Selection of cutting fluid for Gear Hobbing
Factors affecting the hobbing process.
The cutting tools used for tooth production are called hobs, which are very expensive, and it is a very important requirement to extend tool life to increase productivity and improve gear quality.
In an era of economic survival, it has become imperative to explore and evaluate new cutting fluids that can provide longer tool life, improve productivity and reduce overall costs.
When deciding on the type of cutting fluid in India, the following factors should be considered when choosing between water-miscible (water-soluble type) or pure type for different applications.
In summary, as a general guideline it is accepted that low speed and heavy cuts involving considerable force are best served by neat cutting oils with selective EP additives however light cut and high speed operation calls for efficient cooling and hence soluble cutting oils are selected.
For Gear Hobbing which is considered as severe operation where depth of cut or metal removal is relatively large and operating speed is comparatively slow wherein more lubrication rather than cooling is required, as a general guidelines following table helps in selecting or calculating suitable coolant as per the machining operation.
| Module | Victory Range | Types of Base oil |
|---|---|---|
| Bigger Gears > M8 | Above 35 Cst | Ester Based |
| Medium to Bigger Diameter Gears – M4 to M 8type | 30 Cst | Ester Based/ Mineral Base |
| Smaller Gears – Ml to M3 | @15 -20 est | GTL / Ester blended / Mineral Base |
Most of the gears are of MS and HSS material which are more difficult to machine. Hence to achieve desired tool life and good surface finish and higher productivity neat oil with high level of sulphurised and /or chlorinated EP additive type cutting oils are recommended with the different viscosity levels. Different additive and operating temperatures are highlighted below.
One of the main problems in hobbing is the large amount of smoke/gas generated due to the very hard cutting process which is not operator friendly. This is primarily due to poor lubricity and the selection of low burr based cutting fluids and inadequate EP additive packages.
It has also been observed that some older machines are always prone to uncontrolled leakage of hydraulic fluid, affecting cutting fluid performance, thereby reducing tool life and desired surface finish. . As this leads to increased operating costs, it is advisable to provide such machines with a multi-purpose oil. H. Cutting oil containing hydraulic oil to avoid cross-contamination and reduce oil consumption.