Junker recently built a new platform for cylindrical and non-cylindrical grinding of workpieces with a swing diameter of 470 mm and a part length capacity of up to 4,800 mm, initially applied for grinding of large crankshafts

The platform will first be used in the Jucrank series for grinding large crankshafts. As these weigh up to 1,000 kg, it is a challenge just to set the parts up for the process. To adjust the table assemblies, Junker has developed a slide with an integrated length measuring system. As a result, the setup technician first brings the work heads into position, then the steadies.

First, to enable the processing of such unstable workpieces Junker had to develop its own steady. The new patent-pending steadies are CNC-controlled and have only one axis each. This increases their stability and stiffness. Each of up to a maximum of 11 steadies can be controlled individually and applied to a section at any time – even during the process. This key feature allows for higher sequence flexibility of the grinding process. To make this possible, Junker applied its proven control concept to a larger, high-performance control system.

Large crankshafts are mainly produced in small batches, and in some cases as single pieces. Junker has added an integrated measuring system to overcome these challenges.

First, the two grinding wheels, each mounted on a wheelhead with its own X and Z-axis, pre-grind the main and pin bearings. The diameters are measured during the process. The grinding machine is also a measuring machine, as it measures the entire workpiece after pre-grinding.

Based on the measuring data, the Jucrank 8 finishes the grinding process while using the WK axis developed further by Junker: During grinding it swivels the grinding spindle, compensating for tapers in the process. With this technology the grinding machine can provide each main and pin bearing with its own profile shape, i.e. if necessary with specific crowning. With this functionality, the machine then also grinds the two shaft ends if required. These often feature a taper and not a flange or post end.

As a result, the forged crankshaft is completely ground and ready for installation after only one set-up. Another possibility of applying the new Jucrank technology is for the re-grinding of used crankshafts.