Electric drives play an important role in modern injection molding machines because they control the movement, speed, torque, and position of different machine components. Injection molding itself involves several coordinated operations, including mold closing, plasticizing, injection, pressure holding, cooling, mold opening, and ejection. Each movement needs to occur at the appropriate speed and position for the molding cycle to work consistently. An electric drive typically combines an electric motor, drive electronics, feedback devices, and a machine control system. In an all-electric injection molding machine, servo motors can directly operate major machine axes. In servo-hydraulic or hybrid equipment, electric motors may work with hydraulic pumps or alongside hydraulic systems. The choice between these configurations depends on the application rather than on one technology being suitable for every situation. Machine size, required clamping force, cycle time, product requirements, energy consumption, precision, maintenance, and automation all need to be considered. This guide explains the main types of electric drives used with injection molding machines, their functions, applications, benefits, limitations, current developments, and practical selection considerations.
What Is an Electric Drive?
An electric drive is a system used to control an electric motor and convert electrical energy into controlled mechanical movement. The drive receives instructions from the machine controller and regulates the motor according to the required speed, torque, acceleration, and position.
A typical servo-driven system may include:
- Servo motor
- Servo drive or amplifier
- Encoder or position sensor
- Machine controller
- Power supply
- Mechanical transmission components
- Communication interfaces
In injection molding, these systems can control individual machine movements such as injection, screw rotation, mold clamping, and ejection.
For example, Sumitomo (SHI) Demag's all-electric machines use direct-drive technology for injection molding applications, while its product range also includes hybrid and servo-hydraulic machines.
How Electric Drives Work in Injection Molding
The basic operation can be understood as a closed control loop.
1. The Controller Sends a Command
The machine controller determines what movement is required based on the programmed molding cycle.
2. The Servo Drive Processes the Command
The servo drive converts the controller's command into electrical signals for the motor.
3. The Motor Produces Movement
The servo motor generates torque and rotates at the required speed. Mechanical components transfer this movement to the relevant machine axis.
4. Feedback Is Measured
An encoder or another feedback device monitors the motor's actual position and speed.
5. The Drive Corrects the Movement
If the actual movement differs from the requested movement, the control system can adjust motor output.
This process happens continuously during operation. The result is controlled movement that can be useful for applications requiring repeatability and precise positioning.
Main Types of Electric Drive Systems
Electric drives can be used in several injection molding machine configurations.
All-Electric Drive Systems
All-electric injection molding machines use electric motors and servo drives for their primary machine movements. Different motors may be assigned to different functions.
Typical electrically driven functions include:
- Injection
- Screw rotation or plasticizing
- Mold clamping
- Ejection
- Mold adjustment
Sumitomo's all-electric technology, for example, uses direct-drive systems and servo motors for injection molding movements. Its published product range includes all-electric machines from small to large clamping-force classes.
Servo-Hydraulic Drive Systems
A servo-hydraulic machine combines an electric servo motor with a hydraulic pump. Instead of operating a hydraulic pump continuously at a fixed speed, the servo system can adjust motor speed according to hydraulic demand.
This arrangement retains hydraulic power while introducing variable-speed electric control.
Research published in the Journal of Cleaner Production compared several electro-hydraulic power-unit configurations and found that variable-speed and servo-driven systems can reduce energy consumption under certain operating conditions compared with a fixed-displacement pump driven by a conventional asynchronous motor.
Hybrid Drive Systems
Hybrid machines combine electric and hydraulic technologies. Different functions can use different drive arrangements depending on the machine design.
For example, a hybrid machine might use servo-electric movement for the clamping system while using hydraulic technology for injection.
ARBURG describes its hybrid machines as combining servo-electric clamping units with hydraulic injection systems, allowing different movement axes to operate independently.
Direct-Drive Systems
In a direct-drive arrangement, the motor is connected more directly to the driven mechanism. This can reduce the number of intermediate transmission components.
