What Is Milling Machine?
A milling machine is a tool primarily found in the metalworking industry. Milling machines are equipment designed to machine metal, wood, and other solid materials. Often automated, milling machines can be mounted in either a vertical or horizontal orientation to carve the material, depending on a pre-existing design.
In general, this machine is used to shape solid products by removing excess material to form a finished product. Millings machines can be used for a variety of complex cutting tasks – from slot cutting, threading, and rabbeting to routing, planning & drillings.
They are also used in die the sinking, which involves shaping steels block so that they can be used for various tasks, such the moldings, plastics, or coins. This machine can hold more than one device at a time. The cutter spins at high speed, and because of the many cutting edges, it removes metal at a very high rate.
Machines can also hold one or more cutters at a time. Thus, the milling machine is one of the most important machines in the workshop. All the operations can be done in this machine with high accuracy. The metal removal rate is higher as compared to lathe machines, planer machines, and shaper machines. It has good accuracy and a superior surface finish. That is why a milling machine finds wide application in production work.
How Does a Milling Machine Work?
The milling machines were developed backs in the 18th century. Its predecessor models were used to make smaller gears inside watches. A few years later, manufacturers started making for the metal sector. Earlier models are specifically designed to rely heavily on the precision and accuracy of the machinist. In contrast, the latest or CNC mills are run by computers programs or algorithms.
Firsts glances, you might mistake it for a circular saw, which only cuts the material into smaller parts. However, upon closer inspections, you can see that it cuts a workpiece into a specific shape.
It can also carve flat surfaces, smooth edges, and drill holes with threading depending on the type of attachment used. A fast rotating milling or cutting attachment removes parts of the workpiece. The machinist feeds the stock into equipment to produce the desired result.
Main Parts of Milling Machine:
#1. Column and Base
Columns, including the base, are the main casting that supports all other parts of the milling machine.
- The column consists of an oil reservoir and a pump that lubricates the spindle.
- The column rests on the base, and the base contains a coolant reservoir and a pump that is used during machining operations that require coolants.
It is castings that support the saddle & table. All gearing mechanisms are enclosed within the knee.
- It is tied in a dovetail manner in a column.
- The knee is supported & adjusted by verticals positioning screws (lifting screws).
- The lifting screw is used to adjust the knee up and down by raising or lowering the lever, either by hand or by power feed.
#3. Saddle and Swivel Table
The saddle is present at the knee and supports the table. It slides on a horizontal dovetail at the knee and parallel to the axis of the dovetail spindle (in horizontal milling m/c).
- The swivel table (only in universal machines) is attached to the saddle, which can be rotated horizontally in any direction.
#4. Power Feed Mechanism
It is the knee that contains the power feed mechanism. It is used to control longitudinal (left and right), transverse (in and out) and vertical (up and down) feeds.
- To achieve the desired feed rate on machines, the feed selection lever is placed as indicated on the feed selections plates.
- On some universal knee & columns milling machines, feed is achieved by rotating the speed selection handle until the desired feed rate is indicated on the feed dial.
- Most milling machines have a fast traverse lever that can be fitted when a temporary increase in longitudinal, transverse, or vertical feed speed is required. For example, this lever will be engaged when the operator is performing a work position or alignment.
It is a rectangular casting that is present at the top of the saddle.
- It is used to hold work or work-bearing equipment.
- It has multiple T-slots for holding work & work holding devices (i.e., jigs & fixtures).
- Tables can be operated by hand or by electricity. To move the tables by hand, engage & turn the longitudinal hand crank. To move it through the power, engage the longitudinal directions to feed the controls lever.
It is shafted that is used to hold and drive the cutting tool of the milling machine.
- The spindle is mounted on the bearings & supported by the column.
- Spindle driven by electric motors through gear trains. Gear trains are present within the column.
- An internal taper is machined at the face of the spindle near the table. The internal taper at the front of the spindle allows only a tapered cutter holder or arbor. It has two keys on the front that provide a positive drive for the cutter holder or arbor.
