HEE&HATO Engineering Team | Plastics Processing Equipment | Published: August 4, 2026

A hydraulic injection molding machine generates clamping and injection force through pressurised oil. An all-electric machine uses servo motors and ball screws on each axis. Hydraulics still wins on high tonnage, thick walls and mold-mounted hydraulic functions. Electric wins on fast, small, repeatable shots. Tonnage, resin and repeatability decide it.

Three machine types, not two

Most buying guides set up the question as hydraulic against electric. That framing is a decade out of date and it hides the machine most factories actually end up buying.

Fixed-pump hydraulic. A motor runs a pump at constant speed whenever the machine is powered. Flow that the cycle doesn’t need gets dumped across a relief valve and turns into heat in the oil tank. These machines are still traded heavily on the used market and they are the reference point behind almost every “hydraulics wastes energy” claim you will read.

Servo-hydraulic. The same oil circuit, but the pump is driven by a variable-speed servo motor with closed-loop pressure and flow feedback. During cooling and hold, the motor drops toward idle instead of pumping against a relief valve. The force characteristics stay hydraulic; the idle waste largely goes away.

All-electric. Servo motors and ball screws replace the hydraulic actuators on clamp, injection, plasticising and ejection. Because each axis has its own drive, several motions can run at once instead of waiting for oil to be routed to them.

Compared with the fixed-pump machines that dominate the second-hand market and shape most online comparisons, a servo-hydraulic press behaves very differently on the energy meter while behaving almost identically at the mold. Confusing the two is the single most common reason a buyer over-specifies.

Servo-hydraulic vs all-electric: the comparison that matters

Why hydraulics is still specified

Four situations where oil is the engineering answer rather than the legacy one:

Long hold time at high pressure. Thick-wall parts, gas-assist work and structural components can sit under packing pressure for a long stretch of the cycle. A hydraulic cylinder holds that pressure as a static load. An electric drive holding the same force is a motor producing torque at zero speed, which is a heat problem before it is an energy problem.

Tonnage economics. Force in a hydraulic clamp scales with cylinder area and system pressure, which is cheap to increase. Force in an electric clamp scales with drive, ball screw and toggle sizing, which is not. The higher the tonnage, the wider the capex gap.

The mold already needs oil. Core pulls, hydraulic ejectors and sequential valve gates are hydraulic functions living on the mold, not the machine. Buy an all-electric press for a mold with three core pulls and you buy a hydraulic power pack alongside it, giving back part of the oil-free advantage you paid for.

High-viscosity and abrasive compounds. Filled compounds, high-molecular-weight grades and heat-sensitive resins such as PVC need injection pressure available on demand and tolerant of an aggressive screw profile. PVC in particular is usually run on dedicated corrosion-resistant configurations rather than on a general-purpose electric press.

The trade-off is real and worth stating plainly: even a servo-hydraulic machine carries an oil circuit that needs filtration, scheduled fluid changes, leak checks and a cooling loop. That is recurring labour and consumable cost an all-electric press does not have.

Where all-electric earns the price difference

Repeatability is the honest headline, and the mechanism behind it is worth understanding rather than accepting as a claim. On an electric press, injection speed and screw position are controlled by a servo drive with encoder feedback. On a hydraulic press, the same speed is produced by oil flowing through a valve, and the flow through that valve depends on viscosity, which depends on temperature.

That is why hydraulic machines drift during the first hour of a shift, drift again after a long stop, and settle once the oil reaches its working temperature. Closed-loop injection control on a servo-hydraulic machine compensates for a good deal of this. It does not remove the variable.

The other genuine advantages: parallel axis motion cuts dry cycle time on short-cycle thin-wall work; no oil circuit means cleanroom and medical assembly rooms are simpler to qualify; noise at the machine is lower; and the motors draw power only while an axis moves.

The oil temperature problem nobody puts in the brochure

Common misconception: a servo pump upgrades a hydraulic machine to electric-level repeatability. It does not. The servo pump solves the idle-energy problem. Oil viscosity against temperature is a separate problem with a separate fix: an oil temperature control loop, a defined warm-up procedure before the first accepted shot, and closed-loop injection.

