Selection Criteria for Laser Scanning Technology

Retrofitting CMMs and articulated arms with new laser scanners is an option for many manufacturers, and with the right choices in scanning and software technology, mold manufacturers can achieve several advances in their inspection and measurement processes. These advances include:

Measurement coverage. Where many touch probes might achieve input rates of 1 point per second, laser scanning stripes can range from 50 to 200 mm (1.97 to 7.87 inches) in width and scan tens of thousands of data points per second.

Speed. Molds, production dies, complex 3D castings, turbine blades, cell phones and plastic parts can be scanned in a matter of minutes with laser scanning.

Offline and easy-to-understand reporting. Reserving your CMM or articulated arm for measuring, inspecting and transferring data to PC-based reporting software can significantly reduce inspection time and speed time to market.  

Quick, simple, cost-effective retrofits. A range of laser scanning options are compatible with many existing CMM and articulated arm setups. Often retrofits can be accomplished in a matter of hours. 

Ability to automate. Integrated software packages are available that can collect data, measure, compare scanned data to CAD models, and generate reports with both visual representations and tabular data into a single automated process. Incorporating color-coded visuals and tabular data can speed approval processes and make sharing information easier.

Cross scanning. New technologies such as cross scanning combine multiple scanners and digital cameras for scanning complex parts and features without re-orientation.

Many choices exist for CMM-based laser scanning. For entry level, there are single-stripe laser scanners that provide roughly a 50-mm stripe width, generate 20-25 stripes per second and input approximately 20,000 points per second while maintaining an error tolerance of 20 to 25 microns. For more demanding inspection tasks, use a laser scanner that has a 60-mm stripe width while scanning at 75 stripes per second and can maintain an error tolerance of 9 microns. Scanners are also available with smaller fields of view for digitizing small, detailed objects with higher point densities and tolerances as low as 4 microns.

For scanning large objects, laser scanners are available in hand-held models or for attaching to articulated arms, making mobile scanning easier. Depending on the type of scanner, stripe widths can vary between 50 and 200 mm, and digital cameras capture more than 1,000 points per stripe. This provides optimum resolution for efficiently scanning freeform surfaces and features. Cross scanners are also available that incorporate multiple scanners and multiple cameras for measuring or reverse engineering large parts.

A former challenge with laser scanning was scanning highly reflective surfaces that would necessitate spraying the object with a matte spray coating to eliminate obtaining reflective data and other extraneous noise. Today’s laser scanners feature automatic real-time adjustment of sensor settings for each individual point along the laser stripe, effectively handling highly reflective surfaces or those with varying colors.

Software compatibility is another important point to consider. Laser scanning can input tens of thousands of points per second, so effective inspection software should be able to handle a large volume of inspection data (as many as 100 million points) and provide the following tools: automated feature detection algorithms; full part comparison to CAD or STL files; complete set of 2D and 3D features; geometric dimensioning and tolerancing (GD&T) ability; specialized measuring capability, such as wall thickness, flush and gap, and directional comparisons; dedicated inspection modules; and off-line modules that enable users to employ CMMs or articulated arms for inspection, and personal computers for creating or modifying reports and models.

Every manufactured part has its own range of inspection or reverse-engineering issues, and advances in laser scanning technology can address these challenges.