A STUDY ON TOOL DEFLECTION DURING DEEP POCKETING CYCLE ZIKRULHAKIM BIN MUHD ZAHID

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1 i A STUDY ON TOOL DEFLECTION DURING DEEP POCKETING CYCLE ZIKRULHAKIM BIN MUHD ZAHID Report submitted in fulfilment of the requirements for the award of the degree of Bachelor of Manufacturing Engineering FACULTY OF MANUFACTURING ENGINEERING UNIVERSITI MALAYSIA PAHANG JUNE 2013

2 v ABSTRACT Tool deflection during deep pocketing cycle will cause tapper in mould and die. This problem can cause defect on final product and also increases cost and time wasting in manufacturing process. This study basically shows a detailed study to overcome tapper problem in deep pocket. Dimensional accuracy due to tapper problem was analyzed in order to obtain optimum cutting parameters. The pocket part was drawn by using CATIA software. The data collected during experiment was analyzed using signal to noise ratio through Minitab software. From the analysis, it was found that depth of cut has gives the most effect on tapper problem, followed by feed rate and spindle speed. From the result, it is shown that level 1 of depth of cut which is 0.3mm, level 1 of feed rate which is 64mm and level 2 of spindle speed which is 1280rpm was the best cutting parameter. Hence, from these cutting parameters, the tapper problem cause by tool deflection during deep pocketing cycle can be overcome.

3 vi ABSTRAK Pembiasan alat semasa pusingan pempoketan dalam akan menyebabkan ketidakrataan di dalam acuan. Masalah ini akan menyebabkan kecacatan pada produk akhir yang akan meningkatkan kos dan pembaziran masa ketika proses penghasilan. Kajian ini pada asasnya menunjukkan kajian terperinci untuk menangani masalah ketidakrataan di dalam poket. Ketepatan ukuran pada masalah ketidakrataan akan dianalisis untuk mendapatkan rujukan pemotongan paling optimum. Bahagian poket dilukis dengan menggunakan perisian CATIA. Data yang diambil semasa eksperimen telah dianalisis menggunakan nisbah signal kepada noise melalui perisian Minitab. Daripada analisis, ia telah mendapati bahawa kedalaman potongan telah member kesan yang paling tinggi terhadap masalah ketidakrataan, diikuti oleh kadar memotong dan kelajuan mata. Daripada keputusan analisis, ia telah menunjukkan bahawa kedalaman potongan pada tahap 1 iaitu 0.3mm, kadar memotong pada tahap1 iaitu 64mm/min dan kelajuan mata pada tahap 2 iaitu 1280rpm adalah rujukan pemotongan terbaik. Maka, daripada rujukan pemotongan ini, masalah ketidakrataan yang disebabkan oleh pembiasan alat semasa pusingan pempoketan boleh diselesaikan.

4 vii TABLE OF CONTENT Page SUPERVISOR S DECLARATION STUDENT S DECLARATION DEDICATION ACKNOWLEDGEMENT ABSTRACT TABLE OF CONTENTS TABLE OF FIGURES TABLE OF TABLES APPENDICES i ii iii iv v vii x xii xiv CHAPTER 1 Introduction 1.0 Project Title Project Objectives 1

5 viii 1.2 Project Scopes Project Background Problem Statement 2 CHAPTER 2 Literature Review 2.0 Introduction Milling Machine Milling Parameter Feed Rates Cutting Speed Tool Path Spiral Tool Path Zigzag Tool Path Zigzag Tool Path Requirement Machining Strategy Pocketing Strategy Process Planning 15

6 ix 2.5 Cutting Tools Uncoated Carbides Coated Carbides Mild Steel 18 CHAPTER 3 Methodology 3.1 Flow Chart Selection Of Cutting Parameters Calculation Work Piece Material Used Cutting Tool Used Design of Experiment Experimental Procedure Recommendation Conclusion 31

7 x CHAPTER 4 Result and Discussion 4.1 Introduction Data analysis Measuring process Collecting data Data analysis Spindle speed Depth of cut Feed rate Surface plot Dimension vs spindle speed and depth of cut Dimension vs spindle speed and feed rate Dimension vs depth of cut and feed rate Optimum parameters Summary 47

