Lps05 lscheduling

8/13/2018

LEAN SCHEDULING

GVC. ThS. Nguyễn Như Phong
; www.isem.edu.vn
Kỹ thuật Hệ thống Công nghiệp
ĐH BÁCH KHOA – ĐHQG TPHCM
(Tài liệu giảng dạy cho ISE)
2018

LEAN SCHEDULING
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Lean scheduling
Scheduling concepts
The pacemaker
Supermarkets
RRS
Mixed model scheduling
Lean batch sizing & EPE
Kanban & Pull

Material handling route
Heijunka & capacity management

11 April 2003

Nguyễn Như Phong

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LEAN SCHEDULING
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Scheduling
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Push scheduling
Pull scheduling

Pull sys construction
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Building blocks
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Workstation
Buffer / supermarket

Scheduling concepts
Nguyeãn Nhö Phong

11 April 2003

Scheduling concepts
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Scheduling concepts
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enable
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most repetitive-production
many less-regular-flow plants

implement successful lean scheduling sys
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in a value stream

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Scheduling concepts
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Demand smoothing the starting point
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The smoother the demand,
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the more stable the production,
the easier 2 implement

Enable supermarket inventory reduced

Nguyễn Như Phong

11 April 2003

Scheduling concepts
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Takt time - the drumbeat
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Pitch time –
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the repeating increment
Container moved & material handler circulates

Pacemaker
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Production scheduled at one single point
Other stages pulled / flowing
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in a FIFO sequence 2 the final stage
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Scheduling concepts
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Kanban
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Pull sys
Enable the coordination & synchronization of flow
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governed by the pacemaker

Avoid overproduction & high light problems

11 April 2003

Nguyễn Như Phong

Scheduling concepts
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Pacemaker schedule
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aided by 2 concepts
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RRS
Mixed model scheduling

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Scheduling concepts
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RRS
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Runner product – dedicated facilities
Repeaters scheduled at regular intervals
Strangers fitted around repeaters

11 April 2003

Nguyễn Như Phong

Scheduling concepts
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Mixed model scheduling
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Running the smallest pos. repeating batch size down a line
One piece flow – ideal
Inventory reduced, cell balanced
Regularity of flow –
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Making & moving in one repeating sequence all day

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Scheduling concepts

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Lean batch sizing
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Stages involving longer CO operations
Governed by the pacemaker
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Synchronization maintained
Inventories kept low

Nguyễn Như Phong

11 April 2003

Scheduling concepts
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Material handler
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Hold the whole process together
Regular route , circulating around the plant
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Collect up kanbans,
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every pitch increment / round multiple of PI
pick needed parts, deliver the requirement

Look out 4 any deviation
Separate function
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Move parts & prod
Make & assemble
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Scheduling concepts
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Heijunka sys

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Leveling at the pacemaker
Planning & execution sys
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Establish work 4 each pitch increment
Authorize the work 2 begin on time

Also a problem detection tool

11 April 2003

Nguyễn Như Phong

THE PACEMAKER
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Single PM
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The stage around which whole VS scheduled
The heart

Avoid amplification problems
Create synchronization

11 April 2003

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The pacemaker
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Often but need not be a constraint / bottleneck
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Well down stream
Upstream – pulled
Downstream
 Flow 2 be FIFO or
 Go into FG supermarket

Nguyễn Như Phong

11 April 2003

The pacemaker
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Rely on as smooth a demand as pos
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Operate at / near the pitch increment as the drumbeat
Under-capacity scheduling
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95% of the pitch time 2 allow 4 little variation

Heijunka box –
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scheduling mechanism

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SUPERMARKETS & FIFO LANES

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Lean aims at one piece flow
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Flow takes place bw. supermarket
Traditionally
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Large amount of inv. before & after w/s
Waiting to move,
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waiting for the next operation, buffer

SM areas grouped together
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enable MH to visit regular routes,
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go shopping for parts
Nguyeãn Nhö Phong

Supermarkets & FIFO lanes
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SM often established at/where
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the boundary bw. loops of pull
2 VS converge / diverge
2 CONWIP loops meet

WIP permission bw. w/s
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Under visible Kanban control or
CONWIP or
DBR

11 April 2003

Nguyeãn Nhö Phong

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Supermarkets
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WIP in SM
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Types
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Ordinary
SS needed 2 carter 4 uncertainty demand
BS needed 2 carter 4 process uncertainties.

A little more helps highlight the causes of problems

11 April 2003

Nguyễn Như Phong

Supermarkets
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FG SM
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Wall of shame
 demand management & schedule stability
Need 2 regard the inventory dynamically
Clear marker sys shows excess inventory

11 April 2003

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Supermarkets
Not use ASRS as a SM

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more inv,
visibility prevention,
slow response

11 April 2003

Nguyễn Như Phong

The Ten Rules for Supermarkets
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Lot size differences
In front of the customer
Material flow splits up into different directions
Between very different cycle times
Between different shift patterns
When creating different variants
For merging of material flows
For large distance between processes
High demands on flexibility and reaction time
For change of responsibility

11 April 2003

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FIFO lanes
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FIFO lanes
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Inv brought in at one end, removed from the other
Good lean SM practice even though a bit more space
Avoid date sensitive inv problems
Good for visibility & housekeeping
Monitoring easy via dates / color coding

Nguyễn Như Phong

11 April 2003

What FIFO
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FiFo lanes
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an important part of any lean material flow.
a very simple way to define
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both the material & information flows

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Why FIFO
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Decoupling of Processes

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The Rules for FiFo
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No part can overtake another part

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A clearly defined maximum capacity

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Advantages of FiFo Lanes

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A clearly defined material flow.
A lean material flow
A clearly defined information flow.
Helps visual management.

