JIS is sometimes called In-Line Vehicle Sequencing (ILVS).
The sequencing allows companies to further eliminate inventory because the number of component part buffers necessary is reduced to exactly one. Without sequencing, every possible variation of a component must be stocked at the production area. For flexible production lines such as a modern automotive assembly line, the number of options for each component can be over a dozen in the case of engines, or hundreds of possible options for a car's dashboard. When the next order arrives at the work center, the operator or equipment must then chose the appropriate option from one of a handful of buffers or more.
Sequencing eliminates these additional buffers by consolidating all similar components into one sequenced buffer. When the next order arrives at the work center, the operator or equipment simply takes the next item in the sequenced buffer. This strategy thus reduces the line-side inventory buffer and also reduces the likelihood of errors.
Just In Sequence processes are typically implemented only after the company has achieved a high degree of competency on Just In Time processes. The first step for the organization is to implement JIT processes to synchronize all manufacturing and material departments inside the plant and to collaborate with suppliers, customers, and sub-contractors to reduce inventory buffers to within a few hours. This process typically uncovers deep manufacturing and logistic issues that are not easy to overcome (see JIT Implementation for more details). The manufacturing company can only benefit from sequencing items once these problems have been resolved successfully and components are delivered Just In Time.
Sequencing can be implemented in a Just In Time supply operation at many levels, bringing ever-higher inventory reduction and financial benefits:
|Just In Sequence Process||Description||Impact|
|Pick-to-sequence||Items are picked from an on-site buffer, sequenced, and delivered to production||Reduces buffers in production area, improving wip and cycle time|
| Ship-to-sequence then |
|Items are sequenced at the supplier (internal or external), delivered in sequence, and taken directly to the production line||Reduces the amount of component and semi-finished goods inventory overall in the plant, freeing up cash, and reducing carrying costs|
|Items are built according to the sequence in which they will be required by the customer or downstream departments||Reduces the amount of finished goods or semi-finished goods in inventory, freeing up additional cash, and reducing carrying costs|
Just In Sequence implementations introduces a number of new process requirements on top of Just In Time practices. A production sequence or final assembly sequence must be shared across departments, to suppliers, customers, and sub-contractors. In many manufacturing operations, the actual production sequence cannot be planned ahead of time with enough certainty to enable sequencing. The main reason is that some manufacturing processes require re-work so often that the planned sequence becomes irrelevant. For example, painting operations in an automotive plant can have re-work levels of up to 20%. For this and other reasons, the actual production sequence must be "broadcast" out to all relevant parties once it is firm. This "broadcast" can be done over the phone, paper, email, or other automated IT system. UN/EDIFACT supports an EDI message standard called DELJIT as one standardized way to communicate this information.
Once the sequence is broadcast, each party must immediately take action to deliver sequenced parts in time. In many cases the turn-around time from broadcast to final assembly is less than 2 hours, with some components required in 30 minutes or less. With this time frame, there is little room for errors. In addition, quality inspection and poka-yoke must be implemented in the sequencing step to guarantee that the sequenced components match the assembly sequence perfectly. In many cases, suppliers must manage periodic sequence reversals, for example, when loading racks into a truck, since the first rack into the truck is the last one to come out. Employees and systems must also properly manage exceptional scenarios, such as re-processing damaged items after initial sequencing, skipping slots for scrapped items, etc. Just In Sequence implementations can only be successful if all of these processes are implemented correctly and all people involved understand what is at stake.