8 xi CHAPTER 5 Conclusion 5.1 Conclusion Recommendation 50 REFERENCES 51 TABLE OF FIGURE CHAPTER 1 Figure No Dimensional different between upper part and lower part Tool deflection during deep pocketing cycle 4 CHAPTER 2 Figure No Spiral in and spiral out 10

9 xii 2.2. One-way and zigzag Pocket shape and tool path pattern Pocket shape and semi-finishing strategy 15 CHAPTER 3 Figure No Dimension for raw material Design of end mill Cross section of the pocket 27 CHAPTER 4 Figure No. 4.1: Deep pocket part : Upper part measurement : Lower part measurement : Wall measurement : SN ratio graph for spindle speed (A) : Line graph for dimension against spindle speed 38

10 xiii 4.7: SN ratio graph for depth of cut (B) : Line graph for dimension against depth of cut : SN ratio graph for feed rate (C) : Line graph for dimension against feed rate : Surface plot for dimension versus A and B : Surface plot for dimension versus A and C : Surface plot for dimension versus B and C : Graph dimension against depth of cut 47 TABLE OF TABLE CHAPTER 2 Table No Recommended feed rate Recommended cutting speed 9 CHAPTER 3 Table No.

11 xiv 3.1. TiAIN end mill properties Experimental variables 25 CHAPTER 4 Table No Domain of the experiment : Table of result : SN ratio of dimension : Optimum parameters 46 APPENDICES APPENDIX A 52 Appendix A1 53 Appendix A2 54 APPENDIX B 55 Appendix B1

12 1 CHAPTER 1 INTRODUCTION 1.0 Project Title A study of tool deflection during deep pocketing cycle. 1.1 Project Objectives To overcome tool deflection during deep pocketing cycle Come out with best cutting parameter 1.2 Project Scopes In order to achieve the project objective, this project needs a proper plan. The project scopes as shown below. i. Study on cutting tools in milling process for pocketing. ii. Initial study about cutting parameters in milling. iii. Study on tool path during pocketing process.

13 2 1.3 Project Background Pocketing process is widely used in producing mould and die. The advance of modern technology and a new generation of manufacturing equipment, particularly computer numerical control (CNC) machine, have brought enormous changes to the manufacturing sector. Generally, the handbook or human experience is used to select convenient machine parameters in manufacturing industry. In process planning of pocketing process, selecting reasonable milling parameters is necessary to satisfy requirements involving machining economics, quality and safety. In every machining process, defects on final product always occur either surface roughness or dimensional accuracy. Meanwhile in pocketing process, tool deflection will occur during the process and will affect dimensional accuracy of final product. Hence, this study is to overcome the tool deflection problem and come out with the best machining parameters at the end of this project. The machining parameters in milling operations consists of cutting speed, depth of cut, feed rate and number of passes. These machining parameters significantly impact on the cost, productivity and quality of machining parts. The effective optimizations of these parameters affect dramatically the cost and production time of machined components as well as the quality of final products. 1.4 Problem Statement One of the milling processes is pocketing. It is usually to machined mould and die. But it is always comes with tool deflection problem (Figure 1.1 and Figure 1.2). This problem logically can affect entire product that being produce. The defect on products can be costly for manufacturers and its need the best solution to overcome the tool deflection problem. Establishment of efficient machining parameters has been a problem that has confronted manufacturing industries for nearly a century, and is still

14 3 the subject of many studies. Optimum machining parameters are of great concern in manufacturing environments, where economy of machining operation plays a key role in competitiveness in the market. 100mm 99.8m m Figure 1.1: Dimensional different between upper part and lower part Figure 1.2: Tool deflection during deep pocketing cycle

15 4 CHAPTER 2 LITERATURE REVIEW 2.0 Introduction Milling is a process to remove material on work piece. There are several type of milling process such as pocketing, drilling, and face milling. Pocketing clears an area bounded by specified entities such as lines, arc, and free form curves, which constitute outer periphery with or without island. There are rectangular shape, circular shape and inclined shape of pocketing. During deep pocketing, tool deflection occurs and causes the different in measurement between inner and outer part. 2.1 Milling Machine Milling is the process of machining flat, curved, or irregular surfaces by feeding the work piece against a rotating cutter containing a number of cutting edges. The usual mill consists basically of a motor driven spindle, which mounts and revolves the milling cutter, and a reciprocating adjustable worktable, which mounts and feeds the work piece.

