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Robotics Case Studies

DeltaSpot: the Modern Solution to an Age-Old Problem


Welding is a technique almost as old human civilisation. Archaeological finds show that in the fourth millennium BCE, forge welding and soldering were already taking place.

After a five-year development period, we are now in a position to present a solution to some of the problems encountered in resistance welding.

Its name is DeltaSpot.

What is behind DeltaSpot?

DeltaSpot combines a multitude of innovations in the fields of mechanical components, control software, quality monitoring and – last but not least, and indeed most importantly of all – in the field of spot-weld processes.

A process tape is used to stabilise the welding process and achieve reproducible results across high numbers of consecutive spot welds.

The basic concept of this process is not entirely new; in fact it has patents that date from the last century. What is new, however, is the way in which Fronius has combined these old technologies with new ideas.

What advantages does the process tape offer?

Electrode protection

The electrode's contact surface has a significant effect on the welding result. If this surface is characterised by erosion, by build-up of the material to be welded or by sticking of the coating components, then the process will become unstable.

With Delta Spot, electrode tips like the ones shown in the picture are a thing of the past.

The process tape, which runs between the electrode and the material being worked on, prevents this wear-and-tear on the electrodes. Any build-up and coating residues are simply carried away by the process tape, and a new section of tape, with clean surfaces, is spooled over the electrode ready for the next weld.

A clean contact surface means: Long electrode service life, consistent welding conditions, no surface spatters.

Control of the heat balance during welding

The use of a process tape results in noticeable changes in resistance. The resistance situation with a standard resistance welding system is shown in blue, while blue+red shows the situation with DeltaSpot. This increased resistance can be adjusted by changing the material, thickness or coating of the process tape. This additional parameter can be used, for example, to increase the heat generated during the weld process, leading to a reduced current requirement for aluminium welding and to the possibility of influencing the welding-lens position in 3-sheet or multisheet welds and bimetal joints, e.g. between steel and aluminium.

The following simulations of the DeltaSpot process illustrate the difference between welding with and without a process tape. The key aspect here is the thermal input from the process tape during welding.

Economic use of special electrodes

In manufacturing, there will always be problems which cannot be resolved with standard equipment. For reasons of accessibility, sometimes special arm geometry or even a special electrode is needed. But how are these special electrodes serviced, and how long is the electrode life? Is there anything that could be changed or improved upon here? This is where the process tape really comes into its own. As the electrodes are protected from soiling, the problem of milling the electrodes no longer arises.

Among the special features of the DeltaSpot system:

• Fronius X-plorer as the basic software for control and operation.

• DeltaSpot Q-Master for documentation and online observation of the welding spots.

Modern design and many innovations in drive technology.
Fronius X-plorer

The DeltaSpot Control, which is responsible for controlling the process parameters and the whole welding system, is based on the Fronius X-plorer. Thanks to its clear graphic interface and self-explanatory menus, the welder is ready to start adjusting the parameters set by the DeltaSpot system after just a few minutes.

The DeltaSpot Q-Master makes use of the fact that every weld leaves a characteristic print (like a fingerprint) on the process tape. This imprint is recorded by a small camera located on the electrode arm, and then assessed by a learning-capable image processing algorithm.

When using aluminium, we are able to define the position and width of the welding lens to within a few tenths of a millimetre.

Excellent examples of DeltaSpot utilisations

With aluminium:

• Two-(or more)-sheet spot-welded joints

• Thin aluminium foil

• Steel-aluminium spot-welded joints

With steel:

• Two-(or more)-sheet spot-welded joints

• Thin foils or tapes

• From soft- to ultra-hard-coated steel

• Coatings and materials which present problems in conventional spot welding

Using different tapes on each electrode with DeltaSpot makes it possible to control the position of the weld nugget.

H400 DX53 D+Z140MB DX56 D+Z140MB 

Resistance welding was only made possible with the advent of electricity and was first demonstrated by James Prescott Joule as a possible process for joining metals in 1857. Elihu Thompson carried out the critical research for the discovery of resistance welding around 1877. During the following year Nicolai Bernados developed a resistance welding process involving carbon electrodes. Resistance spot welding with copper electrodes was developed by Kleinsmith in 1897, signalling the start of the industrial breakthrough of resistance welding. Around 1910, resistance projection welding and resistance rolling stitch welding techniques were developed. Since 1930, resistance welding has been widely used in industry. Since then, developments in automobiles and resistance welding have been closely linked. For more than 125 years, resistance welding has been an important part of the industry. In the realm of automated welding it retains great popularity because of its simplicity and high level of safety.

All the important developments over the last few decades – from servo-operated spot-weld guns to mid-frequency inverters all the way up to adaptive process control devices – have brought with them many different benefits.

Only a few problems remain unsolved, representing a constant "thorn in the side" of the development of resistance welding.

Among these unsolved problems are the shunt effect, the fitting accuracy of the parts, variations in the base material or variations in the thickness of coatings, and so on.

Take the problem of electrode wear, for example. A great deal of effort has gone into the development of electrode materials or coatings, with no real success.

Even the newest developments in materials, the increasing number of material combinations and new coatings have not managed to resolve the problem. If anything, they have even made it worse!

The solution to some of these problems could be "DeltaSpot"

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