Cycle Time

Cooling Time is the phase of the molding cycle in which the already-packed part loses heat until it is rigid enough to be ejected without distortion. It typically accounts for 50 – 70 % of the total cycle time, so it is the first optimization target. ## Approximate calculation The classic Ballman & Shusman formula scales quadratically with wall thickness: > t_cool ≈ (s² / α·π²) · ln[(4/π) · (T_melt − T_mold)/(T_eject − T_mold)] Where s = wall thickness (m), α = thermal diffusivity (m²/s), T_melt / T_mold / T_eject = temperatures (°C). In practice: doubling the wall quadruples cooling time. ## Typical values - 1 mm wall: 2 – 5 s - 2 mm wall: 8 – 15 s - 3 mm wall: 18 – 30 s - 4 mm wall: 30 – 50 s ## Factors that affect cooling - Mold temperature (colder → faster, until condensation limit) - Resin thermal diffusivity (PE and PP slower than ABS or PS) - Cooling-channel design (proximity, balance, flow rate) - Coolant (water + glycol, conformal cooling) - Wall thickness (dominant factor) ## Optimization Conformal cooling channels following 3D part geometry (built by DMLS), reduce thickness in CAD, separate mold temperature controllers per circuit, and mold temperature monitoring with embedded thermocouples.

Fill Time is the duration measured between screw motion start and the transfer point, during which the cavity is filled to 95 – 99 %. It is one of the most sensitive indicators of injection-molding process stability. ## Why it is critical - Repeatability: variations <2 % indicate a stable process - Dosing: constant time ensures constant volume - Diagnostics: changes in fill time reveal check-valve wear, viscosity shifts or restrictions ## Typical values - Small parts (<10 g): 0.3 – 1 s - Medium parts (10 – 100 g): 1 – 3 s - Large parts (>100 g): 2 – 6 s - Technical parts with fine detail: 1 – 4 s ## Programmed vs. actual time - Programmed: ideal per velocity profile and volume - Actual: effective, may be longer if injection pressure saturates (velocity drops) - Typical difference: <5 % in a stable process ## How to monitor - Automatic logging on the machine (most modern presses) - External screw-position sensors (high end) - Statistical histogram in SPC - Alerts: ±5 % or ±10 % depending on part criticality ## Variation diagnostics - Gradual increase (weeks): check-valve wear, progressive leakage - Sudden increase: gate blockage, contamination, batch change - Gradual decrease: mold temperature drifting up, resin absorbing moisture - Random variations: inconsistent moisture in resin, irregular virgin/regrind mix ## Optimization Seek the shortest time without defects (jetting, splay, burn marks). Every tenth saved multiplies across thousands of cycles. Rule of thumb: fill time = (thinnest wall) / (critical flow velocity of the resin).

Injection Time (Fill Time) is the time the screw takes to move from its initial position to the transfer point, executing the dynamic filling phase. It results from the programmed velocity profile and the shot volume. ## Typical values - Small parts (<10 g): 0.3 – 0.8 s - Medium parts (10 – 100 g): 0.8 – 2.5 s - Large parts (>100 g) or thin walls: 2 – 5 s - Thick technical parts: 3 – 8 s ## Why it matters A repeatable injection time is a stable-process signal. Shot-to-shot variation indicates: - Worn check valve (poor seal, melt back-flow) - Resin viscosity change (moisture, temperature) - Variable gate restriction (degradation, contamination) - Real velocity not reaching programmed (pressure saturation) ## Programmed vs. actual time The programmed time is ideal per the profile; actual can be larger if injection pressure saturates (velocity drops). Monitoring actual time is key in scientific molding. ## Optimization - Constant volumetric flow rate filling requires adjusting velocity per step - Inject as fast as possible without defects (jetting, splay, burn marks) - Short times shorten cycle but generate more shear and orientation ## Variation diagnostics Record injection-time histogram across 100 shots. Deviation >5 % indicates a problem: - Rising trend: check valve wearing out - Random jumps: moisture variation in resin - Sudden increase: partial blockage at some gate

