Machining

Machining is a way to make things by carefully taking away material from a bigger piece, usually metal. This process helps create exact shapes and parts for many objects we use every day. Unlike making things by adding material, such as with 3D printing, machining removes material using special machines called machine tools.

People who work with machining are known as machinists. They often work in places called machine shops, which have many tools to cut and shape materials. Machining isn’t just for metal; it can also be used on wood, plastic, ceramic, and even composites. Today, many machines are controlled by computers, a method called computer numerical control (CNC), which helps make very precise and complicated designs using mills and lathes. This process is important because it helps make everything from car parts to medical tools.

History and terminology

The word machining has changed a lot over the past 150 years as technology has improved. In the 1700s, a machinist was someone who built or fixed machines by hand, using skills like carving wood or shaping metal. Special workers called millwrights built new kinds of machines, like the engines created by James Watt or John Wilkinson.

By the middle of the 1900s, new words like machine tool and to machine were created when these ideas became more common. During the Machine Age, machining meant using traditional methods such as turning, boring, drilling, and milling with tools like lathes and drill presses to shape materials by removing pieces.

Today, there are also newer methods, like electrical discharge machining, that use electricity or other special ways to remove material. When people talk about machining now, they usually mean these traditional methods. As technology continues to develop, especially with additive manufacturing (like 3D printing), the term subtractive manufacturing is sometimes used to describe machining, since it involves removing material instead of adding it.

Machining operations

Machining is a way to shape materials by using a cutting tool to remove pieces from a larger piece, called the workpiece. In traditional machining, the tool and the workpiece move in relation to each other to make this happen. The shape of the tool, how it moves, and how deep it goes into the material all help create the desired shape on the workpiece.

There are two main types of machining: traditional and non-traditional. Traditional machining includes making circular shapes, like turning and drilling, and making straight or varied shapes, like milling and sawing. Each operation uses specific tools and methods to achieve the right shape and smoothness on the material.

Cutting tool

Main article: Cutting tool (machining)

A cutting tool has one or more sharp edges and is made from a harder material than the piece being worked on. This sharp edge cuts away small pieces, called chips, from the workpiece. The tool has two main parts: the rake face, which guides the chip away, and the flank, which protects the workpiece from scratches.

There are two types of cutting tools: single-point tools, which have one sharp edge and are used for turning and planing, and multiple-cutting-edge tools, which have several sharp edges and are used for drilling and milling. Both types help shape the material by removing pieces in a controlled way.

Chip formation

When machining, the material near the cutting tool gets squeezed and twisted, forming small pieces called chips. The size and shape of these chips depend on factors like the material being cut, the tool’s shape, and how fast it moves. Chips can be continuous, broken into pieces, or not form at all, depending on these conditions.

Traditional machining

Circular machining operations

• Turning rotates the outside of a workpiece against a steady cutting tool to create smooth, round shapes. Lathes are the main machines used for turning.
• Boring makes the inside of a hole larger by turning the workpiece or rotating a tool around the hole’s edge.
• Drilling creates or refines holes by moving a rotating tool toward the workpiece. This can be done on lathes, mills, or special drill presses.
• Threading cuts spiral lines, called threads, into a hole or onto a shaft so that pieces like nuts and bolts can screw together.

Various shape machining

• Sawing cuts material into smaller pieces using a spinning or moving saw blade.
• Milling removes material to create flat or detailed shapes using a rotating tool with cutting edges. Milling machines are used for this process.
• Broaching shapes material by pushing or rotating a tool with teeth through it to cut specific shapes, such as squares or hexes.
• Shaping removes material by moving a steady tool across the surface of the workpiece to create flat areas. Shaper machines move back and forth to do this.
• Grinding uses fast-moving abrasive materials, like stone or diamond, to smooth or shape the workpiece by rubbing away tiny pieces.

Non-traditional machining

• Waterjet machining cuts materials using a powerful stream of water, sometimes mixed with sand, to slice through the workpiece.
• Electrical discharge machining (EDM) uses electric sparks to remove material and can create very thin cuts, allowing for detailed shapes without cutting through the edges of the material.
• High-speed machining (HSM) uses very fast speeds and careful settings to cut hard materials quickly and precisely, often used in making complex parts for airplanes and other industries.

A workpiece that still needs machining has extra material that must be removed to create the final product. For example, a metal piece might need a specific size, which a lathe can achieve by spinning the metal and cutting away material to make it smooth and round. A drill can cut a perfect round hole, while other tools like mills, saws, and grinders help shape the material in many ways.

Machining needs careful attention to details to make sure the final product matches the exact plans, called engineering drawings or blueprints. Besides getting the right size, the surface of the workpiece must be smooth. With the right care, machining can create precise and beautiful results.

Cutting conditions

Machining needs movement between the tool and the material to shape it. The main action happens at a certain speed called the cutting speed. The tool also moves sideways across the material at a slower pace, known as the feed. The last part of the cut is how deep the tool goes into the material, called the depth of cut. These three parts—speed, feed, and depth—are called the cutting conditions.

Machining can be split into two main types: roughing cuts and finishing cuts. Roughing cuts quickly remove a lot of material to get close to the final shape. Finishing cuts are careful and precise, making sure the part is exactly the right size and smooth. Often, one or more roughing cuts are done first, followed by one or two finishing cuts. Cool liquid, called a cutting fluid, is sometimes used to keep the tool cool and working well.

Relationship of subtractive and additive techniques

With the growth of additive manufacturing, traditional machining is now often called a subtractive manufacturing method. These two methods may seem different, but they can work well together. Each has its own benefits. Additive manufacturing can create very detailed designs that are hard to make with machining, but it might have limits in strength and the types of materials that can be used.