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By Mark Hoffman

I love spending time on the production floor. Although some say I am the stereotypical engineer, I find one of my comfort zones is being around people who get things done. When I have the opportunity to visit production areas, I like to talk to these people and learn what’s really going on; I have learned a lot through the years.

A question I ask frequently is, “What is preventing you from doing your job?” The answer I hear second most is “Part shortages.” The most common answer: “#&%* part shortages!”

Unplanned Part Shortages Limit Capacity

At Columbia Aircraft Company in Bend, Oregon these words were spoken often. Columbia Aircraft produces a beautiful 4-seat, single-engine certified aircraft. (Their website, www.flycolumbia.com, has more pictures of these gorgeous airplanes.)

When TCA first began working with Columbia, customers had to sit on a waiting list for nearly 2 years before they could take delivery of a new plane. Although the company sold every plane it could make, management knew sales were well below their full potential and felt Columbia Aircraft was losing customers because of the long wait.

The Process

The plant in Bend fabricates and assembles body and structural components and does final aircraft assembly. Additional components and subassemblies are sourced from vendors and other Columbia Aircraft facilities. Regulated by the FAA, these composite body aircraft have a painstakingly defined production process; major steps in include:

• Layup (fiberglass and resin worked into a full-scale mold)
• Bonding
• Painting
• Sub-Assembly
• Upholstery
• Avionics
• Final Assembly
• Flight Test

Finding the Problem

Columbia Aircraft asked TCA to help increase production run rates (output) by creating a Lean Manufacturing Facility Layout in the Bend plant. In collaboration with Columbia Aircraft's own personnel, we created a design and implementation team involving people from Purchasing, Materials & Inventory Control, Production Control, Fabrication, and Assembly. The team’s first step was to look at production capacity at each stage of the process. We discovered adequate machine capacity was available in each stage.

As you might suspect, one of the major issues was fabricated material shortages. Fabrication just did not know when to make the needed upstream part. To add to the problem, a newly implemented ERP system was suspect – plant personnel did not trust it to build accurate schedules for the entire plant.

Demand-Pull System Solution

This situation was perfect for design and implementation of a Demand-Pull System that could answer these questions:

• Which part to make?
• How many are needed?
• Where should they be delivered?
• When are the parts needed?
• What is my priority?

Kanban Approach

Early on, we decided to employ Kanban techniques to implement the Demand-Pull System:

Kanban cards function as a replenishment trigger that communicates consumption of parts to upstream operations. While Kanban cards do have disadvantages (they can be lost), they’re an easy way of knowing exactly what quantity of which part to make when.

Kanban posts are placed in each fabrication cell and assembly area. Kanban cards are added to the post as new requirements are received, then removed from the post as work is completed. The Kanban post answers the 2 remaining questions required for the Demand- Pull System: When are the parts needed? What is my priority? Each Kanban post is a visual representation of the current schedule for its production cell or area.

Kanban Post Scheduling Board

Each Kanban post was divided into 3 zones – green, yellow, and red; 2 rules govern how cards are placed on the board:

  1. Depending on the urgency of the customer location’s need for the part, the card is placed in any of the 3 zones; those in the red or yellow zone take priority and are fabricated first.
  2. First-in first-out (FIFO) principles apply to cards in each zone. Parts are fabricated in order, starting with the oldest card on the board.

We used the “water strider” principle to deliver completed parts (with a Kanban card) to the customer Kanban inventory location. A water-strider is a material handler whose sole responsibility is moving Kanban material and cards. The water strider also collects Kanban cards from the customer Kanban inventory location and returns them to the supplier cell’s Kanban post.

Kanban Cards

Just a few notes about the Kanban cards:

  • • A magnetic strip on the cards and a steel Kanban post board created an easy, clean method for placing the cards on the post

  • • The cards were about ¼ page size – not too large, not too small

    • Cards were laminated for durability

    • All required information was placed on each card (part number, supplier, customer, quantity/card, Kanban inventory location, etc.) along with a picture of the part on the card – a very useful addition

    • Columbia Aircraft instituted a weekly Kanban card inventory procedure to be sure cards weren’t lost.

The Kanban locations were sized correctly to allow comfortable replenishment times and to accommodate any customer service or rework demands. In our case, the run rate was 1 aircraft/day. The team decided to use a min/max replenishment strategy – with a min of 2 and a max of 5 for most production parts.

Results and Lessons

Before the Kanban Demand-Pull System was implemented, fabricated part shortages were a daily occurrence. Now after several months of operation, the system has made a fabricated part shortage rare. And we learned it’s important to:

  • • Keep up daily maintenance; the water strider was required to maintain the system—making certain every part had a card and cards were placed in the right Kanban post location with Kanban inventory locations “perfect” in organization

  • • Move the cards and materials often; we found 4 times a day worked well

    • Develop a system to check on card loss (frequent inventory)

    • Get the right information on the Kanban card

    • Let the supplier cell/work station manage the Kanban post—and do the red zone first

    • Train, train, train frequently; once is not enough because new people come on board, people change and people forget…train, train, train.

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