A milling machine is one the important machines needed in a machine shop as it serves various purposes in the manufacturing process. it is the process of machining using a rotary cutter to remove material by advancing a cutter into a workpiece. It may be performed in a varying direction on one or several axes, depending on cutter head speed and pressure.
Milling machines can perform different operations, from small individual parts to large ones. They are also suitable for heavy-duty gang milling operations and ideal for machining custom parts to precise tolerances. Well, in this reading, we’ll explore what a milling machine is, its applications, parts, diagrams, types, operations, and how it works. You’ll also learn the advantages and disadvantages of milling.
Let’s get started!
What is Milling Machine?
The milling machine as a tool used in industrial workshops offers numerous functions in different operations. These machines contain a cutter that is controlled at a specific speed range in order to create the desired shape. Due to the adjustable speed, generally, milling machines can be controlled for more precise cuts. these machines can handle multiple tanks such as carving, threading, milling, drilling, and cutting.
A milling machine is a device that rotates a circular tool with symmetrical cutting edges around its axis, holding the workpiece in a vise or similar device. These machines are used for machining solid materials like metal, plastic, and wood, and are commonly used to machine irregular and flat surfaces.
Milling machines are powered tools designed to mill or carve material, using various cutting tools such as rotating blades, drills, and abrasives.
The best mills feature high-quality cast iron construction, variable speed engines, power feeds, and cutting tools that move along the x- and y-axis. They are used in various roles from woodworking to metalworking. Milling machines can have self-contained electric drive motors, coolant systems, digital readouts, variable spindle speeds, and power-operated table feeds.
Applications
Below are the applications of milling machine:
- Milling machines are widely used in making gears.
- It is used to produce grooves and slots.
- Milling machines are used to design metal and some other materials.
- Flat and irregular surfaces can be machined on a milling machine.
- Modern milling machines are used to cut super-alloys, titanium, and tensile steel to closer tolerance, greater accuracy, and faster rate of production.
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Components of Milling Machine
The major parts of milling machines include base, column, knee, saddle, table, overhanging arm, spindle, arbor, arbor supports, milling head and ram.
Base
This milling machine part is the foundation of milling that carries the weight of the machine and moves it to the ground. All component is mounted on the base. This base is made of cast iron due to its high compressive strength.
Column
The column is vertically mounted on the base as its supports the knee, table, etc. It also works as housing for all the other driving members. This column is a hollow member that contains driving gears and sometimes motors for the spindle and the spindle and the table.
Knee
The knee is a cast iron that supports the saddle and table as its enclosed all-gear mechanism. It is attached to the column in a dovetail way. The knee is designed to be adjusted by a vertical positioning screw (elevating screw). This screw helps to adjust the knee up and down by raising or lowering the lever either by a power feed or by hand.
Saddle
This machine part is located between the table and the knee as it serves as an intermediate part between them. This move transversely to the face of a column which is to provide motion in the horizontal direction to the workpiece. It is also made of cast iron.
Table
The table is situated over the knee in order to hold the workpiece during the process. it is made of cast iron and has a t-slot cut on it. This provides vertical motion by moving the knee up and down and provides horizontal motion by the feed screw provided by the saddle.
Overhanging arm
The milling machine component is used to fasten the arbor support. It may consist of one or two cylindrical bars that slide through the holes in the column. It is also made with cast iron.
Spindle
The spindle is the part of the machine which holds the tool in place, this spindle offers rotary motion and drives for arbors, cutters, and attachments used on the machine.
Arbor
The arbor serves as an extension part of the spindle in a horizontal mill machine. It is fitted to the spindle whenever it’s needed. The arbor holds the tool and moves it in the correct direction.
Arbor supports
Milling machines generally have two types of arbor supports, the first one has a small diameter bearing hole, 1-inch in maximum diameter, and the second one has a large diameter bearing hole of about 23/4 inches. This milling part contains an oil reservoir that aids the lubrication of the bearing surfaces. This arbor support is used only in the horizontal types of milling machines and it’s clamped anywhere on the overarm.
Milling head
The milling head is the upper part of a vertical mill machine. It consists of a spindle, driving motor, and other controlling mechanisms.
Ram
The milling machine part can move transversely (in and out) on the column by a hand level. One end of the arm is attached to the column and the other ends on the milling head.
Diagram
Types of Milling Machine
Below are the various types of milling machines:
Column and Knee
This machine has 5 basic components just like some other types which include, a table, saddle, head, knee, and overarm. It is one of the simplest and most common. Its cutting device is vertically suspended on the workpiece causing it to drill. It is mostly used when creating car parts because it is portable and handy.
It consists of a vertical column attached to the bed that contains all gear drives that rotate the knee and saddle. The knee which is situated on the base provides vertical motion to the workpiece, making it moves up and down. Also, the saddle is attached to the upper section of the knee which moves in the transverse direction. Finally, the table is placed over, which holds the workpiece with the use of climbing bolts.