Molding Cycle is the complete sequence of phases that produces one injection-molded part, from mold close to the next mold open. Each phase contributes its time and together they determine press productivity and part cost. ## Phases of the cycle 1. Clamp close and full tonnage applied 2. Injection: the screw forces molten material into the cavity along a velocity profile 3. Hold (packing): constant pressure to compensate for shrinkage during initial cooling 4. Cooling + plasticizing: the screw rotates to prepare the next shot while the part cools 5. Clamp open 6. Ejection and robot / EOAT motion ## How to calculate cycle time Cycle time is the sum of every phase: Cycle time = clamp close + injection + hold + cooling + mold open + ejection Plasticizing (screw recovery) runs in parallel with cooling, so it only counts when it is longer than the cooling phase. Cooling dominates and scales with the square of the thickest wall: doubling wall thickness roughly quadruples cooling time. This wall-thickness rule is the single biggest lever on overall cycle time. ## Cycle time example A representative thin-wall part on a 150-ton press: | Phase | Time | |-------|------| | Clamp close | 1.0 s | | Injection | 1.5 s | | Hold | 4.0 s | | Cooling | 8.0 s | | Mold open + eject | 2.0 s | | Total cycle | 16.5 s | ## How does material affect the cycle? Semi-crystalline resins (PP, PA, POM, HDPE) release more latent heat as they crystallize and usually need longer cooling than amorphous resins (ABS, PC, PS) at the same wall thickness. Melt temperature, mold temperature and the resin's ejection (heat-deflection) temperature all set the minimum cooling time. ## Optimization Conformal cooling channels that follow part geometry, a multi-stage injection profile, plasticizing in parallel with opening, valve gates on hot runners for clean closure, and elimination of dead time on the robot side. ## How long is an injection molding cycle? Thin-wall packaging parts cycle in 3–15 s, while thick technical or engineering parts can take 30–60 s or more. Cooling sets the floor: the thicker the wall, the longer the minimum achievable cycle. ## Which phase takes the longest? Cooling, almost always. It typically accounts for 50–70 % of the total cycle, which is why conformal cooling and wall-thickness reduction give the biggest gains. ## What is the difference between molding cycle and cycle time? "Molding cycle" describes the sequence of phases; "cycle time" is the numerical total in seconds reported on the cell's OEE. The cycle is the what, the cycle time is the how long.

Overall cycle time is the real, average time it takes to produce one shot in actual production — including everything that happens between consecutive parts, not just the machine's ideal molding cycle. Where cycle time usually means the clean, repeating machine cycle, overall cycle time is the figure you get by dividing real run time by parts made, so it captures the losses the nameplate cycle ignores. ## What it includes beyond the ideal cycle - The machine molding cycle: fill, pack/hold, cooling time, recovery, mold open, part ejection, mold close. - Operator/automation time: extra seconds in a semi automatic cycle for the operator vs a fully automatic cycle; insert loading, gate cutting, inspection. - Micro-stops and variation: door interlocks, alarms, slow part drop, robot handshakes — small delays that don't show in the "ideal" cycle. - Allocated downtime: depending on definition, brief stoppages and the amortized share of changeovers or scheduled stops. ## Ideal vs overall - Ideal/machine cycle: the best repeating time the press achieves running clean and automatic. - Overall cycle time: actual output rate, always ≥ the ideal — the gap is the improvement opportunity. This distinction matters for costing and capacity: quoting on the ideal cycle but running at a longer overall cycle is how a job loses money. Reducing it means attacking the losses (automate the semi automatic cycle, cut micro-stops, speed handling) as much as the machine cycle itself. ## Why it matters Overall cycle time is the honest basis for capacity planning, machine-hour cost and OEE performance: it ties the theoretical cycle to what the cell really delivers per hour and per shift. ## Related terms - See also: cycle time, molding cycle, cooling time, automatic cycle, scheduled stop ## What is overall cycle time in injection molding? The real average time per shot in production — the machine molding cycle plus operator/automation time, micro-stops, handling and allocated downtime — found by dividing actual run time by parts produced. ## What is the difference between cycle time and overall cycle time? Cycle time usually means the clean, repeating machine cycle; overall cycle time is the real average including operator time, micro-stops, handling and small losses, so it is always equal to or longer than the ideal cycle. ## Why is overall cycle time important for costing? Because quotes and capacity must be based on the real output rate, not the ideal machine cycle; if you price on the ideal cycle but actually run a longer overall cycle, the job runs over budget.