FAQ - INJECTION DEPOT GROUP

Answers to Common Questions

Whether you’re wondering about output, energy use, controls, maintenance or another topic related to all-electric injection molding machines, all electric engineers have a lot of expertise and experience to share. We’ve been at the forefront of this technology since the very beginning. Here are answers to some of the most common questions about all-electric injection molding machines. If you don’t see your question answered here, please don’t hesitate to ask us today

What are the differences between electrics and hydraulics during set up?

The number-one difference we find is that the operator on the hydraulic machine has the tendency to set the ejector positions beyond the mold eject mechanism travel capability. With hydraulics, if the eject plate cannot travel to the set point, the oil ends up being bypassed over a relief valve back into the tank. In comparison, the electric machine motor drive design systems are set to increase the motor torque to achieve the position set point. If the set point is beyond the eject travel capability, then the drive system power will be increased to a point where eventually it will alarm out or mechanical damage can occur. In summary, the electric machine is less forgiving when it comes to setting the positions, but it has higher accuracy and repeatability.
Electric machine positions are set to 0.001” while hydraulic machines are typically only down to 0.01”.
Electric machine responses are faster, so to replicate the process from the hydraulic machine may require additional profile settings.
Most hydraulic machines set the injection pressure in terms of hydraulic pressure. The electric machines, since they have no hydraulic drive trains, measure injection pressure with melt pressure, usually via a load cell. The difference between hydraulic and melt pressures are typically represented by a difference in value of 10:1. Example: 23,000 psi melt pressure is similar to 2,300 hydraulic pressure. This can vary to 8 or 12:1, but 10:1 is a “rule of thumb".

How long can I expect an electric machine to last?

Machines put into service over 20 years ago are still in operation. However, like all electronics, availability of spare parts can start to be an issue as older electronic boards become obsolete and more difficult to support. This is also true of hydraulic machines, since all machines today use some type of micro-processor.
In general, the machines will last as long if not longer than similar-sized hydraulic machines.

What spares should I have on hand?

Normal items such as grease, screw tip assembly, heater bands and thermocouples.

What are the common maintenance needs?

Regular cleaning of the machine and observing for any lubrication issues (lack of).
Cleaning or replacing the air filter for the electrical/drive cabinet.
Replacement of the grease supply.
Listening to the machine for any unusual noise, which might indicate the beginning of a mechanical problem.

Why are the machines cleaner?

The elimination of oil, valves, hoses, etc. requires less housekeeping since leaks are avoided.
Hydraulic systems must have the ability to “breath” when the oil is flowing in and out of their oil reservoirs. This frequently introduces some amount of oil mist through the tank breather into the machine environment, which then adheres to all surfaces

What are the reasons for cycle savings?

Overlapping of operations (ie: clamp and extruder; clamp and injection - pre-injection; eject on fly) is a built-in design capability. This can reduce cycle times over 0.5 seconds.
Since Electric IMM machines have no oil, the ability to quickly ramp up to full speed is easily obtainable in comparison to hydraulic systems, which rely on the electric motor, pumps and valves to ramp up. For example, it is common for a hydraulic system to use +10% of the screw stroke to reach full injection speed while the electric machine can typically achieve this in under 0.05 seconds.
Hydraulic systems are frequently prone to shock in their systems which can cause mechanical failures. Software delays are programmed into the machine to reduce these shocks, which can then add up into longer response and cycle times.
Since the motors are connected directly to the mechanisms of the machines, when the motor is commanded to change speed instantly, the mechanism changes. In comparison, when oil flow is cut off, the mechanical action has inertia, which cannot be stopped without using an “oil braking” system on the opposite side of the hydraulic cylinder piston. Without this, in order to reduce the amount of overshoot caused by the mechanical inertia, the software is tuned so that the velocities are ramped down farther away from the stopping set point. Using the electric machine means that the machine requires less distance to stop and so higher velocity can be held until the last possible moment, resulting in shorter cycles.

