CNC milling machines are one of the most popular tools for machining metals to get the desired workpiece.
These rigid and powerful machines consist of various parts that work in synchronization to perform the desired milling operation.
Parts of a CNC milling machine include a column, base, knee, power feed mechanism, a work table, ram, spindle, milling tool, milling chuck, CNC controller, and an overhanging arm along with arbor support in case of horizontal milling machines.
This article discusses the parts of a CNC milling machine and explains their significance in the operation of the machine.
In the end, the article also discusses the factors to consider when buying a CNC milling machine.
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Parts of a CNC Milling Machine
A CNC milling machine comprises several components, each of which plays an essential role in its functioning.
The CNC controller is the brain of a CNC milling machine. The electronic system executes all the commands entered by the CNC programmer.
It eliminates the need to manually move or interact with components, as it carries out the input in an instance.
You enter the G-codes, after which the CNC controller translates these codes into the respective mechanical operations and executes them by sending the proper signals to the relevant servo or stepper motors.
Column and Base
The column and base are the heaviest elements in a milling machine as they support the load of all other parts of a CNC milling machine.
These are generally made of cast iron to provide rigidity and the ability to dampen the vibrations produced during the operation of the machine.
However, these components are often filled with epoxy granite to enhance their ability to dampen the vibrations during the operation, thereby enhancing the machining quality.
The base supports the weight of the whole machine, whereas the column mainly houses the coolant and oil system and takes the weight of the knee and work table.
The knee is generally made of cast iron and is connected to the column.
It consists of a dovetail slide with vertical positioning screws to move the worktable up and down, i.e., the knee facilitates the vertical movement of the milling table.
CNC milling machines consist of an automatic mechanism to position the knee accurately based on the input received from the CNC controller and a manual hand wheel to position it manually.
A saddle is a cast iron component that rests above the knee.
It facilitates the to-and-fro movement of the worktable to machine the workpiece along the X and Y axes.
CNC milling machines consist of an electromechanical system that controls the three-dimensional movement of the feed mechanism.
It consists of electrical motors that take the input from the controller and produce the required movement in the workpiece to get the required cut.
The worktable is a flat surface made of cast iron, with T-slots on it.
These T-slots provide the ability to fasten the workpiece on the table by using different workpiece clamping tools, thereby holding the workpiece firmly in place to perform milling operations.
The power feed mechanism controls the movement and the feed of the worktable.
Apart from that, some milling machines, such as Millright Mega V provide a hybrid worktable that supports CNC milling and CNC plasma cutting on the same machine.
The ram is a movable arm-shaped support in vertical milling machines, supported on top of the columns. It houses the milling head, which holds the milling tool assembly.
An overhanging arm is a cast iron component supported by the column and dovetail slides.
Similar to ram in vertical machining centers, the overhanging arm is found in horizontal milling machines to house and support the milling tool assembly.
An arbor support is a cast iron component found in horizontal milling machines.
It is connected to the spindle through bearings and supports the milling tool.
It provides structural integrity and support against vibrations experienced during cutting operations.
The high carbon chromium steel spindle is a fundamental component of a CNC machine that drives the milling tool.
It also houses the milling chuck and is connected to the main motor of the CNC machine.
The CNC controller takes in the G-code and rotates the speed according to the CNC program.
A milling chuck is a tool-holding component that consists of jaws to clamp the cutting tool.
These jaws can be tightened or loosened to hold the tool for milling operation.
A milling tool is the main component that performs the cutting operation.
These tools are available in different types, and suitable for different types of milling operations, such as peripheral milling, face milling, etc.
Apart from the operation, each type of material requires different cutting tools.
For example, milling copper or aluminum requires tools with less flute, whereas milling tungsten and titanium require rigid tools.
Accessories Used With CNC Milling Machines
CNC milling machines comprise various accessories.
A coolant system is crucial in a CNC milling machine.
It ensures a continuous flow of coolant to the workpiece and the tool so that they do not heat up excessively during the milling operation, thereby preventing tool or workpiece damage.
The coolant or cutting fluid can be water or oil-based, where water-based coolants are suitable for minimizing heat, and oil-based coolants are ideal to maximize lubrication.
Generally, a coolant system consists of a pump, piping, and nozzles.
Powered drawbars are iron or steel couplings that use a pneumatic system to tighten or loosen the drawbar automatically for tool change.
It is generally used in CNC milling machines integrated with an automatic tool changer.
An enclosure is an acrylic or metallic guard that encloses the workspace of the milling machine so that the chips produced during milling do not fly off.
Generally, professional CNC milling machines, such as Tormach PCNC440 come pre-installed with a safety enclosure.
This adds to the safety of the operation, preventing any injury to the CNC operator.
