Shot size
Why the screw capacity line is a separate number from tonnage.
Shot sizeGlossary
What Is Tonnage? Injection Molding Explained
Tonnage names how much clamp a press can apply, not how good your part will be.
Glossary
Tonnage is the press clamp rating buyers see on quotes
It is easy to treat tonnage as a quality score. It is really a capacity label.
Injection molding machines are sold with a clamp rating, often in US tons. That number is the headline capacity of the press, not a guarantee about your part.
Molders map your projected area, wall design, and resin to a machine window. Two suppliers quoting different tonnage may still be describing compatible plans with different press fleets.
When a quote lists tonnage without CAD context, ask what geometry and material drove the choice.
Vocabulary
Terms buyers mix up on machine lines
Use this when a supplier email swaps words mid thread.
| Term | What it usually means |
|---|---|
| Tonnage | Clamp capacity rating of the press |
| Clamping force | Actual closing force applied during the cycle |
| Platen size | Physical footprint limit, not a pressure substitute |
| Shot size | Plastic volume the screw can deliver per stroke |
Quotes
When tonnage belongs in the conversation
Put it after geometry, not before.
- Large flat panels and thin lids drive projected area faster than small bosses do.
- Glass filled resins often need higher fill pressure than unfilled grades in the same geometry.
- Family tools sum projected area across impressions on the same shot.
Go deeper
Where this term connects
Each link is a different angle on the same program, not a duplicate definition.
Cycle time
Cooling time dominates once the press size is settled.
Cycle timePlastic molding services
How production programs sit on one steel tool.
Plastic molding servicesVisual reference
Photos from molding and tooling programs
Images are selected from the NetProto Forge media library for this topic.
Injection molded production parts on a tray
Injection molded production parts on a tray
Engineer reviewing a molded part drawing
Engineer reviewing a molded part drawing
Plastic housing components from a steel tool
Plastic housing components from a steel tool
FAQ
Tonnage questions
Will NetProto publish a tonnage chart for my part?
No chart replaces your CAD. Upload files to the instant quote platform for a program specific answer.
Is a higher tonnage machine always slower?
Not necessarily. Cycle time is driven by cooling and ejection more than the nameplate tonnage.
Can one tool run on two different tonnage presses?
Sometimes, if mold height and tie bar clearance fit both machines and clamp is adequate on both.
Next step
Stop guessing press size
Send 3D CAD with parting direction so tooling and machine window align on one quote.