In a CNC machining workshop, the machines handle cutting operations automatically, but loading raw workpieces, removing finished parts, and transferring materials often still require manual work. One operator may be responsible for several CNC machines, moving from one to another whenever a machining cycle finishes. If two machines finish at nearly the same time, the operator can only attend to one, leaving the other idle until its parts are changed.
For this project, we integrated a six-axis collaborative robot, a workpiece gripper, and a mobile base into one mobile manipulator system. The robot travels between multiple CNC machining centers and handles loading and unloading according to each machine's machining schedule.
The system can also grow with production. One mobile manipulator currently serves multiple CNC machines, while additional robots can be introduced as the workshop expands. A centralized scheduling system can then coordinate their machine tending tasks.
Project Background and CNC Machine Tending Requirements
The workshop operates multiple CNC machining centers, each running its own machining program and cycle time. With manual tending, operators must open the machine after machining is complete, remove the finished part, load a new blank, and start the next cycle.
Shorter machining cycles mean more frequent part changes. Operators spend time not only loading and clamping workpieces but also walking between machines. When several CNC machines finish at around the same time, some may sit idle while waiting for an operator.
We wanted the robot to take over these repetitive loading and unloading tasks while keeping the existing CNC machines in operation.
Once the mobile manipulator completes a part change at one machine, it can use that machine's machining time to travel to another station. A single robot can therefore work across several CNC machines without requiring a dedicated fixed robotic arm at every machining center.
Mobile Manipulator Configuration and Multi-Machine Tending Operations
The system consists of a mobile base, a six-axis collaborative robot, an end-effector gripper, and onboard workpiece storage. The mobile base carries the robot between CNC stations, while the arm handles part pickup, placement, and loading into the machine fixture.
Mobile Base Positioning at CNC Stations
The robot follows a planned route through the workshop and docks at a predefined position in front of each CNC machine.
The docking position must align with the machine opening and the fixture inside. If the robot stops too far away, the arm may not reach the workholding fixture. A change in the base's position or orientation can also affect part placement.
We therefore set up a corresponding docking position and robot motion program for each CNC station. Once the mobile base has docked and its position has been confirmed, the arm begins the loading and unloading sequence.
The distance between machines also affects operation. When the CNC machines are arranged close together, the robot can switch stations quickly. Machines farther apart require more travel and docking time.
Six-Axis Robot and Automatic Workpiece Changes
When a CNC machine finishes machining, the robot moves into position and runs the loading and unloading program assigned to that machine.
The arm reaches into the machining enclosure, grips the finished part, and places it in the onboard storage area. It then picks up a new blank, positions it in the machine fixture, and completes the loading operation.
Once the arm has cleared the machining area, the CNC machine begins its next cutting cycle. The mobile manipulator can then leave for another CNC station.
The six-axis arm adjusts the gripper's position and orientation to work within the limited space inside the machine enclosure. The end effector is designed around the workpiece dimensions, geometry, and clamping position.
The robot and CNC control systems also work together. The robot can enter the machining area only after machining is complete, the machine door is open, and the required conditions for part handling have been met. The next machining cycle starts after the workpiece is secured and the arm has withdrawn.
Onboard Workpiece Storage for Continuous Tending
The mobile base includes a storage area for unmachined blanks and finished parts.
The robot can carry blanks with it when moving to the next CNC machine. After unloading, the finished part can be placed in the onboard storage area rather than requiring the robot to return immediately to a central material station.
For example, if one robot needs to serve three CNC machines in sequence, the number of blanks it carries and the available space for finished parts both matter. If storage capacity is too limited, the robot will have to make frequent trips for replenishment and unloading, reducing the time available for machine tending.
Onboard storage capacity therefore needs to match the number of CNC machines served, their machining cycles, and the material replenishment arrangement.
CNC Machining Time and Robot Service Capacity
The number of CNC machines one mobile manipulator can serve depends mainly on three factors: machining time, robot loading and unloading time, and the time needed to travel and dock between machines.
Once a CNC machine starts cutting, the robot is free to attend to other stations. Longer machining cycles generally give it more time to complete tasks elsewhere.
Consider a CNC operation with a machining time of 180 seconds. The robot takes 25 seconds to unload and reload a workpiece, while traveling to and docking at the next machine takes 20 seconds.
| Operating Task | Time |
|---|---|
| CNC machining time per part | 180 seconds |
| Robot unloading and loading | 25 seconds |
| Travel and docking between adjacent CNC machines | 20 seconds |
| Robot service and transfer time per station | 45 seconds |
When the robot follows a fixed route between CNC machines, the time required for a complete round is:
| Number of CNC Machines | Time for One Robot Service Round |
|---|---|
| 2 | 90 seconds |
| 3 | 135 seconds |
| 4 | 180 seconds |
| 5 | 225 seconds |
With four CNC machines, the robot needs 180 seconds to complete the loading, unloading, and travel operations across all four stations. Each CNC machine also needs 180 seconds for machining after its workpiece has been changed, so the robot's return to a machine must be coordinated with that machine's completion time.
Ideally, the robot arrives just as machining finishes, removes the finished part, loads a new blank, and moves on to the next machine.
