PpK, and other bits of information like the nominal values, the average, the sigma, and the min and the max. The same table is viewed in the table format by going up into “Table” and switching from “Overview” to “Statistical Trend.”

Now, with all the dimensions relative to the project, you can visualize these trends throughout these five stages and how the diameter, for example, changes throughout the five scans. Another way of viewing this information is through your sources of surface comparisons.

By utilizing color maps, it will take into calculation all five scans for all five stages. By assigning some arbitrary tolerance of .01 inches and hitting OK, a surface comparison is created that is repeated throughout the five stages.

Once the software has calculated these five surface comparisons, change your legend. By linking the two to form a unilateral tolerance, you will then be able to give the option of an adjusted legend tolerance. Choose .01 inches, and you will then be able to see in color, how this specific stage compares to the nominal set of data.

By alternating between the stages, you can visualize the color maps and how they compare to the CAD. Utilizing your trend features, go up top and create a deviation label to be able to create these labels anywhere you’d like to place by holding CTRL and clicking anywhere on the color of the surface comparison. You can then highlight those deviation labels, and, similarly to your previous dimension, you can also visualize these dimensions as a trend so that you can track how those specific points are changing throughout the five stages.

Next, you’ll visualize the surface comparison exclusively by going into “Inspection,” then “Surface Comparisons,” and taking your surface comparison out by itself to show it exclusively. You then have the option to change between your label or legend templates.

In addition, you will have things like minimum and maximum, arithmetic mean, and range. These color maps can also be visualized, taking into consideration all five stages at the same time. By alternating between the timeline, you will notice that the color maps do not change.

Other relevant graphs that can be pulled from this include the CP Value graphs, statistical process controls that can help an engineer figure out where the part is having the most problems. Utilizing color maps, you can then observe all five stages within the same color map.

The simple steps for analyzing trends in GOM Inspect Professional software begin with importing your CAD model, followed by the 3D scan data of your actual parts. Once you have both in the software, you’re then able to measure the changes between those individual stages, and how the features change, for example, the diameter or the cylindrical surface.

Some other interesting applications of this process include tracking a part over the change in time versus temperature. For example, you can scan the same part throughout a typical day to compare how that scan data is affected by the varying temperatures throughout a given day.

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