In smart phone and tablet manufacturing, one of the greatest challenges is to mass-produce high quality touchscreens made of tough, scratchresistant glass, that are smooth to handle and aesthetically pleasing. By its nature this material, often called gorilla glass, is difficult to process and needs external finish machining to achieve the very high quality standards demanded by this industry. Specifically, the external edges of the screen need to be super smooth providing a quality feel to the product, and guaranteeing that no sharp edges exist. This also applies to the apertures for the microphone and camera.
To achieve this, every screen has to be finish-ground using a high speed grinding spindle fitted with a small, accurately profiled grinding wheel. To minimize the cost of grinding every screen individually, it is vital to run the grinding spindle as fast as possible, reducing machining time to a minimum. This has been traditionally achieved using a ball bearing spindle running at speeds up to 60,000 rpm but, at this speed the bearing life and the quality of the finished surface soon degrade, resulting in a failed spindle and scrapped product.
A spindle with an extremely long service life and run speeds of 60,000 rpm and above, is what is required to deliver consistent results.
Celera Motion’s Westwind air bearing spindle M321 is a light industrial precision machining spindle specifically designed to deliver consistent performance at speeds up to 125,000 rpm, with an extremely long bearing life. It is fitted with non-contact, high stiffness radial and axial pressurized air bearings that deliver precision rotation and minimal vibration.
The shaft can be fitted with a range of collet sizes, up to 6 mm shank in diameter, allowing customized grinding tools to be used. For automated grinding machines, the spindle is fitted with a pneumatic automatic tool change piston assembly for rapid grinding wheel exchange. In addition, the M321 has a powerful integrated AC motor, and liquid-cooled bearings for maximum thermal stability at high speed.
The extensive speed range of the Light Industrial Series precision machining spindles ensure maximum flexibility, optimizing each grinding process to suit the selected grinding wheel diameter. When applied to this application, the result is a defect-free surface finish on the edge of the glass screen. Due to the use of air bearings, this quality will be maintained over many thousands of operations.
The air bearing spindle delivers greater maximum speed, compared to traditional ball bearing spindles, which provides opportunity to increase productivity by reducing cycle time. In addition, major cost savings can be achieved, including reduced scrap, reduced machine downtime, and total cost of ownership due to the extremely long product life of the M321 spindle.