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Injection Moulded Part Cost (Clamp, Cycle, Machine, Material, Mould)

Will my moulding machine run this mould, how many parts an hour will it make, and what does each part cost in machine time, plastic and mould against my target price?

Cost check for an injection moulded part: clamp force from the projected area and cavity pressure, shot size against the barrel, cooling time from the wall thickness, cycle time and parts per hour (as the injection moulding estimate tool), then per good part the machine cost at your hourly rate, the plastic including runner and scrap, and the mould amortised over its life quantity, against the target price.

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How this tool works

Inputs, units and where to find them

InputUnitTypical source
Mould
Projected area per partcm²Area of one part projected on the parting plane.
CavitiesNumber of cavities.
Runner projected areacm²Projected area of the runner system.
Cavity pressureMPaAverage cavity pressure for the material and flow length.
Clamp margin%Extra clamp force allowance.
Part volumecm³Volume of one part.
Runner volumecm³Volume of the runner per shot.
Melt densityg/cm³Density of the melt.
Cooling
Wall thicknessmmThickest main wall of the part.
Thermal diffusivity of the plasticmm²/sThermal diffusivity of the plastic.
Melt temperature°CMelt temperature.
Mould temperature°CMould surface temperature.
Ejection temperature°CTemperature at which the part can be ejected.
Other cycle time (fill, hold, open, eject, close)sFill, hold, mould open, eject and close time.
Machine and costs
Machine clamp forcekNRated clamp force of the machine.
Machine shot capacitycm³Shot capacity of the machine.
Machine rate with operator share$/hHourly rate of the machine with its share of an operator (from the machine hour rate tool).
Plastic price$/kgPrice of the plastic.
Scrap rate%Share of parts rejected.
Mould cost$Cost of the mould charged to this part.
Parts over the mould’s charged lifeNumber of parts over which the mould cost is spread.
Target cost per part$Cost per part you need to reach.

What each input means

Open an input to see what it is, its units, the worked example and the common mistakes, with a small diagram.

