Denim manufacturing consists of yarn, warp and fabric manufacturing in sequence followed by finishing processes, each with many sub processes such as winding and sizing for warp manufacturing and bleaching and mercerizing for finish manufacturing. Like garment manufacturing, denim manufacturing is also shaped by the fast-changing nature of customer requirements. Further complicating the issue for denim manufacturing is the excessive number of looms which not only makes effective management of looms very difficult, but also adversely affects the management of warping and finishing processes.

The warping processes are under constant pressure to feed looms to minimize downtime and to meet due dates. In addition to this, warping process usually includes dyeing and dyeing process require costly changeovers. Hence, in order to maintain smooth operation, a balance must be struck for the lengths of the warps to be manufactured – too long and then succeeding customer orders are delayed and work-in- process inventory increases; too short and then too many changeovers are incurred. Another important consideration for warp length is the need to minimize the losses due to remaining yarns. The length of warp to be put on each warp bar for looms which determine the maximum number of looms which can utilize the manufactured warp in parallel. Hence, from factory operations scheduling perspective, the main problems for warping processes are to find the right warp lengths to be manufactured and the right sequencing of jobs over warping processes to maintain changeover losses in check while feeding looms.

The number of looms in a typical facility is quite large. With ever-decreasing order sizes, changeovers are a frequent sight in a loom shop. While there may be many different end products, underlying warp is shared between groups of them, hence it is very important to re-assign remaining warp from cancelled or reduced orders to new or increased orders, which reduces not only the lead times but also changeover times because this operation requires only the changing of the wefts as opposed to changing of reed frame and wefts which is significantly more time consuming. Furthermore, warp re- assignment helps reduce the excess work-in- process inventory. However, the minimum length of each fabric batch must be carefully controlled, consequently, manufacturing too short fabric batches such as a 50-meter batch by re-assigning warp must be avoided for the sake of uniformity in quality. And, again for the sake of uniformity in the quality of the fabric, the system must be able to assign remaining warps from the same warp dyeing work-order to the same customer order which ensures that the color range of the resulting fabric for a single customer order is as uniform as possible.

Both simple weft change type changeovers as well as reed frame change type changeovers require special sets of equipment and trained operators which are both limited in number. Additionally, the number of available reed frames of a specific type is limited, at least for a short time after which the number of reed frames may be assumed to be unlimited. Therefore, from factory operations scheduling perspective, minimizing lost times due to changeovers and associated asset limits while meeting due dates is the primary objective.

The finishing processes are directly fed by looms. Complex predecessor and successor relationships must be resolved to maintain a high utilization of available equipment while meeting due dates. Changeovers are also an important issue but are not as pressing compared to loom and warp processes. Hence, the primary issue is to make sure that fabric batches are directed to the right finishing process as soon as possible to meet tight deadlines.

The output of factory operations scheduling can sometimes be difficult interpret with all its implications. For the case of this industry, the output is further complicated by the assignment of batches of raw materials and semi-finished material to customer orders. NovaLab’s planning software, xS Planner, provides interactive material requirements plan view including batch assignments in addition to warnings related to various aspects of the plan such as late orders and a dashboard for KPIs.

Capacity Requirements Planning

Capacity requirements planning module is used to determine the sufficiency of the available capacity of each restricted resource such as machines and molds over a dynamically generated scenario.
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Factory Operations Scheduling

The factory operations scheduling module of NovaLab’s planning software, xS Planner, offers the interactive planning framework coupled with the fully automated or semi-automated optimization...
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