POLITECNICO DI TORINO Corso di Laurea Magistrale in Ingegneria Gestionale Tesi di Laurea Magistrale Definition of cylindrical grinding process standard for aeronautical gears Relatore Prof. Luca Iuliano Co-relatore Ing. Ivano Moretto (GE Avio S.r.l.) Candidato Davide Brandino Aprile 2019 Contents Introduction .............................................................................................................................. 2 1. The grinding process ............................................................................................................ 4 1.1. The cutting in grinding process ..................................................................................... 5 1.2. Grinding machine types ............................................................................................... 21 1.3. Grinding methods ........................................................................................................ 23 1.4. Grinding wheels ........................................................................................................... 28 1.5. Dressing ....................................................................................................................... 36 1.6. Grinding abuses ........................................................................................................... 43 1.7. Grinding coolant .......................................................................................................... 47 2. Grinding process control methods to detect abuses ........................................................ 50 2.1. Liquid Penetrant Inspection (LPI) ............................................................................... 50 2.2. Magnetic Particle Inspection (MPI) ............................................................................. 51 2.3. Nital Etching ................................................................................................................ 52 2.4. Eddy-Current Testing (ECT) ....................................................................................... 54 2.5. Barkhausen Noise ........................................................................................................ 54 2.6. X-Ray Diffraction ........................................................................................................ 55 2.7. Micro-Hardness Testing and metallographic microstructure analysis ........................ 57 3. Cylindrical grinding of case hardened steel surfaces ...................................................... 58 3.1. The aeronautical gearbox and its gears ........................................................................ 58 3.2. Gearshafts with integral bearing races ......................................................................... 60 3.3. Cylindrical grinding process of gears with integral bearing races............................... 62 3.4. Traditional and CNC grinders...................................................................................... 63 4. Database .............................................................................................................................. 65 4.1. Gearshaft P/Ns selection and process parameters........................................................ 65 4.2. Gather process parameters ........................................................................................... 69 4.3. Gather laboratory validation ........................................................................................ 69 5. Analysis of cylindrical grinding process ........................................................................... 71 5.1. Analysis of current process .......................................................................................... 71 5.1.1. Current process input parameters ....................................................................... 71 5.1.2. Analysis using process control parameters ......................................................... 76 5.2. Identify working strategy ............................................................................................. 86 5.2.1. Machining strategy ............................................................................................. 86 5.2.2. Dressing strategy ................................................................................................ 87 5.3. Grinding power ............................................................................................................ 88 5.3.1. Power model and correlations ............................................................................ 88 6. Modeling of optimized cylindrical grinding process ....................................................... 93 6.1. Input parameters validation tool .................................................................................. 93 6.2. Input parameters optimizer tool ................................................................................. 101 7. Design of Experiments, Grinding Test Plan ................................................................... 107 8. Conclusions........................................................................................................................ 113 References .............................................................................................................................. 114 1 Introduction Grinding is a key technology in metal manufacturing process because it can ensure required surface finish where other manufacturing process may have difficulty meeting product requirements. Grinding is applied in finishing stages of product manufacturing cycle when the value of the machined part is already significant and where mistakes can be very expensive. Besides accuracy of dimensions and surface finish, grinding also influences physical layer properties such as residual stress, hardness and microstructure during the material removal process leading to high risk of a thermal damage of the part surface layer. Grinding is a high-added value manufacturing process. In today's global manufacturer competition, companies that deliver high value in manufacturing have strong financial performance also because of their high quality recognition. However they must constantly improve their performances first of all in terms of quality and delivering time to maintain leadership in their business. This becomes possible only innovating, inventing, investing in Research and Development and last but not least investing in people knowledge. This thesis has been developed in collaboration with Avio Aero, Global Supply Chain in Rivalta plant. Avio Aero is a GE Aviation business that designs, manufactures and maintains components and systems for mechanical transmissions, turbines and combustors. Through continuous investment in research and development and a consolidated network of relationships with major Universities and international Research Centers, Avio Aero has developed a technological and manufacturing excellence globally acknowledged. The aim of this thesis was to define a cylindrical grinding process standard for aeronautical gears in particular for grinding of case hardened steel bearing race. The study has been conducted mainly on four phases, that means my gradual growth in "grindology". The first was a deepened study of grinding process and in the meantime the knowing of aeronautical product in particular gears, the second was a meticulous data collection of current grinding process from the company, the third was a careful analysis of gathered data, and the fourth was a multiple approach to improve the current process looking at the grinding in itself but also at the technologists needs, supporting them in the grinding parameters definition. This Thesis is divided in 8 sections. The first Chapter explores from literature all the aspects of the grinding process, including chips formation theory, grinding methods, abrasive wheels and dressing, damages due to grinding abuses. The second Chapter shows all process control methods to detect grinding abuses. 2 The third Chapter introduces cylindrical grinding application to aeronautical gearshafts with case hardened steel bearing race. Chapter 4 aims to gather all process data relevant to the above gearshafts from the Company’s Product Data Management (PDM). Chapter 5 carefully analyzes current process, using correlations between input and control parameters. This analysis shows in several ways with aggregated data an uneven current process. Thus, the need of a process standard definition. This chapter outlines also the power model, that is a new control parameter to strengthen process control. Chapter 6 is crucial for optimizing the grinding process by means of two spreadsheet tools. The first one is a sort of driven choice to avoid unsafe grinding input parameters, the second is a decision-making solver that gives as a result the grinding input parameters in order to maximize productivity within limits to ensure workpiece integrity. I wrote this tool in excel using Excel Solver VBA putting as decision variables feed rate and workpiece speed, as constraint variables the depth of cut, the speed ratio, the aggressiveness and the chip thickness and as a target the productivity indicator Qw'. Chapter 7, as further improving step, includes the drawing up of a grinding test plan (DOE) to be developed within a research project in collaboration with a University or a technology development center. The preliminary DOE plan is enclosed in this Thesis. Finally, in Chapter