Hello! Our today’s topic is Cylindrical Grinder.
Come; let us learn something about Cylindrical Grinding and the machines which are used for doing it.
What is Cylindrical Grinding?
Cylindrical Grinding is a process where you use a grinding wheel rotating in a horizontal axis to cut or grind a cylindrical work-piece mounted on a chuck or between centers rotating in an axis parallel to the grinding wheel axis, in the same plane.
Abrasive particles on the grinding wheel do the cutting of material.
Why do we use Cylindrical Grinding?
Your objective of doing cylindrical grinding is-
- To get a good surface finish.
- Geometrical accuracy like concentricity between two or more diameters on a shaft or between the bore and outside diameter of a cylindrical work-piece.
- Most importantly, to machine the hardened work-piece for which grinding is the only machining process.
How Cylindrical Grinding works?
Your Cylindrical Grinding Machine consists of a grinding wheel rotating in a horizontal axis and a circular work-piece rotating in an axis parallel to the grinding wheel axis in the same plane.
To start the grinding process, you have to feed the work-piece to the rotating grinding wheel, in a reciprocating motion. You can give the depth of cut by moving the grinding wheel head towards the work-piece. Abrasive particles on the grinding wheel do the cutting action.
The surface (peripheral) speed of the work-piece is much less in comparison with the surface speed of the grinding wheel.
Your grinding cycle normally consists of one or two rough cuts followed by wheel dressing and a fine finish cut.
You can give a depth of cut of 30 to 80 microns during rough grinding (1 micron=0.001 millimeter) depending on the work-piece hardness and a finish cut of 10-20 microns.
Types of Cylindrical Grinding Machines.
- External Cylindrical Grinders.
- Internal Cylindrical Grinders.
- Centerless Grinders.
- Tool and Cutter Grinders.
- CNC Cylindrical Grinder.
Come!! Join me in the exploration of Cylindrical Grinders.
1. External Cylindrical Grinders.
Your External Cylindrical grinder consists of a bed mounted on a base, and the lower table is mounted on the bed and has reciprocating movement in the X axis on the bed guide-ways.
The upper table of your machine is mounted on the lower table and can be swiveled in the longitudinal plane.
Head Stock of your machine (which can be swiveled in some designs) with the drive system for the work-piece and tailstock with a dead center are mounted on the upper table.
You can move the tailstock along the table length and lock at the position required.
The wheel-head of your machine (which can be swiveled in some designs), with an independent motor, is mounted on the bed and moves in the transverse direction (towards or away from the work-piece) for giving depth of cut.
Your machine has a coolant system to flood the cutting area during grinding.
The reciprocating movement of the table of your machine, in the longitudinal (X) axis is hydraulic and the table speed is infinitely variable. You can change the speed of the table movement or stop the movement by using the lever.
There are two movable stoppers on the front of your machine table and they can be moved and locked at any position; the hydraulic valve for reversing the direction of the table’s reciprocating movement is in between these two stoppers and during grinding, the stopper on the moving table strikes the hydraulic valve to reverse the direction.
You have to position the two stoppers in such a way that the table movement is reversed as soon as the work-piece length passes the grinding wheel.
You can synchronize the predetermined depth of cut with the table direction reversal.
Your External Cylindrical Grinding is also called ‘center type’ grinding since external cylindrical grinding work-pieces are shafts with precision centers on both faces and are mounted between centers (with a drive carrier) during grinding.
You can grind the outside diameters (OD) of long or short shafts, with single or multi- diameters and also with tapers. You can maintain the concentricity of all the diameters and tapers on the shaft within the tolerance
You can do the following grinding operations on your cylindrical grinder with concentricity between the different diameters and taper.
- Plane grinding of a single diameter long shaft by feeding the work-piece against the grinding wheel by table reciprocating movement.
- Do plunge grinding of diameter (length of the diameter to be ground is less than the width of the grinding wheel), by directly plunging the grinding wheel into the work-piece.
- Grind Multi diameter long shaft with a combination of plunge and plane grinding.
- Do taper grinding over the length of the work-piece by tilting the table and plunge grinding of short taper by tilting the wheel head.
Your External Cylindrical Grinder can be of the manual type or a semi / fully automatic type where the feed, depth of cut, and wheel dressing happens in auto mode.
