UNIVERSITI TEKNIKAL MALAYSIA MELAKA

Transcription

1 UNIVERSITI TEKNIKAL MALAYSIA MELAKA STUDY ON DEEP CAVITY MACHINING USING EDM DIE SINKING This report submitted in accordance with requirement of the Universiti Teknikal Malaysia Melaka (UTeM) for the Bachelor Degree of Manufacturing Engineering (Manufacturing Design) with Honours. By MUHAMMAD AZFAR BIN ABDULLAH B FACULTY OF MANUFACTURING ENGINEERING 2008

2 UTeM Library (Pind.1/2007) UNIVERSITI TEKNIKAL MALAYSIA MELAKA BORANG PENGESAHAN STATUS TESIS* JUDUL: STUDY ON DEEP CAVITY MACHINING USING EDM DIE SINKING SESI PENGAJIAN : 2008 / 2009 Saya MUHAMMAD AZFAR BIN ABDULLAH (HURUF BESAR) mengaku membenarkan tesis (PSM/Sarjana/Doktor Falsafah) ini disimpan di Perpustakaan Universiti Teknikal Malaysia Melaka (UTeM) dengan syarat-syarat kegunaan seperti berikut: 1. Tesis adalah hak milik Universiti Teknikal Malaysia Melaka. 2. Perpustakaan Universiti Teknikal Malaysia Melaka dibenarkan membuat salinan untuk tujuan pengajian sahaja. 3. Perpustakaan dibenarkan membuat salinan tesis ini sebagai bahan pertukaran antara institusi pengajian tinggi. 4. **Sila tandakan ( ) SULIT TERHAD TIDAK TERHAD (Mengandungi maklumat yang berdarjah keselamatan atau kepentingan Malaysia yang termaktub di dalam AKTA RAHSIA RASMI 1972) (Mengandungi maklumat TERHAD yang telah ditentukan oleh organisasi/badan di mana penyelidikan dijalankan) Disahkan oleh: (TANDATANGAN PENULIS) Alamat Tetap: No 43, Jln Cempaka 14, Tmn Ros Mewah, Senawang, Seremban, Negeri Sembilan. Tarikh: 10 APRIL 2009 (TANDATANGAN PENYELIA) Cop Rasmi: Tarikh: * Tesis dimaksudkan sebagai tesis bagi Ijazah Doktor Falsafah dan Sarjana secara penyelidikan, atau disertasi bagi pengajian secara kerja kursus dan penyelidikan, atau Laporan Projek Sarjana Muda (PSM). ** Jika tesis ini SULIT atau TERHAD, sila lampirkan surat daripada pihak berkuasa/organisasi berkenaan dengan menyatakan sekali sebab dan tempoh tesis ini perlu dikelaskan sebagai SULIT atau TERHAD.

3 DECLARATION I hereby, declare this thesis entitled Study on Deep Cavity Machining Using EDM Die Sinking is the result of my own research except as cited in the reference. Signature : Author s Name : MUHAMMAD AZFAR BIN ABDULLAH Date : 10 APRIL 2009

4 APPROVAL This report is submitted to the Faculty of Manufacturing Engineering of UTeM as a partial fulfillment of the requirements for the degree of Bachelor of Manufacturing Engineering (Manufacturing Design) with Honours. The member of the supervisory committee is as follow:. EN. ABD. HALIM HAKIM BIN ABD. AZIZ Supervisor Faculty of Manufacturing Engineering

5 ABSTRACT Electric Discharge Machine (EDM) is one of advance machining process to cut the material. This project was discussed about the effectiveness of the debris affect on the material that has been cut. At the same time, I learn the process of the Electric Discharge Machine (EDM) Die Sinking (Sodick AQ35L) at EDM Lab. The project represents the illustration of the deep cavity machining on how the debris occurred. In introduction phase, the project indicates about the objectives of the project, scope of the project and problems statement. In literature review phase, the general operating of EDM can explain the process mechanism based on the amps and voltage of the machining. In final stage of the PSM I, there are some methodologies to accomplish the project such as data collection, research study and analyzing the data. For PSM II, the project has started to do practically after finishing all the literature review and methodologies. In experimental setup, there are some machining processes onto the study of deep cavity machining. Then enter to measurement processes which are all the data gathered to do the analysis of the project upon the influences between peak current, voltage and pulse time to evaluate the effect of the debris on the workpiece. i

