Injection Cycle Time
Compute the total cycle time of a plastic injection by adding the injection time (fill + pack), the cooling time and the mold open/eject time. Cooling is usually the largest share (50–80% of the cycle). The cycle time directly determines productivity: parts/hour = 3600/cycle × cavities. Reducing it is the constant focus of optimization. Enter the injection, cooling and opening times.
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Injection cycle time
The cycle time is the clock that governs the economics of plastic injection molding: the shorter it is, the more parts per hour and the lower the unit cost. It adds up three phases: injection (fast filling plus packing under pressure to compensate for shrinkage), cooling (waiting for the part to solidify enough to be ejected without warping) and mold opening/ejection (opening the mold, pushing the part out and closing again). Cooling almost always dominates the cycle — 50% to 80% of the time — and grows with the square of the wall thickness; that is why thinner parts and a well-designed cooling channel layout in the mold are the biggest productivity levers. The arithmetic is direct: parts/hour = 3600 ÷ cycle × number of cavities. Shaving 1 second off a 20 s cycle that runs 24 h a day yields thousands of extra parts every month. Enter the injection, cooling and mold-opening times.
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Injection Shot Volume
Compute the shot volume of a plastic part by dividing the injected mass by the molten material density. The shot is the total volume of plastic injected per cycle (parts + runners), a parameter that must fit the injection barrel capacity. Together with the machine capacity, it defines how many cavities can be filled per cycle. Enter the injected mass (g) and the material density (g/cm³).
Cooling Time (Injection Molding)
Estimate the cooling time of a flat part in injection molding, t = h² ÷ (π²·α), from the wall thickness h and the polymer's thermal diffusivity α. The result, in seconds, is the dominant time of the injection cycle — the part can only be ejected after cooling enough to be rigid. The most critical factor is thickness squared: doubling the thickness quadruples the cooling time (and the cost per part). That is why thin, uniform walls are a golden rule in injection part design. Plastics' low thermal diffusivity makes cooling the productivity bottleneck. Enter the wall thickness and the thermal diffusivity.
Injection Capacity (PS Equivalent)
Convert a machine's nominal injection capacity (always specified in polystyrene, PS, density ~1.05) to the equivalent capacity in another material by multiplying by the density ratio. Since the barrel has a fixed volume, the mass it injects changes with the plastic's density — denser materials yield more grams per shot. Essential to size the machine for the real material. Enter the nominal PS capacity and the material density.
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Calculate the cutting time of one turning pass, t = L ÷ (f·n), from the length to machine L (mm), the feed f (mm/rev) and the rotation n (rpm). The product f·n is the tool feed rate (mm/min); dividing the length by it gives the pass time. This is the PRODUCTIVE cutting time of a longitudinal turning operation (the tool traversing the part length), and the basis of total fabrication time and thus machining cost and production planning. Total time also includes non-productive times (tool approach and retract, part change, measuring, tool change) and the number of passes needed (depending on material to remove and depth per pass). Cutting time — by raising feed and rotation (and thus cutting speed) — is the path to productivity, always within tool life, machine power and required finish limits. This is essential to quote machined parts and size a machine shop's capacity. Enter the length, feed and rotation.
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The results provided by this tool are for general informational and educational purposes only and do not constitute professional, financial, medical, legal, tax or accounting advice. Always confirm important decisions with a qualified professional and official sources.