Machining

Machining is a fundamental manufacturing process used to create specific shapes or parts. It works through the controlled removal of material from a larger, raw piece. This method is known as subtractive manufacturing. It stands in contrast to additive manufacturing, such as 3D printing, which builds objects by adding material layer by layer. While metal is the most common material used, machining can also be applied to wood, plastic, ceramic, and composites.

The core mechanism of machining involves a cutting tool interacting with a workpiece, often called the "work." To remove material, there must be relative motion between the tool and the work. This motion can happen in several ways, such as lateral rotary motion or linear movement. The specific shape of the tool, how it penetrates the work, and the type of motion used all determine the final geometry of the surface.

A cutting tool must be made of a material harder than the workpiece. The tool features sharp edges that separate small fragments of material, known as chips, from the parent work. These tools have specific geometries, including a rake face and a flank. The rake face directs the flow of the newly formed chips at a specific rake angle. The flank provides a relief angle, which creates clearance between the tool and the new surface. This clearance prevents abrasion that would otherwise degrade the surface finish.

Machining operations are generally divided into traditional and non-traditional categories. Traditional operations are further split by the shapes they create. Circular machining includes processes like turning, boring, drilling, reaming, and threading. These often use a lathe to rotate the workpiece against a tool. Other circular tasks include making threads, which are helical shapes used to fasten objects like nuts and bolts.

Various and straight shapes are created through different traditional methods. Milling involves a spinning tool with cutting edges on its cylindrical face. Sawing uses a toothed blade to cut a "kerf," or thickness, through material. Broaching uses a multi-toothed tool to cut specific shapes like squares or hexagons. Shaping uses a non-rotating tool that strokes back and forth to cut flat geometries. Grinding uses fast-moving abrasive materials, such as diamond or aluminum oxide, to wear away the surface.

Non-traditional machining uses different methods to remove material without simple mechanical cutting. For example, electrical discharge machining (EDM) uses an electrically charged metal rod or wire to vaporize material. This allows for very intricate shapes and a very small kerf. Waterjet cutting uses a high-pressure jet of water, sometimes mixed with an abrasive like garnet, to cut through thickness. Other advanced methods include plasma beam machining, electrochemical machining, and ultrasonic machining.

The history of machining shows how technology has transformed the field. In the 18th century, a "machinist" was a person who built or repaired machines by hand. These individuals, including figures like James Watt or John Wilkinson, used manual processes like hand-filing metal. The term "machine tool" did not even exist then. By the middle of the 20th century, the term "machining" became common as specific processes like milling and drilling became widespread.

Today, much of this work is performed using computer numerical control, or CNC. In CNC machining, computers control the precise movement and operation of machines like mills and lathes. This technology is vital in professional machine shops, which can be standalone businesses or internal departments within larger companies. From manufacturing aircraft parts to creating simple manhole covers, machining remains a cornerstone of modern industry.