The perfect surface – lenses between human and machine

The EssilorLuxottica Group operates hundreds of ophthalmic lens production facilities worldwide. Some of them are located in Europe, and one plant is even in the middle of Germany. For 80 years, high-quality ophthalmic lenses have been manufactured in Braunschweig. MAFO took a look at the production facility and talked about pressing current issues. For example, whether the group sees Germany as an interesting and long-term production site or not. The editors also found out why milling the optical surface only accounts for a tiny fraction of the extensive lens journey through production.

Tzschhhh, the machines hum continuously in the background. A slightly chemical, but not necessarily unpleasant smell is in the air. Today’s group of visitors is standing in the middle of the machine hall at the Essilor plant in Braunschweig (Germany), where around 700,000 spectacle lenses are produced every year.

Three milling machines in the factory are the heart of production. These fully automated and networked machines only need 60 seconds to achieve an optical perfect effect. 60 seconds – and then what? May non-experts ask themselves.

For people in the industry, the next steps are obviously no secret. And yet it remains exciting to take a look behind the scenes in this historically developed production facility.

80 years of ophthalmic lens production in Braunschweig

Shortly before entering the hall, visitors were welcomed by Alexander Mohr, Managing Director of Essilor GmbH, Andrea Mazzo, General Manager of Luxottica Wholesale GmbH, and Frank Walenda, Head of Corporate Communications DACH EssilorLuxottica.

The reason for the visit is the 80^th anniversary of the plant. Optik GmbH was founded here in 1945 and taken over by Essilor in 1976. Since then, production has been continuously modernized. In addition to lens production, there is a showroom with the latest equipment for lens consultation, measurement, refraction and further processing in the workshop and, of course, administration.

However, the visit is interesting for another reason: it shows how a globally active group is trying to use its location in Germany and its local proximity to customers as a strength rather than a weakness. 

According to the group, it is following the departure of its competitors with high interest and takes it as confirmation of its own path: “While other manufacturers are withdrawing from Germany, we are consciously focusing on the Braunschweig site and our proximity lab. Our strategy is clear: proximity to the market, tailor-made solutions for our customers and a level of service that can only be achieved through local production. For us, ‘Made in Germany’ is not just a label, but a genuine performance promise – in terms of quality, speed and reliability. And that’s exactly what makes economic sense for us,” says Alexander Mohr. Also the management-team is proud of this seemingly successful strategy but now they are happy to leave the tour of the lens production to the technical experts from Braunschweig.

A total of 152 employees work at the Braunschweig site. 70 of them work in production – and one of them is production manager Tobias Gronau, who is now giving the group a tour of the plant.

Major investments for the future in ­customer proximity

“Come a little closer, otherwise you won’t understand anything,” Gronau greets us humorously. It is loud in the hall and the production manager is about to take the group on a journey of the lenses through the entire production process.

If visitors had toured the plant five years ago, they would have seen much more manual work and kilometers of conveyor belts stretching over two floors of production space. Since then, however, major investments have been made – in new technology but also in streamlining the production area to make it more efficient.

Today, the machinery is located in an area of around 2,500 square meters. That’s about a third of the size of a soccer pitch. The plant is therefore not necessarily huge – but it is well positioned for the future.

“Investing in new technologies and automation was a decisive step for us. This is the only way we can now manufacture high-quality products with a speed and efficiency that makes us competitive on an international level,” says Tobias Gronau “At the same time, the expertise of our employees remains essential, because despite all the technology, experience and competence are needed to meet the high demands,” he adds.

85,000 blanks in stock

While the machines in the background are continuously carrying out their work, i.e. milling, polishing and engraving, the group of visitors stands in front of a shelf full of semi-finished plastic products. It quickly becomes clear here why spectacle lens production is quite unique compared to the manufacture of cars or furniture: no two spectacle lenses are the same. Instead, there are around 1.8 million possible variations.

Measured against this, production is very fast. “All lenses that are not colored are produced within two days,” the production manager proudly explains.

To achieve this, a large warehouse is needed. If you add semi-finished and finished lenses together, there are around 85,000 blanks on the shelves, ready to be processed and transported to the optician as quickly as possible. In the case of semi-finished products, the front surface of the lens has already been processed, and only the back surface is still missing. With the finished lenses, “only” the coating is still missing. Also, experts know this step is anything but trivial.

