In the world of machining, a “machine center” refers to CNC-integrated machines with robotic attachments.
Vertical Machining Center (VMC) is a machine tool with a rotating cutter used to drill, slot, and shape metal workpieces.
VMC machining is a manufacturing operation that uses a vertically oriented machining center to perform operations such as milling, drilling, etc., on different materials. In a vertical machining center (VMC), the cutting tool and workpiece can be moved along their respective axes, and a computer system controls their movement.
The use of VMCs has largely increased in industrial applications, with new models being released every year.
This article discusses VMC machining by looking at its working principles, machine configurations, machining operations, workflow, applications, etc.
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VMC Machining Explained
The axes on VMC machines are automated by a controller using instructions fed through a part program.
A CNC programmer uses CAM software, such as CamBam, MeshCAM, EstlCAM, DeskProto, etc., to prepare the design file for the part program.
VMCs mostly have 3 axes, i.e., 2 horizontal axes (X, Y) and 1 vertical (Z) axis. The axis system on these machines is the same as those of a Cartesian coordinate system.
The work table moves along the horizontal axes, and the spindle column moves along the vertical axis.
| Axes | Transmission |
|---|---|
| X-axis | Moves the work table left and right |
| Y-axis | Moves the work table forward and backward |
| Z-axis | Moves the spindle up and down |
Standard 3-axis setup of VMCs
With the addition of the 4th-axis on VMC, you can turn and work around a workpiece. These machines are even available in a 5-axis configuration.
What’s the Process/Workflow in VMC Machining?
CAD
CAD (computer-aided design) operation is the first step towards making a successful part on a CNC machine.
Generally, CAD software programs like Adobe Illustrator, Autodesk Fusion 360, etc., are used to generate the design file.
CAM
The design is then converted to code using CAM (computer-aided manufacturing) software.
A program code file will have all the coordinate information required for the machine tool.
Some standard CAM software programs are CamBam, MeshCAM, EstlCAM, etc.
Simulation
You can test the generated toolpath using CNC simulation software. It gives you a beforehand look at the machining process and the result you will likely get.
Simulations can help you find errors in the program and save your machine from any possible damage.
Control
In the control stage, we use the generated G-code file to control the machine.
Control software that seamlessly interfaces with the CNC controller on your VMC is used for this process.
Standalone controllers like MASSO G3 have both the controller and its software housed in a touch interface.
For example, Sherline uses such a setup for their Accu-Pro VMCs.
One should set up the machine tools before running the machine. The setup procedure includes setting up the table, the cutting tool, and other necessary components.
The next step is to set up the operation parameters for milling. These include depth of cut, chip load, feed rate, spindle speed, and cutting speed.
Types of VMC Machines
Hard Rail and Linear Rail
VMCs can have a hard or linear rail based on the guide rails on each axis.
VMCs with a hard guideway have a stiff setup that can hold heavy workpieces and offers strong seismic resistance. It is best suited for heavy machining applications.
Linear rail VMCs use a guide rail with ball-bearings, allowing for rapid transmission. These are best suited for quick machining of soft metals.
Low Speed and High Speed
Based on the spindle speed, VMCs are classified as low-speed and high-speed VMCs.
A VMC with a spindle speed over 18,000 RPM is considered a high-speed VMC, and anything below that is considered a low-speed VMC.
Fixed C-Type and Moving Gantry-Type Column
In a gantry-type VMC, the spindle moves along the X and Z axes, while the workbed moves along the Y-axis.
On a fixed C-type column VMC, the spindle only moves along the Z-axis, while the workbed can move along the X and Y axes.
Components of a VMC Machine
CNC controller
CNC controller is one of the major components of a VMC machine. It is the central processing unit that controls the transmissions of each of the axes.
The controller allows you to connect your machine to a computer. You can even operate it offline on VMCs with a connected pendant.
Work Table
The worktable provides an area to mount the workpiece for machining operations.
It slides along a set of rails and generally moves along the X and Y axes on most vertical machine centers.
Spindle
The spindle of a VMC stays above the workbed and lies perpendicular to it. The cutting tools are connected to this rotating spindle.
Generally, VMC spindles provide variable speed control to adjust the spindle speed according to the desired machining operation.
Automatic Tool Changers
Automatic tool changers are commonly seen in industrial-grade VMCs. It helps you bridge the delay in changing tools and allows faster processing.
Coolant System
The coolant system on a VMC flushes the workpiece and tool contact area with a CNC cutting fluid that lubricates the work surface.
This helps extend the tool’s life and provides a smooth surface finish to the machined workpiece.
Enclosure
The enclosure covers the machine’s work area and prevents accidents.
