Digital technologies and CNC milling processes allow for the resolution of many problems which cannot be easily solved using prior methods. It is the present of the manufacturing industry – robotics is the future. CNC mill machines are here to set the precedence for the robotic and machine-controlled future we’ve seen in movies and films.
What is CNC Milling?
We’ll break it down into two;
- Computer Numerical Control (CNC) machining is a manufacturing process that uses pre-programmed computer software to instruct machines and factory tools how and where to move. Different types of machines integrate CNC machining ranging from lathes to grinders and mills.
- On the other hand, milling is a subtraction kind of manufacturing that involves cutting, crushing, grinding, or pressing a material inside a machine. The purpose is to remove bits and pieces of the material to achieve an ideal design.
Thus, combining the two, CNC milling is removing material using a milling cutter while controlling the design through a computer code. The software is needed to convert digitized data (bits and pixels) into numerical code that fits into the X-, Y-, and Z-axis. This enables the program to monitor, automate, and control all machine movements.
This manufacturing process is used in obtaining high-precision tools and machines and has found wide application in several industries. It is ideal in high-quality precision drillings, engravings, cutting along an arc, milling, cutting holes, or carving cutouts.
Types of CNC Milling Machines
As we previously stated, CNC milling is a subtractive process. It contrasts with 3D-printing technology and rapid prototyping, which are additive tech. That said, there are different types of CNC milling machines, but we’ll broadly categorize them into two according to the orientation of the spindle;
- Vertical Milling
- Horizontal Milling.
A significant element differentiating vertical mills is the long and thin cutting tools that make them incredibly versatile. The spindle axis is aligned to move in a vertical formal. Since it has higher compressive strength, the base mainly consists of cast iron to support the weight. Vertical mills are generally more affordable than horizontal milling machines but usually have lower efficiency in the long run.
Two main types of vertical milling machines exist;
- Turret Mill: The turret mill is an ideal preference as an investment for manufacturers as the spindle and table move both parallel and perpendicular to the axis. This allows a broader range of operations, although it doesn’t eliminate the need for an attentive and skilled employee. You’ll still need to be alert when directing the spindle with your hand. Its high functionality and low maintenance cost make it a top preference among vertical mills.
- Bed Mill: Bed milling machines tend to have limited functionality as they only move the table perpendicular to the axis.
The horizontal mill is pretty much the same, with the spindle aligned horizontally. They perform at a speedier rate than their vertical counterparts, works on harder material, thus calling for thicker and deeper grooves, and require less accuracy. However, they are more expensive, although they compensate for that with their higher productivity. They also need minimal employee attention.
Major CNC Milling Operations
The type of milling operation has a profound effect on which type of milling machine to go with. Before settling on any milling operation, we may need to consider the features to be milled or milling configuration. Are the features deeply located, or do they contain interruptions and inclusions?
Although CNC milling has other specialized milling operations, the four main types are;
- Face Milling
- Angular Milling
- Form Milling
- Plain Milling.
Face milling involves machining a flat surface sitting at right angles or perpendicular positioned to the cutter axis. The face milling operation is both applicable in horizontal and vertical methods of CNC milling. When the cutter is appropriately grounded and rotating counterclockwise, the cutter teeth on the periphery will perform most of the cutting while the face teeth finish the work-piece.
Here, the cutting tool’s axis lies at an angle to the workpiece’s flat surface and uses a single milling cutter to mill angular surfaces. The first step is to rough out the groove utilizing a slide milling cutter. Afterward, the CNC engineer will finish the angular sides and base using an angle milling cutter.
Form milling is ideal for irregular surfaces or surfaces with curved flats or all curves. It uses a formed milling cutter or fly cutter to complete a shaping in a single cut. The cutters are mostly either concave or convex-shaped or have rounded corners able to grind to the required circular diameter.
Generally referred to as slab or surface milling. It refers to when the milling cutter axis is parallel to the milled surface. Here, the rotating cutter only moves from one end to the other of the workpiece rather than rotating in a continuous cut. Plain milling can use both narrow and wide cutters. The arbor stands horizontally supported between several arbor supports and the milling machine spindle.
Which Materials are Compatible with CNC Milling?
Before you settle on the ideal material for your CNC milling project, you’ll first need to determine the stress load on the material. The higher the stress load, the easier it is to break, crack, or stain certain materials. Dimensional tolerance is also another vital factor to put into consideration. Dimensional tolerance will influence the cutting method, types of tools and machines used, the final look of the parts and assemblies.
The machining expert should also determine the operating temperatures for the CNC milling operation. The melting point should be ideally lower than that of the operating temperature without adding unnecessary cost.
The manufacturer should also be cautious about the weight of the material. Heavy materials will come in handy for projects that call for excessive weight-bearing capabilities. Lightweight materials are not always the best fit due to their cost implication. Other critical factors that go into consideration include but are not limited to;
- The type of fastening required,
- Outdoor vs. indoor environment,
- Usage of the end product.
Below are the most commonly used materials for CNC milling;
Metals offer high resistance to temperature, weight, and pressure, thus ideal for several operations. The most commonly used metals in CNC milling include aluminum (6061, 7075), brass, stainless steel (303, 304, 316), magnesium AZ31, copper, titanium, and carbon steel 1045.
Plastic is slowly gaining dominance in the market and taking the hot seat that metals have occupied due to their wide range of applications, low cost, and high-temperature resistance. Moreover, plastics are impervious to water, versatile, and easier to manufacture than most materials. Plastics can also be recycled, making them environmentally friendly. Some top choices include PEEK, PVC, and acetal plastics. Other examples are PMMA, ABS plastics, and PA or nylon.
Glass tends to be more brittle, but it’s possible to achieve a classic CNC glass design with the right tools. The top things you’ll need to cut glass on a CNC milling machine are glass drilling bits or diamond burrs, low feeds with high speeds, and lots of coolants. You may need a different CNC machine from the conventional type if glass is your primary material. Glass-fiber-filled plastics are even trickier to design but are more attractive.
Composites are generally non-homogenous and anisotropic, making them quite complicated when machining. Moreover, the high abrasiveness of their reinforcing constituents increases the difficulty levels. Proper tool design and operating conditions are therefore critical to avoid damages to the workpiece.
Finished woodworks are not reusable but can be repurposed as compost or mulch. Since wood is softer than metals and other substances, this material goes easy on the feeds and speeds. Wood is also easier to hold, stain, and paint but leaves your mill stained with chips and wears components faster than steel. Breakage is also common, especially when not using hardwood.
How Does a CNC Milling Machine Work?
We’ve already established that a CNC milling machine uses subtractive technology by combining computer software with grinding, drilling, boring, and cutting tools to transform a casting into a high-precision product with detailed size and shape. This precision and detail from the rotary cutters would otherwise be impossible due to human error.
Today’s market has anything ranging from a 2-axis machine to a 7-axis machine. The first step is to feed the designs to the software, which carries out the dimensional tasks of transforming the CAD to CNC. Once done, the milling can begin.
More industries are turning to CNC-milled products because of their high level of precision. However, these machines are pretty expensive to purchase, not to mention the attention and skill required to design complex products.
Reach out to us for all concerns or inquiries you may have concerning CNC milling and CNC machining in general.