Centreless, Centerless Grinding Machine, Machines
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Centreless / Centerless Grinding Machines

This page describes the technology of centreless (centerless) grinding as well as centreless (centerless) grinding machines from Koyo Machine Industries. With centreless (centerless) grinders, a workpiece is supported by a work rest blade and set between a rubber regulating wheel that rotates the workpiece and a rotating grinding wheel. Koyo remains the world leader in centreless (centerless) grinding technology with products such as our 15-axis CNC control system.

Centreless (Centerless) Grinding Principle

centreless (centerless) grinding is an OD (outer diameter) grinding process. In difference from other cylindrical processes, where the work piece is held in the grinding machine, while grinding between centers, the workpiece is not mechanically constrained during centreless (centerless) grinding. Therefore the parts to be ground on a centreless (centerless) grinder do not need center holes, drivers or workhead fixtures at the ends. Instead, the workpiece is supported in the grinding machine on its own outer diameter by a workblade and by the regulating wheel. The work piece is rotating between a high speed grinding wheel and a slower speed regulating wheel with a smaller diameter.

centreless (centerless) grinding principle

G: Grinding Wheel - R: Regulating Wheel - B: Blade - W: Work piece

The blade of the grinding machine is usually positioned in a way that the center of the work piece is higher than the virtual line between the centers of the regulating wheel and the grinding wheel. Also the blade is designed with an angle in order to ensure that the work piece is fixed between the blade and the regulating wheel. The regulating wheel consists of soft material like rubber and can contain some hard grain material to achieve good traction between work piece and regulating wheel.

Roundness

Centreless (centerless) grinding can perform excellent roundness of the work piece. However, caused by the simultaneous suspending and machining of the work piece surface it is possible that process typical roundness errors are generated. Proper adjustment of the grinding machine and the grinding slot geometry is essential. When a high spot comes in contact with the regulating wheel, then on the other side of the work piece a low point will be ground. However this low point must not be exactly in the opposite side of the work piece. The grinding machine has to be set up in a way that a polygon form is ground with so many corners that it is almost round finally.

roundness achieved with centreless (centerless) grinding

g: grinding wheel - r: regulating wheel - w: work piece - d_g: diameter grinding wheel - d_r: diameter regulating wheel - p: penetration depth - n: polygon order

Grinding Wheels and Dressing

grinding wheel centreless (centerless) grinding machine

Koyo is using on a large percentage of its grinding machines grinding wheels of cubic boron nitride cBN or diamond wheels. For the series 30 and 45 grinding machines a special dressing and truing system is available as an option: electrical discharge truing E-dt.

Automation

There are mainly two different types of centreless (centerless) grinding:
In-feed grinding
The work piece can have different outer diameters over the length and either only part of the work piece is ground or the total work piece is ground using an adapted grinding wheel.
Thru-feed grinding
Cylindrical work pieces can be ground using this method. The work piece can be longer than the grinding wheel and will still be ground over the full length. It is also possible to grind small work pieces with this method. In this case, several work pieces are ground same time in the machine and high throughput can be achieved.

Advantages of centreless (centerless) Grinding Machines

By line wise support of the work piece it is possible to grind soft or brittle work pieces (low tension)
It is not necessary to prepare the work piece for fixing in the grinding machine (faults cause by fixing are eliminated)
Loading/Unloading of the work piece is simple and easy to automate.
When using continues through feed grinding there is no time loss for changing the work piece.
Long work pieces can be handled with rather small machines.
Very high grinding wheel rotation speed can be achieved.

Main Applications for centreless (centerless) Grinding Machines

Mass Production
e.g. bolts, shafts, bearings, hubs, valves, needles, axles, pivots

Special Applications
z.B. bars, tubes, cylinders, rotors, isolators, balls

parts ground by centreless (centerless) grinding machine

parts ground by centreless (centerless) grinding machine

Crystec Technology Trading GmbH, www.crystec.com, +49 8671 882173
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Koyo centreless (centerless) grinding machines

Koyo is proud of it's diverse line of centreless (centerless) grinding machines. Through mechanical and electrical engineering expertise, Koyo continues to re-examine the essential factors in centreless (centerless) grinding technology in order to improve performance and meet the demands of this ever-changing market. These factors include: precision, efficiency, rigidity, stability, automation, and more. Koyo's on-going attention to automation has resulted in another step forward towards minimal manpower and unstaffed operations.
Koyo has been manufacturing grinding machines for over thirty years and is a world leader in centreless (centerless) grinding technology. Roller and ball bearings are standard on our spindles, while easy maintenance and consistent grinding accuracies continue to bring high levels of customer satisfaction.

30/45/60-Series

C3015F	Grinding machine for high-precision	Model C3015F has a new symmetrical bed structure. The workrest is located on the bed center and the table feed screw is fixed to the workrest to offer the utmost static and thermal rigidity. The direct-driven grinding wheel spindle motor reduces vibration and energy costs.
C4520FS	Grinding machine with Slanted R.W. slide	Model C4520FS has a fixed workrest for easy part loading & unloading. The slanted regulating wheel slide offers constant roundness without being affected by grinding wheel or regulating wheel wear.
4515C	Economical grinding machine	In Model 4515C, CNC control for the lower slide is standard equipment, as is the rotary traverse-type regulating wheel dresser. It has a cantilever-type grinding wheel spindle, and the regulating wheel spindle is easily to change.
4515CS	Grinding machine with fixed workrest	In Model 4515CS, the fixed workrest makes it easy to load and unload workpieces. The grinding and regulating wheel slides are movable
4520C	Grinding machine for tough material	In Model 4520C, the regulating wheel housing opens from the top enabling easy wheel change. It has an upper and lower double slide system for easy, automatic feed as well as size correction by CNC controls.
4520CH	High-speed grinding machine	Grinding wheel peripheral speed of 120m/s.
6015C	Compact grinding machine	Model 6015C is compact to minimize floor space but has a ø610mm grinding wheel. It has a rotary traverse-type regulating wheel dresser, a cantilever-type grinding wheel spindle, and the regulating wheel spindle is easily changed.
6020CAS	Angular grinding machine	The 6020CAS grinder increases productivity because it grinds the O.D. and face of the part simultaneously. Constant roundness is achieved with the slanted regulating wheel slide, and the fixed workrest makes the loading process simple.