Step-by-Step: Reduce Energy in Injection Molding

Injection molding machines consume power across several stages of each cycle. Motor heat, heater zones, hydraulic pumps, and compressed air all draw energy from the grid. Most energy reductions come from removing waste and shortening cycle time without sacrificing part quality.

This guide walks through a practical sequence to reduce energy costs in injection molding. It assumes you have access to the machine controller, a multimeter or thermal camera, and the ability to run test shots.

Prerequisites: What You Need Before Starting

Before changing parameters, collect a baseline. Record the current cycle time, energy meter readings, and key process settings for each heater zone, injection pressure, hold pressure, and cooling time.

Gather these items:

• Machine controller access and a printed or screen-accessible process sheet
• Energy meter or submeter with per-cycle or per-hour data
• Thermal imaging camera or non-contact thermometer
• Leak detection soap solution for air lines
• Quality inspection tools: calipers, micrometers, and gauges for your part
• A stable material lot, since moisture or color lot changes can mask or hide adjustments

Keep the material and tooling unchanged during this exercise. If the material changes, the baseline no longer applies.

Step 1: Check Compressed Air Lines for Leaks

Compressed air often goes unnoticed in energy audits, but it can be a major drain. Hissing at fittings, loose quick-connects, and leaking regulator seals waste both air and electricity.

Inspect the air supply to the machine, including the dryer, filters, regulators, and any pneumatic ejector or purge lines. Apply soapy water to fittings. Bubbles mean a leak.

Reason: Compressed air is generated by electricity. A small leak can run continuously, even when the machine is idle. Fixing it reduces draw without touching a process parameter.

Tip: Prioritize leaks near the machine and at the main regulator. These often represent the largest single loss.

Step 2: Verify Heater Zone Temperatures Against the Setpoint

Check each heater zone with a thermal camera or non-contact thermometer. Compare the actual barrel temperature to the setpoint on the controller.

Reason: If a heater zone is running hotter than needed, it wastes power and can degrade the material. If it is running cooler, the machine may be over-compensating elsewhere or the cycle may be unstable.

Look for zones that are significantly above or below the setpoint. A zone that is consistently 10 to 15 degrees Celsius above the setpoint may indicate a sensor offset or a controller loop that is too aggressive.

Do not guess. Record the actual temperature, then consult the machine manual for the acceptable deviation range.

Step 3: Review and Tighten the Injection Profile

Open the injection profile in the controller. Look at the ramp, the switch-over pressure, and the switch-over position.

Reason: A long, slow injection ramp wastes motor time. An overly aggressive ramp can increase pressure spikes and motor load. A well-tuned profile fills the cavity in the shortest stable time.

Start with the injection speed. If the cavity fills slowly, the motor runs longer at partial load. If it fills too fast, you may see flash or short shots. Adjust in small steps.

Next, check the switch-over pressure. If it is set higher than needed, the screw pushes against the gate at high pressure for no benefit. Lower it until the part quality holds, then re-run.

Reason: Lowering switch-over pressure reduces the hydraulic load during the fill phase.

Step 4: Optimize Holding Pressure and Hold Time

Holding pressure and hold time are often set higher than necessary. Excess holding pressure wastes motor and hydraulic energy and can cause sink marks or warpage.

Reason: Holding is needed to compensate for shrinkage, not to overfill the cavity. If the part is already filling correctly, high holding pressure is pure waste.

Reduce hold pressure in small increments, such as 5 to 10 percent, and check part dimensions after each change. If the part shows no change in critical dimensions, the lower setting is acceptable.

Then review hold time. A hold time longer than the melt solidifies wastes energy. If the gate is closed and the melt is set, longer holding does nothing useful.

Reason: Shortening hold time reduces the duration the screw is actively pushing against the gate.

Step 5: Check Cooling Time and Mold Temperature

Cooling time is often the longest part of the cycle. If the mold is not at the optimal temperature, the cycle stretches.

Reason: A cooler mold requires more time for the part to solidify. A warmer mold can shorten the cycle but risks warpage.