- A drawbolt and a jam nut are used to secure the holder and arbor to the spindle.
#7. Over Arm / Overhanging Arm
It is a horizontal beam located at the top of the column. It may be a single casting that slides over the dovetail ways on the top face of the column.
- The overarm is used to fasten the arbor support. It may have one or two cylindrical rods that pass through the holes of the column.
#8. Arbour Support
It is a casting with a bearing that supports the outer end of the arbor. It also helps to align the outers end of the arch with the axle.
- It prevents the springing of the outer edge of the arbor during cutting operations.
- Two types of arbor supports are commonly used in milling machines. The first one has a smaller diameter bearing hole, with a maximum diameter of 1 inch. And the other has a hole with a larger diameter, usually up to 23/4 inch.
- The arbor support contains oil reservoirs that lubricate the bearings surfaces. It can be clamped anywhere on the over arms. Arbor supports used only in horizontal-type milling machines.
The hanging arm in vertical machines is called ram. One end of the rams is mounted on the top of the column, and the other end is fitted with a milling head.
Working Principle of Milling Machine:
The working principle of the milling machines is applied in the metal removal operation on the milling machine. The work is rigidly clamped to the machine table, and the rotating multi-tooth cutter is mounted on either spindle.
The cutter rotates at a normal speed, and the work gradually overtakes the cutter. The work can be fed longitudinally, vertically, or in a cross direction. As the work progresses, the cutter teeth remove the metal from the works surfaces to produce the desired shapes.
Also, Read: Simple Indexing in Milling Machine
Size of Milling Machine:
The size of the millings machines is determined by the dimensions of the maximum lengths of the longitudinal, cross, & vertical travel of the table & also the working surface of the machine.
In addition to the above dimensions, the number of spindle speeds, number of feeds, available power, spindle nose taper, net weight, and required floor space, etc. Consideration should also be given to specifying the machine as a whole.
Types of Milling Machine:
#1. Vertical Milling Machine
In vertical milling machines, the spindle is positioned vertically or vertically on the table. A vertical milling machine is used for machining grooves, slots, etc. They are also used for flat surfaces. The spindle head of the vertical milling machine is fixed with a vertical column, and the vertical column rotates at an angle.
For working with angular surfaces, a milling cutter is mounted on the spindles. In some vertical milling machines, spindles can be adjusted up & down. These machines are equipped with a precision tool that is used to form and shape the workpiece by removing the stock from the metal workpiece. Depending on the material and equipment, plastics and other material is also machined.
The Milling machines can be computer numerical controlled, manually controlled, or combinations of manual and CNC. A rotary cutter is used in the spindle to remove the material of the milling machine.
Because of the vertical spindle movement and movable table cutting options, this machine is more complex than a drill press. Some vertical milling machines have a turret that is rotatable for the upper cutting head, which improves machining options.
Applications for which verticals milling machines are used:
1.1. Boring or Drilling:
Vertical milling machines provide the means to machine holes and accurately index.
1.2. Accurate Cuts:
Keyway slots, slotting, keyway, or flat are cut with the help of vertical milling machines with precise fixings.
In this operation, spots or a flat surface are provided on the workpiece. The facing operation is typically used for workpieces that are irregularly shaped.
#2. Plain or Horizontal Milling Machine
Plain or horizontal milling machines are stronger than hand millers. In horizontal milling machines, the spindle is horizontal. The cutting tools are mounted on spindles that are oriented horizontally, as in the case of a horizontal milling machine which enables them to remove material from the workpiece, which is stationary.
They offer different cutting tools than vertical milling machines. Their design is very similar to each other. Rotating cutting tools are present in the spindle in a horizontal milling machine. The workpiece is pressed to remove the material from the workpiece.
Plain or horizontal milling machines differ from vertical milling machines in several ways. One of the major differences between them is the axis orientation.
In the case of vertical milling machines, the spindle is provided with a vertical orientation, whereas in horizontal milling machines, there are horizontal orientations to the spindle.
