Scheduling heat treatments with SOLV

Faced with an extremely complex scheduling process at their heat treatment facility in Trollhättan, Sweden, managers at GKN Aerospace turned to the OR community for help. What resulted was a business-transforming tool.

Interior of a factory featuring a large metallurgy machine, with an orange glow coming from around and inside it.

The Problem

At its most basic, the ‘job-shop problem’ involves scheduling a given number of tasks to a given number of machines. This was at the core of GKN Aerospace’s scheduling issues at their heat treatment facility in Trollhättan, Sweden. With half a dozen furnaces of varying sizes, managers were struggling to accommodate a large through-put of work, with many jobs requiring multiple treatments to achieve the qualities required in the end products.

Materials would arrive from other parts of the business and from external suppliers; many products would require multiple treatments, some with minimum recommended wait times between treatments and others with maximum wait times; and each product was given a due date by the company’s enterprise resource planning system (ERP). Other factors included preventative maintenance on the furnaces, an unmanned shift on Sundays, and the fact some certain jobs requiring specialist mountings.

A crucial goal, particularly in light of the lengthy processing times involved, would be to identify means of batching jobs together.

The Solution

Following a nine-month concept study, tests on real data showed that it would be possible to implement a scheduling procedure in the Heat Treatment department. The longest computational time in the first round of tests was less than one minute, so the business case was promising. The OR team was given the go-ahead and given the target of improving utilisation of the furnaces by 2% per year – equivalent to an extra 120 heat treatment operations per year.

SOLV is an acronym for Schema Optimalt Lagt i Värmebehandlingen, which translates as Optimal Schedules in Heat Treatment. The system is used to produce a new schedule every day. An operator access the SOLV database and imports or inputs relevant data about the jobs in the HT queue. SOLV then optimises the next 24 hour schedule and results are published on the company’s intranet within minutes. Even the 72 hour schedule produced on Fridays takes less than 20 minutes to create.

The Value

The OR team met their goal of 2% improved furnace utilisation. In fact, utilisation of four of the six furnaces went up by 12% on weekdays while on Sundays furnace use was improved by 45%. Queuing times decreased by 4%, delays by 8% and the reduction of non-productive jobs resulted in yearly energy savings of 250 megawatt hours.

Operators have spoken of a newfound ability to ‘work smarter’. The HT department manager, Jan Dieppe, said: “We gain control over what components to work on and when, and we have a whole other level of predictability compared to previously. This means we can increase volumes and bring in external customers, reducing our hourly costs. Put simply, SOLV helps us to plan our work and fill the business.”

Full article available in Impact Magazine, Spring 2017: ‘Problem SOLVed, pp46-50