CNC machining is capable of creating complex and precise parts thanks to its diverse range of machining processes, such as milling, turning, and drilling. Here, we‘ll focus on milling and drilling to understand their unique capabilities to help you choose the right machining method.
While you can use any process (or combination of processes) to convert your design into a functional product, which process to use depends on the design specifications and final requirements. So let‘s compare milling and drilling in terms of work, tool setup, accuracy, benefits, applications, and more.
CNC milling is a versatile method of machining that allows the use of different rotary cutting tools to precisely cut the workpiece into the desired shape. Here, digital commands (G and M codes) entered in the CNC milling machine determine tool movement and remove material. This controlled automation produces consistent and repeatable parts through digital design.
Due to the multi-axis motion of the tool, milling is suitable for complex designs with fine details. Likewise, it can perform many operations such as cutting, drilling and engraving. Therefore, milling is suitable for industries that require complex parts with tight tolerances.
CNC drilling is another subtractive manufacturing method that focuses on creating precise holes in a workpiece based on an uploaded CAD design. It usually involves a single axis of motion. A drilling machine utilises a computer-controlled rotating drill bit to drill the holes. At the same time, the drill size is exactly or slightly smaller than the desired hole diameter.
Unlike other operations, the CNC drilling process specialises in drilling holes for different applications. Using the appropriate drill bit, you can machine straight holes, centre holes, countersunk holes, submerged holes, tapped holes, reamed holes and other types of holes.
Drilling technology is critical in applications such as electronic components, automotive and aerospace parts, and mechanical assemblies.
A Detailed Comparison of the Differences Between CNC Milling and Drilling
These two CNC processes are known for their superior machining capabilities in different areas. They both have similar machine setups, precision and control mechanisms. But what is the difference between milling and drilling? Let‘s point out the differences in detail and check the different criteria for comparison.
Workflow
A CNC milling machine converts the uploaded CAD design into computer instructions that determine tool control. Next, the workpiece is secured to a vise, clamp or fixture plate. As the tool (usually an end mill) moves to the initial milling position, the rotary tool begins to feed the material at a predetermined feed rate and speed. At the same time, the multi-axis motion allows the tool to move over the workpiece and shape it.
In addition, there are two different workpiece motions possible in CNC milling. In the first, the workpiece moves in the same direction as the rotation of the tool, known as forward or reverse milling. In the second case, the tool rotates against the direction of feed, known as conventional milling or smooth milling.
Drilling works by using a rotary drilling tool to remove material from the area to be drilled. As with CNC milling, a computer controls the drilling tool. After positioning the workpiece to the drilling co-ordinates, the drill begins to rotate and enter the material (usually along the Z-axis) to create an accurate and clean hole.
Motion Path
A significant difference between milling and drilling is the path of motion of the cutting operation. During the operation, the milling tool moves horizontal and vertical moving parts, resulting in more versatile and complex shapes.
In contrast, during a drilling operation, the attachment moves primarily along a vertical path of motion. This is because the focus of drilling is on punching holes or removing material from specific points.
Tools and Setup
Typically, CNC milling involves end mills, face mills, drills, or fly cutters to machine material. The right machine tool is necessary for efficient and accurate milling. That said, drills and end mills are the most common. Therefore, when choosing between end mills and drills, you need to consider the type of material, cutting edges, tool coatings, shape and size, and other factors. Subsequently, the workpiece material is fixed on the machine table and the tool path is perfectly aligned.
The choice of drill for CNC drilling operations depends on the workpiece material, hole depth, size, hardness and finish quality. In addition, some complex drilling may require custom or specialised tools. The tool is mounted on the spindle and the workpiece is fixed to the machine table.
Precision and Capability
These are one of the most precise manufacturing processes available. They offer high precision machining with attention to detail. For illustration purposes, milling produces parts to an accuracy of ±0. 005" (0.127 mm), while drilling can achieve tolerances as low as ±0.002" (0.05 mm).
Milling allows for the manufacture of complex parts or products, from simple slots to complex automotive engine components. On the other hand, drilling focuses on forming holes of different shapes and sizes. It is possible to drill holes up to 2600 mm in depth and 3-32 mm in diameter.
Types of materials
Both processes are compatible with metals, plastics and composites. Therefore, they can use a wide range of materials to meet numerous manufacturing needs.
Commonly used drilling materials
Steel
Aluminium
Brass
Stainless steel
Hardened plastics such as polycarbonate and PEEK
However, milling has more material capabilities than drilling. Drilling is not compatible with milling machinable hardened tool steels, some ceramics and some titanium alloys.
Common Milling Materials
Steel
Aluminium
Brass
Inconel
Garnet
Titanium
Tungsten
Surface Finish Quality
CNC milling with multi-axis motion and a diverse range of tools enables versatile machining surface finishes. Roughness values (Ra) of milled surfaces can be as low as 1.6 µm. Thus, Ra values of up to 3.48 µm can be achieved on drilled surfaces. however, Ra values are affected by depth of cut, material, rotational speed and other factors.
As a result, milling provides a finer surface finish than drilling due to cutting dynamics. Nevertheless, drilling provides a better surface with holes. In addition, milling involves external machining, which makes it easy to obtain a quality machined surface.
Industry and Application Specific
Application is probably the most critical aspect of the comparison between milling and drilling, as it determines where these processes will be applied.CNC milling can accurately machine any flat surface into any complex angle, such as bends and undercuts.
Applications of CNC Milling
Automotive parts such as cylinder heads, engine blocks, gearbox housings, etc.
Prototyping for various industries.
Medical device components and implants
Mould and tool making
CNC milling is preferred over drilling because it can machine detailed geometries. Nevertheless, drilling is still essential when precise cylindrical features are required.
CNC Drilling Applications
Deep and small holes in a variety of materials.
Drilling of fasteners on aircraft fuselages and engines.
Automotive assembly.
Electronic boards with precise and consistent holes for component placement.
Cost Considerations
CNC drilling and milling are both cost-effective manufacturing methods. They justify the cost with precision, sophistication and quick turnaround capabilities. However, in a head-to-head comparison between drilling and milling, the CNC milling process is slightly more expensive.
If we break down the cost factors and considerations, milling costs will vary depending on complexity, workpiece material, machine setup, production speed and number of processes. Meanwhile, drilling costs are also affected by drilling depth, hole diameter and number of holes.
Lead Time
In general, CNC milling operations have longer lead times due to the complexity of the part being machined. In contrast, CNC drilling projects have shorter lead times because drilling is a more straightforward process that focuses on hole machining tasks.
However, several factors determine the lead time for any given milling or drilling project. For example, milling lead times depend on machining complexity, material type, setup time, required accuracy, and operator skills. Similarly, drilling lead times are affected by the number of holes, their depth and diameter, as well as equipment and tool set-up times.
