The JUCRANK non-cylindrical grinding machine accomplishes all grinding tasks on crankshafts. Maximum accuracy and quick cycle times are achieved through oscillation grinding in a single clamping set-up and through the productive machine concept. Ideal dimensional stability and high process reliability are ensured through in-process measurements, for example.
Rough and finish grinding of crankshafts in all batch sizes can be carried out on platforms with various dimensions. For main, pin and thrust bearings, diverse geometric shapes as well as plane surfaces and radii can be ground. Internationally renowned engine manufacturers place their trust in the versatile, productive JUCRANK non-cylindrical grinding machine.
The pendulum grinding method enables crankshafts to be rough and finish ground in a single clamping set-up. The crankshaft rotates around its central axis and the grinding wheel follows the circular motion of the pin bearing by interpolation of the workpiece spindle (C axis) with the grinding spindle (X axis).
To achieve top concentricity quality, crankshafts are frequently supported on a steady. The rough grinding process relieves any hardening stress in the material and an in-process measuring system supplies correction data for finish grinding.
The grinding wheels and the workpiece are arranged in axially parallel formation, enabling straight plunge grinding of the bearings. The grinding wheels are dressed to ensure the geometric shape of the bearings.
Pendulum grinding is made more flexible by a new development from JUNKER: The WK axis. This axis swivels the grinding spindle, on which narrow grinding wheels are mounted, within the micron range during grinding. Benefit: Every main and pin bearing can be given its own profile shape – compensating for tapers and without the need to exchanging the grinding wheel.
The JUCRANK 8 grinds crankshafts with a peripheral diameter of 470 mm and a clamping length of up to 4800 mm completely in a single clamping set-up. The crankshaft is supported by CNC-controlled steadies, measured following rough grinding and then selectively finish ground with the aid of the WK axis – all ensuring that only GO parts ever leave the machine.
In the interests of sustainability: Used crankshafts can be reground. Using an automatic work cycle, whereas the crankshafts are measured in the machine and subsequently ground without operator intervention.
When using large grinding wheels, a CNC-controlled swivel motion of the coolant nozzles follows the pin along the grinding wheel at a constant distance. This guarantees optimum cooling, as the coolant is directed permanently towards the grinding zone.
The control system comes with automatic compensation of runout and disturbing variables such as temperature influences, grinding allowance fluctuations or material changes. Even minimal deviations between the target and actual position of the grinding wheel are automatically corrected.
In order to generate a precise width and angular position of the main and pin bearing, the position must be precisely determined when clamping the crankshaft. For this, a touch probe measures the radial position of the pin bearing and the longitudinal position of the main and pin bearing. The measured values are automatically integrated in the grinding process by the control system.
The Erwin Junker Operator Panel was specifically developed to control grinding machines. All machine components are controlled using the operator panel – irrespective of the series and the used control system. The identical structure, intuitive menu guidance and visualization of the workpiece geometry make for extreme user convenience and flexibility in operation. Programming takes place directly using the operator panel or an external programming tool.
Torque motors are used for direct drive of the C axis. This ensures impressive quiet running, high torque rigidity and superb dynamics in the C axis. Torsionally unstable crankshafts are driven by two C axes.
The X axes, with linear roller ways with high pre-load, takes care of ultra-precise positioning of the grinding and regulating wheel head. Drive is executed by a precise, intrinsically rigid ball screw with infinitely variable servo drive and glass scale.
The B axis of the wheelheads is driven by a backlash-free gear. Every angular position is programmable; the position sensor system has a sensational resolution of 0.00001 of a degree. Extreme low noise (vibration) levels are guaranteed with the JUNKER grinding spindles with direct drive – an in-house development – complete with a structure-borne sound sensor and dynamic balancing system in one or two planes.
The patented 3-point mounting interface allows grinding and dressing wheels as well as work holdings to be mounted and centered on grinding spindles, workpiece spindles and tailstock sleeves in record time. Adjustment of the tailstock and, where applicable, the workhead take place using optionally using a chain wheel, a hydraulic cylinder or a CNC axis with rack and pinion drive. An airlift function simplifies position adjustment. Depending on the workpiece, in addition a wide range of clamping systems are also available
The machine bed made of mineral cast provides impressive damping behavior and torsional rigidity. The temperature stability allows fluctuations in the ambient temperature to be compensated with a minimum of effort, ensuring a high level of dimensional stability throughout the whole day.
Depending on the application, the abrasive CBN or diamond is used. The basic bodies of the grinding wheels comprise steel or carbon. In conjunction with CBN, it can make sense to use a carbon base body: It is light, has vibration-damping properties and remains dimensionally stable even at high speeds.
Grinding wheel dressing is CNC controlled. A driven diamond dressing wheel or a workpiece-dependent diamond profile roller can be used. Dressing takes place manually or using an automatic dressing program with grinding wheel compensation.
JUNKER offers both internal and external loading systems for all its machine series, depending on customer and workpiece requirements. The loading systems can be combined with different infeed and discharge systems such as conveyor belts or custom tailored systems.
The measurement systems are also individually adjusted to the various workpieces and customer specifications. The measurement processes entail evaluating the recorded measured values and utilizing them for measurement correction in line with the prepared measurement strategy. A grinding wheel measuring system to determine the diameter, axial position and width of the grinding wheel completes the wide range of systems on offer.
As an option, self-centering three-point steadies ensure stable support. Tracking hydraulic jaws guarantee a balanced ratio of forces at all three support points, and with it a grinding process with repeat accuracy.
A swivel-in measurement probe carries out an in-process measurement of the diameters of the main and pin bearing. The control system logs the measured values, calculates the correction data and generates the precise shape. After grinding, the Machine is able to measure the entire geometry of the crankshaft – depending on requirements: from the bearing width through the lift height to the taper of each element.
In case of an fire, the machine interior is automatically hermetically sealed, suffocating a fire before it has a chance to spread. If required, extinguishers (CO² or water mist systems) and exhaust air purification systems can be additionally installed. A competent partner for fire protection and filtration solution solutions is LTA Lufttechnik GmbH, which also belongs to the JUNKER Group and which researches, develops and produces filtration systems for industrial air purification.
The Filtration systems