The Cereal Plant That Ran Its Model Before Every Shift
General Mills, Toledo, 1996: Cheerios, and Where Plant Builder Began

General Mills made Cheerios in Toledo, Ohio, until 2002. In 1996 Simulation Dynamics built a model of the plant, and the planners put it to daily work: before each shift, they ran the model to see what could go wrong during that shift, so they could change the plan before the trouble reached the floor. Building it pushed SDI to model cereal as flow instead of as individual items, and the pieces built for Toledo became Plant Builder, the plant-modeling library SDI used for decades after.

The company

General Mills, Cheerios plant, Toledo, Ohio

The question

What is likely to go wrong on the next shift, and what should the plan do about it?

The model

Three to four making lines, about four large storage bins plus small portable totes, and six to seven packing lines

How it was used

Run by the planners before every shift

Source

SDI project records, 1996 and 1999 · SDI’s 2002 Winter Simulation Conference paper

What the plant was up against

A Cheerios plant is a make-store-pack plant. Three to four making lines produced the cereal. Between making and packing sat about four large storage bins and a fleet of small portable totes. Six to seven packing lines filled the boxes.

Making and packing run to different clocks. Making thinks in pounds per hour and long runs. Packing thinks in cartons per minute, package sizes and changeovers. The bins and totes absorb the difference, as long as the right cereal is in the right place when a packing line needs it. When it isn’t, a packing line sits idle while storage is full of product nobody is packing yet, or making has to slow down because there’s nowhere to put what it’s making.

Whether that happens on a given shift depends on the schedule, the state the last shift left the plant in, and which lines are running which sizes. All three change from shift to shift.

Why it needed a new kind of model

The simulation tools of the day moved product through a model one item at a time. Cereal isn’t items. Counting every piece, or even every box, made a model far too slow for a plant that ran around the clock. SDI modeled the cereal as flow instead: rates through the machines and levels in the bins, with an event only when a rate changes.

How the plant used it

This was an operating model, not a one-time study. Before each shift, the planners ran the model on the shift ahead and looked for trouble coming: a packing line about to run out of cereal, storage about to fill, a changeover landing at the wrong moment. If the model showed a problem, there was time to change the plan before the shift started, instead of finding out on the floor.

A model is only useful that way if it runs fast and speaks the plant’s language. Rates, bin levels and schedules are what planners already talk in, and a flow model answers in the same terms.

What came of it

• A plan checked before every shift. SDI’s own project history lists Toledo among its successes: the plant put the model to work instead of shelving it after a study.
• The parts became a product. The building blocks SDI created for the Toledo model were shared with other General Mills plants, and General Mills asked SDI to standardize them. They became SDI Industry (1996) and SDI Plant Builder (1997).
• A second project. SDI went back to the Toledo Cheerios plant for another model in 1999.

Try the same kind of plant

The Sandbox has a demo vegetable plant with the same make-store-pack shape, built the Plant Builder way: two making lines, eight surge bins and five packing lines, with campaigns, changeovers and bins that can only feed lines packing the same product. Open the vegetable plant in the Sandbox →

Where this work comes from

Built by Simulation Dynamics, the team behind ReliaSim · evidence: SDI project records (1996, 1999); R. A. Phelps, D. J. Parsons and A. J. Siprelle, “Non-Item Based Discrete-Event Simulation Tools,” Proceedings of the 2002 Winter Simulation Conference. The Toledo plant ended Cheerios production in 2002 (The Blade, Toledo, July 27, 2002).