Chapter 5: Inspection/Analysis - Comparison to CAD
We are almost ready to move on to downstream applications for 3D models, but before we jump into that, we need to talk about one more application for scan data. Chapter Five will cover how this data can be utilized for quality inspection.
Important Terminology
CMM - Coordinate Measuring Machine, a mechanical device that obtains 3D coordinates by probing, may be either touch probe based or non-contact, portable or stationary, or motorized or manual.
Laser Tracker - sends a laser beam to locate a reflective target held against the object to be measured. The beam reflects back to the tracker and calculates the distance and angle of the targets location. Laser trackers are a great option when you need extreme accuracy over larger measurement ranges.
Color Map - a graphical display for visualizing dimensional differences between the measured shape of an object and its nominal CAD model; deviations are mapped to a color spectrum indicating location and magnitude. A reference key maps the deviations to values.
A History Lesson
While we think of the 3D scanning industry as something very new, the first 3D digitizers, Coordinate Measuring Machines (CMMs), were actually built in the 1960’s and the entire purpose of this development was to perform dimensional inspections. Fifty years later, inspections are still one of the most common uses for 3D digitizing and scanning systems.
In the late 1980s engineers at the then-Martin Marietta (including Direct Dimensions’ founder and president Michael Raphael) became aware of a company making articulating arms for medical measurements and they began working with the company (Faro Technologies) to develop a portable CMM for inspections in the aerospace industry. After the creation of the portable CMM, the options for 3D measurement and inspection exploded. Laser Scanners were added to the portable arms and then Laser Trackers were developed.
Twenty-five years later, portable scan arms are common measurement solution in major manufacturing firms across the world and in industries ranging from aerospace to automotive and power generation to medical.
Types of Inspections
There are many different types of inspections that can be done utilizing 3D technologies:
* One of the fastest and most informative types of inspections is the Dimensional Deviation, CAD to Part Inspection. A typical process for a Scan Arm, the scan data is compared to the original CAD model in a software package which will then show deviations by a color map.
* A variation of the Dimensional Deviation is the Virtual Assembly Analysis. By using reference points, such as interface datums, we have the capability to, in a virtual environment, simulate and identify how parts will fit together in their real-world assembly. We can do this by using assembly characteristics of the part (such as weld points, slots, and holes) to apply the mating constraints during assembly. This is also known as a “reference point fit” which can discreetly control part movement in any axis of each control point. The analysis can show part collision or spacing in a real world scenario done virtual.
* Parts can also be measured while they are in the process of being machined, an On-Machine Inspection allows for important characteristics to be measured and changes to be made while the piece or tool is still being created. These are typically done with either a Portable CMM with probe and scanner, or a laser tracker depending on the size of the object being machined.
* Similar to on-machine inspections, are real time inspections for Installation Alignment. This is helpful for installations of major equipment and is typically done with a laser tracker, PCMM, or similar.
* Perhaps the most comprehensive of the inspections is the First Article Inspection (FAI) which involves a thorough point to point inspection of a physical part against the production drawing dimensions. This is a very typical process for a portable CMM.
Getting Started
In the previous chapters, to get you going, we discussed the software products that we use literally every day here at Direct Dimensions. Below are the products that take the 3D measured data from the portable arms and scanners and perform the inspection analysis processes.
Each of them has some capabilities to perform the two main types of inspection – discreet point dimensional inspection and dense point cloud comparison analysis. Some have more comprehensive capabilities that include GD&T or special case analyses; and some specialize in certain areas such as ease of use or multi-scanner integration more than others.
At Direct Dimensions, we use all of these regularly and help our customer understand the strengths of each package relative to their specific application and company needs. If we are performing the project for someone as a service, they get the satisfaction of knowing we will use the best software for their inspection. Feel free to call us directly for more specifics on how these packages compare for your needs.
* CAM 2 Measure X (by Faro)
* Geomagic Qualify
* InnovMetric PolyWorks Inspector
* Rapidform XOV
* Verisurf
Now what can I do with my model?
Having learned what you can do with your data: inspect, reverse engineer or digitally model, we are now ready for the fun part! Chapter 6 will be an overview of the downstream applications for 3D models. The possibilities are numerous and we and our customers are thinking of new ideas every day.
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