Grinding Camshafts - for the new HEMI

Grinding camshafts for North American auto makers is a challenging business - even more challenging if your focus is on new engine launches, such as the reinvented Dodge HEMI, upon which Chrysler has a lot riding.  You'll find the HEMI in the new Dodge Ram, Durango, as well as other soon-to-come vehicles such as the rear wheel drive Chrysler 300C and Dodge Magnum.  Camshafts for these vehicles are produced exclusively by Krupp Presta, of Danville, IL.

DANVILLE, IL - The Krupp Presta plant has some 160,000 sq. ft dedicated to producing automotive camshafts for the likes of Ford, Chrysler, VW and Audi.  It employs 300, and annually grinds 1.5 million camshafts and assembles 4 million.  Which, according to Carlos Dias, operations manager, makes Krupp Presta one of the largest producers of camshafts (if not the largest producer) in North America.

"We're able to produce such volumes and meet demand," Dias says, "because of our approach to and use of advanced technology.  For example, we have three highly automated grinding lines, 16 machines in all, eight of which are Studer Schaudt CF 41s (now known as Zeus M machines) with special part chucking co-engineered with machine supplier United Grinding Technologies (Miamisburg, OH).  Then, we have a patented camshaft assembly process developed by Thyssen Krupp Automotive in Europe, which is unlike any other."

Camshaft Assembly

The patented camshaft assembly process is unique and assembles 16 lobes on each shaft.  The lobes arrive in bins and are placed in a conveyored system that performs in-process induction hardening, machining the backside of the lobe, followed by a broaching operation.  The tolerances on the lobe are 5 microns and the cycle time of the lobe line is 5 - 6 seconds per lobe.

Next in the process, all camshaft components - shafts, lobes, cams, end plugs— come together separately and are placed in small carts where robots pick the components and assemble them on the shaft.

The camshafts are loaded vertically down into cavities in the press where under extreme but carefully calculated pressure the components are pressed onto the shaft.  "The pressing process is closely monitored," Dias says.  "The pressure must fall within a range - any load above or below the range limits, and the camshaft is rejected and the process is stopped and completely reviewed."

From the assembly press, the shafts pass through four vision systems that check the accuracy of the assembly process.  The shafts then enter a laser gage where more than 160 dimensions are measured per shaft.

The Grinding Process

Dias explains that from the assembly process, the shafts are placed on pallets and are manually loaded onto conveyors.  These travel to a loading station.  From this point forward no one touches a camshaft.  An overhead gantry system of pairs of dual pick and place robots descends and ascends independently and loads and unloads all grinding machines.  There are two lines of four Studer Schaudt machines each producing the camshafts for the HEMI.  From conveyor to the end of the line, there is no operator intervention — with the exception of scheduled preventive maintenance.

The camshaft is some 550 mm long and weighs about 10 - 12 lbs.  Diameter tolerances are ± 10 microns; roundness on the journal bearings is 5 microns, maximum.  These tight tolerances are achieved with a CpK of 1.33, in production.  Camshaft surface finish is guaranteed below 0.4 Ra.

“These machines operate under 0.3 to 0.4 percent scrap and the Studer Schaudt lines often run as high as 95 - 96 percent efficiency.  We run 24/7, with just four operators per line,” Dias says.  “The way that we’re able to hold these tolerances and efficiencies in a production environment.  However, for the HEMI shafts we developed and implemented a significant bit of innovation.”

Unique Chucking

The Studer Schaudt machines are designed with a specially engineered chucking approach that allows the HEMI camshafts to be ground in a single chucking, employing two spindles and wheels on each of the eight machines.  “CBN grinding of camshafts is nothing new.  It’s been done for at least a decade.  What’s unique here,” Dias says, “is that we can grind the journal bearings and cam lobes in a single fixturing, in a single chucking.  We chuck the part once and sequentially grind first the bearings with one spindle and wheel and then the lobes with the second spindle and wheel.  We have four RoboTec steady rests and two Marposs in-process gagging systems. This is very unique in the camshaft business and permits us to achieve the quality and efficiency levels that we do.”

Dias notes that the idea for the chucking approach originated at Krupp Presta and was then discussed for feasibility with UGT.  UGT reviewed the idea and developed the chucking solution specifically for the Chrysler HEMI camshaft lines.

Most other camshafts, Dias says, are ground using a two machine process with two separate chuckings — one machine setup to chuck and grind the bearings and the other machine to grind the lobes.  “With the traditional approach,” Dias notes,“ you have an additional step in the process, a second machine, a second chucking and increased potential for the introduction of error.  Also, should one of the machines go down, the entire line is down.  Not so with our single chucking approach.”

Dias makes the point that if you have 10 machines grinding camshafts, and you’re using the Studer Schaudt two-in-one dual process single chucking approach, and one machine goes down, you’re still producing camshafts on the other nine machines.  In effect, having a single machine down only impacts 10 percent of your productive capacity

Post-Grinding

After camshaft grinding, the gantries place the HEMI shafts on a conveyor that feeds a shuttle system that conveys to the shafts to a second line.  This line, a series of secondary operations, also employs an overhead gantry system of pairs of dual pick and place robots that descend and ascend independently and load and unload all post-grinding operations.

The first such operation is an eddy current crack detection system.  “Normally, with eddy current,” Dias says, “you have a loop device which creates a magnetic field and pass the shaft through the loop.  A crack in the shaft will distort the magnetic field, signaling a flaw.  We, however, worked with a California company, Smart Eddy, to come up with an open probe design.  The probed touches each lobe and bearing and creates a magnetic field at each point and gives us a more accurate reading.  This technology was developed originally for crack detection in the aerospace industry.  We check all camshafts 100 percent for cracks.”

Following crack detection, the robotic gantry system sequentially moves the shafts to an Acme integrated deburring and finishing system, followed by two SupFina finishing and polishing machines.  This is followed by an in-line Marposs gagging system and a Baafel LaserTec laser marking system that records the complete manufacturing history of each shaft.  After this there is a small pin-insertion assembly station, followed by a Durr EcoClean washing system.

The gantry then places the finished camshaft on a final conveyor where they are manually removed and placed in sanitized plastic pallet trays that are then covered and sealed with plastic.  The camshafts are now ready for shipment.  Line cycle time is 14 seconds per shaft.