Vertical Milling Machine
In vertical types of milling machines, the spindle is positioned vertically and no arbor is required. The cutting tool is in a cylindrical shape and the cutting edges are at the circumference of the cylindrical face Vertical mills use a rotating cutting tool resembling a drilling machine or drill press, with a tool head speed ranging from 500 to 50,000 RPM.
Horizontal Milling Machine
In this situation, the spindle is situated horizontally and rotates at a horizontal position. Unlike the vertical type, an arbor is used, which helps to hold the cylindrical disk shape cutter that aids the cutting of the metal workpiece. Horizontal milling machines function similarly to vertical mills but use a rotating table instead of a gantry and a three- or four-pointed main cutter. Cutting speeds for these mills can be as fast as 20,000 RPM.
Universal Milling Machine
The universal types of milling machines are much similar to the horizontal type, except for the arrangement of the swing-up table to 45 degrees in either direction.
Fixed Bed Milling Machine
in this type, the bed is fixed to the machine and there is no arrangement of the knee and saddle that moves vertically and transversally. The worktable is directly attached to the fixed bed and the spindle is mounted on a movable spindle head. Finally, this machine can move in vertical and horizontal directions when cutting.
Turret
The turret is also called the Bridgeport milling machine. Its functionality is advanced as different products can be produced as well as car parts and repositioning can be easily achieved.
C-frame
This machine is sturdier than the turret type. It is mostly found in industrial settings and it is controlled hydraulically, making it very powerful.
Simplex Milling Machine
in this machine, the spindle head or the spindle travels only in one direction, but mostly in the vertical direction
Duplex Milling Machine
In this type, the spindle travels both vertical and horizontal directions.
Triplex Milling Machine
In the triplex type, the spindle moves in all three directions along X, Y, and Z-axis.
Planner Milling Machine
The types of milling machines are widely used for facing operations in mass production. It is similar to the bed type only that it can be mounted on different cutters and spindle heads. Facing operations can be simultaneously performed on this machine making it a great option.
Special Milling Machine
This is one of the modern types of milling machines, which are manufactured for easy milling operations according to the type of jobs.
Tracer Milling Machine
This machine is used to perform complicated operations like, die making the job by synchronizing the tracing unit and can develop any difficult shape. Tracer milling machines are often found in the automobile and aerospace industries.
CNC Milling Machine
The CNC is the most versatile milling machine which is controlled by a computer. It is an upgraded version of the bed type of milling machine, as the spindle also moves in all three directions and the table rotates at 360 degrees. The movement is controlled hydraulically, which is controlled as the computer commands. CNCs are ideal for difficult geometrical objects.
Milling Operations
Below are the various kinds of milling operations:
Plain Milling
Plain milling is a common operation in milling machines, where the axis of the cutter is parallel to the surface being milled. This operation, also known as slab milling, produces a flat, horizontal surface parallel to the axis of rotation of a plain milling cutter. The work and cutter are secured on the machine, and the depth of cut is set by rotating the vertical feed screw. The machine is started after selecting the right speed and feed.
This is when trying to create a plain, flat, horizontal surface parallel to the axis of rotation. It is also known as slab milling. Plain milling is very common and performed in almost all projects and all milling machines can perform this operation.
Face Milling
A face milling operation is a fundamental part of milling, involving a cutter mounted on a stub arbor. This operation creates a flat surface at the workpiece’s face, perpendicular to the cutter’s axis. This operation is the simplest in milling machines, allowing the cutter to rotate about an axis perpendicular to the work surfaces. The depth of the cut is adjusted by rotating the cross-feed screw of the table.
It is performed on surfaces that are perpendicular to the axis of the cutter. Its operation is achieved by a milling cutter mounted on the stub arbor of the machine.
Side Milling
The operation of side milling involves using a cutter to create flat vertical surfaces on the side of a workpiece. The depth of cut is set by rotating the vertical feed screw of the table, ensuring accurate and efficient milling.
This milling machine operation is used to produce a flat vertical surface on the sides of the workpiece by using a side milling cutter. This cutter has teeth on its face as well as its side.
End Milling
End milling is a process that produces a flat surface that can be horizontal, vertical, or at any angle, using cutters like end mills. This process is suitable for producing slots, grooves, or keyways, and is performed using a vertical milling machine. The cutters are used to create a flat surface that can be referenced to the worktable.
Gang Milling
Gang milling is a machining process where multiple milling cutters are mounted on an arbor to perform multiple operations simultaneously. This method saves time and is commonly used in repetitive work. The cutting speed of a gang of cutters is calculated from the cutter with the largest diameter, allowing for efficient and accurate machining of multiple surfaces of a workpiece.
Form Milling
Form milling is a process used to create irregular contours, such as curves or straight lines, using convex, concave, or corner rounding milling cutters. It produces irregular shapes, such as convex or concave, and is inspected by a template gauge after machining. The cutting rate for form milling is 20%-30% lower than plain milling.