11 April 2003

Nguyễn Như Phong

When to Use a FIFO
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Whenever no reason for a supermarket.
The Ten Rules for Supermarkets

11 April 2003

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When to Break FiFo between Two Processes
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Batch Processing
Priority Orders
Parallel FiFo Lanes due to Space Constraints

11 April 2003

Nguyễn Như Phong

When to Break FiFo between Two Processes
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Variation in Storage Cost
Changeover Optimization

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When to Break FiFo between Two Processes
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The part flow not identical for all parts
FiFo almost always gets broken in job shops.
Batching, optimizing, and prioritizing open jobs.
If a supermarket is the better option.

11 April 2003

Nguyễn Như Phong

RRS
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Powerful idea 4 lean scheduling
Prod/prod family
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Runner
Repeater
Stranger

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RRS
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Runner
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Sufficient volume

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Not all the time, at-and-when basis, not 2 share

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to justify dedicated facilities / cells

11 April 2003

Nguyễn Như Phong

RRS
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Repeater
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Intermediate vol
Dedicated facilities not justifiable
Scheduled at regular slots

 Quantity varies, slot time remains constant
 Every day/other day/week
Advantages of order & discipline

11 April 2003

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RRS
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Stranger
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Low/intermittent vol
Fitted into schedule around the regular repeater slots
Lowest priority

Nguyeãn Nhö Phong

11 April 2003

RRS

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Production plan / scheduling construction
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Pareto analysis  RRS categories
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Runners –
Repeaters
Strangers

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RRS
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Runners –
 little concern so long as adequate capacity.
 enjoy own resources
 Heartbeat goes all the time
Repeaters
 Schedule backbone
 Slotted in at regular intervals as often as cap allow
 Max flow & min inventories
 Transfer batches smaller than production batches
 Breakfast every day
Strangers
 fit around the repeaters
 Shopping sometimes

11 April 2003

Nguyễn Như Phong

RRS & ABC classification
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Useful way 2 think of lean scheduling & pull options
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Tight kanban – TK: Small SS
Loose kanban – LK: More SS
MRP: Lack of repetition make kanban less feasible
Forecast based sys - FBS
2 bin - TB
Reorder Point - ROP
Go see – GS
Vendor managed inventory - VMI

11 April 2003

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RRS & ABC classification
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ABC inventory classification
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A – expensive items

B – intermediate
C – low cost commodity items

Efforts 2 convert S  R  R
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Reducing & eventually eliminating MRP

Nguyễn Như Phong

11 April 2003

RRS & ABC classification
Rn

Rp

S

A

TK

TK

MRP / FBS

B

LK

LK

MRP

C

2B/ROP

2B

2B/GS

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RRS - ABC & LT classification
Rn

Rp

S

A long LT

LK

MRP

MRP

A short LT

TK

TK

SK

B long LT

LK

LK

MRP

B short LT

TK

TK

SK

C long LT

2B/ROP

2B

2B

C short LT

VMI

VMI

GS

Nguyễn Như Phong

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MIXED MODEL SCHEDULING
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Scheduling in mixed repeating sequence

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In practical terms,

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rather than in large batches

one small container of a prod,
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followed by a small container of the other, …
then back

rather than a no. container of a prod,
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followed by a no. small container of the other, …
then back.

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Mixed model scheduling
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Reasons
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Powerful aid 2 cell balancing
Reduce WIP & sometimes FG
Lead 2 better cust. service
Result in a constant rate of flow all day

11 April 2003

Nguyễn Như Phong

Mixed model scheduling
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Related 2 lean batch sizing
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to achieve more frequent EPE

11 April 2003

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Mixed model scheduling
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Assembly operations
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No CO - no problem
Short COs
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Min feasible batch:
CO time + Qm * assembly time = Qm * TT
Qm = CO time / (assembly time – TT)
Desirable min no. a product
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kept together in a sequence.
Eg. AAABBCCD -

Nguyễn Như Phong

Mixed model scheduling
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Mixed model sequence
 derived from product mix demand
 Eg. 66%A & 33%B: AABAAB…
 Best sequence
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from the nearest lowest common denominator
Eg. A:B:C = 10:5:2
 5:2:1: ABABACAA-ABABABACA

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Mixed model scheduling
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Heijunka box

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Mixed model sequence placed in the pitch increments
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Use standard pitch increment,
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vary the length of the work day

Derive pitch increment directly from the takt

Batch size/container size
 the pitch increment

Nguyễn Như Phong

11 April 2003

Mixed model scheduling
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Heijunka box
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The no. pitch increment & the prod mix
 the sequence
Eg. 48 10m PIs Heijunka, 6A:3B:2C:1D
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4 12-PI repeating slots / d
ABABACABACAD

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LEAN BATCH SIZING
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CO remains a significant factor
Continue 2 attack CO times
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Improve flow
Allow reduce batch size

Nguyễn Như Phong

11 April 2003

Lean batch sizing
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Economic batch quantity
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totally rejected from a lean perspective
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No account taken of TT & flow rate
Classic batch & queue thinking
CO cost per CO, CO team – a fixed resource
Inv holding cost often understated
Capacity assumed 2 be infinite
Constant & uniform demand - not practical

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