CNC stands for Computer Numerical Control, which is the automated operation of a machine tool by way of a computer the is programmed to perform a series of sequential operations. While there is a multitude of CNC operated machinery, the two most common types of CNC machine tools used in what we would consider traditional machining processes are milling and turning. Generally speaking, CNC Lathes or the Turning process is used to manufacture round parts, and CNC Mills are used to manufacture a variety of different geometric shapes and features. A further explanation of each of these technologies is given below.
A milling machine or mill for short, functions by spinning at very high speeds, a cutting tool (eg- a mill or drill) relative to the work piece (or part to be converted from raw material into finished good) which is held stationary. In some cases the work piece is moved in very slow relative motions in coordination with the cutting tool. When the high speed cutting tool comes in contact with the raw material it starts to shave away the surface layer of the material in small chunks or chips. A good analogy for this would be the way a chisel works on wood, or even a knife through butter. As the cutting tool takes more and more material off, the automated controller continues to extend the tool into the part until the desired shape or dimension is achieved. The speed at which the spindle (the element that holds the cutting tool) spins is referred to as the Spindle Speed or often just Speed. The rate at which the tool moves relative to the work piece (movement along an X, Y or Z axis) is referred to as the Feed Rate or just Feed. The Speed and Feed rates are very critical and need to be highly controlled to conform to the unique characteristics of different materials, cutting tool types, and features being machined. In a CNC this process of material removal is automated and therefore highly controlled and very repeatable.
Metal is perhaps the most common material type to be machined on a CNC Milling Machine, but these machines can also process various plastics, woods, composites and ceramics along with myriad other elements and compounds. Metal machining ranges from carbon and stainless steels to aluminum alloys to brass and copper to a variety of specialty and exotic metals like Inconel, Hastelloy, etc.
While there are several different configurations of CNC milling equipment, in general there are a number of common elements used in each. The diagram below highlights some of the common components of a machine. The spindle is the moving element of the machine that holds the cutting tools (mills, drills, etc). The spindle rotates at very high rates of speed, often up to 20,000 RPM, but some machines can reach speeds up to 60,000 RPM or higher. The part to be machined is held in a workpiece holder or vice. The vice clamps and holds the part in place either through a manual crank or some external force, such as hydraulic or pneumatic vices. Multiple vices can be mounted in a stack to the worktable. The worktable is a flat tabletop often with grooves for mounting accessories like workholding equipment, or rotary axes. The base of the machine is the large frame that supports the entire payload and dynamic forces exerted from the equipment. The user interface houses the machine controller, and can be programmed to enable CNC automated control of the machining process.
In the diagram below there are three different axis of motion to move the workpiece relative to the spindle and cutting tool. In some cases it is the spindle moving, in other cases the workpiece is moving. This varies greatly from one machine design to the next and some machines have as many of 5 separate axes of motion allowing for machining of complex geometries. These would include 3 linear axes of motion (X, Y, Z) and two rotary axes. In some machine designs the spindle axis moves in and out relative to the work piece (typically referred to as the z-axis), while the worktable moves side to side and in and out (the x and y axis. In some designs the spindle moves in 2 axes and the table only moves in one, along with a variety of other designs. Additionally designs vary based on whether the machine is a vertical mill or a horizontal mill as discussed further below. CNC mills will also a tool changing system. This component can house multiple different types and sizes of tools and can index through the tools for quick and automated change-over during the machining process. As a practical example, imagine a project where we need to machine a tapped hole into a square plate. Once the plate is mounted in the vice and the machine is programmed for the operations to be done, the spindle axis will retract to its home position, the tool changer will index to the appropriate tool, in this case a drill to drill the hole for the tap. The size of the drill and the particular tool number in the index will have already been programmed into the CNC. Once the hole is drilled the spindle will retract again, the tool changer will move to the correct tap tool and then replace the drill with the tap, and then the machine continues the operation.
There are several different machine construction styles of CNC Milling Equipment. Three of the most common configurations used in industry today are highlighted below-
Vertical Milling Technologies
A vertical mill is what is shown in the diagram above. In this configuration, the spindle is oriented vertically relative to the worktable. The worktable is almost always parallel with the floor. This means that when the spindle moves to the part it is moving up and down inside of the machine. Typically the worktable moves around under the spindle in the X and Y axis and will sometimes house rotary axis. The spindle either moves up and down to the part or sometimes the worktable will move up and down relative to a fixed spindle.
This configuration is ideal for plunging type machining operations, and also lends itself to larger potential workpiece sizes than horizontal technologies. This is because the work piece size is typically limited to the size and travel of the worktable and not the travel of the spindle.