6 ABSTRAK Mesin Menyahcaskan Elektrik (EDM) adalah salah sebuah pendahuluan memesin proses untuk memotong bahan. Projek ini telah dibincangkan mengenai keberkesanan debris terlibat atas bahan yang telah dipotong. Pada masa yang sama, saya belajar proses Mesin Menyahcaskan Elektrik (EDM) Die Sinking (Sodick AQ35L) di Makmal EDM. Projek ini mewakili contoh rongga dalam memesin mengenai bagaimana debris berlaku. Dalam fasa pengenalan, projek ini menunjukkan mengenai objektif projek, skop projek dan masalah-masalah kenyataan. Dalam fasa ulasan karya, keseluruhan operasi EDM boleh menerangkan mekanisma proses berdasarkan amps dan voltan memesin. Di peringkat akhir PSM saya, terdapat beberapa metodologi untuk mencapai projek ini seperti pengumpulan data, kajian penyelidikan dan menganalisis data. Untuk PSM II, projek ini telah mula dilakukan secara praktikal setelah menghabiskan semua ulasan karya dan metodologi. Dalam penyediaan eksperimen, terdapat sebahagian proses pemesinan ke atas kajian rongga dalam memesin. Kemudian di bahagian proses pengukuran dimana semuan data dikumpul untuk melakukan analisis projek di atas pengaruh antara arus puncak, voltan dan masa denyut untuk menilai kesan bagi debris pada bendakerja. ii

7 ACKNOWLEDGEMENT I would like to convey my appreciation and indebtedness to those who has been great surprised and helpful for the completion at the project to bring it to success in respect with favorable advice and feasible solution. Thank god to ALLAH S.W.T because have inspirit to finish up this project perfectly and just in time it s. I take this golden time to say appreciation to my supervisor, Mr. Abdul Halim Hakim guidance and his advice during this project is completed. He has also given criticisms which built and settlement process to solve problems which arise when making this project. This tribute is aimed also to Mr. Fauzi (CNC Lab Technician) And Mr. Fairuz (MRP Technician) because has given space in terms of time and machine utilization to together in achieving objective of this project. Do not forget also to compatriot mutually give constructive ideas and also as a morale support to together direct success in this study. Last but not least, I also said thank you to my beloved family because has lent a hand indirectly from start learning till end. Remember that without support from them all, this study will not achieve success. iii

8 TABLE OF CONTENTS TITLE PAGES ABSTRACT ACKNOWLEDGEMENT TABLE OF CONTENTS LIST OF FIGURES LIST OF GRAPHS LIST OF TABLES i iii iv vii ix x CHAPTER 1: INTRODUCTION 1.1 Background Objectives Scope of Project Problem Statement 5 CHAPTER 2: LITERATURE REVIEW 2.1 Introduction General Operating Principle of EDM Process Mechanism Illustration Illustration Illustration Illustration Illustration Illustration Illustration Illustration Illustration Advantages of EDM Limitation of EDM 21 iv

9 2.3 Dielectric Fluid The Types of EDM Usage Micro EDM EDM Drilling Wire EDM Abrasive Electro Discharge Grinding (AEDG) Electrode Copper Electrode Graphite Electrode Brass Electrode Stainless Steel Electrode EDM Machine (Die Sinker) Introduction 36 CHAPTER 3: METHODOLOGY 3.1 Introduction Research Methodology Literature Review Understanding the EDM Die Sinking and the Parameter Tool and Workpiece Preparation EDM Parameter Setup and Data Collection Measurement Process and Data Collection Discussion, Recommendation and Conclusion Submitted Thesis and Final Presentation 45 CHAPTER 4: EXPERIMENTAL SETUP 4.1 Overview of the experiment Experimental Equipment and Apparatus EDM Machine Machine Construction and Nomenclature Description of Machine Components EDM Machine Specification Dielectric Tank Specification 53 v

