How do we make... a crankcase?

Posted on March 29, 2013 by Katrin Beck, Images by Robert Hack

The crankcase forms has to be able to withstand immense forces. That is why it is built to tolerances of just a few hundredths of a millimeter.
Friedrichshafen, Germany

The crankcase is the engine’s skeleton – it holds the cylinders, numerous pipes and hoses run through it and innumerable engine components are mounted on it. But it does not only hold the other components, it also has to withstand enormous forces generated by pressures produced by combustion and the movement of the pistons. On top of this there is the oil fl owing through the crankcase at temperatures up to 100°. Extreme pressures and temperatures are one reason why absolute precision is required in production for a crankcase to be capable of withstanding the stresses. Equally important are the tolerances of a few hundredths of a millimeter. The manufacturing process demands extensive skills and experience. So how is a crankcase produced?

A 20-cylinder crankcase for a Series 4000 engine weighs 2.4 tonnes in unfinished condition when delivered from the foundry. To the layperson it might appear ready for assembly at that point. After all, it already has the cutouts for the cylinders and piping. However, you would soon find out in the assembly process that the matching attachments do not fi t. The crankshaft would rub, bolts would not hold. There are four production phases taking four to five days between arrival of the anthracite-gray unmachined casting and completion of the shiny silver crankcase ready for assembly.

Youtube Video

Milling cutters remove the skin

In that time the crankcase passes through three machining centers. Fixed on a variable base called a pallet, the crankcase is conveyed into each of the machining centers. They look like large white cabinets more reminiscent of a garage or a shipping container. But in fact they are high-tech, computer-controlled pieces of kit. At the side of the machining zone in the center is the universal spindle unit. It moves the tool over the workpiece. The unit automatically selects the right cutting tool or drill bit for the machining stage concerned. And then it sets about the crankcase in seven different workholding positions. Underneath a deluge of coolantlubricant fluid, the tools shave metal off surfaces and hone bores to the correct diameters. So that all points can be accessed, the crankcase is fixed in a variety of positions on the pallet. “These fixtures make sure that the unmachined crankcases do not tip over even when they are tilted at 45° or even 90°,” explains Christoph Speck, a Series 4000 production planner. For large surfaces, the milling and drilling tools can take up to four hours to complete the work in a single machining center. In total, 300kg of swarf is removed. It is a process that demands high precision. The tolerances for the crankshaft and camshaft bearings, for example, allow for only 0.02mm divergence between bearing axes.

Milling cutters machine the blank casting under a deluge of coolant-lubricant fluid, shaving off metal until the exact dimensions are obtained.

Handfinished for final inspection

As versatile as the machining centers are, they cannot do everything required to finish a crankcase ready for assembly. Between the various machining stages, manual intervention by production technicians is regularly required for operations such as fitting the bearing caps. “A lot of the work is done automatically by the machines, but there is always a trained technician on hand to intervene if there are problems,” explained Speck. Experience is alsorequired for tasks such as deburring, which involves manually cleaning up the machined edges using small hand tools. “Deburring can make as long as three hours,” said Speck. Anendoscope is used to examine surfaces inside the crankcase that cannot be seen from the outside. A washing stage follows to remove dirt and metal shavings. The crankcase is then examined on a gaging machine for final approval. The machine measure all characteristics critical to function and checks that the surfaces are within tolerance. Then there is a thorough visual inspection in which the crankcase is meticulously examined for swarf and other residues. Before being packed up for assembly, the crankcase has sealing plugs fitted in all the oil and coolant channel openings. Protected by packing to prevent corrosion, the crankcase waits only a few hours before being assembled into a complete Series 4000 engine.

Point of contact

Christoph Speck
+49 7541 90 8465

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