Description of Kanban and CONWIP and in what situation should either be used

1. Decentralized Pull
Systems

2. Some Basic
Definitions
 Throughput time
 Sometimes referred to as flow time, refers to the time from when a
job is released to the shop floor until it is completed.
 During this time the job the considered to be a part ofWork-In-
Progress (WIP)
 LeadTime
 It is the time between recognizing the need to plan and execute a
job, and the completion of the job.
 It includes throughput time, job planning time and the time job
spends waiting to be released.

3. Techniques of
Production
Authorization
 Release of Jobs to the Shop floor
 Any job not released on the shop floor is an inventory.
 If resources on shop floor are occupied, job may not be immediately
released
 Idea is to delay release of jobs on the shop floor till resources are
ready.
 Objective is to reduce inventory to the positive minimum leading to
less investment in inventory.

4. Advantages of
Delayed
Release of Job
 Ordering of the material can be delayed
 Even if the material is inventoried, it is still less in value than the
one inWIP
 Frees Production capacity
 High priority operations can be scheduled in the freed production
capacity
 Reduces WIP flows and movement
 Decreases material handling distances on account of lesserWIP as
there is no need to get the extra WIP out of the way
 Reduces workstation distances that made provisions to
accommodate excessWIP
 Sets up the stage for implementation of JIDOKA (Identification of
quality issues)

5. Information
required for
release of jobs
 What to make
 When to make
 When to start the production

6. The Resources
on theShop
Floor
 Work Stations (Individual machines or operator areas)
 Work Centres (Group of machines doing different operations)
 Bins for holdingWIP inventory
 Conveyors, Gantries & Cranes, Forklifts, trollies.

7. Production
Authorizations
 Give workstations permission to make parts
 A series of mechanisms that communicate authorizations are
developed.
 Instructs workstations to produce given quantity of some part
either immediately or upon fulfilment of certain conditions

8. Types of
Production
Authorizations
 KANBAN Systems
 CONWIP Systems
 Base Stock System
 MRP System

9. KANBAN
Systems

10. CONWIP
Systems

11. BaseStock
Systems

12. MRPSystem

13. Two Stage
KANBAN
Systems

14. Two Stage
MRPSystems

15. KANBANSYSTEMS

16. Kanban
Production
Control
 Introduction to the concept of
internal customers.
 Kanban is a Japanese word for
Card.
 It is one of the corner stones of
widely discussed JIT.

17. Kanban
Production
Control

18. Kanban
Includes
Information
on…
 PartType
 Number of units authorized by the Kanban
 Location of material needed to produce the product
 Colour coding of the cards is used for multiple variants

19. Single Kanban
System
https://www.youtube.com/watch?v=V-Vd3cUoQR4

20. Dual Kanban
System

21. Common Rules
forScheduling
Production
Kanban
 Single-Kanban Priority rule
 Family Rules
 Minimum EOQ
 Signal Kanbans
 Cyclical Production – Continuous time
 Cyclical Production – Periodic review

22. Single-Kanban
Priority Rule
 For brief setup time, the production quantities can be set equal to
the size of the container. i.e. the batch size.
 FCFS is preferred to minimize flow time variability and maximum
flow time.

23. Family Rules
 In some work areas, the parts can be divided into families based on
setup requirements.
 These parts share the same tooling, fixtures to facility quick
changeovers.
 Select the family with the Kanban that is waiting the longest.

24. Minimum EOQ
 To justify a setup from an economic perspective, operator may need
to wait till a minimum number of kanbans of a particular type in on
the board.
 These are group and then that group is selected whose number of
kanbans exceeds the minimum production quantity.
 However the rule of runout rule applies before the EOQ rule as the
priority is higher on account of the parts running out of production.

25. Signal Kanban
 Used for Minimum order quantity.
 Uses the concept of EOQ to trigger replenishment.
 All material is first grouped as per type and stacked together.
 A signal kanban is placed at the point of reorder so that when the
stack reduces, it signals for a replenishment after viewing the
kanban.
 This generally uses a two bin system.

26. Environmental
Requirements
for Kanban
Systems
 Demand should be approximately constant over a planning period
 Setup times should be small to permit for small production
quantities and quick response to demand changes
 Available, flexible capacity on account of frequent short
maintenance.This ensures decrease in breakdown hours and
increase in production hours
 Disciplined workforce that will adhere to the system and Kanban
rules to keep the inventory in check.

27. CONWIPSYSTEMS

28. CONWIP
Systems
 Maintain inventory levels by releasing jobs to the shop to maintain a
level of N jobs in the system at all times
 A list of backlog parts is maintained either because their inventory is low
or a demand surge is anticipated.
 As soon as one batch of parts is completed and leaves the system, the
next batch on the backlog list for which all raw material is available is
dispatched to the shop floor.
 When a job leaves the shop, a message is sent to release the next order.
There is no need to worry about the internal distribution of work on the
shop floor.
 Control is on total inventory in the shop as the entire shop floor is
treated as one single work centre.

29. CONWIP
Systems
Advantages &
Disadvantages
 Automatic and immediate adaptation to unforeseen changes in part
mix.
 If parts not needed in future, then the part type is put in the backlog
list and batches are not produced.
 Prioritization of jobs may be affected because of backlogging of
inventories
 CONWIP requires ample space between workstations

30. CONWIP
Implementation
 Trick in implementation of CONWIP is to average out the demand
and supply so as to average out the WIP inventory.
 Increase the average production rate such that it offsets the
bottleneck n the system by equalling its process rate.
 If demand increases, as evidenced by rapid withdrawal of completed
parts from the output buffer, then new jobs are dispatched to the
shop floor faster and production rate increases.
 Vice versa when demand drops

31. Disadvantage of
the Backlog list
 Development of a core of unusable inventory in the output buffer.
 Can delay or defer release of orders because of inventory in the
output buffer
 The jobs count towards the total inventory N and thus may impede
release of jobs. Its like obsolete parts preventing the release of new
orders.
 Periodic review of such parts is done.