New possibilities in crankshaft microfinishing:

Shoe follows function
View into the working area: Microfinish machining of a truck crankshaft on a CrankStar machine Picture: Thielenhaus Technologies GmbH (PresseBox) (Wuppertal, ) Automobile manufacturers are familiar with the problems associated with the microfinishing of crankshafts: The surface roughness results on the bearings differ from those on the transition radii, the bearing profile cannot always be adhered to, roundness improvements on the pin bearings differ from those of the main bearings, and smaller crankshafts deform as a result of machining forces and workpiece oscillation. For this purpose, innovative solutions based on practical experience have now been developed to make the machining process easier and safer:

After evaluating statistics from its fleet network, a well-known truck manufacturer has ascertained that a high percentage of reported crankshaft damage is due to particularly large loads on the bearings radii. Working closely with the German high-precision machine tool manufacturer Thielenhaus Microfinish, the manufacturer therefore decided to perform finishing work on the bearings as well as on the transition radii. In order to achieve the same surface quality on the crankshaft journals and radii, Thielenhaus developed a special tape contact shoe. The new RadiusFlex shoe technology presses a finishing tape with a special profile on both sides into the radius, allowing radii to be machined up to 90°. This represents a significant break-through from the previous 60°. The manufacturer’s goal was thus successfully achieved.

Flexible in diameter
The leading machine tool manufacturer for microfinishing is developing prototypes and filing patent applications for a variety of other innovative tape contact shoe systems. In addition to the conventional hard or soft shoes, Thielenhaus is developing a shoe that uses a kind of belt system to adapt to the component’s size. With the DiaFlex technology, crankshafts with the same bearing widths but different diameters can be machined without swapping the shoes. In practice, it often happens that, due to higher torques in three- or four-cylinder motors, a few millimetres more of bearing diameter are needed with the same motor concept and gauge. The DiaFlex shoe adapts to the respective diameter and can compensate for differences of up to 15 mm without changing shoes.

Correcting the crown shape
Also currently under development are tape contact shoes for generating or correcting profile and crowning on the bearings. With the ShapeFlex shoe, the tape contact shoe pressure can be varied over the diameters width. This makes it possible to work on the edges of the bearing points with a slightly elevated specific pressure to support or even generate a slight crown shape, or to achieve the desired crowned shape with minimal variation in crowning and symmetry.

Platforms for individual machine concepts
The different shoe systems can all be integrated in Thielenhaus’s CrankStar machine platform, which features horizontal and vertical versions for machining passenger car or truck crankshafts and can be adjusted to the specific needs of each manufacturer. Based on the manufacturer’s requirements regarding part handling, cycle times, quality tolerances, part variations and machining tasks, Thielenhaus can develop a machine concept that is precisely tailored to the needs of the customer.

Consistent roundness improvements
In order to achieve the same roundness improvements on main- and pin bearings, the CrankStar employs pneumatic technology to counterbalance pin bearing forces of +/- 5 Newton. This ensures that the machining forces on the rotating crank pin are kept constant and that the mass forces that occur between the shoe and bearing are compensated. The roundness is thus improved to exactly the same extent on all bearings, whether pin or main bearings.

No more risk of deformation
When microfinishing weight-optimised, small dimensioned crankshafts for compact engines, the machining forces used to clamp and oscillate the workpiece can produce minor deformations. This then has a negative impact on the crankshaft bearing diameters, including profile and cylindricity. To counteract this, the CrankStar regulates axial tailstock forces utilising a hydraulic servo control mechanism. The technology is able to compensate variating oscillation strokes and frequencies as well as different part lengths.

Ergonomics and flexible automation
In the standard version, the CrankStar is capable of machining crankshafts for engines with three to six cylinders, in some cases even without major retooling. In addition to centre- and pin bearings and thrust faces, the CrankStar can finish oil seal diameters and deburr bores in the flange. Thrust face machining occurs via a special unit while the workpiece is oscillated. Even with vertical machine concepts, the CrankStar comes with up to 33 percent longer intervals between tool changes than the industry standard, featuring a tape capacity of 300+ metres. The vertical solution allows a quick belt change from the front of the machine, without requiring the withdrawal of an entire tool carrier package.

The CrankStar can be adapted to a variety of automation systems. Vertical machines are designed to be loaded either from the front or the back. Thielenhaus is currently examining possibilities to minimize idle time during the loading/unloading operation.

New possibilities
Innovative machine solutions and tape contact shoe systems open up new possibilities for engine manufacturers and their suppliers, enabling the microfinishing of crankshafts of various designs simpler, faster and more cost-effective. Via company locations in Europe, the Americas and Asia, Thielenhaus offers its extreme precision microfinishing solutions around the world.

Further information can be obtained from: Thielenhaus Technologies GmbH, Division Microfinish, P.O. Box 201855, 42218 Wuppertal / Germany, Telephone +49 202 481-0, Telefax +49 202 450445, Thielenhaus Microfinish Corporation, 42925 W. Nine Mile Road, Novi, MI 48375 / U.S.A., Telephone +1 248 349-9450, Telefax +1 248 349-9457, or online at www.thielenhaus.us
The machine solution can be viewed via tablet or smartphone in 3D with the CrankStar app, which can be downloaded for free from iTunes or Google Play Store.

Kontakt

Thielenhaus Technologies GmbH
Schwesterstr. 50
D-42285 Wuppertal
Wolfgang D. Riedel
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