‘Made in Germany’ is an integral part of MESTO’s brand promise. The entire value creation is produced at the corporate headquarters in Freiberg am Neckar in southern Germany, and this is to remain unchanged in future. For the production floor this means continuous increases in efficiency, integration of processes and as much automation as possible. The main challenge here: maintaining high flexibility. Together with its partner WITTMANN, MESTO develops manufacturing solutions made to measure to meet these complex requirements.
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The piston manometer serves as a safety valve. Pressures of up to three bar are permissible. Excess pressure can escape safely through the piston. (Photo: WITTMANN) |
“We have a particularly large product range”, explains Élise Sellmayr, Head of Process Optimization, during our visit in Freiberg am Neckar. Economical distribution of liquids is MESTO’s specialty. Here, the South German company with more than a century’s corporate history ranks among the globally leading suppliers. This unwieldy-sounding description is all about products everyone is familiar with: pressure sprayers, backpack sprayers, foam pressure sprayers, trigger sprayers and suction devices. These are found just as naturally in households and allotment gardens as in agriculture, professional horticulture, workshops, in the trades and on building sites, being used for cleaning, disinfecting and pest management, as well as in a great variety of different industries.
All products are available in different versions; major customers such as DIY stores and workshop chains can have their sprayers branded in their own corporate design. This diversity leads to small batch sizes and frequent setup processes. Therefore, flexibility is the main key to efficient production and competitive unit costs.
“We have no typical mass production here”, says Sellmayr and shows us an example. She holds up a small white piston made of a co-polyester, which serves as a pressure gauge in all pressure sprayers with a plastic housing and which has a great deal of responsibility. “The piston pressure gage functions as a safety valve”, explains Sellmayr. Sprayers with housings made of plastic are approved with internal pressures of up to three bar. If more air than that is pumped in, the excess pressure is let out via the piston gage. In the ‘Primer’ and ‘Profi’ series of appliances for professional use, the pressure gages are printed on and perform internal pressure control. Piston valves without print are used in the smaller devices of the “Pico’ series destined for private households and gardens.
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MESTO consistently relies on SmartPower injection molding machines from the WITTMANN Group. Their high energy efficiency was the key factor in favor of this decision. (Photo: WITTMANN) |
For a long time, injection molding and printing were two entirely separate production steps. What is new for MESTO: the printing unit now forms an integral part of the injection molding system.
The change happened after the injection molding machine previously used for making the pistons stopped working. This was taken as an opportunity to scrutinize the entire production process for overall efficiency.
“When walking through the production floor, I always keep my eyes open and think about which processes could be optimized effectively”, Sellmayr emphasizes. Here, she gets many valuable hints from WITTMANN, her supplier of injection molding machines and linear robots. The idea of having the printing process integrated into the injection molding cell was also raised during a joint factory tour, since the printing system used up to then had become somewhat obsolete as well. “We were immediately convinced that we could improve the efficiency and quality of the prints by optimizing the entire process and not just the injection molding side,” says Sellmayr.
Integrated on smallest possible floor space
The main challenge in developing the new integrated production process was extreme time pressure. Here, MESTO was fortunate that there was just a used, but still very young Insider production cell available for immediate delivery. It consisted of a SmartPower 80/525 injection molding machine with a linear robot and conveyor belt, so it was predestined for producing the piston pressure gages. MESTO seized the opportunity and commissioned WITTMANN to integrate a new printer solution.
WITTMANN’s Insider concept is already designed from start to finish for minimal space requirements and maximum efficiency. The protective housing is mounted right next to the conveyor belt. Temperature controllers or other components can be easily placed underneath. Compared to conventional solutions, the required production floor space is reduced by up to 50 per cent. At MESTO, WITTMANN succeeded in integrating the new printing station in such a way that it takes up hardly any extra space. It connects to the rear of the conveyor belt, and its depth remains within the grid dimension of the protective housing.
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Always on the lookout for optimization potentials: Élise Sellmayr (right), here together with marketing specialist Janina Behn. (Photo: WITTMANN) |
A four-cavity mold is used for production. At the end of each cycle, the WITTMANN linear robot removes the four pistons and deposits them on the vertical domes of a small transport carriage, which takes them to the three print heads. The pressure gages are printed on as they pass by. To this end, the domes rotate on the carriage so that the print heads can work all around them without changing their own position. Each piston is given two rings, one red and one black, plus a scale.