10 4.3 Copper Tool Tool Properties Workpiece Workpiece Preparation Machining Process Experimental Procedure for EDM Measurement Equipment Dimensional Accuracy D Scanner Surface Roughness Measurement 66 CHAPTER 5: RESULT AND DISCUSSIONS 5.0 Data Collections Dimensional Accuracy on CMM Dimensional Accuracy on Laser FaroArm Scanner Surface Roughness Side Overcut 79 CHAPTER 6: CONCLUSIONS AND RECOMMENDATIONS 6.1 Conclusions Recommendations in the Future Work 84 REFERENCES 85 APPENDICES 87 vi

11 LIST OF FIGURES 1 Figure 2.1.1: Diagram of EDM Die Sinking Machine 7 2 Figure 2.2.1: Electrical discharge machine 10 3 Figure 2.2.2: Schematic of EDM process 11 4 Figure : The voltage increased in die electric fluid 15 5 Figure : The voltage is constant for the time being 15 6 Figure : The current start to increased 16 7 Figure : The spark occur at heat vaporized 16 8 Figure : The spark rise extremely 17 9 Figure : The current and voltage is stabilized Figure : The temperature decrease rapidly Figure : Quenching the surface Figure : The metal solidifies into tiny spheres Figure 2.3.1: Diagram of EDM machine Figure 2.3.2: Combination of Dielectric Oil Figure 2.4.1: Micro Electrical Discharge Machine (MEDM) Figure 2.4.2: Drilling Electric Discharge Machine Figure 2.4.3: Wire Electric Discharge Machine (WEDM) Figure 2.4.4: Abrasive Electro Discharge Grinding (AEDG) Figure 2.6.1: EDM Die Sinker (Sodick AQ35L) Figure 2.6.2: Nomenclature of EDM Die Sinker (Sodick AQ35L) Figure 3.2: Process Flow of Project Methodology Figure 3.4: Nomenclature of EDM Die Sinker (Sodick AQ35L) Figure 3.7.1: Platinum FaroArm Scanner Figure 3.7.3: Coordinate Measuring Machine (CMM) Figure 4.2.1: Sodick(NC Electrical Discharge Machine)model AQ35L Figure 4.2.2: Nomenclature of EDM Die Sinker (Sodick AQ35L) Figure 4.3: Copper Electrode Figure 4.4: Aluminum material Figure : Band Saw Machine Figure : End Mill process 56 vii

12 31 Figure : Aluminum is ready for machining Figure : Setup the height of the machining Figure : Start machining Figure : Coordinate Measuring Machine (CMM) at left side and Platinum FaroArm Scanner at the right side Figure : Coordinate Measuring Machine (CMM) Figure : Platinum FaroArm Scanner Figure : Laser scanning operation Figure : Point phase unordered point multiple scan Figure 4.6.3: Portable Surface Roughness Tester SJ Figure 5.2.1: Reducing noise using Geomagic Studio software Figure 5.2.2: Analysis for dimensional accuracy using Geomagic Studio software Figure 5.3.1: The surface roughness of depth 2mm of specimen 1. Ra = Figure 5.3.2: The surface roughness of depth 2mm of specimen 2. Ra = Figure 5.3.3: The surface roughness of depth 2mm of specimen 3. Ra = Figure 5.3.4: The surface roughness of depth 3mm of specimen 1. Ra = Figure 5.3.5: The surface roughness of depth 3mm of specimen 2. Ra = Figure 5.3.6: The surface roughness of depth 3mm of specimen 3. Ra = Figure 5.3.7: The surface roughness of depth 4mm of specimen 1. Ra = Figure 5.3.8: The surface roughness of depth 4mm of specimen 2. Ra = Figure 5.3.9: The surface roughness of depth 4mm of specimen 3. Ra = Figure 5.4: Diagram of side overcut. 79 viii

