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How to Select an Injection Molding Robot by Machine Tonnage
Machine tonnage is often the first number a buyer has when searching for an injection molding machine robot. It is useful for narrowing the discussion, but it does not by itself determine the correct robot. The product, mold, removal direction, EOAT and required cycle time must also fit the application.
Direct Answer
The short answer is: use injection molding machine tonnage to create a starting range, then confirm the robot from the mold opening, tie-bar layout, product and runner weight, EOAT weight, required stroke, take-out time and installation space. Two machines with the same tonnage can require different robots because their molds and parts may be completely different.
For straightforward part or sprue removal, a 3-axis servo robot may be sufficient. If the part needs rotation, stacking or controlled orientation, consider a 5-axis configuration. A 6-axis robot or custom automation should be considered only when the process includes movements or stations that a standard linear take-out robot cannot handle efficiently.
Why Machine Tonnage Matters
Machine tonnage gives the buyer a practical way to describe the approximate scale of an injection molding machine. It is connected to the clamping system, platen size and general working envelope. This helps a supplier understand the project before receiving complete drawings.
However, tonnage is not a robot payload rating. It does not tell you how heavy the product is, how far the robot must reach or whether the end-of-arm tooling will fit between the tie bars. Treating tonnage as the final specification can create a robot that is too small, unnecessarily large or difficult to install.
What Tonnage Can and Cannot Tell You
What it can tell you
- Approximate machine scale and likely mold envelope
- A first indication of the size range for a top-entry or side-entry robot
- Which machine drawings and interface information should be requested
- Whether the project may need a larger frame or different mounting arrangement
What it cannot tell you
- Product, runner and EOAT combined weight
- Required vertical, traverse or kick stroke
- Part orientation and drop-off requirements
- Whether vacuum or mechanical gripping is suitable
- Actual take-out time and downstream automation needs
Key Factors After Tonnage
1. Machine and Mold Layout
Collect the machine brand, model, tonnage, platen dimensions, tie-bar spacing, mold thickness range and mold opening. The robot must enter and exit the mold area without interference. A machine drawing is more useful than tonnage alone because it exposes the available clearance and mounting points.
2. Product and Runner Weight
Payload includes the product, runner, grippers, vacuum cups, cylinders, sensors, mounting plates and other EOAT components. Confirm whether the robot removes one product, several cavities, a runner, or product and runner together. The final payload should be based on the complete tooling rather than a product estimate.
3. Stroke and Clearance
Check the mold opening against vertical stroke, kick stroke and traverse stroke. The robot must reach the part, grip it, clear the mold and move to the placement point. A longer stroke is not automatically better if it adds cost or creates a larger installation envelope. A shorter stroke is a problem if the robot cannot safely clear the mold.
4. Cycle Time
Define the required take-out sequence, including mold opening, robot entry, gripping, confirmation, exit and placement. The robot should complete its part of the sequence without becoming the bottleneck. Exact performance depends on the selected model, tooling, motion path and application, so it should be confirmed from project data.
5. EOAT and Product Protection
Flat, smooth parts may be suitable for vacuum cups, while ribs, holes, edges or delicate surfaces may need mechanical grippers or a mixed design. Hot, flexible or cosmetic parts require careful contact-point planning. EOAT weight and gripping force should be reviewed together with part protection and release reliability.
6. Interface and Safety
Confirm robot-ready, mold-open, part-confirmation, safety-gate and emergency-stop signals with the machine supplier. EUROMAP technical recommendations, including EUROMAP 67, are useful references for machine and handling-device interfaces. Project-specific safety assessment is still required.
How to Use a Tonnage-Based Selection Process
- Record the machine model and tonnage.
- Request platen, tie-bar, opening and interface data.
- Measure the mold and define the part removal direction.
- Calculate product, runner and EOAT weight together.
- Set the target take-out time and placement sequence.
- Choose a 3-axis or 5-axis linear configuration only after the motion is understood.
- Review whether downstream inspection, trimming, stacking or packaging needs a larger cell.
For standard machine-side take-out, the Kefan injection molding robot range can be used as a starting point after the application data is collected. A simple part-removal project may fit a 3-axis robot, while orientation or stacking may justify a 5-axis robot.
Who Should Choose What?
| Application | Practical starting solution | Reason |
|---|---|---|
| Simple removal from a standard mold | 3-axis robot | Basic entry, pick and placement are enough |
| Removal with orientation or stacking | 5-axis robot | More control over part attitude and drop-off |
| Complex inspection or assembly after molding | Custom cell with supporting 6-axis integration | Multiple stations may need coordinated motion |
| Special shape or surface protection | Custom EOAT | Tooling must match the actual part |
Common Mistakes
- Choosing a robot from tonnage alone and never checking tie-bar clearance.
- Comparing product weight while excluding EOAT weight.
- Assuming a longer stroke automatically improves the application.
- Ignoring the time needed for gripping, confirmation and exit.
- Leaving machine communication and safety review until installation.
- Specifying a 6-axis robot when a simpler linear robot would solve the real task.
What To Do Next
Before requesting a quotation, prepare the machine model and tonnage, platen and tie-bar dimensions, mold drawing, product drawing or photos, product and runner weight, EOAT concept, target cycle time, placement method and interface information. A supplier can then recommend a configuration based on the application instead of guessing from tonnage.
If your project needs a standard take-out robot or a larger integrated process, contact Kefan Robotics with these details for an application-based review.
Mini FAQ
Can I choose an injection molding machine robot by tonnage?
Tonnage is a useful starting point, but it is not enough for final selection. Confirm mold layout, stroke, payload, EOAT, cycle time, interface and installation space.
Does higher machine tonnage require a bigger robot?
Often the machine envelope grows with tonnage, but the required robot still depends on the part, mold and handling path. The same tonnage can support very different applications.
What information should I send to a robot supplier?
Send the machine model, tonnage, mold dimensions, product and runner weight, product drawings or photos, target cycle time, removal direction and downstream handling requirements.
When is a 5-axis robot needed?
A 5-axis robot is useful when part orientation, rotation, stacking or controlled placement cannot be completed reliably with a simple 3-axis movement.
When is custom automation needed?
Custom automation is appropriate when the process adds inspection, trimming, assembly, packaging or other stations that require coordinated handling beyond basic part removal.
Grace | International Sales Specialist at Kefan Robotics
Grace works with overseas customers on injection molding robots, machine-side take-out, EOAT requirements and automation project communication. She helps customers prepare practical machine, mold and product information for supplier review.