REDUCTION OF CYCLE TIME IN SCREW AIR COMPRESSOR ASSEMBLY LINE USING KAIZEN...

International Journal of Lean Thinking Volume 6, Issue 2 (December 2015)

REDUCTION OF CYCLE TIME IN SCREW AIR COMPRESSOR ASSEMBLY LINE USING KAIZEN SURVEY

D. Rajenthirakumar*

PSG College of Technology, Peelamedu, Coimbatore – 641004, Tamil Nadu, India E-mail: [email protected]

S. Nandhakumar PSG College of Technology, Peelamedu, Coimbatore –

641004, Tamil Nadu, India

A R T I C L E I N F O

A B S T R A C T K E Y W O R D S

________________________________

* Corresponding Author

Kaizen, Lean assembly line, Standardization, cycle time reduction.

Received 21 June 2015 Accepted 22 July 2015 Available online 1 December 2015

In this competitive world, any company has to fulfill its

customer needs to survive in the market. Lean

manufacturing is a technique that can be adopted in a

company to improve the quality of its products, reduce

the cost of the production and also deliver the

products in less time. The goal of this work is to show

the applicability of lean manufacturing’s body of

knowledge in a screw air compressor manufacturing

company. Here, the main objective is to evolve and

test several methodologies to eliminate wastes in the

assembly line as the company at present unable to

meet the customer demand.

A systematic approach is suggested for the

implementation of lean principles to showcase that

lean could be applied to the compressor assembly

line to enhance the productivity thereby making the

line more efficient. In the current assembly line there

was no work standardization followed by absence of

kaizen that has led to an increased assembly time.

Thus with the help of lean tools and techniques such

as 5S, kaizen, standardization, visual management,

poke yoke and string diagram the total cycle time has

been reduced from 236 to 209 minutes. This

reduction has benefitted the company in meeting the

customer demand, increased profit and work

satisfaction.

D. Rajenthirakumar/ International Journal of Lean Thinking Volume 6, Issue 2 (December 2015)

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1. Introduction

Lean manufacturing philosophy was pioneered by a Japanese automotive company, Toyota

during 1950 ’s. Due to its global superiority in cost, quality, flexibility and quick respond, it

was transferred across countries and industries. The influence of lean practices contributed

substantially with the operating performance of the plants and use of lean tools allows the

improvements of results. The main principle of lean manufacturing is to reduce waste in an

operation, such as long lead times, defects and material waste. In order to visually display

whether the manufacturing field is escalating and spreading more widely across the globe, it

is important for companies to adapt to the increasing and evolving business strategies.

In order to be lean the company should follow the lean principles such as (i) Specify the

value desired by the customer (ii) Identify the value stream for each product providing that

value and challenge all of the wasted steps (generally nine out of ten) currently necessary to

provide it (iii) Make the product flow continuously through the remaining value-added steps

(iv) Introduce pull between all steps where continuous flow is possible (v) Manage toward

perfection so that the number of steps and the amount of time and information needed to

serve the customer continually falls. Thus, lean implementation is focused on getting the right

things to the right place at the right time in the right quantity to achieve perfect work flow and

being flexible to change.

2. Brief Review of Literature

Chandandeep Grewal Ludhiana [1] made an attempt to initialize the implementation of lean

manufacturing system using Value Stream Mapping. A case study conducted at a bicycle

manufacturing company illustrated a lot of improvements areas with the help of current state

map. Current state map and future state map were prepared and analyzed to highlight the

benefits of a lean system in a small company. Future state was prepared after proposing some

changes in the process to reduce different wastes. QianWang et al [2] investigated a semi

automated automotive engine assembly line in which the traditional strategy of using fixed

workers in each manual assembly section is replaced by a new strategy of using walking

workers. Ajit Kumar Sahoo et al [3] research addresses the implementation of lean

philosophy in a forging company with a focus on radial forging production flow lines. The

authors used value stream mapping to identify and eliminate waste and Taguchi’s method of

design of experiments is pursued here to minimize the forging defects produced due to

imperfect operating conditions.


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Jorge L et al [4] attempted to determine the critical success factors for Kaizen philosophy

implementations. It is concluded that there is actually no Kaizen methodology that can be

applied successfully in industry, as enterprises are open systems, which react differently to a

situation and those are due to cultural aspects, social and own needs. In their paper, Martín

Tanco et al [5] showed the applicability of lean manufacturing in a seasonal food industry.

Several techniques and analyses such as value stream mapping, overall equipment efficiency,

spaghetti diagrams, work balance, and discrete event simulation were applied and analysed.

Even it was a food process industry a slight modification has been made in the existing lean

tools and been used and it presented promising improvements primarily in lead time and work

cycle efficiency.

