Manufacturing Strategy for Window Fabricators 8 - Scheduling and KANBAN
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:
Determine the factory production capacity at full activity (in squares per day).
Determine the time taken for actually producing the window, this should be around 2 days for most factories.
Work backwards from the delivery date to give the date for ‘seeding’ the order to the factory.
Work backwards from the delivery date to give the date for ‘seeding’ the orders to external suppliers, e.g. glass or panels.
Establish ‘check stations’ for collection of product at the end of each day and determine where the product should be at the end of each day to make sure that it is completed at the right time for delivery.
Accept and schedule orders to only 80% of the factory production capacity for delivery each day. The remaining 20% is the ‘buffer zone’ for emergency orders and remakes. After accepting the total number of orders then ‘close’ the day for production scheduling. No more work should be scheduled for production on this day.
Colour code windows for day of delivery as they are cut on the first day after seeding.
Check that all windows of the specified colour code are at the check station at the end of each day.
Use the ‘spare’ 20% capacity for the rush jobs (colour code them as rush jobs to go straight through the factory system).
Complete the delivery as required.
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.
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.
Simple scheduling and JIT encourages the use of small transfer batches to reduce WIP and does this by using the KANBAN concept. The KANBAN is simply a card or any other indicator that tells you:
How many items are in the batch.
The name and number of the item.
Where it has come from.
Where it is going to.
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:
They reduce the number of toast racks (provided that you insist that no work is produced if the toast rack in front of the station is full).
They limit the spaces for WIP to hide.
They speed the flow of work through the factory.
They show scrap immediately.
They control production in a highly visible manner.
They reduce the transfer batch size.
They quickly improve factory control and WIP reduction efforts.
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.
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
© Tangram Technology Ltd. 2003
Our standard disclaimer regarding Internet data applies.