Implementation of Metal Casting Best Practices - EERE - U.S. ...

Quality Control
The assessment team was impressed by the plant’s quality control measures and attention to
detail. The plant was very orderly and clean. It was apparent to the assessment team that
management pays attention to the housekeeping and maintenance of the plant.
Since this plant serves the three big U.S. automobile manufacturers, it cannot afford to ship out
any unacceptable castings. The plant has developed and implemented a quality control plan that
has limited customer returns at 0.10% of its total castings shipped. The plant employs a thorough
inspection progrm wherein computers monitor the entire casting process. The plant has the
ability to trace a casting back to the melt in which it originated, the die casting machine that
produced it, and the die casting operator. Each of the 36 die casting machines are monitored for
temperature and shot parameters. If the system shows “red,” the operator is notified and the
casting is scrapped. This monitoring system enables the plant to shut down a machine
immediately when scrap is produced, thereby reducing the amount of time, energy, and money
wasted with a machine continuously producing scrap castings. The monitoring system also
enables the plant to plan maintenance for periods when proper resources are available.
2. Areas of Improvement
Impeller Scrap
Despite the computer modeling of all of the new products and the implementation of a strong
quality control program, Die Casting Plant-2 still experiences an abnormally high scrap rate on a
transmission impeller. The part has an in-house scrap rate of over 20%, which means that the
plant must produce 125 of these impellers in order to have 100 good parts shipped. The scrap is
caused by “see through” holes in the impeller veins. When this scrap rate is factored into the total
shipments of this casting facility, the in-house scrap rate rises significantly from 2-3% to as high
as 15%. This is three times the industry average.
The transmission impeller is a legacy part that was designed about 10 or 15 years ago. The part
weighs approximately 5 pounds and is made of A380 aluminum alloy. The plant ships 140,000
to 160,000 of these impellers each year. The plant runs this part on five machines continuously
and the 20% scrap rate implies that one of the five machines is running merely to accommodate
that high rate.
The assessment team recommended that the plant revisit the impeller design and enlist the help
of NADCA and Ohio State University for assistance in optimizing the design. The plant agreed
with the suggestion and NADCA is currently examining this part. The assessment team also
recommended that the plant inspect its entire casting line for potential problems. The plant
should run reduced pressure tests at the holding furnace to determine if there is any gas and/or
dross variability causing the scrap. Finally, the assessment team recommended that the plant
investigate the performance of new die materials such as Dievar * to determine if they can
* Dievar is a commercially available chromium-molybdenum-vanadium alloyed hot work tool steel that provides
good resistance to heat checking, gross cracking, hot wear and plastic deformation.
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