It's natural for designers to focus on function, but when a part is over-engineered - for example adding extra ribs, clips, and thickness without valid reason - it often results in a more complex mold than necessary. That complexity costs more to build, takes longer to machine, and to develop parts to print. It may also require expensive and complex mold movements. 

That's not to say that we're advocating for cutting corners. We recently worked with a customer who came to us after their updated design pushed their mold cost way over budget. By advising them on ways to simplify the geometry and reduce unnecessary features, our expert team helped to bring the price back down to acceptable levels, without compromising on part function. The customer saved money. The part still worked as intended. The mold became easier to develop. Everyone won. 

"Complexity has an exponential influence on the cost of the tool. Put simply: the more complex the part, the more complex the mold, and consequently the price is higher," says Rompa's Tooling Manager, Christophe Beauve. Sometimes by simply changing the draft angle or removing non-functional details, we can significantly reduce mold costs."  

Tight tolerances might sound like good engineering—but they come at a cost. Achieving very small tolerances often requires multiple tuning loops, where the steel in your mold is carefully adjusted after trial injections. Each loop can add weeks to your timeline and rack up cost in toolmaking and validation. 

Many customers request ultra-tight tolerances by default, thinking it's safer. But in many cases, those tolerances don't affect the actual performance of the part. 

"We always ask: do you really need this level of precision? If not, you could reduce costs as well as save weeks in development and avoid unnecessary tool modifications," Christophe said.

A tool that breaks down too soon or wears out mid-program means unexpected costs and production delays. That's why the tool's material and construction need to match the job at hand, especially the expected annual volume and production location. 

For high-volume, high-complexity parts, you'll need special, tool-grade, hardened steel molds and a local toolmaker for quick maintenance. For low-volume parts, a more economical soft steel tool may be sufficient and therefore the smarter choice. Rompa's priority is to recommend the right setup, not just the cheapest one. 

"We've had customers request a high-cavity tool for low-volume parts. That means a high upfront cost with almost no return, and very little machine utilization. It's a lose-lose situation," Christophe explained. "Think of it this way: you don't need a Ferrari to drive your kids to school or visit the grocery store (no matter how much you might want one!) On the other hand, you won't be competitive on the racetrack in an SUV. It's all about making the correct, most cost-effective choice for the task at hand." 

More material means a higher cost per part - and not just because of the price of raw plastic. Thicker walls mean longer cooling times, which directly increases cycle time — the total time it takes to mold one part, from injection to ejection. Since each machine can only make one shot at a time, longer cycle times mean fewer parts produced per hour, which drives up the cost per unit and machine utilization. 

What's worse, overly thick walls with longer cooling times increase the risk of quality issues like sink marks (deformation on the surface of the part), internal voids (gaps within the plastic which affect the strength of the part), and warpage (when parts bend or twist out of shape after molding). These problems can affect how a part looks, fits, or performs. In some cases, they can result in entire batches having to be scrapped. If you don't consider these issues before you build your mold, you may find yourself going back to the drawing board and investing in a replacement mold.  

At Rompa, we help customers avoid these kinds of problems. Right from the start, we use our years of experience to identify areas where it's possible to reduce unnecessary wall thickness and simplify part geometry – proactively preventing waste of costs, time, and materials without compromising function. The same process can also extend mold life and save a whole lot of frustration!  

These changes aren't always obvious to the untrained eye—but they make a significant difference. 

Some molders will give you a quote without asking questions. At Rompa, we see that as a red flag. Every successful plastic part involves a web of interdependent factors: geometry, tolerances, tool material, number of cavities, production volume, and location. 

If a supplier doesn't ask about your annual volume, total lifetime volume, your tolerance needs, or where the parts will be used, they're not giving you the full picture. And they're definitely not giving you a cost that reflects the real total cost of ownership. 

"We ask these questions upfront not to slow you down, but to save you from bigger delays later. That's what makes us a partner, not just a supplier," said Christophe. 

If your goal is to lower costs without sacrificing quality, the real value isn't just in the quote, it's in the expertise behind it. The right partner will look beyond the tool price and help you optimize for lifetime value, not short-term savings. And that's exactly what Rompa does. 

Want some independent advice or a second opinion on your mold design or quote? We'd be happy to set up a call with one of our experts to review how taking a little more time over mold design can reduce the lifetime cost of your injection plastic molding projects.

Book a meeting.