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What is the difference between CNC machining and milling?

Published in Manufacturing Automation 4 mins read

The fundamental difference between CNC machining and milling lies in their scope: CNC machining is the broad category of automated manufacturing processes, while milling is a specific type of cutting operation often performed using CNC technology. Essentially, milling is a subset of CNC machining.

What is the Difference Between CNC Machining and Milling?

CNC (Computer Numerical Control) machining represents the automated control of machine tools using computers. It encompasses a wide array of manufacturing processes, whereas milling is a particular method of removing material from a workpiece using rotating multi-point cutting tools.

Understanding CNC Machining

CNC machining is a digital manufacturing process where pre-programmed computer software dictates the movement of factory tools and machinery. It transforms a digital design (CAD model) into a physical part by precisely controlling machine tools, ensuring high accuracy, repeatability, and efficiency.

Key aspects of CNC machining include:

  • Automation: Reduces human intervention, minimizing errors and improving consistency.
  • Precision: Achieves tight tolerances and complex geometries due to computer control.
  • Versatility: Can be applied to various materials, including metals, plastics, wood, and composites.
  • Processes: Encompasses numerous operations like turning, drilling, grinding, routing, and, critically, milling.

Understanding Milling

Milling is a subtractive manufacturing process that uses rotary cutters to remove material from a workpiece by advancing it at an angle to the tool axis. It's highly effective for creating complex shapes, slots, holes, and contours on a workpiece.

When milling is performed under CNC control, it becomes CNC Milling. This combination leverages the precision of CNC with the versatility of milling to produce highly accurate and intricate parts. CNC mills are particularly noted for their ability to deliver cuts that are more accurate and more intricate than other CNC-controlled tools like routers. The sophisticated configuration of a mill's tooltip allows for the creation of more complex cutting paths and shapes.

The Relationship: Milling as a Form of CNC Machining

The relationship between CNC machining and milling can be best understood as a "parent-child" dynamic. CNC machining is the parent term, referring to the automated control system used in manufacturing. Milling is one of the many "children" processes that can benefit from this CNC control.

For instance, while a traditional mill might be operated manually, modern manufacturing predominantly relies on CNC mills for superior precision, speed, and capability.

Key Differences at a Glance

To clarify the distinction further, consider the following comparison:

Feature CNC Machining Milling
Nature Overarching automation concept and methodology Specific material removal process
Scope Wide range of processes (turning, drilling, routing, grinding, milling, etc.) Utilizes rotary cutters to remove material from a stationary or moving workpiece
Control System Always computer-controlled Can be manual or, more commonly, computer-controlled (CNC Milling)
Primary Goal Automate manufacturing for precision and efficiency Shape a workpiece by removing material with rotating tools
Tool Types Varies widely based on the specific process (e.g., turning inserts, drill bits, laser heads) Primarily uses multi-point cutting tools like end mills, face mills, ball mills
Accuracy & Intricacy High, dependent on the specific machine and process Known for very high accuracy and ability to create intricate designs, surpassing simpler CNC tools like routers.

Types of CNC Machining Beyond Milling

It's important to remember that CNC machining encompasses much more than just milling. Other common CNC processes include:

  • CNC Turning: Used for creating cylindrical parts by rotating the workpiece against a stationary cutting tool (e.g., on a CNC Lathe).
  • CNC Routing: Often used for larger workpieces and softer materials, like wood or plastic, for basic cuts. While less accurate than mills, they are efficient for larger flat sheets.
  • CNC Laser Cutting: Uses a high-powered laser to cut materials, ideal for sheet metal and intricate designs without contact.
  • CNC Plasma Cutting: Employs a plasma torch to cut through electrically conductive materials.
  • CNC Grinding: Uses abrasive wheels to achieve extremely fine finishes and precise dimensions.

Why the Distinction Matters

Understanding this distinction is crucial for anyone involved in manufacturing, design, or procurement:

  1. Process Selection: It helps in choosing the right manufacturing process for a specific part. If a part requires complex 3D contours and high precision in solid material, CNC milling is often the go-to.
  2. Machine Investment: Companies investing in machinery need to differentiate between a general-purpose CNC machine (like a multi-axis mill) and a machine dedicated to a single process (like a CNC laser cutter).
  3. Skill Sets: Operators and engineers often specialize in particular CNC processes. A CNC milling expert may not be proficient in CNC turning, for instance.

In summary, CNC machining is the overarching technology that automates various manufacturing tasks, while milling is a specific and highly versatile method of material removal that frequently benefits from CNC automation to achieve superior results.