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In places that sell a lot of draught beer, a large beer tank is often a good alternative to casks or kegs. Duotank is a global player in that market, and in Waalre in Brabant (NL) it produces more than 1,500 beer tanks of varying dimensions per year. Besides semi-automated welding of lids and bottoms on the tank, the manufacturer has been using a welding robot for some time. Mark Cox, Manager of internal projects and aftersales, talks about what that did for production.

Duotank

Duotank welds beer tanks error free thanks to Arc-Eye seam tracking system

Duotank builds stainless steel and copper beer tanks with a content of 250, 500 or 1,000 litres. The beer tanks consist of an internal and an external tank with cooling pipes in between. Both tank parts consist of a lid, shell and a bottom. The shell part is rolled in-house to the required diameter, the lid and bottom that are supplied by third parties are welded onto it. The internal and the external tank are welded on both sides at the same time with a semi-automated TIG welding process.

The challenge is tracking the weld seams in the former welding sequence

The lid and the bottom elements are both pressed parts and are never cut 100% centred. For welding that means dealing with a welding trajectory that is not consistent and with a risk of gaps between shell and lid. As only one side is controlled digitally, the communication between both sides is a restricting factor. “The operators needed to observe the weld-seam tracking system painstakingly with a screen. For that reason, the seam-tracking system on the semi-automatic is not quite what we expected,” explained Mark Cox.

Welding robot with seam-tracking system solution

So, Duotank started looking for a different system with a camera that tracks the weld seam exactly and in real-time, that is user-friendly in operation and requires minimum setting time. An investigation of the market produced three potential suppliers where Duotank had tests performed. Mark Cox continued “We had a good feeling about the results achieved by Valk Welding with the Arc-Eye seam-tracking system. That system has been developed much further than the other systems that are available in the market. It gave us confidence in the success of the entire project.”

Real-time weld-seam tracking with ARC-EYE

The Arc-Eye weld-seam tracking system consists of software and a rotating scanning laser sensor camera that is fitted in front of the welding torch. Laser sensors are the only systems that can track the weld seams in real time during the welding process, without adverse effects of reflections on stainless steel, aluminium or copper. This laser sensor scans the weld seam at a high frequency and the software corrects every deviation in the position of the weld seam. The Arc-Eye laser sensor produces an exact offset and that makes it the most accurate weld-tracking system, whilst facilitating greater accuracy and higher welding quality.

Better to have a slower process and good quality than the other way around.”

Mark Cox

Internal tank next phase

The external tanks are now welded by the Panasonic TL-1800WGIII welding robot in quantities of 60 tanks per week. Those quantities are also achieved, because the system is fitted with 2 workstations on a torsion-free H-frame, to ensure the welding robot is not idle when the workpiece is changed over. Now welding the external tank has been fully automated successfully with the new welding-robot system, the first tests for welding the internal tank with the welding robot are now being realised.

First time right

The speed at which the tank rotates during welding is crucial to the quality. “Where the semi-automatic welds with high Amperes and speed, the welding robot welds at 80% of the Amperes and about half the speed. This greatly reduces the risk of errors, so it is better to have a slower process and good quality than the other way around. With the new welding-robot system the products are first time right, and final processing is no longer required,” concluded Mark Cox.

Ensure proper welding preparation

Mark Cox commented “The robotised welding process requires accurate preparation. Bottoms and lids need to be of the same height anyway. Furthermore, the tack welds need to be kept as small as possible. The stainless steel external tanks are TIG welded without wire. It is essential to change the TIG electrode on time.”
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