3D laser line scanning boosts CMM inspection productivity and point cloud processing drive a digital inspection process that drastically accelerates design-through-manufacturing by providing full part geometry feedback. Customers in automotive aerospace and general engineeringindustries can implement this exciting technology to speed up their inspection processes.
Benefits of 3D CMM Scanning
- 3D scanning results in a complete digital part copy within minutes
- 3D scanning enables complete inspection and modeling of complex freeform and multi featured parts.
- Using traditional touch probes to measuring complete parts can take hours or even days compared to minutes with 3D scanning.
- 3D scanning is suited for measuring flexible or fragile materials, often a challenge for touch probes due to the risk of indentations or surface scratches.
- Switch between laser probe and touch probe maintains all existing CMM functionality and in addition it’s possible to combine touch probe part alignment and laser scanner measurements.
- 3D scanning can reduce development times since once a digital copy of the prototype has been acquired, product verification, engineering analysis and other design functions can take place concurrently.
Limitation of Tactile CMM Measurements
Sheet metal spring back and plastic part shrinkage illustrate that product quality concerns the entire shape of parts and not just a few geometric features. Even for a limited number of measurement points, CMMs require considerable programming overhead. In addition, tactile measurement falls short on soft and fragile parts. Economic pressure and higher quality standards force the metrology department to provide more detailed geometric information in less time.
To a certain extent, 3 and 5 axis tactile scanning overcomes the limitations of discrete touch trigger measurements. High-speed bridge CMM equipped with this advanced touch sensor speed up dimensional inspection on prismatic driveline parts. Characterizing a drilled hole by scanning a spiral line on its bore surface reveals much more valuable information than 4 discrete points. Also on the aerofoil surface of a turbine blade and other freeform surfaces, 5-axis analog scanning is an improvement compared to traditional tactile inspection. Although analog scanning provides much more data, elaborated CMM programming is required to ensure that the probe tip continuously follows the part surface without colliding with the part or the CMM structure.
3D scanning technology boosts measurement productivity
The sensor that undoubtedly gets most out of a CMM is the non-contact 3D Laser Scanner. New innovations in 3D scanning technology and point cloud processing software are key enable an entirely digital inspection process. The concept of digitizing parts up-front and running inspection on the digital copies of the samples streamlines metrology operations and embeds them into the CAD-centric design-through-manufacturing process. From measurement preparation to final report, this approach is significantly faster, provides more profound insight, and takes advantage of the typical flexibility and automation benefits of the digital process.
A 3D Laser Scanner essentially projects a precision laser stripe on a specimen while its built-in digital camera captures the projected laser line under a fixed angle. Today’s digital 3D scanners with advanced CMOS camera technology offer impressive point resolution and image acquisition rates and capture over 75.000 non-interpolated points per second. As they reconcile high point cloud density with tremendous scanning speed, they accurately digitize freeform surfaces and geometric features at high speed. Line scanners such with a smaller field of view suit detailed inspection of smaller parts by offering measurement accuracy down to 5 micron.
To effectively scan surfaces with varying color or high reflectivity, digital laser scanners dynamically adapt laser source intensity point-per-point. This capability is essential in dealing with different sample materials and surface finishes without operator interaction or powder spraying, also for shiny surfaces and abrupt transitions under any lighting condition. Intelligent intensity adaptation helps automatically scan similar parts in different manufacturing stages; initially dealing with bare sheet metal parts and finally scanning finished products painted in any colour.
Multi-line scanners capture full 3D geometry in a single scan
Laser Line Scanners can be stretched to their limits when digitizing parts with more complex surface shapes or numerous geometric features. For such applications a better solution is the multi-line laser scanner or cross scanner that incorporates 3 lasers in a cross pattern. These scanners realize full coverage on extremely concave surfaces, in between ribs, and inside the cavities of deep pockets. By observing geometric features from 3 sides, a cross scanner is able to digitize the bore of a hole or the flanges of a notch in a single scan.
A cross scanner enables full 3D digitizing of features like slots, notches and edges as well as specialized geometric features, including connection pins, welded bolts and T-studs. Where tactile measurement relies on a handful of accurate points to define the orientation of an elongated feature, optical inspection does a better job by fitting lines through hundreds of points acquired along the feature flange. In this way, geometric features can be extracted from the acquired point cloud with higher confidence and accuracy.
