Multicomponent molder dives into automation

Scuba divers around the world use flippers made by Italy’s Diverplast. The company is answering increased demand for the multicomponent fins with new designs, colors, materials, and automated production.

Multimaterial molding is a hot topic these days, and many molders are discovering how to exploit it. For Guido Zoffoli of Diverplast near Genoa, Italy, multicomponent molding is anything but new. For years, Diverplast has been pushing the technology forward for the numerous lines of swim fins it makes for Scuba divers. It is the very nature of the swim fins—sold around the world under a variety of brand names—that drew the company into multimaterial molding.

A Scuba diver is accustomed to the kind of one-piece, semiflexible fin that Diverplast delivers, but in reality the finished product is a blending of two quite different elements. There is the boot or shoe part of the fin that must fit the foot comfortably and provide precise control. Then there is the blade portion that boosts the swimmer’s propulsive power in the water.

To do its job well, the blade requires a stiffness that would be uncomfortable against your foot. Very different material properties are required. Both materials need elasticity, but their flex moduli must be notably different to achieve maximum performance comfortably. Divers on the Rise

Diverplast got its start in business shortly after World War II building compression molding tools for rubber divers’ fins. Staying with that specialty for more than 50 years has created a wealth of materials, design, and production experience. The company acquired its first injection molding system from Sandretto in the early 1970s and added flipper production to its moldmaking skills. Molding volume now has reached the point where 22 molding machines from 70 to 270 tons, 15 of them Sandrettos, are needed to keep up.

However, demand is still rising, so when the time came to acquire its latest molding machines, Diverplast also wanted to move into the arena of the automated manufacturing line. The company had long searched for a better-performing combination of materials than what it had been using: EVA for the fin blade and various elastomers for the shoe. Well aware of the benefits of an integrated production solution, Diverplast asked Sandretto to help find a way to mold two thermoplastic elastomers with different flex moduli and colors over a premolded fin—and automate the entire operation.

The solution now in production at Diverplast is an integrated production line based on two 165-ton Sandretto Serie Nove BN Multi-Melt Syncro two-component molding presses. A single ABB anthropomorphic robot stationed between them loads previously molded paddles and unloads finished swim fins.

Since Diverplast makes a variety of fins in a range of sizes, a critical element in choosing these machines was the flexibility of distance between the centers of the two nozzles. The range of motion in the Sandretto machine design eliminates the need for special linkage between the machine and the different molds. The ability to horizontally reposition the injection units was also critical for the robot to load and unload the molds efficiently.Both presses are fitted with an automatic centering system for the injection units. Once the correct positions are memorized for a specific mold, the system automatically positions the injection units whenever that mold is remounted for production. The overall system works so well that Diverplast plans to add a second similar production line to keep up with steadily increasing demand for its products.