16 5 Milling machines are basically classified as vertical or horizontal. These machines are also classified as knee-type, ram-type, manufacturing or bed type, and planer type. Most milling machines have self-contained electric drive motors, coolant systems, variable spindle speeds, and power-operated table feeds. [1] A milling machine is a machine tool that cuts metal with a multiple-tooth cutting tool called a milling cutter. The work piece is fastened to the milling machine table and is fed against the revolving milling cutter. The milling cutters can have cutting teeth on the periphery or sides or both. Milling machines can be classified under three main headings: (i) General Purpose machines - these are mainly the column and knee type (horizontal & vertical machines). (ii) High Production types with fixed beds- (horizontal types). (iii) Special Purpose machines such as duplicating, profiling, rise and fall, rotary table, planetary and double end types. Milling attachments can also be fitted to other machine tools including lathes planning machines and drill bench presses can be used with milling cutters. Milling machine is one of the most versatile conventional machine tools with a wide range of metal cutting capability. Many complicated operations such as indexing, gang milling, and straddle milling can be carried out on a milling machine. [2] 2.2 Milling Parameter Optimum machining parameters are of great concern in manufacturing environments, where economy of machining operation plays a key role in competitiveness in the market. Due to high capital and machining costs of the NC

17 6 machines, there is an economic need to operate NC machine as efficiently as possible in order to obtain the required pay back. The success of the machining operation will depend on the selection of machining parameters. A human process planner selects the proper machining parameters using his own experience or from the handbooks on the part geometry, technological requirement, machine tool, a cutting tool and the part material. These parameters do not give optimal result. The effective optimizations of these parameters dramatically minimize the cost and production time of machined components as well as the increase the quality of the final product. [3,4] Feed Rate Feed rate is the velocity at which the cutter is fed, that is, advanced against the work piece. It can be expressed thus for milling also, but it is often expressed in units of distance per time for milling (millimeters per minute), with considerations of how many teeth (or flutes) the cutter has then determining what that means for each tooth. Feed rate is dependent on the: Type of tool Surface finish desired Power available at the spindle Rigidity of the machine and tooling setup Strength of the work piece Characteristic of the material being cut, chip flow depends on material type and feed rate. The ideal chip shape is small and breaks free early, carrying heat away from the tool.

18 7 This formula can be used to figure out the feed rate that the cutter travels into or around the work. This would apply to cutter on a milling machine (Table 2.1). [2] = (1) Where: FR = the calculated feed rate in inches per minute or mm per minute. RPM = is the calculated speed for the cutter T = number of teeth on the cutter CL = the chip load or feed per tooth. This is the size of chip that each tooth of the cutter takes. Table 2.1: Recommended feed rate Type of milling Feed rate (mm/min) Face milling Corner milling Pocket milling Slot milling Slot milling (Source: Courtesy of N.Baskar, P. Asokan, R. Saravanan, G. Prabhaharan (2006). Selection of optimal machining parameters for multi-tool milling operations using a memetic algorithm.)

19 Cutting Speed Cutting speed may be defined as the rate (or speed) that the material moves past the cutting edge of the tool, irrespective of the machining operation used the surface speed. A cutting speed for mild steel is 100ft/min (30meters/min). The hardness of the cutting tool material has a great deal to with the recommended cutting speed. The harder the cutting tool, the faster the cutting speed. The softer the cutting tool material, the slower the recommended cutting speed. For a given material there will be an optimum cutting speed for a certain set of machining conditions, and from this speed the spindle speed (RPM) can be calculated. Factors affecting the calculation of cutting speed are: The material being machined The material the cutter is made from. The economical life of the cutter. Cutting speeds are calculated on the assumption that optimum cutting condition exist (Table 2.2), these include: Metal removal rate Full and constant flow of cutting fluid Rigidity of the machine and tooling setup Continuity of cut Condition of material

