Abrasives companies drill holes and slots into traditional disc grinding wheels to deliver coolant through the spindle to the workpiece. Coolant delivery holes can be unique to the workpiece or material.
All photos courtesy of Norton | Saint-Gobain Abrasives

In use since the late 1800s, disc grinding machines have become more important in recent years as part specifications from automakers and other original equipment manufacturers (OEMs) have become more stringent. For shops considering new grinding equipment or upgrades, the following provides an overview of options for the industry.

Modern, CNC-controlled grinding equipment fits into two basic categories – traditional disc grinders that use aluminum oxide abrasives for metals, ceramics, rubber, and glass; and fine grinding machines that use superabrasive grinding wheels – diamond and cubic-boron nitride (cBN). Machines come in three basic types: single, double horizontal, or vertical spindle. Fine grinding typically uses single-head or double-head vertical spindle design machines.

System options

Selecting the grinder means making two decisions – stock removal method (progressive grind, shear grind, or plunge grind) and part introduction to the machine (through feed, rotary feed, reciprocating feed, or oscillating feed).

Progressive grinding – The most common method, 30%-to-50% of stock is removed at the entrance. The machine removes the rest of the stock progressively as it moves toward exit guides. Visually, the part travels through a funnel, thinning as it exits the machine. Progressive systems typically use rotary feed systems or through-feed style machines. On a through-feed machine, the wheel’s front edge is normally the only setting that requires adjustments. One head remains fixed, the other head moves to create the funnel.

Shear grinding – The second most common grinding setup angles the grinding heads to make the smallest distance between the wheels occur at the entrance guides. This removes the most stock toward the front of machine, as much as 80%. The balance of the material is removed as the part travels to exit guides. This process is common in rotary and through-feed grinding.

Plunge grinding – Often used in reciprocating or swing-arm machines, fine grinding uses this setup with controlled part rotation via a gear part carrier. It allows infeed speed control with multiple steps in the grind cycle (rough, medium, and sparkout). Machine heads operate in parallel, so the wheel faces are flat to each other and axially aligned. The head configuration is easier to set up, less problematic, and produces consistent flatness, parallelism, and surface finish.

Abrasive wheel configurations

Abrasive wheel face modifications improve wheel performance by changing the dynamics between the part being ground and the abrasive, typically reducing the contact area of the wheel and enhancing coolant delivery. For conventional abrasives, holes/perforations added to the wheel reduce the contact area, and manufacturers can add slots to enhance coolant delivery as it exits the grinding wheel spindles. Water-based coolants pumped through the center of the grinding wheel spindles deliver coolant through the wheel perforations or coolant slots to accommodate specific parts and materials.

Norton Vortex from Saint-Gobain Abrasives is an engineered structured abrasive and bond system using permeability to reduce power draw and lower cutting temperatures. Norton Stellar Disc wheels, optimized for uniformity within the wheel, provide consistent performance throughout wheel life, improving part consistency.

Fine grinding wheels

The most common fine grinding bond systems are resin, vitrified, and plated; and on rare occasions, metal bond. cBN and diamond disc wheels on fine grinding machines provide consistent finish, parallelism, flatness, and geometry when machining hard materials for gears, pumps, and bearings. Machines typically use oil coolant.

Cubic-boron nitride (cBN) wheels for fine grinding produce tight-tolerance surface finishes on hard materials, making them important for precision machining as designers tighten part specification tolerances.

Like conventional abrasive disc wheels, special face configurations can enhance machine performance. Wheel design options include continuous rim and pie-shaped segments, custom segment designs, and button shapes (round and hexagonal patterns are common button shapes). cBN and diamond abrasives provide excellent thermal conductivity and wear resistance, typically lasting months.

Disc wheels are not stock items for most wheel manufacturers. Engineered to complement manufacturers’ parts and machinery, the right abrasive choice can enhance part quality, delivery, and per-part pricing to keep producers competitive.

Norton | Saint-Gobain Abrasives https://www.nortonabrasives.com

About the author: Phil Plainte is a senior application engineer at Norton | Saint-Gobain Abrasives.