How Much Energy Does an Injection-Moulding Cell Use While Idle?

Start by separating electrical supplies and defining operating states

The injection-moulding machine, dryer, temperature-control unit, robot and cooling system may have separate electrical supplies. Measuring the incoming supply to one machine cannot account for the electricity used by loads connected elsewhere.

Every historical interval needs an operating state: production, heating, preparation, waiting, mould change or a classified stop. These states must reflect actual operation; the absence of cycles does not mean that every connected load can be switched off.

• An inventory of equipment and electrical supplies included in the measurement.
• Power and energy by supply during an identified period.
• Comparable machine-state records and timestamps across meters and operations.
• Conditions needed to keep materials, moulds or equipment operating safely.
• Production quantity, mass and quality when indicators per part or kilogram are required.

Calculating energy during a waiting period

Energy is the integral of power over time. If a load draws a constant 2 kW for 45 minutes, its consumption is 2 × 45/60 = 1.5 kWh. In practice, equipment power may fluctuate. Use the energy accumulated by the meter or integrate recorded power samples over the interval.

To estimate the monetary value of that energy, use the applicable electricity tariff and contractual cost structure. An estimated cost is not automatically a recoverable saving: the technical need for the load, operating alternatives and process effects must first be established.

Do not add a total supply measurement to the same separately metered loads as if they were independent; this would double-count part of the consumption.

Questions ENERGY: Cell can help investigate

• How much energy did the injection-moulding machine use during production and waiting?
• Which auxiliary equipment remained active after the final cycle?
• What changes between start-up, stabilisation and steady operation?
• Which product reference or period does the energy consumption relate to?
• What additional information becomes available when several cell supplies are measured?

KERN IoP | ENERGY can record selected three-phase and single-phase electrical connections simultaneously. Analysis by operating state and product also requires the operational data and identifiers defined for the application.

Explore KERN IoP | ENERGY: Cell · How to define measurement scope for a manufacturing cell

Make comparisons without assigning effects that were not measured

Always identify the equipment, circuit, product, time interval and operating condition. Total energy may rise because output increased, start-up took longer or another auxiliary was connected. Calculating kWh/kg or kWh/part requires reliable production records for the same interval and a clearly defined denominator.

Measurement provides evidence for proposing and verifying an intervention. Whether consumption can safely be reduced or interrupted requires a separate technical assessment.

Further reading

• Energy management applications
• Documenting energy and time per injection-moulding cycle
• Data required to estimate emissions from electricity use

Editorial basis: earlier KERN IoP publications on manufacturing energy and the machine- and cell-level measurement approach. Numerical values are instructional examples, not verified customer savings.