Maunfacturing process simulation for scenario analysis

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ABSTRACT: Examples disclosed herein relate to mapping a queue of multiple orders that go through a
manufacturing process with more than one steps of different processing time. One implementation is in
the personal computer industry to derive the best job queue by comparing the simulation results of
different queues.
DESCRIPTION
Manufacturing Process Simulation
BACKGROUND
Background: In a manufacturing environment, a production scheduler has to consider multiple factors
such as efficiency, cycle time, order priority, machine utilization, labor availability etc. to sequence jobs.
For example, a personal computer manufacturer that builds desktop and workstation computers
normally have to take efficiency, changeover, order commit delivery date, line balancing, etc. into
account when scheduling customer orders into build sequence.
BRIEF DESCRIPTION OF DRAWINGS
The drawings describe example embodiments. The following detailed description references the
drawings, wherein:
Figure 1 is a job sequence includes X orders and (n1+n2+n3+…+nx) units, all units in each order are
serialized for further calculations
Figure 2 is a processing time matrix for the orders in the job queue in each stage of the manufacturing
process
Figure 3 is a diagram illustrating the calculation of the Clock for each order in the job queue
Figure 4 is a logic matrix to show the derivation of the generalized status checking logic for each unit in
the job queue
Figure 5 is the generalized status checking logic for each unit in the job queue
Figure 6 is a loop diagram to illustrate the simulation process using running time RT as loop iteration
object
Figure 7 is an example of run charts that shows the simulation results that can help with decision making
DETAILED DESCRIPTION
A manufacturer typically has many different product lines with different complexity and configuration,
the customers can choose from these product lines and place orders with any quantity. For many
manufacturers, a pure first in first out order scheduling strategy is not feasible because changeover
exists, and frequent changes of products with different configurations in a production line would
jeopardize the efficiency. Hence, most of the manufacturers are trying to group similar products

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together and build them at the same time in order to eliminate the impact of changeovers. However,
this has to be handled very carefully since the on time delivery of customer orders are becoming more
and more important.
In order to balance different factors when sequencing orders, it is useful to have different job sequences
simulated before actual production, analyze the factors in different scenarios and choose the best
sequence that serves the designated purposes, which can either be quickest finish time, or a more
balanced production line across different steps, or maximum utilization of a certain workstation, etc.
An example is to simulate a personal computer (PC) manufacturer’s shop floor operations which have
four major steps:
Assembly: Assemble the computer based on customer configuration using components like chassis,
motherboard, central processing unit, memory, hard disk drive, optical disk drive, cables, screw, etc.
Depending on the line setup, normally would take 30 seconds to 120 seconds to build a unit.
Pre-test: Basic configuration and firmware test to make sure the computer is built according to the
configuration and all the components are compatible. Normally would take up to 40 minutes.
Run-in: Download and install the operations system and customized image, software. Usually would
take up to 5 hours to finish the process for a single unit.
Pack: Pack the computer and country kit with user’s instructions, cables, keyboard and mouse, etc. to a
cardboard box for shipping. This step only takes 30 seconds to 70 seconds to process one unit.
Changeover time is considered to be more significant in the assembly stage since it’s mostly done
manually, and other 3 stages are more automatic and less impacted by products changeover.
In order to virtually process customer orders, a few inputs are needed including the time required for a
certain configuration of unit to go through each step, the changeover time between two different
configurations, order quantity, run time, one predetermined production sequence, etc. and one
assumption here is that one order has only one product configuration.
The first step for the simulation is to choose orders to form a job queue and serialize every order in the
production sequence. Serialization means arrange every unit in every order in the production sequence
so that they can be tracked later in the process of simulation. In Figure 1, production sequence 1 has
total X orders: Order 1 has n1 units; Order 2 has n2 units; … Order X has nx units, and all units are
arranged in a queue with a serial number. The total unit in the queue is (n1+n2+…+nx).
Next step is to use the processing time information in Figure 2 to construct the simulation, the
processing time can either get from historical data or time studies, and it can be a certain number or a
distribution. When it is a distribution, a user can utilize a computer program to randomly generate
number from the distribution and assign the generated numbers to the serialize units.

