Energy costs can exceed material costs on thin-margin parts. The injection molding machine consumes most of it, but the auxiliaries, cooling, and facility together account for 30 to 50 percent of the total. Understanding where energy actually goes reveals opportunities that energy bills alone obscure.
Injection molding operations that systematically pursue energy efficiency gain competitive advantage through lower operating costs. Energy savings compound over thousands of operating hours annually, accumulating into significant cost reduction over equipment lifecycles. Environmental benefits from reduced energy consumption provide additional value as customers and regulators increasingly emphasize carbon footprint.
Where Energy Goes
Understanding energy distribution identifies the highest-impact improvement opportunities.
Machine drives consume 50 to 70 percent of total machine energy in conventional hydraulic presses. The hydraulic pump runs continuously, maintaining system pressure whether or not the machine is cycling. Clamp movement, injection, and screw recovery all draw from this hydraulic system. Machine drive efficiency varies dramatically by technology: all-electric machines eliminate this continuous hydraulic load entirely.
Heating accounts for 10 to 20 percent of machine energy. Barrel heaters maintain melt temperature. Hot runner systems (when present) require additional heating. Heat loss from uninsulated barrels and manifolds wastes energy continuously. Heating energy requirements depend on material type, throughput rate, and equipment condition.
Cooling represents 10 to 15 percent of facility energy in a typical injection molding operation. Mold cooling removes the heat added during melting and processing. Process cooling maintains hydraulic oil and other system temperatures. Facility cooling addresses heat rejection to the environment. Cooling is often the largest single auxiliary energy consumer.
Auxiliaries include material handling equipment (dryers, loaders, conveyors), robots, and peripheral equipment. Each auxiliary has its own energy profile. Desiccant dryers can be significant energy consumers; a large central drying system may consume more energy than a small molding machine.
Facility loads encompass lighting, HVAC, compressed air, and general building operations. These loads are often overlooked in machine-focused efficiency efforts but contribute meaningfully to total energy consumption.
| Energy Category | Typical Share | Key Variables |
|---|---|---|
| Machine drives | 50-70% | Machine type, utilization, cycle profile |
| Barrel heating | 10-20% | Material, throughput, insulation |
| Mold cooling | 5-10% | Part size, cycle time, water temperature |
| Process cooling | 5-10% | Machine type, ambient conditions |
| Auxiliaries | 5-15% | Dryer type, material handling scope |
| Facility | 5-15% | Building efficiency, climate |
Machine Efficiency
Machine selection and operation determine the largest energy consumption component.
Hydraulic versus servo-hydraulic versus all-electric represents the fundamental efficiency choice. Conventional hydraulic machines run pumps continuously at fixed speed, consuming energy whether working or idling. Servo-hydraulic machines vary pump speed to match demand, reducing energy consumption by 30 to 50 percent. All-electric machines use servo motors directly for all movements, achieving 50 to 70 percent energy reduction compared to conventional hydraulic.
Drive efficiency improvements offer retrofit opportunities for existing machines. Variable frequency drives on hydraulic pumps reduce energy consumption on older machines. Servo retrofit packages convert conventional hydraulic machines to servo-hydraulic operation. These upgrades typically pay back within two to four years through energy savings.
Barrel insulation reduces heat loss from the plasticizing unit. Uninsulated barrels lose heat continuously to the surrounding air, requiring additional heater energy to maintain temperature. Insulation blankets can reduce heating energy by 20 to 40 percent while also improving temperature stability and workplace safety.
Proper machine sizing prevents energy waste from oversized equipment. A 500-ton machine running a job that could run on 200 tons wastes energy on every cycle. Matching machine size to job requirements optimizes energy consumption, but requires adequate machine capacity mix to enable proper sizing.
Process Optimization
Process adjustments reduce energy consumption within any machine type.
Cycle time reduction directly reduces energy per part. Shorter cycles mean less time running hydraulic pumps, maintaining temperatures, and operating auxiliaries. Cooling time optimization often offers the largest cycle time reduction opportunity without sacrificing part quality.
Temperature optimization questions whether current setpoints are appropriate. Higher temperatures require more heating energy and longer cooling time. Many operations run higher temperatures than necessary, either from historical settings or excessive safety margin. Methodical temperature optimization can reduce both heating energy and cycle time.
Idle time management addresses energy consumption when machines aren’t producing parts. Machines waiting for operators, material, or downstream operations consume energy without output. Automatic setback to lower energy state during extended waits reduces unproductive consumption. Scheduling to minimize machine idle time improves both energy efficiency and productivity.
Process monitoring identifies energy waste patterns. Real-time energy monitoring reveals consumption patterns invisible in monthly utility bills. Machines consuming abnormal energy may indicate maintenance needs, process problems, or optimization opportunities.
Cooling System Efficiency
Cooling systems offer significant efficiency improvement opportunities in many facilities.
