Line sequencing and rule types in Assembly Control

Assembly orders generated by APL can be sequenced by using the sequencing engine, resulting in a line mix and line sequence. During this sequencing process, line rules are taken in to account like clustering assembly orders based on items characteristics, or blocking assembly orders based on capacity rules.

The assembly line can either be dedicated to one model or to a mixed model. For example, a large number of product variants can be produced 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, which exist in three types:
    • 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 place option combinations next to each other with the same options, when changing between option involves a long change-over time. For example, place all blue cars next to each other, because changing painting color takes a long time. Assembly Control clusters the option combinations (such as paint color), and a sequence number is assigned to every option combination.

Example

In this example, the assembly orders and their option combinations are planned for a day on line segment 1.

Order 1Option combination red
Order 2Option combination blue
Order 3Option combination black
Order 4Option combination red
Order 5Option combination blue
Order 6Option combination black
Order 7Option combination red
Order 8Option combination blue
Order 9Option combination black
Order 10Option combination red

 

The option combination list Color is defined in Assembly Control as:

Option combination redsequence 1
Option combination blacksequence 2
Option combination bluesequence 3

 

When the assembly orders are sequenced in Assembly Control, based only on the clustering rule Color, the result for line segment 1 is:

Order 1Option combination red
Order 4Option combination red
Order 7Option combination red
Order 10Option combination red
Order 3Option combination black
Order 6Option combination black
Order 9Option combination black
Order 2Option combination blue
Order 5Option combination blue
Order 8Option combination blue

 

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.

Example

In this example, the assembly orders and their option combinations are planned for a day on line segment 1.

Order 1Option combination red
Order 2Option combination blue
Order 3Option combination black
Order 4Option combination red
Order 5Option combination blue
Order 6Option combination black
Order 7Option combination red
Order 8Option combination blue
Order 9Option combination black
Order 10Option combination red

 

The option combination list Color is defined in Assembly Control as:

Option combination redOption combination blue
Option combination redOption combination red

 

The list Color is linked to the blocking rule Color, which is linked to assembly line 1. This rule says that the color red cannot be followed by the color blue or by the color red.

One result of this rule is the following sequence:

Order 1Option combination red
Order 3Option combination black
Order 2Option combination blue
Order 4Option combination red
Order 6Option combination black
Order 5Option combination blue
Order 8Option combination blue
Order 7Option combination red
Order 9Option combination black
Order 10Option combination red

 

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 Work Centers (tirou0101m000) session.

Note

When you confirm a sequence, LN generates the As-built structure for the end item, such as the VIN number and header in the case of a car. You can edit the structure with the Serial End Item - As-Built Headers (timfc0110m000) and Serial End Item - As-Built Components (timfc0111m000) sessions. The serial numbers of the components are generated when you freeze the sequence. When you use the Print Work Instructions (tiasc5450m000) session, a space is provided on the printed form for you to enter the serial number of the components.

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

    [...]

  • Swap assembly orders (1 and 4)

    [...]

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