Computer numerical control (CNC) milling is a highly sophisticated manufacturing process that uses computer-controlled machines to cut and shape materials. It uses a CNC milling machine, a piece of industrial equipment utilizing computer-aided design (CAD) and computer-aided manufacturing (CAM) software. This combination of advanced software precisely controls the movement of cutting tools.
CNC milling has allowed small-scale workshops to compete with larger factories by providing them access to precise manufacturing capabilities. This has led to the democratization of manufacturing, enabling more people to enter the industry and create innovative products. However, this process requires careful consideration to ensure it is carried out effectively and efficiently.
Here are some key considerations that manufacturers must keep in mind to achieve their desired results:
1. Material Selection
Material selection determines the type of cutting tools, feed rates, and spindle speeds required. Therefore, manufacturers must consider each material’s properties — including its hardness, ductility, and thermal conductivity — to determine the optimal machining parameters.
Certain materials are more challenging to machine than others. For example, aluminum and brass require high-speed milling because they are relatively soft and prone to heat buildup. On the other hand, stainless steel and titanium need slower cutting speeds and deeper cuts, as they are harder to machine.
2. Tool Selection
The right cutting tool must be selected based on the material and the type of cut required. The selection process considers tool geometry, coating, material, and cutting speed. Also, it is worth noting that the wrong tool can result in poor surface finish, excessive tool wear, and even damage to the equipment.
The following are three of the most common tools used in CNC milling:
End mills are cutting tools with edges on both the bottom and sides. They are typically used for profile milling and pocketing operations and come in various sizes and shapes, such as square, ball-nose, and corner-radius. Moreover, they are mounted on the milling machine’s spindle and rotate as the equipment moves the workpiece beneath the tool.
Ball mills are designed to create smooth surfaces and detailed shapes. They are characterized by a spherical cutting end, particularly useful for contour milling and finishing operations. Furthermore, the ball mill’s cutting-end design allows it to cut in multiple directions, providing versatility in machining.
Drills are used for creating holes in the workpiece, and they come in different types, such as twist, center, and spotting drills. Twist drills are the most commonly used and are designed to drill holes in various materials. On the other hand, center and spotting drills are used for creating starting holes or marking the hole’s location.
3. Cutting Parameters
Cutting parameters are basic settings that must be configured before milling, including spindle speed, feed rate, cutting depth, and cutting width. Manufacturers must carefully adjust these parameters based on the machined material and the type of cut required.
Fixturing ensures the stability of the workpiece during milling to prevent any undesired movement that can cause inaccuracies. The appropriate fixturing method — including clamps, vises, and magnetic chucks — is selected based on the workpiece’s size, shape, and material.
Post-processing is the final step required after the milling process. It comprises cleaning the workpiece, eliminating unnecessary material, and adding a finish or coating. Different techniques may be used depending on the material and the type of finish required, such as sandblasting or polishing.
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