Free cooling opportunities exist when ambient temperatures are low enough to reject heat without mechanical refrigeration. Cooling towers, dry coolers, or direct water economizers can provide process cooling without chiller operation during cool weather. Facilities in temperate climates may achieve free cooling for half the year or more.
Chiller efficiency varies widely by equipment age, type, and operating condition. Modern high-efficiency chillers achieve significantly better performance than older equipment. Proper chiller sizing, maintenance, and operating parameters maximize efficiency. Multiple smaller chillers may offer better part-load efficiency than single large units.
Pump optimization reduces energy consumed moving cooling water through the system. Variable frequency drives match pump speed to actual demand. Pipe sizing and layout affect pumping energy requirements. Excessive flow rates waste pumping energy without improving cooling performance.
Temperature optimization questions whether cooling water temperatures are appropriate. Colder water requires more refrigeration energy to produce. Many applications achieve adequate cooling with warmer water than currently supplied. Raising chilled water temperature from 7°C to 12°C can reduce chiller energy consumption by 15 to 20 percent.
Drying and Material Handling
Material preparation consumes energy before material reaches the molding machine.
Desiccant dryer efficiency varies significantly by design and operation. Desiccant dryers regenerate moisture-absorbing material using heat; regeneration energy often exceeds drying energy. Low-energy dryer designs minimize regeneration losses. Right-sizing dryers to actual throughput prevents oversized equipment from wasting energy.
Drying temperature optimization ensures materials dry adequately without wasting energy. Higher temperatures dry faster but consume more energy. Lower temperatures may be adequate for some materials or throughput rates. Process validation confirms that optimized drying temperatures still achieve required moisture levels.
Vacuum conveying optimization addresses material transport energy. Conveying systems sized for peak capacity may waste energy at normal throughput. Variable speed blowers match conveying energy to actual demand. Minimizing conveying distances and optimizing line sizes reduce pressure drop and energy consumption.
Centralized versus machine-side equipment decisions affect energy consumption. Centralized drying and conveying systems offer efficiency advantages at scale but may waste energy when partially loaded. Machine-side equipment provides better load matching but may sacrifice some efficiency.
Facility Considerations
Facility energy consumption accumulates from many small sources.
Lighting in injection molding facilities runs many hours annually. LED lighting upgrades reduce consumption by 50 to 70 percent compared to older fluorescent or HID fixtures. Occupancy sensors and daylight harvesting further reduce consumption. Lighting upgrades typically pay back within one to three years.
HVAC energy depends on building envelope, climate, and internal heat loads. Injection molding machines and auxiliaries generate substantial heat that HVAC systems must manage. Heat recovery systems can capture this heat for building heating or preheating process water. Facility temperature setpoints significantly affect HVAC energy consumption.
Compressed air leaks waste energy continuously in most facilities. Leaks typically represent 20 to 30 percent of compressed air system output in facilities without active leak management programs. Regular leak detection and repair pays back quickly through reduced compressor energy.
Power factor correction reduces utility demand charges without reducing energy consumption. Poor power factor from motor loads increases apparent power draw and associated demand charges. Capacitor banks correct power factor and reduce utility costs.
Measurement and Management
Systematic measurement enables targeted improvement.
Energy monitoring systems provide visibility into consumption patterns. Machine-level monitoring identifies high-consuming equipment and abnormal operation. Process-level monitoring links energy consumption to production output. Facility-level monitoring tracks total consumption and demand profiles.
Key metrics quantify efficiency and enable benchmarking. Energy per kilogram processed (kWh/kg) normalizes for production volume. Specific energy consumption by material type accounts for processing differences. Machine-level metrics identify equipment for improvement focus.
Continuous improvement process turns data into action. Regular review of energy data identifies problems and opportunities. Improvement projects address identified opportunities. Verification confirms that improvements deliver expected savings. Ongoing monitoring ensures sustained performance.
| Metric | Calculation | Typical Range |
|---|---|---|
| Specific energy consumption | kWh ÷ kg processed | 0.5-3.0 kWh/kg |
| Machine efficiency | Output ÷ rated capacity | 40-80% |
| Cooling efficiency | Cooling delivered ÷ energy input | COP 3-6 |
| Overall facility efficiency | Production output ÷ total energy | Varies by product mix |
Energy efficiency improvements compound over time. Addressing multiple areas together creates significant reduction in total energy consumption and operating cost. A systematic approach that measures consumption, identifies opportunities, implements improvements, and verifies results delivers ongoing benefit. The investment in efficiency improvement typically pays back through reduced energy costs while simultaneously reducing environmental impact.
Sources
- Plastics Technology. “Energy Efficiency in Injection Molding.” https://www.ptonline.com/
- EUROMAP. “Energy Efficiency Recommendations for Injection Molding Machines.”
- U.S. Department of Energy. “Energy Efficiency in Plastics Processing.”
- RJG Inc. “Scientific Molding and Energy Consumption.”
- ENGEL. “Energy Efficiency in Injection Molding.” https://www.engelglobal.com/
- Plastics Industry Association. “Energy Management Guidelines.”