Mould

What this means: Projected area per part
Illustration: Projected area per partA shaded shape whose enclosed surface is the area Projected area per part.AₚenclosedsurfaceExample: 50 cm²Projected area per part
What it is
The area of one part projected onto the mould parting plane: the outline area seen looking along the direction the mould opens, including holes that the melt surrounds.
Units and format
Enter a number in cm²: square centimetres. The form accepts 0.000001 cm² to 100000 cm². Required: the tool does not calculate until every input is valid.
Example
The form opens with 50 cm² as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
Effect on the result
Clamp force rises in proportion to the total projected area.
Get it right
Projected area, not surface area; deep walls add surface but no projected area.
What this means: Cavities
Illustration: CavitiesA row of identical items being counted; Cavities is how many there are.nExample: 4Cavities
What it is
The number of identical part cavities in the mould, so the number of parts made in each shot.
Units and format
Enter a plain number with no unit. The form accepts 1 to 256. Use a whole number. Required: the tool does not calculate until every input is valid.
Example
The form opens with 4 as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
Effect on the result
More cavities raise parts per hour but also the clamp force and shot size.
What this means: Runner projected area
Illustration: Runner projected areaA shaded shape whose enclosed surface is the area Runner projected area.AᵣenclosedsurfaceExample: 20 cm²Runner projected area
What it is
The area of the runner and sprue system projected onto the parting plane, added once per shot to the parts’ area.
Units and format
Enter a number in cm²: square centimetres. The form accepts 0 cm² to 100000 cm². Required: the tool does not calculate until every input is valid.
Example
The form opens with 20 cm² as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
Get it right
Enter zero for a hot runner whose channels do not fill at the parting plane.
What this means: Cavity pressure
Illustration: Cavity pressureA pressure gauge whose needle moves with Cavity pressure; the needle follows the value you type.pExample: 40 MPaCavity pressure
What it is
The average melt pressure in the cavities that tries to push the mould open, from the resin supplier or moulding experience for the material and flow length.
Units and format
Enter a number in MPa: megapascals (1 MPa = 1 N/mm²). The form accepts 0.000001 MPa to 300 MPa. Required: the tool does not calculate until every input is valid.
Example
The form opens with 40 MPa as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
Effect on the result
Clamp force rises in proportion to it.
Get it right
This is cavity pressure, not the much higher injection pressure set on the machine.
What this means: Clamp margin
Illustration: Clamp marginA bar of 100 parts with the share marked; Clamp margin is that share out of 100. The bar follows the value you type.0 %100 %Example: 10%Clamp margin
What it is
An extra allowance added to the calculated clamp force to keep the mould closed against pressure peaks and flash.
Units and format
Enter a number in %: percent: the number is read as a percentage, so type 8 for 8 %. The form accepts 0% to 100%. Required: the tool does not calculate until every input is valid.
Example
The form opens with 10% as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
Get it right
Type the percentage on top of the calculated force.
What this means: Part volume
Illustration: Part volumeA box drawn in three dimensions; the space it encloses is the volume Part volume.VExample: 30 cm³Part volume
What it is
The volume of plastic in one moulded part, from the CAD model.
Units and format
Enter a number in cm³: cubic centimetres. The form accepts 0.000001 cm³ to 1000000 cm³. Required: the tool does not calculate until every input is valid.
Example
The form opens with 30 cm³ as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
Effect on the result
Shot volume is cavities × part volume + runner volume.
What this means: Runner volume
Illustration: Runner volumeA box drawn in three dimensions; the space it encloses is the volume Runner volume.VExample: 10 cm³Runner volume
What it is
The volume of the cold runner and sprue filled with each shot, which is moulded and paid for but not sold.
Units and format
Enter a number in cm³: cubic centimetres. The form accepts 0 cm³ to 1000000 cm³. Required: the tool does not calculate until every input is valid.
Example
The form opens with 10 cm³ as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
Get it right
Enter zero for a hot runner.
What this means: Melt density
Illustration: Melt densityA cube of material: density Melt density is its mass divided by the volume it fills.massvolumeρExample: 0.95 g/cm³Melt density
What it is
The density of the plastic in the solid moulded state, from the resin data sheet, used to turn shot volume into mass.
Units and format
Enter a number in g/cm³: grams per cubic centimetre (1 g/cm³ = 1000 kg/m³). The form accepts 0.000001 g/cm³ to 3 g/cm³. Required: the tool does not calculate until every input is valid.
Example
The form opens with 0.95 g/cm³ as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
Get it right
This is in grams per cubic centimetre.

