Different type grinders slash part cycle times in their own special ways.
The Uranos M incorporates hardturning and/or superfinishing on an I.D.-grinding-machine platform.
One company, two engin engineering groups. Give them the same challenge, and chances are they'll come up with two different ways of achieving it. In this case, the goal is to reduce part cycle times. One group decided to accomplish it through a multifunction machine design, while the other took a slightly different route and devised an innovative part-changing system.
These cycle-time-slashing ideas come from Schaudt Mikrosa BWF, represented in the U.S. by United Grinding Technologies of Miamisburg, Ohio, and are found on two new grinding machines. The first is basically an I.D. grinder, called the Uranos M, and the other is a plunge-grinding machine named Kronos M.
The Uranos is an open machine system that structurally supports an I.D.-grinding station, two hardturning stations, and either an external grinding or superfinishing station. This design reduces cycle times by eliminating external part-handling equipment and other machines needed for additional operations. (In this case, a turning machine, external grinding machine, and a superfinishing machine.) For some applications, the machine has the potential to reduce cycle times by as much as 25%.
The most important advantage of doing these various operations on one machine is that shops can regulate grinding stock. This means the amount of stock left on the part for the grinding operation will not fluctuate. If it does, operators make adjustments at the hard-turning station.
For example, shops can hardturn parts and maintain, say, 20 or 30 µ for grinding. This stock consistency not only gives the whole part process stability but also eliminates any rough-grinding steps. In addition, it gives shops the option of using large, inexpensive aluminum-oxide wheels for finish grinding.
According to the manufacturer, the Uranos is not just an I. D.- grinding machine with slapped-on extras. Each of its components is engineered for optimized manufacturing.
The machine's horizontal and vertical slides, for instance, are mineral way castings, and the company uses two different sizes — 1,050 and 1,750 mm — for the whole Uranos series — the S (small), M (medium), and L (large) models.
Linear motors along with hydrostatic guideways on the machine's X axis deliver precise movements and a rapid rate of 60 m/min. Its vertical Z axis also runs on hydrostatic guideways and is ballscrew driven for rapid-traverse speeds of 30 m/min.
Uranos workpiece spindles are direct drive and turn at 3,000 rpm. They accommodate three different chuck sizes for the series — 125 mm for the S model, 200 mm for M, and 320 mm for the L. The vertically oriented chuck performs all part handling, so there is no need for extra automation within the machine.
Loading/unloading operations can be configured at either the right or left-hand side of the machine via conveyor system. The pick-up principle of the Uranos, says Matthias Heinemann of the Schaudt Mikrosa BWF Berlin plant, eliminates part-handling equipment that would normally account for up to 20% of a machine's final cost.
For hardturning, stations #3 and #4 on the machine are designed for either block toolholding or a turret. At the I. D. --grinding station, #1, a high-frequency spindle sports bearings with ceramic balls and steel rings. The same spindle type as the machine's workhead is used at the external-grinding station #2. It also includes a dynamic balancing device.
Taking a different route from the norm, Uranos's manufacturer fits the machine with a separate, high-frequency dressing spindle instead of a dressing ring on the workpiece chuck. With this type of setup, shops can dress using small wheels, as opposed to the large chuck rings, which can be difficult and time-consuming to align for zero runout.
In addition, job changes requiring a different chuck typically call for rebalancing the dressing ring. This is not the case with a separate system because the dressing wheel is always balanced and running true. And the design makes for more stable and accurate grinding-wheel dressing.
Besides not having the dressing ring on its chuck, the Uranos M has no touch probes for tool-edge location. Instead, it checks the location by the grinding stock left on the part. For example, when the cutting tools wear or break, the amount of grinding stock will increase. The machine catches this increase at the grind-
ing station through gap-elimination controls. It then gives a signal that the gap has changed, so the operator can change or adjust the cutting tools.
While the Schaudt Mikrosa BWF Uranos M machine shortens part cycle times by performing multiple functions, the company's Kronos M plunge or in-feed grinding machine does it by reducing nonproductive machine time, such as during part loading/unloading and job setup.
The machine's integrated part-handling system is a first for the industry, says the manufacturer. It handles workpiece diameters from 8 to 40 mm and actually moves into the machine's fixed grinding gap.
Two coupled workrest holders, operating as a slide, ride on a sub-structure with a linear roller-guide system. Parts lying lengthwise move in parallel to the grinding axis via a programmable ballscrew drive. Each of the workrest holders can secure several parts, depending on their length. Once in the grinding area, pneumatic cylinders lift the rail's clamping V-blocks, releasing the part and allowing it to be ground.
After grinding, the rail lowers to reclamp the part. The slide unit cycles as each part is ground one after the other.
Combined loading and unloading stations are situated in front of and behind the machine. This makes it possible to exchange raw/finished workpieces as the machine is grinding. According to Ulrich Frenzle, a managing director at Schaudt Mikrosa BWF, the system reduces part-loading/unloading time by 54%, as compared to a typical integrated gantry-style loader.
To make sure job changeover is fast, the Kronos M features simplified grinding wheel and regulating-wheel changing. For instance, exchanging grinding wheels involves removing a torsion rod, taking out two necked-down bolts, hydraulically opening a protective hood, removing the upper bearing shells, and lifting out the wheel with a special device designed for that purpose. Once a new wheel is installed, operators reverse the sequence.
Available Kronos M grinding-wheel widths are 250 and 400 mm. For the 250-mm wheel, the machine can have either a cantilever-type grinding spindle or a double end-supported one, while a double-side system supports 400-mm wheels. The grinding-wheel drive features a precisely balanced, fully enclosed, and water-cooled motor that delivers 22 or 37 kW of power, respectively.
Regulating-wheel changeover is as simple as that of the grinding wheel. Operators disconnect the upper caps by loosening four bolts, axially disconnect the regulating-wheel spindle from the coupling, and lift out the regulating wheel and its spindle using another special device for that specific task.
Also contributing to shorter setup times, says the machine's manufacturer, is an increased regulating-wheel speed. This faster-running wheel reduces dressing time by as much as 50%. It runs up to 900 rpm and delivers a more comprehensive control range for the relation between circumferential speed of the grinding wheel and the rotating speed of the workpiece (degree of coverage).
The Kronos M's regulating-wheel dresser is fixed on the regulating-wheel casing and no longer swivels. A cycle in the machine's Siemens Sinumerik 840D control with PCU50 automatically calculates the largest dressing amount after changing over to new grinding and regulating wheels. This amount is dressed over the whole width of the wheel by short dressing passes with increased lengthening of transversal movements. The result, according to the manufacturer, is a 30% reduction in machine setup time.