Expert Minute: Small tonnage
For Ygor Mikhailoff, Plastics Segment Manager at Stäubli, the real performance question in small and medium injection molding presses is straightforward: how quickly can a plant reach the first good part after every mold change, and how repeatable is that result from shift to shift?
A self‑described “real life production fan,” he spends much of his time on the shop floor, observing how production lines operate. Here, he explains why small tonnage presses present distinct challenges and how rethinking mold setups can help plants produce more good parts per day using the same installed base.
Why small and large tonnage behave differently
The process of manufacturing a protective cap or a car bumper is fundamentally the same: molten material is injected between two mold halves, cooled, and then ejected. The difference lies in scale, expressed through the closing force of the machine, or its tonnage. This force counteracts the pressure of the material pushing against the mold during injection – much like water pressure lifting a sewer cover during a flood.
In large tonnage applications such as automotive, molds can weigh 40 to 50 tons and machines operate at 2,500 to 4,000 tons. Given the investment involved and the risks associated with failure, facilities are typically designed around these assets, with high-capacity cranes, preheating stations, and automated changeover systems integrated from the beginning.
On small presses, with clamping forces typically up to around 500 tons, this level of infrastructure is more difficult to justify. Machines are smaller and molds are lighter, so many plants continue to rely on manual couplings, conventional clamping systems, and lifting equipment shared across the production floor.
This creates two core challenges that are deeply intertwined: a lack of standardization around mold setups, and the human constraints behind them.
The human factor in small tonnage
If a machine is set up to run the same job for years, you could probably put it on the moon and it would still produce parts. Variability often emerges during mold changeovers, where human intervention plays a significant role.
Many facilities have developed their processes around mono couplings and individual hoses, connected and labeled according to local practices. While more or less functional, such systems are rarely standardized across machines and molds. At the same time, attracting and retaining experienced injection molding specialists has become increasingly difficult. Companies rely heavily on internal training, and high staff turnover means less experienced operators often handle changeovers. In smaller operations, a single person may oversee several machines, handling mold changes, startups, and quality checks.
Production patterns add to the challenge. For some small parts—caps, small wheels, technical components—runs are longer and stock is less of an issue than in, say, automotive. Meanwhile, on other lines, mold changes are frequent and highly variable, so operators rarely repeat exactly the same setup. In both cases, it’s harder to build and maintain consistent habits around the process.
In these conditions, the risk of errors rises: cooling lines may be cross-connected, couplings may be missed, or leaks may only become apparent once production has begun. The result can be scrap, unplanned downtime, and extended troubleshooting, particularly when changeovers take place during night shifts.
Building a full “around the mold” solution
Stäubli’s small tonnage solutions are designed to address these challenges by standardizing and simplifying operations around the mold.
One immediate constraint on small presses is machine daylight, defined as the maximum opening between platens. Add thick clamping plates or bulky connection hardware, and it can quickly become impossible to load certain molds. For this reason, Stäubli has developed slim clamping solutions, both mechanical and magnetic, engineered to fit within restricted daylight while maintaining reliability and repeatability.
On the connection side, centralized plates replace multiple individual hoses, reducing complexity around the press. Designed according to Poka-Yoke principles, these systems physically prevent incorrect connections, minimizing reliance on labeling, memory, or operator experience.
Many facilities also rely on overhead cranes during changeovers, meaning heavy tools are lifted vertically and transported above operators and surrounding equipment. Since these cranes are often shared across departments, suspended loads not only introduce risk and require strict procedures, they can also delay mold changes when lifting equipment is unavailable and machines must wait. Our compact rolling carts allow molds to be transported from storage or maintenance directly to the press and positioned horizontally, reducing dependence on overhead lifting, lowering operational risk, and limiting exposure to shared equipment constraints.
These human-centric measures turn a series of variable manual tasks into a more stable and repeatable process. For operators, this reduces complexity and the likelihood of errors. For management, it means less startup variability and better use of installed capacity.
Maximize flexibility
Reduce downtime
Ensure precision
Optimize costs
Investing in the full picture
On small tonnage presses, the speed and consistency with which a plant reaches stable production after a mold change directly affects how many sellable parts are produced per shift. Parts are also manufactured to increasingly tight tolerances, so even minor instability in cooling or clamping during startup can push components outside specification. Variability therefore affects not only scrap rates but also quality assurance and production release timing. In this context, changeover performance becomes a question of asset utilization and overall competitiveness.
Stäubli's response to this is hands-on and site-specific. In one case, for example, a Stäubli sales engineer asked a production manager to quantify the scrap generated at startup after mold changes. The response, expressed in kilograms, reflected parts out of tolerance due to unstable or incorrectly connected temperature control circuits. By working together to define a mold setup configuration suited to the plant’s staffing levels, production targets, and press constraints, they eliminated cross-connections and improved startup stability. The reduction in scrap and shorter time to reach stable production translated directly into increased output using the same machines and shifts.
The Stäubli difference
Since 1965, Stäubli has worked closely with plastics processors, adapting its solutions to evolving industrial requirements. By focusing on concrete pain points in each plant, we translate real‑world constraints into targeted improvements that make immediate sense on the shop floor. Today, that means compact, ergonomic, and error‑proof systems that help plants maintain quality and safety during every changeover, regardless of who performs it – and, above all, reach the first good part faster.
