What is Milling Machine?
The milling machines are also known as the multi-tasking machines (MTMs) which are multi-purpose machines capable of milling and turning the materials as well. The milling machine has got the cutter installed up on it which helps in removing the material from the surface of the work piece.
Definition of Milling Machine
Milling is a process performed with a machine in which the cutters rotate to remove material from the workpiece that is angled along the axis of the tool. With the help of milling machines, many operations and tasks can be done from small objects to large ones.
Milling machining is one of the very common manufacturing processes used in machinery shops and industries to manufacture high precision products and in various shapes and sizes.
Parts of Milling Machine
1) Column and Base
The column is another foundation part of the milling machine. It is a mountain vertically on the base. It supports the knee, table, etc. Work as housing for all the other driving members. It is a hollow member consisting of a driving gear and sometimes a motor for the axle and table. The column has an oil repository and pump to lubricate the axles.
The knee is the first moving part of the milling machine. The saddle and table support casting. The gearing device is included within the knee. The knee is fastened to the pillar by Dowell’s methods. It is maintained and improved by a vertical positioning screw, also recognized as an elevating screw. Elevating screw is used to adjust the knee up and down by moving the lever up or down with the help of a hand or power feed.
3) Saddle and Swivel Table
The saddle is at the knee and supports the table. The saddle slides on the horizontal dovetail on the knee and the dovetail is parallel to the axis of the axis. A swivel table is attached to the saddle which rotates horizontally in both directions.
4) Power Feed mechanism
The power feed mechanism is in the knee. The power feed mechanism is used to control longitudinal, transverse, and vertical feeds. For the desired rate of feed on the machine, the feed selection lever is positioned to point at the feed selection plates. For any column milling machine and universal knee, feed is obtained by turning on the speed selection handle until the rate of feed selection is shown on the dial.
Almost every milling machine, there is a quick-moving lever, which is applied when a temporary boost in longitudinal, transverse, or vertical feed speed is required. This lever is applied when the operator is arranging or positioning the work.
The table is a rectangular casting that is present at the top of the saddle. The table is used to hold a task or for task holding devices. There are several T-slots to hold the work and hold the equipment. It can be performed by hand or by power. To move the table by hand, turn and rotate the longitudinal arm crank. For gait, it feeds the control lever by force, attached, and longitudinal direction.
It is placed between the table and the knee and acts as an intermediate part between them. This column can move transversely on the face. It slides on guide ways that are located at the knee that are perpendicular to the face of the column. Its main function is to move the work piece in a horizontal direction. It is also made of cast iron.
7) Over Arm / Overhanging Arm
It is an overhang on the surface of the column and the other end supports the arbor. It can be a single casting and slide that is at the top of the column in a dowel manner. It is located above the column on a horizontal milling machine. It is made of cast iron.
8) Arbor Support
The arbor support is casting with a bearing that supports the outer end of the arbor. It also helps align the outer end of the arbor with the axle. Arbor support prevents springing of the outer end of the arbor in a cutting operation. Typically, two types of arbor support are used in milling machines. The first one has a small diameter bearing hole with a maximum diameter of 1 inch. The second has a large diameter hole of up to 23/4 inches.
Rams serve as the overhanding arm in a vertical milling machine. One end of the ram is placed on top of the pillar and the milling head is attached to the other. One end of the arm is attached to the pillar and the other end is attached to the milling head.
Types of Milling Machine
Some of the main types of milling machines are as under:
- Horizontal or Plain Milling Machine
- Vertical Milling Machine
- Universal Milling Machine
- Simplex Milling Machine
- Duplex Milling Machine
- Triplex Milling Machine
- Rotary Table Milling Machine
- Tracer Controlled Milling Machine
- CNC Milling Machine
- Drum Milling Machine
Horizontal or Plain Milling Machine
Plain milling machines are more robust than hand millers. The plain milling machines that have a horizontal spindle are also called horizontal milling machines. You can feed the table in vertical, cross, or horizontal directions.
