Drilling Operation in Manufacturing Technology

 

Drilling

Drilling is a metal removing process in which a drill bit to cut a hole of circular cross-section in solid materials. The drill bit is usually a rotary multi-point cutting tool.

A machine consists of a spindle that provides rotary motion to the drilling tool, which finally makes the hole in the workpiece is called drilling machine.

Parts of Drilling Machine

A drilling machine is usually composed of several or all of the following parts.

Base: generally bolted with the ground to support the weight of the drilling machine.

Column: located on one side of the base, can carry the load of the arm and drill head, with a sliding table mounted on it.

Arm: at the top of the column, carries the drill head and the housing of the driving mechanism.

Drill head: mounted on one side of the arm, consists of feed and driving mechanism. It can slide up and down.

Worktable: mounted on the column, can move vertically and horizontally.

Feed mechanism: hand and automatic feed by an electrical motor.

Spindle: holds the drill or cutting tool and revolves in a fixed position in a sleeve. 

Chuck: situated on the spindle, holds the drill jig.

Electric Motor

 

Classification of Drilling Machine

1. Portable drilling machine: generally small in size and contains a universal motor, used for drilling holes on the rocks or any rigid surface, suitable for any location. The piece to be drilled is held in a vice.

2. Bench drilling machine: perfect for producing small holes at high speeds, usually consists of a base, worktable, spindle, drill head, driving mechanism and column. The work is started from the drill fed into the piece by hand.

3. Radial drilling machine: mainly for drilling large and heavy workspaces, the table can be adjusted to suit different heights. It allows the operator to make the spindle directly over the workpiece rather than move the part to the tool, and also capable to create intersecting or angular holds in one setup. 

4. Upright drilling machine: larger and stronger than sensitive drilling machine, designed for handling medium to large-sized holes.

5. Gang drilling machine: can be used for drilling, reaming, counter boring and tapping, just need to move the machine back and forth.

6. Deep mole drilling machine: special type that is designed to drill deep holes in the connecting rods, spindles and others, with high cutting speed and less feed.

7. Multiple spindle drilling machine: with several spindles, perfect for drilling a large amount of holes into a part and drilling same holes on identical workpieces. 

8. CNC drilling machine: computer numerical control drilling machine can automatically change tooling with a turret or automatic tool changer. The program controls the speeds, feeds and table position. 

 

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Grinding: Definition, Advantage, Disadvantage, Application, Specification, Type`s of Grinding

 

Grinding: Definition,  Advantage, Disadvantage, Application, Specification, Type`s of Grinding

It is a material cutting process which engages an abrasive tool whose cutting elements are grains of abrasive material known as grit. Grinding is the most common form of abrasive machining. These grits are characterized by sharp cutting points, high hot hardness, and chemical stability and wear resistance. The grits are held together by a suitable bonding material to give shape of an abrasive tool. Grinding can be compared with milling with an infinite number of cutting edge.

 

ADVANTAGES OF GRINDING OPERATION:

·            This can produce a high surface finish with accurate can obtain.

·            This can machine hard materials.

·            This operation can be done with less pressure applied on work.

·            It can obtain highly accurate dimensions.

·            It can work at high temperature also.

·            Speed of cutting can be done by this process.

·            In grinding abrasive particles, they are self-sharpened action.

·            This can operate for complex things also.

·            Smooth surface can obtain.

 

 

DISADVANTAGES OF GRINDING OPERATIONS:

·            Required tool is high cost.

·            Process is also a costly one.

·            It cannot remove the high amount of material, it only removes a little amount.

·            For removing the required amount from work it consumes more time.

·            You should work carefully, because imperfect contact may lead to damages.

 

Application of Grinding

·        Surface finishing

·        Slitting and parting

·        Descaling, debarring

·        Stock removal (abrasive milling)

·        Finishing of flat as well as cylindrical surface

·        Grinding of tools and cutters and resharpening of the same.

 

Grinding Specification

 

Grinding Ratio

The grinding ratio or G ratio is defined as thee cubic mm of stock removed divided by the cubic mm of wheel lost. The G ratio is a measure of grinding production and reflects the amount of work a wheel can do during its useful life.

 

Grade

The worn out grit must pull out from the bond and make room for fresh sharp grit in order to avoid excessive rise of grinding force and temperature. A soft wheel should be chosen for grinding hard material. A hard wheel should be chosen for grinding soft material.

 

Structure

The structure should be open for grinding wheels engaged in high material removal to provide chip accommodation space. The space between the grits also serves as pocket for holding grinding fluid. Dense structured wheels are used for longer wheel life, for holding precision forms and profiles.

