# Injection Molding Cycle Time Calculator

> Source: https://netray.co/tools/injection-molding-cycle-time-calculator
> Publisher: Netray (netray.co), AI and integration engineering for ERP and manufacturing systems.
> Section: Free Tools

## Short answer

Estimate cooling time from wall thickness and temperatures, then total cycle time, parts per hour and output per shift.

## Category

industry-templates

## Industry

Plastics and Injection Molding

## Audience

- Process engineer
- Production planner
- Quoting estimator

## Tool

**Kind:** calculator

**Inputs:**

#### Maximum wall thickness

**Key:** wall

**Type:** number

**Default:** 2.5

**Min:** 0.3

**Max:** 15

**Step:** 0.1

**Unit:** mm

#### Thermal diffusivity of the resin

**Key:** alpha

**Type:** number

**Default:** 0.09

**Min:** 0.03

**Max:** 0.25

**Step:** 0.01

**Unit:** mm2/s

**Help:** Roughly 0.07 to 0.10 for ABS, PC and PS, about 0.10 to 0.15 for PP and PE.

#### Melt temperature

**Key:** melt

**Type:** number

**Default:** 230

**Min:** 150

**Max:** 400

**Step:** 5

**Unit:** deg C

#### Mold wall temperature

**Key:** mold

**Type:** number

**Default:** 60

**Min:** 10

**Max:** 200

**Step:** 5

**Unit:** deg C

#### Ejection temperature

**Key:** eject

**Type:** number

**Default:** 90

**Min:** 30

**Max:** 250

**Step:** 5

**Unit:** deg C

**Help:** Average part temperature at which it is stiff enough to eject.

#### Injection (fill) time

**Key:** fill

**Type:** number

**Default:** 1.5

**Min:** 0.1

**Step:** 0.1

**Unit:** s

#### Hold (pack) time

**Key:** hold

**Type:** number

**Default:** 6

**Min:** 0

**Step:** 0.5

**Unit:** s

#### Mold open, eject and close time

**Key:** mold_move

**Type:** number

**Default:** 5

**Min:** 0.5

**Step:** 0.5

**Unit:** s

#### Cavities

**Key:** cavities

**Type:** number

**Default:** 4

**Min:** 1

**Step:** 1

#### Press efficiency on the job

**Key:** oee

**Type:** number

**Default:** 85

**Min:** 10

**Max:** 100

**Step:** 1

**Unit:** %

**Outputs:**

#### Estimated cooling time

**Key:** cooling

**Expr:** pow(wall, 2) / (pow(pi, 2) * alpha) * ln(4 / pi * (melt - mold) / (eject - mold))

**Format:** decimal

**Description:** Seconds, measured from the start of fill.

#### Cycle time

**Key:** cycle

**Expr:** fill + max(hold, cooling) + mold_move

**Format:** decimal

**Primary:** true

**Description:** Seconds per shot. Hold is treated as part of cooling.

#### Cooling share of cycle

**Key:** cooling_share

**Expr:** cooling / cycle * 100

**Format:** percent

#### Shots per hour

**Key:** shots_hr

**Expr:** 3600 / cycle

**Format:** number

#### Parts per hour

**Key:** parts_hr

**Expr:** 3600 * cavities / cycle

**Format:** integer

**Primary:** true

#### Good output per 8 hour shift

**Key:** parts_8h

**Expr:** parts_hr * 8 * oee / 100

**Format:** integer

**Chart:**

#### Cycle time (s) vs wall thickness

**Type:** line

**X:** wall

**From:** 1

**To:** 6

**Steps:** 20

**Series:**

- cycle

**Disclaimer:** The cooling formula is a one-dimensional estimate for a flat section. Real cooling depends on channel layout, coolant temperature, material and part geometry.

## Content

**Intro:** Cycle time drives part cost more than almost any other molding variable, and cooling is usually the largest slice. This calculator estimates cooling from wall thickness and temperatures, then builds up to cycle time, parts per hour and shift output.

**Sections:**

#### How to use it

**Body:** Enter the thickest wall that governs cooling, the resin's thermal diffusivity, and the three temperatures: melt, mold wall and ejection. Add fill time, hold time and the dry cycle (mold open, eject and close). Enter cavity count and a realistic efficiency for the job. The tool returns cooling time, total cycle, parts per hour and an eight hour output. Use it during quoting, then compare against actual press data once the job runs.

**Bullets:**

- Use the thickest wall that is not a rib or boss.
- Ejection temperature is the part average, not the surface.
- Check the dry cycle against the press datasheet.

#### The method

**Body:** The estimate uses the classic one-dimensional heat conduction result for a slab: cooling time equals wall thickness squared, divided by pi squared times thermal diffusivity, times the natural log of four over pi times the ratio of melt minus mold temperature to eject minus mold temperature. Cooling grows with the square of thickness, so a 3 mm wall takes about 1.44 times as long as a 2.5 mm wall. Hold time overlaps cooling, so the cycle takes the larger of the two after fill.

#### Worked example and reading results

**Body:** With the defaults (2.5 mm ABS-like wall, 230 C melt, 60 C mold, 90 C eject) cooling comes out near 14 seconds, giving a cycle of roughly 20 seconds. Four cavities then make about 700 parts per hour, or about 4,800 good parts per shift at 85 percent efficiency. If measured cooling on the press is far longer, look at coolant temperature, flow rate, channel distance to the cavity and hot spots rather than just adding time.

#### Common mistakes

**Body:** Using nominal wall rather than the thickest section understates cooling. Setting the mold temperature to the chiller setpoint instead of the actual wall temperature hides poor channel design. Counting hold and cooling as additive double counts time. Finally, remember that plasticizing time can become the limit on large shots with slow screw recovery, so compare recovery time to the cooling time before trusting the result.

**Cta:** If your ERP routings still carry guessed cycle times, we can help compare them with real press data. Reach out for a short review.

**Faq:**

#### How is injection molding cooling time calculated?

**Answer:** A common estimate is wall thickness squared divided by pi squared times thermal diffusivity, multiplied by the natural log of the temperature ratio between melt, mold and ejection temperature. It is a one-dimensional approximation for a flat wall.

#### What share of the cycle is cooling?

**Answer:** For many parts cooling is 50 to 80 percent of the total cycle, rising with wall thickness. Thin-walled packaging is closer to fast fill and short cooling, while thick technical parts are dominated by cooling.

#### How do I reduce cycle time?

**Answer:** Look at cooling first: colder coolant, turbulent flow, conformal or closer channels, thinner walls and a higher allowable ejection temperature. Then trim hold time using a gate-seal study and tighten the dry cycle.

#### Why is my real cycle longer than the estimate?

**Answer:** The estimate ignores robot or degating time, slow ejection, screw recovery, thick ribs and bosses, and cooling circuit inefficiency. Compare each element against a timed cycle breakdown on the press.

## Search terms

injection molding cycle time calculator, cooling time calculation injection molding, injection molding cycle time formula, parts per hour injection molding, molding cycle time estimate, cooling time wall thickness, injection molding output per shift

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