Check the mold temperature control loop. If the mold is running hot, the part takes longer to cool. If it is running cold, the cycle is unnecessarily long.

Adjust the mold temperature controller to the target setpoint. If the mold is too hot, lower it slightly and re-time the cycle. If it is too cold, raise it slightly.

Reason: A stable, optimal mold temperature shortens the cycle without changing the part.

Step 6: Review Hydraulic Pressure and Flow Settings

Check the main hydraulic pressure and the relief valve settings. If the main pressure is higher than the machine needs, the pump runs at a higher load.

Reason: Excess main pressure increases pump wear and energy use. The pump must overcome the full system pressure even when only a small portion is used.

Reduce the main hydraulic pressure until the machine still fills the cavity at the required speed. Many machines operate well below the maximum rated pressure.

Also check for internal leaks in the hydraulic system. Worn pump seals or valve bypasses can cause the pump to work harder than necessary.

Reason: A hydraulic system with low internal leakage maintains pressure without continuous high-load operation.

Step 7: Monitor and Verify with Energy Data

After each change, record the energy per cycle or per hour. Compare it to the baseline.

Reason: Parameter changes can affect multiple parts of the cycle. Energy data tells you what actually happened.

If the energy per cycle drops but part quality suffers, stop and revert the last change. If both improve, document the new settings and move to the next parameter.

Use a spreadsheet or the machine’s data logger to track results over multiple cycles. A single reading is not enough.

Common Mistakes to Avoid

• Changing multiple parameters at once. This makes it impossible to know what caused a quality problem or an energy change.
• Ignoring the material. Moisture, lot changes, or color differences can shift the process. Always use the same material lot during tuning.
• Over-reducing holding pressure too quickly. Part dimensions can shift by small amounts that only show up in the final assembly.
• Skipping the cooling check. A cool mold can make an injection profile look wrong when the real issue is heat.
• Not checking the air side. A small air leak can offset all the gains from hydraulic and heater changes.

Final Verification Step

Run a full production batch with the new settings. Check part dimensions, appearance, and cycle time against the baseline.

Record the energy per cycle. If the reduction is consistent and the parts pass inspection, lock the settings in the process sheet.

Reason: A stable reduction requires a stable material lot, a stable tool, and a stable process. Verify all three.

If the energy per cycle is lower but the part fails inspection, revert the last change and re-run. If the part passes, the reduction is real.

Quick Reference: Energy-Saving Parameter Adjustments

Parameter	What to Adjust	Expected Effect
Switch-over pressure	Lower if part quality holds	Less hydraulic load during fill
Hold pressure	Lower to the minimum that maintains dimensions	Reduced screw load during hold
Hold time	Shorten to match melt solidification	Less active screw pushing
Mold temperature	Stabilize at the optimal setpoint	Shorter or more stable cycle
Main hydraulic pressure	Reduce to the minimum needed for fill	Lower pump load
Compressed air	Fix leaks and check regulator	Eliminates continuous air waste

FAQ

Q: Can I reduce energy costs in injection molding without changing the part design?

A: Yes. Most reductions come from process settings, maintenance, and removing waste in the cycle. Part design changes are a separate decision and should be evaluated separately.

Q: How do I know if a parameter change is safe?

A: Run a small test batch and inspect critical dimensions and appearance. If the part passes, the change is safe. If it fails, revert the change and try a smaller adjustment.

Q: Is it safe to lower the main hydraulic pressure?

A: It is generally safe to reduce the main pressure to the minimum level that still allows the machine to fill the cavity at the required speed. If the fill slows or the pressure drops during fill, increase it back.

Q: Do I need an energy meter to use this method?

A: It is strongly recommended. Without energy data, you are guessing. A submeter or the machine’s built-in energy monitor gives you the numbers you need.

Q: How often should I re-check these settings?

A: Review them after any major change: new material lot, new tool, new operator, or a shift in ambient temperature. A quarterly maintenance check is also a good practice.