What is CNC Milling, advantages and disadvantages?

Mosi Li
Mosi Li

Director Project Engineer at 3Q Machining - China top CNC Machining Custom Part Manufacturer

What is CNC machining used for?
CNC milling or manual milling is a machining process used to process prismatic parts

CNC Milling or manual milling is a machining process used to process prismatic parts. A milling cutter with a rotating cylindrical tool head and multiple flutes is usually called an end mill. It can move along different axes and is used to machine long and narrow voids, grooves, and outer contours. The machine tool for milling is called a milling machine, and the CNC milling machine usually refers to computer numerical control milling. Milling processing includes manual milling and CNC milling.

CNC milling is a mechanical machining process along with drilling, turning, and a variety of other cnc machining processes, meaning that material is removed from the workpiece via mechanical means, such as the actions of the milling machine’s cutting tools.   

This article focuses on the CNC milling , outlining the basics of the process, and the components and tooling of the CNC milling. Additionally, this article explores the various milling operations and provides alternatives to the CNC milling process.

Milling Machine Definition

What is Milling Machine? 

The milling machine mainly refers to a machine tool that uses a milling cutter to process various surfaces of a workpiece. Usually the milling cutter mainly moves by rotation, and the movement of the workpiece and the milling cutter is the feed movement. It can process planes, grooves, various curved surfaces, gears, etc.
A milling machine is a machine tool that uses a milling cutter to mill a workpiece. In addition to milling planes, grooves, gear teeth, threads, and spline shafts, milling machines can also process more complex profiles. The efficiency is higher than that of planing machines. It is widely used in machinery manufacturing and repair departments.

What is 3 axis CNC Machining
How does CNC Milling work? The milling machine is a machine tool with a wide range of uses. It can process planes (horizontal planes, vertical planes), grooves (keyways, T-slots, dovetail grooves, etc.), gear parts (gears, spline shafts, sprockets), Spiral surfaces (threads, spiral grooves) and various curved surfaces. In addition, it can also be used to process the surface and inner hole of the revolving body and cut off the work. When the milling machine is working, the workpiece is mounted on the worktable or the indexing head and other accessories, and the milling cutter rotates as the main motion, supplemented by the feed motion of the worktable or the milling head, and the workpiece can obtain the required processing surface. Due to the multi-edge intermittent cutting, the productivity of the milling machine is high. In simple terms, a milling machine can be a machine tool for milling, drilling and boring workpieces.

Cnc Milling Machining

Overview of CNC Milling Process

CNC milling machines are divided into two categories: without tool magazine and with tool magazine. Among them, a CNC milling machine with a tool magazine is also called a machining center. Let’s take a look at the programming examples of CNC milling machines and detailed explanations of operations and precautions.

  • Designing a CAD model drawing
  • Convert the CAD model drawing into a CNC milling program
  • Setting up the CNC milling machine
  • Executing the milling operation

(1) Programming: Before writing or programming, you should first compile the processing program of the workpiece. If the processing program of the workpiece is longer and more complicated, it is best not to program on the machine tool. Instead, use a programming machine or computer programming to avoid occupation. When the machine is running, short programs should also be written on the program sheet.


(2) Startup: Startup is generally to start the machine tool first and then start the system. In some designs, the two are interlocked, and the machine cannot display information on the CRT without powering on.


(3) Back to reference point: For machine tools with incremental control systems (using incremental position detection components), this step must be executed first to establish the movement reference of each coordinate of the machine tool.


(4) Input program: adjust the processing program according to the storage medium of the program (paper tape or magnetic tape, disk), it can be input by paper tape reader, cassette tape machine, programming machine or serial communication. If it is a simple program, the keyboard can be used directly Input on the CNC control panel. If the program is very simple and only one piece is processed, there is no need to save the program. The MDI method can be used to input and process section by section. In addition, the workpiece origin, tool parameters, offsets, and various compensations used in the program must also be input before processing.


(5) Modify the program: Edit the program if the input program needs to be modified, you must edit it. At this time, place the mode selection switch in the edit position, and use the edit keys to add, delete, and change. For the editing method, see the corresponding manual.


(6) Machine lock: Run the program. This step is to check the program. If there is an error, you need to edit it again.


(7) Upper workpiece: manual incremental movement is used for aligning and tool setting, continuous movement or manual wheel movement of the machine tool. Align the starting point to the beginning of the program, and set the tool benchmark.


