DESIGN AND FABRICATION OF GRINDING ATTACHMENT FOR LATHE MACHINE TOOL

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1 DESIGN AND FABRICATION OF GRINDING ATTACHMENT FOR LATHE MACHINE TOOL Pratik Chavan 1, Sanket Desale 2, Ninad Kantela 3, Priyanka Thanage 4 Prasad Bari 5 1,2,3,4 B.E. Students, Fr. C Rodrigues Institute of Technology, Vashi Navi Mumbai, (India) 5 Assistant Professor, Department of Mechanical Engineering Fr. C Rodrigues Institute of Technology, Vashi Navi Mumbai, (India) ABSTRACT Grinding operation is performed to obtain a fine surface finish after performing turning operation on lathe machine for cylindrical jobs. This is done to obtain required dimensions of part to be used in any assembly. Thus to perform these two operations on same machine the attachment is designed. To verify the design the attachment is fabricated. This work describes an attempt to decrease the time in loading and unloading of workpeice with desired surface finish. The report describes the selection of wheel for grinding. It also considers the rigidity of design, damping of vibration due to motor speed and stress analysis of critical part of design, which is analyzed on INVENTOR software and compared with theoretical calculations. It also lists the various operations performed to fabricate the attachment. The results are obtained in form of tolerance limits which are compared with results of individual grinding machine operation on different machine and the conclusion are stated. Keywords: Grinding, Cylindricity, Rigidity I. INTRODUCTION Lathe has always been the mother of all machines before the invention of CNC machines. The turning operation on lathe is most frequently performed, and then it s transferred to grinding machine for fine surface finish. The time required to do this is generally high and loading and unloading of job causes human fautige. Thus combining these two operations on single machine would benefit and this led to think of grinding on lathe machine. The grinding operation is done using abrasive wheel, grinder which provides fine surface finish. The grinding wheel differs for different materials to be grinded which is made up of abrasives, bond, grit, grade and structure [1]. In this paper we have selected the required grinding wheel depending on workpeice to be used. The main aim of project is to obtain an accuracy of 20microns. Since grinding requires high surface finish thus proper motor speed is selected as required [2]. Since the motor will run at high rpm lot of vibrations will be generated, thus it will be necessary to damp these vibrations using damper [8].Additional to it appropriate rigidity should be provided to clamp the motor on lathe bed. 62 P a g e

2 II. SELECTION OF GRINDING WHEEL Grinding wheel is specified by its grit, grade and structure. For different type of work material and for different dimensions, the requirements of a grinding wheel are different. Thus it is important to select a proper grinding wheel. Following are some major specifications of grinding wheel. 1.1 Abrasives For high tensile strength the abrasive should be tough and should not get fractured easily. Thus Aluminium oxide was selected as an abrasive, assuming maximum work to be done on mild steel. 1.2 Grit Grit is grain size. Smaller the grit finer is the surface finish. For high stock removal rate and better control of surface finish Grain size should be Therefore grit is selected as Grade Grade is to define hardness of the bond holding the grains together. For better compromise between soft and hard bond so that wheel wear and cost will be less intermediate grade P is selected. 1.4 Structure Structure is the void spacing between the grains. Lesser the structure, higher is the density of grains on the wheel. Densely packed grains are required for fine cuts. Therefore structure is selected as Bond Bond is the type of adhesive used to hold grains together on the wheel. It depends on rate of stock removal, rigidity and required precision. For high stock removal, rigidity and suitable precision grinding vitrified bonds are preferred. Therefore V99 bond is selected. Selected wheel specification is A60P5V99 III. SELECTION OF MOTOR For this attachment, it is necessary to select drive with proper speed and torque. The dimensions of grinding wheel and speed of the motor are interrelated. For grinding wheel with 150mm diameter, desired speed is 2880 rpm. Thus 3phase AC motor with power of 0.75 HP and 2880 rpm is selected. IV. DESIGN To achieve the objective of this project some important issues must be focused which will guarantee accuracy of 20microns and desired fine surface finish. Following are three major issues 4.1 Absorption of Vibrations Due to a very high speed of motor, there are a lot of vibrations involved. Static deflection was found to be m. The effectiveness of the isolaton produced by the isolator is characterized by transmissibility which is defined as the ratio of force transmitted by an isolator to the exciting force due to machine. Selection of an isolator is done on the basis of damping ratio. Following graph shows the relation between transmissibility and damping ratios from the graph shown below, suitable damping ratio was found to be Thus rubber was selected as an isolator. 63 P a g e

Fig. 1 Relation between Transmissibility and Damping Ratio Table 1 Damping Ratios of Isolators. Material Damping Ratio Steel Spring 0.005 Natural Rubber 0.05 Neoprene 0.05 Elastomers 0.12-0.

And it was found necessary to clamp the motor. For clamping the lathe has cross slide which has provision of T slots. Thus an external attachment can easily be mounted on the cross slide.

