Coolant lubricants make a decisive contribution to the high performance level of numerous production processes. By removing process heat from the contact site between the workpiece and tool as well as reducing the heat generated by friction in the machining process, the material removal rate of the machine tool can be increased, tool life extended and the quality of the workpieces improved. In this way, the use of coolant lubricants can save costs while at the same time achieving better results.
Coolant lubricant tasks
Coolant lubricant tasks may be divided into primary and secondary tasks. As the name already suggests, the primary tasks are lubricating and cooling:
- Lubricating: The reduction of friction between the tool and workpiece through the formation of a stable lubricating film.
- Cooling: The cooling of the contact zone and workpiece surface through heat absorption and transport.
Besides the primary tasks, the coolant lubricant also has other jobs to fulfil. The secondary tasks include:
- Cleaning the tool and the workpiece,
- Chip removal away from the machining site as well as corrosion protection for the machine and workpiece
Depending on the machining requirements, other tasks of the coolant lubricant may play a more important role, as the machining process is influenced decisively by the physical, chemical and biological properties of the coolant lubricants.
Challenges in coolant lubricant use
Coolant lubricant supply
It is not the high volume of coolant lubricant which is supplied to the machining site that is decisive, but rather how much of this actually reaches it. It is thus advisable to effectively penetrate the air cushion rotating with the tool in order to ensure that the coolant lubricant jet reaches the machining site. An important reference value is the exit speed of the coolant lubricant from the coolant lubricant nozzle. This is determined by the pressure in front of the coolant lubricant nozzle. This must be adapted to the production process, otherwise thermal damage may occur on the part.
Grinding with coolant lubricant
During grinding, high temperatures are generated in the machining zone. These may be so high that they cause thermal damage to both the workpiece as well as the grinding wheel. This leads to a structural change, also referred to as “grinding burn” in the workpiece rim zone, resulting in undesired tensile residual stresses. These induce microcracks in the workpiece rim zone which, when subjected to dynamic load during part use, may lead to failure (fracture, etc.).
On the tool side, too, these thermal influences have a negative effect. Improper cooling may cause the grit and the bonding material to become so thermally overloaded that the grinding tools wear considerably faster. It is important to avoid both effects. For this reason, targeted and clean coolant lubricant supply is essential.
One way of achieving optimum coolant lubricant supply is through the use of coolant lubricant nozzles in which the correlation between coolant lubricant exit speed and coolant lubricant pressure is known. With the aid of the nozzles, a fast coolant lubricant jet which fulfils the relevant requirements can be led to the machining zone.
This requires precise positioning of the nozzle. If the coolant lubricant nozzle sprays past the machining zone even by only a few millimetres, this can lead to the tool and part suffering thermal damage. For this reason, suitable positioning aids (e.g. articulated metal coolant lubricant tubes) are necessary. Furthermore, by using suitable measuring technology, the volume flow, pressure and coolant lubricant exit speed should be monitored in order to adapt them to the requirements of your production process.
Quellen: Klocke, F.; König, W.: Fertigungsverfahren 1 (2008); Klocke, F.; König, W.: Fertigungsverfahren 2 (2005); Richtlinie VDI 3397, Blatt 1 (2007)
Although grinding is a widely used manufacturing process, it is complex and in many places carries the risk of making mistakes. These have an effect on efficiency and component quality in all cases.
Thermal edge zone damage due to microstructural changes - commonly known as grinding burn. We explain the material-technical background and give first approaches for the prevention of grinding burn.
The grinding wheel is the tool inside the grinding machine. How a grinding wheel is structured, how it works and what must be taken into account when selecting and performing grinding wheels, you can look up here.
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