Optimal and Heuristic Lead-Time Quotation For an Integrated Steel Mill With a Minimum Batch Size

This paper presents a model of lead-time policies for a production system, such as an integrated steel mill, in which the bottleneck process requires a minimum batch size. An accurate understanding of internal lead-time quotations is necessary for making good customer delivery-date promises, which must take into account processing time, queueing time and time for arrival of the requisite volume of orders to complete the minimum batch size requirement. The problem is modeled as a stochastic dynamic program with a large state space. A computational study demonstrates that lead time for an arriving order should generally be a decreasing function of the amount of that product already on order (and waiting for minimum batch size to accumulate), which leads to a very fast and accurate heuristic. The computational study also provides insights into the relationship between lead-time quotation, arrival rate, and the sensitivity of customers to the length of delivery promises

Production Scheduling in Integrated Steel Manufacturing

Steel manufacturing is both energy and capital intensive, and it includes multiple production stages, such as iron-making, steelmaking, and rolling. This dissertation investigates the order schedule coordination problem in a multi-stage manufacturing context. A mixed-integer linear programming model is proposed to generate operational (up to the minute) schedules for the steelmaking and rolling stages simultaneously. The proposed multi-stage scheduling model in integrated steel manufacturing can provide a broader view of the cost impact on the individual stages. It also extends the current order scheduling literature in steel manufacturing from a single-stage focus to the coordinated multi-stage focus. Experiments are introduced to study the impact of problem size (number of order batches), order due time and demand pattern on solution performance. Preliminary results from small data instances are reported. A novel heuristic algorithm, Wind Driven Algorithm (WDO), is explained in detail, and numerical parameter study is presented. Another well-known and effective heuristic approach based on Particle Swarm Optimization (PSO) is used as a benchmark for performance comparison. Both algorithms are implemented to solve the scheduling model. Results show that WDO outperforms PSO for the proposed model on solving large sample data instances. Novel contributions and future research areas are highlighted in the conclusion

Integrated Production-Inventory Models in Steel Mills Operating in a Fuzzy Environment

Despite the paramount importance of the steel rolling industry and its vital contributions to a nation’s economic growth and pace of development, production planning in this industry has not received as much attention as opposed to other industries. The work presented in this thesis tackles the master production scheduling (MPS) problem encountered frequently in steel rolling mills producing reinforced steel bars of different grades and dimensions. At first, the production planning problem is dealt with under static demand conditions and is formulated as a mixed integer bilinear program (MIBLP) where the objective of this deterministic model is to provide insights into the combined effect of several interrelated factors such as batch production, scrap rate, complex setup time structure, overtime, backlogging and product substitution, on the planning decisions. Typically, MIBLPs are not readily solvable using off-the-shelf optimization packages necessitating the development of specifically tailored solution algorithms that can efficiently handle this class of models. The classical linearization approaches are first discussed and employed to the model at hand, and then a hybrid linearization-Benders decomposition technique is developed in order to separate the complicating variables from the non-complicating ones. As a third alternative, a modified Branch-and-Bound (B&B) algorithm is proposed where the branching, bounding and fathoming criteria differ from those of classical B&B algorithms previously established in the literature. Numerical experiments have shown that the proposed B&B algorithm outperforms the other two approaches for larger problem instances with savings in computational time amounting to 48%. The second part of this thesis extends the previous analysis to allow for the incorporation of internal as well as external sources of uncertainty associated with end customers’ demand and production capacity in the planning decisions. In such situations, the implementation of the model on a rolling horizon basis is a common business practice but it requires the repetitive solution of the model at the beginning of each time period. As such, viable approximations that result in a tractable number of binary and/or integer variables and generate only exact schedules are developed. Computational experiments suggest that a fair compromise between the quality of the solutions and substantial computational time savings is achieved via the employment of these approximate models. The dynamic nature of the operating environment can also be captured using the concept of fuzzy set theory (FST). The use of FST allows for the incorporation of the decision maker’s subjective judgment in the context of mathematical models through flexible mathematical programming (FMP) approach and possibilistic programming (PP) approach. In this work, both of these approaches are combined where the volatility in demand is reflected by a flexible constraint expressed by a fuzzy set having a triangular membership function, and the production capacity is expressed as a triangular fuzzy number. Numerical analysis illustrates the economical benefits obtained from using the fuzzy approach as compared to its deterministic counterpart

Resource selection and route generation in discrete manufacturing environment

When put to various sources, the question of which sequence of operations and machines is best for producing a particular component will often receive a wide range of answers. When the factors of optimum cutting conditions, minimum time, minimum cost, and uniform equipment utilisation are added to the equation, the range of answers becomes even more extensive. Many of these answers will be 'correct', however only one can be the best or optimum solution. When a process planner chooses a route and the accompanying machining conditions for a job, he will often rely on his experience to make the choice. Clearly, a manual generation of routes does not take all the important considerations into account. The planner may not be aware of all the factors and routes available to him. A large workshop might have hundreds of possible routes, even if he did know it all', he will never be able to go through all the routes and calculate accurately which is the most suitable for each process - to do this, something faster is required. This thesis describes the design and implementation of an Intelligent Route Generator. The aim is to provide the planner with accurate calculations of all possible production routes m a factory. This will lead up to the selection of an optimum solution according to minimum cost and time. The ultimate goal will be the generation of fast decisions based on expert information. Background knowledge of machining processes and machine tools was initially required, followed by an identification of the role of the knowledge base and the database within the system. An expert system builder. Crystal, and a database software package, DBase III Plus, were chosen for the project. Recommendations for possible expansion of and improvements to the expert system have been suggested for future development

