Point-exact welding at SITEC avoids recall actions

SITEC industrial technology GmbH, Chemnitz has been active for years in the industry of special purpose machine building, among other things, within the range of the automobile and supporting industry. Apart from handling systems, assembly plants and testing facilities, special plants for laser welding processes are designed and converted.

From a complex setting of tasks for the laser welding of hydraulic transformed pipes arose new starting points for the employment of innovative technologies for accurate positioning of the adhered parts under the laser welding head during simultaneous examination of certain quality criteria. The logical consequence: the usage of an Omron vision sensor for the securing of a 100% manufacturing quality.

An emphasis of the automation of the welding process was the very exact positioning of the gap - joint between two pipes - of the later seam, with relatively large individual part tolerance. The usage of the vision sensor makes a flexible evaluation possible of different valuation criteria, which are of importance for the welding process.

Multi-axes control

After inserting and stretching the individual work pieces these are positioned 'more or less' under the camera by a multi-axis control. The device is equipped with a telecentric objective to ensure as large a depth sharpness as possible with a view field of 1.2 x 1.0 mm and is installed at a distance of 200 mm. A red LED spot with integrated lens system serves as background lighting. This provides sharp illustration of the contours and creates uniform measurement conditions during the period of the inspection.

During this the following evaluations are made in the image field:

• Height misalignment of two work pieces
• Number of columns (monitoring of the surface roughness/evenness)
• Gap width at the top margin
• Gap width 0.4 mm under top margin
• Gap depth, identifying of open gaps
• Relative side misalignment (computed gap center) to the laser

As result, measurements of all criteria in the permissible range of tolerance of relative side misalignment are emitted in 1/100 mm by a communication interface to the super ordinate control and the positioning procedure is initiated. In the event of an error, digital exits are activated for the determination of the source of error and this is brought over to a control terminal as announcement.

To convert over all tasks comfortably and to place different measuring windows on the basis of purposeful characteristics, a PC software composer was used. Via the integrated graphic parameterization and a revalued operating system, one receives an even larger range of functions, which also lets appear complex solutions in the configuration as a clear flow chart.

But there was still a second setting of tasks to solve in the framework of the machine concept. Technologically it can come to a plasma development attributable to a too high energy entry during the welding process. This turns around the process into a cutting process, becomes noticeable by a color change of the flame and in the long run leads to the production of faulty pieces. To indicate this incorrect condition to the operator the welding process is supervised by means of a colour sensor. It is designed as passive sensor and registers deviation in brightness and chromatic spectrum during the welding process.

Trouble free since October 2000

Trouble free since October 2000 The advantages are obvious. Complex solutions do not always have to be expensive, the targeted usage of innovative inexpensive solutions have also in this case with highest requirements led to a quality assurance. And so is also the co-operation between Mr. Wollmann (SITEC) and Mr. Ring (Omron) rewarded by success in the long run. After targeted test runs and a successful sample phase the plant runs trouble free since October 2000.