Simultaneous valve gating
- All drops open together for straight fill
- Lower controller scope and fewer sequence trials
- More weld line risk on large visible flats
Glossary
Sequential Valve Gating (SVG): Control Weld Lines, Fill Sequence, and Clamp Force on Large Molded Parts
Sequential valve gating (SVG) programs multiple valve gates in order to steer fill, weld lines, and pressure on large or cosmetic parts.
Definition
Sequential Valve Gating (SVG) in Injection Molding
SVG is not a separate gate type. It is a programmed open and close sequence across multiple valve gates on a hot runner.
The goal is to control melt front progression, weld line placement, peak pressure, and warpage on large or cosmetic parts.
Each drop uses a valve gate pin. SVG adds controller logic that times those pins across the manifold.
Programs still need hot runner hardware, a sequence controller, and validation on press.
Operation
How Sequential Valve Gating Works
Shops call this cascade fill or staged fill when melt fronts are kept from colliding on cosmetic land.
Drop 1 opens first. Melt advances from the chosen start zone, often a remote or edge drop on large flats.
Drop 2 opens when a trigger is met: elapsed time, screw position, or cavity pressure rise at a sensor location.
Earlier drops may stay open, close at handoff, or switch to pack depending on the sequence profile.
Simultaneous valve gating opens every drop at once. SVG staggers starts so flow fronts merge where the drawing allows.
Mold flow simulation often presets the sequence. Press data from cavity pressure or screw position fine tunes timing on machine.
Time based delays are common for initial sequence setup. Cavity pressure or screw position override fine tunes the actual trigger during T0 trials.
Comparison
Sequential vs Simultaneous Valve Gating
Simultaneous fill is simpler to tune. SVG trades controller and trial cost for fill control on demanding geometries.
Sequential valve gating (SVG)
- Staggered drop opening for cascade fill
- Can relocate knit lines toward non cosmetic zones on some layouts
- Needs documented sequence, acceptance, and validation
Concept
Sequential Valve Gating vs a Single Valve Gate
A valve gate is hardware on one drop. SVG is the timing strategy across many drops.
Valve gate (one drop)
- Mechanical pin shuts off flow at one cavity entry
- Controls vestige and drool at that drop
- Does not by itself coordinate multi drop fill order
Sequential valve gating (SVG)
- Coordinates multiple valve gates in a programmed order
- Targets weld location, pressure peaks, and pack across the part
- Requires hot runner, controller, and cosmetic map on the drawing
Selection
When SVG Pays Off
Use when fill control saves appearance or tooling margin on large programs.
Automotive Class A panels and wide exterior land
TV bezels, display frames, and appliance front panels
Large flat parts where simultaneous fill leaves weld on visible faces
Family molds with unequal cavity fill that needs balanced sequence
Areas near living hinges or high stress knit lines that need relocation
Selection
When SVG Is Not Worth It
Small or low cosmetic parts rarely justify sequence controller cost.
Skip SVG when
- Single drop or cold runner meets fill and cosmetics
- Hidden utility internals with loose weld acceptance
- Tight tooling budget with no mold flow or sequence trial allowance
- Small parts where simultaneous hot tip or valve fill is enough
Engineering results SVG can target
- Move or reduce visible weld lines on mapped faces
- Lower peak injection pressure on some large layouts
- Reduce clamp demand when peak pressure drops on validated sequences
- Flatter large surfaces with more controlled pack progression
Trade-offs
Risks and Costs to Plan For
Budget controller, maintenance, and trial time in the RFQ.
Hot runner controller and valve actuation cost per drop
Valve pin wear and alignment like any valve gate program
Short shot and sequence trials during process development
Mistimed opening can cause hesitation, air traps, or new weld witness
Process data
Mold flow, cavity pressure, and scientific molding
SVG programs usually start in simulation, then get confirmed with press data.
- Mold flow analysis can preset drop order and open delay before steel is cut.
- Cavity pressure sensors and screw position traces verify triggers during tuning.
- Scientific molding discipline helps lock a sequence that repeats in production.
DFM
Quote and Mold Spec Checklist
Send these with CAD before drop sequence is frozen.
Drop count and nominal open order on the drawing
Cosmetic map showing where weld lines are allowed
Actuation type expected: pneumatic, hydraulic, or electric valve
Whether mold flow report is required before build signoff
Who owns final sequence: mold maker, molder, or shared
Go deeper
Where this term connects
Each link is a different angle on the same program, not a duplicate definition.
Valve gate
Single drop shutoff hardware.
Valve gateHot runner
Manifold and drop context.
Hot runnerGate
Weld line and vestige vocabulary.
GateMold flow analysis
When simulation pays off before build.
Mold flow analysisCavity pressure
Sensors for sequence tuning.
Cavity pressureVisual 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
Frequently Asked Questions About Sequential Valve Gating
Is sequential valve gating the same as a valve gate?
No. A valve gate is the shutoff mechanism on one hot runner drop. SVG is the programmed timing strategy that opens and closes multiple valve gates in order.
Do I need SVG on my part?
Only when part size, weld line placement, or peak pressure on large layouts justify hot runner, controller, and trial cost versus simultaneous fill.
Does SVG reduce clamp tonnage or injection pressure?
On some large flat parts, staggered fill can lower peak injection pressure during fill, which may reduce clamp demand versus all drops opening at once. Results depend on geometry and must be validated on press.
How many drops before SVG makes sense?
There is no fixed rule. Teams usually discuss SVG when several valve drops serve one large cosmetic cavity or when family mold imbalance needs staged balance, not for a single drop part.
Do I need Moldflow before specifying SVG?
Mold flow analysis is commonly used to propose drop order and delay before steel is cut. Many programs still fine tune triggers with cavity pressure or screw position during trials.
Pneumatic, hydraulic, or electric valve actuators?
All three appear in production tools. Pneumatic is common on many lines. Hydraulic suits high force or tight timing. Electric valves add precision at higher component cost. Match actuation to supplier capability in the mold spec.
Can SVG cause new defects if mistimed?
Yes. Late or early drop opening can create hesitation marks, air traps, short fill, or a new visible weld. Sequence trials and signed T0 acceptance reduce surprise at production scale.
Does SVG help thin wall large parts?
Staged fill can help wide thin panels by avoiding a single massive flow front, but wall thickness, venting, and material still set the limit. SVG is not a substitute for wall and rib DFM.
Can SVG hide all weld lines?
SVG moves or reduces knit witness on many layouts. Some mark may remain and should be mapped on the cosmetic drawing with T0 signoff.
Does SVG affect cooling uniformity or warpage?
Staggered fill can improve pack consistency across large surfaces, which may reduce differential shrinkage and warpage compared to simultaneous fill. The effect depends on wall thickness variation, cooling channel layout, and material shrinkage behavior. Mold flow analysis is the best way to evaluate warpage before committing to a sequence plan.
Next step
Planning sequential valve gating?
Upload CAD with drop count, cosmetic map, and weld line acceptance before the hot runner sequence is frozen.