Will I have a problem with high pack pressure and times?

Newer electric machine designs and technology today have motors and drives with more power capability than ever before. But while an electric machine being overmatched has become a very infrequent issue (less than 1%), there are still cases where the combination of part design and resin types can cause the injection motor to become overloaded. If there’s some uncertainty about this possibility in a given situation, machinery manufacturers including Milacron frequently have some alternative design combinations to address the issue. If you have a concern, you should share the details up front with your machine manufacturer.

What is the maintenance cost for a typical all-electric machine?

With good maintenance and proper operation, the annual cost has been under $500 per year.

How long do belts last?

Belt technology has advanced over the 30 years of all-electric technology, and today’s belts can be expected to last +10 years. Belt failures are mostly caused by incorrect machine parameter settings that cause excessive stress.

Should you maintain or replace equipment?

Many factors need to be considered, and every customer will have different circumstances in making a decision to either maintain or replace their existing hydraulic machines. These factors can include:

Type of products being produced and the necessary precision.
Type of customer base you’re going after.
What kind of maintenance issues the hydraulic machines are having and the cost associated with keeping them in good working order.
Cost of energy.
Skill level of the maintenance department.
Cost of capital.
Hourly machine rates and cycle time improvement opportunities.
New construction of facility in the evaluation of utility requirements such as power drop sizes and HVAC considerations.

Why are the machines more repeatable?

Hydraulic oil tends to behave differently as temperatures change and also as the oil becomes dirty. Temperature changes result in viscosity and flow variations through the hydraulic system. This is why many machine manufacturers incorporate an oil pre-heat cycle when initially starting the hydraulic pumps to reduce the time necessary to warm the oil to operating temperatures (wasted energy). Also, as the oil temperature migrates into the steel of the valves, pumps, cylinders, etc., it often results in behavior changes from the thermal expansion and tolerance change between components. As oil becomes old, it can begin to break down resulting from heat and moisture. The most common visual change comes from what is known as “varnish” build-up. This brownish build-up can be found on all areas where the oil experiences higher temperatures. Frequently, when removing the spool from the valve body, you can actually see varnish built up on the lands of the spool.
Mechanical drives with servo motion control use absolute encoders with capability to detect as low as 0.01mm positioning. This capability, working in conjunction with tight machine tolerances, enables precise and repeatable machine operation.

How much energy can I save?

There are several answers to this, depending on the age and type of technology used in the machine being replaced and the molding cycle conditions. Ultimately, the best way to analyze this is to perform an energy audit.
When replacing most machines that were produced using older technology, the energy savings could be over 400%. Early machines used hydraulic and electric motor designs, which are not energy efficient. Machines with inefficient electric motors and fixed (single/multi) pumping systems are primarily those in this category.
Newer technology that became available in the 1980s could still see savings in the 200% range. Machines using variable flow/pressure pumping systems with and without separate fixed-pump systems would fall into this category.
Today’s technology using electric servo motor controlled pump systems may see 25-50% reductions. Systems using variable frequency motors coupled to fixed pumps also provide savings, but may see performance issues.
In cases of long cycle times where a normal electric/pump system is operating without any work produced, you will see greater savings than you would in a scenario in which the motor/pump system is constantly at work, as would be found in a fast cycle resulting in a high resin output (Lbs/hr).

15 Things to Know About Servo-Driven Injection Machines
Drive technology for injection molding machines has been continuously evolving, and servo motors have become widely used in a variety of roles. Here’s what molders need to know about today’s servo drives in terms of cost, performance, maintenance, and training.

