Molding Cycle

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.

Injection stages are the phases of pushing the shot into the mold, split into two fundamentally different control modes — a velocity-controlled fill (first stage) and a pressure-controlled pack-and-hold (second stage) — with a transfer point between them. ## First stage — fill (velocity-controlled) The screw advances at a set injection speed to fill about 95–99 % of the cavity quickly. Speed, not pressure, is the controlled variable; injection pressure is only the ceiling that allows that speed. ## Transfer (cut-off) At the transfer position cut off the machine switches from speed control to pressure control — the single most important transition for shot consistency. It is usually set by screw position (sometimes by pressure or time). ## Second stage — pack & hold (pressure-controlled) hold pressure packs in a little more melt to compensate shrinkage as the part freezes, until the gate seals — this is the fill second stage. A stable cushion must remain so the pressure keeps transmitting. ## Why it matters Decoupling fill (speed) from pack (pressure) at the right transfer point is the heart of scientific molding: it makes the fill repeatable and lets pack control final weight and dimensions independently. ## Related terms - See also: transfer position cut off, injection speed, hold pressure, fill second stage, molding cycle ## What are the injection stages in injection molding? First-stage fill (velocity-controlled, about 95–99 % full), transfer/cut-off, and second-stage pack and hold (pressure-controlled) until gate seal. ## What is the difference between first and second stage? First stage is speed-controlled filling; second stage is pressure-controlled packing and holding. The transfer point switches between them. ## Why decouple fill and pack? So the fill repeats the same way every shot (by speed) while pack pressure independently sets final part weight and dimensions — the basis of a stable, scientific process.

The injection molding process is the method that turns plastic pellets into finished parts by melting resin and forcing it into a mold under pressure. One full pass through its steps is the molding cycle, repeated thousands of times in production on an injection molding machine imm. ## The steps of the process 1. Clamp close: the clamp unit closes and locks the mold under tonnage. 2. Injection (fill): the screw pushes melt through the nozzle to fill the cavity (see injection stages). 3. Pack & hold: hold pressure adds a little more melt to compensate shrinkage as the part freezes. 4. Cooling + recovery: the part cools (cooling time) while the screw turns to meter the next shot (recovery). 5. Clamp open: the mold opens. 6. Ejection: ejector pins push the part out (part ejection); then the cycle repeats. ## Process parameters The process is controlled by a handful of inputs: melt temperature, mold temperature, injection speed, pack/hold pressure and time, cooling time and back pressure. Tuning these to a documented window is the heart of scientific molding. ## Process vs cycle - Process: the overall method and its sequence of steps (this term). - molding cycle: one repeating loop of that sequence and its time breakdown (cycle time). ## Related terms - See also: molding cycle, injection molding machine imm, injection stages, hold pressure, cooling time ## What is the injection molding process? It is the method of melting plastic and injecting it into a mold to make parts, through the steps clamp-close, inject, pack/hold, cool, open and eject — one pass being a molding cycle. ## What are the stages of the injection molding process? Clamp close, injection (fill), pack and hold, cooling with screw recovery, mold open, and part ejection. ## What is the difference between molding process and molding cycle? The process is the overall method and its sequence; the molding cycle is one timed repetition of that sequence, measured as cycle time.

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.