3. Problem Environment and Objectives

The company, IJK Limited is a leading compressor manufacturer in India which produces a

range of reciprocating and screw compressor. After several brain storming and a thorough

study of the shop floor, it was observed that manufacturing operations sequence consists

various forms of non-value-adding activities as follows: (i) The total assembly time for the

Small Electrical Power Screw Air Compressor (SEPSAC) is 236 minutes (ii) Currently the

company is unable to meet the customer demand due to high lead time (iii) Operator

unbalance which increases the man power (iv) The flow of materials from the stores to the

assembly line is not uniform (v) Unwanted movement of people for the search of tools and

equipments and (vi) Inline reworks.

The main goal is to develop different strategies to reduce the level of non value activities

present in any form by implementing the various lean tools. The work targets are given below

and Fig. 1 illustrates the methodology adopted in this work to fulfill the below mentioned

objectives.

To reduce the total assembly time of SEPSAC by 10%.

To identify the bottle neck area in the entire assembly process and overcome with the

help of lean tools and techniques

To do Line balancing with respect to takt time

To streamline the material flow from the stores to the assembly line

To reduce the inline reworks


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Fig. 1 Methodology – Implementation of lean assembly line

4. Implementation and Results

As a first step to establish continuous flow, VSM is done. The current state map [Fig. 2]

presents the existing position of the company. The critical problem areas and different kinds

of non-value added activities are identified in this stage. The next step is development of

future state map. In order to develop the future state map, the current state map was analysed

using the steps and guidelines developed by Rother and Shook [6]. The last step is analysis of

the results obtained after implementing the proposed changes. This has to be quantified in

terms of lead time reduction, cycle time reduction, inventory reduction, etc. Before mapping

the current state it is important to calculate the takt time for the product. The takt time [24

minutes] is the amount of time that must elapse between two consecutive unit completions in

order to meet the demand. It helps to achieve a consistent continuous flow of production

eliminate the waste of over production by producing to actual customer demands.


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Fig. 2 Current state map

From the Current state value stream mapping the time for each stations [Fig. 3] are noted

down. In this work, the focus is on the sub assemblies and the station 1 to station 6. Further,

the total work content analysis of each station in the assembly line with respect to takt time is

noted and given in Fig. 4. It can be noted that the maximum time of the operator is taken as

the station operating time.

Each station with their cycle time and the number of operators working in the respective

stations is given in Table 1. It is noted that the stations 1 and 2 have two operators and the

remaining stations have only one operator each.


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Fig. 3 Station wise operating time

Fig. 4 Work Content analysis

Table 1 Assembly stations with operators and cycle time

Station No of operators Cycle time in minutes

Small parts sub assembly 1 24

Tank sub assembly 1 31

Cooler sub assembly 1 23

Main assembly Station 1 2 25



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4.1 Kaizen Survey

Kaizen is one of the most important methodologies used to manage continuous improvement

[7]. However, despite the popularity of this philosophy, Kaizen implementations in

companies had little success. So in order to validate kaizen two surveys were conducted with

a list of questionnaire having a set of question and it is distributed among the employees in

the company (SEPSAC Assembly line) with respect to compressors and another one with

respect to general aspects. These studies were conducted with marks maximum of 10. Fig. 5

and 6 represents the kaizen survey with respect to compressors and in general aspects. In the

Fig. 5, the X axis represents the following factors: Creation of screw air compressor

standard document ,factor II - Regular Kaizen identification in the assembly line, factor III -

Identification for tools and fixed point location in the shop floor, factor IV - Standard

operating procedure audit, factor V Visual identification of operator skill level, factor VI -

Implementation of projects from kaizen regularly, factor VII - Rotation plan between the

compressor assembly line to be made and Ensured, factor VIII - Gemba Walk by operation

head, factor IX - Shop standard audit by Engineers, factor X - Parts visibly identified by part

numbers, quantity, and sequence number. Similarly, in the Fig. 6, the following factors

represented: factor XI - Creation of Multi skilling plan for Financial year, factor XII -

Commitment and motivation of staff, factor XIII - Support from senior management, factor

XIV - Allocated resources (time, economic, spaces), factor XV - Developing a culture of

continuous improvement, factor XVI - Set goals for improvement programs, factor XVII -

Using an appropriate methodology, factor XVIII - Standardization and process measurement,

factor X IX - Interdepartmental communication, factor XX - Training and education.


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Fig. 5 Kaizen survey – Compressor specific

Fig. 6 Kaizen survey – Generic in nature

From the survey it is concluded that there is awareness about kaizen in the employees both in

the shop floor and also in office staffs before the commencement of this work. As a result, a

separate plan was prepared especially for kaizen projects and operator skill level. Target dates

are set and persons are allocated the responsibility to meet it. In order to encourage and make

it as a culture in the organization, at the end of every month, from the kaizen list, the best is

selected and implemented. Based on its impact, the concerned worker is awarded with a price.

