Gear Contact Testing – Validation and Benefits

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Accurate control of gear contact patches is fundamental to achieving durable and low noise gears – but does anyone ever check them via testing? Today, Hewland has performed such a test to validate that our micro geometry has been correctly designed and manufactured. By applying marking compound to the gears and running the gearbox under load, we can see the contact patch directly imprinted on to the gear flanks. This gives us tremendous confidence to proceed with endurance testing knowing that this critical aspect of gear design aligns well with our analytical models.

I know from talking to my fellow gear engineers that almost everyone has a story about the incorrect application of lead slope. Given the sheer number of different sign conventions and coordinate systems it is not surprising, as there is rarely consistency between the analysis software, the drawing and the grinding machines. This is where Hewland has a real advantage – we have full control over the design, analysis, manufacture and inspection processes. We know our machines and the coordinate systems they use, and we use this expert knowledge to ensure consistency in our lead slope definition at every step of the process.

This removes the need for any mental gymnastics when trying to compare drawings to inspection charts that are defined in different coordinate systems. The real pain starts if the lead slope has been applied incorrectly as it is usually the last manufacturing operation so results in costly delays as there is usually no hope in saving the part. Applying lead slope incorrectly means the micro geometry no longer counters the mesh misalignment – it exaggerates it, directly reducing gear life and impacting NVH.

LH– Gear contact results in Simulation RH– Gear contact results validated by marking compound

The reasons for championing this test are two-fold; firstly, the test is very quick to perform – taking only minutes of rig time and secondly, the results are simple to interpret and validate many aspects of the micro geometry design and manufacture. Care must be taken when applying the marking compound but thankfully Hewland has vast experience of conducting these kinds of tests so are expertly placed to advise and support.

Given the complexities of manufacturing micro geometry and the reassurance you get from seeing your analytical models validated, can you really afford not to perform this simple test?

If you have questions about this test or how best to define micro geometry on your drawings, please reach out to Hewland and we will be happy to work with you.