"Big Yellow" automated induction heating systems processes family of diesel crankshafts.

A major diesel engine manufacturer recently took delivery of a new, highly automated induction hardening system engineered to handle a family of six-cylinder diesel crankshafts. The system, dubbed "Big Yellow" by the engineers at Robotron-Elotherm, Inc., of Southfield, Mich., who designed and built it, features several advanced technologies, which enhance the quality and durability of the crankshafts it processes for use in the diesel engines that power the manufacturer's equipment.

Engineered to process four different six-cylinder crankshafts intended for engines with displacements from 7.6 to 12.5 liters, "Big Yellow" combines state-of-the-art power control and inductor technologies with field-proven shuttle-type part transfers, and precision mechanical part rotation to produce 25 crankshafts per hour meeting customer quality standards.

Changeover from one crank to another can be accomplished in 45 minutes or less, and requires only replacement of inductors, chuck inserts, and rests.

Although induction hardening of diesel crankshaft pins and journals has been the industry standard since the 30s, the process is still evolving as new inductor, power supply and control technologies give engineers the tools needed to achieve previously impossible results. In the case of "Big Yellow" the challenge was to reliably process the pins and journals in spite of the fact that the cheeks between them were much thinner than normal for a crank of their size.

"At first glance, processing a crankshaft looks like it should be really easy," explained Rudy Schwarz, induction heating product manager, "but that is not the case. There is a tremendous mass difference between the pins and journals and the cheeks, and that can lead to all sorts of complications with one feature or the other acting as a heat sink to complicate the heat flow dynamics.

"Worse yet, the relationship isn't even uniform. For example, at Top Dead Center on a crank pin there is very little cheek metal, almost none really, while at Bottom Dead Center on the same pin the heated area is virtually surrounded by a huge heat sink. If you simply put an inductor in place and turn on the power, you will overheat the cheeks at TDC, and underheat the pin in the fillet area at BDC.

"The journals tend to be a bit more uniform in terms of cheek mass, but they have their own set of problems that are just as challenging. And, of course, everything has to be accomplished with very, very low levels of distortion at the end of the process. Distortion is not a word anyone wants to hear when you're dealing with something as expensive as a crankshaft."

"Big Yellow" uses a "pulsed" power system to meet the challenge of uniformly processing pins and journals. This system varies the amount of energy delivered by the inductor in real-time as the pin or journal is rotated under it to produce uniform heating. The power supply used in "Big Yellow" is provided by Robotron-Elotherm's parent company, Elotherm of Remscheid, Germany.

"Elotherm has supplied more than 350 crankshaft machines worldwide." Schwarz said, "The trick here was to synchronize the part rotation with the power pulsing in real-time, and do it fast enough to meet the customer's throughput requirements.

"It was not an easy assignment," Schwarz continued. "The system we delivered has three different converters to provide the energy required to process six pins and seven journals on four different crankshafts. They're all controlled through a Modicon Premier Series PLC which is operating near the top end of its capabilities to provide the 10 msec response time required by the system to continuously vary the output as the crank rotates."

"Big Yellow" is manually loaded by an operator who places a green crankshaft onto a set of roller rests on the system shuttle. A bar code reader identifies the crankshaft by its unique manufacturing number and registers it with the PLC for quality tracking purposes.

The shuttle then moves into position to retrieve a processed crank from the chucks that rotate it through the induction hardening process stations. The heated crank is placed on a set of V-blocks on the shuttle, which then positions the previously loaded green crank for pick-up by the chucks.

Once the green crank is in the chucks, the shuttle moves the processed crank to a cool-down station, and then to a TIR (total indicated runout) measurement station where it is checked for distortion. From there, the processed crank is moved to the load/unload station where the operator replaces it with a green part to begin the process cycle again.

While this is happening, the crank inside "Big Yellow" is being moved under the pin-processing inductors. In the first operation, pins #1 and #6 are processed, then the crank is reoriented to process pins #2 and #5, and finally pins #3 and #4 are processed. Six separate inductors are used to process the pins.

Then the crank shuttles into the journal processing station where inductors are positioned over journals #1, #2, #3, #5, #6, and #7. Bearings #1, #2, #6, and #7 are then heated and quenched, followed by heating and quenching bearings #3 and #5. Finally, the six inductors that have been used are raised away from the crank, and the inductor for journal #4 is lowered to process the last bearing. Upon completion of the processing cycle, the hot crank is placed on the shuttle and moved through the cooling and test stations prior to being unloaded.

"One of the interesting aspects of this job," Schwarz added, "is that the cranks are self-tempering because we can control the thermal inputs so precisely, That, in turn, is one of the advantages of the advanced process control system used in "Big Yellow." It actually monitors the power consumption of each individual inductor throughout each individual cycle and compares it to known set standards to calculate the effective amount of energy imparted to the work piece.

"Once we know that, we can reliably predict the effectiveness of the hardening cycle, and also of the subsequent mar-tempering process. By doing this in real-time while the crank is being processed, we can optimize the individual heating operation and increase the production of good parts.

"The other major challenge," Schwarz continued, "is to minimize distortion during the hardening process. It's not practical to straighten a hardened crank because doing that introduces additional stresses into the structure that can shorten its life.

"What we have found is that most deformation problems are the result of residual stresses left in the crankshaft by other processes. If those factors can be controlled, then the heat treatment process can be defined to produce very little distortion. We worked very closely with customer engineers to eliminate as many pre-heat process variables as possible in the cranks going through 'Big Yellow.' In practice, these cranks reliably meet the customer's TIR standard after processing, and minimize the need for excessive hard turning or grinding without straightening, which lowers production costs.

"We know it works," Schwarz added, "because 'Big Yellow' tracks every part it processes through that unique bar code. Our customer can trace every crank they produce and account for every process performed on it. Some suppliers might not like that kind of accountability, but we welcome it. We know what 'Big Yellow' can do, and we are very happy to be a fully accountable member of the customer team."

Another advantage for the manufacturer is the cost savings, based on the ability to eliminate the straightening and oven tempering process from the production line. The customer, in turn, receives a crank that is processed to become straight without mechanical straightening and any residual weakening from that process. The likelihood of crank failure is reduced, for better run life under load and a similarly reduced likelihood of rebuild costs.

Elotherm is part of The Global Induction Group, which includes Robotron in North America, Fuji Electronics Industry Company, Ltd., of Yao-City, Osaka, Japan, and AILO in China.

Robotron-Elotherm, originally founded in 1948 as Robotron Corporation, is a world-class, ISO9001 certified supplier of a wide range of induction heating systems for heat treatment and bonding, billet heating, tube welding and thixoforming. The purchase of Robotron by Elotherm in 1998 has positioned the company as one of the world's largest producers of induction heat-treating technologies.