In order to get a better understanding of today’s available machine technologies, it is important to use a common language for the different drive technologies for modern injection molding machines. Varied uses of servo motors is one of the complicating factors. This article will discuss and explain 15 of the most common terms and concepts involving machine drive technology, regarding cost, performance, maintenance, and employee training.
1. Full-electric IMM
Following the standards of the Plastics Industry Association (formerly SPI), a full-electric injection molding machine is one that has at least its three main axes (clamp movement, injection, and metering/plasticating) driven by servo motors. The remaining three axes (nozzle touch, ejection, and mold-height adjustment) can still be driven by hydraulics. The most efficient machines are capable of
using a kinetic-energy recovery system (KERS). This patented process makes use of the servo motors as generators and can collect all deceleration energy from each axis and convert it back into electric energy. The converted energy is then fed back into the machine, usually for heating or control functions.
2. Hybrid IMM
Machines that have one or more of the three main axes driven by hydraulics but do have at least one electric-driven axis are called hybrid machines. One common example of this is a hydraulic machine with servo-driven metering. The metering is the biggest energy draw (besides barrel heating) on any IMM. Therefore, it is a smart decision to at least use a servo-electric drive for the metering. Hybrid machines are not machines with a servo-driven pump, because all movements on the latter are still driven by hydraulics.
3. Servo (driven) hydraulic IMM
A servo-driven hydraulic (or servo-hydraulic) machine is a full- hydraulic IMM with a servo motor to drive the hydraulic pump. These machines often have a fixed-displacement-pump, but could also have variable-displacement-pumps (often DFEE or DFEC) with a swash-plate.
4. Standard hydraulic IMM with variable-displacement pump
These machines usually have a constant-speed motor and a variable-displacement pump with a swash plate that can be adjusted by the control to regulate the oil-volume flow of the pump adjusting to the current demand of the hydraulic system. If the machine does not move at all, the pumps will still idle and waste energy.
5. Energy efficiency
The European plastics industry has developed a system to classify energy efficiency of IMMs. The Euromap 60.1 standard categorizes machines in certain categories and has developed certain standards to compare the energy efficiency of similar machines from different suppliers or executions (full-electric, hybrid, and so on).
Servo-driven pump (or servo-pump) machines unsurprisingly show much better energy efficiency than machines with a constant-speed motor and a variable-displacement pump. So what is a servo pump and what does it do? The servo motor on the servo-driven pump machine only operates if the hydraulics demand oil flow. During the time when no axis is operating, there is no pump movement, and therefore no energy consumption by the pump. Of course, the amount of energy savings depends highly on the process point of each specific application. A fast-cycling pack- aging application will have a lower percentage energy savings than an application with a long cooling time when the constant-speed motor would be idling for seconds or minutes.
Full-electric machines, where the electric energy is directly converted into kinetic energy, have the best energy efficiency, since there is no transformation from electric energy to hydraulic pressure and then to kinetic energy.
A very rough classification would be:
• Hydraulic machine with constant speed motor: 100% energy consumption;
• Hybrid machine with only metering fully electric: 75% to 80% energy consumption;
• Servo-driven pump machines: 65% to 70% energy consumption;
• Full-electric machines: 45% to 60% energy consumption.
6. Repeatability of electric vs. hydraulic drives
On full-electric machines, the repeatability of a servo-driven axis is at least 10 times higher than hydraulic-driven axis. An active servo-driven axis has almost no delays, while delays with hydraulics are inevitable. Acceleration, and specifically deceleration, are also more accurate with a servo drive than on hydraulic-driven machines. Full-electric machines also allow for instant production stability, as there is no necessary oil warm-up, and start-up is faster after production has timed out. This is an advantage for full-electric machines, not for servo-driven pump machines.
7. Noise level
Full-electric and servo-driven pump machines usually have a noise level that is far lower than a standard hydraulic machine. Modern full-electric and servo-driven pump machines should have a noise level around 68 dbA.
8. Speed and/or acceleration
Comparison of servo versus hydraulic speed and/or acceleration is matter of lively debate in the industry. Full-electric drives have great acceleration—much better than a pump ramp-up in a hydraulic system, which suffers due to compressibility of the oil and the hydraulic hoses and lines that expand. The counterpoint cited by some suppliers is that a perfectly designed hydraulic system with accumulators and strategically placed valves can be even more spontaneous and agile than the servo-driven machines.
