SMED: Single Minute Exchange Die, Fundamental Concepts

The essence of the SMED philosophy consists in eliminating the concept of manufacturing batch, minimizing the machine preparation time. For companies that want to increase their flexibility and at the same time reduce their stock levels, it is critical to minimize the times for both tool changes and preparations.

Introduction

This need is in turn inserted within the philosophy of time reduction or maximum speed, which today invades everything, from the capacity for rapid attention to the reduction of response times, and shorter terms from research and design to the start. of the production and placing of the product on the market, and the reduction in processing times. Time is worth gold, and every day it becomes more important both from the point of view of customer satisfaction, as well as from the costs and the competitive capacity of the company.

Eliminate the concept of manufacturing batch, minimizing the preparation time of machines and materials, this is, in essence, the SMED philosophy. Today there is a commitment not only to reduce preparation times to a minimum, but also repair and maintenance times.

In the late 1960s, it took Toyota more than four hours to change models on an 800-ton stamping press, when its Volkswagen equivalent required just two hours. The engineer Shigeo Shingo before a research activity assigned by the Toyota manager, Mr. Ohno, (destined to consolidate and make feasible the Just in Time Production System, with the clear and precise objective of reducing waiting times and levels of inventories of both work-in-progress and finished products -both being cataloged among the seven classic changes), he proceeds to develop a system that allowed reducing the aforementioned time to just three minutes.

The implementation of the SMED had begun, thereby overcoming one of the biggest obstacles that Toyota had at that time to implement “just in time” production, a system that would become famous throughout the world as the Toyota Production System ( TPS).

When a company has worked on reducing the setup time of a specific machine for several years, it finds that it is possible to radically reduce the changeover time from several tens of hours to less than ten. Later and for the same machine, times of tens of minutes can be achieved. A little further on we can talk about changeover times of less than ten minutes. Some companies have even achieved the ultimate goal: first-touch changes, where time is close to zero. No company can afford to stop working on reducing changeover times until they reach this goal. It is not about analyzing whether or not it is possible, but about seeing what needs to be done and how long it will take to achieve it.

Not only Toyota serves as an example, but we can also mention the company Kodak (USA) which in 1984 managed to reduce the changeover time from approximately two hours to thirty minutes in terms of plastic injection presses; a few months later, it was reduced again to six minutes.

Although there are a large number of techniques aimed at increasing or improving productivity, the reduction in preparation times deserves special consideration and is important for three reasons:

1. When the changeover time is high, the production batches are large and, therefore, the investment in inventory is high. When the changeover time is negligible, the necessary quantity can be produced daily, almost eliminating the need to invest in inventories.
2. Quick and simple change methods eliminate the possibility of tool and fixture adjustment errors. The new changeover methods substantially reduce defects and eliminate the need for inspections.
3. With quick changes, you can increase the capacity of the machine. If the machines run seven days a week, 24 hours a day, one option to have more capacity, without buying new machines, is to reduce your changeover and setup time.

One of the most important advantages of reducing preparation times to single-digit figures is that the company can go from working against the warehouse to manufacturing to order. Since for some factories, the investment in finished product inventory is the greatest asset, its conversion into cash can be used to finance other investments or reduce debts.

The SMED is without a doubt a highly innovative concept generated by the Japanese within the field of industrial engineering. It should be noted that in Japanese companies, the reduction of preparation times not only falls on the engineering staff but also on the Quality Control Circles (QCC).

It is worth mentioning that currently this work philosophy is not only applied to tool changes and preparation of machines and equipment but also to the preparation and fine-tuning of operating rooms, preparation of air shipments, attention to Formula One cars, and others. service-related activities.

Methodology for method change

As in the case of other work methods, various techniques are used, being the:

• Pareto analysis: intended to differentiate the trivial many from the vital few. In other words, concentrate on those few activities that absorb most of the change and/or preparation time.
• The six classic questions: What? – As? – Where? – Who? – When? and the respective Why? corresponding to each of the respective answers, to eliminate the unnecessary, combine or rearrange the tasks, and simplify them.
• The five Why? successive: to detect possibilities of change, simplification, or elimination of tasks included in the process of changing tools or preparing machines or equipment. This technique is fundamentally focused on the search for the root cause, that is, on the factors that in this specific case determine the preparation times or change of tools.