13 LIST OF GRAPHS 1 Graph 5.1: Dimensional accuracy versus parameter on Coordinate Measuring Machine 69 2 Graph 5.2: Dimensional accuracy versus parameter on Laser FaroArm Scanner 73 3 Graph 5.3: Surface roughness versus parameter 78 4 Graph 5.4.1: Side Overcut vs. Parameter (Coordinate Measuring Machine) 81 5 Graph 5.4.2: Side Overcut vs. Parameter (Laser FaroArm Scanner) 82 ix

14 LIST OF TABLES 1 Table 2.5.1: Properties of Copper Electrode 32 2 Table 2.5.2: Properties of Graphite Electrode 33 3 Table 2.5.3: Properties of Brass Electrode 34 4 Table 2.5.4: Properties of stainless steel 35 5 Table 2.6.1: Part name of the basic components 38 6 Table 4.2.2: Basic Components of EDM Machine 48 7 Table 4.2.4: EDM Sodick Die Sinking 51 8 Table 4.2.5: CNC Power Supply Specification 52 9 Table 4.2.5: Dielectric Tank Specification Table 4.3.1: Properties of Copper Electrode Table 5.0: Result after Electric Discharge Machining Table 5.1: Dimensional accuracy on coordinate measuring machine Table 5.2.1: Dimensional accuracy on depth 2mm Table 5.2.2: Dimensional accuracy on depth 3mm Table 5.2.3: Dimensional accuracy on depth 4mm Table 5.3: Surface roughness of the specimen Table 5.4.1: Side Overcut on Coordinate Measuring Machine Table 5.4.2: Side Overcut on Laser FaroArm Scanner 80 x

15 CHAPTER 1 INTRODUCTION 1.1 Background Today s society could not exist without modern manufacturing and production techniques. In fact, one of the indicators used to measure a country s economic strength is its manufacturing and production capability. Mass production with interchangeable parts is vital to our standard living. One cannot even imagine the difficulty involved in making an automobile, a modern tractor used on a farm, or a commercial aircraft if all the parts had to be made by hand. Without modern manufacturing methods, we could not even the present population. Electrical Discharge Machining (EDM) is a non-traditional manufacturing process based on removing material from a part means of a series of repeated electrical discharges between a tool, called electrode, and the part being machined in the presence of a dielectric fluid. There are many of parameters that must to indicate such as surface roughness, semi-finish machining and finishing. But in this research, I will come out the patent (debris) upon the work piece based on the current signal. EDM is using electric sparks to remove certain material from the metal. An electrode is lowered into dielectric fluid where the piece of metal being cut is submerged. The electrode can be made of carbon, brass, or bronze. Brass and bronze are the better material to use for electrodes because unlike carbon, they won t break. The electrode is used to connect to the metal to conduct a large enough electric potential to create a spark that would remove material from the metal. The electrode is constantly fed down to the work piece at a certain rate to maintain a constant gap. Plus, a hose that discharge dielectric field is constantly used after a cut 1

16 to remove excess material. The most important parameters in this lab are the spark frequency (which is proportional to gap voltage) and the discharge current. If either one of those parameter are increased, the removal rate of metal increases but also the roughness of the job. EDM is a nontraditional machining process since it does not remove material with a cutting tool. It is used on materials that are extremely hard or and brittle, the features to be made are extremely complex or small, and also the temperature rise or stress in the work piece can not be tolerated. There is a voltage gap between the electrode and the work piece that form the spark vaporizes minute particles of the work piece material, which is then washed out from the gap by the continuously flushing dielectric fluid. The two main types of the EDM are Ram and Wire cutting. EDM is a diverse process that produces products ranging from tiny electric connectors, medical parts, and automatic stamping dies and aircraft body panels. EDM has replaced much of the machining, grinding steps needed in die making which represents the largest single use of EDM. Die component cut with EDM can often be made in a single piece no matter how complex the internal form. The single piece die are always stronger than those made of segments. Die cut are from hardened steel, heat-treated steel, carbide. Other materials that can be EDM are polycrystalline diamond, titanium, hot rolled and cold rolled steel, copper, brass and high temperature alloys. 2

