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Spampinato, Alessio (2018) Dressing tools with controlled abrasive grain population for grinding aerospace materials. PhD thesis, University of Nottingham.

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Abstract

In aerospace manufacturing, strict tolerances (i.e. <5 μm) and specific roughness (i.e. Ra<1 μm) of the machined surfaces are mandatory requirements, in order to obtain high performance of complex systems such as turbine engines. In this regard, the grinding operation plays a fundamental role in machining of aerospace components, such as fir-tree roots of turbine blades, characterised by complex profiles and employing heat resistant materials (e.g. nickel-based superalloy).

The results of the grinding process (e.g. surface roughness and forces), in addition to the appropriate set of operational parameters, strongly depend on the conditions of the wheel abrasive surface (e.g. opened/closed structure, grains protrusion) and the profile accuracy. Thus, the dressing operation is utilized to obtain the required grinding wheel conditions, restoring the profile and preparing the wheel surface through the utilisation of diamond abrasive tools.

The state-of-the-art in dressing technology presents several limitations in terms of abrasive arrangement (grain size, shape, protrusion and distribution), leading to non-optimal process results and limiting the tool life; this limits the tool performance, with consequent increasing of the costs related to both dressing and grinding.

The main objective of this project was the development of a novel rotary diamond dresser characterized by high control of the abrasive characteristics; specifically, abrasive features will be realized on the tool external surface employing the pulsed laser ablation technique, tailoring the tools characteristics to meet the operational requirements.

To address the current technology limitations, this thesis proposes a novel design concept of a rotary dresser, which in contrast to conventional tool offers a complete control of abrasive surface characteristics. This presents regularly spaced truncated-pyramid abrasive grains with controlled sizes, density and protrusions thus, overcoming the stochasticity of the conventional tools. Each abrasive feature on the proposed dresser has controlled dimension with geometrical characteristics obtained as a function of conventional grain mesh size, while inter-grain spacing and protrusion are optimised as a function of increased tool durability and dressing action. The proposed dressers were tested in plunge (radial feed, no axial movement of the tool) dressing operations, comparing their surface condition (e.g. wear) and output forces with conventional (random, handset) rotary dressers, for different sets of operational parameters, showing improved wear resistance and significant (~50%) reduction of radial forces when compared with conventional tools.

In addition to the experimental work, a modelling framework was developed to predict the abrasive removal mechanisms at the contact between the roller dresser and grinding wheel, studying the case of two rotating bodies with stochastically distributed micro-geometries (i.e. abrasive grains), considering their granular structures and the relative motion of different sets of abrasive elements from both tools. Based on a preliminary simulation of the rotary tools abrasive characteristics (e.g. grain size, concentration, material properties) the described approach allows computing individual collisional events between grains with statistically dominated properties (e.g. grain size following a normal probability distribution) on both the dresser and grinding wheel surface, combining them to predict the total dressing effect at a macro-level (modelled contact region) in terms of output forces and generated abrasive characteristics (open/close structure resulting from fractured/removed grains). This lead to a deep understanding of the mechanisms regulating the dressing operation, clarifying the relations between the operational/design parameters and the process outputs (i.e. forces and wheel characteristics) and enabling the dresser abrasive optimisation previously described.

In an industrial scenario, the described dressers with controllable abrasives would lead to a reduction in costs (and improvement of machine capacity) associated with the necessity of replacing the diamond rotary dresser (the same concept can be applicable to the case of super-abrasive wheels/pins), estimating around 90% reduction in lead time (typical lead times are 10 to 16 weeks).

Item Type:	Thesis (University of Nottingham only) (PhD)
Supervisors:	Axinte, Dragos Butler-Smith, Paul
Keywords:	dressing, grinding, laser, ablation, modelling, abrasive, controlled, tool, aerospace, material, diamond, grain, turbine, blade
Subjects:	T Technology > TJ Mechanical engineering and machinery
Faculties/Schools:	UK Campuses > Faculty of Engineering
Item ID:	55258
Depositing User:	Spampinato, Alessio
Date Deposited:	09 Mar 2021 09:11
Last Modified:	29 Feb 2024 15:35
URI:	https://eprints.nottingham.ac.uk/id/eprint/55258

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