Modeling Sequences

You use a single sequence to represent a simple, linear series of production steps in production.

If you want to represent a complex series of production steps, you link several sequences with relationships to predecessors and successors.

In the simplest case, a routing has one sequence, the standard sequence. Every other sequence is either an alternative or a parallel sequence, depending on whether you perform its operations as an alternative to the standard sequence or in parallel (at the same time) with the standard sequence. Only routings can have alternative sequences. You can create parallel sequences in both routings and rate routings.

Parallel sequences are special types of overlapping operation that can be used in various industries.

A parallel sequence enables you to process several operations at the same time and is carried out as the corresponding section in the standard sequence.

The following are examples of parallel sequencing:

• In mechanical engineering, for assembly lines with individual component manufacturing, a parallel sequence allows for several individual components from the bill of material (BOM) to be prepared as smaller units for final assembly.
• In the chemical industry, you can use parallel sequences to model analytical processes that occur parallel to the production process.

Sequence Scheduling

An alignment key defines the start of the individual parallel sequences and, consequently, the position of the sequence buffers.

Only the first operation of a referenced operation set (or reference rate routing) that has not been unlocked can be used as a branch or as a return operation for alternative or parallel sequences. To use other operations within a reference operation set (or reference rate routing) for your parallel sequence, you must first unlock the reference.

You can create parallel sequences in routings and rate routings but not in reference operation sets or reference rate routings.

An alternative sequence in a routing is a linear sequence of operations that is an alternative to a sequence of operations in the standard sequence.

You can use an alternative sequence in the following situations:

• The production flow is different for certain lot-size ranges. In such situations, you can machine a work piece on, for example, a conventional machine or on a numerically controlled (NC) machine. An NC machine has a longer setup time than a conventional machine. However, the machining costs are considerably less. Therefore, using NC machines depends upon the lot size.
• The production flow changes under certain business conditions. For example, if you have a capacity problem, you can have a vendor perform some production steps externally.

You can enter a lot size range so that the system automatically selects the alternative sequence if an order lies within this range. The lot size range of an alternative sequence can differ from the one specified in the routing header. However, it must overlap, at least partially, with the lot size range in the routing header.

Alternative sequences are linked to the standard sequence. Branch operations in the standard sequence are ignored in the procedure.

You can use only the first operation of an unlocked reference operation set as a branch or return operation for alternative or parallel sequences. To use other operations within a reference operation set for your alternative sequence, you must first unlock the reference.

You can only create alternative sequences in routings. You cannot create them in reference operation sets, reference rate routings, or rate routings.

Watch the following video and understand how parallel sequences could look like.