(8) Continuous processing: starting coordinate feed for continuous processing generally uses programs in the memory for processing. This method has a lower failure rate than the program on paper tape. The feed rate during processing can be adjusted by the feedrate override switch. During processing, you can press the feed hold button to pause the feed movement, observe the processing conditions or perform manual measurement. Press the cycle start button again to resume processing. In order to ensure that the program is correct, it should be checked again before processing. In the milling process, for the plane curve workpiece, a pencil can be used instead of the cutter to set the contour of the workpiece on the paper, which is more intuitive. If the system has a tool path simulation function, it can be used to check the correctness of the program.


(9) Operation display: Use each screen of the CRT to display the position of the workbench or the tool, the program and the state of the machine tool, so that the operator can monitor the processing situation.


(10) Save the program: After the program output processing is completed, if it is necessary to save the program, it can be left in the CNC’s memory. If the program is too long, the program in the memory can be output to an external device (such as a punching machine). Save it on tape (or tape, disk, etc.).


(11) Shutdown: Generally, the machine tool should be shut down before shutting down the system.

CNC Milling Machining Operations

What is the CNC milling machine used for? CNC milling is a machining process suitable for producing high accuracy, high tolerance parts in prototype, one-off, and small to medium production runs. While parts are typically produced with tolerances ranging between +/- 0.001 in. to +/- 0.005 in., some milling machines can achieve tolerances of up to and greater than +/- 0.0005 in. The versatility of the cnc milling process allows it to be used in a wide range of industries and for a variety of part features and designs, including slots, chamfers, threads, and pockets. The most common CNC milling operations include:

  • Face milling
  • Vertical milling
  • Profile milling

01: Face Milling

Processing plane. Face milling is the most common type of milling used for milling planes parallel to the tool face. The milling cutter is often installed on the spindle. To complete face milling, you can use a tool with a certain diameter, so that the workpiece can be processed in one stroke, or you can use a milling cutter of the type that requires several strokes to complete the workpiece.

[face milling cnc milling 

02:Vertical milling

Process approximately 90 stepped surfaces. This kind of milling is somewhat similar to face milling, but the angle of the circumferential cutting edge plays a decisive role. If a part of the workpiece to be machined is a 90° shoulder, this tool can only be used. The side of the tool (entering angle) is parallel to the axis of rotation. This milling is also called step milling, shoulder milling or end milling.

[vertical milling cnc milling 

03:Profile milling

Machining a special-shaped surface (curved surface).

profile milling cnc milling 

Other Milling Machine Operations: Plain milling; Angular milling; Form milling ; Straddle milling; Gang milling; Gear cutting; 

Since cnc milling machines support the use of other machine tools besides milling tools, they can be used for machining processes other than milling, such as drilling, boring, reaming, and tapping.

CNC milling advantages and disadvantages

Milling Machine: The price of ordinary milling machines is low, but the efficiency is low in mass production, the processing quality is greatly affected by the technical level of the operators, and the processing consistency is not good.
CNC Milling Machine: The CNC milling machine has high efficiency in mass production, good processing consistency and stable quality. However, the price is high, and programming takes a lot of time when the processing quantity is small, which is not economical.

Advantages: ① The number of tooling is greatly reduced, and complex tooling is not required for processing parts with complex shapes. If you want to change the shape and size of the part, you only need to modify the part processing procedure, which is suitable for new product development and improvement.
②The processing quality is stable, the processing precision is high, and the repeat accuracy is high, which can meet the high-quality processing requirements.
③The production efficiency is higher in the case of multi-variety and small batch production, which can reduce the time of production preparation, machine tool adjustment and process inspection, and reduce the cutting time due to the use of the best cutting amount.
④It can process complex profiles that are difficult to process by conventional methods, and even process some unobservable processing parts.
Disadvantage of CNC milling machining is that the cost of machine tools is expensive and requires a high level of maintenance personnel.

Support software for CNC Milling

Like most of CNC machining processes, the CNC milling process uses CAD software to produce the initial part design and CAM software to generate the CNC program which provides the machining instructions to produce the part. The CNC program is then loaded to the CNC machine of choice to initiate and execute the milling process.

Material options

CNC Milling can machine verity of metal and plastic materials including of aluminum, steel, brass, titanium; and ABS, PC, NYLON; also workable for

  • Elastomers
  • Ceramics
  • Composites
  • Glass
Benefits of aluminum CNC machining

Outlined above are the basics of the CNC milling process, various CNC milling operations and their required software, materials which workable for cnc milling, and some of the considerations that may be taken into account by manufacturers and machine shops when deciding what kind of CNC milling  or other machining is the most optimal solution for their particular machining application.

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