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The Single Minute Exchange of Die (SMED) method was developed by Shigeo Shingo from the late 1950s to the early 1960s. Shingo was a consultant for many Japanese organizations, including Toyota, who managed to obtain excellent results with this method on traditional car body molding presses. SMED is vital to achieve quick changeover, which reduces WIP and improves lead time. Unfortunately, many companies believe that SMED and quick changeover is the same thing.

SMED was developed on presses, where the classic stamp change represents changeover to produce a different code. Lately, however, reducing changeover time has been the object of discussion for many different types of machines and service processes. Nowadays we even have applications that reduce changeover time in hospitals, reducing time between one operation and another, or applications that make it possible to host various events in the same conference room and so on. The main concept is that of quick changeover, whereas SMED is linked more to machine and stamp changes; in any case, from here on these two concepts will be considered equivalent. Reducing changeover time is vital when striving to reduce WIP. It is fairly obvious that if changeover time is high, according to the concept of

“economical lots”, large lots will need to be produced before stopping and chang-ing. Organizations that apply SMED also list other benefits, such as:

• Improvement in safety regarding the plant;

• Improved ergonomics for the workers who perform changeover.

To apply SMED, changeover activities need to be divided into four stages.

6.8.1 The Four Stages of SMED

The organizations that apply SMED usually follow these four steps:

• Stage 1: Identification of internal and outer set-ups and preparation.

• Stage 2: Conversion of as many internal set-ups as possible into outer ones.

• Stage 3: Improvement of internal set-ups.

• Stage 4: Improvement of outer set-ups.

Internal set-ups (Internal Exchange of Die, IED) are activities that can only take place when the machine or process has been frozen; for example physically remov-ing the stamp or its components, or movremov-ing a patient from the operation room.

Outer set-ups (Outer Exchange of Die, OED) are activities that can take place while the process continues to flow. For example removing the next stamp from the warehouse and preparing it for the job, anesthetizing a patient, preparing material for the next event. Outer set-ups can be carried out while the process works normally, thus saving time.

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Having completed all four stages, Kaizen teams need to repeat them at various times so as to effectively improve changeover times. Many manufacturing companies have seen that it is quite easy to move from changeover times lasting a few hours to ones lasting under an hour. To achieve changeover in less than 10 min, however, SMED has to be repeated various times, over many years, maybe even through modifications to the machinery or redesigning of the product/service.

6.8.2 Identifying Internal and Outer Set-Ups and Preparation

This stage is vital because it separates activities that can only be carried out when the process has been frozen from those that can be carried out during flow.

The problem is that many workers do not realize that some operations can be carried out while the machines are working, and processes are often stopped unnecessarily. When formula one drivers stop in their paddock they have to leave it as quick as possible; in fact everything is prepared and kept ready so that the time the driver spends stationary is kept as short as possible.

On average, changeover can be reduced by 60% by converting internal set-up operations to outer ones (results obviously depend on the initial situation). During changeover preparation, some simple tasks can be carried out to save time:

• Preparation of checklists and set-up operations;

• Performance checks on equipment and tools;

• Improvements regarding transportation of various components.

The checklist lists everything needed for set-up, including:

• Tools, equipment, instructions and workers;

• The necessary working conditions (e.g. temperature, pressure, electricity, size, etc.);

• Any measures that need to be taken.

Figure 6.22 shows one such checklist; they are especially useful to avoid mistakes or to avoid the wasting of time looking for tools, and are always specifi-cally tailored for the machine concerned.

The checklist also mentions health and safety conditions for workers, and environmental issues; these are very important and must never be neglected. The list refers to kits and sets: these contain tools and equipment needed for set up that have been prepared beforehand thanks to 5S. This means that workers do not have to waste time searching for things they need. Checklists should be prepared specifically for each machine because general lists only create chaos.

Checklists can also be used for activities that are not linked to manufacturing.

According to theNew England Journal of Medicine, checklists not only reduced patient changeover time by 30%, but also reduced deaths caused by operations by 40% (from 1.5% down to 0.8%). Checklists are incredibly useful when preparing for changeover and they reduce mistakes considerably.

Checklists, however, cannot really avoid the waste of time caused by the performance of tools. Workers may be fully prepared during set up, but if when changeover occurs they realize that a tool has not been sharpened and the screw-driver is not working, then all the preparation was, indeed, pointless.

