Experimental Verification of Single Minute Exchange of Dies (SMED)

Recent Research in Science and Technology 2011, 3(3): 92-97 ISSN: 2076-5061 www.recent-science.com MECHANICAL ENGINEERING

EXPERIMENTAL VERIFICATION OF SINGLE MINUTE EXCHANGE OF DIES (SMED) M. Sivasankar1∗, N. Dhandapani2, ManojKumar. S3, Karthick. N3, Raja. K3, Yuvaraj. J3 1Professor and Head, 2Lecturer, 3Students, Mechanical Engineering, Arunai Engineering College, Tiruvannamalai – 606 603, India. Abstract In the present world scenario, the flexibility and responsiveness to customer demands are the imperative task. Here, in the expander machine of rim manufacturing unit, additional time is needed for exchange of setup. These in turn stop the activities of other processes for about 90 minutes, which probably breaks the production of rim in this unit. As this setup exchange is inevitable, the only solution is to reduce the time consumption. At this point, the process of Single Minute Exchange of Die (SMED) comes into play. SMED is indirectly indicated as quick changeover of setup. It is a suitable method not only for improving manufacturing process but also for the equipment design development. Customers will be in need of reliable products in a short time. To accomplish this, it is needed to eliminate and improve productivity and quality. It is a customer driven requirement who demands product and service diversity, high reliability and quality.

Keywords: Change over, SMED, Reduction of time

∗ Corresponding Author, Email: [email protected]

Introduction Single Minute Exchange of Die concept has been

initiated at Toyo Kogyo’s Mazda plant in Hiroshima, Japan when its author, Shiego Shingo conducted a production efficiency improvement study in 1950. The term SMED refers to the theory and techniques for performing setup operations in less than ten minutes. Although not every setup can literally be completed in single-digit minutes, this is the goal of the system. Even where it cannot, reduction is still possible and results are compromising with the concept. In general, SMED considers about changing machines by taking out dies or mechanical structures and replacing them with other dies or structures.

Need for Purging There is a certain amount of "purging" of current

product to allow for the introduction of the "new" product or specific different elements.

Definition of SMED The phrase “single minute” does not mean all

changeovers and startups should take only one minute, but they should take less than 10 minutes (in other words, “single digit minute”). Many companies now recognize the importance for minimal machine downtime during changeovers and have created entire systems for completing changeovers and setups very quickly. Likewise, many equipment manufacturers have begun integrating quick change systems into capital equipment as a major selling point.

Effects of the SMED implementation • Stockless production which drives

capital turnover rate. • Reduction in footprint of processes

with reduced inventory freeing floor space. • Productivity increases or reduced

production time. • Increased machine work rates from

reduced setup times, even if number of changeovers increases.

• Elimination of setup errors and elimination of trial runs reduces defect rates.

• Increased safety from simpler setups.

Key-Factor for Applying the SMED Concept The SMED concepts can be applied accordingly to

certain pre-determined conventional process, Plan-Do-Check-Act (PDCA) cycle (Fig) is a checklist of four stages which must be gone through, to get from ‘problem-faced’ to ‘problem-solved’.

Description of PDCA cycle

• Plan to improve the operations first by finding out what things are going wrong (that is identify the problems faced) and come up with ideas for solving these problems.

• Do changes designed to solve the problems on a small or experimental scale first. This minimizes disruption to routine activity while testing whether the changes will work or not.

Dr.Sivasankar et al./Rec Res Sci Tech 3 (2011) 92-97

• Check whether the small scale or experimental changes are achieving the desired result or not. Also, continuously check nominated key activities to ensure that the quality of the output is at all times to identify any new problems when they crop up.

• Act to implement changes on a large scale if the experiment is successful. This means making the changes a routine part of activity. Also act to involve other persons (other departments, suppliers, or customers) affected by the changes and whose cooperation is needed to implement them on a larger scale.

The four stages of Plan-Do-Check-Act are carried out in the cycle illustrated in Fig 1:

Fig 1

Conceptual Stages of SMED The process of SMED can be applied as in the

following steps: • Observe the current process • Categorize internal and external operations • Convert internal activities into external

activities • Make the remaining activities to flow • Optimize the external activities • Document the new procedure

• Continuous improvement for perfection Of these, the first two steps deal with analyzing

the setup exchange. The next three steps deal about the ‘quick changeover’ and the final two steps are the process of implementing new concept. Reduction of setting time is probably achieved by implementing these first five steps which can be graphically represented as shown in Fig 2:

Fig 2

In this process, time study is noticed by observing the time for every individual machines working in a particular rim line. It is categorized as loading, operation and unloading time.

