Non-Contact Inspection of Internal Threads of Machined Parts E. Hong | H. Zhang | R. Katz | J.S. Agapiou Presentation by Guy Pinkas & Jonathan Avidan

Terminology Non-contact inspection Internal threads Laser sensor Image processing

Introduction Importance of threaded joints (50% of all joints) Common defects (Missing thread crest, Scratches or defects, Discontinuities) Primary methods for threads metrology and inspection Contact gauges (Go / No-Go) CMM (Coordinate Measurement Machine) Nondestructive techniques present some challenges Suggestion of 2 new methods “Optimet” conoprobe sensor (laser sensor) CCD camera and an illumination system

Angular Position of Internal Thread First challenge – Spark plug Locating the starting point of the internal thread The technique Thread is scanned in 4 internal lines The location is determined by comparing the 4 values The largest and smallest measured distances must be neighbors Can be extended by dividing the quadrants The technique provides information about the angular position and direction of the thread

Standard Thread Profile Main geometrical parameters Pitch [ p ] Minor Diameter [ DMIN ] Pitch Diameter [ DP ] Major Diameter [ DMAJ ] Thread Height [ H ] Flank Angle Helix Angle Parameters determination Minimum of 2 profile laser scan Opposite 180° More Scans will increase accuracy but will take more time

Surface Inspection – Laser Sensor Using the Optimet conoprobe laser sensor for measurements Internal cylindrical surface check adaptation Designed and built a unique motorized periscope Designed mechanically and geometrically for circular scan Combined motion – linear and rotation

Surface Inspection – CCD Camera Use line scan to acquire a high quality image (of the surface) Use sight pipe optical device with a conical mirror - 360° view Scans annular sections & Unwrapping the scanned images Combine the sectors to flat image and inspect with algorithm Method can also use to inspect surface defects

Experimental Setup Laser scan Internal thread inspection 3 linear motion stages & rotary stage Internal thread inspection 3 linear motion stages 2 tilt adjustment stages CCD camera Optical lenses Ring led light Set of sight pipes (for each diameter)

Experimental Results Detection of a thread starting point Inspection on M12x1.25 nut PS’ depicts the corrected PS after self-calibration From the results : PS’1 > PS’2 > PS’3 > PS’4 Starting point located in quadrant 4 The helix is a clockwise rotation 270° 180° 90° 0° 0.44 1.082 2.379 2.531 PS [mm] 1.384 1.942 2.288 PS’ [mm]

Experimental Results Internal thread dimensional measurement Standard Max Min Average Parameter 1.251 Pitch 12.36 12 12.108 Major Diameter 10.912 10.647 10.863 Minor Diameter

Conclusion 2 new methods for non-contact inspection of internal threads Laser sensor and a motorized periscope CCD camera with sight pump The methods functionality Find angular position of internal thread starting point Reduce measuring time and cost Measure long internal threads of small diameter Allow inspection of 100% of threads used in safety related parts Detect internal flaws found on threads surfaces

Questions ?