SMED

Definition

SMED (Single-Minute Exchange of Die) is a systematic approach to reducing the time required to change over a piece of equipment from producing one product to producing another. The goal implied by the name is to reduce changeover time to single-digit minutes — under 10 minutes — though the method can be applied to push changeover time far lower.

Fast changeovers are essential to Just-in-Time production. When changeovers are slow and expensive, the economic response is to produce in large batches to amortize the changeover cost. Large batches create long lead times, excess inventory, and inflexibility. By making changeovers fast, SMED makes small lot sizes economical, which enables leveled production (heijunka), shorter lead times, and the flexibility to respond to changing customer demand.

Japanese Origin

Shinguru dandori (シングル段取り) combines the borrowed English “single” with 段取り (dandori, “setup” or “preparation”). Dandori is the standard Japanese manufacturing term for the changeover process — all the activities required to switch equipment from one product to another. The “single” refers to single-digit minutes.

History

The history of quick changeover at Toyota is longer, broader, and more complex than the commonly told story. It spans multiple decades, multiple technologies, and many people — and the role of its most famous chronicler, Shigeo Shingo, requires careful clarification.

Looms: Zero Changeover Before Automobiles

Quick changeover thinking at Toyota predates the automobile. Sakichi Toyoda’s automatic looms were designed for rapid shuttle and bobbin changes — effectively zero changeover time for material replenishment. The principle that equipment should not stop for setup was embedded in the Toyoda family’s manufacturing DNA before Toyota Motor Corporation existed.

Machine Tools: Ohno’s Background in Seconds-Level Changeovers

Taiichi Ohno came from a machine shop background. In machining, tool changes are measured in seconds or minutes — a cutting tool insert can be indexed or replaced quickly, and fixtures are designed for rapid workpiece loading. Ohno’s formative experience was in an environment where changeover was already fast by nature. When he turned his attention to stamping, the multi-hour changeover times were unacceptable by comparison. His frame of reference was machining, where minutes — not hours — was the norm.

Stamping: Decades of Internal Improvement

Toyota’s core changeover challenge was in its stamping shops. Stamping presses use large dies to form body panels, and changing dies was a major operation — often taking hours. Because Toyota produced far fewer vehicles than American competitors, it could not dedicate a press to a single part. Toyota needed to change dies frequently on the same press, making changeover speed a competitive necessity.

The work to reduce stamping changeover times was led internally over many years by Katsuya Jibika and many other Toyota engineers. This was not a single project or breakthrough — it was decades of systematic improvement. Jibika and his colleagues modified equipment to make it easier to align dies, clamp and unclamp, move heavy tooling, preheat dies, and eliminate adjustment steps. Each improvement shaved time from the process.

1960: Danly QDC Presses at Motomachi

In 1960, Toyota installed fourteen 600-ton stamping presses from the Danly Machine Corporation (based in Cicero, Illinois) at the Motomachi plant — Japan’s first automobile plant built exclusively for producing passenger cars. Danly had pioneered QDC (Quick Die Change) technology featuring moving bolsters and other innovations that dramatically reduced die change times.

These machines represented a step change in what was technologically possible. Eiji Toyoda, who chaired the Motomachi Plant Construction Committee from 1958, would have been directly involved in the equipment procurement decisions. The Danly presses, combined with Toyota’s ongoing internal improvement work, further accelerated the reduction of changeover times across the company.

One of the original Danly 600-ton presses — standing 11.5 meters tall and weighing 235 tons — is preserved today in the Toyota Commemorative Museum of Industry and Technology in Nagoya, where live stamping demonstrations are still conducted. First-generation Corolla stamped parts are displayed alongside it. It is the largest exhibit in the museum.

Equipment Standards: TMS and Vendor Specifications

Toyota’s internal improvements were not confined to existing equipment. The engineering lessons learned from decades of changeover reduction were codified in TMS (Toyota Manufacturing Standards) — the equipment specification and purchasing standards that Toyota uses when buying new machines. These standards specified quick-changeover features so that all new equipment came into the company with these improvements built in from the start.

Japanese equipment vendors studied Toyota’s requirements and incorporated quick-changeover features into their standard designs, which in turn spread the technology across the broader Japanese manufacturing industry.

