Cycle time is the one specification that compounds. A machine that runs a second faster does not save you a second. It saves you a second on every shot, of every hour, of every shift, for the life of the machine.
Which makes it worth understanding where the seconds actually go, and which of them you can do anything about.
Anatomy of a cycle
A molding cycle is a sequence, and each stage has a different character.
Mold close. Mechanical movement. Fast, and largely a function of the machine’s clamp speed.
Injection. Filling the cavity. Usually short. Governed by injection speed, shot size, and how hard the part is to fill.
Hold and pack. Maintaining pressure while the material begins to solidify, compensating for shrinkage. Short, but not optional; cut it and you get sink marks and dimensional variation.
Cooling. The long one. On most parts this is the largest single block of the cycle, and it is governed by physics rather than by the machine: cooling time scales with the square of wall thickness. Double the wall, and you have roughly quadrupled the cooling requirement.
Charging. The screw rotates and retracts, preparing the next shot. This runs concurrently with cooling on a well-set machine, which is precisely why screw recovery rate matters.
Mold open and ejection. Mechanical again, and a function of clamp speed and stroke.
Where the machine can and cannot help
Here is the honest division, and it matters for anyone hoping a new machine will fix a slow cycle.
The machine cannot shorten cooling time. That is set by your part’s wall thickness, your resin, and your mold’s cooling design. No press will change the thermodynamics. If cooling dominates your cycle, the answer lies in the mold and the part design, not in the machine specification.
The machine absolutely can shorten everything else. Clamp movements, injection response, hold precision, and screw recovery are all machine functions, and this is where a faster, better-controlled press earns its money.
What that looks like in practice
We ran a controlled comparison on this, and the numbers are worth looking at because they show exactly where the time comes from.
The test part was a PP snack box: 21 g, 0.43 mm wall thickness, two cavities, on a 250-ton machine. We ran the same part, with the same settings and the same displacement, on three different hydraulic systems: a fixed displacement pump, a variable displacement pump, and our S8 servo system.
| Stage (seconds) | Fixed displacement | Variable displacement | S8 servo |
| Close mold | 1.8 | 1.8 | 1.6 |
| Injection | 1.5 | 1.2 | 1.0 |
| Hold pressure | 0.5 | 0.4 | 0.2 |
| Charging | 2.2 | 2.2 | 1.8 |
| Open mold | 1.4 | 1.4 | 1.4 |
| Total cycle | 7.4 | 7.0 | 6.0 |
Read that table carefully, because it makes the point better than any argument could.
Mold open time did not change at all. 1.4 seconds on all three machines. That is a mechanical movement, and the servo system offers no advantage there. We could have quietly left that row out. It is more useful left in, because it tells you what a servo drive does and does not do.
Everything responsive got faster. Injection dropped from 1.5 to 1.0 seconds. Hold pressure dropped from 0.5 to 0.2. Charging dropped from 2.2 to 1.8. These are the stages where the drive’s ability to deliver exactly the required power, immediately, actually changes the outcome.
Total cycle: 7.4 seconds down to 6.0.
What 1.4 seconds is worth
On its own, 1.4 seconds sounds like nothing. Compounded, it is the whole argument.
Over the same test period, the fixed displacement machine produced 973 shots. The S8 servo produced 1,200. Same part, same mold, same settings. That is roughly a 23 percent increase in output from the same tonnage of machine, occupying the same floor space, run by the same operator.
And the energy went the other way. Power consumption per hour fell from 12.3 kW to 8.8 kW. Annualised, on 18 hours a day, 25 days a month, 300 days a year, that is 66,420 kW against 47,520 kW: a saving of nearly 19,000 kW a year, on one machine. The overall energy saving measured 45.5 percent against the fixed displacement system.
More parts, less power. That is not a marketing claim; it is what the meter said.
The honest caveat
That test was a thin-walled PP part with a 0.43 mm wall, which cools very quickly. On a part like that, the machine-controlled stages are a large proportion of the cycle, and the servo advantage shows up dramatically.
Mold a thick-walled bucket and the picture changes. Cooling will dominate the cycle, the machine-controlled stages become a smaller fraction of the total, and the percentage cycle improvement will be smaller. The energy saving still applies, because that comes from the drive rather than from the cycle. But the throughput gain will be less dramatic.
Anyone who tells you a servo machine delivers the same percentage cycle reduction across every part is not being straight with you. The gain depends on how much of your cycle is machine and how much is physics.
Find out what it does to your cycle
The only way to know what a servo drive is worth on your part is to look at your cycle and see where the seconds currently sit. If cooling is eighty percent of it, a faster machine will help you less than a better-cooled mold. If your cycle is dominated by injection, hold, and recovery, the gain could be substantial.
Send us your part, your resin, your current cycle, and your wall thickness through the application worksheet. We will tell you honestly which camp you are in.
See the machines running
Our YouTube channel carries machine demonstrations across the S8 and S9 ranges, which is a reasonable way to see how these machines behave before you get into specifications.
After the sale
Spare parts for LOG machines are available through Virtus Equipment Direct, our online store. Our field service engineers are certification-trained, and we offer operator training and processing assistance, including mold tests and help with difficult engineering resins, because a correctly specified machine still has to be run correctly.
Frequently asked questions
What actually determines injection molding cycle time?
A cycle is mold close, injection, hold and pack, cooling, charging, and mold open plus ejection. Cooling is usually the largest single block, and it scales with the square of wall thickness, so doubling the wall roughly quadruples the cooling requirement. The remaining stages are machine-controlled.
Can a faster machine shorten my cycle time?
It can shorten the machine-controlled stages: clamp movements, injection, hold precision, and screw recovery. It cannot shorten cooling, which is governed by your part’s wall thickness, your resin, and your mold’s cooling design. If cooling dominates your cycle, the answer is in the mold, not the press.
How much cycle time does the S8 servo system actually save?
In our own controlled test on a 21 g PP snack box with a 0.43 mm wall on a 250-ton machine, total cycle fell from 7.4 seconds on a fixed displacement system to 6.0 seconds on the S8 servo. Injection dropped from 1.5 to 1.0 seconds, hold from 0.5 to 0.2, and charging from 2.2 to 1.8. Mold open time was unchanged at 1.4 seconds, because that is a mechanical movement the drive cannot improve.
Will I see the same gain on a thick-walled part?
Probably not, and it is worth being straight about that. The test part was thin-walled and cooled quickly, so machine-controlled stages were a large share of the cycle. On a thick-walled part, cooling dominates and the percentage cycle improvement will be smaller. The energy saving still applies, because that comes from the drive rather than the cycle.
Terms worth knowing
Cycle time. The total time to produce one shot, from mold close to mold close. It compounds across every shot for the life of the machine.
Cooling time. Usually the largest block of the cycle. It scales with the square of wall thickness and is governed by part design, resin, and mold cooling rather than by the machine.
Charging. Screw rotation and retraction to prepare the next shot. On a well-set machine this runs concurrently with cooling, which is why screw recovery rate matters.
Hold and pack. Maintaining pressure as material solidifies, compensating for shrinkage. Cutting it short produces sink marks and dimensional variation.
Fixed displacement pump. A conventional hydraulic pump that runs at constant output regardless of demand, throttling away the excess. It is the baseline against which servo energy savings are measured.