The edge case this creates. Intermittent production is where hydraulic drift does the most damage. A plant running two hours, stopping for a mold change, running three more hours and stopping overnight never lets the oil settle. Scrap concentrates in the first shots after each restart. If that describes your run pattern, an all-electric machine can be the cheaper choice even at low annual volume, because the saving arrives as scrap you don’t make rather than as kilowatt-hours you don’t buy.

A second misconception, about energy numbers. Percentage savings quoted on machine drive systems describe the drive, not the plant. On thick-wall parts with long cooling times, barrel heating and the chiller carry a large share of total consumption, and neither changes when you switch drive technology. Energy figures also only compare if they were measured the same way. EUROMAP 60.1, published by the European Plastics and Rubber Machinery Association, defines how macchina per lo stampaggio a iniezione energy consumption is determined and declared. Ask any supplier which standard their figure was measured under, including this one.

How to run the selection in six steps

• Calculate required clamping tonnage. Projected part area including runners, multiplied by the cavity pressure the resin and wall section demand. Add margin, then choose from available frame sizes rather than the reverse.
• Check shot weight against barrel capacity. Common practice is to size so the shot falls in the middle band of barrel capacity rather than at either extreme, since very small shots against a large barrel raise residence time and degradation risk, and shots near maximum leave nothing for cushion and hold.
• Audit the mold’s own hydraulic requirements. List every core pull, hydraulic ejector and valve gate. Each one erases part of the case for going oil-free.
• Define repeatability as a measured number. “High precision” is not a specification. Part weight variation across 50 consecutive shots, in grams and as a percentage, is. Set the target against your part tolerance, then decide whether your variance budget is dominated by the machine or by mold cooling and material handling — often it is the latter, in which case a more expensive drive buys nothing.
• Describe the run pattern honestly. Continuous three-shift running, or start-stop with frequent changeovers. This determines both energy payback period and the scrap exposure described above.
• Compare energy last, on a same-basis declaration. Ask for the measurement standard, the tested cycle, and the resin. Refuse bare percentages.

Steps 1 through 5 usually settle the decision before step 6 is reached. That ordering is the point.

Worked example: the IJT-SV330 servo-hydraulic configuration

The IJT-SV330 Standard Servo IMM is the reference machine for this comparison, and its configuration illustrates where a servo-hydraulic design puts its engineering effort.

Imported hydraulic pump and control valve. The pump and proportional valve set the resolution of pressure and flow control, which is the ceiling on how tightly injection speed can be held. This is where hydraulic repeatability is won or lost.

FEM-designed platens. Platen deflection under clamp force is what causes flash on multi-cavity molds, particularly in the outer cavities. Finite element design targets the deflection distribution across the platen face rather than raw plate thickness.

Five-point inward-moving double toggle. The toggle multiplies motor and cylinder force mechanically, so the clamp cylinder can be smaller for the same tonnage, which means less oil moved per cycle and less heat generated. The inward-moving geometry distributes the clamp load toward the mold centre and reduces the platen bending that produces cavity-to-cavity weight differences.

Automatic mold height adjustment. Clamp force accuracy degrades when mold height is set by hand across frequent changeovers, and the resulting error is invisible until parts start flashing. Automatic adjustment removes an operator variable, which matters most in plants running short campaigns.

Dual-pillar support and dual-cylinder injection balance. Injection cylinders acting off-centre put a side load on the screw, and that side load shows up as shot-to-shot weight variation and accelerated barrel wear. Balancing across two cylinders addresses the mechanism directly.

Clamping tonnage, shot volume, platen size and stroke on this series are configured per application, so those numbers belong on a project datasheet rather than in an article. The IJT line covers both servo-hydraulic and all-electric systems, and is built for thin-wall packaging, multi-cavity production and hot-runner molds. Machines are designed to meet CE and ISO requirements; for EU-bound equipment, the applicable frameworks are the EU Machinery Directive 2006/42/EC and ISO 12100 on machinery risk assessment, and those documents are the ones to name in a purchase specification.

