SMED / Line Balancing / TOC: Three Levers for Line Efficiency
What Are the Three Tools?
SMED (Single-Minute Exchange of Die) compresses changeover time by converting internal setup (machine must stop) into external setup (can be prepared in advance); line balancing reallocates workload across stations to remove bottlenecks and shorten takt; TOC (Theory of Constraints) focuses on the weakest link of the system and lets the constraint set the pace. All three target the same goal - higher capacity and flexibility - and together form the classic lean production combination. Used in sequence they systematically raise capacity, shorten delivery time and lower manufacturing cost.
Using SMED
The tool provides a changeover breakdown table: record each changeover action, separate internal and external work, move external work out of downtime, then compress internal work with parallel operations, quick clamping, pre-mounted tooling and standardization. It automatically computes the changeover time and saving before and after improvement. A typical result drops a 30-60 minute changeover to under 10 minutes, making mixed-model small-batch production economical. Track changeover time for about a month after the improvement to confirm the gain, then replicate the method to other machines and lines.
Calculating Line Balance
Enter each station's standard work time and the tool computes total work content, bottleneck takt, line balance rate (sum of station times divided by bottleneck time x number of stations) and throughput time per unit. Below 85% balance, prioritize splitting the bottleneck station, moving work content or adding a parallel station. Use a stacked bar (Yamazumi) chart to compare station loads at a glance and spot the bottleneck, and compare multiple scenarios (adding staff, splitting tasks, parallel work) before implementing.
The TOC Five Focusing Steps
The tool guides the TOC five-step loop: identify the constraint, exploit it (keep the bottleneck busy), subordinate everything else (schedule to the bottleneck takt), elevate the constraint, then return to step one when the constraint shifts. Bottlenecks drift, so after improvement re-identify the new constraint to sustain the improvement cycle. Combine with Run@Rate to verify post-improvement capacity and with VSM to see where the constraint sits in the overall value stream.