Machining center ATCs and magazines work together to automate the swapping of cutting tools in CNC machines. These Tool changers are primarily found on CNC vertical machining centers and CNC horizontal machining centers. Without a tool changer, the machine would only use one tool at a time before a human operator would need to manually change the tool. This would be unacceptable at most any level of production.
Automatic Tool Changer Types
An automatic tool changer (ATC) removes a tool from the spindle and replaces it with another tool from the magazine.
Dual Arm
The dual-arm tool changer uses a cam mechanism to drive dual arms with grippers at the end. The arms simultaneously insert a replacement tool while putting away the tool in the spindle.
Image: (“ATC | Micro Dynamics FA”)
Dual-arm tool changers are designed specially for the job of changing cutting tools. By design they are very fast and reliable. You’ll find tool-to-tool change times as quick as 800 milliseconds for 40 taper tools. In addition, many manufacturers test these tool changers to well over a million cycles, so you can rest assured they will stand up to production use. Plus, the ATC designs support the maximum tool sizes in terms of length, width, and weight.
The tool change sequence happens as follows:
- Spindle moves to the tool-change position.
- The magazine presents the next tool at the ATC position.
- The dual arm rotates 90 degrees to simultaneously engage the grippers on the spindle tool and magazine tool.
- The spindle and magazine unclamp the tool knobs to release the tools.
- The dual arm extends in the Z direction so the tools clear the spindle and magazine.
- The dual arm rotates 180 degrees to swap the tools.
- The dual arm retracts in the Z direction so the tools are in the spindle and magazine.
- The spindle and magazine clamp the tool knobs to secure the tools.
- The dual arm rotates 90 degrees to clear the spindle.
- The spindle moves away from the tool-change position for the next cut.
Pros:
- Rapid tool-to-tool change time.
- Highly reliable.
Cons:
- Higher machine price.
- Requires space in the machine for the maximum-sized tool exchange.
- Sometimes restricts the tool weight due to the gripper strength.
Spindle Drop-Off
This type of tool changer isn’t a dedicated tool changer, but rather uses the spindle’s movement to drop off the tool in the magazine and pick up the next tool. The tool change sequence happens as follows:
- Spindle moves to the tool-change position.
- The magazine presents an empty holder.
- The spindle places the tool into the empty holder.
- The spindle releases the tool knob and moves in the Z-axis to clear the tool.
- The magazine moves to present the next tool to the spindle.
- The spindle moves in the Z-axis to engage the tool and clamps the tool knob.
- The spindle moves away from the magazine.
Image: (“Mazak VTC-41 CNC Vertical Machining Center w/ Mazatrol EIA Controller”)
Pros:
- No need for a separate ATC mechanism.
- Lower machine price.
Cons:
- Slower tool changes.
- Requires the spindle to move to the tool change position for each tool change.
- Additional wear on the ball screws at the tool change position due to repetitive movement to exchange the tools.
Other
You’ll find many other simple and ingenious tool changer designs. For example many drill and tap centers with small 30-taper tool holders use a drum carousel mixed with a cam as a tool changer, thereby delivering extremely rapid and reliable tool changes.
Magazines
Magazines store the cutting tools when they are not used in the spindle.
More or Less Tools
For CNC machining centers, the magazine tool quantity ranges from 20 to over 350 tools. Why would you choose a certain capacity other than the cost of the capacity?
Low capacities are ideal for:
- Attended operations where an operator can exchange tools in the magazine.
- Low volume production where it’s okay to stop the machine to load tools.
- Low investment machines where you are conserving cash flow.
High capacities are ideal for:
- High-mix production where many tools are required to meet the many cutting operations for a large mixture of part numbers.
- Unattended production where redundant tools are required because multiple tools wear out before an operator returns to insert fresh ones.
Magazine Tool Loading
Magazines can be loaded by two methods. The first method is through the spindle where the magazine is loaded by manually loading the tool in the spindle, and then using the ATC to move the tool into the magazine. We refer to this method as “spindle loading”.
- The magazine must typically be loaded by stopping the machine, opening the front door, inserting the tool in the spindle, and then using the ATC to place the tool in the magazine.
- This configuration is cheaper to build but less productive because the spindle is idle when loading a tool.
- Machines with this configuration often have a button on the front of the spindle for the operator to press when they want to release a tool from the spindle.
The second method is through a magazine door where the magazine has a separate door just for loading tools. The operator opens the door and inserts the tool into the magazine.
- Opening the door deactivates the tool magazine movement to protect the operator. If the operator loads the tool while the machine is cutting, the machine continues cutting during tool loading. If the operator is still loading when the machine needs the next tool, the machine waits for the operator to finish.
- This configuration is more expensive to build, but it is more productive.
Stationary Carousel
Carousel magazines store the tools in a round magazine that rotates to bring the selected tool to the tool change position. For a stationary carousel, the entire carousel remains in a fixed position. The ATC is either of the dual-arm or drop-off type.
Image: (“20-Pocket Carousel Tool Changer”)
Pros:
- It’s a relatively simple design for storing tools making it reliable and affordable.
