Quality, productivity, availability – the JUMAT external and internal cylindrical grinding machine leaves nothing to be desired. Various sizes and a large number of wheelhead versions offer unrivaled versatility. Paired with the concentrated expertise of JUNKER, each machine is specially matched to the customer‘s requirements.
The cylindrical grinding machines of the JUMAT series can perform both OD and ID grinding in a single clamping set-up. CBN and diamond grinding wheels enable high-speed grinding, provide for high cutting performance and enable grinding of difficult materials.
During external cylindrical grinding, the workpieces are clamped between tips or in a collet chuck. To increase productivity, grinding wheel sets are used for some applications. The JUMAT uses the straight and inclined plunge-cut grinding process.
With straight plunge-grinding, the cutting and feed movement is carried out radially to the workpiece. The diameters are ground either in one feed or with several feeds and axial twisting.
With inclined plunge-cut grinding, the grinding wheel is at an angle and the wheelhead (B-axis) is swiveled. The X and Z-axis interpolate. This makes it possible to grind the diameter and flat surfaces in a single feed.
To grind grooves or to pre-grind threads, a galvanically bonded grinding wheel is usually used.
Internal cylindrical grinding enables precise grinding of inside functional surfaces, such as drilled holes, cones or flat surfaces. High-speed grinding spindles are used to achieve the desired cutting speed, despite the smaller grinding wheel diameter.
The center drive is a special drive system which clamps the workpiece in the center and drives it via a servomotor. This enables both workpiece ends to be ground at the same time.
In the automotive industry, electromechanical, axially parallel power steering systems are increasingly used. The JUMAT grinds the outside thread of the steering rod in as single clamping set-up from a solid blank. Pre-grinding is carried out with galvanically bonded grinding wheels, and finish grinding with vitrified bonded CBN grinding wheels.
The double workpiece headstock, with two opposing clamping devices, minimizes the downtime when grinding threads of ball screw nuts: While grinding is being carried out on one side, loading and unloading, positioning and clamping are carried out on the other. The only downtime: Swiveling by 180 degrees in less than 3 seconds.
A touch probe measures the longitudinal position of the workpiece on a flat surface to compensate for unmachined part fluctuations. 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.
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.
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.
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.