20 9 Table 1.2: Recommended cutting speed Type of milling Cutting speed (m/min) Face milling Corner milling Pocket milling Slot milling Slot milling (Source: Courtesy of N.Baskar, P. Asokan, R. Saravanan, G. Prabhaharan (2006). Selection of optimal machining parameters for multi-tool milling operations using a memetic algorithm.) 2.3 Tool Path Milling is one of the most widely used metal removal processes. Pocket milling clears an area bounded by a set of specified entities such as lines, arcs, and free-form curves, which constitute outer periphery with or without islands. The machining sequence may be either in the order of entities selected or in reverse order. Types of pockets include rectangular, circular, and inclined. Based on the contour shapes and machining methods, pocketing tool paths are classified into spiraling and zigzag types. Although there are many possible ways of planning a tool path in pocket-milling operation, traditionally contour augmentation (spiral) and zigzag (or staircase) milling, have been the two standard procedures practiced. Zigzag or staircase milling involves the movement of the tool in a number of parallel passes to cover an entire area of the polygon to be machined.[3]

21 Spiral Tool Path To generate spiral tool path, the boundary profile are streaked inwards while the island profiles outwards using the appropriate steps. In spiral-out option, the tool paths track from the centre of pocket to the outer boundary of the pocket, whereas in spiral-in option, the tool-path track from the outer boundary of the pocket towards the centre inwardly, as in Figure 2.1. Contour augmentation (spiral) milling method requires a relatively larger tool overlap between successive passes to avoid the undercut projections on the surface of the polygon. This results in an increased length of the tool path, and consequently, machining time. [5] Figure 2.1: Spiral in and spiral out Zigzag Tool Path In the zigzag method of pocketing, the tool paths generated are parallel to a predefined vector direction and the tool moves back and forth. This method is used when a machine tool has a preferred direction of cut, like along the major axis of machine or the grain direction of the material calls for a particular direction of machining. One way machining, the tool always cuts the material in one way, along or against the spindle

22 11 direction in the entire process as in Figure 2.2. The offset chains of pocket entities are intersected with a sequence of equidistant parallel lines, curves and arcs, which are oriented along the selected direction of cut. In successive zigzag method, machining takes place bidirectional parallel to a selected axis. In bidirectional milling, the cutting edge changes alternatively left and right sided, up milling and climb milling. Zigzag (staircase) milling requires more number of stops and turns, requiring more machining time. [5, 6] Figure 2.2: One-way and Zigzag Zigzag Tool Path Requirement Generally accepted user requirements of a zigzag machining include efficient machining using minimum machining time, fine surface quality without tool marks, and no gouge against boundary curves. Considering the above functional requirements, tool- path generation algorithm developed in this study includes the following [5]: (i) Minimization of tool retractions. Tool retractions cause non-cutting tool motions in the air and tool marks on the machined surface. These types of motions have to be minimized.

23 12 (ii) Minimization of tool-path elements At the end of tool path elements, the feed rate should be slowed to avoid machining error caused by rapid change of feed direction. Minimizing the number of tool-path elements improves both productivity and quality of machined parts. (iii) Maximization of average tool-path length Tool-path elements having longer length allow constant feed rate and direction, which in turn improves surface quality. (iv) Technological requirements The tool-path planning system should be able to adapt to the various technological requirements or constraints such as one way milling or zigzag milling and up or down milling. (v) Motion along boundary curve Linear tool motion between tool-path elements may cause gouging at the sharp vertices of boundary curves and which has to be checked. 2.4 Machining Strategy Most computer aided manufacturing (CAM) systems have predefined pocketing routines which require selection of axial and radial depth of cut, and the starting point and directions of the tool path for each layer of cut. Tool paths may start from the center

24 13 of the pocket towards walls with zigzag and lace paths which are all based on the geometric relationship between the cutter and pocket features. The material removal rate is defined by the product of depth and width of cut, spindle speed and feed, which are presently selected based on trials and past experience. Some researchers manipulated the feed rate to increase the material removal rate while respecting cutting force and power limits along the tool path. However, incorrect spindle speed, axial and radial depths of cut cause chatter vibrations and leaves poor surface finish. [7] Pocketing strategy The pocketing requires identification of cutting conditions (radial and axial depth of cut, spindle speed and feed) and tool path strategy to be used by the CAM system. The objective is to determine the most time optimal strategy with highest material removal rate (MRR) without violating the chatter, torque and power limit of the machine tool. Although the pocket geometries vary significantly depending on the part and die/mold features, two basic pocket shapes are considered here to develop a general pocketing strategy [7].

Chapter 24 Machining Processes Used to Produce Various Shapes.

Chapter 24 Machining Processes Used to Produce Various Shapes. 24.1 Introduction In addition to parts with various external or internal round profiles, machining operations can produce many other parts