Tonnage Factor

Clamp force (clamping force or tonnage) is the force the machine applies to hold the mold halves shut against the pressure of the melt during injection and pack. If it is lower than the force trying to push the mold open, the parting line separates and the part flashes — that is why sizing it correctly is a first-step machine-selection decision. ## How to calculate clamp tonnage The standard estimate: Clamp force = projected area × clamp factor - projected area is the part-plus-runner area seen along the mold-opening direction (in² or cm²). - The clamp factor (see tonnage factor) is an empirical pressure in tons per in² (or bar of cavity pressure). Example: a 50 in² projected area at 3 tons/in² needs 50 × 3 = 150 US tons; add ~10 % margin and pick a press rated near 165–200 tons. ## Typical clamp factors | Resin / situation | Clamp factor (tons/in²) | |---|---| | Easy-flow commodity (PE, PP) | 2–3 | | General engineering (ABS, PA, PC) | 3–5 | | Thin-wall, long-flow, glass-filled | 5–8 | Metric rule of thumb: clamp force in kN ≈ projected area (cm²) × cavity pressure (bar) ÷ 10. ## Why it matters - Too little: flash, dimensional drift and the mold opening during pack — see flash. - Too much: crushed vents and shutoffs, faster mold wear, wasted energy and ruling out otherwise-suitable presses. Most shops size the press from the estimated tonnage required plus a safety margin, without overspending on an oversized machine. ## Related terms - See also: projected area, tonnage factor, estimated tonnage required, flash, injection molding machine imm ## What is clamp force in injection molding? It is the force that keeps the mold closed against injection pressure, quoted in tons (or kN). Too little lets the mold open and the part flashes. ## How do you calculate clamp tonnage? Multiply the projected area by a clamp factor (tons/in²) and add ~10 % margin. A 50 in² part at 3 tons/in² needs about 150 tons, so you would choose a press around 165–200 tons. ## What happens if clamp force is too low? Melt pressure forces the parting line open, giving flash, heavier and dimensionally unstable parts, and eventually damage to the shutoff faces of the mold.

Estimated tonnage required is the clamp tonnage a given part needs to keep the mold shut during injection — the number you calculate before selecting a machine. It is estimated, not measured: you compute it from the part geometry, then choose a press with margin above it. ## How it is estimated Estimated tonnage = projected area × tonnage factor - projected area: the part-plus-runner area seen along the mold-opening direction (in² or cm²). - tonnage factor: an empirical pressure per unit area (tons/in²) that depends on the resin and the wall thickness / flow length. Example: 50 in² × 3 tons/in² ≈ 150 US tons; add ~10 % margin → choose a press of ~165–200 t. ## How it is used It drives machine selection: pick an injection molding machine imm whose rated clamp force tonnage comfortably exceeds the estimate. Too little tonnage and the part flashes; too much wastes energy and rules out otherwise-suitable presses. Confirm on the press, since real cavity pressure and venting shift the true requirement. ## Why it matters Getting this number right up front avoids quoting a job onto the wrong machine. It is the planning side of clamp force tonnage (the force itself) and feeds capacity and cost estimates. ## Related terms - See also: projected area, tonnage factor, clamp force tonnage, injection molding machine imm, flash ## What is estimated tonnage required in injection molding? It is the clamp tonnage a part needs, estimated as projected area × tonnage factor, used to pick a machine before running the job. ## How do you estimate required tonnage? Multiply the projected area by the resin's tonnage factor and add ~10 % margin; e.g. 50 in² × 3 t/in² ≈ 150 t → choose ~165–200 t. ## Is estimated tonnage the same as clamp force? It is the same quantity (tons of clamp force), but framed as the required value for machine selection; the running clamp force should comfortably exceed it.

A material data sheet (technical data sheet, TDS) is the document a resin supplier publishes for a specific grade, listing its tested properties and the conditions used to measure them. It is the starting reference for choosing a material and for setting up a molding process — not a guarantee for every part. ## What it contains - Rheological / processing: melt flow rate (MFR/MFI), recommended melt and barrel temperature, mold temperature, drying time/temperature and target moisture content, injection speed/pressure guidance. - Mechanical: tensile strength and modulus, elongation, flexural and impact (Izod/Charpy) values. - Thermal: heat deflection temperature (HDT), melting or softening point, continuous use temperature. - Physical: density / specific weight, mold contraction (shrinkage) — often different along and across flow, water absorption, flammability (UL94). ## How to read it Each value comes with a test standard (ISO or ASTM) and conditions; numbers are only comparable when the standards match. Most data is measured on dried virgin resin on standardized specimens, so real parts with regrind, fillers, weld lines or thin walls can differ. Use the sheet for drying and start-up settings, then confirm with your own process and parts. ## Related terms - See also: resin, moisture content, specific weight, contraction, regrind ## What is a material data sheet? A supplier document for a specific resin grade listing its tested mechanical, thermal, physical and processing properties, together with the test standards and conditions used to measure them. ## What information is on a material data sheet? Melt flow rate, recommended melt/mold temperatures, drying conditions and moisture target, density/shrinkage, plus tensile, flexural, impact and heat-deflection values — each tied to an ISO or ASTM test method. ## Why are data sheet values different from my real parts? Because the sheet is measured on dried virgin resin using standardized specimens; regrind, fillers, moisture, weld lines, wall thickness and your actual process all shift the real-world results.

Projected area is the sum of the flat areas that a part —and the runners in cold-runner molds— occupies when projected onto the parting plane. It is the key input for calculating the clamp tonnage of the injection press. ## What it is used for The required clamp force comes from multiplying projected area by the specific cavity pressure (tonnage factor) of each resin: > Tonnage (t) = Projected area (cm²) × Tonnage factor (t/cm²) A safety margin of 10 – 20 % is applied to avoid flash at end of fill or due to imbalance between cavities. ## Typical tonnage factor by resin - PE / PP: 2.5 – 4 t/cm² - PS / ABS: 3 – 5 t/cm² - PA / PC: 4 – 6 t/cm² - POM: 4 – 6 t/cm² - Fiber-filled grades: +20 – 50 % - Thin walls (<1 mm) or long flow: +50 – 100 % ## How to measure projected area - In CAD: project the 3D model onto the mold's XY plane, export as a sketch and sum areas. - In 2D: planimetry on the parting plane. - In flow analysis (Moldflow, Moldex3D, Cadmould): automatic calculation with the resin factor. ## Common mistakes Forgetting to include runners in cold-runner molds (underestimates tonnage by 5 – 15 %), using the flat area instead of the projected one on parts with sloped walls, and changing resin without recomputing the factor.