Calculation of Cycle time

Loading time is that which takes to insert a work piece into the machine.

Operation time is the time which spends on working of the machine.

Unloading time is the time to separate finished work piece from that particular machine.

The time study of the rim line is as shown in the

Table-1:

Table 1

Observations from the Current Process The current process was initially analyzed through video

capturing which include the time study of each and every individual activity during the setup exchange in detail. Time required for the transport, operation and delay are noted. The total required for the setup exchange process is calculated as 5287 seconds.

Categorizing Internal and External Activities

Internal activities are those that can only be performed when the process is stopped, while external activities can be done even the process is going on. The internal and external activities can be classified as follow:

Process Loading time (sec)

Machine time (sec)

Unloading time (sec)

Total cycle time(sec)

Expanding 8.07 28.67 4.81 41.55


Internal activities • Removing the die set • Inversion of the die set • Exchange of die blocks • Fixing the die set • Tightening of bolts

External activities • Bringing the new die blocks • Bringing the necessary tools • Moving of conveyor table • Bringing the fork lifter • Wearing gloves

Converting Internal into External Activities

‘Externalization’ means performing changeover tasks either before or after the changeover, ‘externally’ to the changeover time. One common activity that takes place during changeover is that the operator will collect the various parts required. If this is done during the changeover, it will

extend changeover time. This is something that can be done ahead of time so that all the required parts are available the moment they are needed. The die exchange is performed according to the type and the dimension of the rim varies accordingly. Batch Production

The rim manufacturing is carried out by batch production the primary characteristic of batch production is that all components are completed at a workstation before they move to the next one. The production equipment must be stopped, re-configured, and its output tested before the next batch can be produced. The word ‘conversion’ apparently explicit the concept of making the process in the expander easier by reducing the internal activities. As in the current expander assembly, there is a necessity of changing the dies which includes the prolonged changeover. It is evident from the table 2 as follows which lists the main internal activities of the die-exchange.

Table 2 Internal Activities Consumed

time(sec) Loosening and removing the bolts of the m/c

115

To separate die from machine

149

To setup the pneumatic wrench

49

Inversion of die set 88 Assembling the packing rings

47

Loosening and removing the bolts of the die set

370

Dismantling the old die blocks

86

Aligning the new die blocks

208

Insertion and tightening of bolts

375

Lubrication 175 Inverting the die set 75 Assembling the die set 331 Moving conveyors 211 Delay due to various reasons

1729

Total 4008 Previously, the internal time was 5287 seconds. By

converting the internal activities into external activities, the time has been reduced to 4008 seconds. Thus, about 29% of the time taken for the internal activities is saved. It is also important to consider a point that, this die exchange cannot be done in a frenetic way as it is conscious process. Factors which reduces internal time

Through analyses there are certain key factors which reduce the internal activities:

• Reducing the time of fork lifter usage / to find the alternate for the fork lifter which efficiently replaces it.

• Reducing the number of bolts • Changing the bolts position • New methodology for inversion of die sets • Reducing the weight of the block • Replace least parts possible • Positioning dies for quick insertion into the machine.


Proposed Ideas The fork lifter is used here to remove the die set from the

assembly. The usage of this is because of the heavy weight of the dies so that it can’t be lifted normally unless some machine is used. Abruptly the fork lifter cannot be eliminated as it is highly impossible considering the present circumstances. The usage of that nearly consumes 32% of the total time of 90 minutes. Because of this initial significant task is in finding out the alternative for that fork lifter. Here are some of the ideas: • Use of lifting metal ring • Pneumatic devices

The circumstances at the starting stage the fork lifter is the main consumption of total time, in effect to that the above mentioned ideas are mainly focused to avoid the inversion of the whole die block. But these have some limitations. Use of the lifting ring which temporarily bears the weight of the whole dies must want to be changed accordingly to the design of the dies and it often interrupts the loosening and tightening of bolts. The utilization of pneumatic devices and applying those concepts seems to be highly complicated to implement because the ideology was the use of pneumatic table which automatically goes inside and invert the die set and comes out. As it is extrinsic, it is quite good enough to replace, but the design of that pneumatic table, conveyors, devices and assisting components would take some of the arena opposite to the machine. Practically it is not possible because of small area is only available in front-side of the machine.

