Highly innovative welding system for forklift frames and overhead safety guards by Linde MH

Next generation of robotic welding

Following a planning and implementation phase lasting several years, Linde Material Handling (MH) has put into operation a highly automated robot welding system for the production of forklift frames and overhead safety guards. The project shows how a broad variety of variants with demanding quality requirements and economical series production can be combined in continuously automated manufacturing. As a general contractor, welding technology expert Yaskawa focuses on pioneering robotics and the innovative Yaskawa Production System YPS.

Industrias
Logistics
Metal

Cliente
Linde Material Handling

With the 1251 series, Linde Material Handling – one of the world's largest manufacturers of industrial trucks – has replaced the successful 386 series. The new three- and four-wheel electric forklifts in the load range of one to two tons set standards in their class: they are compact and powerful, and manufactured in a wide variety of variants. For each model, the user can choose between lead-acid or lithium-ion battery. The basic design is also prepared for fuel cell operation.

The variance is even greater for the overhead safety guards manufactured in parallel on the plant and then “married” to the frame. The new tack welding equipment must produce seven frame types and 14 different safety guards – in large quantities, according to the highest quality standards and with a very high degree of automation. At the same time it should offer great flexibility, since each forklift is manufactured to order. In addition, Linde MH planners wanted sophisticated inline quality assurance and a fully automatic spot repair station.

Wanted: competent general contractor with robotics expertise

At an early stage of facility planning, Linde MH was faced with the question: With which partner can such a technology project be realized? Christopher Taupp, Project Manager Industrialization Projects at Linde MH: “In order to efficiently plan, implement and commission a system of this complexity it was crucial for us to find a partner who combines comprehensive manufacturing and automation expertise with a high-performance project organization.”

The positive experiences from a previous successfully implemented forklift project also played an important role in the selection of the system partner. Already at this stage, Linde MH was able to convince itself of Yaskawa’s welding and automation expertise.

In addition, with the Yaskawa Production System YPS Yaskawa has a groundbreaking platform that makes all data from complex welding systems transparent, thus enabling optimal control of production processes.

Picture: View of the module with the welding stations – and the visualization generated by the Yaskawa Production System (YPS).

Automated welding processes with a total of 33 robots

The facility is divided into two modules. In Module 1, the different frame types are tack-welded into a complete component at so-called GEO stations. Module 2 has a dual task: the previously tack-welded frames are finish-welded in redundant welding cells. All types of safety guards are first tack-welded at a GEO station and then finish-welded.

Christopher Taupp: “The division into two modules is due to structural constraints. It also offers the advantage that we are able to provide a buffer between the two main processes. This brings us additional flexibility.”

The first module consists of several highly complex fully automated GEO tack-welding stations with both manual and automated material provision. A total of eleven AR2010 welding robots, divided into twin and triple stations, handle the tack-welding tasks. The material transfer from individual parts to the finish-welded frame is carried out by two GP600 handling robots with fully automatic gripper changing systems mounted on a joint floor track system. The gripper changing stations are located to the right and left of the roadway. This saves space and permits changes “in passing.”

Picture: Among the innovations first implemented by Yaskawa for Linde MH is robot-assisted polishing.

Wide variety of variants, great flexibility

In the second module, robots at five stations take over the welding out of the frames stapled in Module 1. Yaskawa robots of the AR2010 series with an internal hose package are also used here. As in Module 1, a Type GP600 handling robot mounted on a floor track is responsible for component handling between the individual stations.

Before the components are fed into the automated inline measurement, they pass through a two-story circulation cooling section. Two floor track-mounted GP600 handling robots are also used. In addition, the overhead safety guards in this section are tack-welded, then finish-welded. Here again, two GP600 handling robots on a seventh, floor-mounted axle feed the individual parts from the automatic provisioning stations.

A total of 33 robots – divided into welding and handling robots – are used. The system is designed for a series cycle of 12.5 minutes and enables a high degree of variant flexibility in the production of frames and safety guards. The system planners also had to consider the aspect of flexibility over the lifetime of the plant: in future there will certainly be new variants to be integrated into the production flow.

Picture: At the end of the line, the safety guards are “married” to the corresponding “made to order” frame.