In other words, horizontal milling machines mount the cutting tool on a horizontally oriented spindle that’s able to selectively remove material from the stationary workpiece. Furthermore, horizontal milling machines usually feature different cutting tools than vertical milling machines.
Horizontal milling machines feature a similar design in which a spindle containing a rotating cutting tool presses against a workpiece to remove material from the workpiece. With that said, horizontal milling machines differ from their vertical counterparts in several ways.
The biggest difference between these two types of milling machines is the orientation of the spindle. With vertical milling machines, the spindle features a vertical orientation. With horizontal milling machines, the spindle features a horizontal orientation. The feed includes:
- Verticle – adjusts the table vertically.
- Cross – moves the table parallel to the spindle.
- Longitudinal – rotates the table
Vertical Milling Machine
The position of the spindle on a vertical milling machine is perpendicular or vertical to the table. You can use this machine for slots, machining grooves, and flat surfaces. The spindle head is fixed to a vertical column, which rotates at an angle. The milling cutter is fixed on the spindle to work with angular surfaces. In some vertical milling machines, you can adjust the spindle up and down.
The vertical milling machine is a precision tool used for shaping and fabrication by the removal of stock typically from metallic work pieces. Plastics and other materials can also be machined on the mill depending upon tooling and material.
Mill controls may be manually operated, computer numerical controlled (CNC), or a combination of both. Mill machining and material removal are typically made by a rotary cutter held in a spindle.
Cutting options are more sophisticated and variable than a drill press by virtue of a moveable table and/or vise (x and y-axes) and vertical spindle movement (z-axis). Many vertical mills also have a rotatable turret for the upper cutting head which provides even greater machining options (b-axis).
A diagram is included in this procedure to help illustrate the varying axes. Some of the common operations that can be performed on the mill include:
- Milling: These operations provide a flat surface or spot on a workpiece, typically with a specific orientation to other workpiece features, surfaces, or another piece. Facing is sometimes used on an irregularly shaped workpiece to “true” one surface at a time to ensure that all surfaces have appropriate specific geometric relationships with each other.
- Slotting or keyways Slots, flats, or keyways can be cut with proper fixturing.
- Drilling or boring Where specific orientations are required between workpiece features, the vertical mill provides the means to accurately index and machine holes.
Universal Milling Machine
Universal Milling Machine is a milling machine having a table fitted with all motions and a dividing head with change gears so that it can perform any type of milling operation.
Universal milling machines can adapt to perform a wide range of operations. The table can pivot at any angle for up to 45-degrees on both sides from the normal position. As the table of the horizontal milling machine can move in three directions, it also boasts the fourth movement. This machine can also perform helical milling operations. You can also use additional attachments to increase the capacity of the machine. Some special attachments include:
- Slotting attachment
- Rotary attachment
- Vertical milling attachment
- Index head or dividing head
You can produce a milling cutter, reamer, twist drill, spiral, bevel, spur, and much more from this machine. You can perform all the operations that a shaper machine does with the universal milling machine.
Simplex Milling Machine
The spindle or the spindle head can travel in one direction only. The most common direction in which it can move is vertical.
- Stable Milling
- Excellent Surface Finish and Flatness of Milled Surfaces.
- High tool life, high productivity & low maintenance.
Duplex Milling Machine
Duplex milling machines are two machines located one opposite the other, which can work separately or as a single milling machine, when workpiece can be machined with 2 simultaneous spindles. The spindle can move in both horizontal and vertical directions.
Main advantages of duplex solution:
- Production increase of up to 50% in relation to conventional solutions, i.e. individual milling machines
- Improvements in part precision, by managing to do the machining of the part in one single setup, in most of the cases
- One sole operator can control the DUPLEX milling machines
- Reduced space and investment requirement comparing with two single machines
- Fast investment amortization due to the high productivity
- Duplex solution admits different configurations: single working area, pendulum working areas, or pallet changing system
Triplex Milling Machine
The spindle can move in all three directions i.e. X Y and Z axis.
- Special application based on the customer’s requirements of related accuracies.
- Highly productive and accurate.
