Injection Speed

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

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 Pressure is the pressure the screw exerts on the molten material during dynamic filling, up to the transfer point. It is an output of the process, not a setpoint: it rises as much as needed to maintain the programmed injection velocity. ## Pressure types - Plastic (Ppsi): actual pressure on the material, in bar - Hydraulic (Hpsi): oil pressure in the hydraulic cylinder - Relation: Ppsi = Hpsi × intensification ratio (typically 10:1 to 15:1 depending on screw diameter) ## Typical values by resin - Commodity (PE, PP): 400 – 1200 bar plastic - Engineering (ABS, PC, PA): 700 – 1800 bar - Fiber-reinforced: 1000 – 2200 bar - High-viscosity resins (PEEK, PSU): up to 2500 bar - Modern machines: up to 2400 bar maximum ## Why it matters If pressure saturates (hits machine max), velocity drops and the part fills slower → cold part, cold weld lines, short shot. Design to not saturate: enlarge gates, runners or thickness, or reduce flow length. ## Diagnostics - Repeatable peaks shot-to-shot: stable process - Rising peaks: worn check valve, contamination, partially blocked gate - Falling peaks: mold temperature rising, gate wearing ## Optimization Raise melt temperature, enlarge gates if the restriction is there, switch to higher-MFI resin, or move to a higher-pressure machine (rarely needed with well-designed molds).

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

Input parameters are the settings a technician dials into the machine to run a molding process — the knobs you control. They are the cause side of the process; the effects they produce are the outputs values you measure. Telling the two apart is the foundation of scientific method scientific molding: you change an input and watch the outputs respond. ## Typical input parameters - Injection: injection speed (fill velocity/profile), injection pressure limit and the transfer/cut-off position. - Pack & hold: hold pressure level and hold time. - Plastication: screw RPM, back pressure, shot size and decompression. - Temperatures: barrel temperature zones, nozzle and mold temperature. - Timing: cooling time and overall cycle time components. ## Inputs vs outputs - Input parameter (set): what you enter — e.g. "fill speed 80 mm/s", "hold 600 bar for 3 s". - outputs values (measured): what the machine and part report back — fill time, peak injection pressure, cushion, part weight, actual cooling. A setting is an input; a reading is an output. The same input can yield different outputs if the material, mold or machine drifts — which is exactly why outputs are monitored. ## Why it matters Documenting input parameters makes a process repeatable and transferable: a setup sheet of inputs lets another shift or machine reproduce the run. But because identical inputs don't guarantee identical parts, robust processes are validated by confirming the outputs values stay in range — not just that the inputs match. Develop inputs from the plastic's behavior (e.g. a viscosity curve) rather than by trial and error. ## Related terms - See also: outputs values, scientific method scientific molding, molding process, injection speed, hold pressure ## What are input parameters in injection molding? The machine settings a technician enters to run the process — injection speed, pressures, hold, screw RPM, back pressure, temperatures and timers; they are the controllable causes whose effects show up as the measured output values. ## What is the difference between input parameters and output values? Input parameters are what you set (fill speed, hold pressure, temperatures); output values are what you measure in response (fill time, peak pressure, cushion, part weight). Inputs are causes; outputs are effects. ## Why document input parameters? So a process is repeatable and transferable across shifts and machines; a documented setup sheet lets the run be reproduced, though robust process control also confirms the resulting output values, since identical inputs don't always give identical parts.