Improving the Efficiency of Steam Turbine Rotor Manufacturing

Improving the Efficiency of Steam Turbine Rotor Manufacturing

Sharanakumar1

1. ech student, Department of IEM M S Ramaiah Institute of Technology Bangalore, India

   Dr. Chethan Kumar C S2, S. Appaiap

   Professor2, 3, Department of IEM M S Ramaiah Institute of Technology

   Bangalore, India

   AbstractThe project was carried out at a reputed steam turbine rotor manufacturing unit, Bangalore. The product considered is steam turbine rotor used for generating power in sugar plant, it is a job order production. Previously, when this rotor was manufactured, the company was not able to supply the product to the customer at the promised time. The customer was not satisfied with this and demanded that the rotor be supplied in time. The cause for this was that the time required to manufacture this particular rotor was 7207 minutes which is quite high. The objective of this project is to reduce the cycle time of the steam turbine rotor manufacturing. The operations involved in steam turbine rotor manufacturing were noted and data was collected for each operation. The operations were classified into value added and non-value added activities and critical examination was applied to non-value added activities that took place on the CNC machine. The non-value added activities that were identified were approach checking, checking dimension values, inspection and chip cleaning. By the application of critical examination, the non-value added activity time was reduced from 1669 minutes to an estimated time of 635 minutes. Single Minute Exchange of Dies technique was applied for the three set up operations. The activities involved in the set up operations were divided into internal and external activities, reducing external and internal activities and then streamlining the internal activities. By doing so the set up operation time was reduced from 2280 minutes to an estimated time of 2140 minutes. By the application of critical examination and single minute exchange of dies technique, the cycle time to manufacture the steam turbine rotor is reduced from 7207 minutes to 6033 minutes. The estimated savings because of the cycle time reduction is found to be Rs. 1, 17,400/-.

   Keywords Cycle Time, Value Added Activities, Non Value Added Activities, SMED, Internal Activities, External Activities, Setup time.

   1. INTRODUCTION

      Method study is the technique of systematic recording and critical examination of existing and proposed ways of doing work and developing an easier and economical method [7] [8]. Method study is essentially used for finding better ways of doing work. It is a technique for cost reduction [9]. The philosophy of method study is that 'there is always a better way of doing a job' and the tools of method study are designed to systematically arrive at this better way of doing a job [12]. This procedure involves seven basic steps as follows [10]:

      1. Select the work to be studied.

      2. Record all facts about the method by direct observation.

      3. Examine the above facts critically.

      4. Develop the most efficient and economic method.

      5. Define the new method.

      6. Install the new method

      7. Maintain the new method by regular checking

      Single Minute Exchange of Die (SMED) is one of the many lean production methods for reducing waste in a manufacturing process [3]. It provides a rapid and efficient way of converting a manufacturing process from running the current product to running the next product [1]. This rapid changeover is key to reducing production lot sizes and thereby improving flow [11]. The phrase "single minute" does not mean that all changeovers and startups should take only one minute, but that they should take less than 10 minutes (in other words, "single-digit minute")[2]. Closely associated is a yet more difficult concept, One-Touch Exchange of Die, (OTED), which says changeovers can and should take less than 100 seconds.

   2. OBJECTIVES

      Productivity improvement by reducing the cycle time for Rotor manufacturing.

   3. METHODOLOGY

      • Selection of study to be carried out i.e., manufacturing of turbine rotor

      • First the entire processes during manufacturing of turbine rotor are recorded.

      • Identified Value added activities and Non Value added activities.

      • Total time taken for these above activities is recorded.

      • Critical Examination is done on Non value Added activities using Questioning technique

      • To reduce the setup time SMED technique is applied

      • Setup operations are recorded and analyzed.

      • Operations are divided into smaller elements and time taken for each element is noted.

      • Identify the internal and external element

      • Convert from internal steps into external steps

      • Reduce time consumed by the internal steps

      • Streamline the new process.

   4. EXISTING METHOD

      After recording the timings of all the operations the following observations were done.

      Setup time in min	Machining time in min	Non-value added time in min	Total time in min
      2280	3258	1669	7207

      Table 1: Components of Total time

      The non-value added activities time had the following components: approach checking, checking dimension values, inspection and chip cleaning.

      Approach checking time In min	Inspection time In min	Checking Dimension values In min	Chip cleaning time In min
      378	213	408	670

      Table 2: Components of Total time

      Present method time:

      Setup time = 2280 min

      Total Actual cutting time in min = 3258 min Total non value added time in min = 1669 min Total time = 7207 min

      Total time in hrs = 120 hr 6 min

   5. PROPOSED METHOD

      1. Critical Examination by Questioning Technique

         Develop For checking program dimensions values

         Before running the program, the operator has to check the dimension values with the data sheet. To avoid this, check list has been developed. By doing so we can eliminate or reduce this time. Before keying the programs to the machine, programmer has to cross check the dimension values in the program. Then inspector in the programming department has to recheck the program and it has to be approved by the programming department. Later it has to be sent to the production department for the process.

