THE EFFECT OF CHATTER ON CUTTING TOOL IN CNC MILLING MACHINE CRISPIN JULIP JAINUL

Transcription

1 THE EFFECT OF CHATTER ON CUTTING TOOL IN CNC MILLING MACHINE CRISPIN JULIP JAINUL Thesis submitted in fulfilment of the requirements for the award of the degree of Bachelor of Mechanical Engineering with Manufacturing Faculty of Mechanical Engineering UNIVERSITI MALAYSIA PAHANG NOVEMBER 2009

2 SUPERVISOR S DECLARATION I hereby declare that I have checked this project and in my opinion, this project is adequate in terms of scope and quality for the award of the degree of Bachelor of Mechanical Engineering with Manufacturing. Signature :.. Name of Supervisor : Mdm. Mas Ayu Bt. Hassan Position : Lecturer of Faculty Mechanical Engineering Date :..

3 ii STUDENT S DECLARATION I hereby declare that the work in this project is my own except for quotations and summaries which have been duly acknowledged. The project has not been accepted for any degree and is not concurrently submitted for award of other degree. Signature Name ID Number Date :. : Crispin Julip Jainul : ME06055 :.

4 iii DEDICATION Special dedication to my family members especially both of my parents (Mr. Julip Jainul & Mdm. Catherine Lintar) who always give me encouragement in my life, my study and to finish my undergraduate project To my supervisor Madam Mas Ayu binti Hassan To my Academic Advisor En. Rosdi Daud To all FKM s staffs and lecturers To all my classmates And all my friends out there Thank you for your supporting and teaching. Thank you for everything that you gave during my studies and the knowledge that we shared. THANK YOU SO MUCH

5 iv ACKNOWLEDGEMENTS I would like to express my sincere gratitude to my supervisor Madam Mas Ayu Bt Hassan for her germinal ideas, invaluable guidance, continuous encouragement and constant support in making this research possible. She has always impressed me with her outstanding professional conduct and her strong conviction in engineering and science. I really appreciate her consistent support from the first day I applied to graduate program to these concluding moments. I am truly grateful for her progressive vision about my training in engineering, her tolerance of my naive mistakes and her commitment to my future career. I also would like to express very special thanks to my co-supervisor Mr Rosdi Daud for his suggestions and co-operation throughout this study. I also sincerely thanks for the time spent proofreading and correcting my mistakes. I acknowledge my sincere indebtedness and gratitude to my parents for their love, and sacrifice throughout my life. I cannot find the appropriate words that could properly describe my appreciation for their devotion, support and faith in my ability to attain my goals. Special thank should also be given to my members. I would like to acknowledge their comments and suggestions, which was crucial for the successful completion of this study.

6 v ABSTRACT This study focuses on chatter analysis after undergone milling process. The first objective of this project is to get the value of chatter using DYNO-METER on the CNC milling machine. After getting value of chatter, the second objective is to analyze the chatter using ALGOR software. The output that needs to get is in term of stresses. Minitab software also was performed to analyze the parameters involved in the experiment. In this project, Master Cam software will be used to design the work piece that will be used throughout this study. This software also will be used to simulate and generate the G-code to help user to operate with CNC milling machine. The work piece material that will be used was high carbon steel (AISI-D12) and its parameter is 100x100x50 mm. From the results obtained after machining, the most significant factor for the chatter were depth of cut and spindle speed. This means whenever the depth of cut is too depth and the spindle speed is slow, the maximum chatter will occurred with high cutting force applied. From the Algor analysis, the results showed that the different forces will result in different value of stresses. It is obvious that when cutting force is higher, the value of stress is also higher. The depth of cut also influences the chatter in this study. Spindle speed and feed rate should have an appropriate setting in to reduce the chatter. Based on this study, the analysis showed that higher chatter tends to increase the tool wear or tool breakage.

