An article from HotNews no.2, October 2006

Convinced by the quality and flexibility of the process, Ford USA is expanding the use of low-pressure heat treatment for parts of its six-speed automatic transmissions. And the result? A substantial reduction in production costs. 

No less than a million dollars are expected to be saved every year: at the half-way stage of its massive deployment plan for several ICBP units in its Sharonville plant (Ohio, USA), Ford is already counting the benefits due to low-pressure carburizing. The car manufacturer released these figures within the context of its production facilities modernization plan. The successive launch of several six-speed transmissions confirms the advantages of this process, such as the possibility of heat-treating distortion-prone ring gears, or using less expensive alloys.

Ramp up 

Low-pressure carburizing began to pull ahead at Ford in 2004, at which time it had only atmosphere heat-treatment furnaces. After several series of tests at different suppliers, and convinced by the metallurgical quality obtained at ECM in Kenosha (Wisconsin, USA), the car manufacturer installed its first ICBP unit that same year in order to pursue tests on an industrial scale. The launch of Ford’s 6-speed rear-wheel-drive transmission (codename 6R) was about to change the plans dramatically. "When we ordered the system in 2002, there was very little vacuum carburizing going on in North America. As we got it running, our management wanted to pull ahead" recalls Ron Lucas, Technical Specialist in metallurgical processes at Ford. As a result, four of the six cells of the ICBP were immediately used for production of 6R components, and only the last two cells were left for test purposes.  

A few months later, following the introduction of a new family of 6-speed front-wheel-drive transmissions (codename 6F), Ford needed to ramp up production. More components treated, greater volumes: in 2004, the car manufacturer ordered four additional ICBP units, followed by another two in 2005. Eventually, its Sharonville plant will be equipped with four 6-cell and four 8-cell ICBPs, all equipped with a gas-quenching system. Three of these are already operational, and the next systems are currently in different phases of installation. As a result, Ford will have the capacity to low pressure carburize over 35 million gears annually. Simply impressive!

Turning point

The launch of the 6F program was in fact the real turning point. The number of vacuum-treated parts per transmission unit rose from six for the 6R (three pinions and three sun gears) to 13 for the 6F. Four ring gears and three output gears extended the list of vacuum-carburized components. Moreover, for one of these ring gears, the combination of low-pressure carburizing and gas quenching proved critical in order to meet the specified tolerance limits, this part being highly distortion-prone as a result of its large diameter and thin metal section. "Thanks to pressure and quenching time adjustment accuracy, we were able to meet the requirements of our product engineers" comments Ron Lucas. This was important cost-wise, as the only alternative would have been to use a different, more difficult machine-able material along with outside supplier services. In other words: a more expensive process.

A final factor soon sealed the fate of atmosphere carburizing at Ford. Thanks to low-pressure carburizing, Ford was able to make general use of a new alternative alloy, 5120M (20MnCr5), and abandon the 8620 (20NiCrMo2) used up till then in atmosphere heat treatment. "We previously used 8620 in order to reduce oxidation. But under vacuum, this risk is no longer a factor. So a simpler, less expensive alloy can be used" explains Ron Lucas. Here again, significant savings could be made, several cents per pound of material: unlike the 8620, the 5120 alloy does not contain nickel – a raw material that has seen a price hike of 300% in three years.

At Ford, Ron Lucas remembers having worked with his colleagues to find an ideal heat treatment process. This was during the early years of the new millennium. And the conclusion: "With low-pressure carburizing, we have effectively found what we were looking for back then."