         1. Purpose What should be done?

            Provide the check list to reduce checking dimension values time.

         2. Place Where should it be done?

            It should be done at the programming department

         3. Sequence When should it be done?

            Soon after preparing the programs and before keying it into the machine

         4. Person Who should do it? Programming dept should do it.

         5. Means How should it be done?

            It should be done using process sheet.

            For approach checking

            This can be avoided by providing the checklist for the programming department. The programmer can cross check the program after developing the program. The same should be approved by the programming department. This reduces the operators time to check the program.

            1. Purpose What should be done?

               Provide the check list to reduce approach checking.

            2. Place Where should it be done?

               It should be done by the programming department

            3. Sequence When should it be done?

               After preparing the programs by the programmer

            4. Person Who should do it?

            Programming department should do it.

            Check list for Checking Dimension values and Tool approach checking during programming

            The checklist was prepared after discussion with the production engineer, supervisor, programmer and programming department head. This checklist has to be filled by the programmer after developing the program and get the program and the checklist checked and approved by the concerned authority.

            Project: Steam turbine rotor Frame: 012

            Drawing no: 002

            Table 3: Checklist

            Sl. No.	Tool Description	Tool path description	Approach checking	Checking Dimension Values	Checked by
            1
            2
            3
            166

            Inspection time reduction Straight groove and coupling flange holes

            Inspection at the straight groove and coupling flange holes using slip gauges takes more time. To avoid this, inspection has to be done by using plug gauges. This would takes less time.

            Time reduction for Chip cleaning

            Chip cleaning activity is doing by manually and it is time consuming. To avoid this problem chip breaker has to be provided. By providing chip breaker, chip-cleaning time can be reduced.

            Estimated time savings after the application of Questioning Technique

            Sl. No.	Setup Operations	Internal Activity time in min	External Activity time in min	Remarks
            13	Dis-engage both the weight support & engage of weight support in middle of component	15
            14	Machine the steady band areas. Select the depth of cut, cutting speed & feed rate	20
            15	Move the steadies in right positions & close them	15
            16	Machine 4 disc which are required to align component in this without chattering marks	40
            17	Adjust the steady rest by dial gauge in X-Y axis	45
            18	The tail stock end side disc can be aligned in X-axis by using a dial & adjustment screw provided on tailstock	35
            19	Work offset taken for probing	70
            20	Probe program altered outer diameter runned for X- Y alignment	65
            21	X-Y alignment probing	85
            22	Measure the same by measuring program and adjust the steady rest until to control the parameter	120
            23	Ensure the parameter readings once again that tolerance is within the limit(10-20 microns)	45
            24	check the raw part allowance related with the rough turning program	70
            25	After rough machining gross check the alignment of component by measuring program	40
            26	Disengage the both weight support and engage of weight support in the required position	40
            27	Remove the tail stock	5
            28	Probe program called and run	55
            29	X&Y Alignment done within 0.002micron	80
            30	Linear distance cross checked for disc 2-12	65
            31	Run out checked after alignment completion within 0.015micron	110
            32	Winding the rotor with belt	10
            33	Hook the rotor to the crane & check the belt is in balancing for lifting	20
            34	Disengage the steady rest Open the jaws and lift the rotor	5
            35	Open the jaws and lift the rotor	40
            36	Place the rotor on the rotor stand(without removing the belt with crane support)	10		External (Parallel to jaws removing)
            37	Hard jaws removed and soft jaws mounted		35	External (Parallel to positionin g steady rest)
            38	Cleaning		15	External (Parallel to placing rotor)
            39	weight support steady rest position have to be found out so that the weight of the component uniformly distributed from the chuck till tail stock as per the position which has arrived from the following	40
            40	Check the jaws to be opened to enter the component Also check the Z-axis support length where the component rested which machining		5	External (Parallel to loading the componen t)

            1. first disc nearby chuck

            2. Second & third diameter nearby steady rest

            3. Fourth one nearby tail stock

            Table 4: Estimated cycle time for proposed method

            Setup time in min	Actual cutting time in min	Non-value added time in min	Total time in min
            2280	3258	635	6173

            Table 5: Non-value added time (Estimated) in proposed method

            Approach time In min	Inspection time In min	Checking D- values In min	Chip cleaning time In min
            Nil	104	Nil	531

      2. Single Minute Exchange of Dies technique

      The setup time in manufacturing of steam turbine rotor was

      more; to reduce this set up time we had applied Single Minute Exchange of Dies technique.

