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Tactical Design

In the phase of the tactical Rhythm Wheel design, the most important parameters such as product sequence, cycle length, and Inventory Replenishment Level are determined.

Sequence

The product sequence is the first step to designing the ideal Rhythm Wheel. It is essential that the sequence is set such that changeover times are minimized. A non-optimal sequence is waste, since changeovers consume more time than actually required. The quality of the changeover sequence has a major impact on the cycle length. The longer the changeover time in total, the longer is the Rhythm Wheel cycle. The longer the cycle length is, the higher the required inventory levels.

In process industries, an optimized production sequence is especially important due to extreme sequence dependency of setup times. In many cases, the optimal sequence can be found without using advanced algorithms. The sequence can be derived from long lasting experience of production planners who have created rules for optimizing the production sequence. One example of an obviously optimized production sequence from the field of chemical pigments is the production in a color sequence from bright colors to dark colors. The changeover effort from a bright to a darker color is rather small, while the changeover in the opposite direction requires intensive cleaning.

Cycle length

The cycle length is one of the most important parameters designing the Rhythm Wheel. It defines the length of the repetitive production pattern, and therefore directly determines both the lot sizes and the sizing of inventory levels. If the Rhythm Wheel cycle is long, lot sizes are big and inventory levels high. On the other hand, if the Rhythm Wheel cycle is short, smaller lot sizes lead to lower inventory levels. Therefore, it is desirable to achieve a short Rhythm Wheel cycle.


But the Rhythm Wheel cycle length has to be chosen with care: A cycle which is too short might lead to an infeasible production plan, which cannot be adhered to in execution. This happens when the cycle is too short to cover all setup and production times and when production quantities are too small to cover the demand during the cycle. A loss of customer service is the consequence. On the other hand, if the cycle length is chosen too long, production quantities are bigger than required, which lead to higher stock levels and more working capital tied up in inventories.

In an High-Mix Rhythm Wheel concept, not every product needs to be produced in every cycle, which is especially sensible for low-volume products. Those products are then scheduled, for instance, only every second or third cycle. In this way, set-up time for low-volume products can be saved while the cycle length of the production asset is maintained stable.

The correct cycle length design depends on several influencing parameters. The three main parameters are changeover times, production rates, and demand patterns of the product portfolio. Besides that, shift patterns, maintenance, and downtimes have to be taken into account, since they determine the available time for production.