What Is a Gantry Type Machining Center?
A gantry type machining center is a type of machining center that is automatically controlled by CNC (computer numerical control) commands.
It is classified as the largest machining center and consists of a spindle, table, column, NC unit, and automatic tool changer (ATC). It is so called because the structure supporting the spindle, which rotates the cutting tool, is gantry-shaped when viewed from the front of the machine.
Because of its structure which allows for a large width and length of the table for loading the cutting workpiece, it is used for heavy-duty cutting of large products. Because it is a very large facility, it is used only in a limited number of processing plants.
Because of the large size of double-column machining centers, there are only a limited number of domestic manufacturers of these machines. On the other hand, demand for double-column machining centers is increasing for use in larger semiconductor facilities and in the production of molds for electric vehicles.
Uses of Gantry Type Machining Centers
The gantry type machining centers currently in operation in Japan are capable of machining workpieces up to 12 m or more in length, 4 m or more in width, and 1 m or more in height, so their main applications are for large products.
Because of their extremely precise positioning and cutting accuracy, they are used in the machining of rotating parts for wind and hydropower generation equipment, nuclear power generation equipment, structural parts for aircraft, large vacuum chambers for semiconductor manufacturing equipment. They are also used for chambers for FPD manufacturing equipment such as liquid crystal and organic EL, parts for large ship motors, and parts for the automotive and aerospace industries. The principle of the double-column machining center is as follows.
Principle of Gantry Type Machining Centers
The structure of a gantry type machining center consists of a table on the floor for loading the workpiece to be machined, columns on either side of the table (the vertical pillars of the “gantry”), crossrails connecting the columns above the floor, and a spindle that moves on the crossrails.
Although large, it is suitable for precision cutting because of its high-precision positioning of around 2μm, and can be used for a variety of machining operations by changing the spindle attachment. However, the equipment itself is very expensive and the machining cost is also high.
Types of Gantry Type Machining Centers
Gantry type machining centers are classified into the following types according to the way each part moves. Each of the following types has a different rigidity, or direction to improve accuracy, and is selected mainly according to the axial direction in which accuracy is desired.
1. Fixed Crossrail Type
The column is fixed, and the spindle moves left and right on the crossrail. The spindle itself moves up and down, and the table moves in a direction perpendicular to the crossrail.
2. Crossrail Moving Type
The column is fixed; the spindle moves left and right on the crossrail, and the crossrail moves up and down. The table moves in the same way as in the fixed crossrail type.
3. Gantry Type
The table is fixed, and the column moves along the table. There are two types of crossrail movement: fixed type and movable type.
Structure of Gantry Type Machining Centers
A gantry type machining center consists of the following components:
1. Spindle
The spindle is used to mount and control the rotation of the cutting tools. In gantry type machining centers, the spindle number is No. 50 to accommodate heavy-duty cutting. The shank is larger than that of No. 40, which is often used in machining centers.
2. Bed
The bed is equipped with a guide surface to guide the table and supports the bottom of the machining center.
3. Table
The table is a surface on which the workpiece is placed and has grooves for holding and securing the workpiece with T-shaped nuts. The table is wide enough to accommodate workpieces over 2 m in length, and a crane is often used to remove and install workpieces.
4. Column
This is a column-like entity connected to the bed and extending vertically, and is the component that supports the main spindle. The main feature of the gate type is that the column is supported by two columns, which form a gate-like shape.
5. Operation Panel
This is an operation panel for operating the machine tool, such as creating NC programs and manually operating the machine by means of handles.
6. Cross Rail
Crossrail is a rail that supports the spindle. It can be divided into two types: a movable type in which the crossrail moves up and down and a fixed type in which the spindle moves up and down.