9. Parallel movements
Full-electric IMMs generally use a separate servo drive for each axis. This makes those machines very flexible since it allows all axes to be used with parallel movements, which makes sense when it is necessary to meter during mold opening and ejection, inject during mold closing, eject during mold opening, and so on. Servo-driven pump machines and standard hydraulic machines do not necessarily have that advantage. Most suppliers offer a second or even a third pump and hydraulic accumulators as an option.
10. Hydraulic Design
A standard hydraulic machine creates a lot of wasted heat through shearing and friction of the oil during idling, which is mainly related to the design and work principle of a variable-displacement pump and the constant-speed motor. The servo-driven pump machine does create a smaller amount of heat in the hydraulic system. In fact, some manufacturers run a special oil-heating sequence to keep the oil at operating temperature during production, depending on the process point, the machine’s operating environment, and the process sequence of the specific product/process.
11. Machine cost
A full-electric machine is was always more expensive than a hydraulic machine ( But in the Year 2020 were most OEMs are now on Multiple generations on average you would see only 10% or less difference in price versus Servo- driven pump machines) due to the necessary number of electric drives and motors and gears (ballscrew or gearbox or rack and pinion) for the former. However, in many cases it is easy to calculate an ROI using energy savings and improved utilization (faster cycle due to parallel movements and greater uptime due to less maintenance), as well as energy rebates that some states and energy companies offer. Servo- driven pump machines can (with some suppliers) still be slightly more expensive than standard hydraulic machines, but since servo-driven pump technology is being pushed hard by the industry as a whole, there is more and more competition even among component suppliers, which allows the difference in price (where it still exists) to be narrowed down to a minimum.
12. Service of pumps, servo motors
In cases where a hydraulic pump must be changed, fixed-displacement pumps that need no calibration are faster and easier to change than variable-displacement pumps. Fixed-displacement pumps also are usually much less expensive than variable-displacement pumps. Even though a servo motor may be more expensive than a constant-speed motor, it is more likely over time that a molder will need to exchange or maintain the pump.
Of course, full-electric machines either never, or only rarely, need to deal with pump maintenance at all. The well-known Rotex coupling (spider-gear) does not exist on servo-driven pump machines and full-electric machines, and therefore does not need to be exchanged. This is some- thing that the maintenance crew in every molding shop knows all too well.
In general, modern machines offer much better analysis features than their predecessors. Servo drives can usually be analyzed with ease through embedded oscilloscope functions, which some suppliers offer as a standard addition to their modern machine controls. This, together with the possibility to access the machine through web service, creates a powerful tool to service and troubleshoot machines remotely. Constant-speed pump motors usually do not offer that possibility. Even alarm messages on the control of a servo-driven machine are more precise since the monitoring of servo drives is so much more detailed.
13. Oil quality & maintenance
On servo-driven pump machines, the oil does not get stressed very much and the oil quality therefore degrades slower than on a standard hydraulic machine. Of course, this always depends on the process and how much the oil is moved and sheared; but as a general rule of thumb, the hydraulic machine puts more strain on the oil. Full-electric machines might not have to deal with oil at all.
14. Complexity of machines
Hydraulic machines in general, whether they are servo-driven or not, have electronics, mechanical parts, and hydraulics. Full-electric machines might only have electronics and mechanical parts, which reduces the complexity. A good electrician can work on the machine without needing to understand hydraulics.
15. Training of maintenance staff
One point that is easily forgotten is the training of the molder’s own maintenance staff. For standard hydraulic machines, it is recommended that the hydraulics be calibrated once a year. Better training of staff can lead to better calibration and spotting of problems. No pump-related calibration is needed on electric machines, so the necessary training of the staff is less complex.
These 15 critical points of interest and comparison about partially and fully servo-driven and hydraulic machines are important for every molder to know. With these points in mind, suppliers can help work with molders to find the best machine for their desired process.

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