3D scanning drastically reduces required CMM time
Due to high 3D scanning speed and short scanner motion paths with limited or no head indexing, laser scanners digitize freeform surfaces and geometric features in a fraction of the time taken by tactile probes.
With laser scanning, the entire CMM inspection process is executed more than 10 times faster
High standoff distance and field-of-view depth enable cross scanners to realize major time savings when inspecting automotive cast and moulded parts. To perform a full 3D scan of one side of an engine block, cylinder head or transmission casting, the CMM only needs to move the scanner along parallel motion paths without indexing the head. With such limited CMM motion, the scanner captures the complete surface, including full 3D characteristics of ribs, holes, flanges and pockets, at incredible speeds.
Hours v Days to set up and execute CMM inspection
Besides drastic inspection cycle time reductions, 3D scanning offers additional productivity gains. Considerable CMM time can be saved by programming a CMM off-line allocating CMMs exclusively for inspection. Furthermore, laser scanning preparation is more straightforward than specifying individual touch sensor points for a tactile inspection job. It suffices to move the scanner along linear and polygon motion paths to keep part surfaces within the boundaries of the field-of-view depth of the laser scanner probe. Interactive software procedures offer a helping hand by streamlining the creation of scan macros.
Clicking on a CAD surface area triggers the automatic generation of a scan path with optimum probe angles. Virtual point cloud simulation reveals where to generate additional scan paths for surface areas falling outside the scanner’s field of view. Point cloud simulation also serves another very important purpose. Obtaining the point cloud as if it would be acquired on a CMM enables users to prepare the downstream analysis and reporting workflow before even switching on the CMM.
Flexible part analysis
A complete scan consists of a dense cloud of hundreds of thousands or even millions of accurate surface points covering the entire part, including potential anomalies that remain unnoticed through touch probing. Point cloud processing automatically filters the data and meshes the point cloud. The point cloud or mesh is then aligned with nominal CAD geometry using best-fist, feature-align or another method of choice. Graphic reports include part-to-CAD comparison plots with color-coded areas marking local geometry deviation and GD&T information comprising of pass/fail status and tolerance data. They indicate where molding and stamping equipment need adjustment, or illustrate how flush & gap evolves along complete spines between mating hood and front fender parts. Interactive reports can be evaluated from different viewpoints and underlying metrology data can be consulted by clicking any location of interest.
The digital inspection process quickly delivers “go”/”no go” status, while keeping the acquired data available for more in-depth analysis should this be desired, even if the physical part is no longer available in the metrology lab.
Increased productivity throughout the design-through-manufacturing process
As 3D scanning provides complete and detailed 3D data requiring minimum preparation and measurement time, it can provide insightful information much sooner in every stage of the design-through-manufacturing process. This results in fewer iterations and shorter cycle times. Laser scanning responds to vehicle designers requesting that their manually tuned prototypes are converted into CAD overnight. A few hours are sufficient for a dual-horizontal-arm CMM equipped with laser scanners to generate a digital model of the full car.
Setting up a plastic injection molding machine to start producing plastic trim components is a complex and tedious process that requires multiple iterations. Graphic part-to-CAD comparison charts obtained by digitizing first prototype samples instantly reveal how process settings can be optimized best in order to reduce the number of costly iterations. Also when starting up new assembly lines, laser scanning enables car manufacturers to save time and cost. They virtually assemble digitized sheet metal body parts in order to identify potential part fitting issues, before bringing together the physically parts from multiple remote fabrication plants. Besides eliminating expensive checking fixtures, they succeed in reducing time-to-market for new car models, increasing competitive edge in the fiercely competitive automotive industry.
As a conclusion, laser scanning not only brings increased productivity to the CMM; it also enables the metrology department to contribute to the success of the entire design-through-manufacturing process. Laser scanners can be supplied with a new CMM or retrofitted easily onto any existing CMM installation, requiring limited investment while the return of the investment can be extremely significant.
|3D scanning highlights · Optimized CMM time by reducing probe reorientations and CMM movements · Off-line setup of scanner motion and inspection program frees up CMM time · Digitizing parts without user interaction or powder spray · Full analysis flexibility, anywhere, anytime · Non-contact technology is ideal for flexible and fragile parts · Better insights increase productivity in the entire design-through-manufacturing processinsert|