#3. Duplex Milling Machine
A duplex milling machines are basically a combination of two machines that are placed opposite to each other. They work separately. When the workpiece is machined with two spindles, they work as a milling machine. The spindle of a duplex milling machine can rotate in both vertical and horizontal directions.
The major advantages of duplex milling machines are:
- Duplex milling machines increase production by up to 50 percent compared to other milling machines.
- The precision is highly improved in these machines.
- Duplexes milling machines can be controlled with the help of a single operator.
- The investment requirement and space are reduced as compared to 2 single milling machines.
- Duplexes milling machines have different configurations such as pendulum work zones, single work zones, or pallet changing systems.
- The high productivity of duplex milling machines can result in faster investment amortization.
#4. Universal Milling Machine
In a universal milling machine, there is a table equipped with all split heads and motions (with changes in gears). Therefore it can carry out a variety of milling operations. Universal milling machines are used to perform many tasks.
The table is rotated from the normal position at an angle of 45 degrees from both sides. The table of horizontal milling machines can be moved in three directions. Helical milling work is also done by this machine. Additional attachments are used to increase the capacity of the machine.
The special attachments used are:
- Rotary Attachment
- Slotting Attachment
- Dividing Head or Index Head
- Vertical Milling Attachment
Universal milling machines produce reamers, milling cutters, spirals, twist drills, spurs, bevels, etc. The operations performed by shaper machines can be performed by universal milling machines.
#5. Simplex Milling Machine
In these milling machines, the spindle head or spindle can travel in only one direction. The vertical direction is a very common direction in which the simplex milling machine can operate.
Simplex milling machines have the flatness of milled surfaces & excellent surface finish, stable milling, high productivity, high tool life, and low maintenance.
#6. CNC Milling Machine
CNC Milling Machine is also known as Computer Numerical Control Milling Machine. They have computerized the controls for the machining process.
Cutting tools use multipoint rotations to sequentially remove material from the workpiece resulting in the production of custom-designed products or parts. (Types of CNC Machine)
A computer numerical control milling machine consists of a rotating cylindrical cutter that moves along several axes and creates holes, slots, and wide material to turn it into a mechanical part or vehicle. Different machines operate with three to five axes which provide greater detail and accuracy.
Modern computer numerical control milling machine has both vertical and horizontal machining centers. The components of a CNC milling machine are made of materials such as ceramics, plastics, and composite metal materials. Tool magazine and carousel, automatic tool changer, enclosure, and coolant system are technical features of CNC milling machine.
#7. Triplex Milling Machine
In triple milling machines, the spindle of the machines moves in three directions which are the x-axis, y-axis, and z-axis. Triplex milling machines are very precise as well as highly productive. Triplex Milling Machines are suitable for applications that are based on the accuracy required by the customers.
#8. Drum Milling Machine
These machines are used in production work. Drum milling machines have a vertical central drum that is rotated on a horizontal axis like a ferry wheel. Face mill type cutters are provided.
The finishing and roughing cutters provided in a drum milling machine are similar to a rotary-table miller. The fixture rotates slowly, which works against the rotating cutter in the operation of drum milling machines. Typically three or four cutter spindles are provided.
Operation is continued after the machined parts are removed, and new ones are added at the end of the work cycle. Drum milling machines are commonly used in industrial operations. (type of milling machine)
#9. Bed Type Milling Machine
In the case of bed-type milling machines, the worktable is placed on the bed. To allow longitudinal motion in a bed-type milling machine, the knee is omitted.
#10. Rotary Table Milling Machine
Rotary tables milling machines have the ability to perform up to 2D and 2.5D machine cycles at or around the end of the cylinder. When the machine is being operated in the radial direction, the motion in parallel or parallel to the rotary axis is restricted.
Rotary table milling machines are oriented radially along the centerline of the rotary axis. They have a circular table that can rotate along a vertical axis. In this milling machine, many cutters have to be installed at different heights.
