Stamping houses in Europe and the United States can look at a servo or adjustable-stroke press and reach opposite conclusions: where some see measurable value, others prefer to stick with the tried-and-true mechanical press. Stamping Productivity presented this observation to Tobias Prataviera, sales area manager for Italian machine builder Sangiacomo Presses, and René Zwahlen, president of Sangiacomo Presses Americas. Here’s what they had to say about the servo-versus-mechanical calculus and why it looks so different depending on where a shop sits and what it means for signing on the bottom line.
Stamping Productivity: What’s driving servo press investment in Europe and how does that compare with the United States?
Prataviera: In Europe, investments in servo presses have generally been driven by applications where programmable slide motion delivers measurable technical or economic value. In the United States, by comparison, many manufacturers invest in servo presses primarily to achieve shorter strokes in pendulum mode, even though this is possible on an adjustable-stroke press.
Zwahlen is unsure whether Europeans are actually ahead of North American customers in terms of using servo technology; where they are ahead is on the tooling and process side.
Zwahlen: The competency level there is somewhat higher. Regardless, servo technology isn’t magic. With complex parts, the speed is limited at some point because you need time for forming, so shops end up optimizing the process itself rather than the output. But if I optimize the process and then realize I could actually run it twice as fast, I haven’t really optimized anything. So, there are a lot of variables to juggle and very few people have that kind of holistic expertise.
STP: Can you elaborate on what’s possible with an adjustable-stroke press?
Prataviera: For many conventional stamping operations, adjustable-stroke presses provide sufficient flexibility at a significantly lower capital cost, reducing the incentive to adopt servo technology. I’m not saying adjustable-stroke presses are ‘good enough,’ because they offer many advantages, many of which are discussed on our website.
One notable example is Sangiacomo’s white paper “Why Use the Shortest Possible Stroke in Metal Stamping?” It explains how reducing stroke distance from 40 mm to 20 mm allocates 10 additional degrees of crank rotation to forming time – a 45 percent increase – while also reducing impact velocity at the point of contact by 28 percent. The result? Fewer punch breakages, longer intervals between sharpening and less vibration and noise. None of that requires a servo motor; it’s a function of stroke length alone, whatever the press type.
Zwahlen: That’s why I say there are so many variables to consider, because to reach for the optimum, you first have to define what ‘optimum’ means. Most of the time, it’s quantified by quality: fewer defects or output. But let’s say I reduce my defects to almost nothing and think I’ve built the optimal process – only to find out someone in Europe is producing twice as many parts on the same press in the same amount of time, but with maybe two more rejects than I have. Which one is actually optimal? That’s the bigger question only real expertise can answer.
STP: Setting aside the servo versus adjustable-stroke discussion, is there a broader trend pulling investment back to American stamping floors?
Zwahlen: Certainly, and
it’s a trend that’s been in motion for quite some time. Back in the Clinton and early Bush years, we were rebuilding presses just to send them overseas – give it a paint job, change the voltage, then ship it to China or wherever the customer was setting up. That demand has since stopped and then slowly reversed, with sales of new machinery on the rise over the past decade. I think this will continue – people will keep more stamping here in the United States rather than investing abroad.
STP: To play devil’s advocate, can you share any instances where the servo press isn’t a good fit?
Zwahlen: I admit it isn’t better for every application – it just makes some things possible that a mechanical press can’t do. Once you get to higher speeds, servo presses aren’t the ideal choice. Nor are they ideal for simpler parts. Let’s say you want to blank coins as fast as possible – I’ll tell you to get a mechanical press, run it at maximum stroke rate and get everything out of it you can.
Unfortunately, shops too often say, ‘I’ve always run it this way and we know 200 strokes per min. is the maximum,’ without ever asking about the alternatives. So, there are two different mindsets at play. Determining the correct one for the application requires a level of analysis that’s too often bypassed in favor of the status quo.
STP: So where do servo presses actually earn their higher cost?
According to Prataviera, the greatest benefits of servo presses are realized in applications that fully exploit programmable slide motion.
