Part Storage System Carousel of Vtl by Low Cost Automation

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Part Storage System Carousel of Vtl by Low Cost Automation
  Proceedings of the 2 nd  International Conference on Current Trends in Engineering and Management ICCTEM -2014 17 – 19, July 2014, Mysore, Karnataka, India   239 PART STORAGE SYSTEM (CAROUSEL) OF VTL BY LOW COST AUTOMATION MALATESHA S KRISHNA 1 , KRISHNAMURTHY L 2 , AJITH KUMAR G 3 , PRAKASH K R 4 1, 2, 4 (Department of Mechanical Engineering, the National Institute of Engineering, Mysore, India) 3 (Design and Development, Ace Designers Private Limited, Bangalore, India) ABSTRACT Part storage systems (carousel) are the enablers for unattended cell operation. Unattended time of the manufacturing cell depends upon the ability of the storage system to store the number of unfinished part. Using conventional methods like circular and square layouts it is difficult to increase the storage capacity. This paper mainly addresses the concept of increasing the storage capacity of Inverted Vertical Turret Lathe by using layouts of different shapes by using double rod cylinder with hook mechanism. It has been proposed in this paper, to employ this concept to reduce the number of cylinders required and other hardware components which would lead to low cost automation. Keywords: Computer Numerical Control (CNC), Part Storage System (Carousel), Vertical Turret Lathe (VTL).  I. INTRODUCTION Computer Numerical Control (CNC) Lathes are classified into two types; Vertical and Horizontal. Many modern horizontal CNC turning centers are of the slant bed design. Advantage of the slant bed includes: easy access for loading and unloading and measuring; allowance for the chips to fall free; minimum floor space utilization; easy and quickness of tool change; better strength and rigidity [1]. Vertical CNC turning centers are modern versions of the manual Vertical Turret Lathe (VTL). Although principally designed for larger and difficult to handle work pieces, vertical turning center advanced considerably in terms of state-of-art technology [1]. In VTLs there are two versions; a) Spindle facing upwards b) Spindle facing downwards. At present, very few manufacturers are providing layouts in VTL. It has to be emphasized here that the use of layouts becomes imperative since it increases the storage capacity. Horizontal and Vertical CNC are well-known single cell manufacturing cells, which are being extensively used in present day industries. Further, Computer Numerical Controlled machines are employed for mass production by replacing conventional lathes to improve productivity and quality. However recently machine tool manufacturers have found solutions for automatic loading and unloading to reduce the fatigue of labor and reduce cycle time, increasing productivity [2]. Need for auto loading and unloading includes expensive gantry, robot with loading system, machine guarding consisting of ladder and automatically operated by only M-codes through CNC controller [3]. Part Storage System (Carousel) is the integrated subsystems of automatic loading and unloading. The part storage system and automatic transfer of parts between the storage system (Carousels) & the processing station are the necessary condition for an automated cell that operates unattended for extended period of time. If all of the parts are identical and requires the same, then unattended time UT of operation is given by [4].   INTERNATIONAL JOURNAL OF MECHANICAL ENGINEERING AND TECHNOLOGY (IJMET) ISSN 0976 – 6340 (Print) ISSN 0976 – 6359 (Online) Volume 5, Issue 9, September (2014), pp. 239-244 © IAEME: Journal Impact Factor (2014): 7.5377 (Calculated by GISI)   IJMET   © I A E M E    Proceedings of the 2 nd  International Conference on Current Trends in Engineering and Management ICCTEM -2014 17 – 19, July 2014, Mysore, Karnataka, India   240 UT = n p T c  (1) Where n p is the capacity of the part storage system, T c  = Cycle time for the given part. In the conventional carousel systems on can use the drives and mechanism like 1.   Stepper motor and Servo drives 2.   CAM mechanisms 3.   Indexing mechanisms like Ratchet pawl, Rack and pinion, Geneva wheel [4]. To increase the capacity of the parts storage system here is a necessity of different shaped layouts consisting of T, L, and O  shapes. The schematic representation of the layouts is shown in Fig.1, Fig.2 and Fig.3 respectively. The rectangle indicates the pallets carrying the work piece; arrow indicates circulation of the pallets which carries the along the shape of the layout. The cross symbol indicates the pick-up site in the layout by inverted spindle with hydraulic chuck. Here hydraulic chuck performs two functions namely 1.   Automatic pick-up of the work piece from part storage (carousel). 2.   Turning operation of the work piece takes place in the same hydraulic chuck itself. Fig. 1: T- Shaped Layout Fig. 2: L- Shaped Layout Fig. 3: O-Shaped Layout This paper converges to part storage system (carousel), not on the automatic loading and unloading. The shape of the layout depends upon the storage capacity, external shape of the VTL and space availability In this paper further discussions are carried out by taking L- shaped layout into consideration because pallets are shifted in 6 directions which are indicated by arrows.  Proceedings of the 2 nd  International Conference on Current Trends in Engineering and Management ICCTEM -2014 17 – 19, July 2014, Mysore, Karnataka, India   241 II. OBJECTIVES The core objectives of this paper includes (a) maximize the storage capacity of the part storage system (carousel) (b) increase the unattended time of operation (c) low cost automation by reducing the number of elements i.e. cylinders, sensors etc.. III. METHODOLOGY Hook is the main part of the concept. Hook is equipped with torsion spring [5]. Hook is connected to the cylinder by link. Hook deflects in the downward direction due to torsion spring and traces the path of the external geometrical feature like Cam and followers. (Fig. 4, 5 and 7) Fig. 4: Hook with Torsion Spring Fig. 5: Hook Moves in Downward Direction During one side stroke (extending/retracting) hook engages/latches the pallet (which carries the work piece but, the work piece is not shown in Figure) as shown in Fig. 6. Hook disengages pallet during the return motion (Fig. 7). Fig. 6: Pallet Engaged by Hook Fig. 7: Hook Disengaging Movement The following cross-sections of layout illustrates the impression behind the concept Fig. 8: Hook Engages/Latches the Pallet Fig. 9: Pallets are Shifted by One Pallet Length (stroke length of cylinder) through Hook which is connected to Cylinder   Fig. 10: Disengaging Movement  Proceedings of the 2 nd  International Co Sequence of operations: The   pallets discussed above are p is equal to stroke length of the cylinder in material to the picking station is as explai vertical hydraulic chuck places the finished by moving the pallets in both X and Y direc  Fig. 11(a):Placement of Finished Part a Fig. 11(c): Vertical Chuck Facilit Work Piece for Machini Fig. 11(e): Shifting of Pallets by Length in Y-Direction ference on Current Trends in Engineering and Manage 17 – 19, July 2014, Myso 242 sitioned throughout the layout. Pallets get shifted by on each direction. This sequence of operations required to ed below. The sequence of operation begins with the part. From Fig. 11(b) to Fig. 11(j) depicts the further s tions. ter Machining Fig. 11(b): Supply of New Work P ting New Fig. 11(d): Movement of Pallets i ng One Pallet Fig. 11(f): Shifting of Pallets Length in X-Direc  ent ICCTEM -2014 re, Karnataka, India   pallet length which deliver the new raw Fig. 11(a) wherein quencing operations iece to Machining the X-direction y One Pallet tion
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