Sunday, December 8, 2013

The SMED System: Shigeo Shingo's Explanation


Before the SMED system development by Shingo, efficiency of setup required two things:

1. Knowledge relating to the structure and function of the machinery and equipment, as well as a thorough acquaitenance with tools, blades, dies, jigs, etc.

2. Skill in mounting and removing these items, and also in measuring, centering, adjusting, and calibrating after trial runs.


The History of SMED

In 1950, Shingo was conducting an efficiency improvement survey at Toyo Kogyo's Mazda plant. As the large body-molding presses of 350, 750 and 800 tons were declared as bottlenecks, Shingo did a production study.

There was an incident of a missing bolt and one hour was wasted in finding the bolt. Shingo had written that gave him the idea that external set operations have to set up as standard procedures and one has to make sure that all items required for set up are there before one starts the set up procedure. Shingo established the external set up procedure of making all items required for a set up  and the efficiency was raised by 50% and the bottle neck problem disappeared.

The Second Idea

In 1957, Shingo was studying the operation of a large planer which is machining diesel engine beds. He noticed that centering and dimensioning of the engine bed had to be done and was being conducted on the planer table only. He came with the idea of buying an extra planer table on which this activity can be done while on the machine a job is getting machined. When the job was completed, the table was pushed out and the second table was pushed in ready with the job. This solution resulted in 40% increase in productivity.

The Third Important Event

In 1969, Shingo studied the set operation of 1,000 ton press at Toyoto Motor Company/s plant. The setup time was four hours and it was known that Volkswagen in Germany was doing the same set up in two hours. Shingo in association with Toyota engineers have identified the external setup operations and internal setup operations and improve the process to a time of 90 minutes. According to Shingo, it took six months of effort to reach that stage.

At this stage, Toyota management thought of a challenging goal. Can be reduced drastically to only  three minutes? This challenge resulted in the inspiring insight in Shingo. Can we convert much more internal activity (setup activity that was being done on the machine) to external activity. So a search began for eliminating activities from internal setup activity to move them the external activity. Shingo had written that 8 ideas came in quick succession and they developed these 8 ideas in 3 months time to reach the single digit setup time. So Shingo remarked that it took 19 years of time to make a drastic improvement to the setup operations.


The SMED System - Book by Shigeo Shingo - Chapter Summaries 


Foreword

SMED system is the most essential method for achieving Just-In-Time Production. SMED system will revolunize existing production systems and I hope you will practice it after reading this book.

Introduction

In many factories, diversified low-volume production is a problem. The main difficulty is the setup operations and adjustments required - calibration, switching of tools or dies etc. Frequent setups of course are necessary to produce a large variety of goods in small lots.

But now I can tell you, you can cut your setup time and increase productivity. You can do setups in three minutes for tasks which had taken 3 hours earlier. The theory and techniques are made available to you in this book. Japanese industrial engineers have long understood the need to reduce setup times and many examples are made available by them in books. But in this book for the first time principles are provided so that you can apply them to your situation even though it does not match any of the previous examples or applications.

Why the setup times remained high for long. Managers and industrial engineers neglected the task and left it to the skill of workers.

People have to realize that high volume production and large lot production are the same. Even high volume production can be achieved through small lots and economy of manufacturing can be realized.  Traditional production planning assumes inventory as inevitable but new production system based on SMED works on the concept of confirmed production and eliminates inventory.

It took 19 long years for me to develop the SMED system.

Chapter 1 The Structure of Production


Production activities may best be understood as a process consisting of operations.

A process refers to a continuous flow by which raw materials are converted into finished goods. An operation is action performed by men, machine or equipment on raw materials, or intermediate or finished goods (for example packing). A process can have one or more operations.

Manufacturing processes can be further divided into four distinct phases (traditional IE categories)

1. Processing (termed as operation) 2. Inspection  3. Transportation 4. Storage.

The storage phase can be further categorised into:
1. Storage of raw materials.
2. Storage of finished goods
3. Lot waiting for process: The entire lot is in a queue before a machine
4. Waiting for a lot: Some of items of the lot are yet to be processed and some are processed.

Each operation on a lot will have preparation and clearing. These are termed setup operations.
The principal operation carried out on workpieces include essential operation, auxiliary operation like loading the workpiece and removing it and margin allowances (activities) that irregularly happen like sweeping up cuttings and personal activities of the operator like taking rest for fatigue and drinking water etc.

It is important to note that there are setup operations in inspection, transportation and storage also.

Chapter 2. Setup Operations in the Past


The blind spot: The unspoken assumption that drastic reductions in setup time are not possible. But with the development of SMED, the concept of economic lot size has diappeared from the profit-engineering agenda. Moreover, SMED has substantially reduced the level of skill required for setups and production operators themselves can do the setup.

3. Fundamentals of SMED


In the spring of 1950, Shingo was conducting an efficiency improvement survey at Toyo Kogyo's Mazda plant. At the presses were bottleneck machines, Shingo conducted a production analysis and observed a die change.  As he observed the time wasted after the machine was stopped for setup change, it dawned to him that setup operations fundamentally were two types: Internal setups which are to be done after a machine is stopped and external setups which can be conducted when the machine is in operation. The external set up were identified and only internal setups were done when the machine is stopped. The setup time reduced by 50%.

