Sixty Years of Injection Molding
Let’s reflect on the good and bad with injection molding machines.
1966. Molding machines were loud, slow, leaked oil, and not very precise. All were hydraulic. By then the vertical barrel, horizontal barrel with plunger designs had largely faded away. All had plasticizing screws. Robotic interfaces were home built. Names like IMPCO, Van Dorn, Lester, HPM, Newbury, New Britian, and Reed are all gone today.
2026. Molding machines are pretty much the opposite.
A molding machine in 1966 had simple “Ice Cube” relays which were easy to replace, usually from inventory. That’s the good part. Running an 8 second cycle was nearly impossible, and when the stars aligned and it took place the machine looked like it was going to implode. No variable clamp speeds, nor ejectors that could vary in speed and distance on every stroke. You had to spend extra for hydraulic ejection. Arburgs just had stationary rods that extended into a mold when the mold retracted. For multiple eject strokes, you had to stroke the mold. Injection speeds were controlled with a flow and separate pressure valves on most machines, and they had. One speed. Ditto screw speed, clamp speed, and back pressure. Low pressure mold close was nearly non-existent and mold damage was common and extensive. But the machines worked and technicians felt it was an art. Gone are the days when a “tech” would spit on a barrel to see how hot it was.
Today machines are faster, safer, more precise and less expensive to operate, and yes, a lot more expensive to buy and maintain.With electric servo machines a 5 or 6 second cycle is possible, and with a skilled technician taking advantage of all the programable motions, the machine looks like it is barely working up a sweat. Holding a cushion with .001” variation over a week is possible with a good barrel and check ring. Mold protect will stop with a foam ear plug getting between the clamps as they close. Mechanical operations on an all-electric machine will require only 30% of the electricity of even a 1997 servo valve machine. They don’t leak oil. They don’t require cooling water except for the throat, and a mold heater. They can even teach themselves to fine tune a process using AI.
Today’s alternative to all-electric molding machines are servo pump machines. While a distant cousin to a 1966 machine they also use 30% of the electricity that a 1966 equivalent machine would use for mechanical activity. While heater bands are more effective today, they haven’t seen the dramatic changes seen on the rest of the machine.
This servo pump machine is less precise, slower, and less expensive than an all-electric machine, and less expensive to operate in comparison to serve valve machines as well. For an idea of precision, back in 1966 a cushion that varied by .100 would be great if you could even measure it. On a 2026 servo valve machine a .010” cushion can be expected, where the all-electric is typically .004” with minimum fine tuning. Expected minimum cycle would be 10-11 seconds, and it wouldn’t be as effortless as an all-electric machine.
Both servo pump, and servo electric (ball lead screw) have one weak point. Long, maximum, injection/hold pressures of let’s say one minute at max pressure will overheat a servo very quickly. Those old “ice cubes” didn’t have the same issues. This problem can be mitigated with larger than normal machines with much smaller screw diameters producing very high-pressure machines, reducing the total load. It was the same as in the past to some extent. To get very high-pressures, and hold the mold closed you needed a special machine, like a 150 ton machine with a one-ounce shot.
The machines of 1966 were basic requiring more of an artist and years of experience to fully master. Today they are far more technical, an engineering marvel, that constantly amazes someone with the perspective of time. To see someone with 20 years of experience discover a feature like “coining” on a standard machine is fun to watch. Sometimes I think these all-electric machines are smarter than some of us.
Per Flem
Recto Molded Products