Paperi- ja terästeollisuuden tuotannonsuunnittelumenetelmät

Tämän diplomityön tarkoituksena on ollut tutkia, kuinka paperiteollisuuden tuotannon suunnittelun eroavat ja yhtenevät terästeollisuuden tuotannon suunnittelun kanssa. Tavoitteena on ollut tutustua tuotannon suunnitteluun ja sen ongelmiin ensin yleisellä tasolla, minkä jälkeen on keskitytty kuvaamaan tarkemmin tarkastelussa olevien teollisuudenalojen erityispiirteitä. Lopuksi on tehty prosessien vertailuja ja johtopäätöksiä niistä löydetyistä yhtäläisyyksistä. Työssä on kuvattu sekä paperin että teräksen tuotantoprosessit ja materiaalivirrat. Karkealla tasolla tarkasteltuna prosessit ovat hyvinkin samantyyliset, koska kummassakin prosessissa juoksevassa muodossa olevista raaka-aineista valmistetaan ensin isompi yksikkö, joka paloitellaan pienemmiksi palasiksi asiakkaiden tilausten mukaan. Syvemmät prosessien tarkastelut tuovat kuitenkin esiin niiden ainutlaatuiset erityispiirteet, jotka vaikeuttavat tuotannon suunnittelua ja yhtäläisyyksien löytämistä. Eräs työn alkuperäisistä tavoitteista oli tehdä abstraktiot molemmista prosesseista, minkä avulla niiden samankaltaisuudet tulisivat parhaiten esille. Työn edistyessä kävi kuitenkin ilmi, että syvempien abstraktioiden tekeminen ei ollut järkevää ja parempiin tuloksiin päästäisiin vertailemalla prosesseja rinnakkain ilman harhaanjohtavia yleistyksiä. Paperikone on hyvin merkittävässä roolissa koko tuotannon ajoituksen ja suunnittelun kannalta. Paperiteollisuudessa suurin hävikki aiheutuu yleensä lajinvaihdoista ja trimmihukasta. Lajinvaihdoista aiheutuvan hukan minimoimiseksi eri paperilaatujen tuotanto-ohjelma suunnitellaan sykliseksi, jolloin paperin ominaisuudet muuttuvat vain vähän kerrallaan ja lajinvaihtohukka on pieni. Toinen tärkeä suunnittelun kohde on siis trimmitys. Sen tarkoituksena on suunnitella emorullan leikkauskohdat siten, että pystytään hyödyntämään käytettävissä oleva rullaleveys ja -pituus mahdollisimman tarkasti huomioiden samalla asiakkaiden vaatimukset. Terästeollisuudesta ei ole löydettävissä paperiteollisuutta vastaavaa syklisyyttä. Siellä tärkein suunnittelukohde on sulaton ajoitus ja käytössä olevan konvertterikoon mahdollisimman tarkka hyödyntäminen. Paperiteollisuudesta tuttua lajinvaihto-ongelmaa ei itse teräksen teossa ole. Sen sijaan muut tuotannon yksikköprosessit vaativat tarkkaa suunnittelua juuri lajinvaihtojen osalta. Tuotteiden erilaiset paksuudet, leveydet ja lämpötilat ovat ongelmana terästuotannon jatkuvatoimisissa linjoissa, sillä peräkkäisten tuotteiden ominaisuudet eivät saisi poiketa toisistaan liian paljon. Koska teräksestä tehdään paperin tapaan määrämittaisia levyjä ja nauhoja, paperiteollisuuden kaltaiset trimmitys- ja leikkuuongelmat tulevat esille sielläkin. Teräksen teossa leikkuuongelma ei kuitenkaan ole yhtä merkittävä kuin paperin teossa, sillä lopputuotteiden mitat voidaan huomioida jo aihiokokoa suunniteltaessa. Paperiteollisuuden tuotannon suunnittelu on paljon pidemmälle vietyä ja kokonaisvaltaisempaa kuin terästeollisuudessa. Tähän vaikuttaa prosessien erilainen luonne ja paperin lyhyempi valmistusaika. Teräksen teossa on myös paljon enemmän erillisiä tuotantovaiheita kuin paperin valmistuksessa

Manufacturing Value Modelling, Flexibility, and Sustainability: from theoretical definition to empirical validation

The aim of this PhD thesis is to investigate the relevance of flexibility and sustainability within the smart manufacturing environment and understand if they could be adopted as emerging competitive dimensions and help firms to take decisions and delivering value