      Setup time reduction by SMED Technique

      Table No 6: Streamline the Internal and External activities

      35

      Sl. No.	Setup Operations	Internal Activity time in min	External Activity time in min	Remarks
      1	cleaning of machine	90
      2	Removal of old jaws and fixing new jaws by manually		External (Parallel to cleaning)
      3	weight support steady rest position have to be found out so that the weight of the component uniformly distributed from the chuck till tail stock as per the position which has arrived from the following		40	External (Parallel to cleaning)
      4	check the jaws to be opened to enter the component Also check the Z-axis support length where the component rested which machining		5	External (Parallel to cleaning)
      5	winding the rotor with belt		10	External (Parallel to cleaning)
      6	Hook the rotor to the crane & check the belt is in balancing for lifting	20
      7	Load the component in the machine & close the jaws softly so that the component is approximately in the center of the machine	60
      8	Remove the belt from rotor	10
      9	Engage the tail stock center. Ensure Z-axis butting	5
      10	Engage the weight support on steady rest 1& 2	10
      11	Check & correct the run out of component near by check. Tighten the hard jaws fully	125
      12	Once again check run out of the component on same diameter within same limit	30

      Contd..

      Contd…

      Sl. No.	Setup Operations	Internal Activity time in min	External Activity time in min	Remarks
      41	Load the component in the machine and close the jaws softly, so that the component is approximately in the center.	60
      42	Remove the belt from the rotor	10
      43	Engage the tail stock center. Ensure Z-axis is butting	5
      44	Engage the weight support on steady rest 1&2	10
      45	Check and correct the run out of the component nearby chuck. Tightened the hard jaws fully	120
      46	Once again check run out of component on same diameter within the same limit	30
      47	Steady holding on thrust collar outer diameter re- centering done	80
      48	Work offset taken for probing	70
      49	Probe program altered outer diameter run for X-Y axis alignment	65
      50	X-Y alignment probing	85
      51	Work offset taken and cross checked by measuring linear dimension	70
      52	C-axis done zero	65
      TOTAL		2195	185

      Table No 7: Results

      Operations		Present Method (time in min)	Proposed Method (time in min)	Savings (time in min)
      Non value added Activity	Approach Checking	378	Nil	378
      	Inspection	213	104	109
      	Checking dimension values	408	Nil	408
      	Chip cleaning	670	531	139
      Set up operations		2280	2140	140
      Total		3949	2775	1174

   6. RESULTS AND CONCLUSIONS

Critical examination was done for non-value added activities and the non-value added activities time was reduced from 1669 min to 635 min.

SMED Technique was applied to set up operations and set up time was reduced from 2280 min to 2140 min. Following table gives time taken for non-value added activities and set up operations for both present and proposed methods. Hence the cycle time was reduced from 7207 min to 6033 min.

1. Results obtained

   Savings (estimated) after applying critical examination and single minute exchange of dies (SMED) technique.

   Cycle time (present method) = 7207 min Cycle time (proposed method) = 6033 Total saved time in min =1174

2. Estimated savings (in terms of cost) to the company

   Loss to the company if machining operation is stopped per hour = Rs 6000

   Loss per min if machining operation is stopped = Rs 100 Total saved time in min (Estimated) = 1174

   Net savings per Rotor (Estimated) = 1174*100 Net savings per Rotor (Estimated) = Rs. 117400

   Most of the suggestions given for reducing the cycle time of this steam turbine rotor hold good for many of other types of rotor also. Hence, these suggestions can be implemented for other rotors and cycle time and cost can be reduced to a great extent.

   REFERENCES

   1. Holweg, M., (2006). The genealogy of lean production.Journal of Operations Management, 25, 420437.

   2. Johansen, P., McGuire, K. J. (1986). A lesson in SMED with Shigeo Shingo. Industrial Engineering, 18, 26-33.

   3. Liker, J.K. (2004). The Toyota Way: 14 Management Principles from the Worlds Greatest Manufacturer. McGraw-Hill, New York.

   4. Mcintosh, R., Culley, S., Mileham, T., Owen, G. (2000).A critical evaluation of Shingos SMED (Single Minute Exchange of Die) methodology. International Journal of production Research, 38(11), 2377-2395.

   5. Shingo, S. (1985). A Revolution in Manufacturing: the SMED System. Productivity Press, Cambridge, MA.

   6. Process Planning and cost Estimation, 2nd Edition By R. Kesavan,

3. Elanchezhian

1. Badiru, A. (Ed.) (2005). Handbook of Industrial and systems engineering. CRC Press. ISBN 0849327199

2. Blanchard, B. and Fabrycky, W. (2005). Systems Engineering and Analysis (4th Edition). Prentice-Hall. ISBN 0131869779

3. Salvendy, G. (Ed.) (2001). Handbook of industrial engineering: Technology and operations management. Wiley-Interscience. ISBN 0471330574

4. Turner, W. et al. (1992). Introduction to industrial and systems engineering (Third edition). Prentice Hall. ISBN 0134817893.

5. Dr.C.S. Chethan Kumar and Dr.NVR Naidu (2014).Implementation of SMED Procedures To Reduce The Setup -Time Of FSF Machine- AMMMT-2013 International Conference on Advanced Materials, Manufacturing, Management and Thermal Sciences. During 3 rd-4th May, 2013, Tumkur.

6. Dr.C.S. Chethan Kumar and Dr.NVR Naidu (2014). International Conference on Modeling Optimization and Computing during 10th

-11 th April, 2014, NI University, Tamil Nadu.