Understanding Grinding Machines: Definitions, Types, and Applications

What is a Grinding Machine?

A grinding machine, often shortened to grinder, is one of the power tools or machine tools used for grinding, it is a type of machining using an abrasive wheel as the cutting tool. Each grain of abrasive on the wheel’s surface cuts a small chip from the workpiece via shear deformation.

Grinding is used to finish workpieces that must show high surface quality (e.g., low surface roughness) and high accuracy of shape and dimension. As the accuracy in dimensions in grinding is of the order of 0.000025 mm, in most applications, it tends to be a finishing operation and removes comparatively little metal, about 0.25 to 0.50 mm depth.

However, there are some roughing applications in which grinding removes high volumes of metal quite rapidly. Thus, grinding is a diverse field.

Overview

The grinding machine consists of a bed with a fixture to guide and hold the workpiece, and a power-driven grinding wheel spinning at the required speed. The speed is determined by the wheel’s diameter and the manufacturer’s rating. The grinding head can travel across a fixed workpiece, or the workpiece can be moved while the grinding head stays in a fixed position.

Fine control of the grinding head or table position is possible using a vernier calibrated hand wheel or using the features of numerical controls.

Grinding machines remove material from the workpiece by abrasion, which can generate substantial amounts of heat. To cool the workpiece so that it does not overheat and go outside its tolerance, grinding machines incorporate a coolant.

The coolant also benefits the machinist as the heat generated may cause burns. In high-precision grinding machines (most cylindrical and surface grinders), the final grinding stages are usually set up so that they remove about 200 nm (less than 1/10000 in) per pass – this generates so little heat that even with no coolant, the temperature rise is negligible.

Types of Grinding Machines

These machines include the:

• Belt grinder, which is usually used as a machining method to process metals and other materials, with the aid of coated abrasives. Analogous to a belt sander (which itself is often used for wood but sometimes metal). Belt grinding is a versatile process suitable for all kind of applications, including finishing, deburring, and stock removal.
• Bench grinder, which usually has two wheels of different grain sizes for roughing and finishing operations and is secured to a workbench or floor stand. Its uses include shaping tool bits or various tools that need to be made or repaired. Bench grinders are manually operated.
• Cylindrical Grinders: A cylindrical grinder is used for shaping the outside of a workpiece. These machines accept workpieces in a variety of shapes as long as they can be rotated through a central axis. In a cylindrical grinder, both the workpiece and grinding wheel are simultaneously rotated. Outside diameter grinders, internal diameter grinders, and centerless grinders are all types of cylindrical grinders.
• Surface Grinders: A surface grinder consists of an abrasive wheel, a chuck (a workpiece holding device), and a rotary table. The chuck is used to hold the material in place while the wheel and object are rotated to produce a smooth finish.
• Centerless Grinders: A centerless grinder is a type of cylindrical grinder which uses two rotary wheels to secure the workpiece in place. Unlike a centered grinder, a centerless grinder does not make use of a spindle. The speed of the rotation of the wheels determines at what rate the material is removed.
• Tool & Cutter Grinders: A tool and cutter grinder makes use of a CNC machine tool with up to 5 axes and multiple grinding wheels. These devices are used for sharpening and producing milling cutters such as drills, endmills, and step tools. It is also widely used for producing the tools needed in the woodworking and metal cutting industries.
• Jig grinder, which as the name implies, has a variety of uses when finishing jigs, dies, and fixtures. Its primary function is in the realm of grinding holes for drill bushings and grinding pins. It can also be used for complex surface grinding to finish work started on a mill.
• Gear grinder, which is usually employed as the final machining process when manufacturing a high-precision gear. The primary function of these machines is to remove the remaining few thousandths of an inch of material left by other manufacturing methods (such as gashing or hobbling).
• Centre grinder, which is usually employed as a machining process when manufacturing all kinds of high-precision shafts. The primary function of these machines is to grind the centers of a shaft very precisely. Accurate round center holes on both sides ensure a position with high repeat accuracy on the live centers.
• Die grinder, which is a high-speed hand-held rotary tool with a small diameter grinding bit. They are typically air driven (using compressed air), but can be driven with a small electric motor directly or via a flexible shaft.
• Angle grinder, another handheld power tool, often used in fabrication and construction work.