 

Glazing

With continuous use a grinding wheel becomes dull with the sharp abrasive grains becoming rounded. This condition of a dull grinding wheel with worn out grains is termed as glazing.

 

Loading

Some grinding chips get lodged into the spaces between the grits resulting in a condition known as loaded wheel. Loading is generally caused during the grinding of soft and ductile materials. A loaded grinding wheel cannot cut properly and need dressing.

 

Dressing

Dressing is the conditioning of the wheel surface which ensures that grit cutting edges are exposed from the bond and thus able to penetrate into the workpiece material. n dressing attempts are made to splinter the abrasive grains to make them sharp and free cutting and also to remove any residue left by material being ground.

 

Truing

Truing is the act of regenerating the required geometry on the grinding wheel. Truing is also required on a new conventional wheel to ensure concentricity with specific mounting system.

 

Creep Feed Grinding

This machine enables single pass grinding of a surface with a larger down feed but slower table speed than that adopted for multi‐pass conventional surface grinding. In creep‐feed grinding, the entire depth of cut is completed in one pass only using very small in‐feed rates.

 

Cylindrical Grinding

Center‐type cylindrical grinding is commonly used for producing external cylindrical surfaces. The grinding wheel revolves at an ordinary cutting speed, and the workpiece rotates on centers at a much slower speed. Grinding machines are available in which the workpiece is held in a chuck for grinding both external and internal cylindrical surfaces.

 

Centerless Grinding

Centerless grinding makes it possible to grind both external and internal cylindrical surfaces without requiring the workpiece to be mounted between centers or in a chuck. Two wheels are used. The larger one operates at regular grinding speeds and does the actual grinding. The smaller wheel is the regulating wheel. It is mounted at an angle to the plane of the grinding wheel. The regulating wheel controls the rotation and longitudinal motion of the workpiece and usually is a plastic‐ or rubber‐bonded wheel with a fairly wide face.

 

Lapping

Lapping is basically an abrasive process in which loose abrasives function as cutting points finding momentary support from the laps.

 

Honing

Honing is a finishing process, in which a tool called hone carries out a combined rotary and reciprocating motion

while the workpiece does not perform any working motion. Most honing is done on internal cylindrical surface, such as automobile cylindrical walls. The honing stones are held against the workpiece with controlled light pressure. The honing head is not guided externally but, instead, floats in the hole, being guided by the work surface.

 

Buffing

Buffing is a polishing operation in which the workpiece is brought into contact with a revolving cloth wheel that has been charged with a fine abrasive, such as polishing rough. The wheels are made of disks of linen, cotton, broadcloth, or canvas, and achieve the desired degree of firmness through the amount of stitching used to fasten the layers of cloth together.

 

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Milling Machine : Definition, Working, Type`s, Parts, Operation, Advantage

Milling Machine : Definition, Working, Type`s, Parts, Operation, Advantage

Milling is a process performed with a machine in which the cutters rotate to remove the material from the work piece present in the direction of the angle with the tool axis. With the help of the milling machines one can perform many operations and functions starting from small objects to large ones.

 Milling is the cutting operation that removes metal by feeding the work against a rotating, cutter having single or multiple cutting edges. Flat or curved surfaces of many shapes can be machined by milling with good finish and accuracy. A milling machine may also be used for drilling, slotting, making a circular profile and gear cutting by having suitable attachments.

Working Principle: The workpiece is holding on the worktable of the machine. The table movement controls the feed of workpiece against the rotating cutter. The cutter is mounted on a spindle or arbor and revolves at high speed. Except for rotation the cutter has no other motion. As the workpiece advances, the cutter teeth remove the metal from the surface of workpiece and the desired shape is produced.

Types of Milling Machines

The two main configurations of the milling machining operations are the types of milling machines. These are the vertical mill and the horizontal mill. They are further discussed below:

Vertical Milling Machines

The vertical mill has a vertically arranged spindle axis and rotate by staying at the same axis. The spindle can also be extended and performing functions such as drilling and cutting. Vertical mill has got two further categories as well: turret mill and bed mill.

The turret mill has got a table that moves perpendicularly and parallel to the spindle axis in order to cut the material. The spindle is, however, stationary. Two cutting methods can be performed with this by moving the knee and by lowering or raising the quill.

The other is the bed mill in which the table moves perpendicular to the axis of the spindle and the spindle moves parallel to its axis.

