Transfer Position / Cut Off

Cushion (residual cushion) is the small amount of melt left in front of the screw at the end of injection and hold, so the screw never bottoms out on the barrel. It is what lets the machine keep transmitting hold pressure into the cavity through the pack phase. ## Typical values A cushion is usually a few millimetres of screw position — commonly 2–10 mm (often 3–6 mm), or roughly 5–10 % of the shot stroke. It should be small but never zero. ## Why it matters - Pressure transmission: with melt still ahead of the screw, hold pressure reaches the cavity. If the cushion goes to zero the screw bottoms out, pack pressure is lost, and you get sink marks, short shots and a weight drop. - Repeatability & diagnostics: a cushion that repeats shot to shot signals a healthy process. A drifting cushion is the classic symptom of a leaking check valve. ## How it is set The cushion is the gap between where dosing / the transfer position cut off leaves the screw and screw-bottom. Adjust the shot size / dosing volume so a consistent few-millimetre cushion remains; the monitored value is the cushion position. ## Related terms - See also: check valve, hold pressure, transfer position cut off, cushion position, shot size ## What is cushion in injection molding? It is the residual melt left in front of the screw at the end of pack so the screw never bottoms out and can keep transmitting hold pressure — typically a few millimetres. ## What is a good cushion value? Usually 2–10 mm (often 3–6 mm) and, above all, stable shot to shot — small but never zero. ## What does a changing cushion mean? A cushion that drifts from shot to shot with no process change usually means the check valve (non-return valve) is leaking and needs inspection.

Cushion position is the screw position the machine reports at the end of pack/hold — the resting place of the screw when a small cushion of melt still remains in front of it. It is one of the most-watched outputs values on the controller because, shot to shot, a stable cushion position is one of the clearest signals that the process is healthy. ## What it tells you The cushion is the small melt reserve left so the screw can keep transmitting hold pressure; the cushion position is where the screw stops to leave it. Because it is a measured output, not a setting, it reacts to what the plastic and machine actually did: - Stable position = consistent fill, melt and check valve sealing — a repeatable process. - Drifting/wandering position = a problem to chase: a worn or leaking check valve (screw drifts forward, cushion shrinks), inconsistent shot size or recovery, material or temperature variation. - Cushion gone (bottoming out) = the screw hit zero; pressure transfer is lost, giving short shots and weight swings. ## How it is used - Process monitoring: cushion position is trended and alarmed within a window; leaving the window flags trouble before bad parts ship — a core check in a robust process and the injection stages handoff at transfer position cut off. - Setup target: enough cushion is dialed in (via shot size and transfer position) to maintain pressure, but not so much that residence time and waste grow. ## Why it matters A wandering cushion position is often the first visible sign of a failing check valve or unstable shot — catching it early prevents scrap. Together with fill time and part weight, it is one of the simplest, most powerful health indicators on the machine. ## Related terms - See also: cushion, check valve, hold pressure, shot size, outputs values ## What is cushion position in injection molding? The screw position the machine shows at the end of hold, where a small melt cushion remains; it is a monitored output value whose shot-to-shot consistency indicates a stable process. ## Why does cushion position drift? Usually a worn or leaking check valve lets the screw creep forward and the cushion shrink; inconsistent recovery, shot size, or material and temperature variation also move it. A drifting cushion is an early warning of trouble. ## What happens if the cushion bottoms out? If the screw reaches zero cushion it can no longer transmit hold pressure, causing short shots, sink and part-weight variation; the fix is more cushion (shot size/transfer) or addressing the check valve.

Fill (First Stage) is the phase of the cycle in which the screw advances under velocity control, filling the mold cavity approximately to 95 – 99 % of its volume. It ends at the transfer point, where control switches to pressure. ## Key characteristics - Control: velocity (mm/s or cm³/s), not pressure - Purpose: fast and reproducible dynamic filling - Duration: 0.3 – 5 s typically - Volume filled: 95 – 99 % of cavity ## Why separated from hold First stage prioritizes velocity for a uniform flow front; second stage (hold) prioritizes constant pressure to compensate shrinkage. Mixing both in a single-stage process reduces quality and increases variability. ## Multi-stage profile Modern machines allow 5 – 10 velocity steps along the screw stroke: 1. Slow at gate entry (avoids jetting) 2. Fast in wide cavities 3. Slow near critical vents 4. Slow at end for smooth transition ## Typical parameters - Velocity: 30 – 200 mm/s depending on part and resin - Actual pressure (not control): may hit saturation if geometry is restrictive - Time: 0.5 – 3 s on technical parts - Residual volume: 5 – 10 % cushion as margin for hold stage ## Indicators of a good first stage - Uniform flow front (visible in short-shot studies) - Repeatable fill time (±2 % shot-to-shot) - Repeatable pressure peak - Stable final cushion ## Common mistakes - Velocity too high: jetting, splay, burn marks - Velocity too low: cold parts, visible weld lines, short shot - Late transfer: flash, over-pack - Early transfer: sinks, low dimensions

