WHAT IS CNC MACHINING?

The term CNC stands for 'computer numerical control', and the CNC machining definition is that it is a subtractive manufacturing process that typically employs computerized controls and machine tools to remove layers of material from a stock piece—known as the blank or workpiece—and produces a custom-designed part. This process is suitable for a wide range of materials, including metals, plastics, wood, glass, foam, and composites, and finds application in a variety of industries, such as large CNC machining, machining of parts and prototypes for telecommunications, and CNC machining aerospace parts, which require tighter tolerances than other industries. Note there is a difference between the CNC machining definition and the CNC machine definition—one is a process and the other is a machine. A CNC machine (sometimes incorrectly referred to as a C and C machine) is a programmable machine that is capable of autonomously performing the operations of CNC machining.

CNC machining as a manufacturing process and service is available worldwide. You can readily find CNC machining services in Europe, as well as in Asia, North America, and elsewhere around the globe.

Subtractive manufacturing processes, such as CNC machining, are often presented in contrast to additive manufacturing processes, such as 3D printing, or formative manufacturing processes, such as liquid injection molding. While subtractive processes remove layers of material from the workpiece to produce custom shapes and designs, additive processes assemble layers of material to produce the desired form and formative processes deform and displace stock material into the desired shape. The automated nature of CNC machining enables the production of high precision and high accuracy, simple parts and cost-effectiveness when fulfilling one-off and medium-volume production runs. However, while CNC machining demonstrates certain advantages over other manufacturing processes, the degree of complexity and intricacy attainable for part design and the cost-effectiveness of producing complex parts is limited.

While each type of manufacturing process has its advantages and disadvantages, this article focuses on the CNC machining process, outlining the basics of the process, and the various components and tooling of the CNC machine. Additionally, this article explores various mechanical CNC machining operations and presents alternatives to the CNC machining process.

Overview of CNC Machining Process

Evolving from the numerical control (NC) machining process which utilized punched tape cards, CNC machining is a manufacturing process which utilizes computerized controls to operate and manipulate machine and cutting tools to shape stock material—e.g., metal, plastic, wood, foam, composite, etc.—into custom parts and designs. While the CNC machining process offers various capabilities and operations, the fundamental principles of the process remain largely the same throughout all of them. The basic CNC machining process includes the following stages:

· Designing the CAD model

· Converting the CAD file to a CNC program

· Preparing the CNC machine

· Executing the machining operation

CNC Machining Tolerances Tables

When specifying parts to a machine shop, it's important to include any necessary tolerances. Though CNC machines are very accurate, they still leave some slight variation between duplicates of the same part, generally around + or - .005 in (.127 mm), which is roughly twice the width of a human hair. To save on costs, buyers should only specify tolerances in areas of the part that will need to be especially accurate because they will come into contact with other parts. While there are standard tolerances for different levels of machining (as shown in the tables below), not all tolerances are equal. If, for example, a part absolutely cannot be larger than the measurement, it might have a specified tolerance of +0.0/-0.5 to show it can be slightly smaller, but no larger in that area.

Table 1: Linear Tolerances in CNC Machining

Table 2: Angle Tolerances in CNC Machining

Table 3: Radius and Chamfer Tolerances in CNC Machining

Types of CNC Machining Operations

CNC machining is a manufacturing process suitable for a wide variety of industries, including automotive, aerospace, construction, and agriculture, and able to produce a range of products, such as automobile frames, surgical equipment, airplane engines, gears, and hand and garden tools. The process encompasses several different computer-controlled machining operations—including mechanical, chemical, electrical, and thermal processes—which remove the necessary material from the workpiece to produce a custom-designed part or product. While chemical, electrical, and thermal machining processes are covered in a later section, this section explores some of the most common mechanical CNC machining operations including:

· Drilling

· Milling

· Turning

Types of CNC Machining Support Software

The CNC machining process employs software applications to ensure the optimization, precision, and accuracy of the custom-designed part or product. Software applications used include:

· CAD

· CAM

· CAE

CNC Machining Materials

The CNC machining process is suitable for a variety of engineering materials, including:

· Metal (e.g., aluminum, brass, stainless steel, alloy steel, etc.)

· Plastic (e.g., PEEK, PTFE, nylon, etc.)

· Wood

· Foam

· Composites