Projected Area

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.

Parting Line is the line or surface where the two halves of the mold (cavity and core) meet when closed. It defines how the mold opens to eject the part and leaves a linear mark on the plastic that is usually visible. ## Importance in design - Determines the mold's opening plane - Defines which surfaces are cosmetic and which can accept the mark - Conditions the location of gates, vents and ejectors - Affects mold complexity and cost ## Parting-line types - Flat: simplest, single horizontal or vertical plane - Stepped: with offsets to accommodate geometries - Curved / 3D: follows the part contour, requires 5-axis machining - Multiple: when there are slides for undercuts ## Design rules - Place the parting line on the part's "natural" edges (corners, flanges) - Avoid crossing cosmetic surfaces - Guarantee accessibility for machining and polishing - Maintain minimum draft of 0.5° on both sides - Plan venting through the parting line ## Associated defects - Flash: the most common, material exits through a poorly sealed line - Visible mark: noticeable on cosmetic parts; mitigated with texture or hidden location - Asymmetric wear: if pressure is poorly distributed across cavities - No venting: if the line is polished perfectly with no air paths ## Maintenance - Visual inspection every 100,000 cycles - Re-grind plates if the line shows recurring flash - Vent cleaning: 0.02 – 0.05 mm standard depth - Plate flatness check: <0.01 mm in precision molds

Tonnage Factor is the specific cavity pressure needed to keep the mold closed during injection, expressed as tons per square centimeter of projected area. It is the constant that links clamp force to part geometry and resin choice. ## Basic formula > Tonnage (t) = Projected area (cm²) × Tonnage factor (t/cm²) Apply a 10 – 20 % safety margin for process variation and cavity imbalance. ## Typical tonnage factor by resin - LDPE, HDPE: 2.0 – 3.5 t/cm² - PP: 2.5 – 3.5 t/cm² - PS: 3.0 – 4.5 t/cm² - ABS, SAN: 3.0 – 5.0 t/cm² - PA, PC: 4.0 – 6.0 t/cm² - POM, PBT: 4.5 – 6.0 t/cm² - PEEK, PPS: 5.0 – 7.5 t/cm² - Fiber-reinforced: +20 – 50 % vs. unfilled ## Factor modifiers - Thin wall (<1 mm): +50 – 100 % - Very long flow (L/T >150): +30 – 80 % - Low mold temperature: higher viscosity → higher factor - High injection velocity: shear thinning may lower the factor - Hot runner vs. cold runner: cold runner adds to total projected area ## How it is determined - Supplier data (technical data sheets) - Flow analysis software (Moldflow, Moldex3D, Cadmould) computes actual cavity pressure - Experience with similar parts - Cavity-pressure sensors in instrumented molds ## Common mistakes - Using a generic factor without adjusting for thickness or flow length - Forgetting to include runners in cold-runner molds - Not accounting for fiber reinforcement when switching grades - Confusing the factor with injection pressure (they are different)