In the production of plastic components for dialysis products in the cleanroom, maximum precision is required for every shot. The task is to combine precision with process stability and cost effectiveness. Fresenius Medical Care masters this challenge with all-electric high-performance injection moulding machines by ENGEL.
The lives of two and a half million people with chronic kidney failure depend on what look like inconspicuous plastic cylinders at first glance: dialysers are the central element in dialysis (artificial kidney) machines. On closer inspection, the FX-class series dialysis cartridges by Fresenius Medical Care are highly sophisticated. They contain up to 20,000 hollow fibres as wide as a hair with microscopic pores, through which toxins, urea, excess salts and water are removed from the blood during haemodialysis. The process takes four hours. The patients need to be connected to the machine three times a week.
Each FX-class filter cartridge needs six thermoplastic components, which Fresenius Medical Care SMAD injection moulds in L'Arbresle, about 20 kilometres northwest of Lyon. The components include the transparent cylindrical housing and the blue caps that seal the cylinder with the hollow fibre bundle at the top and bottom and house the connections for the dialysis fluids.
Number of injection moulding machines doubled
According to its own statements, Fresenius Medical Care is the world market leader in the treatment of kidney disease. "At least one Fresenius Medical Care product is involved in every second dialysis performed worldwide," explains the project manager, Alain Philibert.
L’Arbresle, one of 44 production plants worldwide and the only one in France, produces 36 million cartridges a year.
The top priority is uncompromising quality, and it was also a quality-driven decision to exclusively equip the location with all-electric injection moulding machines from ENGEL's high-performance e-motion series.
Today, 26 e-motion injection moulding machines – each with a clamping force of 2200 kN – are deployed in the cleanroom. They all operate 24/7 with a utilisation of well over 90%.
"We have to be able to rely on the machines' repeatability, and we need maximum precision and absolute cleanliness," says Laurent Branchereau, head of the injection moulding shop at the plant, explaining the choice of machines. Every four hours, random samples of the parts are visually inspected and the critical dimensions are measured.
Cylinder housings need constant dimensions
The cylindrical filter housings are particularly demanding. They are injection moulded from polypropylene in a 4-cavity mould. The wall thickness is 1.5 mm throughout, but the filigree structures at the ends, each with a circular undercut, require a sophisticated injection profile to be completely filled. Injection takes place from two sides at the centre of the cylinder. There are two core pulls for each cavity that move out to the left and right respectively for part removal.
"The e-motion machines ensure high dimensional accuracy across all cavities," as Branchereau points out. "This is all the more important because we assemble the cartridges in a fully automated process."
The material poses a further challenge because PP has a lot of shrinkage. On the other hand, it offers benefits in other areas. While filter housings are often produced from polycarbonate, Fresenius Medical Care deliberately chose polypropylene because it is significantly lighter and therefore boosts efficiency in both logistics and waste management.
Temperature control water monitoring for added process stability
"In-house production makes us more flexible," as technical director Thibaud Robin-Rivoire explains. "We can very easily adapt products to our customers' requirements, especially since these requirements regularly change."
Six moulds, for three different cylinder diameters, are currently deployed in cylinder production at L'Arbresle. In total, the FX dialysers are available in five sizes. The version used depends on the patient's size and weight. A mould change is scheduled at least once a week. This was already taken into account in the design of the machines. The e-flomo electronic temperature control water manifold systems, for example, were installed outside the mould area to allow flexible mounting of different sized moulds. Each mould has a different number of cooling circuits.
"E-flomo helps us respond quickly if the flow stalls in a circuit," says Branchereau. "That gives us a good safety margin, especially at night when there are fewer machine operators on duty."
Focusing on one type of machine also contributes to the goal of maximum production stability. "The CC300 control unit of the ENGEL machines with its large display is genuinely intuitive to operate and helps us achieve great process stability. And at the end of the day, that gives us better quality." points out Eric Biguet, a set-up technician responsible for smooth production operations. "
Leveraging quality potential with iQ
"ENGEL also customises the machines to meet highly individual requirements. That's what characterises our collaboration with ENGEL." emphasises Robin-Rivoire. Digital solutions, such as the iQ smart assistance systems from the inject 4.0 program, are currently being evaluated.
"iQ clamp control is particularly interesting for us," says Philibert citing an example. The smart assistance system determines the optimum clamping force for the injection moulding process in question. In most cases, the optimum clamping force is lower than the value set manually. Clamping force correction then not only improves quality consistency, but also saves energy. The trend towards greater sustainability has long since arrived in medical technology, too, and not just following the rapid rise in energy prices.
Energy efficiency, but also material efficiency, is a focus of continuous product development at Fresenius. You can see one example of this by following the path of freshly injection moulded dialyser housings. After a short interim storage period, they are filled with the hollow fibres, which are also produced on-site, and tightly sealed with yellow lids made of polyurethane. It is only after steam sterilisation that the yellow lids are replaced by functional closures in blue polypropylene. The polyurethane lids are disposable parts, and that is precisely what is due to change.
"We have developed new closures with a core made of glass-fibre-reinforced polypropylene," Alain Philibert reports. "They are so robust that we can reuse them up to 50 times."