7 vi ABSTRAK Tesis ini tertumpu pada analisis gegaran selepas permesinan giling dilakukan. Tujuan pertama daripada projek ini adalah untuk mendapatkan nilai gegaran menggunakan Dyno-METER di CNC mesin giling. Setelah mendapatkan nilai daripada gegaran, yang kedua ialah mencapai tujuan adalah untuk menganalisis gegaran di perisisan ALGOR. Output yang perlu didapatkan adalah tekanan. Perisian Minitab juga dilakukan untuk menganalisis parameter yang terlibat dalam percubaan. Dalam projek ini, Master Cam juga perisian yang akan digunakan untuk merancang kerja potongan. Pada saat yang sama, software ini akan melakukan simulasi dan menghasilkan G-kod untuk membantu pengguna untuk mengoperasikan CNC mesin giling. Keluli karbon quality (AISI-D12) dipilih sebagai bahan dan parameter ialah 100x100x50 mm. Dari keputusan eksperiman, faktor yang paling signifikan bagi gegaran berlaku adalah kedalaman potong dan kelajuan spindle yang kurang. Dari analisis Algor, hasilnya menunjukkan bahawa kekuatan-kekuatan yang berbeza menunjukkan nilai yang berbeza dari segi tekanan. Jelas bahawa ketika gaya pemotongan lebih tinggi nilai tekanan yang lebih tinggi. Nilai pemotongan mempengaruhi gegaran pada mesin.oleh itu, eksperimen ini harus mempunyai parameter yang sesuai untuk menjalankan proses penggilingan. Kedua-dua analisis membuktikan teori bahawa gegaran yang lebih tinggi cenderung meningkatkan kerosakan pada alat pemotongan.

8 vii TABLE OF CONTENTS STUDENT S DECLARATION ACKNOWLEDGEMENTS ABSTRACT ABSTRAK TABLE OF CONTENTS LIST OF TABLES LIST OF FIGURES LIST OF ABBREVIATIONS Page ii iv v vi vii x xi xiii CHAPTER 1 INTRODUCTION 1.1 Project Background Objective Scope Problem Statement Solution Introduction 5 CHAPTER 2 LITERATURE REVIEW 2.2 Chatter detection Technique Force Sensor Two Dimensional vibration Suppressing in Turning Using Optimal 5

9 viii Control of Cutting 2.4 The Effect of Cutting Tool Vibrations On Surface Roughness of Work Piece in Dry Turning 2.5 AISI D 12 Carbon Steel Application of AISI D Existing Research A New Method for Chatter detection in Grinding Chatter Prediction and Control for HSM Tool Wear 7 12 CHAPTER 3 METHODOLOGY 3.1 Introduction Flow Chart For Final Project Flow Chart For Experiment Finding Data Simulation Using Mastercam Procedure Analysis in Minitab software Procedure Analysis in Algor Software Procedure in Algor Experiment Setup 33 CHAPTER 4 RESULTS AND DISCUSSION Introduction Result For Getting Cutting Forces Discussion Result For Stress in Algor 37

10 ix Discussion Result in Minitab Analysis Discussion 48 CHAPTER 5 CONCLUSION AND RECOMMENDATION Introduction Conclusion Recommendation REFERENCES 52 APPENDICES 54 A Gantt Chart 54 B Attachment from the Minitab 56 C Attachment from the simulation ALGOR software 59

11 x LIST OF TABLES Table No. Title Page 2.1 Properties table of AISI D Conditions of experiment Results of cutting forces in CNC milling machining 35

12 xi LIST OF FIGURES Figure No. Title Page 2.1 Cutting force model Element in AISI D Sketch of the experimental set-up in grinding machine Normalized coarse-grained entropy rate versus specific material volume for the chatter-free and chatter Example of recommended surface Flow chart for Final year project Flow chart for experiment Drawing sketch for starting Second Phase of drawing for the design Define stage of exact dimension Defining the process and cutting tool Defining diameter of cutting tool Defining stage for cutting depth Simulation ready Simulation of milling started Data of cutting force

13 xii First stage of Minitab analysis Defining the input data Define the response for output data Analysis after defining input data Defining coordinate The sketch after inserting the given coordinates Applying mesh for both parts Selecting the material and define as the user wanted Starting the Algor analysis Sketch of experiment Modeling in Algor before analysis Result in test 1 Result in test 2 Result in test 3 Result in test 4 Result in test 5 Result in test 6 Result in test 7 Result in test 27 Analysis from Minitab Graph of stress versus depth of cut Graph of stress versus feed rate

14 xiii LIST OF SYMBOLS/ABBREVIATIONS mm N rpm SLD V CNC DOE D F x, y CAD IGES IMECS Millimeter Newton Radial per minute stability lobes diagram cutting speed Computer numerical control Design of experiment depth of cut feed rate determined experimentally computer-aided design Initial Graphics Exchange Specification International Multi Conference of Engineers and Computer Scientists