Following printing, the gripper of the linear robot picks up the parts again and places them on the conveyor belt. When pistons are manufactured for the ‘Pico’ series, which requires no marking, the printing station can be simply passed by. In that case, the robot places the pistons on the conveyor belt directly after demolding.
A complete work step saved
The injection molding process dictates the timing for printing on finished parts. The printing process must be fully completed within the cycle time. This is why the only feasible option was a direct print requiring neither pretreatment nor a long drying time. The print must not be blurred when the gripper picks up the parts again immediately after printing.
WITTMANN evaluated many different printing methods, colorants and suppliers. Pad printing was ruled out due to the required pretreatment, and many colorants did not pass the stringent durability tests. Wipe and abrasion tests were carried out with various solvents. For later on, when used inside the sprayers, the piston pressure gages can be exposed to aggressive media such as pesticides or detergents.
The final choice was an ink jet printer from Videojet, which not only delivered the best result in colorant durability, but also in terms of flexibility. “We are now able to print out very fine variations in the position of the scale”, says Sellmayr.
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The WITTMANN linear robot integrated in the Insider production system removes the pistons from the 4-cavity mold (Photo: WITTMANN) |
The trend towards process integration is on the increase – a trend that WITTMANN also observes among other injection molders. The aim in each case is optimal utilization of each system component’s capacities.
Especially robots often have free capacity for handling additional tasks during the injection and cooling process, such as printing on finished parts as done at MESTO.
“The more tasks the robot can take over inside the injection molding cell, the less labor input we have in the assembly”, says Élise Sellmayr. “The piston manometers leave the injection molding cell ready for mounting. By integrating the printer, we save a complete work step.” And that saves a lot of logistic expense, too, since the piston manometers were previously produced on stock first, and then printed later on.
Power consumption reduced by a third
SmartPower injection molding machines dominate the scene on MESTO’s production floor. Ever since the company started a comprehensive project in 2017 to increase its energy efficiency, old injection molding machines are being consistently replaced by servo-hydraulic SmartPower models. The high energy efficiency of the WITTMANN machines tipped the balance. “With the changeover, we immediately saw some first savings”, Élise Sellmayr reports. “Up to now, we have been able to reduce our power consumption by a third with the same number of machines.”
A further benefit: focusing on just one brand of machinery makes daily work easier for machine setters and operators. “They all get along very well with the WITTMANN control system”, says Sellmayr.
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To produce the pressure vessel tops, the piston rods are directly over-molded. The material processed is fiberglass-reinforced polypropylene. (Photo: WITTMANN) |
On our company tour, we have now arrived next to a SmartPower 180 injection molding machine. Pressure vessel tops are running off the conveyor belt, flat black discs with piston rods protruding from their centers. In a 2-cavity mold, the container lids are molded directly onto the piston rods. The material processed is a fiberglass-reinforced polypropylene.
An extremely compact arrangement of all components also catches the eye in this production cell. And here too, flexibility is an important issue. In this system, WITTMANN has integrated the feeding device for the metal rods to be insert-molded into the overall concept. The challenge for this system was to process various types of piston rods for different sprayer models, which were all to be fed in through the same magazine.
The piston rods come in varying lengths and diameters. There are rotationally symmetric rods and rod bars with wings and threaded sides, which must all be inserted precisely in a certain position. The material of the rods and consequently their magnetic behavior also varies.
All of these aspects had to be considered in planning the gripper concept. The task was further complicated by the fact that insertion of the metal rods and removal of the finished parts had to take place from the same side of the mold. Accordingly, all of the gripper’s functions had to be united on only one side, and that very compactly, so that it could still operate safely inside the open mold.
In all considerations concerning the gripper layout, the size and complexity of the resulting gripper and its efficiency in production were weighed against each other. In this way, all requirements could be accommodated on two grippers, with a fully automatic gripper changeover.
The ultimate goal in all projects is: “no overengineering!” For this would counteract efficiency, flexibility and easy operation. “In every new project, I let people show me what is possible and what new ideas are available”, Élise Sellmayr emphasizes. “Then we make up our minds about which innovation level makes sense. At the end of the day, these are all customized special machines that are only built once each. Precisely that makes it so exciting. “
Author: Susanne Zinckgraf, Head of Strategic Marketing, WITTMANN Group