Grooves Milling
This process helps in producing grooves on the surface of the workpiece with the use of a saw-milling cutter or end-milling cutter. It is achieved by fixing the workpiece on the milling machine and fixing the end milling cutter on an arbor which enables adjustment for the cutting depth. The work is fed against the cutter to cut the groove on the work surface.
T-slot Milling
The T-slot milling is done by using a T-slot milling cutter on the workpiece.
Gear-Cutting
The milling process involves cutting gears on a workpiece using involute gear cutters. A form-relieved cutter, either cylindrical or end mill type, is used in a milling machine. The cutter profile fits the tooth space of the gear, and equally spaced gear teeth are cut on a gear blank by holding the work on a universal diving head and indexing it.
Straddle Milling
The straddle types of milling operations are operations carried out on both sides of a workpiece, creating a flat vertical surface. This is achieved by using two side milling cutters mounted on the same arbor, which is adjusted using a spacing collar. This operation is used to produce hexagonal or square surfaces.
Helical Milling
Helical milling is a process used to create helical-shaped objects like helical gears and twisted drills on the periphery of a cylindrical workpiece. It involves rotating the table to the required helix angle and feeding the workpiece against rotary cutting edges of a milling cutter. This process can be performed on a drill blank or a reamer.
Thread Milling
Thread milling is a process used in special machines to produce precise threads in small or large quantities. It involves using a single or multiple cutters and requires three driving motions: one for the cutter, one for the work, and the third for the longitudinal movement of the cutter.
Cam Milling
Cams are made using this milling process. The IC engines’ valves are opened and closed by means of these cams.
Groove and Slot Milling
This is a process used to create keyways, grooves, and slots on a workpiece. This can be done using various tools such as a plain milling cutter, a metal slitting saw, an end mill, or a side milling cutter. Open slots can be cut using these tools, while closed slots are created using endmills.
Special cutters are used to create dovetail slots or T-slots, while the second slot is cut at right angles to the first slot. Woodruff keys are designed using woodruff key slot cutters. Standard keyways are cut on the shaft using side milling cutters or end mills, set at the workpiece’s centerline.
Angular Milling
Angular milling, also known as angle milling, is a process used to create flat surfaces that are neither parallel nor perpendicular to the milling cutter’s axis. This operation involves using a single-angle milling cutter to create an angular surface on a workpiece, which can be single or double angle and varies in included angle depending on the cutter type and contour. An example of angular milling is the production of V-blocks.
Profile Milling
Profile milling is a process that reproduces the outline of a template or complex shape of a master die on a workpiece, using various cutters, with an end mill being a widely used milling cutter in profile milling work.
Saw Milling
Saw milling is a process that creates narrow grooves or slots on a workpiece using a saw-milling cutter. It can also be used for parting-off operations. The cutter and workpiece are set so that the cutter is directly placed over one of the T-slots on the table.
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How Does Milling Works?
A milling machine operates by holding a workpiece on a worktable, which is controlled by the table’s movement against a rotating cutter. The cutter, fixed on a spindle or arbor, moves against the workpiece to remove metal from the surface, producing the desired shape. The milling process involves several phases, including milling cutters, surface finish, and gang milling.
End mills are designed with a special cutting surface for drilling and extended cutting surfaces for peripheral milling. They have small cutters at the end corners and are made of highly resistant materials to reduce friction between tools and workpieces.
Surface finish is achieved through regular intervals of cutting area with regular ridges on the sides, which depend on the feed rate, cutter diameter, and number of cutting surfaces. Gang milling involves multiple milling cutters in a horizontal milling setup, often used for duplicate parts.
Before starting a cutting job, ensure the workpiece, table, taper in the spindle, and arbor are free from chips, nicks, or burrs. Select a milling cutter of the necessary diameter and check the machine’s running order, lubrication, and movement. Consider the rotation direction, as some cutters can be reversed on the arbor.
Feed the workpiece in a direction opposite the rotation of the milling cutter (conventional milling). Do not change feeds or speeds while the machine is in operation. Secure the workpiece with tight clamps and use recommended cutting oil liberally. Use good judgment and common sense in planning every job and set up jobs as close to the milling machine spindle as possible.
Safety Precautions In Milling Workshop
Milling machines require special safety precautions, such as not making contact with the revolving cutter, placing a wooden pad over the table surface, using the buddy system when moving heavy attachments, and not tightening arbor nuts using machine power. When installing or removing cutters, hold them with a rag to prevent cutting hands.
Install the cutter last to avoid being cut. Never adjust workpieces or work mounting devices while the machine is operating. Remove chips with a rake and brush, and shut the machine off before making adjustments or measurements. Use splash guards when using cutting oil to prevent splashing.
Advantages and Disadvantages of Milling
Advantages
The following are the benefits of a milling machine:
- Milling machines can produce complex shapes with the use of multi-tooth.
- Operation costs can be very moderate.
- It is used for key-way making.
- it requires less experience for its operation.
- The mailing machine is the perfect option for making individual pieces and small batches.
Disadvantages
- The process is more expensive than some other processes.
- Milling is not suitable for mass production.
- The machine is expensive.
- Speed changing takes time.