Sumitomo describes its direct-drive injection system as using a low-inertia servo motor and direct transmission of movement between the motor and actuator.
Comparison of Electric Drive Configurations
| Configuration | Main Technology | Typical Characteristics | Maintenance Considerations |
|---|---|---|---|
| All-Electric | Servo motors and drives | Precise control of multiple axes | Focus on motors, drives, sensors and electronics |
| Servo-Hydraulic | Servo motor plus hydraulic pump | Variable-speed hydraulic operation | Electrical and hydraulic maintenance |
| Hybrid | Electric and hydraulic systems | Different technologies for different functions | Both systems require attention |
| Direct Drive | Motor connected closely to mechanism | Reduced transmission components | Motor, feedback and mechanical components |
This table provides a general comparison. Actual machine architecture differs between manufacturers and models.
Functions of Electric Drives
Electric drives can perform several important functions during the molding cycle.
Injection Control
The injection drive moves the screw forward to push molten plastic into the mold. Control of speed, acceleration, position, and pressure-related parameters can affect filling behavior.
Plasticizing
The drive rotates the screw while plastic pellets or other feedstock are melted and prepared for the next injection cycle.
Mold Clamping
Electric drives can control mold opening and closing movements and, depending on the machine design, contribute to precise clamping operation.
Ejection
After the mold opens, an electric drive can operate the ejector mechanism to remove the molded part.
Mold Adjustment
Some machines use electric drives to adjust mold height or other mechanical settings.
Coordinated Motion
Multiple servo axes can operate according to coordinated commands. This can help manufacturers manage complex molding cycles and automate certain movements.
Applications of Electric Drives
Electric-drive technology is used in many injection molding applications.
Precision Components
Electric drives can provide controlled movement for components where dimensional consistency is important.
Medical Products
Injection molding for medical components may require repeatable processes and controlled machine operation. Electric machines are available for such applications, although suitability depends on the complete machine, mold, material, and production environment.
Electronics
Small plastic housings, connectors, switches, and other components can require accurate injection and repeatable movement.
Packaging
Packaging applications can involve short cycles and high production volumes. Machine selection therefore involves both motion requirements and cycle-time considerations.
Automotive Components
Larger molded components can require substantial clamping force and injection capability. Both electric and hybrid technologies are available for different automotive molding requirements.
Consumer Products
Household products, closures, containers, and other plastic components can be produced using electric, hybrid, or hydraulic injection molding machines depending on their requirements.
Benefits of Electric Drives
Precise Motion Control
Servo drives can control motor speed, torque, and position through feedback systems.
Repeatable Operation
Closed-loop control allows the system to compare requested and actual movement, which can support repeatable machine cycles.
Energy Management
Electric drives can adjust power delivery according to machine demand. Research on electro-hydraulic injection molding power units has found substantial differences in energy consumption between drive configurations, although results depend on the system and operating conditions.
Reduced Hydraulic Dependence
A fully electric machine does not need a conventional hydraulic power circuit for its primary movements. This can eliminate many hydraulic components and the associated hydraulic-fluid maintenance.
Fast Response
Servo motors can provide rapid changes in speed and torque, which can be useful in applications requiring fast machine movements.
Independent Axis Control
Individual motors can control different axes. This can allow certain machine movements to occur independently or overlap where the machine's design permits it.
Process Monitoring
Modern electric drive systems can provide information about motor position, speed, torque, current, and other parameters that can be used for monitoring and diagnostics.
Limitations of Electric Drives
Electric drives also have limitations.
Higher Electronic Complexity
Servo motors, drives, encoders, controllers, and communication systems require specialized technical knowledge.
Initial Equipment Cost
The initial cost of an all-electric or advanced servo system can differ from a conventional hydraulic machine. The appropriate comparison should consider the complete machine and operating requirements.
Electronic Maintenance
Electronic components require appropriate cooling, clean control cabinets, suitable electrical conditions, and qualified troubleshooting.