17 1.2 Objectives The overall objective of this study is to find the fundamental process for deep cavity machining using Electric Discharge Machine (EDM). The study will look at the fundamental relationship of the machining parameter or process variable and the workpiece parameters. The machining parameter involves are machining ON time and OFF time (Pulse Time), servo voltage (SV) and peak current (IP). While the workpiece parameter involve is the effect of debris in dimensional accuracy. Beside that, the study also observes the problem that occurs during machining. Specific objective of the proposed study are: 1. To study the influence of process parameter on dimensional accuracy of deep cavity machining. 2. To investigate the effect of debris on deep cavity machining. 3. To study the surface texture under the influence of debris machining. 4. To study the effect of debris machining based on surface roughness on the workpiece. 3

18 1.3 Scope of the Project The scope of this project is to establish an optimum machining condition for deep cavity machining. 1. Current and voltage of EDM machine a. Voltage and current in the gap define electric power in the gap (P=UI). There exists the optimal set of the setup parameters' values to obtain the certain power in the gap and the discharge voltage is nearly constant at all machining regimes, thus the power in the gap depends only on the current in the gap. In the literature, the boundary surface current density is given rather then boundary surface power density and it is stated that stable EDM process is achieved when the surface current density is less than 0.1 A. 2. Dimensional accuracy a. Surface Texture To get good surface texture, there are some parameters to consider. When the charge electrode near the workpiece, the spark will occur and produce debris which affected the surface texture of the workplace. In this experiment, there are some factors to study such as the current and voltage and also the surface roughness. 4

19 1.4 Problem Statement To establish an optimum condition for deep cavity machining: 1. Debris Machining The debris movement caused by the electrostatic force in the narrow gap filled with the dielectric liquid in the EDM process. It happen when the pump provides pressure for flushing the work area and moving the oil while the filter system removes and traps the debris in the oil. Debris would collect making the spark unstable. This situation could create a DC arc which can damage the electrode and the workpiece. 2. Machining Guide In our labs, there is no specific guide or references about debris machining. 5

20 CHAPTER 2 LITERATURE REVIEW 2.1 Introduction In electric-arc welding, the electric arc melts the metal where the arc hits it. If that melted could be removed continuously, a separating process would occur. The process removing metal with an electric arc is called electric discharge machine (EDM). One of newer manufacturing processes, EDM allows us to perform some operations that are nearly impossible to do any other way. Electrical Discharge Machining (EDM) is a machining method primarily used for hard metals or those that would be impossible to machine with traditional techniques. One critical limitation, however, is that EDM only works with materials that are electrically conductive, and generally those materials are ferrous alloys. EDM can cut small or odd-shaped angles, intricate contours or cavities in pre-hardened steel without the need for heat treatment to soften and re-harden them as well as exotic metals such as titanium, hastelloy, kovar, and inconel. I.Puertas (2003). Sometimes referred to as spark machining or spark eroding, EDM is a non-traditional method of removing material by a series of rapidly recurring electric arcing discharges between an electrode (the cutting tool) and the workpiece, in the presence of an energetic electric field. The EDM cutting tool is guided along the desired path very close to the work but it does not touch the piece. Consecutive sparks produce a series of micro-craters on the work piece and remove material along the cutting path by melting and vaporization. The particles are washed away by the continuously flushing dielectric fluid. It is also important to note that a similar micro-crater is formed on the surface of the electrode, the debris from which must also be flushed away. These micro-craters result in the gradual erosion of the electrode, many times necessitating several different electrodes of varying tolerances 6

21 to be used, or, in the case of wire EDM machining, constant replacement of the wire by feeding from a spool. W. Koenig (1998). Electrical discharge machining or EDM is a thermal erosion process in which the work piece material is removed through a series of rapidly reoccurring electrical discharge between electrode (cutting tool) and an electrical conductive work piece in a presence of a dielectric fluid. Figure 2.1.1: Diagram of EDM Die Sinking Machine The process of EDM has many benefits since the work piece and electrode never touch, no cutting forces are generated this makes EDM will suited to produce fragile parts that can not take the stress of conventional machining, burr free edges, intricate details, superior surfaces. EDM process eliminates the risk of damaging expensive work pieces, allows heat treatment before final machining. Final EDM tools with build in process knowledge helps reduce the training workers need to produce complex parts. The EDM process also has its limitations. The metal removal rates are low compared to conventional metal cutting processes. Complex materials require leadtime for fabrication and are consumable while cutting and the work piece materials must be conductive. The basic components of the electrical discharge machine are relatively simple. The electrode is attached to the RAM, which is connected to one 7