One cutter of the machine is used to rough the workpiece, while the rest is used to finish the surface. When the machine is working, the operator can unload and load the workpiece continuously, and this is the major advantage of using a rotary table milling machine.
#11. Tracer Controlled Milling Machine
These milling machines have tools that have the ability to copy with tracer control hence the reproduction of the car or the copying of interior and exterior geometry in two dimensions.
This machine is used for machining grooves, cams, contour surfaces, etc. (type of milling machine)
They are the perfect machine for reproducing irregular and complex shaped dyes and trace elements.
Some tracer-controlled milling machines have servo mechanism arrangements, and this mechanism is complex. Processes that involve machining cavities such as die-sinking take place on three-dimension duplicators or profilers.
#12. Column Milling Machine
Column milling machines are commonly used for making car parts. This machine is the simplest type of milling machine. They have five major parts, which are the head, the working table, the knee, and the saddle. This machine uses a drill that is suspended vertically.
#13. Turret Milling Machine
These machines are very versatile machines & are generally used to make a wide variety of parts. Turret milling machines are also called Bridgeport-type milling machines and have recessed openings and have a wider range of uses.
#14. C-Frame Milling Machine
These machines are strong and powerful. C-frames milling machine uses hydraulic motor for its working. They are ideal for industrial use.
C-frame milling machines are designed to produce duplicate parts based on the master model. Tracer-controlled milling machines are typically used for contouring surfaces and machining grooves.
Milling Machine Operation:
The different milling machine operation is:
#1. Face Milling
This operation creates a flat surface on the face of the workpiece. This machining operation is performed on surfaces that are perpendicular to the axis of the cutter. The operation is done by a face milling cutter mounted on the stub arbor of the machine.
#2. Side Milling
It is the machining process that produces flat vertical surfaces at the edges of the workpiece. This operation is performed using side milling cutters.
#3. Plain Milling
It is a process of joining flat surfaces with the cutter axis parallel to the surface. It is also called surfaces milling or slab milling. Plain milling cutters are used for plane milling.
#4. Straddle Milling
It is a process in which two sides millings cutters are used to simultaneously machine two opposite sides of a workpiece. The straddles milling operations are shown in the figure below.
#5. Angular Milling
It is a process of milling flats surfaces that are neither parallel nor perpendicular to the axis of the milling cutter. It is also called angle milling. Single-angle milling cutters are used to perform this operation.
#6. Gang Milling
Thy is machinings processes in which two or more milling cutters are used together to perform different milling operations simultaneously. In gang milling, the cutter is mounted on the arbor.
#7. Form milling
It is the process of special machining contours made up of curves, straight lines, or complete curves on a single cut. To perform this operation, a milling cutter made in the shape of the cut contour is used. This operation is accomplished using convex, concave & corner rounding milling cutters.
#8. Profile Milling:
These millings operations are used to cut a profile on workpieces.
#9. End Milling
It is the process of producing flats surfaces that can be workable at horizontal, vertical, and at any angle, taking as reference. An end milling cutter is used to accomplish this operation.
#10. Saw Milling
It is the machining process used to create narrow grooves or slots on a workpiece.
- It is also used to divide the workpiece into two equal or unequal parts.
- This milling operation is performed using a jigsaw milling cutter.
- The width of this cutter is much less than the width of the workpiece.
#11. Milling Key Methods, Grooves, and Slots
This milling operation is used to create keyways, grooves, and slots on the workpiece.
#12. Gear Milling
This is the milling process used to cut gears on the workpiece. This operation is performed by using a formed milling cutter called involute gear cutter.
#13. Helical Milling
This milling operation is performed for the production of helical design items such as helical gears, twisted drills, etc. This is done on the periphery of the cylindrical workpiece.
#14. Cam Milling
It is a machining process used to make cams. Cams are used to open and close valves in internal combustions engines.
#15. Thread Milling
It is a process of milling used to cuts threads on cylindrical workpieces. It’s all about milling machine-operation parts & types.
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