Understanding Machining Processes: Turning, Milling, Planing, Drilling, and Grinding
Machining Processes: A Detailed Overview
Turning
Turning is a machining process based on rotating a workpiece around an axis to create cylindrical shapes. It involves a uniform rotational motion around a fixed axis. The primary movements include cutting, advancement, and penetration. Turning is used to create cylindrical, conical, and contoured surfaces, as well as threads. The machine consists of the body, transmission system, axle drive, fastening systems, tool, and controls for movements and speeds.
Milling
Milling is a mechanical machining process performed using milling machines and milling cutters. It involves removing excess material from a workpiece to achieve the desired shape and finish. Various cutters are used, including those for opening channels at specific angles, creating convex or concave surfaces, and forming gear teeth.
Planing
Planing is a machining operation performed with shaping machines to create flat surfaces, whether horizontal, vertical, or inclined. This process uses single-edged tools to remove material with linear motion.
The shaping-plane uses alternating rectilinear motion to move the tool across the workpiece. The planer table performs similar work, and can be adapted for milling and grinding. The key difference is that the planer table reciprocates. Planing steps include setting the play, fixing the tool, preparing the machine, executing the initial reference pass, and zeroing the graduated ring.
Drilling
Drilling is a machining operation used to create holes in workpieces. It often serves as a preparatory step for other operations like enlarging holes or tapping threads. The main parts of a drill are the rod, body, and tip.
- Spotting drill: Used to create a pilot hole for twist drills.
- Step drill: Designed to create holes and recesses in a single operation.
- Cannon drill: Features a single cutting edge, suitable for deep holes where standard drills are impractical.
- Coolant-fed drill: Used in continuous production to speed up deep hole drilling.
Major drill types include portable, column, benchtop, floor-standing, and radial drills. Accessories include mandrels, conical bushings, and wedge or mandrel extractors. Operations include boring, hole creation, and countersinking.
Grinding
Grinding is a machining process that uses abrasion to refine the surface of a workpiece. Grinding machines provide greater accuracy and a better finish compared to conventional machines. Compressed air is often recommended as a cutting fluid for iron castings.
There are three main types of grinding: tangential surface grinding, vertical surface grinding, and universal cylindrical grinding. Centerless grinding is commonly used in mass production. The cutting tool is a grinding wheel made of abrasive grains like aluminum oxide or carbide.
Key elements of a grinding wheel include:
- Abrasive: The material containing the grinding grains.
- Grain Size: The size of the abrasive grains.
- Bond: The material that holds the abrasive grains together.
- Hardness: The bond’s resistance to wear.
- Structure: The porosity of the abrasive disc.