Machining centers (MCs) are advanced computer-controlled machine tools that can be used for performing different machining operations.
How does a machining center work? What are its features and applications?
This article provides a detailed guide on machining centers, their features, types, operations performed with them, and their industrial applications.
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Machining Center: Explained
A machining center is a CNC machine tool that can perform different operations like milling, boring, and drilling, with high accuracy and minimal time. It consists of an automatic tool-changing mechanism that enables it to use multiple cutting tools during the machining process.
Traditional machines feature turrets or other mechanisms of manual tool change that are time-consuming and tedious.
Whereas an automatic tool changer (ATC) unit enables quick change of the cutting tool to perform multiple machining operations, thereby improving production efficiency and reducing cycle time.
Components of a Machining Center
Different components in a machining center work in coordination to perform the desired machining operation.
Main Spindle Area
The main spindle area consists of the spindle, motors, couplings, power locks, and highly durable oil-resistant belts.
A spindle plays a fundamental role in the working of a machining center as it houses the cutting tools and rotates them at high speed.
Machining centers housing a directly coupled servo motor system comprise a motor connected to the spindle shaft via couplings, which provides rotary motion to the spindle.
The spindle of a directly coupled motor is fastened to the rotors with the help of power locks.
On the other hand, indirectly coupled motor systems use a belt and pulley system to transmit the rotary motion from the motor to the spindle shaft.
Taper Feed Mechanism
The taper feed mechanism consists of components such as servo motor couplings, ball screws, etc., that ensure spindle and table movement along the different axes.
These sub-components have a long life and ensure quiet and smooth operation.
Automatic Tool Changer (ATC) System
ATC systems are generally of two types: drum type and chain type.
Drum type ATC, as the name suggests, consists of a drum-shaped tool magazine that is used when the number of tools required for a machining operation is under 30.
On the other hand, chain-type ATC usually comprises chain and sprocket systems with power locks that enable automatic tool change movement.
These ATCs can hold more than 30 different tools but the tool change speed of drum type ATC is comparatively faster.
When the CNC program runs and executes the tool change command, the motor-driven ATC arm selects the desired tool from the tool magazine, bringing it into position while the power locks ensure that the new tool is fastened properly onto the spindle.
Tool Magazine
A tool magazine is a motor-driven drum or chain system housing different tools required in a machining operation.
It is interlinked with the ATC system via the ATC arm that picks the required tool from the tool magazine, as per the CNC program.
Automatic Pallet Changer (APC) System
Pallets are structural supports between the machining center and the work table on which the workpiece sits. An APC system automatically replaces them.
Automatic pallet changing significantly improves the speed of transition to a new workpiece, which makes continuous machining possible and improves production efficiency.
APC system consists of reducers and couplings for the servo motor that reduce the motor RPM as per requirement.
Chip and Coolant Handling System
This system mainly consists of chip conveyors and a CNC cutting fluid delivery system.
The cutting fluid facilitates easy chip clearance and ensures that the tool or workpiece does not heat up due to friction.
Chip conveyors comprise a belt and motor system to carry away the metal chips produced during the cutting operation.
These chips and used cutting fluid are then collected in a waste recovery system for proper disposal.
Overload and Wear Detectors
These sensors and devices monitor electric power fluctuations and detect overloads, usually caused by excessively high tool feed or wrong tool positioning.
An overload protection device can help avoid tool damage or defects in your workpiece.
Automatic Door Operation Mechanism
Machining centers have an automatic door operation that uses a belt or a zip chain system with a linear actuator that converts the rotary motion of the motor into linear motion of the door.
Types of Machining Centers
Machining centers are classified based on their number of axes, the dimensions of the working area, spindle position, and the machine options available.
Horizontal Machining Center
A horizontal machining center (HMC) houses a horizontal spindle that moves sideways, thus machining the workpiece horizontally.
The tool magazine can store between 16 to 100 tools at once, and the automatic pallet changer (APC) consists of six or eight pallets, each substituting the preceding one to work on different workpieces.
HMCs usually consist of relatively large tools, capable of performing machining operations with a high material removal rate (MRR).
They can machine up to 4 surfaces of a workpiece without the need to manually change the workpiece orientation.
Moreover, the metal chips fall vertically, which prevents their accumulation on the workpiece surface.
The horizontal alignment and easy chip clearance make it ideal for boring machining by using a boring bar.
Some HMCs have an additional feature of rotating the spindle to a vertical position, allowing greater flexibility in machining operations. Such models fall under the category of universal machining centers.
The most common application of HMCs is the mass production of components like gears.
TAICNC is one of the leading manufacturers of machining centers. Their TC-540W horizontal machining center provides the ability to house 16 different tools in their ATC system.
Vertical Machining Center (VMC)
A vertical machining center (VMC) houses a vertically positioned spindle.
VMCs also consist of ATC and APC systems, but with a lower tool and pallet capacity. As a result, they occupy relatively less space, making them more portable and convenient for DIY users.
However, due to the spindle and tool position, metal chips accumulate on the workpiece surface and should be washed off using a lubricant or a blower.
Although 3-axis VMCs are more common, some models, such as 4-axis CNC routers, can access the workpiece from four sides without manually changing the workpiece orientation.
Tormach PCNC 440 is an example of a VMC that can be used for milling operations of different materials.
The most common industrial applications include engraving workpiece surfaces and mold processing.
Universal Machine Center (UMC)
A universal machining center (UMC) has a spindle that can be oriented horizontally or vertically.
Generally, a universal machining center comprises a 5-axis system or higher, thus making it possible to access the workpiece from 5 or more different sides in a single setup.
For instance, in 5-axis UMC, the cutting tool can move along the X, Y, and Z linear axes and rotate about the A and B axes.
