DFMA Assembly

Design First, Lean Second: A Case Study

October 31, 2011
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To illustrate how to get more from lean manufacturing by first applying the principles of DFMA, let’s examine a simple product comprised of two pieces of sheet metal that are stamped on turret presses, bent on press brakes, and fastened together with two rivets. The product is produced from low carbon steel at a volume of 100,000 parts annually.

To manufacture this design will require:
  • two turret press setups.
  • two press brake setups.
  • one assembly worker and station.
  • A hand tool to insert and secure the rivets.
  • 26.35 seconds of assembly labor.
Analyzing this information early in the design phase is important. At this stage, a design team has options without any sunk costs, such as the cost of tooling, the assembly station and press brake tooling. In addition, changes in the manufacturing techniques and the design of the product itself are still on the table.

Traditionally, however, this design would simply be passed to the manufacturing team and production would begin. During production, if management discovers that cost cutting is needed to increase profit margins, engineers would look to apply lean manufacturing techniques to the process.

With lean, the following steps could be taken to make the process more efficient:
  • Reduce setup times of the presses and brake by training workers.
  • Reduce the amount of scrap by nesting parts or changing to a more appropriate sheet size.
  • Reduce the part-to-part and part-to-sheet edge clearances to use more material.
  • Reduce movement of material between stations by rearranging the shop floor layout.
  • Employ fixtures to facilitate riveting of the parts. Neither part has any self-locating features.
After applying lean methodologies, the bottom line cost savings is $0.194, or a reduction of roughly 11 percent.

If instead we applied DFMA techniques to the design, the manufacturing process would require:
  • One turret press setup.
  • One press brake setup.
  • Zero seconds of assembly labor.
The redesigned part costs $1.31-roughly 48 percent less than the original design and 34 percent lower than the cost of the “leaned” product design.

Now, applying lean to the manufacturing process would enable us to get the most benefit from all the tools at our disposal. We can also consider alternative manufacturing techniques. Progressive die stamping, for example, would prove to be a lower cost option than stamping and bending. With a better design, lean manufacturing lowers the cost of the part by an additional $0.35, including the cost of the progressive die tooling.

In the end, DFMA and lean achieved a cost reduction of $0.987 per part-more than half the cost of the original designs.

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