15 1 CHAPTER 1 INTRODUCTION 1.1 PROJECT BACKGROUND The research work in this thesis involves an experimental and theoretical investigation of chatter during machining AISI 12 carbon steels. Experimental runs will be carried out to determine the chatter of the machine. The result will show how the properties of the material will affect the cutting tool of the machine. A device known as DYNO- METER will be used for this project. The purpose is to measure how strong the vibration will be produced during machining. The theory is the bigger of the vibration will caused the cutting tool take several damages such as tool wear. The important thing is the result of the product. Instability in cutting process causes chatter which generally diminishes the quality of products and therefore has to be detected, prevented and eventually also predicted. Various techniques have already been proposed for this purpose and mainly based on the spectral analysis of the cutting tool and force vibrations. Beside this, the oscillating signal shape and various statistical characteristics have also been used for identification of chatter.

16 2 1.2 OBJECTIVE The objective of this project is to get the value of chatter using DYNO-METER on the CNC milling machine. After getting value of chatter, the second objective need to achieve is to analyze the chatter using ALGOR software in term of stress. Minitab software also will be used to analyze the parameters involved in the experiment. 1.3 SCOPE In this project, CNC milling machine will be used to perform the machining process on material AISI D12. At the same time, DYNO METER will be used to get the response in term of cutting force from each milling process. From the response, ALGOR analysis will be performed to analyze stress. Then Full Factorial analysis will be carried out using Minitab software to predict the parameter that affects the value of chatter during the milling processes. 1.4 PROBLEM STATEMENT Usually designer or engineer facing problem in material selection for their products. This is the most important part in manufacturing process. This is the responsibility for person who called engineer to handle this task. Here the result of this project will help to decide whether material AISI D12 is necessary to apply in products for example car parts and the body of an aircraft. Chatter vibration is an unfavorable phenomenon encountered in various machining processes. Its occurrence in grinding can be particularly critical, since it affects the geometrical form accuracy and surface finish of the ground work pieces. Automatically also effect the cutting tool. These are the two main objectives of milling as designing and finishing operation. Reliable and early detection of chatter is therefore one of the most important features of monitoring systems for milling process.

17 3 1.5 SOLUTION To overcome these problems, for the problem, the project will help to specify on AISI D12 carbon steels. A further research needs to be done to avoid the chatter during machining.

18 4 CHAPTER 2 LITERATURE REVIEW 2.1 INTRODUCTION In milling operations, chatter vibration is one of the main factors that lower the productivity. This phenomenon is responsible of poor surface quality and increases cutting forces. Higher efforts tend to accelerate tool wear and can lead to tool breakage. Two main fields of research try to improve control of the process. There are prediction and on line detection. Prediction techniques simulate behavior of the machining system and try to anticipate vibratory behavior in order to compute optimal parameters for a given operation (spindle speed, depth of cut). On line detection techniques try to detect instability using sensors (force sensor, accelerometer, and microphone) and signal processing. 2.2 CHATTER DETECTION TECHNIQUE In milling operation, chatter occurred and is one of the factors that limit the productivity. The consequences of this phenomenon is poor quality of surface, higher cutting forces implying higher wear of the tool or even tool breakage. It is important to detect chatter earlier.

19 Force Sensor Cutting forces can be measured to detect chatter, but also to monitor tool wear and tool breakage. There are two main types of force sensor in milling and there are dynamometric table on which the blank is attach and rotating dynamometers holding the tool and rotating with the spindle. To calculate the dynamic cutting force in ball end milling, a structural dynamic model of the ball end mill was linked to a mechanistic cutting force model. Cutter run out and penetration effects were also considered in our models to permit a more accurate evaluation of the machining (Seon-Jae Kim, Han Ui Lee and Dong- Woo Cho, 2001). Figure 2.1 shows the example of cutting force model. Figure 2.1: Cutting force model Source: IMECS 2009

