How to reduce changeover times in your manufacturing process

Every manufacturing process has periods where equipment is unavailable due to tooling changes, material changes, part changes, program changes, or any other changes to production that must be performed while the machine is stopped. Collectively, these events are referred to as “changeover times,” or alternately as “setup,” “make ready,” or “planned downtime”. Changeover times can range from a few minutes to several weeks, as when an automotive plant retools for a new model.

Strictly speaking, changeover time is measured from the moment the last good part of the previous run is produced to the moment the first good part of the next run is produced. Reducing changeover time is a critical component of implementing a pull production system which operates with as little inventory as possible.

Why should changeover times be optimised

Reducing changeover time frees up more productive (value-added) time for running production. Another benefit is that by reducing changeover time, you can reduce production batch sizes, work-in-process (WIP), and inventory. Consequently, sales teams can quote shorter lead times and improve customer satisfaction.

Improving changeover times with SMED

Far and away, the most commonly accepted best practice for reducing changeover time is Single-Minute Exchange of Die (SMED). Single-minute refers to reducing changeover times to less than 10 minutes, and the exchange of dies refers back to the initial work by Shigeo Shingo on automotive presses. SMED became one of the core methods of the Toyota Production System and of Lean manufacturing.

In SMED, the changeover process is broken into a sequenced list of steps called elements. The objective of SMED is to remove as many portions from the changeover process as possible by separating or converting them and then streamlining any remaining elements (completing them faster, easier, or in parallel with other parts). The essence of the SMED system is to convert as many changeover steps as possible to “external” (performed while the equipment is running), and to simplify and streamline the remaining steps.

A successful SMED programme will have the following benefits:

• Lower manufacturing cost (faster changeovers mean less equipment downtime);
• Smaller lot sizes (faster changeovers enable more frequent product changes);
• Improved responsiveness to customer demand (smaller lot sizes enable more flexible scheduling);
• Lower inventory levels (smaller lot sizes result in lower inventory levels);
• Smoother startups (standardised processes improve consistency and quality).

A SMED example: a die change on a press

1. Record the current changeover. Film one changeover from last good part to first good part, and list every element with its duration.
2. Separate internal and external tasks. Internal tasks can only be done with the press stopped: unclamping, removing and fitting the die. Many tasks on the list are usually external but done while the press stands still: fetching the next die, finding clamps and tools, looking for the setup sheet.
3. Convert internal to external. Before the press stops, bring the next die to the press on a changeover cart with every clamp, tool and the setup sheet. Pre-set what can be pre-set.
4. Streamline what is left. Standardise clamping heights so one tool fits every die. Use quick-release clamps instead of bolts and locating pins instead of measuring alignment. Split the work between two people working in parallel.
5. Standardise and record the new method. Write the improved changeover down as a standard work instruction, with the settings for each product, and train every shift on it. Without this step, the improvements drift back to the old way.

Standardise the new method

The fastest path to improved changeover times is typically through non-technical improvements, such as creating standardised work instructions, marking down known settings on equipment, and displaying real-time metrics. Video-based instructions are well suited to documenting changeover procedures because they show the exact sequence, the tools and the settings, and they are quick to update when the method improves.

When changeover procedures exist only in paper binders, referencing and using the standards becomes a burden. Instructions on a tablet or smartphone, in a rugged case if needed, are at hand during the changeover. And unlike paper copies, digital instructions don’t leave old standards floating around the production floor, so operators work from the current best practice.

At MANN+HUMMEL, the same work was being learned and done differently across plants and shifts. Standardised video instructions for training, changeovers and everyday reference brought changeover inefficiency down by 15%. Changeovers matter even more in high-mix assembly, where they happen many times per shift.

Where REWO fits

REWO turns a filmed changeover into a step-by-step video guide that goes through approval before it reaches the line. Operators open the current version from a QR code at the machine or from the MES, and Analytics shows who has confirmed which version.

Read next: Work instructions for high-mix assembly · Standard work instructions and Lean manufacturing · REWO for Lean and CI managers