Additive Solutions for Subtractive Problems in Cutting Tool Design

Abstract

A cutting tool, such as an end mill, is designed to remove material from a workpiece in the form of chips during machining. This process can cause the tool to reach high temperatures, which increases the tool wear and, in turn, shortens the tool life. To reduce the temperature, cutting fluids are sprayed at the tool and workpiece. These fluids account for 17% of the total cost to manufacture a part, are not environmentally friendly and can be harmful to operators. Additionally, certain industries, such as medical and nuclear, require their parts to be contamination free and so cutting fluids cannot be used.

Internal cooling of cutting tools is an alternative method to cutting fluids, to reduce the high temperatures of the tools, that is gaining traction in industry and academia. The aim of this thesis is to document research that investigates one branch of internal cooling, namely, heat pipe embedded end mills. In particular, the design of an axially grooved heat pipe that is formed directly inside an additively manufactured end mill is investigated. This is achieved through the analysis of heat pipe operating limit equations; to explore their use in selecting the optimum heat pipe design and derive a design of experiments (DOE). Based on this DOEaset of heat pipe embedded tools with a variety of internal heat pipe designs are manufactured and are tested, both statically and rotationally, to observe the performance of the different designs.

The results obtained from the analysis of the equations and the static and rotational testing show that additive manufacturing can be utilised to produce heat pipe embedded end mills. It is further found that the design of an axially grooved heat pipe can be uniquely parametrised by the internal diameter, number of grooves, height of the grooves and width of the grooves. The testing shows that a larger number of grooves, smaller total groove cross sectional area and higher groove ratio (ratio of groove width to height) are beneficial features of the pipe. However, the optimum size of the internal diameter is not universally conclusive and instead should be chosen such that it is complementary to the other parameters. It was also observed that the increase in tool rotational speed causes an increase in the redistribution of the temperature away from the tool tip to the shank. Whereas, wickless heat pipes perform poorly in comparison to the axial designs when stationary but outperform axial designs when rotated. Additionally, it is seen that for all the pipe designs, the performance increases until reaching a steady state condition within 400s when not rotating and 200s when rotated. This suggests that when machining, the tools should be preheated to ensure the pipe has passed the start-up phase before use.

For the materials tested, the heat pipe limiting equations are advantageous to identify which parameters should be investigated. Since the research on heat pipe operating limit equations states that they are estimates and often conservative, the experimental results for the best design features should be used in future work.

The research documented in this thesis has, for the first time, utilised additive manufacturing to remove thermal contact issues introduced due to previous manufacturing methods used to produce heat pipe embedded end mills. The optimum selection of parameters for axially grooved heat pipe embedded in an end mill are also determined. The process established to produce the end mills can be utilised for future developments and the experimental results can be used to narrow the design selection for further testing.

To further develop this technology, machining experiments should be undertaken to establish the effect of embedded heat pipes during use. Additionally, a CFD model developed to improve understanding of physical processes inside the heat pipe and optimise the design as well as exploring further design features that could be applied to the heat pipes, such as tapering the pipe.

Date of Award	22 Jun 2022
Original language	English
Awarding Institution	University of Bath
Supervisor	Vimal Dhokia (Supervisor), Joseph Flynn (Supervisor) & Andrew Cookson (Supervisor)