In Braunschweig, only high-quality lenses run over the conveyor belt. Varilux progressive lenses as well as Stellest, Eyezen, Transitions Gen S and AVA lenses are produced here or receive their final coating here. Standard lenses, on the other hand, are no longer manufactured in Germany, nor are mineral lenses.

Perfectly imperfect in 60 seconds

The process continues and if you listen carefully, you can hear the whirring sound of first the milling machine and then a real diamond steadily removing millimeter after millimeter of plastic blanks and turning them into plastic shavings

The group stands in front of the first machine, a fully automatic freeform generator which gives the lens its optical effect. With the help of the diamond, a completely individual progression surface is created, with a different effect on every square millimeter if required. “In traditional manufacturing in the past, you could only drive two radii. The new machines can mill everything that is physically possible, to an accuracy of 0.3 μm,” explains Gronau. As a result, the progressive lens surfaces are getting better and better.

“Here you go,” the production manager motivates the group to take the lenses in their hands. “Theoretically, you could fit the lens into the glasses right now and you could look, because it’s already optically finished – but as soon as you clean the lens, it would probably break”.

The new generators work with what is known as Alloy Replacement Technology (ART). This replaces the lead alloy, which is usually used to bond the blank to a block piece for processing, with a special adhesive. According to EssilorLuxottica, the switch to ART technology has not only improved the environmental balance, but also optimized and streamlined processes. 

Thinner blanks = less waste

Anyone who sees how large parts of semi-finished products turn into plastic shavings in seconds and end up in the bin can hardly avoid the question of sustainability. Plastic waste is difficult to recycle as it is a mix of materials from different indices.

Gronau demonstrates an improvement: “Look, this is the same lens with an identical front curve,” explains the production manager. One blank is significantly thinner than the other (Fig. 3). A life cycle analysis carried out by an independent institute certified a 19% reduction in plastic consumption for the innovative lenses with “Eco-design”.

In future, the company would like to go one step further. The keyword here is circular economy. A specially created project team is working on a concept that will make it possible to return grinding chips to the production process. This is not an easy task, but if it succeeds, it would be a real innovation.

Sustainable energy generation

Sustainability and energy costs in Germany are generally an important topic at the plant. This production is powered 100% by green electricity and a water recycling system reduces water consumption enormously. In addition, a solar system is to be installed on the roof in the future.

“Of course, we are also feeling the effects of high energy prices. That’s why we’ve been focusing on sustainable solutions for years to make ourselves more independent – from photovoltaic systems to the use of 100% green electricity. We also continuously invest in energy-efficient technologies that reduce electricity consumption. This not only helps us with costs, but also contributes to our ‘Eyes on the Planet’ sustainability strategy. For us, this is not a short-term reaction, but a long-term plan,” explains Alexander Mohr later.

After the optical surface has been created in just 60 seconds, many more steps follow. After milling, the lenses are polished, engraved with a laser and separated from the block again.

In addition, conscientious inspection of the finished lenses is a high priority: “If we don’t pay attention here and errors go undetected, we will break 250 lenses per hour,” says the production manager. Incidentally, the lenses have to pass the trained eyes of the highly qualified experts up to 60 times during the entire production process.

The perfect color – an art in itself

Things are a little quieter in the next room. Red, yellow or blue liquids simmer in a row in rectangular color pools. Light steam rises in places. It does not take much imagination to realize that the visitors are in the dye works. Soon, depending on the weather in April or May, the dyeing season will start. That is when it gets busy here. But now it is the end of February.

At 97° Celsius, the plastic lenses are slowly and evenly immersed in the dipping tanks. The longer the lenses are immersed, the darker they become. The heat is crucial so that the color pigments can penetrate the plastics well. As each material reacts differently to the color solution, a separate machine is needed for each index.

In the last room, the group of visitors experienced live that state-of-the-art generators and more are crucial for the quality. The main task of the employees there was to monitor the fully automated and networked machines, to check the lenses and intervene if necessary.

Here in the dyeing room it is exactly the opposite. The machines seem to be more of an accessory. Even the best machines cannot deliver good results without the manual work and expertise of the employees, some of whom have decades of experience.