Shigeo Shingo and the SMED Book

Shigeo Shingo began his relationship with Toyota around 1955 as an industrial engineering trainer, teaching productivity improvement courses (known as “P courses”) to young engineers and team leaders. His training covered time study, motion study, operation analysis, and process improvement from an industrial engineering viewpoint, and he made genuine contributions to Toyota’s kaizen training programs over many years.

In 1985 (Japanese edition 1983), Shingo published A Revolution in Manufacturing: The SMED System, which systematized the approach to changeover reduction into a clear methodology. The book’s central framework — distinguishing between internal setup (work that can only be done when the machine is stopped) and external setup (work that can be done while the machine is running), then systematically converting internal to external and streamlining both — gave the world a structured, teachable method for attacking changeover time. Whether Shingo originated this framework or codified what he observed at Toyota and elsewhere, the book remains the definitive published work on the topic and is rightly credited with introducing the SMED concept to a global audience.

Results at Toyota

Through these combined efforts — internal engineering, purchased technology, equipment standards, and continuous improvement — Toyota reduced stamping press changeover times from several hours to under 10 minutes, and eventually to as little as 3 minutes for some operations. This enabled Toyota to stamp small batches of different panels on the same press throughout the day, rather than producing weeks’ worth of one panel before switching. The inventory and lead time reductions were transformative.

How It Actually Works

The core distinction — internal vs. external setup:

• Internal setup (IED) — operations that can only be performed when the machine is stopped. Examples: physically removing the old die and installing the new one.
• External setup (OED) — operations that can be performed while the machine is still running the previous product. Examples: preparing the next die, staging tools, preheating, adjusting settings on a spare fixture.

The SMED stages:

1. Observe and document the current changeover. Video the entire changeover process. Record every step, its duration, and who performs it. Most organizations are surprised by how long their changeovers actually take and how much of the time is spent on non-essential activities.

2. Separate internal from external. Identify which steps truly require the machine to be stopped and which can be done before or after. Often 30-50% of changeover steps that are currently performed with the machine stopped could be done externally.

3. Convert internal to external. Redesign steps so they can be performed while the machine is still running. Pre-stage dies, pre-heat tooling, use duplicate fixtures that can be set up offline, prepare fasteners and tools in advance.

4. Streamline internal operations. For the steps that must remain internal, reduce their time: use quick-release fasteners instead of bolts, eliminate adjustments through precision locating devices, parallelize tasks with multiple operators working simultaneously.

5. Streamline external operations. Organize tool carts, standardize die storage locations, create checklists for preparation, and ensure everything needed for the next changeover is staged and ready.

Implementation Guidance

Start with observation. Video the changeover. Many organizations have never actually timed their changeovers or documented the steps. The current state is almost always worse than people assume.

Focus on the internal/external split first. The biggest gains come from moving work out of the internal window. This often requires no engineering changes — just better preparation and organization.

Involve the operators. The people who perform changeovers daily know where the time goes. Their ideas for improvement are essential. Imposing engineering solutions without operator input usually misses the real problems.

Set aggressive targets. The SMED name itself sets the target: single-digit minutes. Do not accept “we reduced changeover from 4 hours to 2 hours” as success. The method is designed to achieve order-of-magnitude reductions.

Common Mistakes

Accepting long changeovers as a given. Many operations assume their changeover times are fixed by the nature of the equipment. SMED has been successfully applied to stamping presses, injection molding machines, CNC equipment, printing presses, and virtually every type of production equipment. The question is not whether changeover time can be reduced, but by how much.

Reducing changeover time but not reducing batch size. The purpose of SMED is to enable smaller batches. If changeover time is cut from 4 hours to 10 minutes but batch sizes remain unchanged, the benefit is lost — the organization has faster changeovers but the same overproduction and inventory.

Solving the problem with capital investment. The first instinct is often to buy duplicate equipment so changeovers are not needed. SMED achieves the same flexibility at a fraction of the cost by making the existing equipment more changeover-friendly.

One-time effort without sustained follow-through. Changeover times tend to creep back up as tooling wears, standards drift, and new products are introduced. SMED is not a one-time project but an ongoing discipline of observing, measuring, and improving changeover performance.