It also blocks the coolant and chips from shooting out of the machine.
Chip Conveyor
Chip conveyor moves the chips from the bottom of your machines and pushes them out to a chip storage box.
It also helps keep the coolant clean by clearing the chips away from the work area.
Some machines power the conveyors directly while others may require additional wirings.
VMC Machining Operations
Milling
Milling is a machining process in which the machine tool moves along a linear axis and cuts away material from the surface of a workpiece.
Boring
In a boring operation, the machine tool enlarges already drilled holes in a workpiece using rotating cutting tools.
External borers, such as a boring block or a boring bar, are used to create holes larger than the diameter of the borer’s shank and are typically used for boring larger holes.
Internal borers have shanks with diameters equal to or less than the hole they will create.
Drilling
Drilling is a machining operation that uses a rotary drill bit to cut holes in the material. Drills are used for both metal and non-metal materials.
VMC can perform single-point or multi-point drilling operations.
Single-point VMC is designed to cut holes of one size, while multi-point VMCs use automatic tool changers to swap tools that can create different size holes depending on the tool being used.
Tapping
Tapping is a machining process that makes a hole in a workpiece. This hole is usually threaded, meaning it has internal threads to allow the fastening of screws.
It is done using a tap, a tool with cutting edges and flutes (grooves) on its circumference.
The tap cuts into the surface of the workpiece and forms an internal thread by means of cutting action as it rotates.
Threading
Threading is a machining operation similar to tapping, but threading is performed on the outer diameter of a workpiece, by using a cutter having helical flutes or teeth.
Thread milling operation is a versatile operation where a single cutting tool can be used to cut internal and external threads of various sizes.
Threads are used to join two parts together or to form the screw threads on bolts and screws.
Applications of VMC Machining
VMC machines are used in various industries to manufacture different parts and components.
They can make parts with high precision and accuracy (+/-0.0001″). These machines are largely employed in the large-scale production of repeatable parts.
Some of their common applications are in aerospace, medical equipment, military, machine parts, automobiles, etc.
If you are looking for a good VMC for your workshop, DMG Mori is the most popular manufacturer that produces VMC centers such as CMX 600 Vi, I 30 V, NVX 7000, etc.
However, if you are looking for a comparatively more affordable Chinese alternative, you can look for VMCs manufactured by TAICNC.
Difference between VMC and HMC
| Parameter | VMC | HMC |
|---|---|---|
| Size | Comparatively smaller | Comparatively large |
| Z-axis | Along vertical plane | Along horizontal plane |
| Price | Comparatively less | Comparatively more |
| Chip flow | Poor, against the gravity | Good, downwards along the gravity |
| Workpiece Capability | Ideal for small and simple workpieces | Ideal for larger and complex workpieces |
| Ideal for | Disk, sleeve, plate, etc. | Box, cylinder, shells, etc. |
VMC vs HMC
Vertical machining centers (VMC), as the name suggests, have a vertical configuration where the cutting tool moves up and down along the Z-axis.
Whereas a horizontal machining center (HMC) consists of a horizontal cutting tool (parallel to the ground) that moves along the length of the workpiece, to perform the cutting action.
VMC has a comparatively smaller size with simple construction, which thereby reduces the overall price of the equipment, making it ideal for small-scale applications.
The horizontal spindle orientation in HMC facilitates easy chip under the action of gravity, whereas on a VMC configuration requires chip clearance against the action of gravity.
As a result, on VMC, the accumulated chips in the cutting area result in a comparatively poor surface finish.
Apart from that, HMCs are comparatively more automation ready than VMC, making them ideal for applications involving the machining of complex geometries.
Overall, both tools provide excellent results for their respective applications. VMCs are recommended for applications where machining of flat workpieces, such as disks, sleeves, plates, etc.
Whereas HMC is ideal for machining boxes, cylinders, shells, etc.
Final Thoughts
VMC machining is a great alternative to manual machining centers as these machines are automated using a CNC system
This reduces most of the manual work of a machinist. In addition, the high accuracy and repeatability of VMCs allow you to create precise parts with minimal effort.
Frequently Asked Questions
What does VMC mean in machining?
VMC in machining stands for Vertical Machining Centers. These CNC machines can drill, tap, mill, and bore on different materials, including metals.
How many axes are in a VMC machine?
A VMC can have multiple axes, but 3-axis VMCs are the most used type. These machines are also available in 4-axis and 5-axis setups.
What’s the difference between HMC and VMC?
The difference between an HMC and VMC is that VMC (vertical machining center) has a vertical spindle that is perpendicular to the ground. In contrast, HMC (horizontal machining center) employs a spindle that is parallel to the ground.