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Then next step is to calculate the time available for each order in the queue to be processed, hereinafter
referred as “Clock”. In Figure 3, for run time RT, Order1 has RT available to be processed, so Clock1
equals run time RT. And Order2 has the time Clock1 minus whatever needed to process Order1 then
minus changeover time if Order1 and Order2 are different in terms of product configuration. For Order3,
Clock3 equals Clock2 minus processing time for Order2 minus changeover, so on and so forth; the last
row in Figure 3 generalized the calculation for ‘Clock’ of each order in the queue.
Next, the logic matrix shown in Figure 4 can be used to determine if a unit is in which process, and a
generalized logic is provided in Figure 5, where:
OrderX is any one order in a production queue
nx is the serial number for a unit in OrderX
ClockX is the time available to process OrderX
TX1, TX2, TX3 and TX4 represent the time needed to handle the unit in each process
For each stage in the manufacturing process, a unit in the queue has three statuses: not start, being
processed, and finished. For a given run time RT, the algorithm in Figure 5 can tell if any one unit of any
orders in the queue is in which status in any steps of the manufacturing process. Total number of units
in queue waiting to be processed is just adding up all units that are with status not started. Summing up
the units being processed gives the work in progress level. And units at finished status are what can be
processed during the RT time.
To get the run charts for order in queue, work in progress level and units finished in each step, in Figure
6, an algorithm loops RT from 1 to the time required by user, sums up the units in each status for each
single RT value in the loop. In Figure 7, three run charts can be produced from plotting the sum values
against RT. A user can simulate several job queues and compare the performance data charts for each
manufacturing stage, then make decision of which job queue serves the current goal the best. A user
can also compare the work in progress number and available capacity for any one step, and makes
decision on whether to increase the capacity so as to prevent the buildup of inventory before the station
and level up the whole manufacturing process.
CLAIMS
1. A manufacturing simulation algorithm, comprising 5 steps:
a) Serialization of orders in the job queue
b) Collection of processing time, run time, changeover time, order quantity, and predetermined job
queue
c) Use of “Clock” as a way to incorporate the changeover time in the logic
d) Use logic provided in Figure 4 and Figure 5 to determine the status of the units in the job queue
e) Simulation of the job queue and collection of the performance data for each step by looping
through the run time

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2. The manufacturing simulation algorithm claim 1, wherein the manufacturing is further refer to the
personal computer assembly, testing, imaging and packing.
3. The manufacturing simulation algorithm claim 1, wherein the serialization comprises the choosing
and sequencing of orders from available customer orders.
4. The manufacturing simulation algorithm claim 1, wherein the “Clock” is further to be calculated by
the formula provided in Figure 3.
5. The manufacturing simulation algorithm claim 1, wherein the simulation of the job queue and
collection of the performance data for each step comprise: looping through the run time provided by
user, collecting data in each loop, summing up the status of units, logging and charting the sum value
against run time.

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Figure 1
Production Sequence Serial # Queue
Unit 1 1
Order1 Unit 2 2
… …
Unit n1 n1
Unit 1 n1+1
Order2 Unit 2 n1+2
… …
Unit n2 n1+n2
Unit 1 n1+n2+1
Order3 Unit 2 n1+n2+2
… …
Unit n3 n1+n2+n3
… … …
… … …
Unit 1 n1+n2+n3+…+1
OrderX Unit 2 n1+n2+n3+…+2
… …
Unit nx n1+n2+n3+…+nx

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Figure 2
Stage 1 Stage 2 Stage 3 Stage 4
Assembly Pre-test Run-in Pack
Order1 T11 T12 T13 T14
… … … … …
OrderX TX1 TX2 TX3 TX4

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Figure 3
Sequence Time for order
Order1 Clock1 = RT
Order2 Clock2 = Clock1 - T11 × n1 – changeover{Order1&Order2}
Order3 Clock3 = Clock2 - T21 × n2 – changeover{Order2&Order3}
… … …
OrderX ClockX = Clock(X-1) - T(X-11) × n(X-1) - changeover{Order(X-1)&OrderX}