Your machine may have a built-in wheel dresser.
Your External Cylindrical Grinder may have an internal grinding attachment and such machines are called Universal Cylindrical Grinders.
To make the External Cylindrical Grinder more productive, you can have many variants that are specific to the type of grinding required.
- Plain Cylindrical Grinder for grinding long shafts with one or two diameters and taper.
- Plunge grinder for plunge grinding of small length diameters on a shaft.
- Plunge grinding of journal diameters on a crankshaft, with the built-in special fixture. This machine may be called ‘Crankshaft Grinder”.
The above variants of your External Cylindrical Grinder are not versatile, but they are more productive.
If you have a work-piece with a large diameter and short length (without centers on the face) you can use the chuck (three jaws or four jaws chuck) for clamping. You can grind the outside diameter of such work-pieces by truing the OD of the work-piece or its bore (if there is a bore).
2. Internal Cylindrical Grinders
You use Internal Cylindrical Grinders to grind the bore (internal diameter) in a work-piece and the bore can be either straight or tapered or a groove.
Your Internal Cylindrical Grinder has a cast-iron bed mounted on a cast-iron or cement base. Further, your machine has a horizontal work-head with a spindle and a grinding wheel-head; the work-head and the wheel-head have their own motors.
The reciprocating motion and transverse motion in your machine, for feed and depth of cut, are normally given to the grinding wheel-head; however, in some designs, it may be with the work-head of your machine.
The reciprocating motion of the wheel-head and reversal of direction in your machine can be similar to the External Cylindrical Grinder.
You can swivel the work-head for doing taper grinding operation.
Your machine has a coolant system to flood the cutting area during grinding.
Your machine will have a built-in wheel dresser.
You can mount the work-piece on a chuck (three or four jaws), magnetic chuck or, a special fixture. You can do plane internal grinding, taper internal grinding, plunge type internal grinding of grooves, and face grinding.
The direction of rotation of your grinding wheel and the work-piece at the point of contact is normally opposing to each other.
You have to verify the internal-grinding wheel chart to select the size and type of the grinding wheel which depends on the size of the bore to be ground & work-piece material.
Your Internal Cylindrical Grinder can be of the manual type or a semi / fully automatic type where the feed, depth of cut, and wheel dressing happens in auto mode.
You use Vertical Type Internal Cylindrical Grinder for internal grinding of large and heavy work-pieces. Your machine will have a rotary table for mounting the work-piece and a vertical wheel-head moving up and down. Your machine can have the cross-movement (depth of cut) with the wheel-head or the work table.
3. Tool and Cutter Grinders
As the name indicates, your Tool and Cutter Grinder is designed to sharpen the worn-out cutting tools viz. milling cutters, drills, broaches, hobs, etc.
Your machine is very versatile and has many attachments that are specifically used to grind or sharpen the concerned tools.
You must be highly skilled and have a good knowledge of tool geometry to work on this machine; many of the operations depend on operator judgement and skill.
Your machine is generally equipped with a grinding vice and other precision work holding devices. Your Tool and Cutter Grinder is a compact machine built for tool sharpening in the workshop.
Your machine can also be used to a limited extent to perform internal grinding, cylindrical grinding, and surface grinding operations and this versatility is mainly for grinding new raw tools.
You can make use of these features to grind small components if there is no load of tool sharpening.
4. CNC Cylindrical Grinders
Your CNC (Computer Numerical Control) Cylindrical Grinder is operated using CNC systems where the Grinder follows the step-by-step instructions given by the CNC system. You can feed the instructions into the CNC system either by directly using the system keyboard or design it offline on a Computer-Aided Design (CAD)/ Computer-Aided Manufacturing (CAM) system and transfer it to the CNC system. Your CNC Cylindrical Grinder can start production, once you establish a trial component.
Unlike in your CNC turning or CNC milling, the grinding wheel in a CNC Cylindrical Grinder (or other types of CNC Grinder) needs dressing for the finish cut and dressing leads to a reduction in the grinding wheel diameter. Your machine will have an arrangement to auto measure and compensate by effecting necessary required corrections.
Your machine has a coolant system to flood the cutting area during grinding and a built-in wheel dresser.
