Milling machine is one of the most important machines used in the manufacturing. Milling machine can have several tools that shape flat or irregular surfaces. In a typical milling machine, a vertical motor continuously rotates the cutting tools that trim the workpiece. Unlike lathe machines which rotates the workpiece, the milling machine rotates the tool while the job (workpiece) is rotated through the bed.
The milling process is a type of machining that allows modeling in complex forms and trimming pieces of several materials such as metal, wood, plastic, composites etc. and meanwhile the removal of chips and processing residues. The milling is carried out using machine such as milling machines or machining centres.
Types of Milling Machines
There are several types of milling machines each separate from each other in terms of size, tools, direction etc that are used in several different implementations. Milling machines are used to produce slots, cutting, boring and drilling etc. The milling machines are regularly used in gears creation. The milling machine is one of the most precise machines which produces finished quality products.
Milling machines comes in two directions (vertical and horizontal). Milling machines comes in various sizes to create and form individual parts to large and heavy-duty gang milling operations.
Gang Milling Machine
Gang milling is an operation in which two or more cutters are mounted on the same arbor (tool post) and used to cut horizontal surfaces. All cutters may perform the same type of operation or each cutter may perform a different type of operation.
Knee-Type Milling Machine
The milling machine which has a knee like projection at the middle is called knee-type milling machine. It is characterised by a vertical adjustable work table resting on a saddle supported by a knee.
Ram-Type Milling Machine
A milling machine which has a ram on the top of the column is called ram type milling machine. Generally ram is used in vertical milling machine. It can be moved on the column in transverse direction (i.e. in and out when operated from the knee side).
Milling Machine Orientation
Milling machine comes in two distinct types by orientation (Horizontal Milling Machine and Vertical Milling Machine)
Horizontal Milling Machine
The main benefit of horizontal mills is that the workpiece can be fed from all three axis. Horizontal milling machines are mostly used for end-to-end facing. The main disadvantage is that the operation is relatively slower.
Vertical MIlling Machine
As suggested by its name, The spindle axis in the vertical milling machine is vertically oriented. The tool (cutter) is held in the spindle and rotate on its axis.
To demonstrate a simple drilling operation, consider a scenario where a motor is rotating the tool, the milling machine bed can be raised to trim the workpiece. Alternatively, the spindle can also be lowered for this operation.
Factors to Choose the right Milling Machine
There are some important factors to consider in choosing milling machines. Milling feed direction, cutting speeds, feed rates are among the key factors.
Features and Important factors of a milling cutter
The main feature of a milling cutter is its shape which determines the type of its cutting operation. There are several factors that can increase or decrease the work efficiency of a cutting tool. Therefore the features of the cutting tool has to be carefully considered. These features include the shape, helix angle, shank, flutes and coating etc).
In order to achieve effective cutting, the features of the milling cutter must be critically considered. The milling cutter
features include shape, flutes, center cutting, helix angle, shank, roughing, and coatings. Shape. The shape of the cutter determines the type of cutting operation it can perform.
There are several types of cutters each for their specific purpose. Few important and regularly used cutters are mentioned below.
Milling Cutting Tools
Milling cutters are specific tools that are mounted on the spindle of a milling machine. As the machine starts, a heavy duty motor rotates the tool which cuts the workpiece.
- Helical Cutter
- Plain Cutter
- End Cutter
- Face Cutter
- Side Cutter
- End Milling cutter
Helical Milling Cutters
Helical milling cutters are designed for profiling. In the helical cutters, the cutting flutes are configured in a negative helix angle. These cutters can be used in high feed (metal removal rates). The benefit of using Helical milling cutter is that it distributes the trimming process on the whole tool.
Plain Milling cutter
Plain milling cutter has straight edge for cutting. The complete surface of the tool is touches to the workpiece. As a result the tool has to take more load as compared to helical milling cutter.
End Milling Cutter
End milling cutter is a special type of cutter which is used where precise trimming is required. The end milling cutter is used for producing flat surfaces, slots, grooves and to provide finishing to the edge of the workpiece.
Face milling cutter
Face mill. A face mill is a cutter designed for facing. The cutting edges of face mills are always located along its sides. As such it must always cut in a horizontal direction at a given depth coming from outside the stock.
Side milling cutter
A plain side milling cutter has teeth on both sides and also on the periphery. When teeth are added to one side only, the cutter is called a half-side milling cutter and is identified as being either a right-hand or left-hand cutter. Side milling cutters are generally used for slotting and straddle milling.
Typical Milling Operations
The machining process of flat surfaces which are at right angle to the axis of the cutter is called face milling. It is done with face milling tools.
Plain Milling, also called Surface Milling or Slab Milling, is the process of milling flat surfaces with the cutter axis parallel to the surface being milled.
Angular milling is a machining process of flat surfaces which are at an inclination to the axis of the cutter. The cutting operation is applied at a specific angle.
The process of form milling is to milling a surfaces having an irregular outline.
It is the machining process which produces flat vertical surface at the sides of a workpiece. This operation is performed by using side milling cutter.
it is a process in which two side milling cutter are used to machined two opposite sides of a workpiece simultaneously.
It is the machining process in which two or more milling cutters are used together to perform different milling operation simultaneously. In gang milling the cutters are mounted on the arbor.
This milling operation is used to put a profile on the workpiece.
It is machining process which is used to produce narrow grooves or slots on the workpiece. It is also used for the parting off the workpiece into two parts. This milling operation is performed by using saw milling cutter.
Important Terms of Milling Process
The spindle speed is the rotational frequency of the spindle of the machine, measured in revolutions per minute (RPM). The preferred speed is determined by working backward from the desired surface speed (sfm or m/min) and incorporating the diameter (of workpiece or cutter).
Feed rate is the time in which workpiece is provided for operation. Feed rate is measured in (mm/minute: millimeter per minute) OR (in/minute: inch per minute).