"Your CBN technology is so economical. Do you also have a machine for grinding large crankshafts?" was a question repeatedly posed to JUNKER. The grinding machine specialist researched the request and discovered: To one point, primarily antiquated machines are installed worldwide for large crankshaft grinding. To another point, downsizing can be observed in generator and marine engine design; several smaller engines are of course easier to handle than one large one. As a result, the need for modern production methods and new machines is on the rise. To satisfy this need, JUNKER decided to develop a larger platform with many technical refinements.
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.
Newly developed steady with CNC control
First, to enable the processing of such unstable workpieces JUNKER had to develop its own steady. Currently available systems are simply too bulky and not rigid enough for high speed grinding. The new patent-pending steadies are CNC-controlled and have only one axis each. This considerably 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. After all, in its simplest execution the JUCRANK 8 already offers 24 CNC axes.
Large crankshafts are mainly produced in small batches, and in some cases as single pieces. Furthermore, the forging and hardening costs are so high that scrapping a part is disastrous. 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. Then it becomes apparent that the grinding machine is also a measuring machine, as it measures the entire workpiece after pre-grinding: The taper of each element, the bearing widths, lift heights - simply everything - is measured.
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. The crankshafts are ground based on the measurements taken by the machine in record time.
Prospective applications outside of crankshafts
The first two machines were ordered for grinding of large crankshafts, however there is also plenty of potential for other applications – for example: printing rollers, electric motor shafts, and many more. JUNKER therefore built the first JUCRANK 8 for its technology center to develop the grinding of new applications together with its customers.