This feature makes them ideal for complex machining operations to manufacture components like impellers or tire molds with high precision and accuracy.
UMCs use shorter cutting tools with higher speeds and a broader range of orientations, which reduces cycle time, improves production efficiency, and leads to lower vibration levels.
Conclusively, UMCs are a blend of HMC and VMC.
Features of a Machining Center
Machining centers have various features that have significant practical usage.
| Features | Use |
|---|---|
| High accuracy and precision | For complex geometry workpieces |
| Automatic tool changing | High volume/bulk production of products |
| Multiple tool option | For multiple machining operations in a single setup |
| Chip Removal | Keeping the worktable and workpiece clean |
| Coolant Management | Preventing tool or workpiece damage due to heat |
| Multiple cutting axes/ orientation | For complex geometry workpieces |
| Ergonomical and safe | For a simple and straightforward machining operation |
| Automatic Pallet change | High volume/bulk production operations |
Distinctive features of a machining center
Multiple Axis System
Machining centers generally consist of a 3-axis system, in which the cutting tool moves along the X, Y, and Z-axis to access the workpiece from three sides.
However, modern CNC machining centers can consist of higher axis systems such as 5 or 6-axis systems, making it possible to machine extremely complex geometries with high precision and accuracy.
Automatic Tool Changing
The automatic tool changer eliminates the need for the tool to be manually changed after each operation, thereby reducing the cycle time and making bulk production of goods convenient.
It consists of a tool magazine that holds multiple tools. The G-code commands the machine to execute the tool-changing operation and select the appropriate tool for the process.
Chip Removal and Coolant System
The chip removal ensures that the worktable and workpiece surface stays clean, whereas the coolant system prevents overheating, thereby reducing tool wear and preventing dimensional inaccuracy.
Safety and Automation (ATC and APC)
All the machining operations in a machining center are automated, including tool changes.
This eliminates the need for manual handling of tools and workpieces, reducing the probability of any injury, and improving the working conditions of the operator.
Furthermore, the automatic pallet changer automatically loads the new workpiece on the workbed of the machine, making it ideal for mass production applications.
Applications of Machining Centers
Machining centers have vast industrial applications, commonly employed in power generation, automobile, aerospace, and marine industries.
Dies and Mold manufacturing
Machining centers are used for manufacturing dies and molds, mainly through the processes of drilling and milling.
These dies and molds are then used to manufacture components like automobile engines, airplane sheet metal parts, other glass, and rubber parts, etc.
Complex Components
Due to their ability to produce complex parts with high accuracy, machining centers are used for manufacturing highly complex parts such as wing frames, impellers, propellers, heat sinks, etc.
Large-scale Manufacturing
The automated nature of machining centers provides them with high repeatability, making them ideal for bulk production of identical components like spur gears.
Technological advancements have led to the development of 9-axis machining centers that combine the functionality of a CNC lathe and a CNC router, making them highly versatile and fast.
How much does Machining Center Cost?
| Type of Machining Center | Cost Range |
|---|---|
| Entry-level Production VMC | $50,000 – $150,000 |
| Professional 3-axis VMC | $150,000 – $400,000 |
| 5-axis Mill | Above $300,000 |
| Entry Level Production HMC | $25,000 – $250,000 |
| Professional HMC | $300,000 – $500,000 |
| Multi-spindle/Multi-axis Lathe | Above $500,000 |
Cost of a machining center
The cost of a machining center depends upon various factors such as size, rigidity, speed, power, functionality, brand, and accessories provided with it.
Generally, a machining center that provides a larger work area is comparatively more costly than its smaller counterpart, and even a slight increase in the work area drastically affects the cost of the machine.
Apart from the size, the rigidity of the machine also plays an important role in the cost. A machining center with rigid construction can deliver a stronger cutting force, making it ideal for machining various materials.
Similarly, the speed and power of a machining center affect its ability to perform clean cuts with minimum cycle time, and therefore directly affects its productivity.
The functionality is one of the most important factors in industrial-grade machines.
A CNC machining center with a multi-axis (5 or 6-axis) system is considered a universal machining center, capable of performing almost any operation.
As the number of axes increases, the cost of the machining center also increases.
Brand plays an important role in terms of the quality of products and aftersale services. Generally, cheaper brands provide similar machines at lower cost by compromising the quality.
However, machining centers from popular brands such as Haas, TAICNC, Tormac, etc., can be comparatively more costly than Chinese brands, but they offer a reliable service and excellent quality.
Furthermore, the accessories provided with the machine also affect the cost of the machine. Some of the popular accessories for machining centers include cooling systems, automatic tool changer, chip conveyor, etc.
Final Thoughts
Machining centers are powerful industrial tools that are available in different types, each with unique characteristics.
The automatic tool changer (ATC) and automatic pallet changing (APC) features make machining centers ideal for large-scale applications where similar operations are to be performed on multiple workpieces.
Modern machining centers are available in 6-axis configuration, making it possible to move the cutting tool from horizontal configuration to vertical configuration, combining the functionality of two machines in one.
This improves production efficiency, reduces cycle time, and makes it more convenient to perform different machining operations on a single machine.
Frequently Asked Questions (FAQ)
What programming language do CNC machining centers use?
G-code is one of the most popularly used programming languages for CNC machinery.
What are the common problems encountered in CNC machining centers?
Tool and workpiece heating, unwanted vibrations, programming errors, wrong tool settings, and solid-waste disposal are some common problems encountered in CNC machining centers.
What are the A and B-axis in universal machining centers?
A-axis is the rotary axis around the X-axis, while the B-axis is the rotary axis around the Y-axis.