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Figure 4

Stage 1 Stage2 Stage 3 Stage 4
Production
Sequence
Serial
# Assembly Pre-test Run-in Pack
Order1 Unit 1 IF Clock1/T11≥ 1
THEN finish stage 1
OTHERWISE not start
IF previous stage is not done
THEN unit not started yet
ELSE IF previous stage is done
THEN IF (Clock1-T12)/T11≥ 1
THEN unit finish stage 2
OTHERWISE unit is being processed
THEN IF (Clock1-T12-T13)/T11≥ 1
THEN IF (Clock1-T12-T13-T14)/T11≥ 1
THEN finish stage 1
OTHERWISE not start
Order1 … … … … …
Order1 Unit
n1
IF Clock1/T11≥ n1
THEN finish stage 1
OTHERWISE not start
THEN IF (Clock1-T12)/T11≥ n1
THEN IF (Clock1-T12-T13)/T11≥ n1
THEN IF(Clock1-T12-T13-T14)/T11≥ n1
THEN finish stage 1
OTHERWISE not start
THEN finish stage 1
OTHERWISE not start
Order2 … … … … …
Order2 Unit
n2
IF Clock2/T21≥ n2
THEN finish stage 1
OTHERWISE not start
THEN finish stage 1
OTHERWISE not start
THEN finish stage 1
OTHERWISE not start
Order3 … … … … …
Order3 Unit
n3
IF Clock3/T31≥ n3
THEN finish stage 1
OTHERWISE not start
… … … … … …
OrderX Unit 1 IF ClockX/TX1≥ 1
THEN finish stage 1
OTHERWISE not start
THEN IF (ClockX-TX2)/TX1≥ 1
THEN IF (ClockX-TX2-TX3)/TX1≥ 1
THEN IF (ClockX-TX2-TX3-TX4)/TX1≥ 1
OrderX Unit 2 IF ClockX/TX1≥ 2
THEN finish stage 1
OTHERWISE not start
THEN IF (ClockX-TX2)/TX1≥ 2
THEN IF (ClockX-TX2-TX3)/TX1≥ 2
THEN IF (ClockX-TX2-TX3-TX4)/TX1≥ 2
OrderX … … … … …

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Figure 5
Stage 1 Stage 2
order Serial # Assembly Pre-test
OrderX Unit nx IF ClockX/TX1≥ nx
THEN finish Stage 1
OTHERWISE not start yet
IF previous process is not done
THEN IF (ClockX-TX2)/TX1≥ nx
THEN unit finish Stage 2

Process 3 Process 4
Run-in Pack
THEN IF (ClockX-TX2-TX3)/TX1≥ nx
THEN IF (ClockX-TX2-TX3-TX4)/TX1≥ nx

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Figure 6
Unit Status for a Station

Not start
Being
Processed Finished
RT = 1 Sum(1)

Sum(a) Sum(i)
RT = 2 Sum(2) Sum(b) Sum(ii)
RT = 3 Sum(3)

Sum(c) Sum(iii)
RT = 4 Sum(4)

Sum(d) Sum(iv)
RT = 5 Sum(5)

Sum(e) Sum(v)
RT = 6 Sum(6)

Sum(f) Sum(vi)
RT = 7 Sum(7)

Sum(g) Sum(vii)
… … … …

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Figure 7

1 2 3 4 5 6 7
RT
Status:Not Start (Assembly)
1 2 3 4 5 6 7
RT
Status:Being Processed (Assembly)
1 2 3 4 5 6 7
RT
Status:Finished (Assembly)
Sum (1)
Sum (2)
Sum (3)
Sum (4)
Sum (5)
Sum (6)
Sum (7)
Sum (a)
Sum (b)
Sum(c)
Sum (d)
Sum (e)
Sum (f)
Sum (g)
Sum (i)
Sum (ii)
Sum (iii)
Sum (iv)
Sum (v)
Sum (vi)
Sum (vii)

Maunfacturing process simulation for scenario analysis

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