Prataviera: Achieving these advantages typically requires not only the press itself but also optimized tooling and process design. Servo presses are particularly well-suited for demanding forming operations, processing high-strength steels, precision forming and applications where increased productivity or improved part quality justifies the higher investment cost.
Zwahlen: Where the servo press has a real advantage is deep drawing where you need to work the metal more aggressively – very hard materials or heavy deformation – or in automation and part handling. For example, flipping a part inside a tool or a transfer where the feed or handling actually takes more time than the stamping itself. That’s really where you want a servo press – it doesn’t care about starting and stopping. A mechanical press has to engage and disengage the clutch every time you single-stroke it. A servo press just runs.
STP: Which of these benefits are most important to job shops and how does it justify the investment?
Zwahlen: Servo presses deliver greater flexibility, so that naturally drives up the cost. And if they don’t utilize it, that’s considered a waste, but job shops have unique requirements. They typically face shorter runs, more changeovers, more variation. It’s nothing like a shop that stamps the same battery cap day in and day out. Different environments require different equipment.
STP: Does that mean servo is gradually replacing the mechanical press?
Prataviera: Not necessarily. Mechanical and servo presses should be viewed as complementary technologies that serve different production requirements, rather than as one replacing the other. Mechanical presses remain the preferred solution for many standard stamping operations where initial cost is lower and performance is guaranteed.
According to Zwahlen, shops should look at the whole project, not just the press.
Zwahlen: You can start by looking at how you’re going to move the parts. The forming process is one thing – you can control slide velocity, which is the servo’s real advantage – but you can also pause the slide at any position to maneuver the part, whether that’s feeding, indexing, robotics or a transfer mechanism. You don’t need a long stroke to do that. Remember, the drawback of a long stroke is that it increases dynamic forces.
STP: Why do so many shops buy the same kind of press again instead of reassessing what they actually need?
Zwahlen: Sometimes, the technology offers something genuinely unique to the process – it’s a whole new world and you need servo technology to get there. But if a shop has been running the same press for 10 years, they’ll probably just buy the same thing again because it’s been working all these years, so it must be good. That’s playing it safe and repeating the mistake.
Other times, people want a servo press because it’s seen as the modern technology or it can do things a mechanical press can’t. Sometimes people ask for a servo, and even after I tell them it isn’t the right fit, they buy one anyway.
STP: You’ve talked about shops buying more machine than they need. Do you have an example of that going wrong?
Zwahlen: Just recently, a customer asked us to quote a replacement press with the same specifications as their current one. I told them I wasn’t going to quote it because they were asking for the wrong press for the process. In fact, their original press was wrong from the very start:
- The bed was way too big for a small tool, so tonnage was concentrated at the center, bending the ram.
- They had a conveyor running through the bottom that weakened the structure. The die was open way too wide for a flat part.
- The press had a longitudinal crankshaft rather than one with two transverse shafts, which would allow the sideways forces to cancel out.
Because of these and other factors – one of their jobs was so loud they could only run it on the night shift after the office staff went home – they had a 10-in. stroke stamping a flat blank that could easily run on a 1-in. stroke. They kept asking whether they could afford to replace the machine. The real question was whether they can afford not to. When that press stands still, the plant stands still.
STP: How common is that kind of mismatch?
Zwahlen notes it’s more common than one might think; when asked what percentage of presses have a variable-length stroke, he guesses it isn’t even one in 10.
Zwahlen: You need to see what’s actually possible, because there are so many variables at play. Many customers tell me they can’t run a certain job faster because the feed line can’t keep up. It never occurs to them that they could just install a more capable feeder. But in a production mindset, they assume the current speed is the limit, whereas in Europe, people tend to ask the next question much faster: If the feed is the problem, what can we do about it?
So again, it’s critical to balance the whole process. The trouble is almost nobody actually owns the entire picture. A tool and die maker provides a tool that shapes the part and handles the feeding and timing, but there’s also the press supplier, the downstream operation and the quality to think about. Everything takes time and no one person is an expert in all of it – it’s collaborative know-how that gets the best result. That’s where stamping houses – wherever they are – will see the greatest return on investment.
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