If it arrives early, it must wait for machining to finish. If it arrives late, the CNC machine remains idle until the robot is available.
With five CNC machines, one service round takes 225 seconds. For CNC machines with 180-second machining cycles, some may have to wait after machining is complete, reducing actual output.
Longer machining times may allow one robot to serve more CNC machines. Shorter machining cycles or greater distances between machines may require a different number of robots or a revised service route.
Mobile Manipulator Technical Specifications
| Parameter | Configuration / Value |
|---|---|
| Equipment type | Mobile manipulator |
| Application | Automated loading and unloading for multiple CNC machining centers |
| Robotic arm | Six-axis collaborative robot |
| Mobile platform | Autonomous mobile base |
| Workpiece handling | End-effector gripping, loading, and transfer |
| Workpiece storage | Onboard workpiece storage |
| CNC machining time per part | 180 seconds |
| Robot loading and unloading time | 25 seconds |
| Travel and docking between adjacent CNC machines | 20 seconds |
| Service and transfer time per station | 45 seconds |
| Operating method | Machine tending scheduled according to CNC machining status |
| System expansion | Additional mobile manipulators and multi-robot scheduling |
Labor Costs and Investment Payback for Multi-CNC Machine Tending
The mobile manipulator handles loading and unloading across multiple CNC machines, so an operator no longer needs to stay beside the machines throughout production.
In a machining cell with four CNC machines, the robot schedules its loading and unloading tasks around each machine's machining status. Operators are relieved of repetitive part handling and focus mainly on replenishing blanks, collecting finished parts, monitoring equipment, and handling exceptions.
While one CNC machine is cutting, the robot can tend another. This allows a single robot to handle part changes at multiple stations and reduces the time operators spend moving between machines.
Staffing and Equipment Investment
In a four-CNC machining cell, the automated system reduces the requirement by one dedicated machine tending operator per shift. The fully loaded monthly labor cost per operator is RMB 8,000.
The total investment in the mobile manipulator, end-effector gripper, onboard storage, and system integration is RMB 280,000.
| Financial Metric | Single Shift | Two Shifts |
|---|---|---|
| Dedicated machine tending positions eliminated | 1 | 2 |
| Monthly labor cost savings | RMB 8,000 | RMB 16,000 |
| Additional monthly operating and maintenance costs | RMB 1,000 | RMB 2,000 |
| Monthly net cost savings | RMB 7,000 | RMB 14,000 |
| Total robot system investment | RMB 280,000 | RMB 280,000 |
| Simple payback period | 40 months | 20 months |
With two shifts, dedicated machine tending labor costs fall by RMB 16,000 per month. After RMB 2,000 in additional operating and maintenance expenses, monthly net savings are RMB 14,000, giving the system a simple payback period of 20 months.
If the original CNC machining cell requires more dedicated operators, the potential labor cost reduction will also differ. As the robot serves more machines, the investment in one system can be spread across more CNC stations.
Scaling from One Mobile Manipulator to a Multi-Robot System
The project currently uses one mobile manipulator to serve multiple CNC machining centers. The robot travels to the machines that need loading or unloading according to their machining schedules.
If the factory adds more CNC machines and the existing robot can no longer complete every part change on time, a second or third mobile manipulator can be added.
The original robot continues operating while the new robots receive assignments through a centralized scheduling system. Each robot can serve a designated machining area, or tasks can be assigned according to CNC machining status and robot location.
| System Configuration | Operating Arrangement |
|---|---|
| 1 mobile manipulator | Travels between multiple CNC machines to perform loading and unloading |
| 2 mobile manipulators | Share tending tasks across more CNC machines, reducing travel and waiting time |
| 3 mobile manipulators | Cover more machining stations with centrally assigned tasks |
| Additional robots | Expand according to CNC count, machining cycles, and workshop layout |
With multiple robots operating at the same time, travel routes and access to CNC stations must be coordinated.
For example, if two robots can both serve the same CNC machine, the system can assign the task based on their current locations, estimated arrival times, and the machine's machining status.
This reduces unnecessary long-distance travel and prevents two robots from heading to the same CNC station for the same task.
As more machines are brought into the automated system, blank replenishment, finished-part collection, charging, and robot standby areas can also be coordinated.
A factory can begin with one mobile manipulator serving multiple CNC machines, then gradually add robots as the number of machining centers and production demand increase, without having to automate the entire workshop at once.
Project Summary
The mobile manipulator combines a six-axis collaborative robot, workpiece gripper, onboard storage, and autonomous mobile base. One robot can travel between multiple CNC machines to load blanks, remove finished parts, and transfer workpieces.
CNC machining time, robot loading and unloading time, and travel time between stations determine how many machines one robot can serve. Coordinating machining schedules with robot assignments helps reduce manual part handling and machine idle time.
As the number of CNC machines increases, more mobile manipulators can be added, with centralized scheduling distributing tending tasks across the expanded system.
Robotlyne offers free machine tending feasibility assessments based on the number of CNC machines, machining cycle times, workpiece dimensions, fixture designs, and workshop layout, followed by a customized mobile manipulator system proposal.