Garment Production Scheduling
The daily production of clothing deals with many work orders, so it is necessary to complete scheduling. Scheduling means determining the order of carrying out jobs. Priorities can be determined on the basis of several rules:
– FIFO (first-in, first-out),
– LIFO (last-in, first-out),
– DDATE (earliest due date) – which product must be made first,
– CUSTPR (highest customer priority) – first the product for priority customers,
– SETUP (similar setup) – first the similar products which require a minimum setting of machines,
– SPT (shortest processing time) – priority for products that last for the shortest period,
– LPT (Longest Processing Time) – priority for products that last for the longest period.
Priority DDATE can have variations:
– SLACK (Slack minimum) – priority for jobs that have less time margin:
– CR (smallest critical ratio) – priority for jobs with smaller ratio of the remaining time to maturity and remaining processing time:
If CR > 1, then the product is made before the deadline
If CR < 1, then it’s late
If CR = 1, then it is done on time
Already deployed operations often change their order, since there are new jobs coming into production. Scheduling is performed according to the above rules, which can be modified in a way that corresponds to the number of resources or the complex global rules:
– Expanded SPT (shortest processing time) – jobs are divided into A, B and C, according to their duration. Jobs A are performed with a minimum duration, but every few hours the production is interrupted and job B is performed. Jobs C are performed every day each.
– WINQ (work-in-next-queue) – sees the duration of performing job at the next resource.
– NOPN (fewest number of remaining operation) – according to the number of resources that are yet to be used.
– S/OPN (Slack per remaining operation) -according to the time reserve for the rest of the job.
– RWK (Remaining work) – a variant of SPT, the duration of performing whole job on all resources.
Prof. dr Gordana Colovic
The College of Textile -Design, Technology and Menagement, Belgrade
Address: Belgrade, Serbia