Cooling Strategy Influence on Temperature in ETD Center

Abstract: Striving for increased productivity while maintaining hole quality and high process robustness when drilling requires knowledge about the working principles of heat generation, mechanics and a proper cutting fluid that aids in cooling, lubricating and evacuating chips from the cutting zone. If the heat generated in the tool-workpiece and tool-chip interfaces does not exit the cutting zone adequately through the chips, the workpiece material or the redistribution of coolant the hole quality can be impacted negatively and breakdowns may occur which reduces overall productivity. During product testing, a sudden type of drill failure was observed when machining 316L stainless steel. When modifying the coolant design this was avoided which led to the assumption that the failure was caused by a large amount of heat being generated due to poor conductivity in the material combined with insuffcient cooling. However, this theory couldn't be investigated because of a lack of an existing method. To evaluate, three modifications of the CoroDrill 870 with dimensions Ø16mm and length 3xD were designed using Siemens NX 12 to observe whether coolant design choices have a significant impact on heat generation when drilling. To examine this a testing methodology was developed which utilizes IR-thermography and a combination of type K and J thermocouples inserted into the workpiece and onto the back surface, which measures its temperature in the cutting zone. Several tests were conducted with the developed setup to gather a larger data set to reduce impact from random error and to perform further analysis. Although the experiment setup is promising due to being simple and applicable to different materials there are large sources of variation associated with the placement of thermocouples. The results indicate some difference in registered temperature between the modifications however it is diffcult to draw conclusions based on the relatively few trustworthy measurements made.