By PolyTakt Team · 7/10/2026
V/P transfer is where fill ends and pack begins. A first stage of 95–98% by volume is widely taught, and it does not always mean the same appearance. This article sets out both readings, how to see them on fill-only shots, and how to document the job you have given pack.
V/P transfer is the point at which the machine switches from velocity-controlled injection (fill) to pressure-controlled pack and hold.
Common transfer methods:
Each method has strengths and limitations.
The right choice depends on machine capability, part geometry, and measurement available — not on what the last job used.
Transfer should occur at a point where:
Transfer is not a universal percentage.
It is a process decision based on fill behaviour, gate location, venting, and part geometry.
The question is not "95% or 98%."
The question is: where does fill become pack's responsibility, and what does the fill-only part look like at that point?
A first-stage fill of about 95–98% is widely taught.
The percentage is of fill volume. A percentage of the packed part's weight is a different quantity. Packing adds mass into a cavity that is already full, so 95% of a packed weight is often a part that was already full at transfer.
Courses that quote the same numbers do not always mean the same appearance.
One reading: the cavity is full and not packed. The outline is complete. Sinks and voids are still present. Pack densifies. It does not have to finish an unfilled volume.
The other reading: the part is visibly short of complete. Pack finishes the remaining volume and then densifies. That last volume moves under pack pressure, not at the injection speed from the viscosity study. On a thin wall, a flow front that has stopped may freeze and never restart.
Both readings are trying to keep first-stage velocity from packing the cavity. They disagree on what the fill-only part should look like, and on what pack is then asked to do.
There is no wall-thickness rule that settles it. A thick section can look complete while the missing volume is sink. A thin section can flash once the outline is complete, and the same thin section can freeze if transfer is early enough that pack has to restart the front.
If first stage cannot produce the fill state you intended, find which limit you have hit before you move transfer and call the result 95%.
Is the fill pressure-limited? Peak injection pressure is on the machine limit before the cavity is full, so the screw is no longer at the set speed. The demand may be the tool — flow length, wall, gate, venting — or the machine: available plastic pressure, the check ring, or the barrel. Pack will not finish a cavity that first stage never reached under velocity.
Is the clamp opening during injection? Flash on a fill-only shot means the parting line moved under fill pressure, before pack. That is clamp force, tie-bar balance, projected area, or the condition of the steel. If the part only flashes in the last of the fill, at fill speed, slow the end of fill with a velocity profile and keep the fill time already established. If it flashes well before the outline is complete, a slower ending will not supply clamp that is not there.
A small short is sometimes the state you can hold without flash. Record it as a short. A short large enough for the front to freeze is a cavity that was not filled under velocity.
Before establishing transfer:
Fix for the transfer study:
Set both to zero. A pack timer left running at zero pressure is not a fill-only shot.
When injection stops, melt ahead of the screw is still pressurised. A small reverse movement is expected as that pressure equalises. It is not a fault, and it is not cured by moving time from pack to cooling.
The gate is still open at the end of fill. If recovery starts at once, back pressure can push more melt into the cavity, and the part looks fuller than first stage delivered. The charge delay lets the gate freeze before recovery. Charge delay, recovery delay, and refill delay are the same timer on different controls.
Where a single speed flashes at the end of fill, a velocity profile can slow that ending. Raise the earlier segments so the fill time stays the one set in the viscosity study. What you are protecting is the fill you already characterised.
Run a series of fill-only shots at decreasing transfer positions (increasing fill volume), with the charge delay in place.
Observe:
Continue until you can see the states the two readings describe: a visible short of the outline, and, where the tool and machine allow it, a complete outline that still has sinks and voids and does not flash.
If the complete outline flashes, or a short front freezes and will not fill out under pack, use the pressure and clamp questions above before you settle. A velocity profile, with fill time held, is the first process change when flash is only at the end of fill.
The selected transfer is one of those states, chosen deliberately. If it is a short, record it as a short.
Where possible, move from visual assessment to measurement:
While the cavity is still short, weight rises in step with screw movement. Once the flow front reaches the end, cavity pressure rises sharply and further movement packs the melt. Weight may still increase, and flash may start.
