Enter wall thickness, temperatures and machine times to get the cycle and parts per hour; with resin price, press rate and mold cost, see the cost of each good part and how many cavities pay off at your volume.
Pre-sizing and estimating tool: results do not replace design, calculations or reports signed by a licensed professional, nor verification against the applicable codes and standards.
Time of each step in one cycle, in seconds. Screw recovery only shows if it exceeds the cooling left after pack and hold.
Material, machine and mold amortization per good part. Faded bars do not fit in the available hours.
Plate formula with the temperatures and diffusivity entered. The dashed line is the current thickness.
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It estimates how long each molding cycle takes, how many good parts come off per hour and what each part costs, adding resin, press time and mold amortization. It also compares 1 to 32 cavities to show the most economical count for your annual volume. Use it to quote a new part, compare molds or decide whether thinning the wall pays off.
With the classic formula for a plate cooled on both faces: time grows with the square of wall thickness and depends on melt, mold and ejection temperatures and the resin’s thermal diffusivity. In the example, a 0.08 in PP wall at 446 °F melt, with the mold at 104 °F and ejection at 194 °F, takes 6.6 s to cool.
From the press panel if the part is already running, or from a similar part. For a new part, start with typical values and adjust after the first trial: fill 0.5 to 2 s, pack and hold 2 to 5 s, and open, eject and close 3 to 6 s on mid-size presses. Screw recovery only lengthens the cycle if it exceeds the cooling left after pack.
With an 11.6 s cycle, 4 cavities, 2% scrap and 85% efficiency, the press makes 1,031 good parts per hour. The part costs $0.201: $0.057 resin, $0.073 press time ($75/h divided by 1,031) and $0.070 mold ($106,000 spread over 1.5 million parts in 3 years), or about $201 per thousand.
For each cavity count it adds up a year of resin, press hours and mold cost divided by the amortization years; the mold gets pricier with more cavities (0.7 exponent, after Boothroyd and Dewhurst) while the press hour is spread over more parts. In the example, at 500,000 parts a year, 6 cavities give $0.199 a part, within 3% of the 4-cavity mold, so 4 is still a sound choice. Counts that do not fit in the available hours show faded on the chart.
The formula assumes a uniform wall; thick corners, uncooled cores and poorly placed water lines make the real cycle longer. The diffusivity and temperatures in the list are approximate: use the resin data sheet. The hour rate is fixed, but a mold with more cavities needs a larger press with a higher rate; check the clamp force and rework the rate in the machine hour cost calculator.
Important notice: Indus Metrics tools produce estimates and pre-sizing results from the data you enter and from published engineering methods. They do not replace design, calculations or reports signed by a licensed professional engineer (PE), nor verification against the applicable codes, standards and regulations, such as OSHA rules and the ASME codes. Material and fuel properties vary: check manufacturer data or your own process analyses before deciding. By using this site you agree to the Terms of Use.
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