19.1 THE IMPORTANCE OF CENTERLESS GRINDING
Centerless grinding is used for fast production and high accuracy. The process is best for larger batches where set-up times are small compared to machining time. Small rollers and needles, for example, are machined to close tolerances in quantities of millions by through-feed centerless grinding.
Batch quantities do not need to be large to be cost-effective. Set-up times can be reduced with appropriate set-up fixtures. An advantage of centerless grinding is that center holes are not required for the purpose of location. Location of the workpiece during machining is provided from the newly machined surface itself. This eliminates a production operation and saves cost. It also avoids shape errors associated with out-of-roundness of the center holes. Another advantage is that the workpiece does not need to be clamped to a drive device. This saves time, and accuracy is improved since driving devices are a source of errors.
The range of workpieces and materials produced by centerless grinding is wide. Notable examples include:
• Steel bar stock
• Needles
• Ball and roller bearings
• Bearing rings
• Glass rods
• Plastic rods
• Bottle corks
• Uranium rods
• Formed valve spools
• Axles
• Valve stems
Centerless grinding is used for rapidly cleaning up, roughing, and finish grinding. Workpieces may be straight or formed cylindrical shapes. Workpiece surfaces can be either internal or external cylindrical shapes. The process is often automated with barrel vibration feeders or other devices using sequential pneumatics, hydraulics, or robots. This means that machines can continue production with minimal supervision.
The following list features characterizing the efficiency of the process and factors that make these features possible.
Feature
Sometimes faster than turning Long wheel life Fast loading and unloading Accuracy
Hard materials machined