The transfer you select should sit on the side of that break that matches the appearance you chose: still on the fill slope for a deliberate short, or at the start of the pressure rise for a complete outline that is not yet packed. Small position changes should produce a predictable weight change.
Run ten or more consecutive shots at the selected transfer position.
Confirm the chosen appearance repeats:
Document the appearance and the average fill weight at transfer. The weight becomes the reference for pack development and for interpreting shot weight at V/P in production. It is only meaningful for the appearance you recorded.
Time transfer switches at elapsed injection time rather than screw position.
Use when:
Procedure:
Caution: time transfer does not compensate for viscosity change as automatically as a well-set position transfer on a stable machine.
Material lot variation or temperature drift may require re-verification.
Pressure transfer switches when injection pressure reaches a set threshold — sometimes described as hydraulic pressure transfer or cavity pressure transfer where instrumentation exists.
Use when:
Procedure:
Pressure transfer can compensate for some viscosity variation.
It demands reliable pressure measurement — not all machines provide it equally. A pressure threshold set past the end-of-fill rise will pack on first stage.
| Method | Strength | Weakness |
|---|---|---|
| Position | Direct, widely available | Sensitive to check ring leakage and cushion variation |
| Time | Simple on some machines | Less responsive to viscosity change |
| Pressure | Can track material response | Depends on measurement quality and machine hydraulics |
Many robust processes use position transfer with pressure monitoring as verification — not as a substitute for understanding fill.
Transfer too late (overfill) First stage has gone past fill and is packing the cavity. Flash risk increases. The process window narrows. This is the failure of a complete-outline target that was set too far.
Transfer earlier than the job you gave pack A visible short asks pack to finish fill and then densify. A small, stable short can be a chosen process. A larger short, or a front that freezes, makes weight and dimensions hold-sensitive in ways that are hard to hold.
Using packed-part weight as the fill percentage 95% of a packed part is not 95% fill volume. The packed part already contains the mass added during pack.
Not recording which appearance you chose Later pack work cannot be interpreted. A weight change means something different when pack was only densifying than when pack was also finishing the fill.
Establishing transfer with hold pressure active Hold masks fill state. Evaluate transfer on fill-only shots first, with a charge delay so recovery does not fill the part after transfer.
Copying transfer position from another machine Screw diameter, check ring condition, and hydraulic response differ. Transfer must be established on the machine that will run production.
Ignoring imbalance On multi-cavity tools, a transfer that fills one cavity may leave another short, or flash the heavy cavity while the light cavity is still short. Address balance before finalising transfer. On an unbalanced tool the heavy cavity is the one that defines "full."
Treating transfer as fixed forever Tool wear, material change, and maintenance shift fill behaviour. Transfer limits in validation should reflect known sensitivity.
Decoupled moulding depends on separating fill from pack.
Transfer is the separation point.
The separation is only real if pack is doing the job you documented. If you transferred on a complete outline, pack densifies. If you transferred on a short, pack also finishes the fill. Either can be a stable process. Neither is stable if the fill state moves and pack is left to cover the difference.
If fill is inconsistent at transfer:
Establishing transfer properly is how decoupling becomes real instead of nominal.
Validated processes typically document:
Changes to transfer method, setpoint, or the fill appearance after OQ are change-control events.
Initial establishment should occur during process development with data supporting the selected point — not during PQ under production pressure without records.
Auditors ask: how do you know this is the right transfer point?
The fill-only series, the appearance you selected, the weight data, and the repeatability run are the answer.
Store with process development documentation for the tool.
V/P transfer is not a default setting.
It is the handoff between velocity-controlled fill and pressure-controlled pack — and it must be established with data on the production machine.
95–98% fill by volume does not name a single appearance. Run the fill-only series. Decide which reading you are using on this tool. Measure. Confirm that appearance repeats. Document what you have asked pack to do.
Everything downstream — gate seal, hold optimisation, process window mapping — depends on this step being done properly.
Rush transfer, and the process will spend the rest of its life compensating.
