What Is A Bridge Milling Machine?

Posted on Jan 3, 2021

Bridge Milling Machine

A CNC machining center can be a CNC lathe, a CNC turning center, or a CNC router. The CNC lathe and turning center are more of a C-frame machine while a router is known for its bridge-style configuration and therefore a CNC router is sometimes called a bridge milling machine.

A Brief Introduction to Milling Machines

The bridge milling machine is a type of milling machine. A milling machine is a machine tool used primarily for milling operations. To date, a milling machine is referred to as a multi-purpose machining operation platform. This type of machine is essential in the modern manufacturing and engineering industry since the advanced machining center allows multiple types of machining works to be performed. In a modern manufacturing setting, the machining centers frequently incorporate the computer numerical control (CNC) system in order to carry out the precision machining works with efficiency. Sometimes a CNC milling machine is regarded as the main form of the machining center.

The fundamental components of a milling machine include a lathe bed and a spindle head. The lathe bed is where the workpieces are positioned and machining processes take place. In some models, the machine adapts different forms of the worktable to process particular types of workpieces. The spindle head is the rotating part that performs the machining operations. A CNC machining center can be a CNC lathe, a CNC turning center, or a CNC router. The CNC lathe and turning center are more of a C-frame machine while a router is known for its bridge-style configuration and therefore a CNC router is sometimes called a bridge milling machine.

What Is a Bridge-style Machining Center?

When it comes to a bridge-style machining center or a bridge milling machine, it is usually a CNC router or a CNC gantry machining center that comes to people's minds. The CNC router is called a bridge milling machine because there is a gantry that bridges over the machining surface. Since the gantry is supported over the lathe bed by two columns on its two ends, the bridge milling machine is also known as the double column milling machine or double column machining center. The two supporting columns are attached to a rail set at the longitudinal sides of the machine which allows the gantry to move across the lathe bed surface.

:: Read More: CNC Bridge Mill - A Bridge Type Vertical Machining Center

The Machining Surface of a Bridge Milling Machine

There is always a milling surface on a CNC machining center; the milling surface can be a lathe bed, a faceplate, or a flat with linear guides and bolt screws. Regardless of the style the milling surface is, it is the place where the workpieces are held and where the machining operations are performed. The way a workpiece is secured on a bridge milling machine varies based on the work-holding system it accommodates with. The most common work holding systems are jaw chuck, magnetic chuck, or vice just to name a few.

In most machining processes, the workpieces are held stationary in place; yet, in some other processes, the workpieces are secured by the work-holding system and the system can move along the axes of the milling machine so that multiple machining operations can be performed at once. On a typical CNC turning center, it is usually a servo motor that controls the movement. As for a bridge milling machine, the lathe bed is a flat surface mounted onto bolt screws with linear guides. With such configuration, the workpieces are allowed with a linear movement along with the CNC router.

How Do CNC Gantry & Spindle Head Work?

Unlike a typical CNC turning center that is equipped with a standalone spindle head, a double column machining center has the spindle head and the cutting tool attached to the gantry bridge. Because the gantry is supported by the columns on the rail set along the machining center, the gantry is allowed with the moving ability across the lathe bed. Therefore, the spindle head that attaches to the gantry can perform the milling operations along the longitudinal axis of the lathe bed. Such movement is known as the X-axis movement.

Besides the X-axis movement, the spindle head has an additional Y-axis movement capability. The Y-axis movement refers to the movement of the spindle head across the gantry bridge. With the X- and Y-axis movement capability, the spindle head can perform milling processes along both the longitudinal axis and latitudinal axis of the lathe bed, which basically covers the entire milling surface. A bridge milling machine with 2-axis movement capability is ideal for processing the workpieces that have a wide surface.

Z-Axis Milling Capability of a Bridge Mill

A conventional double-column CNC machining center is used primarily to process the workpieces with a wide surface or sheet metals. The goal of the machine is to create a profile, drill holes, grooves, and slots, or make marks on the surface of the workpiece. This type of machining center cannot handle the workpieces that have significant altitudinal differences. In order for the bridge-style milling machine to carry out more complex surface designs on a workpiece, an additional Z-axis movement capability is required. Z-axis movement capability allows the machine to perform more delicate machining operations

Generally speaking, Z-axis machining refers to the vertical movement of the spindle head. The vertical movement is driven by a power system that is responsible for lifting and lowering the spindle head on the CNC gantry. The power system is usually a hydraulic system or a pneumatic system on a console-style CNC router. The power source may also be an electrical motor on a smaller scale bridge milling machine. With the Z-axis capability, the versatility of a bridge-style milling machine is improved. The 3-axis double-column machining centers are ideal for a wide variety of part manufacturing applications such as die/ mold manufacturing.

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