Computer Numerical Control milling is a mechanical machining process. Once a CNC milling machine has been pre-programmed with instructions, the machine uses computerized controls and rotating cutting tools to progressively remove layers of a workpiece to produce custom-designed products or parts. CNC milling machines are ideal for machining a broad range of materials, such as metals, plastics, wood, ceramics, and glass. The versatility of materials that CNC milling machines can handle, coupled with the machinery’s extremely high precision capabilities, makes the machines ideal for use in a wide variety of manufacturing industries. Let us take a closer look at CNC milling machines and how they work.
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Before looking at how the CNC milling process works, you need to know that there are several types of CNC milling machines available. Each one is suitable for a variety of machining tasks. The most common types of CNC milling machines include:
- Knee-type, which uses a fixed spindle and a vertically adjustable worktable that rests on the saddle and is supported by the knee. Knee-type CNC milling machines include bench-type and floor-mounted machines.
- Ram-type, which uses a spindle affixed to a movable ram on the column, allowing the machine to move along the XY axes. These types of machines include floor-mounted universal horizontal machines and swivel cutter head machines.
- Bed-type, which employs worktables affixed directly to the machine bed to prevent the workpiece from moving along the Y and Z axes. Bed-type machines include simplex, duplex, and triplex machines.
- Planer-type, which are similar to bed-type CNC milling machines. The main difference is planer-type machinery can support multiple machine tools simultaneously, which reduces the lead time for manufacturing complex parts.
There are also specialized CNC milling machines available, such as planetary, rotary table, and drum machines. With planetary machines, the worktable is stationary and the workpiece is cylindrical. Rotary table CNC milling machines have circular work tables that rotate around the vertical axis and use machine tools positioned at various heights for finishing operations. Drum machines are similar but the worktable is referred to as a drum and it rotates around the horizontal axis. Whatever sort of machine you want to use, new and used CNC milling machines of various types are available from well-known brands like Haas, Hurco and Cincinnati.
In basic terms, the CNC milling process uses computerized controls to operate and manipulate the tools that cut and shape the material. The process follows the same basic production steps that all CNC machining processes follow. The first stage involves designing a part or product in a Computer-Aided Design program. Once the design is complete, it is converted by CAM software into a CNC-compatible format like G-Code. The computer instructions dictate the actions and movements of the CNC milling machine. Depending on the specificities and requirements of the particular milling application, a vertical or horizontal CNC-enabled milling machine can be used. When the automatic CNC milling process begins, the machine rotates the cutting tools at extremely high speeds and performs its pre-programmed actions.
In general terms, CNC milling machines are categorized into vertical and horizontal configurations, but they are also differentiated based on the number of axes of motion. In horizontal CNC milling machinery, the spindle is oriented horizontally. In vertical milling machines, the spindle is vertically oriented. Horizontal machines also use arbors for additional stability and support during the milling process. They have the capabilities for multiple cutting tools too.
The actual machine controls of both horizontal and vertical CNC milling machines are dependent on the specific machine you use. Some machines can raise and lower the spindle and move laterally across the worktable, while others have stationary spindles and worktables that move vertically, horizontally, and rotationally. When choosing a CNC milling machine, you need to consider the requirements of your milling application, such as the part’s size and shape and the number of surfaces requiring milling. Ancillary equipment that modifies horizontal or vertical CNC milling machinery to support the opposing process is also available.
CNC milling machines enable very high precision. They can also produce identical repeatable parts, products, or prototypes again and again. Pieces are typically produced with tolerances that range between +/- 0.001 inches to +/- 0.005 inches, but some CNC milling machines can reach tolerances up to and even greater than +/- 0.0005 inches. Due to the high versatility of the CNC milling process, it can be used by a broad range of industries for producing all kinds of items. There are four main CNC milling operations. They are plain milling, face milling, form milling, and angular milling.
Typically, CNC milling is best used as a secondary or finishing process. It can provide definition to parts or products and produce features like slots, holes, and threads. However, the CNC milling process can also be used to shape a stock workpiece from beginning to end.