Training Requirements
Technicians may need knowledge of servo systems, motor control, encoders, PLCs, machine software, and industrial communication networks.
Application Dependence
An electric drive does not automatically make a machine suitable for every application. Required force, speed, part size, material, mold design, and production volume remain important.
Key Features to Consider
When evaluating electric drives, consider more than the motor's rated power.
Motor Torque
The motor must provide sufficient torque for the required machine movement.
Motor Speed
The available speed range affects injection, plasticizing, clamping, and other operations.
Drive Capacity
The servo drive must be appropriately matched to the motor and application.
Feedback Resolution
Encoders and other feedback devices provide information used for closed-loop control.
Injection Speed
Injection speed can influence filling behavior, particularly in thin-wall or high-speed applications.
Position Accuracy
Accurate position control can be important for repeatable machine movements.
Control Response
The response of the motor and drive affects how quickly the machine reacts to changes in command.
Cooling
Motors and drive electronics generate heat and require appropriate cooling according to manufacturer specifications.
Communication
Modern machines may use industrial communication networks to connect servo drives, controllers, robots, sensors, and production-monitoring systems.
Latest Trends and Innovations
Electric drive technology continues to develop alongside automation and digital manufacturing.
Direct-Drive Technology
Direct-drive systems continue to be developed for injection applications. Sumitomo states that its direct-drive technology has evolved through multiple generations, focusing on motor inertia, acceleration, and responsive screw control.
Regenerative Energy
Some drive systems can recover energy during braking or deceleration and return it to the electrical system. The practical value depends on the machine architecture and operating cycle.
Smart Monitoring
Drive systems increasingly provide operating data such as motor temperature, torque, position, current, and fault information.
Integrated Automation
Injection molding machines can be connected with robots, conveyors, inspection systems, material handling equipment, and production software. Sumitomo, for example, offers automation solutions combining molding machines, robotics, conveyors, and control systems.
Advanced Servo-Hydraulic Systems
Servo-driven hydraulic systems continue to be developed as an alternative to conventional fixed-speed hydraulic power units. Research has demonstrated that variable-speed and servo-driven power units can have significant energy advantages under particular operating conditions.
Higher-Speed Electric Machines
Electric drive systems are also used in high-speed molding equipment. For example, Sumitomo's published SE-HSZ system uses AC servo motors and closed-loop control for injection movement.
Companies and Electric Drive Solutions
Several established manufacturers offer injection molding machines using electric, hybrid, or servo-hydraulic technologies.
FANUC
FANUC offers ROBOSHOT injection molding machines based around CNC and electric-drive technology. Its machines are designed for applications requiring controlled machine movements and automated production.
ARBURG
ARBURG offers electric and hybrid ALLROUNDER machines. Its hybrid systems combine electric and hydraulic technologies, while its electric platforms use servo-electric machine movements.
Sumitomo (SHI) Demag
Sumitomo (SHI) Demag offers all-electric, hybrid, and servo-hydraulic injection molding machines. Its IntElect range uses direct-drive technology, while its Systec range uses servo-motor-driven hydraulic technology.
Sumitomo Heavy Industries
Sumitomo Heavy Industries has developed all-electric injection molding technology using direct-drive systems. Its published material describes direct-drive screw control and multiple generations of servo motor development.
When comparing manufacturers, users should examine published specifications, service support, replacement parts, machine controls, tooling compatibility, application requirements, and local technical support rather than comparing brands only.
How to Choose the Right Electric Drive
The selection process should begin with the molding application.
Selection Checklist
- Identify the required clamping force.
- Determine required injection speed.
- Calculate the required screw torque and plasticizing capacity.
- Establish the target cycle time.
- Determine the required position accuracy.
- Consider production volume and operating hours.
- Review energy-consumption requirements.
- Check available electrical infrastructure.
