Grinding Machine: Definition, Types, Parts, Working & Operations


In this article, we will learn what is grinding machine, its definition, types, parts, working, operations, etc. After machining a certain part or molding it in a mold there’s always some surface roughness and irregularities on the surface of items. This happens in the machined parts due to the cutting action of tools and they cannot possibly produce a completely smooth surface and for the molded parts this happens due to the irregularities of the molds and loosely packed mold grains. A grinding machine is one of the most useful instruments for producing smooth surface finishes and achieving high accuracy.

The grinding wheel consists of many abrasive particles that act as a cutting tool removing the material from the surface as a multi-point cutting tool.

What is Grinding Machine? Definition

A grinding machine or in short ‘grinder’ is a surface finishing and roughness removal machine with help of an abrasive wheel attached in different orientations and machines as per requirement. It can also be defined as follows:

A machine with an abrasive wheel or belt which is used to remove surface roughness and achieve high finishing is known as a grinding machine.

Types of Grinding Machine

The grinding machines are classified into the following types:

  • Surface Grinding Machine
  • Bench Grinding Machine
  • Centerless Grinding Machine
  • Belt Grinding Machine
  • Portable Grinding Machine
  • Gear Grinder
  • Universal Grinding Machine

Let us discuss all types of grinding machines:

Surface Grinding Machine: Parts, Working, Advantages & Disadvantages

What is Surface Grinding Machine?

It is used to machine flat surfaces; the grinding wheel is used to remove the irregularities from the surface of the workpiece. Surface grinding is the most commonly used process and is installed in all major manufacturing processes for surface finishing operations.

Parts of Surface Grinding Machine

Base

It supports the entire machine assembly and acts as an absorber of vibrations generated by the grinding operations.

Hand wheel (Traverse)

The worktable is adjusted using the hand wheel, by rotating the hand wheel we can adjust the worktable in a longitudinal direction i.e., forward, and backward.

Handwheel (Cross slide)

Cross slide handwheel is used to adjust the workpiece in up and down motion, with this wheel we can adjust the exact dimension to be machined by the grinding wheel.

Handwheel (Feed head)

It is used to adjust the depth of cut on the surface of the material by the movement of the wheel head in the vertical direction. 

Saddle

It is placed on top of the base and helps in the movement of the workpiece in x (Left & right) and y (in & out) axis directions.

Worktable

It is an extremely flat plate where the workpiece is fixed before grinding operation.

Column

It is a vertical column where the abrasive wheel, wheel head, and guard are mounted.

Grinding wheel

It is a tool through which the workpiece is machined. It is made up of multiple abrasives sticks on a single wheel performing cutting operations when they rotate producing higher accuracy.

Coolant

Coolant is used to cool the workpiece when it gets heated up due to the continuous grinding operation. In the surface grinding, the coolant medium used is water.

How Does Surface Grinding Machine Work?

The surface grinding machine uses a rotating wheel mounted on a wheel head to remove the material from the surface of the workpiece with the abrasive action of the wheel.

Step 1: Mount the workpiece on the worktable and fix it.

Step 2: Adjust the handwheels as per the workpiece dimensions

Step 3: Adjust feed with the infeed handwheel as per the depth of cut required. Start the coolant to dissipate the heat.

Step 4: After starting the machine slowly rotate the handwheel to move over the workpiece. The wheel rotates over the workpiece to remove the material from the surface until high surface finish and dimensional accuracy are achieved.

The grinding operation is completed, and you get a smooth finish workpiece. Diamonds, aluminium oxide particles, cubic boron nitride, and silicon carbide are the types of abrasives used on the surface of the grinding wheel.

Advantages of Surface Grinding Machine

  • High surface finish is achieved
  • Unskilled workers can also perform the operation
  • Automation can be done to achieve higher accuracy and productivity
  • Metallic and non-metallic workpieces can be machined with ease

Disadvantages of Surface Grinding Machine

  • Grinding operation cannot be done in the reverse direction
  • Spindle power required is more and the abrasives from the wheel keep degrading

Bench Grinding Machine: Parts, Working

What is Bench Grinding Machine?

It is the most common type of grinding machine found in tool rooms and workshops. It is used to sharpen the tools, grind the workpiece surface and remove roughness. Small items in the labs are machined using a bench grinder.

Parts of Bench Grinding Machine

Motor

A high power and high speed motor is installed at the center of the grinder. The grinding power of the machine is determined using the horsepower of the motor.