4th Axis or Rotary Kit
A rotary kit adds a 4th axis to the milling system and provides the ability to mill curved or cylindrical workpieces.
It generally consists of rotary rollers that can hold cylindrical workpieces and rotate them to access the workpiece from all sides.
Rotary kits are also available for entry-level CNC routers and mills to engrave parts such as furniture legs, tumblers, etc.
Automatic Tool Changer (ATC)
An automatic tool changer enables easy and fast tool change, especially when you require different milling operations on a workpiece.
These tool changers are available in different types, such as chain type, drum type, disk type, turret type, etc., and each type provides a different tool holding capacity.
Generally, chain-type ATC can hold around 100 tools at a time, while a drum type is suitable for holding around 32 tools, while the turret type can hold 8 tools.
An ATC can either be mounted on the column or separately from the machine and the G-code from the CNC program activates the CNC tool changer to automatically replace the tool for further machining.
However, CNC tool changers or ATCs can be expensive and are only suitable for industrial applications where high productivity is of utmost importance.
A chip tray collects all the chips generated during the milling operations.
The high-pressure coolant flushes the chips from the cutting area and collects them in the chip tray, where the cutting fluid is filtered out and collected in a separate tank while the chips are accumulated in the chip tray.
This minimizes the need for cleaning and enhances the productivity of the process by reducing maintenance time.
According to ISO 13849, machining safety is crucial and demands machine guards be installed against moving parts of the machine.
Unlike enclosures, machine guards only cover the cutting area and prevent the chips from flying off and injuring the operator.
Machine guards are generally made of metal or thick plastic covering the milling tool's cutting area.
Although they do not affect the performance of the machine, they can minimize the risk of any serious accidents.
Tools Used with CNC Milling Machines
CNC milling tools generally operate by rotating at high speed and removing the material from the surface of the workpiece, producing the desired cut.
These tools have a cylindrical structure and are clamped in the milling chuck, which then rotates them with the help of a spindle.
There are different tools, each differing in size, number of teeth, and shape.
The selection of the milling tool is based upon the type of milling operation to be performed, such as a face mill is suitable for face milling, an end mill is suitable for carving operations, etc.
Moreover, the required surface finish, material removal per revolution (Chip Load), depth of cut, cutting speed, and feed govern your choice of milling tool selection.
Generally, milling tools with fewer flutes and higher helix angles are suitable for milling ductile metals like copper and aluminum.
Whereas milling tools with more flutes are preferable for high material removal rate, and to achieve burr-free cuts.
Milling tools with longer cutting edges are ideal for roughing cuts as it leads to higher material/chip removal.
Contrarily, milling tools with shorter cutting edges are ideal for smoothing or finishing cuts as it leads to lower material/chip removal.
The milling tool should have an ideal length and runout so that it does not experience any unwanted vibrations or fatigue that could fracture it over time.
Apart from that, carbide end mills are suitable for machining hard metals where strong cutting force is to be delivered, whereas HSS tools are ideal for small-scale and DIY applications where tool wear is minimal.
Factors That Affect The Cost of a CNC Milling Machine
Various factors affect the cost of a CNC milling machine.
Table size directly affects the cost, meaning the more extensive the table, the more it will cost, but the larger the workpieces it can handle.
Therefore, it is important to understand your requirements and select the best CNC milling machine that offers the required table size.
Spindle power affects the milling capability. A powerful spindle costs higher but can machine metal workpieces with a clean surface finish.
For machining softer materials like aluminum, plastic, wood, or laminate, 0.8 to 5.6 kW spindle power is preferable.
The cutter size also plays a part in this selection. The larger the cutter size, the greater the spindle power it will require.
Generally, machining steel requires 3.3 to 10 kW of spindle power.
Rigidity of the Frame
The rigidity of the frame depends upon the frame material. The higher the rigidity, the lesser the vibrations and the better the ability to deliver effective cutting forces.
Generally, CNC mills are used for machining metal workpieces and therefore require rigid frames made of metal.
Steel is one of the most commonly used metals for the chassis of CNC mills.
The stronger the frame, the better the machining capability, and the higher will be the price.
Frequently Asked Questions (FAQ)
What are dovetail slides?
Dovetail slides are interlocking sliding joints consisting of a fixed and a movable member, in which the movable member slides along the fixed member’s rails.
What are the safety precautions you need to follow during the CNC milling operation?
The safety precautions you must follow during the CNC milling operations include wearing a safety face shield, safety gloves, safety boots, and headgear. Although machine guards usually cover the workspace in CNC machines, personal protective equipment is a last line of defense against any possible injury.
What are some of the most popular CNC milling machine brands?
Some of the most popular CNC milling machine brands include Fanuc, Tormach, Yamazaki, and Haas Automation.
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