3 Fig. 1 Relation between Transmissibility and Damping Ratio Table 1 Damping Ratios of Isolators. Material Damping Ratio Steel Spring Natural Rubber 0.05 Neoprene 0.05 Elastomers Glass fiber pad Composite pad Rigidity of Attachment Due to high speed of motor, rigidity of attachment becomes the major concern. The forces acting due to motor were calculated. And it was found necessary to clamp the motor. For clamping the lathe has cross slide which has provision of T slots. Thus an external attachment can easily be mounted on the cross slide. So that for feed and depth of cut extra efforts are not required. So the frame of mild steel was designed according to the dimensional constraints of the cross slide. Motor was to be mounted on this frame. Thus it was important to ensure the rigid clamping of motor on the frame. Four bolts which are holding the motor were simulated and tested for failure. Software analysis was verified by mathematical calculations. Thus ensured the rigidity of the attachment. Result of analysis is shown in Fig. 2 and Table 2. Fig. 2 Analysis of Bolts Holding Motor 64 P a g e

4 Table 2 Stress Analysis Particular Minimum Maximum Stress XX MPa MPa Stress XY MPa MPa Stress XZ MPa 0.009MPa Stress YY MPa MPa Stress YZ MPa MPa Stress ZZ MPa MPa 4.3 Cylindricity of Workpiece After ensuring the rigidity, next major concern was Cylindricity of workpiece. This was to maintain circular cross section area constant throughout the given length. To assure cylindricity the shaft axis of motor should be parallel to chuck axis of shaft. At the same time the linear motion of the wheel should also be parallel to axis. This was confirmed by maintaining parallelism in the surfaces. This was measured by dial gauges. The next factor that affect cylindricity is that the forces due to grinding will act on shaft thus any deflection in shaft will not result in perfect cylindricity. Thus to confirm the deflection analysis of shaft was made on INVENTOR software applying the calculated grinding forces. The deflection encountered was within tolerance limit and was confirmed with theoretical calculations. Thus deflection of shaft would not affect the cylindricity of workpeice. The calculation for maximum allowable depth of cut is as follows, The material removal rate is given by, MRR = v.d.b (1) = x d x 25 x 103 MRR = 625 x d mm3/sec Power = u x MRR (2) 740 = 35 x 625 x d d = 33.8 x 10-3 mm Therefore maximum depth of cut for grinding is 33.8 microns. V. FABRICATION 5.1 Frame Since the motor needs to be mounted on lathe carriage, it cannot be directly clamped, thus frame is fabricated. The frame size is constrained to 200*200*30 mm of MS due to space available on lathe carriage. A slot of 15mm deep is made using shaper machine. 8 holes of diameter 12mm are drilled to hold the frame in carriage with help of T-bolts. Additionally 4 more holes of diameter 10mm are drilled using vertical drilling machine. These 4 holes are used to mount the motor on the frame, and are countered bored using radial drilling machine to rest the bolt head in it. 65 P a g e

Fig. 3 Frame 5.2 Coupling The motor shaft and shaft on which wheel will be mounted are connected using flange coupling.

These hubs are fabricated using lathe machine and keyway are made using slotting machine. The keys are made of MS plate.

3 Shaft Standard shaft diameter of 19.05mm and length 80mm is manufactured using lathe by turning operation.

5 Fig. 3 Frame 5.2 Coupling The motor shaft and shaft on which wheel will be mounted are connected using flange coupling. Two flanges of outer diameter 60mm with 4 holes are used, to which external hub is welded so as to hold the shaft. These hubs are fabricated using lathe machine and keyway are made using slotting machine. The keys are made of MS plate. The hub is tapped for M6 Allen bolt on opposite side of key, this provides additional force to hold shaft firmly in hub. Fig. 4 Coupling 5.3 Shaft Standard shaft diameter of 19.05mm and length 80mm is manufactured using lathe by turning operation. Collar of diameter 30 mm and 5mm thickness is provided to hold the wheel firmly and restrict its motion. The other end of shaft has threads of M19 cut on it using lathe machine, so as to hold the grinding wheel properly from other end. Also bushes are used, because the inner diameter of wheel is 32mm. Keyway on shaft is made using shaper machine and finishing is obtained using needle file. Fig. 5 Shaft 66 P a g e

5.4 Layout After fabrication all the components are assembled. VI. CONCLUSION Fig. 6 Layout The attachment is fabricated and mounted successfully according to the proposed design.

6 5.4 Layout After fabrication all the components are assembled. VI. CONCLUSION Fig. 6 Layout The attachment is fabricated and mounted successfully according to the proposed design. After mounting the attachment there was a considerable reduction in the human effort required in loading and unloading the workpiece. This has also led to reduction in the lead time. By using the attachment an accuracy of upto 20 microns can be achieved with fine surface finish. VII. ACKNOWLEDGEMENT The authors would sincerely like to thank Mr. K.P.Rajesh, Superintendent, Central Workshop, FCRIT, Vashi and Mr.Moreshwar Kor, Instructor, Central Workshop, FCRIT, Vashi for their valuable guidance in fabrication. The authors would also like to thank Dr. S. M. Khot, Head of Department, Mechanical Engineering, FCRIT, Vashi for guiding us to have correct approach towards the project. REFERENCES [1]. S.K. and A.K. Hajra Choudhury and Nirjhar Roy Elements of workshop technology vol-2 machine tools, pp [2]. Gerling All about machine tools, skeep series vol-3 pp [3]. Design Data, PSG College of Technology. [4]. M. D. Dayal, Strength of Materials 3rd edition. [5]. Machine Shop, Joe Sullivan, 12/15/2000 Choosing the Right Grinding Wheel. [6]. Sterling Abrasive ltd Grinding Process, pp [7]. Prof J.S. Colton Manufacturing processes and systems Georgia Institute of Technology 2009, version 1 p [8]. Vibration calculation - [9]. Shaft stress calculation P a g e

Increase in productivity by attachment of grinding setup On lathe machine

Increase in productivity by attachment of grinding setup On lathe machine Prof.Aslam Hirani 1,Shohin Naik 2,Toufik Pathan 3,Vaibhav Patil 4, Swarupanand Lugade 5 1,2,3,4,5 Mechanical Engineering, Mumbai