An Automatic tool changer or ATC is used in computerized numerical controlmachine tools to improve the production and tool carrying capacity of the machine. ATC changes the tool very quickly, reducing the non-productive time. Generally, it is used to improve the capacity of the machine to work with a number of tools. It is also used to change worn out or broken tools. It is one more step towards complete automation.
Description
Simple CNC machines work with a single tool. Turrets can work with a large number of tools. But if even more tools are required, then ATC is provided. The tools are stored on a magazine. It allows the machine to work with a large number of tools without an operator. The main parts of an automatic tool changer are the base, the gripper arm, the tool holder, the support arm and tool magazines. Although the ATC increases the reliability, speed and accuracy, it creates more challenges compared to manual tool change, for example the tooling used must be easy to centre, be easy for the changer to grab and there should be a simple way to provide the tool's self-disengagement. Tools used in ATC are secured in toolholders specially designed for this purpose.
Types of ATC
Depending on the shape of the magazine, ATC can be of two types: Drum Type changers are used when the number of tools is lower than 30. The tools are stored on the periphery of the drum. Chain type changers are used when the number of tools is higher than 30. But the tool search speed will be lower in this case.
Automatic Tool Changer Mechanism
After receiving the tool change command, the tool to be changed will assume a fixed position known as the "tool change position". The ATC arm comes to this position and picks up the tool. The arm swivels between machine turret and magazine. It will have one gripper on each of the two sides. Each gripper can rotate 90°, to deliver tools to the front face of the turret. One will pick up the old tool from turret and the other will pick up the new tool from the magazine. It then rotates to 180° and places the tools into their due position.
ATCs were first used on chip-removal machinery, such as mills and lathes. Systems for automatic rearrangement of tools have also been used on sheet metal working machinery as well. Panel benders have an integrated, CNC-controlled device that allows to move punches according to the size of the part. Automated tool change on press brakes was limited to machines integrated on a robotic bending cell. Typically, a 6-axis robot used for handling sheet metal blanks is also in charge of changing punches and dies between different batches. Since the second decade of the XXI century, though, automatic tool changers have appeared on non-robotized press brakes. The most common configuration is a tool rack on the side of the press brakes, with a shuttle picking up tools and positioning them where needed. This reduces physical strain on the operator and increases overall productivity.
Functions of ATC
The use of automatic changers increases the productive time and reduces the unproductive time to a large extent. It provides the storage of the tools which are returned automatically to the machine tool after carrying out the required operations, increases the flexibility of the machine tool, makes it easier to change heavy and large tools, and permits the automatic renewal of cutting edges. .
