Grinding machines are machine tools that machine by abrasion, that is, without producing chips in the conventional sense. They work with grinding wheels and operate on three axes. They are also fitted with a coolant system. There are various types of grinding machine on the market, such as the tangential surface grinder, the universal knee-type grinder and the fixed-bed grinder.
Features of the tangential surface grinder
Grinding machines can carry out many different machining operations, such as facing and boring. These machine tools achieve precise results not only in dimensions but also in surface finish; after grinding, parts can also undergo polishing and lapping.
A grinding machine can handle parts made of heat-treated hardened steel, and its most important elements are the robust discs known as grinding wheels. These wheels remove excess material easily and precisely. Grinding machines are regarded as the most accurate machine tools there are, because of their ability to achieve tight dimensional and surface tolerances on a part.
Tangential surface grinders, like all other grinding machines used in industry, are characterised by a large disproportion between the size of the workpiece and the machine; the aim is to avoid vibration, which is why grinding machine components are very robust and large.
Types of grinding machine
The choice of grinding machine should be based on the machining requirements: the shape and characteristics of the parts, as well as ease of clamping, production capacity and the speed the grinding wheel can reach.
The main types of grinding machine are:
- Universal cylindrical grinder. Used to machine straight, curved and flat faces on rotational surfaces. It grinds external and internal cylinders, internal and external tapers, faces and surfaces of revolution. These machines are generally large.
- Tangential surface grinder or surface grinder, with a wheel head and a reciprocating longitudinal table on which the workpiece is placed. It is used to grind flat parts, and also dies.
- Face grinder. On this machine tool the wheel rotates on a vertical spindle and the feed motion is linear. These machines are used for their high stock removal rates, although some can be very precise.
- Centreless grinder or centerless. Used to grind small cylindrical parts such as bushes. It is well suited to series production.
- Tool and cutter grinder. Used to sharpen cutting tools and instruments.
What is a tangential surface grinder?
A tangential surface grinder (or tangential flat grinder) is a high-precision machine tool used to grind flat surfaces. The workpiece is machined through tangential contact with the periphery of a cylindrical grinding wheel on a horizontal axis. On this machine the motion is circular and, as on the universal grinder, excess material is removed by abrasion.
The tangential surface grinder consists of a solid bed, at the rear of which is the assembly that carries the wheel head, where the abrasive tool is mounted. The wheel head is made up of a cast housing with guideways that fit onto the column, and seats that house the spindle.
On these grinders the motor is coupled to one end of the spindle by a flexible coupling. The spindle moves vertically and is controlled by a handwheel, either manually or automatically. As mentioned above, the most important part of any grinding machine is the grinding wheel. It is made of abrasive grains that are extremely hard and highly resistant to wear, breakage and heat. Depending on the wheel diameter, its rotational speed can reach 30,000 revolutions per minute (rpm).
In addition, a cross slide runs along the bed guideways and supports the machine table, which moves longitudinally.
Operation and axes of motion
The tangential surface grinder is used to machine flat surfaces and straight profiles by abrasion. The workpiece is clamped on the machine table using a magnetic chuck or another dedicated fixture. The wheel is then started, rotating at high speed, and approaches the surface of the workpiece tangentially.
On this type of grinder the vertical and cross axes are controlled very precisely and, if the workpiece is positioned correctly, the periphery of the wheel can be used to grind surfaces, while the side of the wheel is used for face grinding.
The tangential surface grinder has three axes of motion:
- Z axis, which provides the cutting power; the grinding wheel is mounted on it.
- X axis, horizontal and parallel to the surface on which the workpiece is held. The X axis is horizontal relative to Z.
- Y axis, vertical and perpendicular to the X axis. This axis brings the wheel and the workpiece surface closer together.