Usually, after having used the tools and before placing them back where they belong (an area designated by 5S), the tools should be accurately checked so that if they need repairing or maintenance it can be carried out before their next use. These checks should be standardized and included in the instructions all workers have to follow. Last but not least, components and tools should be moved from the warehouse to the workstation while the process is still at work, so as not to waste time when flow is stopped. If the objects that need to be moved are heavy or bulky Machine TH4 checklist

SMED operation

Tick off Necessary items

Competent workers (check worker ability report) Necessary tools

Pneumatic screwdriver Keys n° TH

Mold components

Mold part A Mold part B TH screw set TH body anchor set Other necessary equipment

Magnetic lifter

Personal protection equipment (refer to instructions ILSS08) CTH4 gauge

Oil collector and cleaning kits

Refer to instructions: ILQ15 “Changing press molds instructions”

ILSS08 “Protections for maintenance and set up”

ILA02 “Managing environmental impact on presses”

Fig. 6.22 Checklist (tailored according to the machine)

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this could already save a lot of time. Figure6.23(an example of a SMED applica-tion) shows such an example: it involves the mold changeover of a hot press.

Figure6.23shows an improvement to SMED brought by a Kaizen workshop. In the improved situation, a second cushion made it possible to reduce total mold transportation time. In fact, after the workshop, the crane moves the new mold from the warehouse to cushion number 2. The machine is then switched off; the mold is removed and placed on cushion number 1. The new mold is then installed and the old one is moved towards the warehouse. Before the workshop, the machine had to be switched off, the old mold was removed and moved to the warehouse; here a new mold was picked up, transported to the machine and installed. Changeover time was reduced by 10% by applying these small modifications. This example comes from an excellent German organization that boasts among the best set-up times in the world.

Before

After

6

3

4 5

1 2

4 5

3 7 2

8

Press 1

Press

Cushion 1

Cushion 1 Cushion 2

Mold Warehouse

Mold Warehouse

Fig. 6.23 Improvement in mold change of a large press

6.8.3 Converting Internal Set-Ups to Outer Ones

After the preparation stage, which involved creating checklists, applying checks and improving transportation, the next stage involves converting internal set-ups to outer ones. This stage allows a further decrease in times and can be divided into three different aspects:

• Preparing working conditions;

• Standardizing operations;

• Use of jigs.

Preparation of working conditions includes following the checklists; thus not only having components, tools and equipment at the ready but also having prepared perfect working conditions. While the machine is still working, conditions such as temperature, pressure, lubrication, cleaning and components can be prepared. This includes, for example, preheating molds and lubricating them or, in a hospital, preparing a certain surgical tool beforehand.

Standardizing operations helps reduce changeover time considerably. Videos taken during a SMED Kaizen workshop, for example, show workers wasting time by adjusting, measuring or fixing a machine in preparation for a new mold. Often changeover can be speeded up by always using stamps of the same size and thickness to avoid unnecessary adjustments. Similarly, tools that permit quick centering can be installed on machines. Jigs can also be used to standardize mold installation.

6.8.4 Improving Internal and Outer Set-Up Activities

To improve internal set-up operations, most companies rely on four steps:

• Carrying out operations in parallel

• Carrying out operations in parallel usually involves two workers working at the same time to save time. The downside is obviously that manpower costs increase, but often one single worker takes more than double the time of two workers to carry out the same activity. When the set-up area is quite big, for example, spaghetti-charts show that if there is only one worker, 80% of time is wasted in movements. Two workers, by contrast, can separate and work at the same time in different areas.

• Using clamps

Molds and tools that are attached by using screws, bolts and nuts are just a waste of time. Screws go missing quite a lot, especially when there are a lot of them;

they get mixed up easily, and they obviously have to be screwed in, which is a waste of time. Clamps are quicker and can be used directly on the machine.

• Eliminating adjustments

Methods that quickly fix molds and tools include:

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– Single-movement levers;

– Magnetic systems;

– Interlocking systems;

– Making the system visible and easy to use by applying instructions to the machines.

• Using the most efficient tools and equipment available

• When set-up has been improved following the aforementioned steps, many organizations choose to replace tools and equipment with more efficient versions. Photos and videos of SMED could show that a trolley would be faster than a crane (or vice versa), or that a transpallet could improve workers’ speed in certain situations.