A great deal of knowledge and experience is required to achieve the perfect tint for every lens. For example, it is a great art to tint the lenses in pairs if the strength of the lenses is different. This is why almost every lens is dipped again by hand.

“We have lenses here that only take ten seconds in the bath. But there are also lenses that spend up to two days in the tinting shop until they are perfect,” explains Production Manager Gronau. There are already 170 different Essilor colors in the official range and every special customer request is also fulfilled.

Hard lacquer by dipping process

Gronau hands over to his colleague Sven Hahn for the rest of the tour. The process engineer and plant manager has been with the company for 18 years and knows everything about the coating steps that follow. The group enters the next room.

Before the lenses receive their hard coating, they run through the preparation system – in simple terms, a washing line. Thanks to ultrasound, heat and various chemicals, each lens is perfectly cleaned and finally stained a little to make it rougher and ensure that the coating holds well later on.

The group moves on to hard lacquering. Put very simply, the lacquer is similar in structure to a two-component adhesive. A first coat with a thickness of 0.8 μm is applied by dipping. The second coat has a thickness of 2.5 μm.

Hahn explains pictorially how the speed determines the layer thickness: “If you pull the spoon out of the honey quickly, you have a lot of honey on the spoon. If you pull it out slowly, you have less honey on the spoon, and that’s how it works here too.”

After this process, the lenses are sent for cosmetic inspection, which means they are inspected extremely critically for defects by an employee – within seconds. This is because 32 new lenses come out of the system every six minutes. 

Approximately 97% of the lenses come out of the dip coating system without defects. However, around 3% have small defects, such as waves. This does not mean that the lenses are rejects. “We then have the option of etching off the lacquer again and starting from scratch,” says Hahn. Only after tempering at 100° Celsius is it virtually impossible to remove the coating again.

It is getting hot

During training, you learn that a spectacle lens reflects 6% of the light on each side. In order to avoid this 12% loss of light, the next step is to enter the high-vacuum coating system for around 45 minutes per side. This is where the anti-reflective coating is applied, and the residual reflections are reduced to around 1% in total. The anti-reflective coating also provides additional scratch protection.

For the anti-reflective coating to work, a perfectly sophisticated interplay of materials and coating thicknesses is required.

The aim is to achieve erasure by placing wave troughs and wave crests exactly on each other. 20 different layers are combined here, and a wide variety of high- and low-refractive materials are vapor-deposited. To do this, they must first be heated to the melting point, which is 1200° Celsius for quartz, for example. In addition, the layer thickness depends on the nanometer, i.e. the unimaginably small number of millionths of a meter. This is the only way to achieve the extinction of the light waves in the end: “I shift the wavelengths and in the end only blue, green or orange light comes out,” the editors learn from Hahn. This is the visible residual reflection.

The highly complex systems here cost around 1.2 million euros and the energy consumption is enormous, as the vacuum has to be created, and the temperature has to be kept high. This and the complex work involved explain why the anti-reflective coating in particular has its price.

If the lens now passes the final inspection in an automated system, it receives the final stamp and can be sent to the customer after packaging. If the inspection machine reveals any abnormalities, the critical employees decide how to proceed with the lens or whether the journey starts all over again. Even if the lens is to be edged, it does not go directly to the customer. Instead, it is sent to another plant in Hanau (Germany), where it is given the final shape to match the frame.

A journey through many climate zones comes to an end

The group is approaching the end of the tour and has still passed the machine hall much faster than the fastest spectacle lenses. After all, creating the perfect spectacle lens takes a lot more than 60 seconds of milling. Because this step is followed by hours or even days in which the lens is engraved, possibly colored, dried, washed, dipped, steamed, tempered and checked over and over again – often under extreme forces, temperatures and pressures.

This leaves only the last – and perhaps most important – question unanswered. The editors asked the Managing Director: Can you promise our readers that EssilorLuxottica will continue to manufacture lenses in Germany?

“We are clearly committed to Germany as a location. For us, ‘Made in Germany’ is more than just a prestige label – it is part of our service and quality strategy. Our customers benefit from the shortest delivery times, maximum flexibility and a production facility that can quickly adapt to their needs,” explains Alexander Mohr. “This is why we are continuing to invest in Braunschweig and will continue our proximity strategy. Our partner opticians can therefore rely on this: Essilor will continue to produce innovative ­ophthalmic lenses in Germany!”