The CNC system on your Cylindrical Grinder has closed-loop feedback and monitors the program continuously in real-time and implements corrections to ensure repetitive mass production of components.
You have learned about the types of Cylindrical Grinders and how the grinding is done by the movement of the table (holding the work-piece) and the wheel head.
In your CNC Cylindrical Grinder, the movements of the table and the wheel head are under the control of the CNC System. You can have any type of grinder machine with a CNC system.
Servo motors, Linear Motion (LM) guide-ways, and ball screws are used for the precise and accurate axial movement of the table or the wheel head in your CNC grinders.
The CNC System gives you the freedom to make the machine more productive because you can do more than one operation simultaneously and have a predetermined relative movement between the work-piece and the grinding wheel to generate intricate profiles.
For example, you can program to do external grinding and internal grinding simultaneously by having independent wheel heads for external grinding and internal grinding.
You can have an indexing type of wheel head carrying 4 different grinding wheels for executing external grinding, bore grinding, profile grinding, face grinding, etc. and you can program to do all the required grinding operations in a continuous sequence.
You can program your CNC Grinder for planned intermittent cuts on the work-piece where the grinding wheel head moves back and forth in a sequence to generate cam or any special profile. You can use a similar technique to generate concave or convex profiles.
The possibilities are infinite in your CNC Grinders and machines can be built depending on the grinding operations to be performed.
Your CNC grinder may have provision for wheel balancing.
Your CNC grinder may have two or more axes controlled by CNC.
You can find a typical 5-axis CNC controlled grinding machine, which apart from grinding, does milling, drilling, and tapping also; such CNC grinding machines having simultaneous movements in up to 5 or more axis are very useful in faster and precision manufacture of critical components for the aerospace industry.
Cylindrical Grinding Wheels
Your grinding wheel contains abrasive particles bonded into the shape by a bonding material, and it has a matrix of the following constituents:
|Type of abrasive||Aluminum oxide, silicon carbide, cubic boron nitride, and diamond (all these are manufactured abrasives). Aluminum oxide is a popular choice.|
|Grain size||The grain size can be 8 (coarse) to 600 (fine).|
|Type of bond||Vitrified, silicate, resinoid, shellac, and metallic bond. Vitrified bond is the most used.|
|Grade of the wheel||The grade (also referred to as hardness) of the wheel and it can be A to Z, A is soft, M is medium and Z is hard.|
|Structure of the wheel||The structure indicates the blank space or air pockets in the grinding wheel and it is designated with numbers 1-15, where 1 is dense and 15 is open.|
You have to select the grinding wheel with a combination of the above and the combination depends on two factors- one is material (including hardness) to be ground and the other is the rate of material removal.
Your external grinder wheel diameter can be 300 to 500 or more with the corresponding width and bore suitable for clamping flanges; the surface speed of the grinding wheel can be 40- 45 meters per second (peripheral speed) or more.
You have to select the size of the internal grinding wheel from the manufacturer’s chart and the size depends on the diameter of the bore to be ground.
Your CNC External Cylindrical Grinder uses both straight and angular type grinding wheels.
Before using a new grinding wheel, you must do the inspection of the wheel (including ring test), balancing, and dressing.
For successful Cylindrical Grinding operation, choice of the grinding wheel, speed of the grinding wheel, and relative speed of the work-piece is important and follow the manufacturer’s guidelines in this matter.
When you work on your Cylindrical Grinding Machine, the surface of the work-piece in contact with the grinding wheel develops considerable heat.
The cooling system of your machine cools the work-piece, reduces the effect of friction, removes heat from the work-zone, and increases rate-of-material-removal, without further damage to the work-piece surface finish.
The most commonly used grinding fluids in your machine are water-based emulsions and grinding oils.
Since the grinding process in your machine produces a lot of heat, flooding the coolant at the point of cut is most effective; the quantity of the coolant depends on the length of contact between the grinding wheel and the work-piece, larger the contact area more should be the quantity of coolant.
If you can work on a cylindrical grinder, you will be considered as a skilled worker, because every machinist may not be comfortable working on a Cylindrical Grinder.
With the advent of CNC controlled cylindrical grinders, the requirement of the level of skill has come down.
Your Cylindrical Grinders are important and a must for every workshop, be it an automobile industry or a consumer product industry.