I
INDEX
ABSTRACT IV ACKNOWLEDGMENTS V1 INTRODUCTION
1
1.1 INTRODUCTION 21.2 QUALITY ORIENTED PROCESS CONTROL 2 1.2.1 Compensation of systematic non-conformities 3 1.2.2 Tackling accidental non conformities 3
1.3 THEORETICAL APPROACH 4
1.4 OBJECTIVE 6
1.5 REFERENCE 7
2
TOOL CONDITION MONITORING: DEFINITION AND
STATE OF THE ART
8
2.1 INTRODUCTION 9
2.2 TOOL CONDITION MONITORING A GENERAL OVERVIEW
10
2.3 SINGLE MEASUREMENT APPROACHES IN DRILLING 11 2.3.1 Direct measurements 12 2.3.2 Indirect measurements 14
2.4 MULTIPLE SENSOR TCM 15
2.4.1 Intelligent data treatment for multiple sensor TCM
19
2.5 FUTURE TRENDS AND CONCLUSIONS 20
2.6 REFERENCES 21
3
MONITORING AND CONTROL OF THE CFRP
DRILLING PROCESS
25
3.1 INTRODUCTION 26
3.2 DRILLING OF FIBER REINFORCED PLASTICS 26
II
3.3.1 Drill wear measurements 27 3.3.2 Push Out Delamination (POD) measurements 29 3.4 RESULTS AND DISCUSSION 30
3.4.1 Thrust force 30
3.4.2 Tool wear 32
3.4.3 Composite damage 33
3.5 PROPOSAL OF A FUZZY LOGIC CONTROL 35 3.5.1 Design of membership functions 35 3.5.2 Diagnosis of delamination 36 3.5.3 Fuzzy control for feed rate 38
3.6 CONCLUSIONS 38
3.7 REFERENCES 39
4
MONITORING OF THE MARBLE SAWING OF
PROCESS
40
4.1 INTRODUCTION 41
4.2 STONE MACHINING 42
4.3 EXPERIMENTAL SET-UP 43
4.4 RESULTS AND DISCUSSION 46
4.5 CUTTING PRESSURES 52
4.6 CONCLUSIONS 54
4.7 REFERENCES 55
5
CONTROL OF LASER BASED MACHINING OF
POLYMERS
56
5.1 INTRODUCTION 57
5.2 LASER BEAM MACHINING OF POLYMERS 58 5.3 MODELLING OF HEAT TRANSFER: STEADY CASE 60 5.4 MODELLING OF HEAT TRANSFER: UNSTEADY CASE 68
5.5 CONCLUSIONS 70
5.6 REFERENCES 71
6
CONTROL OF THE SELECTIVE LASER SINTERING
OF NYLON POWDERS
III
6.1 INTRODUCTION 73
6.2 MODELLING OF THE SLS PROCESS 75
6.3 EXPERIMENTAL ANALYSIS 78
6.4 RESULTS 81
6.5 CONCLUSIONS 84
6.6 REFERENCES 85
7
MONITORING OF LASER VAPORIZATION OF
ACRYLIC POLYMERS
87
7.1 INTRODUCTION 88
7.2 IR LASER BEAM MACHINING OF POLYMERS 89 7.3 INFRARED LASE VAPORIZATION OF PMMA 90
7.4 EXPERIMENTAL SET-UP 91
7.5 CHANNEL PROFILE 91
7.6 BLIND CAVITIES 97
7.7 BONDING PMMA SUBSTRATES 101
7.8 THERMAL BONDING 101
7.9 BONDING STRENGTH CHARACTERIZATION 102
7.10 CONCLUSIONS 103
7.11 REFERENCES 104
8
ANALYSIS OF UV-ABLATION OF CARBON FIBER
REINFORCED PLASTICS
106
8.1 INTRODUCTION 107
8.2 LASER MACHINING OF CFRPS 107
8.3 UV-ABLATION OF CFRPS 108
8.4 SELECTIVE REMOVAL OF MATRIX 112
8.5 DRILLING 112
8.6 LAMINATE REPAIR 119
8.7 CONCLUSIONS 123
8.8 REFERENCES 123
IV
ABSTRACT
The research during three years of doctoral degree has focused on the development of a general sensor-based strategy than enables to control and solve drawbacks for critical applications. Methods for monitoring production processes have been studied, through the use of advanced Tool Condition Monitoring (TCM) systems and through the theoretical and experimental study of the influence of parameters involved.