22 pole of the electric power supply. The work piece is connected to the other power supply. The work piece is then positioned so that there is a small piece between work piece and electrode. This gap is flooded with dielectric fluid which acts as insulator until the power is turned out. Once on, the machine delivers thousands of electric pulses per second to the gap and erosion begins. The sparks are generated at on time but it ranges from 100s up to 1000s of time per second. Each spark has a temperature of 1400 up to degrees Fahrenheit. As erosion continues the machine control advances the electrode through the material and is containing a constant gap distance. To understand how EDM removes the material lets examine a single spark in the erosion process. As a pulse of DC Electricity reaches the electrode and part an intense electric field develops in the gap, microscopic contaminates suspended in the dielectric fluid are attracted by the field and concentrated in the field s strongest point. These contaminates builds a high conductivity along the gap as the field s voltage increases. These materials in the conductive bridge heat up. Some pieces ionize to form a spark between the electrode and the work piece. At this point the both the temperature and pressure in the channel increase generating a spark. A small amount of the material melts and vaporizes from the material and the work piece at the point of spark contact. A bubble composed of gaseous by products vaporize rapidly expands rapidly outward from the spark generated. Once the pulse ends the spark and the heating action stop collapsing the spark channel. Dielectric fluid then rushes into the gap forcing melted material out from the surfaces. This EDM residue consists of solidified parts of material and gas bubbles. The resulting EDM cut can have several observable surface layers. The top surface is created when expelled molten material and small amount of electrode material melt forms spheres on part of the surfaces, this layer is easily removed. The next layer is a recast or white layer as EDM has altered the piece metallurgical structure. This layer can be reduced by using the right settings or by polishing the part. The third layer is the heat affected zone or annealed layer. It has been only heated not melted. The part surface is a function of EDM cycles that has on time and off time expressed in microseconds. All work occurs during the on time so pulse duration and the number of cycles per second. The sum of on time and off time is 8

23 important. Metal removal is proportion to the amount of energy during on time that energy is controlled by the time variables. The peak Amperage or intensity of the spark and the length of the on time. The larger the on time the more the metal erodes. It may also produce a larger recast layer and a deeper heat affected zone. Off time also affects speed and stability of the EDM cut. Too shorten off time; the ejected material will not flood easily with the dielectric fluid. The next spark may then be not stable. The duty cycle is the percentage of on time relative to the total cycle time. The higher the duty cycle means increased cutting efficiency. Gap distance between work piece material and the electrode also impact the material removal rate. Generally the smaller the gap the better the accuracy and the surface finish are and the metal removal rate is. The EDM cavity is always larger than the electrode with the difference called the Kerf. The average off time and on time increases also the over cut. It is important to know the expected over cut during EDM because the electrode can probably be under sized. 9

24 2.2 General Operating Principle of EDM Electrical discharge machining (EDM) is one of the most widely used nontraditional machining processes. The main attraction of EDM over traditional machining processes such as metal cutting using different tools and grinding is that this technique utilizes thermoelectric process to erode undesired materials from the workpiece by a series of discrete electrical sparks between the workpiece and the electrode. A picture of EDM machine in operation is shown in Figure Figure 2.2.1: Electrical discharge machine The traditional machining processes rely on harder tool or abrasive material to remove the softer material whereas non-traditional machining processes such as EDM uses electrical spark or thermal energy to erode unwanted material in order to create desired shape. So, the hardness of the material is no longer a dominating factor for EDM process. A schematic of an EDM process is shown in Figure 2.2.2, where the tool and the workpiece are immersed in a dielectric fluid. 10