Horizontal Milling Technologies
Picture taking the spindle of the vertical mill and flipping it 90 degrees on it side, and you will be left with a Horizontal Mill. Here the spindle is oriented parallel to the worktable and thus the floor. The spindle moves in and out rather than up and down. The in and out motion is called the Z axis, just as with the vertical mill, and in some cases the spindle moves in the Z, sometimes the table moves and in some cases both both in the Z. The X motion is made moving side to side (parallel to the floor) and the Y motion is up and down (perpendicular to the floor). X and Y can be performed on the worktable or the spindle depending on the design. There is also typically a rotary axis, often referred to as the B-Axis, on the worktable making this a 4 axis machine. This rotary axis often includes a workholding fixture referred to as a tombstone or clamping pillar. These tombstones sit on top of a pallet, which is on the rotary table. There are typically multiple pallets on a horizontal mill, allowing for changeout of the workpiece on one tombstone, while the other is undergoing machining. This makes for a highly efficient process.
Horizontal Mills are ideal for machining grooves, slots and facing off a part, as well as parts that have multiple sides or faces that need to be machined.
Boring Mill Technologies
Like traditional milling equipment boring mills can be segmented into vertical and horizontal configurations. Horizontal boring mills functions much like a horizontal milling machine as highlighted above. Vertical boring mills (sometimes referred to as a VTL- Vertical Turret Lathe) are more similar to vertical turning equipment and will thus be covered under the Vertical Turning Technologies section. Probably the largest differentiating characteristic between boring equipment and standard milling machinery is the size and scale. Boring mills are generally much larger in size, allowing them to machine much larger work. As the name indicates, boring mills are designed to bore or enlarge large holes in materials. They are also ideal to face off (machine the entire surface on a single plane) material. The orientation of a horizontal boring mill is set-up exactly like the horizontal mill, with the Z-axis being the in and out motion of the spindle relative to the part, the X-axis moving side to side and the Y-axis moving vertically. Any rotary axis would be referred to a the B-axis.
Our CNC Milling Process and Approach
At Alle-Kiski CNC Machining is the backbone of our business. We have 17 modern CNC centers to serve a variety of different unique machining requirements. We are constantly reinvesting in our business and adding new machine tools to our equipment portfolio. We have predominantly standardized on Mazak systems, as we have found that the durability, performance and ease of use is unmatched. Additionally, we have a number of high performance Haas systems to maximize our range of capabilities.
For a current list of all of our equipment see our Equipment List.
Our milling equipment includes both horizontal and vertical machinery, which we leverage to ensure that we can cover a broad range of applications and requirements and do so as cost-effectively and efficiently as possible. Our machines are all staffed with our experienced team of journeymen machinists. The pool of talent and experience in our machining area is the secret to our success. Their combined know-how allows us handle complex machining challenges along with giving us a great deal of flexibility to program parts right at the machine and adapt to changes or unique needs from our customers.
Our approach is focused around flexibility. We thrive in projects that range from low volumes or even single piece such as prototyping, to high volume production runs. We can support a variety of materials, from steel to stainless steel to aluminum to plastics to exotic metals and everything in between. We cover industries from medical, to energy to defense to instrumentation and robotics and more.From small high precision parts to large part requirements, our goal is to service a wide range of needs for our customers. To supplement our internal capabilities, we have built out a strong partner network that allows us to fill in any gaps, and maximize response time.
Have a current or upcoming project? Have a member of our team contact you to discuss.
CNC Milling Applications
Generally speaking any milling operation, whether CNC controlled or manually operated, is optimal for industries and applications that require removal of metal from a raw material to reshape it into a specified dimensional footprint or with specific dimensional features. Some example operations include but are not limited to:
- Drilling of holes for mounting- eg screw holes, clearance or access holes, ports, etc
- Threading of holes
- Boring or opening up holes- eg- enlarging a hole in a casting to a specified dimension
- Milling of a planar surface (referred to as face-milling) to achieve a flatness or straightness specification
- Milling of slots or grooves- eg. bearing seats, keyways
- Surface contouring- to achieve unique surface geometries
- Gear cutting
The Advantages of CNC Milling
Because of the automation that CNC equipment provides CNC mills are generally more ideal for larger production runs (greater consistency through automation) and parts with greater complexity in shape and contour. Conversely small run volumes of parts with limited complexity may be more ideal for a manual process as the time to program the machine is eliminated, making overall run time shorter and therefore more cost-effective to produce.