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Production Schedules- Guidelines

Jay Gorajia

Jay Gorajia

Posted Dec 14, 2011
1 Comment

Production Schedules….Scheduled! – “General Guidelines”

In this post, I’d like to review some basic guidelines that most production planners and schedulers seem to agree upon.  Not meant to be the cure-all defacto standard, but based on polling several factories of various sizes and strategy seems to be a core list.

1)     Plan the schedule to ensure up to 99% capacity of the bottleneck operation or resource.

Planners should plan for the bottleneck operation or resource to be constantly and smoothly worked by providing and scheduling material and work for that bottleneck operation or resource.  This may also require larger buffers in front of these specific operations or resources to ensure smooth, constant work even if the upstream operation is starved or goes down for a period of time.  In some factories, burn-in is a bottleneck, while others it might be test or even specific equipment in an operation such as the reflow oven.  If the bottleneck operation or resource stops, there is no chance of hitting the-on time delivery metric.

2)     Align scheduling and planning (work order release) to business goals (on time delivery vs. maximum throughput vs. minimum cost or minimum WIP).  This might vary from quarter to quarter.  However these trade-offs must be considered in the scheduling.

3)     Agree on the metrics and checklists for feasible lead time quoting to Sales.  When sales promises undeliverable timelines, no one wins.

4)     Calculate “lead time variance” and set start dates based on the lead time variance to achieve delivery goals.

Chart distribution of lead time vs. the probability of achieving that lead time.  If the goal of on-time delivery is 95%, then we need to plan job release using a lead time to fall within the 95% lead time probability.  This might practically be eight weeks out, although the average lead time in a factory may be six weeks.  If a planner releases jobs and plans on the average lead time, then by definition the plan will miss 50% of the job’s on-time delivery measurement!  The average calculation determines that 50% will be less than that average value, and 50% above. Instead of relying on the average, plan for the practical job release to hit on-time delivery.

5)     Calculate “quality variance” to plan overage

Calculate yield distributions vs. the percentage of expected overages for an order to meet delivery requirements.  Using this framework, a production planner can use a more reliable metric to calculate the overage needed to produce the required quantities considering quality fall out.  However, if you plan for too low quality, then the overage amounts will be too high, and lead to waste.  The same framework can be used to schedule safety stocks of semi-finished goods.  For high-runners or frequently re-ordered products, only the amount to cover forecasted uncertainty should be calculated and kept in stock, rather than building overage each time.

6)     Use real-time information on assets, resources, material, WIP, yield, etc. to ensure a feasible daily job release and scheduling on factory floor.

7)     Use real-time notification that the schedule can no longer be met.

Production planning and factory management should be notified if schedules can no longer be met due to factory condition changes.  These may include yield, machine availability, productivity levels, and resource availability.  Manufacturing Execution Systems or Manufacturing Operation Management systems (e.g. Valor MSS™ ) would be key to achieving this goal.

8)     Schedule must be available to everyone, and easily understood.

Publish the schedule and have it available for everyone to see.  This ensure visibility to the risks and goals in front of every department.

The above guidelines are a consolidation of discussions by various factory planners, production planners, and ERP users, in addition to references selected.

What of the above is in practice in your factory?  What is not, and should be?

Next installment we cover other factors that affect production schedules.

Stay tuned…..

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Jay GorajiaJay Gorajia is Worldwide Consulting Manager, PCB DFM and Manufacturing Solutions, for the Consulting Division of Mentor Graphics. He works to improve efficiency and help define productivity solutions in design, manufacturing engineering and production for OEMs and PCB Assembly manufacturers. Mr. Gorajia holds a Bachelor’s degree (B.Sc.) in Electronic Engineering and a Masters in Business Administration (MBA) in Technology Management. He has published a number of articles and White Papers in industry leading technical magazines and industry conferences. Visit Electronics Assembly .… Exposed

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Comments 1

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This is a well grounded article, whose principles can be used in many industries. Your treatment of bottlenecks was excellent, but may cause the lean people to cringe.

Jefff
7:39 PM Mar 23, 2012

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