Why the Furnace Sets Plant Output
Molding presses and compaction presses run in seconds per cycle, while debinding and sintering run in hours. A plant can mold far more parts than its furnaces can process, creating a growing pile of green and brown parts in work in progress. Because green parts can be fragile and sometimes age or degrade, a queue is not harmless.
Scheduling should therefore start from the furnace: determine its capacity in loads per week, then release molding or pressing only to the level that keeps the furnace fed. Releasing by order date instead floods WIP and hides the real constraint.
Building Compatible Loads
A load can mix parts only if they share the sintering program, atmosphere, setter material and temperature, and if customer rules allow mixing. Different alloys, such as 316L and 17-4PH, usually need different profiles. Parts that must not be co-sintered, for example because of contamination concerns or traceability rules, need separate loads.
Load building then becomes a bin-packing problem: fill setter area or belt kilograms while respecting compatibility and due dates. Keep a compatibility matrix by alloy, program and customer, and let planners see candidate jobs ready for each program.
- Compatibility by alloy, atmosphere and cycle program
- Customer rules against mixing lots
- Setter area or belt weight capacity
- Due date priority within a compatible group
Fill Versus Due Date
A half-empty load is expensive because the cycle costs the same. A fully loaded run that delays a late order is also expensive. The usual rule is to set a minimum fill target, such as a share of full load, and allow overrides for urgent jobs with an explicit cost.
Track furnace utilization as loaded kilograms or setter area divided by capacity, along with idle hours. Review weekly why loads ran below target: missing parts from molding, waiting for debinding, mixed program conflict, or an urgent order. These reasons show where to fix upstream flow instead of just blaming the furnace.
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Cycle Time & Capacity Calculator
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Debind Queues and Furnace Downtime
Solvent or catalytic debinding adds a step before sintering with its own equipment and cycle time, and thermal debinding may be integrated into the furnace run. Keep a buffer of debound parts large enough to build loads but small enough to avoid handling damage and oxidation. Plan preventive maintenance such as hot zone work, thermocouple calibration and leak checks as scheduled blocks, since an unplanned shutdown stops the entire plant.
Calibration and temperature uniformity surveys may also be required by customer quality systems, so the schedule should include them like any other job.
When Spreadsheets Stop Working
With one furnace and a handful of programs, a planner with a whiteboard or spreadsheet can do fine. As furnaces, alloys and customers multiply, the compatibility rules and due dates exceed what a person can juggle, and finite scheduling inside the ERP or a dedicated tool pays back. Start by capturing real cycle durations and fill rates for a month.
If most loads already run full and on time, more tooling will not help. If fill is erratic, the fix may be release control upstream, not a software purchase.
Frequently asked questions
How do I decide the minimum fill for a sintering load?
Compare the cycle cost to the cost of delaying the jobs that would fill it. Many plants set a target such as most of full capacity and allow exceptions for urgent orders. Record each exception and its reason so you can review the pattern monthly and adjust upstream release rules.
Can different alloys be sintered in the same load?
Only if they share the validated cycle program, atmosphere and setter requirements, and customer quality rules permit it. Most plants keep alloys such as stainless and low-alloy steels on separate programs. Maintain a compatibility matrix approved by your process engineer and enforce it in the load planning step.
What should be measured to improve furnace scheduling?
Loaded weight or setter area versus capacity, idle hours, load cancellations, reasons for partial loads, WIP age waiting for the furnace, and on-time shipment for furnace-dependent jobs. Together these show whether the limit is furnace capacity, upstream flow or planning rules.
Netray can surface furnace fill rate, queue age and late-order impact from your ERP data through plain-language questions, so planners see the bottleneck before it shows up as a late shipment.