Line sequencing and rule types in Assembly Control

The assembly line can be dedicated to one model, or to a mixed model, producing either one product variant or a large number of product variants on the same assembly line.

Four major aspects of line sequencing are discussed:

• Sequence rules
• Sequence process
• Rescheduling
• Line sequence status

SEQUENCE RULES

Sequence rules are made up of the following elements:

Mixing process

Mix rules, which exist in three types:

• • Capacity restriction rules
  • Proportional rules
  • Relative proportional rules

Placement rules

There are three types of rules:

• Clustering rules
• Blocking rules
• Priority rules

The (re)mixing process in Assembly Control

You can remix the orders within the Assembly Control module by using the Remix Line Mix (tiasl3220m000) session. Rules are defined for particular option combinations. Remixing attempts to schedule the orders so that the number of orders for each option combination is as close as possible to the maximum number of orders for each option combination. The better the mix, the better the sequence quality.

Mix rules

There are three types of mix rules:

• Capacity Restriction

  The total capacity of the line is limited, for example: maximum 500 cars with option combination CityCar in one day.

  For Capacity Restriction rules, you can select one of three types of dispersion:

  • Average Dispersion The option combination is spread evenly throughout the line sequence.
  • Sliding Window Avg. Disp. A window is a certain number of adjacent sequence positions. That window is being slid position by position. Within each window the product sequence is optimized. Adjacent sequence positions means a continuous range of sequence positions. In each window the option combination is dispersed as evenly as possible. For example, each group of 10 positions should have the same number of RedCars.
  • Sliding Window Cap. Resr. Within each window, there is a limit to the number of orders for the option combination. For example, no more than two RedCars in any window of 10 positions.

• Proportional

  Option combinations must be present in fixed proportion of the total order, for example, the ratio of CityCar to other orders must be 1:2.

  You can define two dispersion types for Proportional rules:

  • Average Dispersion The option combination is spread evenly throughout the line sequence.
  • Sliding Window Avg. Disp. In each window, there is a maximum ratio of a given option combination and any other option combination. For example, for every RedCar option combination, there must be at least one other option combination within any four option combinations (ratio = 1:2, window =4).

• Relative Proportional

  The same as Proportional, except that the Method of Dispersion is always Relative Dispersion. You must specify a second option combination in which the first option combination is dispersed in relation to. The option combination is placed in a particular relation to another option combination. For example, red cars and blue cars can only be assembled alternately; you cannot assemble two red cars in a row.

During remixing, the priority of orders is taken into account, as described in one of the following paragraphs.

Because rules can conflict with each other, it is possible that not all sequence rules can be met. In that case you can give some rules a higher priority. However, this results in a less efficient order sequence, and you must solve these conflicts by redesigning the assembly process, not by performing more line sequencing.

Placement rules

Placement rules are used to determine how products are placed in relation to other products. There are three types of placement rules:

• Clustering

  Use this rule to group specific option combinations, for example, group all the blue cars because changing paint color takes a long time. This rule also allows you to sequence the clusters based on the characteristics defined in the Option Combination Lists (tiasl1511m000) session in Assembly Control on the option combination list that is attached to each cluster.

  Using the options defined in the combination list, Assembly Control can sequence the clusters as efficiently as possible.

  You can assign each cluster a priority (0 to 99). Additionally, priority can be given to sequencing specifically by selecting high priority numbers in the sequence in the clustered option combination list.

• Blocking

  Certain option combinations must not be placed next to other option combinations. For example, light colors must not be painted after dark colors to minimize effects of paint contamination.

Priority

Priority rules are enforced in the following order:

1. Orders with a later Requested Offline Date are given a lower priority.
2. Orders that are sold (a demand order) have priority over orders not yet sold.
3. Assembly orders with a lower priority number are processed first (for example, orders with a priority number of 1 are processed before orders with a priority number of 4). You define the order priority in the Assembly Order (tiasc2100s000) session.
4. Cost function value.

THE SEQUENCING PROCESS

When you add new orders to an assembly line, LN generates in the Simulate and Create Line Sequences (tiasl4200m000) session an initial sequence for the line for the appropriate offline date.

A line segment that follows a buffer can only be sequenced, if the buffer has more than one random access place. To define a buffer's number of random access places, enter a value in the Number of Random Access Places field in the Stations (tiasl1545m000) session.

RESCHEDULING

You can also manually alter the sequence with the Reschedule Assembly Orders (tiasl4220m000) session. The session uses two types of rules:

• Move

  An order is taken from one position and inserted into another position. All orders in between the two positions are shifted one position towards the initial position.

• Swap

  Two orders are interchanged, and nothing else is changed.

The automatic sequencing process uses the swap method. You can change the maximum swap/insert distance that is used in the automatic sequence generation in the Remix/Sequence Parameters (tiasl4110m000) session.

When you have swapped orders to another line mix, you can run the Remix Line Mix (tiasl3220m000) session for a better sequence.

LINE SEQUENCE STATUS

A line sequence can have one of the following statuses:

• Planned
• Started
• Completed

A line sequence has the status Planned when it is first created. When the first line-station order is completed, the status becomes Started. When the last line station order is completed, the status of that segment becomes Completed.

You can see the status in the Line Segment - Line Sequence (tiasl4500m000) session.

You can sequence the assembly orders on two levels:

• Assembly line level (line mix)
• Line segment level (line sequence)

An initial line mix is generated by Assembly Planning. Remix assembly orders consider assembly orders with the status Planned and Sequenced, and use the existing assembly line mix as the starting point.

The remix process is important under these circumstances:

• When a backlog must be cleared.
• When an existing mix must be improved.
• Because offline dates of assembly orders have changed.
• Priority on assembly orders is altered.

A line sequence is generated based on the line mix. A line sequence specifies the order in which assembly orders must start on the corresponding line segments. For each line segment that is present in the assembly process, a line sequence must be generated. The line sequence algorithm takes the assembly order with the status Planned and Sequenced within a specific production period as input. On the last line segment of a supplying line, a line sequence is fixed. The line sequence of the connected line segment on the parent line determines the line sequence of the last line segment on the supplying line.

After sequencing, you can manually reschedule the assembly orders per line segment. Two types of rescheduling are possible:

• Move assembly orders

  Initial	1	2	3	4	5
  New	2	3	4	1	5

• Swap assembly orders (1 and 4)

  Initial	1	2	3	4	5
  New	4	2	3	1	5