The waterproof membrane is automatically glued to the upper sole of high-quality outdoor shoes. This central production step is raised to a new level of quality thanks to the smooth tool change and highly complex image processing.

Ludwig Wiesböck founded Wiekon 2020 in Rohrdorf, Bavaria, as a mechanical engineering company that develops customer-specific automation solutions as a full-service provider in the footwear, textile and general industry sectors and supports them from the concept phase through to project implementation.

Hotmelt gluing process transferred to production automation

During a period of parental leave, the 32-year-old mechanical engineer had been thinking intensively about how a hotmelt bonding process could be transferred to production automation. The uppers of high-quality shoes for leisure and work that need to be waterproof - such as hiking boots or firefighting boots - are fitted with a polytetrafluoroethylene (PTFE) membrane. This waterproof, breathable membrane must be sealed in the sole structure to prevent water from penetrating. The leather and membrane are stretched around the last on the upper, and this edge must be sealed all around with hotmelt adhesive. As each shoe is an individual product, this edge is also individual. In the manual process, the shoemaker applies the adhesive along this edge to seal it completely.

This manual application is not without its problems: on the one hand, because the worker cannot apply the required amount of adhesive with absolute repeat accuracy; in this way, more adhesive is used than is actually required. Secondly, because the isocyanate-containing adhesive, which is 160 degrees hot, emits hazardous fumes to which the worker is directly exposed at arm's length. Thirdly, the quality of the manual application is also an important aspect: as the course of the membrane edge is different for every shoe, it is not always possible to ensure precise adhesive application - and therefore absolute impermeability. The result: rejects, complaints, waste of material.

Quick-change system supports automated gluing process

This is where the newly developed Wiekon system comes to the rescue: first, an employee places a pair of uppers on a special gripper, on which two expanding mandrels clamp the uppers. Right here at this point, the edges of the membrane and leather on the soles are scanned by a camera; the image processing algorithm is used to define the individual adhesive application paths for the robot for these two shafts. The robot then picks up the gripper together with the pair of uppers via the Schunk changing system and guides it to the gluing station. Here, the six-axis robot precisely follows the individually calculated path - one shank at a time.

Meanwhile, the dosing system dispenses the exact amount of adhesive required at the correct sole position. The robot then picks up the two lids for the clamped pair from the suction gripper designed in-house and transfers the gripper - again via the Schunk quick-change system SWS - to the pressing station, where the two lids are glued together. After the pressing process, the robot picks up the pair of sockets again and takes it to the input or output point, where it is dispensed via the SWS. The employee receives the pair and feeds it into the further sole construction process so that the upper becomes a shoe.

Three pick-up grippers are installed in the Wiekon system; one module is always positioned at the cell transfer station near the employee, who inserts the pair of sockets here and picks them up again after the gluing and pressing process. Another gripper is always on the robot, which fetches, brings, transfers and takes over non-stop. A third gripper is used at the press. This ensures a continuous work process. Schunk has supplied a whole range of components for the system: Specifically, a total of five Schunk SWK-011 quick-change heads and eight SWA-011 quick-change adapters, which are equipped with electrical feed-through modules, have been installed. Their robust design and precise repeatability enable fast, reliable and smooth gripper changes. Locking and unlocking takes just milliseconds.

The shoe manufacturer using this system benefits from a number of advantages: First and foremost, the employees are no longer in contact with the isocyanate-containing, carcinogenic adhesive. In addition, the membrane sealing process is reliable and repeatable. Ludwig Wiesböck puts the cycle time for processing a pair of sockets - picking up, scanning, gluing, pressing, dispensing - at 25 seconds, which is faster than would be possible with a manual process. The quality of the glued strip is top in every single case, as it is placed precisely on the edge of the membrane in a shoe-specific manner thanks to the complex image processing.

Reduced error rate

This results in less "slippage" - i.e. shoes that have gone through the gluing process but are not waterproof in the end because the adhesive strip does not fit exactly and the membrane does not seal completely. This slip rate is relatively high in the manual process. In addition, a precisely laid and precisely dosed membrane results in around 40 percent adhesive savings - a significant cost factor for the shoe manufacturer. The lower consumption results in fewer emissions, which is also of great interest: the shoe manufacturer is subject to an official emissions limit at its production site, which can hinder production.

The Wiekon system not only improves employee health and product quality, but also increases production volume. Another advantage is the complete flexibility: shoes are produced in sizes from 3 to 14, including intermediate sizes. There are several last variants for each size, as well as narrow, wide and normal versions. And finally, there are left shoes and right shoes. "There are several thousand upper variants," says Wiekon CEO Ludwig Wiesböck. Thanks to image processing and the algorithm developed in-house for path calculation, the Wiekon system implements the batch size 1 gluing process for all these variants. Last but not least, the robot cell also helps to compensate for the shortage of skilled workers in shoe production, as many traditional shoemakers will soon be retiring, meaning that the industry will have to switch to automated processes.

Best material, clever minds

The SWS from Schunk is a decisive and indispensable centerpiece of this automation solution. Using a robot changing system from Schunk was not even a question for Ludwig Wiesböck right from the start. "I know Schunk components from previous jobs, they simply do what they are supposed to do, even after years," he confirms. "In a project like this, I need robust, absolutely reliable components that have to be top of the range so that I can get on with the job in hand."

The contact with Norman Franck, Technical Consulting and Sales Gripping Systems at Schunk, already existed. "I got what I needed directly from Schunk," recalls Ludwig Wiesböck of the uncomplicated procurement process. "The functional properties of the change system as a whole, including the absolutely secure locking of the head and adapter, left no other choice." Cooperation with top people is also important for Wiesböck. "In a young company, you need not only the best material but also the brightest minds". This is why Wiekon, which also includes master electrician Matthäus Ackermann, Head of Assembly and Commissioning, in addition to Ludwig Wiesböck, works together with other, equally young companies.

The project duration for this special system was around 30 weeks. Ludwig Wiesböck has made a success of this installation. The six-axle vehicle has now been purchased and a second one has been added. The Wiesböcks celebrated the child's birthday properly - and the project idea anyway. Because it has literally turned into a real shoe.

Schunk, schunk.com

Wiekon, wiekon.de