Scheduling Problem in Steel Industry

SNU MAI LAB seminar2000.10.20

Lee Hyoung Gon(hungry@ultra.snu.ac.kr)

Synchronized Scheduling Method in Manufacturing Steel Sheets

RYOJI TAMURA, MEGUMI NAGAIInformation Systems Department, Sumitomo Metal Industries, Fukuoka.IFORS, Vol. 5, No. 3, pp. 189~199, 1998

Introduction New Scheduling System Casting to a rolling process in steel sheets manufact

uring multiobjective assigning and sequencing problem with lots

of constraints Two-Stage algorithm composed of macro-scheduling

and micro-scheduling

Steel Sheets Manufacturing Process(1/2)

Cast-to-roll scheduling problem

Primary Production Scheduling at Steelmaking Industries

H.S. Lee, S.S. MurthyIBM J. RES. DEVELOP. Vol 40 No. 2 March 1996

Overview of steelmaking and the primary steelmaking process(1/2) Ironmaking

Combining the raw ingredients of steel into a generic intermediate product known as hot iron or pig iron.

Primary steelmaking Accepts the supply of hot iron from the blast furnace and t

ransforms it into semifinished products in a variety of grades(specific metallurgical compositions of steel), shapes, and dimensions

Overview of steelmaking and the primary steelmaking process(2/2)

Finishing Consists of numerous operations that can be applied selectiv

ely to the semifinished products of the primary steelmaking process, to achieve customers’ specifications

Cold-rolling -> precise dimension, surface finish, mechanical property

Annealing : material’s grain size, ductility Tempering : internal stresses, ductility Pickling : clean the surface Coatings : corrosion resistance

Scheduling issues in primary steel production Utilization of manufacturing units Allocation of production among parallel manufacturing Specification of heats or heat groups Specification of rolling groups Sequencing of heats/rolling groups for manufacturing Coordination of schedules between production stages Rescheduling

Scheduling for continuous casters(1/3) Simple mixed-integer linear programming model

“A model for sequencing a continuous casting operation to minimize costs”(1987)

Electric arc furnace, no change of width in continuous casters, single objective cost function

Scheduling for continuous casters(2/3) Complex models using heuristics(LTV caster scheduli

ng model) Implemented in 1983, in support of the first continuous ca

ster installed at LTV Cleveland Works. Maximization of on-time delivery Maximization of caster productivity Satisfaction of quality requirements Minimization of semifinished inventory

“A Scheduling Model for LTV Steel’s Cleveland Work’s Twin-Strand Continuous Slab Caster”(1988)

“Twin Strand Continuous Slab Caster Scheduling Model”(1990)

Scheduling for continuous casters(3/3) Cooperative scheduling approach in which an expert

system assists a scheduler(Scheiker Scheduling) “Cooperative scheduling and its application to steelmaking

processes”(1991) Iteratively modifies an existing schedule through the user i

nterface Scheduler typically makes global changes that increase glo

bal efficiency Scheduling engine uses a rule base to recognize violations

of local constraints

Scheduling for hot strip mill “Roll-A-Round program”(1991)

Uses heuristics based on the traveling-salesman problem and linear programming

BACK TO…Synchronized Scheduling Method in Manufacturing Steel Sheets

RYOJI TAMURA, MEGUMI NAGAIInformation Systems Department, Sumitomo Metal Industries, Fukuoka.IFORS, Vol. 5, No. 3, pp. 189~199, 1998

Steel Sheets Manufacturing Process(2/2) – some terms “heat” : necessary amount of molten steel to

be poured into the BOF once. “try” : the molten steel is poured 5-7times

consecutively, and this sequence of heat is called a “try”.

“chance” : rolls are exchanged after rolling one try amount of slabs, and this exchange interval is called a “chance”. Thus one “try” in casting corresponds to one

“chance” in rolling.

The Problem(1/3)- Three Main Objectives1. To incorporate particular instructed orders/slabs int

o the schedule2. To attain the target supply quantity for subsequent

processes3. To meet the rolling due-date

The Problem(2/3)- Constraints Cast Constraints

The same ingredient orders must be gathered The “first” heat requires about 270 tons The last slab of a “try” requires low grade order

Roll Constraints The strip width has to be changed from wider to narrower The strip thickness should be transmitted smoothly Particular orders requires positional limits in rolling sequence Etc.

The Problem(3/3)- conventional scheduling

24 hours, 5-7 roll “chances”,

three shifts of workers(4) Select and sequence 60-80

pieces among 5000 orders per roll chance

Consecutively, select 50-70 pieces among 3000 non-D/C slabs in the yard, and insert them between orders.

Some know-how is established to some extent, but for the most part it depends upon a trial-and-error method.

Functional Partition

Formulation of cast scheduling problem

Formulation of roll scheduling problem

The reason of taking the two-stage approach Main reason

Reduction of computing time by avoiding combinatorial explosion. Following advantages

Creating a balanced schedule to avoid differences from the expected one.

Improving solution precision and easiness to check the schedule by user participability

Program flexibility for environmental changes.

Two-stage scheduling on order distribution map

Details of scheduling algorithm

Macro Scheduling

1. Generating a feasible route.-feasible block sequence.

2. Pseudo-assignment of slabs to the route.3. Repetition for all feasible routes.4. Determination of the optimum route.

Micro Scheduling 1. Selecting a block on the route.2. Selecting a previous path sequence.3. Generating a feasible path.4. Pseudo-assignment of slabs to the path.5. Linking a path to the previous path sequence and evaluating th

e new path sequence.6. Repetition for all feasible paths.7. Repetition for all previous path sequences.8. Reduction of the path sequences.9. Repetition of all blocks.10. Determination of the optimum sequence and assignment of sla

bs.

User Interface Preparation

Operators can refer to necessary information(order, slab spec, input parameter)

Modification Refine the schedule(insert slabs, delete slabs or

exchange the slab position)

Hardware configuration

Conclusion Human-machine harmonization scheduling

system Now this system largely contributes to

efficient scheduling, in Kashima Steel Works.