20 6 2.3 TWO DIMENSIONAL VIBRATION SUPRESSIN IN TURNING USING OPTIMAL CONTROL OF THE CUTTING Quality of a machined surface is affected by the cutting process variables such as, the depth of the cut, feed rate, part dimensions and tool wear. It is also affected by the vibration of the machine tool structure. In this work, an optimal control strategy is utilized for isolating the cutter from the vibration of the machine-tool in both the radial and feed directions. A random model with Gaussian distribution for the cutting process is constructed. The mean and variance of the distribution are proportional to depth of cut, feed rate and diameter of the work piece. The basis for using surface texture as a means of process control is derived from the fact that a slight change in the manufacturing process manifests itself as a corresponding change in the resulting surface geometry. On the other hand, tool vibration, metal shearing during chip formation, works piece material properties. Interacts in a complex manner and their effects are dealt with as the random portion of the roughness profile. Evaluation of the random or stochastic components of the surface profile is still a work in progress. More recently, researchers have tried to establish quantitative relations between the surface finish and the cutting parameters of the depth of cut, feed and cutting speed using methods such as, among others, wavelength decomposition surface roughness, wavelet analysis and tool vibration (Abouelatta and Madl, 2001; Fu et al., 2003; Lin et al., 2001; Risbood et al., 2003).

21 7 A Kalman estimator-based controller, developed by the researchers during the course of this study will be used for isolating the tool (cutter) from the machine tool structure in two orthogonal directions namely, the feed and radial (depth of cut) directions. Simulation results will be used to verify the effectiveness of the proposed process and to enhance the current understanding of the mechanisms responsible for generating both stochastic and deterministic components of the surface texture. Simulation work of the proposed modeling and control techniques will be based on actual parameters for the actuators and the cutting process, which is readily available in the literature (El-Sinawi et al., 2005). 2.4 THE EFFECT OF CUTTING TOOL VIBRATION ON SURFACE ROUGHNESS OF WORK PIECE IN DRY TURNING In the turning operation, vibration is a frequent problem, which affects the result of the machining, and, in particular, the surface finish. Tool life is also influenced by vibration. Severe acoustic noise in the working environment frequently occurs as a result of dynamic motion between the cutting tool and the work piece. In all cutting operations like turning, boring and milling, vibrations are induced due to the deformation of the workpiece. This implies several disadvantages economical as well as environmental Today the standard procedure to avoid vibration during machining is by careful planning of the cutting parameters. The methods are usually based on experience and trial and error to obtain suitable cutting data for each cutting operation involved in machining a product. Machining vibration exists throughout the cutting process. While influenced by many sources, such as machine structure, tool type, and work material. The composition of the machining vibration is complicated. However, at least two types of vibrations, forced vibration and self excited vibration, were identified as machining vibrations.

22 8 Forced vibration is a result of certain periodical forces that exist within the machine. The source of these forces can be bad gear drives, unbalanced machine-tool components, misalignment, or motors and pumps, etc. Self-excited vibration, which is also known as chatter, is caused by the interaction of the chip removal process and the structure of the machine tool, which results in disturbances in the cutting zone. Chatter always indicates defects on the machined surface; vibration especially self-excited vibration is associated with the machined surface roughness. The surface roughness can be affected by built up edge formation (Safeen Y. Kassab, 2007). 2.5 AISI D12 CARBON STEEL AISI D2 is a high-carbon, high-chromium tool steel alloyed with molybdenum and vanadium characterized by high wear resistance, high compressive strength, good throughhardening properties, high stability in hardening, and good resistance to tempering-back. The details of the material can be referred on figure 2.2 Figure 2.2: Element in AISI D 12

23 Application of AISI D 12 AISI D2 is recommended for tools requiring very high wear resistance, combined with moderate toughness (shock-resistance). AISI D2 can be supplied in various finishes, including the hot-rolled, pre-machined and fine machined condition. Table 2.1 shows the properties of AISI D12. Table 2.1: Properties table of AISI D12

24 EXISTING RESEARCH Before this, there a few researchers doing the same research but different in machining and material. They are using various techniques on how to detect chatter. For example using microphone as their sensor of chatter (T.L. Schmitz, K. Medicus, and B. Dutterer, 2002). When instability is reached, some other frequencies appear. The detection of peak at frequency different from spindle speed or tooth passing frequency is a way to detect chatter. The use of a microphone is simple and does not imply positioning problems as the other types of sensors (T. Insperger an Al., 2003) A New Method for Chatter Detection in Grinding A new method for automatic chatter detection in outer-diameter grinding is proposed which exploits significant changes in grinding dynamics caused by the onset of chatter. The method is based on monitoring of a non-linear statistic called the coarsegrained entropy rate. The entropy rate is calculated from the fluctuations of the normal grinding force. Values of the entropy rate close to zero are typical of chatter, whereas larger values are typical of chatter-free grinding. If the entropy rate is normalized, a threshold value can be set which enables automatic distinction between chatter-free grinding and chatter. The sketch of the experiment can be referred in figure 2.3.