What a spec sheet won’t tell you about running cost

Capex difference is visible. The rest is not.

Hydraulic machines carry oil purchase and disposal, filter elements, seal and valve replacement, hose inspection, and a cooling load on the plant chiller. Against that, spare parts are commodity items and a competent maintenance technician can usually diagnose and fix a hydraulic fault without a factory visit.

All-electric machines carry no oil cost, but ball screws, belts and servo drives are wear items with finite life, and replacement parts are usually factory-sourced. A drive failure on a machine whose supplier has no regional stock is a long stop.

For reference, the general company figure across projects is 20–40% energy savings with stable output reached within two weeks of commissioning. That is an aggregate claim across installations, not a measured result from any single named project, and it should be treated that way when you build a payback model.

Pricing depends on model, tonnage or output, automation level and final configuration. Share your material, part geometry and capacity targets — our engineers reply within 24–48 hours with a recommended configuration and lead time.

FAQ

Q: Why is hydraulics used in injection moulding at all, if electric is more efficient?

A: Because force in a hydraulic system is cheap to scale and cheap to hold. Pressure acting on a cylinder area produces clamping force without a drivetrain sized to match, and holding that force for a long packing phase costs the machine very little mechanically. Add that most molds carry hydraulic core pulls and ejectors of their own, and oil remains the practical answer for thick-wall, high-tonnage and mold-hydraulic-heavy work.

Q: Is an electrical injection moulding machine always more accurate?

A: More consistent, which is not the same thing. Electric drives remove oil viscosity as a variable, so drift after restarts and during warm-up largely disappears. Absolute part accuracy is still governed by mold quality, cooling uniformity, resin batch consistency and drying. If your scrap traces to any of those, the drive technology will not fix it.

Q: Does all-electric mean there is no hydraulics anywhere in the cell?

A: Only if the mold has no hydraulic functions. Core pulls, hydraulic ejectors and sequential valve gates need a hydraulic supply, so an all-electric press serving such a mold usually gets an auxiliary power pack. Budget for it before comparing quotations.

Q: Can I run PVC on a servo-hydraulic machine?

A: PVC is normally run on a dedicated configuration with corrosion-resistant screw, barrel and flow-path components, because the degradation products attack standard steels. A general-purpose machine of either drive type is the wrong starting point. Specify the PVC configuration rather than adapting a standard one.

Q: At what tonnage does hydraulic become the clearly cheaper choice?

A: There is no universal crossover, because it depends on resin, cycle time, shift pattern and local electricity price. The capex gap widens with tonnage while energy savings scale with running hours, so the crossover moves with your utilisation. Model it with your own numbers over a five-year horizon rather than accepting a supplier’s payback figure.

Q: How much does a hydraulic injection molding machine cost?

A: Pricing is not published, because tonnage, screw configuration, automation level and auxiliaries change the figure substantially. Send your material, part geometry and target output and you will get a configured quotation with lead time; any number quoted before those inputs is a placeholder.

Q: Is “CE certified” something I should look for on the quotation?

A: Look for the technical file and the declaration of conformity, not a phrase. Under the EU Machinery Directive, the manufacturer declares conformity and holds supporting documentation. Ask which harmonised standards were applied and request the declaration in writing before shipment.

Before you sign anything

Two things worth doing that most buyers skip.

First, run a weight study on the candidate machine using your resin and, if possible, a mold close to your part. Fifty consecutive shots, weighed, with the standard deviation calculated. That single number tells you more about whether you need an electric drive than any comparison article, this one included.

Second, ask the supplier for the energy declaration and its measurement basis in the same email as the price. Suppliers who measured properly answer in a sentence.

One topic this article did not cover: hybrid and multi-material machines, including dual-colour and clear dual-colour configurations, where an electric injection unit is paired with a hydraulic clamp. That combination changes the calculation again, and it is the right question to ask if your part needs two materials or an overmoulded seal.