The fill second stage is the second of the injection stages: the pressure-controlled pack and hold phase that follows the velocity-controlled first stage. The screw hands off at the transfer position cut off when the cavity is roughly 95–99 % full, and the machine switches from filling by speed to pressing on the melt by pressure — applying hold pressure to finish filling and compensate for shrink. ## What happens in second stage - Pack: a brief, higher pressure tops off the last 1–5 % of the cavity and densifies the part so it copies the steel. - Hold: pressure is maintained while the gate is still open, pushing extra melt in to make up for the volume the plastic loses as it cools and contracts (contraction). Hold ends when the gate freezes — more hold after that does nothing. - Cushion preserved: a small cushion must remain so the screw can keep transmitting pressure during hold. ## First vs second stage - First stage (fill): velocity-controlled, fills ~95–99 %, sets the flow-front behavior and most cosmetic results. - Second stage (pack/hold): pressure-controlled, finishes the fill and sets part weight, dimensions and sink/voids. Separating the two cleanly at the transfer position cut off is the heart of decoupled, scientific molding. ## Why it matters Second stage governs the things customers measure: dimensions, weight and internal soundness. Too little pack/hold gives short shots, sink and voids; too much gives flash, overpacking, high stress and ejection problems. Hold time is set by a gate-seal study (weigh the part as hold time increases until weight stops rising). ## Related terms - See also: injection stages, hold pressure, transfer position cut off, cushion, contraction ## What is the fill second stage in injection molding? The pressure-controlled pack-and-hold phase after the velocity-controlled first stage; it tops off the last few percent of the cavity and holds pressure to compensate for shrink, setting part weight and dimensions. ## What is the difference between first and second stage? First stage (fill) is velocity-controlled and fills ~95–99 % of the cavity; second stage (pack/hold) is pressure-controlled, finishes the fill and compensates for cooling shrink — they switch at the transfer/cut-off position. ## How do you set second-stage hold time? With a gate-seal (gate-freeze) study: increase hold time and weigh the part each step; once part weight stops increasing, the gate has frozen and that is the minimum effective hold time.

Recovery (also called plasticizing, dosing or charging) is the stage of the cycle where the screw rotates and retracts to melt and meter the next shot. It runs during cooling, building a reservoir of melt ahead of the screw tip up to the set shot size while leaving a cushion. ## How it works As the screw turns, the flights convey pellets forward; shear plus barrel heat melt them and the new melt collects ahead of the screw (the check valve opens to let it pass), pushing the screw back to the metering position. Two main controls: - Screw rotation speed (RPM): how fast the shot is built. - Back pressure: resistance to the screw's retreat — more back pressure improves mixing, colour dispersion and melt uniformity, but adds shear, heat and residence time. ## Timing — keep it off the critical path Recovery should finish within the cooling time so it is not the cycle-limiting step. If recovery takes longer than cooling, the cycle waits on the screw. Use recovery protect time and rotate delay recovery delay to manage when it starts. ## Why it matters A repeatable recovery time and a stable cushion signal a healthy melt-delivery system; erratic recovery points to feed problems, a worn check valve or wrong back pressure. ## Related terms - See also: screw, shot size, cushion, cooling time, check valve ## What is recovery in injection molding? It is the plasticizing/dosing stage where the screw rotates to melt and meter the next shot during cooling, controlled by screw speed and back pressure. ## What is the difference between recovery and injection? Recovery builds and meters the next shot (the screw rotates and retreats); injection pushes that shot forward into the mold (the screw moves forward without rotating). ## What does back pressure do during recovery? It resists the screw's retreat, improving melt mixing, homogeneity and colour dispersion, at the cost of more shear, higher melt temperature and longer residence time.