The imperative reason to use the fork lifter here is due to the weight of the die block assembly. Each and every pieces of setting block weighs 20 kg which contributes high in the whole weight of expander assembly which is in older ones. Through these ideas and analysis, it is found that these ideas are trivial things to reduce the time consumption. The weight of the dies is the greatest factor which is one of the manufacturing wastes and also includes the seven wastes of manufacturing like, Manufacturing Wastes • Overproduction: Making more parts than you can sell, • Delay: Waiting for processing, parts sitting in storage,

etc., • Transporting: Parts/Materials: Moving parts to various

storage locations, from process to process, etc., • Over-processing: Doing more “work” to a part than is

required, • Inventory: Committing money and storage space to

parts not sold, • Motion: Moving parts more than the minimum needed

to complete and transport them, • Making defective parts: Creating parts that cannot be

sold “as is” or that must be reworked etc., • Ultimately the weight of the die is the problem and it is

overcome by dividing the die into three parts which involves the concept of minimizing the number of joining components.

Streamlining of the Remaining Activities The adoption of the new proposed idea must not affect

the flow of the process in anyway as it would affect the process chain and also it is obvious that it reduces the time, wastes and synchronize with that of the process flow. Generally by streamlining of all aspects of set-up operation includes techniques like, • Improving storage and transportation of dies etc. • Implementing parallel operations • Using functional clamps • Eliminating adjustments • Least common multiple (LCM) system • Mechanization.

As mentioned earlier the SMED process is particularly applied in the expander assembly of the rim manufacturing unit. The expander assembly is as shown in Fig 3.

Fig 3

The Potential of Design Change Particularly in the context of the “streamlining” stage of

the methodology it is useful to consider how design change physically alter existing manufacturing hardware can be applied. At the same time it is useful to reflect on how the incidence of design change strongly promotes improvement by low-cost organizational refinement. Design modifications can completely alter individual tasks, on occasion enabling some tasks to be eliminated altogether. Contrasted to organizational improvement, hardware modifications, whether by addition or adaptation, potentially allow better things to be done during the changeover, rather than simply doing existing things better. Analysis of design indicates that, on occasions, little or no contribution to improvement need be contemplated in terms of maximizing external time activity.

Description of the New Idea

The design of the old block was as in as below in Fig 4:

Fig 4

Rajkumar et al./Rec Res Sci Tech 3 (2011) 92-97

Actually, the weight of each block is 20 kg. This weight cannot be lifted manually and so the exchange of die blocks is done by inverting the die set with the help of fork lifter. By proposing an alternative idea of dividing the block into three parts, the weight of die block can be reduced. Also, it avoids the time wasted in separating and inverting the die set.

The hypothetical weights of the divided parts are Adaptor plate – 4 kg Main block - 7 kg Inserter - 3 kg

Components of New Die block

The designs of these three parts are made in such a way that only the inserter is influenced on the expansion of the rim and perhaps it alone going to be exchanged instead of the whole die set.

The components of the newly designed die block are • Adaptor • Main block • Inserter

The designs of these are as shown in Fig 5,6 & 7:

Fig 5

Adaptor Plate

Fig 6

Main Block

Fig 7

Inserter

As it is inferred from the above designs, the adaptor plate and the main block is well adjoined to the machine and it is not necessary to often change that module. The die set exchange according to the size and design of the rim is going to be effected from the design of the inserter which is to be fixed into the main block through the T-slot and bolts. The flow of process is definitely not affected as the fixing of the inserter would not take much time and it consumes less time than that of the fork lifter. The inversion of the die block is eliminated. So, obviously the fork lifter is not going to play a role. Here, the inserter can be handled manually by the worker. Analyzing the Designed Product

Fig 8

In analyzing the design using ANSYS, the top portion and back portion are fixed in all degrees of freedom (DOF), as they are attached to the machine. The side portion is also fixed, as the blocks are adjacent to each other. A pressure of each 17 bar is equally applied on the front portion of all the ten blocks. Here, the change of stress is indicated by the colour change, it is due to fixing the DOF of top, back and side portions. The deformation on the front portion, as seen in the analysis, is to be transferred to the rim, and accordingly it expands. The analysis using ANSYS is shown as in Fig 8. Optimization of the External Activities