Cooling

What this means: Wall thickness
Illustration: Wall thicknessThe cross-section of a plate or wall with a dimension across its thickness, marking Wall thickness.ssection through the materialExample: 2.5 mmWall thickness
What it is
The thickness of the thickest main wall of the part, which takes longest to cool and so sets the cooling time.
Units and format
Enter a number in mm: millimetres. The form accepts 0.000001 mm to 50 mm. Required: the tool does not calculate until every input is valid.
Example
The form opens with 2.5 mm as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
Effect on the result
Cooling time rises with the square of the wall thickness.
Get it right
Use the full wall thickness, not half of it.
What this means: Thermal diffusivity of the plastic
Illustration: Thermal diffusivity of the plasticHeat flowing from a hot side to a cold side through a wall or into a material; Thermal diffusivity of the plastic sets how much heat moves or is stored.hotcoldaExample: 0.09 mm²/sThermal diffusivity of the plastic
What it is
The thermal diffusivity of the plastic, a measure of how fast heat spreads through it, from the resin data sheet or a materials database.
Units and format
Enter a number in mm²/s: mm²/s. The form accepts 0.000001 mm²/s to 1 mm²/s. Required: the tool does not calculate until every input is valid.
Example
The form opens with 0.09 mm²/s as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
Effect on the result
Cooling time is inversely proportional to diffusivity.
Get it right
This is in square millimetres per second, not conductivity.
What this means: Melt temperature
Illustration: Melt temperatureA thermometer whose level rises with Melt temperature; the level follows the value you type.TₘExample: 230 °CMelt temperature
What it is
The temperature of the plastic melt as it is injected, from the resin data sheet or the machine setting.
Units and format
Enter a number in °C: degrees Celsius. The form accepts 0.000001 °C to 450 °C. Required: the tool does not calculate until every input is valid.
Example
The form opens with 230 °C as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
Get it right
It must be higher than the ejection temperature.
What this means: Mould temperature
Illustration: Mould temperatureA thermometer whose level rises with Mould temperature; the level follows the value you type.T_wExample: 40 °CMould temperature
What it is
The temperature of the mould cavity surface during moulding, set by the mould temperature controller.
Units and format
Enter a number in °C: degrees Celsius. The form accepts 0.000001 °C to 200 °C. Required: the tool does not calculate until every input is valid.
Example
The form opens with 40 °C as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
Get it right
It must be lower than the ejection temperature.
What this means: Ejection temperature
Illustration: Ejection temperatureA thermometer whose level rises with Ejection temperature; the level follows the value you type.TₑExample: 90 °CEjection temperature
What it is
The temperature the thickest wall must cool to before the part is rigid enough to eject without distortion, from the resin data sheet.
Units and format
Enter a number in °C: degrees Celsius. The form accepts 0.000001 °C to 300 °C. Required: the tool does not calculate until every input is valid.
Example
The form opens with 90 °C as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
Effect on the result
A lower ejection temperature lengthens the cooling time.
Get it right
It must lie between the mould temperature and the melt temperature.
What this means: Other cycle time (fill, hold, open, eject, clos…
Illustration: Other cycle time (fill, hold, open, eject, close)A timeline from a start mark to an end mark; Other cycle time (fill, hold, open, eject, close) is the time between them.startendtExample: 8 sOther cycle time (fill, hold, open, eject, cl…
What it is
The part of the cycle that is not cooling: injection fill, hold, mould opening, ejection and closing.
Units and format
Enter a number in s: seconds. The form accepts 0 s to 600 s. Required: the tool does not calculate until every input is valid.
Example
The form opens with 8 s as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
Effect on the result
Added directly to the cooling time to give the cycle time.