Grinding wheel

Two wheels are used for grinding the workpiece, one is an abrasive wheel with coarse grain abrasives for higher material removal and the other is with fine grains for finishing operations.

Casing

A metallic casing is provided under which the grinding wheels are mounted.

Eye shield

When the workpiece is machined on a grinding wheel tiny, degraded particles fly out and can be fatal for the human eye. For safety, an eye shield is installed over the wheel to avoid any damage from the flying particles.

Tool rest

It is attached with the grinding machine to hold the workpiece or item to be machined. It also aids in the holding of the workpiece when changing or readjusting the speed of the wheel. To prevent the workpiece from falling or slipping down, it needs to be secured tightly within 1/16 inch to 1/8 inch distance of the wheel.

How Does Bench Grinding Machine Work?

  • It’s easy to use and grinding can be done on any type of workpiece. Bench grinders are applicable for grinding harder materials like steel and are not used on soft materials like aluminium. The item to be machined is held on the abrasive wheel and the grinding operation is performed until the desired surface is achieved.
  • Shaping operation is also performed on the bench grinder, the workpiece is held on the grinding wheel and is rotated from all directions till the desired shape is achieved.
  • Grinding wheel is also used for sharpening the cutting tools, especially the lathe cutting tool using their coarse wheel and then finer sharpening is done with fine grain wheel.
  • The buffing wheel is attached to the bench grinder to perform the buffing operations which preserve the real texture of the material.
  • A tank or bucket of water is used as a coolant and the workpiece is continuously dipped in it after the grinding operation is done.

Centerless Grinding Machine: Parts, Working, Advantages & Disadvantages

A grinding machine used for grinding cylindrical, tapered, and curved surfaces of the workpiece and is not held on the center or fixed using a fixture or jig is known as the centerless grinding operation.

  • The workpiece is held by rollers, of which, one is a supporting roller that rotates at slow speed and the other is a grinding roller rotating at high speed.
  • The item is kept at the rest blade, and when the machine is turned on, material removal takes place from the surface of the object.
  • Both rollers rotate in the same direction allowing the workpiece to rotate in the reverse direction.
  • The forward movement of the workpiece is achieved by providing a tilting angle to the regulating/supporting wheel. Angle adjustments up to 8 to 10 degrees are provided for the axial movement of the workpiece.
  • In one pass the diameter of the workpiece is reduced by 0.02 to 0.3mm based on the wheel adjustments.

Centerless Grinding Operations

Centerless grinding has three types of operations –

Infeed centerless grinding

The workpiece is kept fixed during infeed grinding, and the grinding wheel is pushed over the workpiece.

End feed centerless grinding

It is similar to infeed grinding but this is used to make tapers. The tapered grinding wheel or the regulating wheel is used to produce a tapered shape on the workpiece.

Through feed centerless grinding

In this type of grinding operation, the workpiece is completely passed through the grinding wheels. This method is applicable when there is no external part or irregularity on the surface of the item. Long shafts, bars, and cylinders are generally machined using this method.

Advantages of Centerless Grinding Machine

  • High production rate as compared to other grinding methods.
  • No fixtures and jigs are required for fixing the workpiece
  • Time spent in centering the workpiece is saved as no centering is required
  • Low wear and tear of the workpiece
  • High stability can be achieved with a centerless grinding

Disadvantages of Centerless Grinding Machine

  • The manufacturing cost is significantly higher when compared to other operations.
  • A single workpiece with a varied diameter across its body length is difficult to machine
  • Only straight cylindrical parts can be used for the grinding operation.

Belt Grinding Machine

What is Belt Grinding Machine?

A belt type grinding machine is growing in use now after the belt manufacturing process is getting easier and cheap. In this type of grinding, abrasives are stick on the surface of the belt and it is rotated at high speed. The workpiece is usually handheld, and the workers can apply pressure with their hands and achieve the desired surface finish. The finishing accuracy of up to 0.8 microns can be achieved with a belt grinding machine.

Parts of Belt Grinding Machine

Abrasive belt

Leather or synthetic belt is used on which the abrasive materials are attached. This belt comes in various sizes based on the size of the machine. The roughness of the belt is varied as per the type of grinding operation required, it can be a highly coarse-grained or fine-grained abrasive belt.

Induction motor

A single phase induction motor is used to drive the belt and pulley assembly which in turn drives the abrasive belt. It is characterized by horsepower and RPM.

Belt drive

A belt drive is used to regulate the grinding belt; the belt drive transfers the rotation of the motor to the grinding belt. It is a combination of V-type pulleys, roller shafts, and belts.