Fundamental concepts of SMED

To reduce preparation times, four key concepts must be taken into consideration, consisting of:

1. Separate the internal preparation from the external. Internal preparation must be understood as all those activities for which it is necessary to stop the machine or equipment. While the external includes all those activities that can be carried out while the machine is running.
2. Convert as much internal preparation as possible to external preparation. In this way, many activities that must be carried out with the machine stopped can be carried out while it is running. Example: The pressure caster can be preheated using the excess heat from the oven that serves this machine. This means that the test shot to heat the metal mold of the machine can be eliminated.
3. Elimination of adjustment processes. Adjustment activities can represent between 50 and 70 percent of total internal activities. For this reason, it is imperative to systematically reduce the adjustment time to reduce the total preparation time. The key is not to reduce adjustment, but to “eliminate” it through creative thinking (eg adjusting tools in one touch-up).
4. Suppress the preparation phase itself. To completely dispense with preparation, two criteria can be adopted. The first is to use a uniform product design or use the same part for different products, and the second approach is to produce different parts at the same time. The latter can be achieved by two methods. The first method is the whole system. For example, in the same die, two different shapes are carved. The second method consists of die-cutting the different pieces in parallel, through the use of several lower-cost machines.

Application techniques

Six techniques are used in the SMED designed to apply the four concepts previously exposed.

Technique No1: Standardize external preparation activities. The operations of preparation of the molds, tools, and materials must become habitual and standardized procedures. Such standardized operations must be collected in writing and posted on the wall so that the operators can view them. Later, the workers must receive the corresponding training to master them.

Technique No. 2: Standardize only the necessary parts of the machine. If the size and shape of all the dies are fully standardized, the setup time will be greatly reduced. But since it results in high cost, it is advised to standardize only the part of the function needed for the preparations.

Technique No. 3: Use a fast-fixing element. Although the most widespread fastening element is the bolt, since it holds in the last turn of the nut and can loosen in the first turn, various elements have been devised that allow a more effective and efficient fastening. Such elements include the use of the pear-shaped hole, the U-shaped washer, and the grooved nut and bolt.

Technique No4: Use a complementary tool. It takes a long time to attach a die or jaws directly to a die press or lathe chuck. Consequently, the die or jaws must be attached to a companion tool in the external setup phase, and then in the internal setup phase, this tool can be clamped into the machine almost instantly. To make this feasible, it is necessary to proceed with the standardization of complementary tools. Mention can be made, as an example of this technique, the rotating mobile table.

Technique No. 5: Make use of operations in parallel. A large punch press or large die-casting machine will have many clamping positions on all four sides. The setup operations of such machines will take up a lot of the operator’s time. But, if parallel operations are applied to such machines by two people, useless movements can be eliminated and thus the set-up time can be reduced.

Technique No. 6: Use of a mechanical preparation system. When setting the die, use could be made of hydraulic or pneumatic systems for simultaneous fixing of several positions in a matter of seconds. On the other hand, the heights of the dies of a punch press could be adjusted by an electronic mechanism.

Most common problems when making tool changes or preparations

When preparation activities take too long or preparation time varies considerably, the following problems or inconveniences may be occurring:

1. The completion of the preparation is uncertain.
2. The preparation procedure has not been standardized.
3. The procedure is not properly observed.
4. Materials, tools, and jigs are not ready before the start of setup operations.
5. Mating and separation activities take too long.
6. The number of adjustment operations is high.
7. Preparation activities have not been adequately evaluated.
8. Non-random variations in machine setup times.

These obstacles can and must be overcome through daily research and repeated questioning of preparation conditions in the workplace.

Importance of the Five “S” in the application of the SMED

The Organization-Order-Cleaning-Standardization and Discipline activities are essential and fundamental for the correct and optimal implementation of the SMED system.

Being able to quickly find the tools, having all the equipment and workplace in a clean state, and having visual elements that allow the best adjustment, are benefits that the systematic application of the Five “S” brings with it.

Procedures to improve readiness

In addition to video recordings and time and motion studies related to setup activities, there are four more procedures for making improvements. The first is to separate the internal preparation from the external preparation. The second is reducing internal preparation time by improving operations. The third, in promoting a further reduction in internal preparation time by improving the equipment. And, the fourth is the challenge of reducing it to zero.