Machine and costs

What this means: Machine clamp force
Illustration: Machine clamp forceA block with an arrow pushing on it; the arrow is the force Machine clamp force.FExample: 1500 kNMachine clamp force
What it is
The rated clamp force of the moulding machine you plan to use, from its specification plate.
Units and format
Enter a number in kN: kilonewtons (1 kN = 1000 N). The form accepts 0.000001 kN to 100000 kN. Required: the tool does not calculate until every input is valid.
Example
The form opens with 1500 kN as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
Get it right
Machines are often rated in tonnes; this tool uses kilonewtons.
What this means: Machine shot capacity
Illustration: Machine shot capacityA box drawn in three dimensions; the space it encloses is the volume Machine shot capacity.VExample: 300 cm³Machine shot capacity
What it is
The maximum shot volume the machine’s barrel and screw can inject, from the machine specification.
Units and format
Enter a number in cm³: cubic centimetres. The form accepts 0.000001 cm³ to 1000000 cm³. Required: the tool does not calculate until every input is valid.
Example
The form opens with 300 cm³ as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
Get it right
Use the volume figure, not the shot weight in polystyrene that some makers quote.
What this means: Machine rate with operator share
Illustration: Machine rate with operator shareA price tag on one unit of measure; Machine rate with operator share is the cost for each unit (per hour, per kilogram and so on).$cost foreach unitExample: $60/hMachine rate with operator share
What it is
The hourly cost of running the moulding machine including its share of an operator, from your machine hour rate.
Units and format
Enter a number in $/h: money per hour. The form accepts $0/h to $100000/h. Required: the tool does not calculate until every input is valid.
Example
The form opens with $60/h as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
Effect on the result
Machine cost per good part = this rate ÷ good parts per hour.
What this means: Plastic price
Illustration: Plastic priceA price tag on one unit of measure; Plastic price is the cost for each unit (per hour, per kilogram and so on).$cost foreach unitExample: $2.5/kgPlastic price
What it is
The price you pay for each kilogram of the plastic, including colourant if used.
Units and format
Enter a number in $/kg: money per kilogram. The form accepts $0/kg to $10000/kg. Required: the tool does not calculate until every input is valid.
Example
The form opens with $2.5/kg as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
Effect on the result
Plastic cost per part rises in proportion to it.
What this means: Scrap rate
Illustration: Scrap rateA bar of 100 parts with the share marked; Scrap rate is that share out of 100. The bar follows the value you type.0 %100 %Example: 3%Scrap rate
What it is
The share of moulded parts that are rejected, so their machine time and plastic are paid for by the good parts.
Units and format
Enter a number in %: percent: the number is read as a percentage, so type 8 for 8 %. The form accepts 0% to 50%. Required: the tool does not calculate until every input is valid.
Example
The form opens with 3% as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
Get it right
Type the percentage of parts rejected.
What this means: Mould cost
Illustration: Mould costA stack of coins and a note representing the money amount Mould cost.$Example: $40000Mould cost
What it is
The cost of the mould that is charged to this part, including design, manufacture and trial.
Units and format
Enter a number in $: an amount of money; use one currency for every money input. The form accepts $0 or more. Required: the tool does not calculate until every input is valid.
Example
The form opens with $40000 as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
Effect on the result
Divided by the charged life quantity to give the mould cost per part.
What this means: Parts over the mould’s charged life
Illustration: Parts over the mould’s charged lifeA row of identical items being counted; Parts over the mould’s charged life is how many there are.nExample: 200000Parts over the mould’s charged life
What it is
The number of parts over which the mould cost is spread, such as the expected order quantity or the life agreed with the customer.
Units and format
Enter a plain number with no unit. The form accepts 1 or more. Use a whole number. Required: the tool does not calculate until every input is valid.
Example
The form opens with 200000 as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
Effect on the result
More parts give a lower mould cost per part.
What this means: Target cost per part
Illustration: Target cost per partA price tag on one unit of measure; Target cost per part is the cost for each unit (per hour, per kilogram and so on).$cost foreach unitExample: $0.4Target cost per part
What it is
The cost per good part you need to reach, from the customer’s target price or your costing.
Units and format
Enter a number in $: an amount of money; use one currency for every money input. The form accepts $0 to $1000000. Required: the tool does not calculate until every input is valid.
Example
The form opens with $0.4 as a worked example. It is an illustration, not a recommended value: replace it with your own figure.

Method and formulas

  1. Clamp force = projected area × cavity pressure × (1 + margin); shot = cavities × part + runner; cooling time t = s² ÷ (π² a) × ln[4 ÷ π × (T_m − T_w) ÷ (T_e − T_w)]; parts per hour = cavities × 3600 ÷ cycle (as the injection moulding estimate tool).
  2. Machine cost per good part = rate ÷ [parts per hour × (1 − scrap)]; plastic per good part = shot mass ÷ cavities × price ÷ (1 − scrap).
  3. Mould per part = mould cost ÷ life quantity; total against target.
  4. Example: 754.2 parts an hour; each good part costs 0.36159 $ (machine 0.082015, plastic 0.079575, mould 0.2).

Limitations

  • Plate cooling estimate for the thickest wall; ribs and bosses can control the cycle.
  • Runner material assumed not reground.
  • Example values are illustrations. Replace them with values for your actual task.

Typical uses

  • Quote a moulded part
  • Compare cavity numbers
  • Check a mould suits a machine before a trial

Who it is for

  • Moulding estimators
  • Product designers
  • Production managers

What you get

  • Clamp force, shot and barrel use
  • Cooling time, cycle and parts per hour
  • Machine, plastic and mould cost per good part

Interpreting the result

  • More cavities cut the machine cost per part but raise the mould cost and clamp force.

References

  • Machinery’s Handbook, 29th edition (Industrial Press, 2012), printed pp. 584–592, 134–146. Topic reference; no source tables or recommended settings are reproduced.

Learn the Concepts Behind This Tool

These BIZOMAT Library readings explain the method this tool uses, with worked examples.

BIZOMAT tools are screening and decision-support utilities. Verify important financial, engineering, safety, legal or operational decisions using appropriate professional standards and your organisation’s approved data.

Open the Injection Moulded Part Cost (Clamp, Cycle, Machine, Material, Mould) calculator

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