Frame

A cast iron frame is used that forms the base of the machine and it absorbs all the vibrations generated by the grinding operations.

Advantages of Belt Grinding Machine

  • It can be used in any type of workshop and industry for metals and non-metals.
  • As belt drive is used for running the machine, different diameter pulleys can be used to vary the speed of the grinder belt.
  • It is a low maintenance machine.

Disadvantage of Belt Grinding Machine

  • The belt needs to be replaced for the grinding operation of different materials.

Portable Grinding Machine

  • A portable grinder is similar to a handheld drill machine in which a grinding wheel is attached. A person can hold it with their hand and perform the grinding operation wherever required.
  • Another machine with a similar function is a flexible shaft grinding machine which works in the same way as a portable grinder. The only difference is that the flexible shaft grinder has a flexible shaft which helps in grinding intricate parts.
  • Highly coarse abrasive wheels are used for roughing and snagging operations while the smaller and fine grain wheels are used for burring.

Gear Grinding Machine

  • Gears are manufactured using different processes like milling, hobbing, etc. These gears have a rough surface and need surface finishing for smoother operations.
  • Gear grinding is used to get precise gear dimensions and higher surface accuracy on gears.
  • Abrasion is used to remove surface roughness from the gear blank. It is done by rubbing the rough abrasive wheel on the surface of the gear which results in the removal of burrs and unnecessary material.

Based on the method of material removal, gear grinding is classified into two types:

Generating gear grinder

In this straight-sided gear grinding technique, the gear moves along the abrasive tool to form the splines. Once the splines are created, the gear grinding procedure is not complete. To enhance the grinding of the gear, a final polishing operation is performed. Rather than constructing splines, polishing helps smooth out the face of the gear. In this operation, a polishing wheel is used to make the surface of the gear bright and shiny, with no defects.

Form Grinding

Non-generating grinding is another name for this technique of gear grinding. In this grinding technique, a disc wheel is used to grind both sides of the space between splines at the same time. To guide the grinding action, an involute structure is connected to the wheel.

Universal Grinding Machine

  • Universal type of grinding machine is normally used in workshops, labs, and toolrooms for sharpening, grinding, and polishing tools.
  • It is similar to a surface grinding machine with handwheels and slides that can be slides and swiveled in the x and y axis at any angle.
  • Auxiliary attachments can be installed with the universal grinding machine to perform internal grinding operations. The extra wheel can be attached to the small wheels to achieve higher velocities in grinding operations.
  • High precision grinding operations can be performed with a universal grinding machine by setting a perfect depth of cut and turning the handwheels slowly in the direction of the wheel.

Abrasives Used in Grinding Machne

There are various types of abrasives available that are selected based on various physical factors such as fracture resistance, toughness, and hardness for polishing and grinding operations. These are further classified into 2 types –

Natural abrasive

These abrasives are obtained from the earth’s crust that includes diamonds, sandstones, emery, corundum, etc. Soft materials are grinded by sandstone, hard materials are machined using diamonds as it is the hardest abrasive available, and iron-carbide tools are machined using this.

Emery and corundum contain aluminum oxide and have high hardness than sandstone.  Corundum has higher aluminium oxide content than emery.

Artificial abrasives

Artificial abrasives are classified in two major types:

Aluminium oxide abrasives – Denoted by the letter ‘A’

Different minerals like bauxite, silica, iron oxide, titanium oxide, etc. are heated with coke and iron borings in an arc type furnace. Aluminium oxide is better suited to grinding high tensile strength materials such as most steels, carbon steels, high speed steels, and resistant bronzes because it is robust and does not easily fracture.

Silicon carbide – Denoted by the letter ‘S’

Silicon carbide is manufactured in a huge rectangular electric resistance furnace using loose bricks comprised of 56 parts silica, 34 parts powdered coke, 2 parts salt, and 12 parts sawdust. Silicon carbide abrasives in green and black grain are available. Silicon carbide is placed second to diamond in terms of hardness. It is not, however, as tough as aluminium oxide. It is used to grind materials with low tensile strength, such as cemented carbides, ceramics, grey brass, bronze, copper, aluminium, vulcanized rubber, and so on.

Conclusion

This article speaks about different types of grinding machines, parts, and their working. A workshop can have a single grinding machine or multiple grinding machines based on the surface finish requirements of the workpiece. This is normally the last operation performed on an item to achieve high precision.

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