Nikon Metrology

Cross Scanners Automate Inspection of “Christmas Trees”

CMM Laser Scanning, Nikon Metrology

3D digitizing and point cloud processing drive a digital inspection process that drastically improves CMM productivity while accelerating design-through-manufacturing by providing full geometry feedback. Customers in automotive, aerospace or general manufacturing industries use this exciting technology to speed up their inspection process.

Benefits of 3D digitizing

  •  3D digitizing results in a complete digital copy within minutes
    • 3D scanning enables complete inspection and modeling of complex freeform, multi-filleted or featured parts.
    • Using traditional touch probes measuring complete parts can take hours or even days
  • 3D digitizing is a non-contact measurement technology
    • 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.
  • 3D digitizing is fully compatible with touch probe technology
    • The operator can easily switch between laser probe and touch probe maintaining all existing functionality  of  the  coordinate  measuring  machine  (CMM).  In  addition  it  is  possible  to combine touch probe alignments and scanner measurements.
  • 3D digitizing shortens the development cycle and improves product performance
    • Once a digital copy of the prototype has been acquired, product verification, engineering
    • analysis  and  other  functions  can  take  place  concurrently  by  OEM’s  and  suppliers  at different locations.
  • A tightly integrated 3D digitizing solution from digitizing to inspection or reverse engineering
    • Using  a  whole  product  approach  reduces  the  total  measurement  and  analysis  time, hence increasing efficiency of the inspection process and reducing costs.

 


XC65D digital laser scanner 1
3D scanning of sheet metal with digital Cross Scanner XC65D
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Getting more out of your CMM with 3D digitizing
 

Limitations of tactile inspection
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 CMMs 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.
 
 
 

 

Digital Laser scanner LC60 digitizing sheet metal part LC60D digital scanner for inspection, casting, software
LC60D Digital line scanners reconciles high point cloud density with tremendous 3D scanning speed.  Graphic part-to-CAD comparison charts highlight local geometry deviation resulting from 3D scanning

3D digitizing technology boosts measurement productivity

The sensor that undoubtedly gets most out of a CMM is a non-contact 3D laser scanner. New innovations in 3D scanning technology and point cloud processing software are key enablers of 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 a 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 offering impressive point resolution and image acquisition rates, 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 as LC15 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 color.
 
 
 

 

XC65D digital laser scanner 3 3D scanning - Focus Scan Offline dashboard
By observing a part from 3 directions, a cross scanner captures complex surfaces and features in a single scan. Scan paths for 3D scanning are easily generated with a click of the mouse A scan macro is automatically generated in Focus Scan using point cloud simulation.

Multi-line scanners capture full 3D geometry in a single scan

Line scanners may be stretched to their limits when digitizing parts with more complex surface shapes or numerous geometric features. For such applications, manufacturers better opt for a multi-line scanner, known as the Metris 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.
 
 
 
 

 

XC65D digital laser scanner 2 Connection features for automotive sheet metal
By digitizing the full geometry of complex “Christmas tree” features, car manufacturers verify the positioning of these features multiple times faster.

3D scanning drastically reduces required CMM time

Thanks 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.
At car manufacturers, cross scanners automate the inspection of so-called “Christmas tree” features. Robots weld these complex metal features on sheet metal body parts to allow trim to be easily and securely connected by means of screws. In roughly 5 seconds, a cross scanner digitizes the complete geometry of a single Christmas tree feature in order to determine its actual welding position. Scanning avoids spending hours manually mounting cylindrical extensions on the Christmas trees required for tactile measurement and removing them afterwards. 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 casted parts. To take a full 3D scan of one side of an engine block, cylinder head or gearbox cover, the CMM only needs to move the scanner along parallel motion paths without indexing the head. With such limited CMM overhead, the scanner captures the complete surface, including full 3D characteristics of ribs, holes, flanges and pockets, at record speed. One hour is sufficient to set up and execute inspection, whereas detailed tactile inspection easily lasts more than a day.

visit www.nikonmetrology.com to learn more.