4.2 Improvements in main assembly station 2

Fig. 7 illustrates the motor and air end subassembly in station 2. First the motor and air end is

shifted to the sub assembly table. Then the intake valve is assembled in the air end followed

by the coupler assembly in motor and air end shaft. Then the hub is assembled in between the

motor and air end. Then at last the discharge control pipe is assembled and the entire sub

assembly is shifted to the main assembly and assembled in the main frame. To identify the

value added and non value added activities in station 2, time study (with stop clock) and


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video study is conducted. It is found that the total time (2100 seconds) consists 1357 seconds

as value added and 743 as non value added. Causes for the non value added time are studied

during the assembly process and also through discussion with the operators. Figure 8

represents the fish bone diagram associated with station 2 and Table 2 shows the kaizen with

respective time reductions. It can be concluded that the kaizen result in significant operating

time reduction i.e. 24 minutes from 35 minutes.

Fig. 7 Motor air end sub assembly

Fig. 8 Station 2: Fish bone diagram


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Table 2 Kaizen: Station 2

Sl No Activity Total time

(Sec)

1 A bin set up can be used such that the operator can place

all the fasteners in the bin at a single time rather than

moving frequently

60

2 Provide the tools in his required position 55

3 The Material trolley should be placed nearer to the sub

assembly table to reduce the movement of the operator

20

4 Adapter ring needs to be grinded 35

5 Check the dimension of the washer. The coupler is a

bought out item so the dimension for the coupler should

be checked with respect to the motor and air end

drawings.

120

6 Torque value for thermal valve tightness should be

checked to avoid bending in the valve

77

7 Instead of entering the details of the motor and air end in

inbuilt card we can go for card(re writable) swiping

250

4.3 Tank sub-assembly - improvements:

The second bottle neck station is tank sub assembly. The assembly process involves in

loading the tank in the assembly fixture with 1253 minutes as value added time and 602

minutes as non value adding. Also, ball valve assembled with the connector and then the top

plate is removed, filter mesh is assembled. Safety valve, oil plug and oil indicator are further

assembled. Once the sub assembly is over then it is moved to main assembly and assembled

in station 2. Like in the previous case, root cause analysis for the tank sub assembly is done

and Fig. 9 gives the Pareto chart. Also kaizen identified (Table 3) results in reduction of non

value added time and the operating time is reduced to 24 minutes.


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Fig. 9 Pareto chart for tank sub assembly

Table 3 Kaizen: Tank sub-assembly

Sl

No

Problem Kaizen Time reduction

(Sec)

1 Movement of the operator for

Searching the fastener and

tool

Provide the fasteners in his

station itself

122

2 Setting of the fixture such

that the tank outlet pipe does

not change its position

Fixture is designed 108

3 Movement of the tank sub

assembly to the station 2

The wheel base in the

trolley can be made

heavier for easy movement

15

4 Operator noting down the

details of the tank in the

inbuilt card

The time can be reduced

by swipe card

70

5 Operator waiting in front of

punching machine.

This process can be shifted

to pre PDI station

130

Total time in seconds 445

5. Summary of Improvements and Conclusion

As a result of implementing kaizen in the bottle-neck stations and reducing the non value

added activities, the total operating time comes below the calculated takt time (Fig 10). Cost-


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benefit analysis (Table 4) reveals substantial cost savings. Further, the total assembly time of

SEPSAC is reduced to 209 minutes from 236 minute (11%). This work gives a set of

alternatives to improve the output of a productive system without incurring in major

investment.

Fig. 10 Station time after improvements

Table 4 Cost benefit analysis

SL No Description Before improvements After

kaizen

1 Cycle time (in minutes) 236 209

2 Cycle time reduction (%) 11

3 Cost of labor per hour Rs.100

4 Total number of labors 11

5 Total cost for labor per day Rs.9900

6 Number of days utilized per

month

21 + 2 (over time) 21

7 Number of days saved 2

8 Cost saved (per month) Rs.19800


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References

[1] Chandandeep Grewal “An Initiative to Implement Lean Manufacturing using Value

Stream Mapping in a Small Company ", Int. J. Manufacturing Technology and Management,

Vol. 15, Nos. 3/4, 2008

[2] Qian Wang, Martin Sowden, Antony R. Mileham “Modelling human performance within

an automotive engine assembly line”, Int J Adv Manuf Technol (2013) 68:141–148

[3] Ajit Kumar Sahoo, N. K. Singh, Ravi Shankar, M. K. Tiwari “Lean philosophy:

implementation in a forging company”, Int J Adv Manuf Technol (2008) 36:451–462

[4] Jorge L. García, Denisse G. Rivera, Alejandro Alvarado Iniesta ”Critical success factors

for Kaizen implementation in manufacturing industries in Mexico”, Int J Adv Manuf Technol

(2013) 68:537–545

[5] Martín Tanco, Javier Santos, Jose Luis Rodriguez, Juan Reich “Applying lean techniques

to nougat fabrication: a seasonal case study”, Int J Adv Manuf Technol (2013) 68:1639–1654

[6] Rother, M., Shook, J. “Learning to See: Value Stream Mapping to Add Value and

Eliminate Muda”, The Lean Enterprise Institute, 1998

[7] Womack JP, Jones DT, “Lean thinking: banish waste and create wealth for your

corporation”, Simon & Schuster, New York, 1996

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