3D inline test system for gear wheels gives information about defects in the manufacturing process and enables ad hoc optimisation

In cooperation with various universities, the French manufacturer Mesure-Systems-3D (MS3D) has specially developed a contactless in line testing system for gears. With GearINSPECTION, a gear with 23 gear teeth for example can be fully measured in 3D in less than 15 seconds. With 3D inline testing, the manufacturer obtains real-time information about the effects any changes to the production parameters will have. This is not possible through comparable checking with tactile measuring machines, which takes at least five minutes. GearINSPECTION thereby enables optimisation of the ongoing process, which also generates major savings.

Two procedures are now used for the testing of gears: On the one hand, the finished gear is tested using master gears. This allows only to check the distance between axes and doesn’t give any information about part conformity. The second type of check is meant to precisely verify the geometry, special tactile measuring machines are used to inspect the gears. These machines only check about four gear teeth and requires five minutes to perform it. It creates six profiles along the length of the side and three along the length of the flank, so that a total of 18 squares are created, from which the involutes and the helix curvature can be determined. However, the standard cycle length for the manufacture of gear wheels can be as short as 10 to 20 seconds, meaning the process clearly takes too long to be able to control every gear not speaking of every teeth.

Challenge: eliminating measurement noise

With the new type of test procedure from MS3D, on the other hand, gears with 23 gear teeth, for example can be fully – meaning all teeth – inspected in 3D and checked in the factory in under 10 seconds. It thus makes sure that no faulty part gets through to final assembly and also gives information about defects in the process parametrisation. Cylindrical straight, helical as well as bevel gears can be checked and measured using five sensors which may be positioned differently depending on the diameter, the module and helix angle of the gear. Each of the sensors thereby digitizes part of the teeth flank surface generating a dense cloud of points at the rhythm of 700 data points per 4 thousandth of a second.
Those 4 sensors – the fifth one is used to measure the gear axis – generated cloud of points are then stitched together to get the complete surface data of all teeth flanks.
Within a second, millions of data points are generated, from which a 3D model can be calculated. This point cloud is then used to identify the profile of the gear teeth, helix angle, helix curvature, diameter on flank, thickness of teeth and the pitch between the gear teeth. The particular challenge of the geometry calculation using cloud of points generated by lasers is that the raw data is very “noisy” due to reflections of the laser on other areas (eg. The opposite flank) or the high gloss of the surface (eg. honed surfaces). If not eliminated this noise leads to measuring imprecision and poor repeatability. This issue has been successfully overcome by specific algorithms developed by MS3D thanks to its 10 years’ experience in dealing with in line non-contact inspection of complex metallic parts.
Today MS3D is able to propose a highly reliable inspection system making sure that no faulty part can reach assembly.
Saving the time spent to assemble a faulty gearbox, testing it, dismounting it, checking every gear individually to identify the faulty one and mounting the gearbox anew is one of the major benefits of using MS3D GearINSPECTION in line.
Return on Investment is estimated to be extremely short; a few months.
Therefore, not only can manufacturers generate considerable savings, they can also give their customers a zero-defect guarantee.

Further development for inline testing of gear axles

As the specifications of gears can differ according to applications, the machine has been designed, with in mind automobile manufacturers as well as gear subcontractors suppliers requirements. GearINSPECTION is currently suitable, for gear diameters  between 30 and 90mm. The special software for gear inspection was tested successfully in September/October 2015 with real customer parts supplied to MS3D, making the machine ready for delivery at the end of 2015/beginning of 2016. Besides this, further development for inline testing of gear axles is planned for 2016.


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