Manufacturing Strategy for Window Fabricators 8 - Scheduling and KANBAN




Scheduling the use of machines is a basic in production management and there are some simple skills and methods to scheduling that can make it a lot easier.

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The fabrication market is extremely competitive and one advantage is the ability to meet short lead time orders as well as to meet orders that have been in the system for some time. Scheduling of the factory to meet these requirements is a major difficulty but also a major source of competitive advantage. Setting and achieving a robust but simple schedule is often a major concern for factory managers. The daily schedule seems to change randomly as customers change their minds or as situations change and because the order book is rarely longer than 10 to 15 days, window production is almost always based around short term planning schedules and simple planning methods.

Despite this it is also necessary to take into account the longer term schedule needs and to set up a 4 layer system to cope with the various time frames. This system can be used to funnel in to the precise daily production requirements. The time frames are:

Long term (4 to 12 months):

There is a need to develop some long term planning for machinery and factory needs. This level is the scheduling horizon for strategic decisions regarding machine purchases, factory requirements, supplier development, major customer acquisition and implementation of JIT plans. Fabricators need to examine the monthly trends in ordering (down in the early part of the year and up in the latter part of the year) and separate these from the underlying trend for the business - is real business growing and what needs to be done about new production capacity?

Medium term (2 - 4 months):

At this level, seasonal demands can be predicted and included in the schedule, regular and large customers can provide an outline of their requirements (but not firm orders) and the general production capacity plan can be created and checked. The need is to check that capacity (particularly manpower needs) is adequate for the seasonal variations.

Short term (0 - 2 months):

This is the scheduling horizon for general machine and people availability. At this level the schedule can remain flexible but action needs to be taken for manpower and some broad orders to major suppliers can be confirmed.


Daily production can be scheduled by the following steps:

Funnelling in to the daily production but remaining flexible about the actual demands.

This system works simply and easily to prevent delays and achieve on-time delivery - the only extra requirement is the factory management and discipline necessary to keep to the colour schedule but nobody ever said life had to be easy!

Schedules built under this system work because they have inbuilt commitment, workers know the requirements and can clearly see what has to be done to achieve the schedule - visible management works.

Transfer batches (KANBAN)

Within this type of schedule there is a need to reduce the size of transfer batches as much as possible. Most manufacturers like to process product in batches because of Economic Batch Quantities (EBQ) and the size of the EBQ effectively determines the amount of WIP in the factory. How many fabricators cut or process in large batches and what does this do to the cost of work in progress? If you have lots of space for WIP e.g. toast racks, then you can be sure that they will fill up but you can also be sure that it will fill up with the wrong stock i.e. the stuff you can never move.

For window fabrication it can be a toast rack or a marked space on the factory floor.

The space defines for the operator the amount of good work to process and when it is full then he does other work until the KANBAN space requires more product, he cannot and must not produce more product than this on the basis of 'just-in-case'. Note: Work is also prioritised strictly on the colour code system.

The benefits of KANBAN are:

KANBAN can also be used to reduce the size of the factory. If there is a lot of space in any factory, then it will fill up with WIP. It is also certain that the space will fill up with the wrong WIP such as rejects or stock that is not really needed. KANBAN prevent the build-up of WIP and can reduce the space needed.

Using toast racks as KANBAN controls or ‘check points’ for scheduling and production control will reduce WIP, clean out the factory and improve delivery reliability.

'Manufacturing Strategy' Series.

The 'Manufacturing Strategy' series is designed to give window fabricators a set of ideas for managing production. The series is being published in Fenestra on a monthly basis and published here after the Fenestra publication. The series is:

Part 1: The Essential Part 
Part 2: The Systems
Part 3: Just-in-Time

Part 4: Optimised Production Technology

Part 5: Work Cells

Part 6: Machines
Part 7: Machines (2)

Part 8: Scheduling

Part 9: Waste (Methods)

Part 10: Waste (Materials)

Part 11: Supply Chain

Part 12: Measurement
Part 13: Things to do NOW!
Part 14: The Cost of Quality

Part 15: The Hidden costs of inventory

Part 16: Environmental management

Part 17: Continuous Improvement

Last edited: 11/03/10

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