- Decide whether all-electric, servo-hydraulic, or hybrid operation is appropriate.
- Check mold dimensions and machine working space.
- Review automation requirements.
- Check controller and communication compatibility.
- Evaluate maintenance resources.
- Review spare-parts availability.
- Check manufacturer training and technical support.
- Compare total operating requirements rather than one specification.
For example, a high-precision component may place greater emphasis on position and repeatability, while a high-volume packaging application may place greater emphasis on speed, cycle time, and coordinated automation.
Best Practices for Use and Maintenance
Maintain Proper Cooling
Servo drives and motors generate heat. Keep cooling systems and ventilation arrangements within the manufacturer's specified conditions.
Inspect Cables and Connections
Loose, damaged, or contaminated electrical connections can cause intermittent faults or drive errors.
Monitor Feedback Devices
Encoders and feedback sensors are important to closed-loop operation. Check connectors, cables, and sensor condition according to the maintenance schedule.
Keep Control Cabinets Clean
Dust and contamination can interfere with cooling and electronic components.
Monitor Alarms
Repeated servo alarms should be investigated rather than repeatedly reset.
Check Motor Performance
Unexpected vibration, noise, temperature, or current behavior can indicate a developing issue.
Protect Parameters
Machine parameters should only be changed by appropriately trained personnel. Important settings should be documented before modifications.
Follow Manufacturer Maintenance Schedules
Maintenance intervals vary between machines. Manufacturer instructions should be followed for calibration, lubrication, inspections, component replacement, and software updates.
Frequently Asked Questions
What is an electric drive in an injection molding machine?
An electric drive is a system that controls an electric motor used to perform machine movements. It normally includes a motor, servo drive, feedback device, and connection to the machine controller.
What does a servo motor do in injection molding?
Depending on the machine design, a servo motor can control injection, screw rotation, mold clamping, ejection, or other movements. Its speed, torque, and position can be controlled by the drive system.
What is an all-electric injection molding machine?
An all-electric injection molding machine uses electric motors and drives for its primary machine movements instead of relying on a conventional hydraulic power circuit.
What is a servo-hydraulic injection molding machine?
A servo-hydraulic machine uses an electric servo motor to drive a hydraulic pump. The hydraulic system then provides power to the relevant machine actuators.
Are electric drives energy efficient?
Electric and servo-driven systems can offer energy advantages in suitable applications. However, actual energy consumption depends on the machine architecture, molding cycle, material, mold, auxiliary equipment, and operating conditions.
Do electric drives require maintenance?
Yes. Maintenance can include inspecting motors, cables, encoders, cooling systems, control cabinets, connectors, and drive electronics.
Can electric drives be used for high-speed molding?
Yes. Servo systems can provide rapid acceleration and controlled movement, and electric machines are used in high-speed applications. The appropriate system depends on the complete molding process.
What is direct drive in injection molding?
Direct drive connects the motor more directly to the driven mechanism, reducing some intermediate transmission components. Sumitomo describes direct-drive technology as part of its all-electric injection molding approach.
Conclusion
Electric drives have become an important technology in injection molding because they provide controlled movement, feedback-based positioning, and flexible management of motor speed and torque. They can be used in all-electric machines as well as hybrid and servo-hydraulic configurations.
The main benefits include precise motion control, repeatability, adjustable operation, and the ability to coordinate multiple machine axes. However, electric drives also introduce electronic complexity and require appropriate technical knowledge and maintenance.
When selecting an injection molding machine, the drive system should be considered as part of the complete machine rather than as an isolated component. Motor torque, speed, feedback, injection requirements, clamping force, cycle time, energy use, automation, maintenance, and available technical support all influence the suitability of a particular configuration.
A practical selection process therefore starts with the application. By clearly defining the required molding process and then comparing all-electric, servo-hydraulic, and hybrid options against those requirements, users can better understand the available technologies and choose a drive configuration that fits their production environment.