The first step of SMED was discovered and Shingo started advising companies on improving setups.

The second insight

Shingo was doing study of open-sided planer at the Mitsubishi Heavy Industries Shipyard for methods improvement. He observed that marking-off procedure for centering and dimensioning the engine bed ws being conducted on the planer table and it was taking significant time. The idea came came to install a second planer table and perform the setup operation on it separately. Then the table was shifted in less time and it saved time and increased productivity.

The third experience

In 1969, the divisional manager of body shop at Toyota Motor Company told Shingo that they were taking 4 hours to make a die change and they know that in Volkswagen they were doing in two hours. Shingo worked with them to separate internal and external setup items and got the die change time reduced to one and half hours.

After a month, Shingo was informed that management want the setup time to go to three minutes. Shingo was strartled but challenged. The thinking led to the idea that some more internal elements can be converted into external elements. In three months, three minute goal was reached and Shingo says, he named the method SMED.

This SMED concept then spread to all types of setups in Toyota.

Basic steps in the Setup Procedure

1. Preparation, checking of all required items, tools and materials   30%
2. Removing old tools and mounting new tools 5%
3. Centering, dimensioning and setting other conditions 15%
4. Trial runs and adjustments 50%
5. Returning Old tools - Negligible

The time taken for trail runs and adjustments can be shortened by improving the prior process of centering, dimension and setting.

Basic Steps of SMED

Separating Internal and External Setup
Converting Internal Operations to External Operations
Improving Internal Setup Operations
Improving External Operations

4. Techniques for Applying SMED





Separating Internal and External Setup

Doing External Setup Operations Efficiently - Preliminary Steps

Use a checklist

Make a list of all the parts required with names and specifications and make sure that they are there before the setup. For it to happen without any shortcoming, Shingo recommended that a drawing is made with all the parts pictures and keep the parts on those drawing.

Then there has to be one more list that specifies details of pressure, temperature and other settings that are part of external setup. One has to go through this checklist and ensure that every item is having the required specification and also functioning. These list of items and checklists have to be separate for every machine.

The old die and related items should be transported back either after the setup is completed or by people who are specific to transportation. The machine should not be made to idle due to the transport operation of old die and related items.


Converting Internal Operations to External Operations

The first step in converting internal operations to external operations is to create operating conditions of the dies externally. Then only internal operations are to push the dies and attach them to ram and body.


Preheating Dies

Old practice was to heat dies in die casting by injecting hot metal between them. Instead of that if dies were preheated using gas or electric heat externally, 30 minutes could be saved.

Standardization of dies of various sizes or items on a machine can be done by shape standardization to reduce setup time. But the dies of even small parts can be large because of that. Instead Shingo suggested function standardization.

Function Standardization

What are the functions in attaching die to machine? Clamping, centering, dimensioning, expelling,grasping, and maintaining loads.

Efficient function standardization requires that for each die, the function providing features are only standardized as required by examining the die feature by feature or element by element.

Clamping height can be changed by adding shims to smaller dies. Centering can be done centering jigs. The dies can be made as a set and they can be inserted and withdrawn like a casette so that die inserting time can be only 20 seconds. Various locating elements can be used to adjust the dies in the required positions externally.


5 Applying SMED to Internal Operations

Improving Internal Operations or Reducing Time of Internal Operations

Implementation of Parallel Operations

Die-change operations on plastic molding machines, and die-casting machines and large presses require work both at front and at the back of the machine. If two work parallelly  one at the back and one at the front lot of time is saved.

The Use of Function Clamp

The length of the bolt should be determined such that only one turn is required for fastening or loosening. Such bolt will be called functional clamp.

Examples of One Turn Attachments

The Pear Shaped Hole Method

The U Shaped Washer Method

The Split Thread Method

The U-Slot Method

The Clamp Method

One Motion Methods
  Cams and clamps
  Wedges, tapered pins and knock pins
   springs

Magnetism and Vacuum Suction

Interlocking Methods
(Punch and die assembly for making interlocking integral fasteners - Patent No. US2924312)

Instead of fastening, many times, two pieces can be interlocked and it is sufficient.

Interlocking Method for Press Dies

In a press, the upper die is attached to the machine ram and the lower die is attached to the machine tool. Why there should be same number and diameter of bolts in both sides. While the die attached to the ram has to be supported against gravity, the die attached to the machine bed need not be so supported. Shingo suggests holding plates and cradles for the holding plate to hold the die.


Seeing is believing. Watch in YouTube video die changes in less than 9 minutes
SMED - YouTube Videos


Related Development:

Design for changeovers
http://etidweb.tamu.edu/hsieh/ENTC410/Design%20for%20Mass%20Customerization/DesignForChangeOver.pdf
The paper is on original equipment manufacturer making design of machine that facilitates quick setup changes

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