Rotary Table Milling Machine
Rotary Milling is the ability to perform 2D and 2.5D machining cycles around or on the end of a cylinder. When performing radial machining (around the cylinder), the tool is restricted to moving parallel to and around the rotary axis. The tool is always oriented radially to the centreline of the rotary axis.
The rotary table milling machine consists of a circular table that rotates in a vertical axis. You need to set multiple cutters at different heights. The machine works with one cutter roughing up the workpiece, and the rest of the cutters finishing the surface. The operator can load and unload the workpieces continuously while the machine is working, and that is the most significant advantage of the rotary table milling machine.
Tracer Controlled Milling Machine
Tracer-controlled milling machines are equipped with copying capabilities through tracer control, and hence car reproduces or duplicates external or internal geometries in two dimensions. Tracer controlled milling machines are used for machining cams, grooves, contoured surfaces, etc.
This machine is perfect for tracing the elements and reproducing dies with complex and irregular shapes. The stylus energizes the oil relay system, operating the primary hydraulic system of the table. This type of arrangement is called servomechanism and is complicated.
Tracer controlled milling machines are used for machining cams, grooves, contoured surfaces etc. Die sinking and other processes involving the machining of cavities can be done on three-dimension profilers or duplicators.
CNC Milling Machine
CNC milling, or computer numerical control milling, is a machining process that employs computerized controls and rotating multipoint cutting tools to progressively remove material from the workpiece and produce a custom-designed part or product.
A CNC Milling Machine uses a rotating cylindrical cutter to move along multiple axes, and create slots, holes, and details in material to turn it into a vehicle or mechanical part. Most machines operate on three to five axes, creating much more precision and detail.
Modern CNC milling machines are assembled as both horizontal and vertical machining centers. Components can be made with materials such as plastics, ceramics, and composite materials, in addition to metals.
Technical features include automatic tool changers, tool carousels & magazines, coolant systems, and enclosures to keep machines running smoothly on their own without manual interference.
Drum Milling Machine
Drum milling machines are used for production work only. This type of machine has a vertical central drum which rotates on a horizontal axis much like a Ferry’s wheel. The cutters are of face mill type and usually both roughening and finishing cutters similar to those of a rotary-table miller are employed.
In operation, the drum- fixture rotates slowly, carrying the work against the rotating cutters. Usually there are four cutter spindles. The operation is continuous, since machined parts are removed and new ones added after the work has completed its cycle. Automobile cylinder heads and small shafts are milled on this machine.
Advantages of Milling Machine
The following advantages of Milling machine, they are:
- The size and durable construction of the milling machine give tremendous support to handle large and heavier machines without damaging itself.
- It provides flexible computer control options for cutting purposes.
- It reduces the chances of human errors.
- It assures accurate cuts.
- Availability of customization.
- Use of multiple cutters.
- It can do multiple cuts simultaneously.
- Milling is perfect for producing individual pieces in small or large batches.
- It has the capability of producing complicated shapes, using multi-tooth and single point cutting tools.
- The operation costs can be controlled to a great extent if general-purpose cutters and equipment are used.
- Greater precision in the finishing of the work compared to other machines..
Disadvantages of Milling machine
These are the following disadvantages of milling machine:
- It is more expensive than casting, cold forming, extrusion, etc. If these processes can provide the required flatness, surface finish, and dimensional accuracy for the part.
- For mass production, it becomes economically necessary to use special-purpose machines.
- They can cost millions of dollars but the cost is justified when handling labor which is virtually eliminated and machining accuracy and repetition are ensured.
Application of Milling machine
Milling machines are very versatile. They are usually used to machine flat surfaces, but can also produce irregular surfaces. They can also be used to drill, bore, cut gears, and produce slots. The type of milling machine most commonly found in student shops is a vertical spindle machine with a swiveling head. These milling machines have the following applications:
- This machine is used to make gears.
- Typically used for a machined flat surface, but can also produce irregular surfaces.
- Used to produce a drain or slot.
- The modern mill machine cut supra-alloys, titanium, ductile steel to closer tolerances, greater accuracy, and faster rate.
- This machine is used to design metals and other materials.