Injection Time

Cycle Time is the total time an injection molding machine takes to produce a complete part, measured from one mold close to the next. It is the most critical economic indicator of the process: every second saved multiplies by the number of cavities and the annual volume. ## Phases of the cycle 1. Mold close and clamp 2. Injection (dynamic filling of the cavity) 3. Hold (packing pressure) 4. Cooling and plasticizing in parallel 5. Mold opening 6. Part ejection and robot motion ## Typical values per part - Small parts (<10 g): 5 – 15 s - Medium caps and containers: 8 – 25 s - Large housings (>200 g): 25 – 60 s - Technical parts with inserts: 30 – 90 s Cooling usually accounts for 50 – 70 % of total cycle. ## Factors that affect cycle time Wall thickness (quadratic relation with cooling), resin type (crystalline > amorphous), cooling-channel design, injection profile, robot/EOAT efficiency, and dead time from difficult ejection. ## Reducing cycle time Optimize conformal cooling, tune injection velocity profile, balance cavities, switch to valve gates on hot runners, parallel plasticizing with opening, and remove unnecessary robot moves.

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 Speed (Injection Velocity) is the linear speed at which the screw advances during fill, programmed in mm/s (or volumetric cm³/s). It is one of the parameters that controls fill quality, alongside temperature and hold pressure. ## Why it matters Speed determines: - Fill time: 0.3 – 3 s on technical parts - Shear on the material (faster → more shear → lower effective viscosity) - Cosmetic marks: jetting (excessive speed on small gate), flow marks (too slow or interrupted) - Molecular orientation and residual stress ## 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 vent zones (avoid air trap) 4. Slow at end of fill for smooth transition to hold ## Typical values - Commodity resins, standard wall thickness: 50 – 150 mm/s - Technical detailed parts: 30 – 80 mm/s - Very thin wall parts (<0.8 mm): 200 – 500 mm/s (high-dynamic servo machines) - Shear-sensitive resins (PVC, PMMA): moderate speed ## Optimization Moldflow / Moldex3D analysis to define theoretical profile, iterative tuning with short-shot studies, and melt-temperature monitoring at end of fill (must not rise more than 5 – 10 °C from over-shear). ## Common issues Jetting from high speed on point gates, flow marks from insufficient speed, burn marks from trapped air at end of fill, and delamination if the flow front cools partially.

Output values are the measured results a molding cycle reports back — the readings the machine and the part give you in response to the input parameters you set. Inputs are what you control; outputs are what actually happened. Watching outputs, not just inputs, is the core discipline of scientific method scientific molding, because the same settings can drift into different parts. ## Typical output values - Process readings (per shot): actual fill time, peak injection pressure, the cushion left, recovery time, actual cooling and overall cycle time. - Part results: weight of the molded part (or cavity weight), dimensions, sink/voids, flash and cosmetics. - Trends: shot-to-shot variation of these values, which reveals process stability over a run. ## Outputs vs inputs - input parameters (set, cause): fill speed, hold pressure, temperatures, timers. - Output values (measured, effect): fill time, peak pressure, cushion, part weight, actual cycle. A drifting output with unchanged inputs is the early-warning signal: a rising fill time or falling cushion points to a worn check valve, wet resin or a temperature shift before bad parts appear. ## Why it matters Output values are how a process is verified, not just set. Robust process control (and a quality system) defines acceptable ranges for key outputs and alarms or rejects when they leave the window — catching problems the input settings alone would hide. Monitoring part weight and fill time is one of the simplest, most powerful output checks on the floor. ## Related terms - See also: input parameters, scientific method scientific molding, cushion, cavity weight, cycle time ## What are output values in injection molding? The measured results of a cycle — actual fill time, peak injection pressure, cushion, part weight, real cooling and cycle time — that report what the process and part actually did in response to the input settings. ## What is the difference between output values and input parameters? Input parameters are the settings you control (speed, pressure, temperature); output values are the measured response (fill time, peak pressure, cushion, weight). Inputs are causes, outputs are effects — and outputs are what verify the process. ## Why monitor output values instead of just settings? Because identical input settings can still produce different parts as the material, mold or machine drift; tracking outputs like fill time, cushion and part weight catches that drift early, before scrap is made.