Machining is a term often used within the manufacturing industry, and it can be misleading to understand what operations are related to machining. As an engineer, you will come across the term machining, making it essential to understand its meaning. Here we will explain what machining is, the important types of machining and their differences.
What Is Machining?
Machining is one of the most proven manufacturing operations used in the industry. The process aims to produce a shape of a desired shape and size by material-removing in a controlled fashion. The material-removal core of the process means it is considered a subtractive manufacturing process – the opposite of additive manufacturing. Metal is the most popular material used during machining, although machining is also operated on other materials such as wood and ceramics. The subtractive nature of the process means that metals are work hardened during the operation.
Machining is a mechanical process that utilises cutting tools, abrasive wheels and discs. Dependent on the requirement of the final product, certain operations are applied to meet them.
What Are The Important Types of Machining Operations?
There are three types of machining operations, and each one of them is crucial. The three main types of machining are turning, milling and drilling.
Turning
Turning is a machining operation consisting of the workpiece rotated at high speeds. Whilst the workpiece is being rotated, a non-rotating cutting tool moves across it to remove material. A lathe and a CNC (Computer Numerical Controlled) machine are the two types of machinery capable of turning. A lathe requires manual input from an operator to move the cutting tool. A CNC machine is programmed such that, once the program commences, no manual input from the operator is necessary.
Turning can remove material from internal or external surfaces. Boring is the term used when material removal occurs from internal surfaces and is used to create tubular shapes. Additionally, facing is a well-known process in turning. Facing is when the cutting tool moves along an axis perpendicular to the axis of rotation of the workpiece. It tends to be performed during the first and last stages of the turning process.
Milling
Milling is a machining operation that consists of a rotating cutting tool that travels over a stationary workpiece. The core concept is the opposite of Turning. The machines used for milling vary. Some allow movement and rotation of the cutting tool whilst the workpiece is stationary. Others allow movement in both the cutting tool and workpiece. A milling machine, jig and milling cutter are necessary to undertake milling.
Milling is utilised for numerous purposes, but mostly for three distinct types of holes: oversized round hols, round slotted holes and rectangular holes.
Face Milling & Peripheral Milling
The major milling processes are facing and peripheral milling. Facing takes place at the end of the milling cutter. Face milling cuts flat surfaces into the workpiece or cuts flat bottoms for cavities. Peripheral milling as the name suggest occurs at the periphery of the milling cutter resulting in the cross-section of the milled surface taking on the shape of the milling cutter. Peripheral milling is often used for deep groove applications such as threads and gears.
Drilling
Drilling is a machining operation that forms a circular hole in the workpiece. The cutting tool used for drilling is called a drill bit. The process tends to be operated on a drilling machine however it is possible to perform drilling operations on a milling machine. The drill bit is pressed against the material whilst rotating resulting in chips (swarf) being removed from the workpiece.
When a workpiece has been drilled, it is characterised by sharp edges at the entrance of the hole and the presence of burrs at the exit (unless they have been removed, which is best practice).
During the process, it is good practice to use cutting oil as it helps lubricate the workpiece and the cutting tool. It serves a number of good purposes:
– Helps increase drill bit life
– Reduces heat in the workpiece
– Helps chips get removed during the process
Additionally, marking the positions for holes to be drilled is a good practice to implement as it removes the tendency for the drill bit to ‘walk’. Using a centre punch creates an indent on the workpiece, which in turn helps provide stability for the drill bit when the initial drilling commences.