Cons:
- The magazine size is limited since the round shape quickly grows in diameter as more tools are needed along the circumference..
Side-Mounted Carousel
The side-mounted carousel is mounted on the side of the spindle and carried along during cutting. The ATC and magazine move with the spindle.
Image: (“30+1 Side-Mount Tool Changer”)
Storage capacity:
- VMCs 4-axis or less:
- HMCs:
Pros:
- The tools are always next to the spindle, so ATC time is quick and the spindle doesn’t need to travel to a tool change position near the top of the work envelope.
Cons:
- The Z-axis must carry the weight of the ATC, magazine, and tools, and the total mass of these affects dynamic performance.
- The magazine size is limited since larger magazines size would intrude too much into the work envelope and weight would affect dynamic performance.
- Typically requires loading tools by first loading them in the spindle.
Chain
For chain magazines, tools are mounted on a chain that circulates within the magazine on rollers. A servo drive with a sprocket turns to move the chain and present the selected tool for changing. Chain magazines are typically designed with multiple winding shapes to store the most tools in a limited space.
Image: (“Application: Large Capacity Chain-Type Automatic Tool Changers”)
Pros:
- Holds more tools.
- Dense tool storage within a given space.
Cons
- Due to the chain plus the tool weight, the chain can become heavy and slow to move.
- While the chain can hold many tools, it must also move up to half the chain length to a chosen tool, potentially delaying a cutting operation during that time.
Rack
Rack magazines store the tools in fixed locations arranged like a wine rack. A shuttle moved by a two-axis servo system moves across the rack to pick the tools from the storage locations. The shuttle brings the tool to the tool change location where typically a dual-arm ATC exchanges the replacement tool with the spindle tool. The ATC is chosen for this design because racks are large and the spindle would sit idle while the shuttle puts away the first tool and brings back a replacement tool. Rack magazines are found on horizontal machining centers.
Image: (“Tool Changer-Gifu”)
Pros:
- Holds the most tools.
- Dense tool storage within a given space.
- Rapid tool retrieval using the servo system even when there are many tools.
- Does not depend on the full weight of all loaded tools like a carousel or chain design.
Cons
- Among the most expensive magazines due to the servo system and size.
Magazine Access Types
Magazines are accessed using two programmed methods.
- Fixed position – The tools are returned to the same location in the magazine each time they are returned. This is convenient for tracking the location of your tools in the magazine.
- Random access – The tools are placed in the nearest empty location in the magazine when they are returned to accelerate tool change times. The control tracks which magazine location holds which tool.
Production Tips
- Mount additional tools that can save manual operation time, like probes and wash.
- Mount tools in the order they will be used to minimize the magazine’s travel during a tool change.
- Measure tool offsets using a stand-alone tool presetter. Then use a network connection or tool chip to transfer the offsets to the machine once loaded.
Warning
Ensure your spindle and the magazine support the tool type, like CAT, BT, or HSK. Mostly these types are not interchangeable and can damage the tool, magazine, and ATC if an incompatible type is loaded in the machine.
Important Specifications
- Tool-to-tool time – Once the spindle and magazine are in position for a tool change, this is the time required to exchange tools.
- Chip-to-chip time – This is the time to leave the average cutting position and get in position for a tool change, plus the tool-to-tool time, and the time to return to the cutting position. This specification heavily depends on the machine’s rapid traverse rates.
- Max tool weight – The total weight supported when including the tool holder, tool retention knob, and tool.
- Max tool diameter (adjacent empty) – The total diameter permitted for the tool when the adjacent location in the magazine is empty.
- Max tool diameter (adjacent full) – The total diameter permitted for the tool when the adjacent location in the magazine is occupied. This includes the diameter supported by the ATC.
- Max tool length – The maximum length of the tool from the tool holder’s gauge line to the end of the tool.
- Max tool moment – The maximum torque or “moment” for the tool. This is rarely specified but can be important in certain machines for tools that are heavy near the end of their length.
Sources
“Application: Large Capacity Chain-Type Automatic Tool Changers.” TAC Rockford, https://tacrockford.com/product/machine-components/milling-machine/chain-type-automatic-tool-changers/. Accessed 28 September 2023.
“ATC | Micro Dynamics FA.” Micro Dynamics CNC Machines, https://www.microdynamicsfa.com/atc. Accessed 28 September 2023.
“Mazak VTC-41 CNC Vertical Machining Center w/ Mazatrol EIA Controller.” The Equipment Hub, https://theequipmenthub.com/product/mazak-vtc-41-vertical-machining-center/. Accessed 28 September 2023.
“30+1 Side-Mount Tool Changer.” Haas Automation Inc., https://www.haascnc.com/productivity/tool-changer/smtc-30-40t.html. Accessed 28 September 2023.
“Tool Changer-Gifu.” Tool Changer-Gifu, https://www.atcgifu.com/eng/product_show.php?id=188. Accessed 28 September 2023.
“20-Pocket Carousel Tool Changer.” Haas Automation Inc., https://www.haascnc.com/productivity/tool-changer/tc-20.html. Accessed 28 September 2023.
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