CNC spindles have brought a previously unattainable level of precision and speed to the manufacturing arena. Like anything else, though, there are ways to improve performance even more. One of the more significant improvements in the history of CNC machining comes in the form of automatic tooling spindles for CNC machine operations. These are also called automatic tool change spindles (ATC).

ATC spindles do what their name implies: they automate the tool changing process. When the CNC spindle completes an operation- drilling a hole, for instance- the automatic tool changer spindle automatically ejects the drill tool into a predetermined holder and replaces it with the appropriate tapping tool from another holder. The magazine holding the tools moves in on a predetermined path and positions itself to retrieve the tool from the spindle. Various systems use sensors and pneumatics or hydraulics for regulating and powering the changing of tools.  

ATC spindles can perform any function of a conventional spindle, including drilling, tapping, grinding, honing, and other machining operations.

The system is computer-controlled. An ATC spindle can repeat a process thousands of times during a shift and never require the operator to make tool changes. Even better, the right tool is always chosen since the tool selection is pre-designated by the operator. There is less chance of error.

Automatic tool change spindles increase efficiencies for applications or projects where a workpiece or product requires several different CNC processes. The benefits include:

• Shorter production times: Without ATC, each tool change requires the operator to stop the CNC spindle and change out the tool before moving on to the next step. Some ATC systems can switch out tools in seconds.
• Frees up the CNC operator: Operators can now focus on other CNC responsibilities, making their workflow more efficient.
• Safety concerns: Repeated manual tool changes expose the operator to machinery and the potential for injury.
• Decrease errors: Multiple manual tool changes increase the possibility of operator error (even the best CNC operators are prone to selecting the wrong tool when switching).

There are several different types of automatic tool change systems.

Sometimes referred to as a carousel spindle, in this system the magazine resembles an umbrella mounted above the spindle or to the side and rotates or moves into position to change the tools.

This automatic tool change spindle features a magazine on the side of the spindle. The spindle moves along the magazine, using mechanical arms to switch out tools during the process.

In this format, individual tool holders interlock to form a chain. This chain of tools moves along a track from one position to another, allowing the spindle to select the right tool.

There are other types of tool changing mechanisms, but these represent the most common formats used with CNC spindles in machining.

There are several parameters for deciding which automatic tool change spindle works best for you. Your initial integration of a new spindle into your CNC operation might not require that you immediately invest in an ATC model. Still, you know that it will be a necessary addition in the near future.  

Let’s look at the factors you should consider when evaluating an automatic tool change spindle.

There are automatic tool changers that hold only six to eight tools. This will suffice if your projects fall within this range of tools needed to complete the job. When you go through the retooling process for a new project, simply identify the necessary tools and change them in the magazine and program the selection of tools. These types of tool changers are great in applications that have limited space. However, if your projects require more tools for completion, a tool changer with a larger capacity comes in handy. Some machines hold up to 20 tools. There are also chain-type systems that hold hundreds of tools.

If production times are essential, then you will be concerned about speed. Look for automatic tool changers that switch tools quickly. An arm-type tool changer can switch tools in seconds.

Every automatic tool change system has a footprint. You need to determine how much space you have in your CNC center. Some of these systems are compact. Others, like chain-type tool changers, can be quite large.

Ensure that whatever ATC spindle you purchase is compatible with the rest of your CNC system. The tool change system needs to be compatible with it.

Do your research. If you are considering a purchase, contact other owners and find out how it works for them. Are there certain tools that are more likely to cause a problem? If these are the tools you use, you need to look at other systems.

There are spindles designed for automatic tool change systems, and there are spindles designed for manual tool change. In most cases you cannot adapt a manual tool change spindle for an automatic tool change system. Therefore it is important to consider future spindle needs when you purchase a new ATC spindle for your CNC operations. 

Automatic tool change spindles can come equipped with a variety of several key characteristics and optional enhancements. A few of these features to consider include:

In the event that machining debris—chips, swarf, excess oil or lubricant—builds up on the taper or tool mount area, a taper cleaning function can help eliminate this contamination. Compressed air systems work especially well.

An air purge system that maintains a continuous air stream between the shaft and housing can remove additional machining debris. This protects the spindle parts from contamination-related damage and increases functional safety.

Quality ATC spindles have a low failure rate for loading a new tool, but you should be concerned about additional safeguards in case this happens. One of the most frequent indicators of an incorrect tool load is a new vibration. Vibration sensors immediately detect these vibrations and alert the operator.

The drawbar is part of the system that holds the tool in place using a clamping mechanism. All ATC spindles include drawbar monitoring systems that indicate “tool clamped”, “tool unclamped”, or “clamped without tool”. This reduces spindle damage and increases operator safety.

Tool changes often require a corresponding change in the bearing preload to match machining requirements. This feature allows operators to easily accomplish that.

Hydraulic unclamp units  are stronger and take less room. Pneumatic unclamp units are larger but not as powerful. Pneumatic unclamp units don’t require hydraulic oil like hydraulic unclamp units, making them a cleaner option.

Like any system with many moving parts, there are maintenance considerations with automatic tool change spindles that you must watch for and take care of regularly.

Operators need to routinely look over the performance of the automatic tool change spindle. Are tools releasing and getting picked up easily? Are they free from wear and damage? Is the magazine moving smoothly? Pay careful attention when disassembling your system for periodic spindle repair and maintenance, looking for irregularities that could cause problems.

CNC machining involves a fair share of materials that could cause contamination of the automatic tool change spindle, including cooling fluid, lubrication oil from the spindle system, and metal chips and shavings. Keep the spindle and ATC parts free of excessive buildup. Take the time to wipe individual tools clean, too, and look for signs of wear and damage.

A smoothly operating tool change system will generate some noise, but there will be a rhythm or pattern. Listen for any noises or vibrations that are out of the ordinary.

Inconsistencies in accuracy and performance can often occur due to misaligned components or faulty sensors.

All those moving parts generate heat. Faulty lubrication or a problem in the cooling system can cause this overheating. These are areas you should monitor and examine regularly.

GMN USA carries a complete line of CNC spindles incorporating the latest technology for automatic tool change systems, with options for synchronous or asynchronous motors. Our models are capable of turning at speeds of up to 90,000 RPM, feature oil/air lubricated bearings, and are exceptionally accurate. If you’re in the market for repairs rather than a brand new spindle, the technicians at GMN USA are also experts at general spindle repairing services for all brands.  

Contact GMN USA Today to Find The Perfect Match for Your Automatic Tool Change Spindle Needs.