Case Schuitemaker Machines
Offline programming not only for efficiency – but also for quality!
Schuitemaker Machines located in Rijssen, Netherlands is welding agricultural equipment at three arc welding robot stations. There are two older CLOOS stations and a new big Yaskawa twin-robot welding gantry with multiple external axes. All the robot programs for both CLOOS and Yaskawa are created offline using Delfoi ARC, generic OLP software. Offline programming is applied normally when a company wants to keep the robot uptime high. Besides increased productivity, Schuitemaker is also achieving better welds of consistent quality. Even the accuracy in offline programming was exceptionally good. The greatest measured error was only 3 mm. The software commissioning was realized by Defloi’s expert partner in the Netherlands, LAC.
The welding process
Schuitemaker Machines invested in a big Yaskawa robot gantry with two arc welding robots to be able to shorten welding time for the large lower and upper frames of agricultural wagons measuring up to 9 metres in length, 2.55 metres in width and 1 metre in height. There is a 12-metre single-axis ‘grill’ positioner for wagons. At both ends of the robot station, there are two L-positioners capable of handling components up to 3.6 metres in diameter and weighing up to 3,000 kilograms. Before the twin-robot welding gantry was acquired, the wagons were welded manually: two welders did tack welding for two hours and two more completed the welding in four hours. For one type of frame, preliminary results show that the twin robot system completes the welding in only one hour and ten minutes. For this frame type, this means a welding process that is four times faster than before. When the robot station has been in use for a longer period, more statistics for welding times for a variety of different products will be available.
Shorter lead times, more capacity means more revenue
Schuitemaker is constantly developing new products and also moving existing manually welded parts to be welded by the robots. If the robot programming had been accomplished with conventional online teaching, this would have increased robot down-time significantly. The robots would have remained idle during the programming time, and no new wagons or any components would have been produced during that time. One hour and ten minutes of welding time would have been lost if the robot station had been stopped for programming for at least one full week.
The company decided to apply offline programming (OLP) software to avoid production stoppages due to programming. This means that robots are able to weld the products, while new programs are created and simulated offline. High robot uptime means shorter lead times, more capacity and thus also the ability to sell more end-products. It also means increased revenue for Schuitemaker.
All the welded assemblies and components are modelled using 3D CAD software. These models together with fixture models are the starting point for offline programming. A robot programmer reads the product model with fixtures into OLP, creates the welds in the right welding order, simulates the program, for example for collisions and joint violations, and downloads the verified program to a server PC to wait for execution on the robot station, CLOOS or Yaskawa.
Picture. CAD-based, parametric Delfoi ARC software effectively utilizes CAD features and symmetry. Features like cloning and mirroring welds with automatic calculation of external axes values support product families very well, as at Schuitemaker.
Sander Oude Vrielink, mechanical engineer and IWT at Schuitemaker Machines, says that it took one full week to create a welding program offline for the first time for a frame with a welding length of 7.5 metres, and it took 80 searches. Programming two robots at the same time makes programming much more challenging than programming one robot. Avoiding collisions and exceeding joint limits require constant simulation checking. Mr Oude Vrielink estimates that the programming time for the second frame will be 50% shorter as the programming procedures stored in the WPS are available for re-use. Before starting welding with the robots, the programs are checked on the shop floor, but no manual touch-ups are made there. All the required program modifications are done offline, so the offline program is always 100% the same as the online program.
Wagon side panels measuring two times one meter are welded at the two CLOOS stations. The down time is already halved due to offline programming.
When asked about the ease of programming and Graphical User Interface (GUI), Sander Oude Vrielink says that “when you are getting used to it, it is easy. For operators, CLOOS is easier, but Yaskawa is not that easy due to its twin-robot system. One strong point of the GUI is its icons, which make it very easy to use and help the operators to use the software.”
Better and constant quality
Before, when we used online teaching for the CLOOS stations, “on Monday the quality was different to what it was on Friday for example. Each robot operator used their own welding values. Also in manual welding the quality was changing,” says Oude Vrielink.
Now the welding quality is high regardless of who is programming. The welding values are stored in a database. The database contains welding jobs of all the standard welding types and positions for Yaskawa 128. Only for the ‘special’ types and positions WPS files are still needed to complete the database. After this work is done and the welding values are in the WPS, there is no longer any need for prototypes when the plate thicknesses are the same and the welding types, positions, torch angles and wire lengths, etc. are also the same.
The software commissioning
The software commissioning was realized by Delfoi’s expert partner in Netherlands, LAC. LAC is a professional organization specialized in robot welding. The commissioning work included
- robot work cell modelling: both two CLOOS stations and the big Yaskawa gantry
- robot work cell measurements and calibrations
- training of Schuitemaker personnel
An acceptable result in robot accuracy (absolute accuracy) for complex and large robot stations is about 10 millimeters. This error is compensated for in the welding process by applying seam search and seam tracking. Ten millimeter accuracy is not sufficient for Schuitemaker. “On plates we aim to use searching as little as possible. We only use searching on square tubes because they are inaccurate,” says Sander Oude Vrielink and continues, “we use seam searching and seam following for both CLOOS and Yaskawa, nozzle search for CLOOS and wire search for Yaskawa."
In calibration measurements, LAC applied the welding robots themselves as the measuring apparatus. No external device such as a Leica Laser Tracker was used. The calibration algorithms in Delfoi ARC software support the robot measuring method.
Achieved accuracy in the Yaskawa station is excellent, between 1 mm and 3 mm:
- the greatest measured deviation in L-positioners was only 1 mm in every single position of the manipulator
- the greatest error along the full length of the 12-metre single-axis positioner was only 3 mm
“Implementing offline programming software with such a big robot installation is a challenging work. This is what we normally do ourselves. The Schuitemaker project has proved that in Netherlands, and why not for the projects in other parts of the world as well, we have now an expert partner to be able to fully deploy the software," says Heikki Aalto, EVP, Delfoi.
About Schuitemaker Machines
Schuitemaker has been developing, producing and selling agricultural machinery for over 95 years in the areas of fodder production, feeding and manure spreading. Besides the agricultural branch, Schuitemaker also offers a total package of winter solutions for the Dutch market.
More Information: Schuitemaker
LAC is an independent foundation connected to the University of Twente. LAC fully supports Delfoi Arc system integration for all robot brands, such as ABB, Cloos, Yaskawa and OTC.
LAC also offers training in Delfoi Arc and feasibility studies based on this software. LAC has an integral partnership with NIL (The Dutch Institute for Welding technologies, IWF), so the organization can provide robot welding certification as well.
More Information: LAC