The effectiveness of the proposed techniques was investigated through its application in five processes of relevant technical interest but not yet consolidated in industry, belonging to the cutting of anisotropic and non-homogeneous materials and laser technology.
As far as mechanical removal is concerned, TCM systems will be adopted to analyze the drilling of Carbon Fiber Reinforced Plastics laminates (CFRPs) and the quarrying of marble blocks. Both cases are derived from industrial needs and will be analyzed with single or multiple sensors with the twofold purpose of increasing the process stability and performance of tools and machine adopted.
Further step is to show that the former approach used for conventional machining process is also suitable for an innovative production process like laser technology. In this case several efforts will be devoted to better understand the interaction between laser light at different wavelengths and workpiece of different nature thus allowing the development of straightforward mathematical processes to assess process control. An on-line monitoring of process parameters and thermal effects on the workpiece will be used to confirm the efficiency of the proposed models. SOMMARIO
L’attività di ricerca svolta durante i tre anni di dottorato si è concentrata sullo sviluppo di una strategia di monitoraggio sensoriale capace di controllare processi produttivi critici e risolverne i principali inconvenienti. A tal proposito sono stati studiati dei metodi di controllo attraverso l’impiego di sistemi avanzati di monitoraggio utensile (TCM) da abbinare ad una precedente analisi teorico-sperimentale volta a determinare l’influenza dei parametri in gioco.
L’efficacia della tecnica proposta è stata verificata attraverso la sua applicazione a cinque casi pratici di rilevante interesse tecnologico, ma non ancora consolidati nell’impiego industriale. Questi processi possono essere suddivisi in due settori: il taglio di materiali non omogenei ed anisotropi e le lavorazioni laser di materiali polimerici.
Per quanto riguarda i processi di lavorazione convenzionali, i sistemi TCM sono stati utilizzati allo scopo di analizzare la foratura delle plastiche rinforzate con fibra di carbonio (CFRP) ed il taglio in cava di blocchi di marmo. Entrambi i casi, derivanti da necessità industriali, sono stati analizzati mediante la combinazione di uno o più sensori con il duplice obiettivo di aumentare sia la stabilità del processo di asportazione che le performance degli utensili e delle macchine utilizzate.
Un ulteriore passo della ricerca è stato rappresentato dall’introduzione di strategie di monitoraggio per il controllo di processi di lavorazione laser. A tal proposito è stata studiata l’interazione tra radiazione laser e pezzo per diverse lunghezze d’onda e diversi tipi di polimero, in modo da sviluppare modelli matematici semplici da utilizzare per l’ottimizzazione dei processi. Un monitoraggio on-line dei parametri di processo e degli effetti termici indotti è stato utilizzato per confermare l’efficienza dei modelli proposti.
V
ACKNOWLEDGMENTS
I would like firstly to thank all those who directly contributed to the outcome of these three years of research.
Prof. Gino Dini and Prof. Giovanni Tantussi are sincerely acknowledged for their guidance through this important training period and for the precious suggestions in refining the scientific activity.
I owe my sincere thanks also to Prof. Alessandro Franco and Prof. Marco Beghini for guiding me respectively through the study of thermal conduction in laser processing and the mechanics of composite materials.
I am grateful to Dr. Fabian Fischer and all the Microtechnology Group of the Laser Zentrum of Hannover (LZH) for welcoming and inserting me in the productive field of research on laser processing of carbon fibers.
Finally I would express my gratitude to all those colleagues whose support played an active role during this working period: Muhshin, Mithu, Gualtiero, Marco, Francesco, Flavio, Salvatore and Gabriele.
A special thought goes to my family:
I thank my mother and my father for the continuous patience and encouragement, Ilaria and Giulio from which I have been too far away to do this job.
