Casting of the Year.
As the National Aeronautics and Space Administration (NASA) returns its space shuttles to flight this spring, it has been with the help of ME Global Inc. The steel sand casting company in Duluth, Minn., partnered with NASA and the United Space Alliance (USA) to develop new track shoes for the shuttle crawler transporters, which bring space shuttles from the Vehicle Assembly Building to the launch pad.
ME Global (a wholly owned business of Elecmetal, Santiago, Chile) came onto the space scene in the winter of 2002 when the company learned that the original track shoes on the transporters (dating back to the 1960s) and the inventory of spare shoes soon were to be refurbisned. The steel caster proposed to NASA that it could cast entirely new sets of shoes at a similar price as refurbishing. But NASA declined because it had prior success with refurbishing the shoes (adding stock to existing roller paths and pin holes and then remachining them to fit the original design specifications).
However, several months later, NASA and USA took a second look into the idea of newly cast shoes. ME Global was asked to make a presentation in mid-2002 at Kennedy Space Center (KSC), Cape Canaveral, Fla., to show NASA exactly how this would be possible.
Late in 2003, ME Global's research helped prompt NASA to overturn the refurbishment program and charter USA (NASA's largest contractor. which is responsible for the shuttle ground transport systems including the transporters) to immediately start procurement processes to outfit both transporters with new shoes. NASA was obligated to leave the bidding open to other metalcasting companies, but in May 2004, ME Global was awarded the contract. Now it had to deliver more than 1,000 shoes in six months.
NASA has two crawler transporters, which carry the space shuttle assembly (the shuttle, two solid rocket boosters and the external fuel tank) and the mobile launch platform to one of two launch pads at KSC at a pace of 1 mph (1.6 km/h). Both transporters weigh 6 million lbs. (2.7 million kg) each, but that triples to 18 million lbs. (8.2 million kg) when carrying the mobile launch platform and the pre-launch shuttle. A professional-size baseball diamond could comfortably be placed on top of the transporter.
There are four double-tracked, 10 x 41-ft. (3 x 12.5 m) crawler units (similar to a tank) on each vehicle, and each track has 57 shoes for a total of 456 shoes per transporter. Each vehicle has two 16-cylinder, 2,750-hp engines with a 5,000-gal fuel capacity but only gets 42 ft. (12.8 m) per gallon.
To completely re-inventory USA with its track shoes, ME Global supplied a set of 456 shoes for each transporter, plus a set of spares for a total of 1,024 track shoes. Each shoe measures 90 in. (2.2 m) long, 25 in. (0.63) wide, 16.5 in. (0.41 m) tall and weighs 2,200 lbs. (998 kg).
The shoe development was divided into three phases. Phase 1 was to produce a prototype that met all the requirements of USA and NASA and also confirm that the casting process is capable of producing more than 1,000 track shoes. Phase 2 was to outfit one transporter. Phase 3 was to outfit the other transporter. Based on the successful completion of Phase 1, ME Global was awarded Phases 2 and 3.
A significant challenge the company encountered in Phase 1 was trying to obtain the desired mechanical properties with the given NASA shoe design and alloy. USA specified steel alloy 8640 for the project, but it was found to be impossible to manufacture on a large-scale basis as the prototype castings cracked during heat treatment. At the same time, NASA would not alter the shoe design, which forced ME Global to investigate different alloys. The company turned to the CKQ alloys of which the original shoes were made and also alloy 8630, but neither met NASA's specifications.
ME Global then looked to alloy M4320 (which it recently used successfully in another project), and it achieved the requirements needed for the shoes. A low-carbon alloy, M4320 was determined to be the proper casting material in August, but this left ME Global with only four months to complete the project on time.
With the assistance of 20 extra employees the company hired to work on the track shoe project, ME Global began casting the shoes through V-process molding, which uses unbonded silica sand under one atmosphere of pressure to form and maintain the shape of the mold.
As the castings were completed, they were sent to Remmele Engineering, Big Lake, Minn., for machining. USA sent several quality assurance inspectors to Remmele, and ME Global had one of its principal metallurgists work full time on-site at Remmele to keep the project at pace. Once the track shoes were approved, they were sent from Remmele to KSC and installed on the crawler transporters.
We Have Liftoff
With the newly cast track shoes, NASA initiated a trial run of the crawler transporters carrying a mobile launch platform to one of the launch pads in January. Then, in April, ME Global's castings were used to bring the entire space shuttle Discovery assembly to launch pad 39B, where it rests until its ascension into space this summer.
Crawler Transporter Tread Belt Shoe
ME Global Inc. (Elecmetal), Duluth, Minnesota
Metal: Modified 4320 steel.
Weight: 2,200 lbs. (998 kg),
Dimensions: 7.5 x 1.5 ft. (2.29 x 0.47 m).
Application: Tread shoe for transporter that carries space shuttles to launching pads.
Benefits of the Casting Design:
* Prototype shoes were developed to replace older shoes. The prototype overcame technical challenges, including alloy changes and a shoe design change to eliminate shrinkage porosity; alloy changes and precise treatment and quench regimens to meet reduced surface hardness requirements while maintaining high material strength; and shoe design refinements to enhance operational characteristics.
* The qualification process required pouring more than 40 castings to identify the alloy and manufacturing process that could repeatedly produce acceptable shoes.
* The first prototype shoes were completed one week behind the baseline schedule, despite alloy changes and two casting design changes. ME Global successfully delivered more than 1,000 shoes in less than six months.
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|Title Annotation:||ME Global Inc|
|Date:||Jun 1, 2005|
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