Scheduling Architectural Glass Fabrication Around the Tempering Furnace

In architectural glass fabrication, the tempering furnace sets the pace and nothing else comes close. EDGEBIC by User Solutions models the furnace as finite capacity with a setup matrix on thickness and coating, carries laminating and heat soak as real elapsed cycles, and schedules the whole job backward from the date the truck has to leave for the site.

Cutting, edging, and glazing bead are all schedulable in the ordinary way. Temper is where a fabricator loses days, and it is usually the one resource whose real sequencing cost nobody has written down.

The Furnace Is the Constraint, So Schedule It First

A roller hearth tempering furnace does not care how many lites you feed it. It cares about thickness, coating, and the recipe that goes with them. Change from 6 mm clear to 10 mm low-e and you are into a ramp, a new set of parameters, and test lites before the first production load runs.

Enter the furnace as its own work center with a real calendar so two loads cannot be promised the same window. Then flag it as the constraint and the schedule anchors around it, placing cutting and edging to feed the furnace at the rate the furnace can absorb rather than at the rate the cutting table can produce. That single change usually shrinks the rack of washed, edged glass waiting on temper more than any amount of expediting does. The general principle is covered in finite vs infinite capacity scheduling and the diagnosis in production bottleneck identification.

Grouping Loads by Thickness and Coating Family

Two lites that share thickness and coating can share a load. Two that do not, cannot, and forcing them together costs you both.

Build a setup matrix on the furnace so each transition carries its real cost. A same-thickness, same-coating transition costs load and unload. A thickness change costs a recipe change and test lites. A move onto or off a soft-coat low-e product costs more again. Rather than mapping every part number against every other, group your products into five or six families (6 mm clear, 6 mm low-e, 10 mm clear, 10 mm low-e, laminated interlayers, spandrel) and record family-to-family transition hours. Six families is thirty-six cells, which is a table a scheduler maintains in an afternoon. See how setup families reduce scheduling complexity and sequence-dependent setup times.

With real numbers in the matrix, the sequence optimizer groups compatible loads on the furnace. The multi-run layer is guaranteed never to return a schedule worse than the baseline it started from, so running it carries no downside: compare total recipe changes and late-job count, then accept only if it wins. For how the optimizer reports its own confidence, see how a proven optimality gap builds trust.

Backward From the Truck, Not Forward From Today

Architectural glass ships to a construction schedule, and a curtain wall package delivered three weeks early is a rack problem, not a win. Set the required ship date on the job and schedule backward so each operation lands as late as it can and still make the load.

Backward scheduling also answers the question the project manager keeps asking, which is not "when will it be done" but "how late can you release it and still be safe." That number falls straight out of the plan. The mechanics are in forward vs backward scheduling.

Elapsed Cycles: Laminate, Heat Soak, and Cure

An autoclave cycle and a heat soak test are elapsed time, not worked time. They run through the night and they do not pause at 3:30 PM. Model each as its own step with the real elapsed window, and place unload on the first shift that is genuinely staffed.

A heat soak test that runs sixteen hours started Wednesday at 4 PM finishes Thursday at 8 AM, and the IG line picks it up on first shift. A schedule that clips those sixteen hours to worked hours is wrong by most of a day on every heat soaked job, and on a spandrel-heavy package that error compounds across every floor.

The IG Line and the Machines That Feed It

Insulating glass assembly is a line, and lines are where lot streaming pays. If the IG line can start on the first rack of finished lites rather than waiting for the whole job, set a transfer quantity on the routing so downstream begins after that many pieces are ready instead of after the full order clears temper. See what is lot streaming.

Upstream, the interchangeable CNC edge and drill machines belong in a work center group rather than being hard-named on the routing. The engine expands the group at schedule time and places each lot on whichever member finishes it soonest against live load, carrying that member's own effective run time. See how a work center group shops a pool of machines.

A Worked Package

A 380-unit insulating glass package for a twelve-story curtain wall, released in three floor phases.

Temper landed Thursday because Thursday already carried a 6 mm low-e load, so the transition cost load and unload rather than a full recipe change. The IG line started Friday on the first rack instead of waiting for all 380 lites. Edging landed on the second CNC machine, not the one written in the routing.

When Glass Breaks

Breakage is not an exception in this industry, it is a rate. Enter the remake as its own job with the real ship date and let it compete for furnace and IG capacity like anything else, so you can see what it displaced.

Operators log start, stop, and quantity at a floor station, so the plan reflects the shop within the shift rather than at the end of the week. Completed operations are never moved by a reschedule, which means the lites already through temper stay exactly where the record says they went, no matter how many times you replan around the remake. See how a reschedule uses last night's actuals.

Heritage in Glass and in Constrained Job Shops

User Solutions has built finite capacity scheduling since 1991, more than 35 years, for operations where one shared resource sets the pace: US Navy, GE, BAE Systems, and Cummins across 33 locations. In the same lineage that leads to EDGEBIC, Technical Glass Products of Snoqualmie, Washington used Resource Manager DB to model cross-training and rebalance its plan, and accommodated a four percent increase in business with the existing workforce while holding on-time shipping. That was a glass job shop solving a capacity problem with scheduling rather than with hiring.

Where to Start

Enter your furnace, autoclave, heat soak oven, and IG line as work centers with real calendars. Group your products into five or six temper families and record the transition hours between them. Put ship dates on the jobs and schedule backward. Then count how many recipe changes the grouping removed in the first full week.

For fundamentals, what is production scheduling covers the basics. A neighboring sector with the same batch-recipe shape is glass manufacturing continuous process scheduling. The industry fit guide maps the rest and EDGEBIC is the product hub. Want to know what your real cost per recipe change is? Contact US for a demo.