Challenge: jig design

The design of the complex jigs that form the foundation for the automated processes was particularly challenging. One example is the tack-welding jig for the overhead safety guard. The latter must cater for all 14 variants within a single fixture. This means that a variety of setup states must be taken into account, combined with a high number of hydraulic clamping circuits.

In addition, besides precise fixing of the components, the jig must meet the requirements of the automated handling and welding processes. Taupp: “The combination of variant diversity, complex clamping technology and automated process chain makes these jigs among the most demanding elements in system planning.”

In the process directly after welding, Yaskawa – as a globally recognized specialist in automated welding – was the first to implement a remarkable innovation: fully automated inline polishing. A robot works on defined areas of the welding assemblies using abrasive tools such as a cup brush to remove welding spatter, silicates and smoke deposits, thus readying the surface for subsequent CDC coating.

Picture: Especially when tack-welding, the jigs are very complex. The robot, on the other hand, appears very slender.

Groundbreaking, user-friendly inline measurement

At the end of the manufacturing process is a fully automated inline measurement process. First, the assemblies – as a combination of frame and associated safety guard – are comprehensively measured with geometric accuracy, and all values compared with the target values. In addition, a weld seam check is carried out, during which the length, position and seam geometry are measured, and irregularities such as pores or end craters are detected. All collected data is clearly assigned to the respective component ID and documented. The data is simultaneously displayed on two monitors – one for each measuring system.

Christopher Taupp explains the complex manner in which this measuring cell alone is integrated into the overall production process at the data and control level: “We have four welding stations in the system for all frame types. Slightly different welding results – always within tolerances, of course – are obtained in each station. The measuring cell has its own measuring program for each product derivative and each welding cell. This in turn results in a further increase in the variety of variants.” Is this high investment really necessary? “Yes, it’s an essential part of our quality concept. The measurement data allows us to identify trends and deviations at an early stage, and to optimize the processes in individual welding cells.”

Picture: The jigs in the tacking and welding stations are complex, and the process is clearly visualized at each station.

Transparency and connectivity with the Yaskawa Production System

The entire plant is connected to Linde MH’s ERP and MES system via the Yaskawa Production System (YPS). This ensures a consistent flow of data. The current status of the process is displayed on large monitors at each cell. This is particularly helpful for those cells that are manually fed with components. Taupp: “The operator sees every order and every component here and receives all relevant information for correct insertion.”

In the event of a malfunction, a tablet connected to the control system provides a detailed insight into the system structure down to individual hydraulic blocks and valves. This allows the cause of errors to be identified and instantaneously corrected. Especially during the commissioning of the system, this function has proved to be a valuable support and contributed significantly to the efficient optimization of processes.

In addition, a reporting tool integrated into the Yaskawa Production System displays all current data up to OEE (Overall Equipment Effectiveness) on large screens in the hall. This also serves to ensure a stable process and to detect irregularities at an early stage.

Picture: Yaskawa Production System (YPS)

Joint planning over four years

The experts from Linde MH and Yaskawa worked closely together over the entire process, that took almost four years from the initial concept phase to commissioning. Taupp explains: “Thanks to the simulation tools used by Yaskawa, we were able to virtually walk through the facility at an early stage of the project and evaluate various layout variants using data glasses. This enabled us to optimize the system concept at an early point and make important decisions on a sound basis.”

The real plant was initially built at the Yaskawa facility in Allershausen. Together with the experts from Linde MH, the devices were put into operation and extensive tests carried out under series conditions. Linde MH employees had already manufactured pilot and start-up series of forklift frames and safety guards at the facility. Delivery approval was only granted after completion of this test and optimization phase lasting several months. This was followed by dismantling, transport to Aschaffenburg, reconstruction and final commissioning. Today, the plant produces reliably in series operation and meets the exacting requirements for quality, productivity and flexibility.

Taupp draws a positive conclusion: “Yaskawa already convincingly addressed our requirements in the concept and offer phase, contributing a high degree of welding automation know-how. Due to the complexity and scope of the project, it was important to us to have a partner who can assume overall responsibility and efficiently coordinate all trades. In Yaskawa we found a reliable general contractor who has consistently implemented our requirements, from planning through implementation to successful commissioning.”