The external activities which are transferred from the internal activities can be effectively utilized and the best results can be obtained through the following steps: • The initial loosening of bolts can be started once the

last good part is passed through the conveyor. • Conveyors can be dismantled earlier. • Proper arrangement and orderliness of the inserter. • Keeping the necessary tools near to reduce the time. • Pre-arrangement of stand, gloves and pneumatic

devices. The optimization is the use of best as well the prominent

one. In prominent use of the SMED methodology, there is also continuing emphasis when applying it upon the objective of externalizing changeover tasks. Even in instances when the SMED methodology is not adopted, for example when practitioners approach improvement by seeking to brainstorm potential opportunities or by seeking to eliminate waste in


current operations, the objective to externalize changeover tasks can still be strongly manifest.

Document the New Procedure

The documentation of the newly designed procedure finds the way to measure the success of this process. The new

procedure ensures the new facet of production which includes many advantages, complicated face of inversion of die set by fork lifter is desperately eliminated. The die blocks are designed, its sizes are reduced and set as such according to the design features of rim. The documentation is tabulated as in Table 3.

Table 3

Thus, this applied SMED process reduced the setting

time from 90 minutes to 21 minutes, by implementing the new design. Conclusion

Here by implementing the new process and new design it is evident that exchanging the dies within 20 minutes. Ultimately this is the success of SMED process as it reduces the time consumption from 90 to 20 minutes. Further optimizing the external activities by reducing the threads of the bolts the time can be further reduced. SMED improvement techniques may be assessed both in terms of their allocation to the methodology’s stages and in terms of their collective representation of a full range of potential improvement options. In this way each of the techniques adopted in the conceptual stages can be unambiguously assigned such as “preparing operation conditions in advance” “improving die transportation”. In making any such judgment, it is of course crucial to understand exactly what the methodology’s successive stages are attempting to achieve and how they differ from one another. The compatibility of the technique “implementing parallel operations” in streamlining stage is also to be questioned. Other potential improvement options are enhancing maintenance, good communication and the adoption of best practice standard procedure Scope for Future Work

The SMED stages describe sequential high-level improvement objectives. The methodology is prescriptive in terms of the sequence in which these objectives are to be considered and, hence, if being strictly adopted, also in terms of when individual improvement techniques might be applied.

Such a structured approach has likely advantages in that complex evaluation of how improvement is to be gained might be side-stepped. However, it is an approach which necessarily depends for its success upon all changeover situations being largely similar. In particular, it depends upon an extensive proportion of pre-improvement changeover tasks being needlessly conducted in internal time. Evidence is available that it may in fact be more advantageous to forego a programme of prescriptive improvement and instead tailor improvement to the specific situation in hand, applying selected SMED techniques on merit. It is observed undertaking improvement to a model manufacturing process includes the assessment of opportunities in sequence, in accordance with the methodology, commencing with externalizing existing tasks. References Benjamin W Niebel. (1987) ‘Motion and Time study’, 7th edition. James B.Dilworth. (1993) ‘Production and Operations

management’, 5th edition. Richard McIntosh, Geraint Owen, Steve Culley and Tony

Mileham.(2007), ‘Changeover Improvement: Reinterpreting Shingo’s SMED Methodology’- IEEE Transactions on Engineering Management, Vol. 54, No. 1

Roberto 0. Agustin, Fely Santiago. (1996), ‘Single-Minute Exchange of Die’, IEEE SEMI Advanced Semiconductor Manufacturing Conference.

Stefan Schmidt ‘Total Productive Maintenance and Change over Reduction Engineering a Way to Increase Quality and Productivity’, IEEE explore.

www.wikipedia.com, Single minute exchange of dies.

Activities Time(Sec) Bringing down the die to the expander base 3 Disengaging conveyor lock 5 Removing the conveyor 30 Loosening the bolts 270 Disengaging the blocks 152 Inserting and initial tightening of bolts 280 Tightening of bolts using pneumatic wrench 320 Tightening of bolts using key 170 Bringing down the die to the expander base 3 Pushing the conveyor 50 Engaging the conveyor lock 2 Total 1285

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Experimental Verification of Single Minute Exchange of Dies (SMED)