Phase 1: Differentiation of external and internal preparation. By internal preparation, as previously stated, all those activities that require the machine to stop are included to carry them out. While external preparation refers to the activities that can be carried out while the machine works. The main objective of this phase is to separate the internal preparation from the external preparation and to convert as much of the internal preparation as possible into external preparation. To convert internal preparation to external preparation and reduce preparation time for the latter, the following four points are essential:

• Prepare in advance the templates, tools dies, and materials.
• Maintain dies in good operating condition (TPM).
• Create tables of operations for external preparation.
• Maintain good order and cleanliness in the storage area of ​​the removed templates and dies (Five “S”).

The most important of these four points is the last one: keeping the storage area for tools, templates, and dies clean and tidy. If tools are haphazardly stored in a toolbox, workers will waste time finding the ones they need; it is the typical useless operation that does not create additional value.

Phase 2: Internal preparations that cannot become external must be subject to continuous improvement and control. To this end, the following points are considered key to their continuous improvement :

• Keep tool and die storage areas clean and orderly (Five “S”).
• Monitor the effects of changes introduced in the sequence of operations.
• Monitor the personnel needs for each operation.
• Monitor the need for each operation.

The continuous examination of the points described above will reveal opportunities for improvement.

Phase 3: Equipment improvement. Until now, all measures taken to reduce setup times have referred to operations or activities. The next strategy focuses on improving the team. Here are some ways to make it feasible.

• Arrange external slides and modify equipment so that different slides can be selected at the push of a button.
• Recycle the heat from machining operations and use it to preheat ovens.
• Modify the structure of the team or invent tools that allow a reduction in preparation and start-up.
• Eliminate adjustments required to set the height or position of dies or jigs by using a limit switch or convert manual adjustments to automatic.
• Review standard operations sequence sheets and train operators when equipment is upgraded.

Phase 4: Zero Preparation. The ideal preparation time is zero. To achieve this, it is necessary to use a common part for several products. This could be achieved in the development and design phase of the new models.

Conclusions

The times invested in preparation and change of tools and tools are one of the key factors for a world-class manufacturer. The reduction of the times of change of tools allows the reduction in the size of the batches, thus making it possible to reduce the inventories in the process. The reduction of batches makes it feasible to reduce cycle times; the reduction of the latter allows the company to give a faster response to customers, reducing or eliminating the need to maintain inventories of finished products.

A typical factory will have numerous tool change processes, and a significant part of continuous improvement will be directly related to gradually and systematically reducing tool change times.

The Just-in-Time Production System is not feasible if the batch sizes are voluminous, and such batches can only be reduced if the times for tool change and equipment preparation are reduced.

In the past, the need to speed up tool changes was not given much importance, but the widespread acceptance of Just in Time has brought this issue to the forefront of many manufacturing plants.

Many companies have verified that tool change times can be significantly reduced (in the order of 50 to 75%) with the mere study of the problem and the subsequent improvement in the organization of activities. Additional reductions can be achieved through relatively small modifications to machines, tools, fixtures, or products. Only after having implemented these kinds of simple improvements is it necessary or necessary to incur capital investments of a certain level.

The current cost of obtaining significant improvements in terms of time is feasible merely with the time allocated, firstly, to training the operators and secondly, to the daily attention they provide to the machines and that of the necessary technicians and engineers. for advisory and support activities.

Since there are relatively few factories without switching costs, most have the opportunity to reduce them and reduce the associated inventory investment. Preparation costs are not limited to conventional mechanical workshops, they also affect process and assembly industries, such as pharmaceuticals, paper, food, chemicals, and electronics, among many others.

The important point is that the operations of preparation of machines and change of tools, tools, templates, and accessories are one of the most substantial wastes in manufacturing. It is only enough to consider that if in a factory all operations related to tool changes and preparation times (retooling times) are reduced to a minimum, they can normally reduce manufacturing costs by 20% or more.

Annex – Checklist to be carried out with the machine running die

1. It is in the right place?
2. Has each part of the die been checked?
3. Is it really clean?
4. Is it cracked?

Tools

1. Are there wrenches?
2. Are there screwdrivers?
3. Are there spring clips?
4. Are there clean rags?
5. Are there level gauges?
6. Are there brushes?
7. Are all the tools in their correct place?

Control means

1. Are the necessary micrometers available?
2. Are there adjustable gauges?
3. Are there tube gauges?
4. Are there magnifying glasses?
5. Do you have dial gauges?
6. Are all the inspection tools there?
7. Are there templates for measurement?
8. Everything is in perfect condition?
9. Are all the means of control in the correct place?

Bibliography

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