Horizontal Milling Machines

The horizontal mill is also the similar cutter but their cutters are placed on a horizontal arbor. A lot of horizontal mills have got rotary tables that help in milling in various angles. These tables are called the universal tables. Apart from this all the tools that are used in a vertical mill can also be used in the horizontal mill.

Parts of the Milling Machine

1.     Column and Base

Column and base provide support for the other parts of the milling machine. There is an oil reservoir and pump in the column to lubricate the spindle. The column rests on the base and also it has a coolant reservoir and a pump to provide coolant in machining operations.

2.     Knee

Saddle and table have the support of casting. The gearing mechanism is enclosed within the knee. The knee is fastened to the column by dovetail ways. It is supported and adjusted by a vertical positioning screw also known as an elevating screw. The use of the elevating screw is to adjust the knee up and down by raising or lowering the lever with the help of hand or power feed.

3.     Saddle and Swivel Table

The saddle is on the knee and supports the table. Saddle slides on horizontal dovetail on the knee and dovetail are parallel to the axis of the spindle (in horizontal milling m/c). Swivel table is attached to the saddle that swiveled (revolved) horizontally in both directions.

4.     Power Feed mechanism

The power feed mechanism is in the knee. The power feed mechanism is used to control in longitudinal (left and right), transverse (in and out) and vertical (up and down) feeds. For the desired rate of feed on the machine, the feed selection lever is placed to indicate on the feed selection plates. For some universal knee and column milling machine, feed is obtained by turning the speed selection handle till the required rate of feed is shown on feed dial. Almost in every milling machine, there is a rapid traverse lever which is used when a temporary increase in the speed of the longitudinal, transverse, or vertical feeds is required. This lever is used when the operator is aligning or positioning the work.

5.     Table

The table is a rectangular casting that is present on the top of the saddle. The table is used to hold the work or for work holding devices. There are several T-slots to hold work and work holding devices (jigs and fixtures). It can be operated by hand or by power. For moving the table by hand, engage, and turn the longitudinal hand crank. For move, it by power, engage and longitudinal direction feeds control lever.

6.     Spindle

The spindle is used to holding and drives the cutting tools of the milling machine. It is mounted on the bearings and has the support of the column. The spindle is driven by an electric motor via gear trains and gear trains are on the column. The spindle face lies near the table and having an internal taper machined on it. There are two keys at the front face provides a positive drive for cutter holder or arbor.

7.     Over Arm / Overhanging Arm

Over arm is a horizontal beam and it is on the top face of the column. It may be a single casting and slides on the dovetail ways which is on the top face of the column.

8.     Arbor Support

Arbor support is casting with a bearing that supports the outer end of the arbor. It also helps to align the outer end of the arbor with the spindle. Arbor support prevents the springing of the outer end of arbor in cutting operations. Generally, there are two types of arbor supports used in the milling machines. The first one has a small diameter bearing hole of a maximum diameter of 1 inch. The second one has a large diameter bearing hole of up to 23/4 inch.

9.     Ram

The ram is an overhanging arm in a vertical milling machine. The one end of the ram is mounted on the top of the column and the milling head is attached to another.

Milling Machine Operations:

The following Operation is performed by the Milling Machine:

·         Plain Milling or Slab Milling Operation

·         UP and DOWN Milling Operation

·         Face Milling Operation

·         End Milling Operation

·         Gang Milling Operation

·         Straddle Milling Operation

·         Groove Milling Operation

·         Gear Milling Operation

·         Side Milling Operation and

·         T-Slot Milling Operatio

 

Up Milling and Down Milling:

Up milling is a method of milling operation in which the cutter and the workpiece both moves in the opposite direction.

Down Milling is a method of milling operation in which the direction of the rotation of the cutter coincides with the direction of the work feed. 

Chip Thickness will be minimum in the beginning and maximum at the end in the case of up -milling. Whereas, the chip thickness will be greater in the beginning and lesser at the end in the case of down-milling.

Tool Life will is more in the case of down-milling as compared with the up-milling.

The surface finish will be more in the case of the down-milling as compared with the up-milling method due to which down-milling method is used for the finishing operations in the industries.

Accuracy will be more in the case of up-milling as compared with the down-milling process since in up-milling the workpiece is pulled against the table so the fasteners will be under tension and we know that under tension the backlash error will not have any effect which ultimately results in the better accuracy in up-milling.

Advantages of Milling Machine:

The various advantages of Milling are:

·         High speed

·         Better surface finish

·         Increase productivity

·         High accuracy

 

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