More than 20% material savings is only one of the numerous advantages of stitch bead in comparison to a common bead application. Learn how you can push the productivity, safety and quality of your hybrid joining process to the next level – all while lowering your total cost of ownership.
April 21, 2020
At times of lightweight and multi-material design, hybrid joining is one of the major trends in automotive body shops. With hybrid joining, high-strength adhesives for structural bonding are combined with other joining technologies like spot welding, flow drill fastening or self-pierce riveting. This offers major benefits:
The combination of adhesive dispensing and other joining techniques poses many challenges. At welding or rivet spots, adhesive material can get squeezed out. This leads to material waste and rework. When used with spot welding, the adhesive is destroyed by the heat of the welding process, and this can lead to the emission of toxic fumes. On top of that, a higher welding current is required, and the system needs more time to weld through. Common error patterns:
Atlas Copco offers an application pattern that is especially developed for hybrid joining to resolve these challenges. The so-called stitch bead is an interrupted application with defined material gaps at the weld areas that offers numerous benefits:
|Bead diameter||3 mm|
|Adhesive gap||12 mm|
|Material savings per spot:||0.15 cm * 0.15 cm * 3.14 * 1.2cm = 0.0848 ccm|
|Material savings per side panel (98 weld spots):||98 * 0.0848 ccm = 8.3 ccm|
|Material savings per car body:||2*8.3 ccm = 16.6 ccm|
|Material savings per day (1000 car bodies):||16.6 ccm * 1.355 g/ccm = 22.5 kg|
|Cost saving per day:||22,5 kg * 14 €/kg = 315 € (side panels only)|
|Cost savings per year:||315 € * 225 = ca. 70.875 € (side panels only)|
The advantages of stitch bead in hybrid joining are exceptional compared to common continuous bead applications. Nevertheless, there are significant challenges in the application process regarding robot speed and application flexibility. High volume production lines require robot speeds of up to 500 mm/s and more. At the same time, car geometries get more complex. Bead and gap sizes must be freely definable – and need to be applied precisely and reliably to the car part. But switching times between robot, system control and applicator delay the response of the valve needle that opens and closes the nozzle. This is where common application systems reach their limits.
Example: required switching times at a robot speed of 350 mm/s:
Teaching via robot control
In many industrial dispensing systems, the stitch bead has to be programmed via the robot controller, entering the bead length and gap length manually. The switching time must be matched with the robot speed, otherwise the length of the bead and the gaps are not equivalent to the mm specification. This requires a high programming effort, resulting in higher costs.
Realization via system control
Modern industrial adhesive dispensing systems from Atlas Copco´s SCA product line offer a special software for stitch bead applications. The bead and gap lengths can be entered directly into the application control system. The robot control only starts the application with the “applicator open” signal. The controller autonomously triggers the valve according to the specified bead and gap lengths and the robot speed. The feedback is performed via a position sensor and is included into the calculation. The robot programmer has only to control the application speed, start signal and the robot path. All other signals for the applicator are handled within the application control.
Benefits of software-based programming:
The stitch bead is a true problem solver in hybrid joining, especially when combined with spot welding. With material savings up to 20%, significant cost savings can be achieved, along with many other advantages that boost your productivity, safety and quality – and reduce your total cost of ownership. But robot speed can be a challenge in the application process. Considering the high requirements coming from the industry, many common dispensing systems reach their limits. Atlas Copco has developed a special high-speed applicator to reliably perform robot speeds of 500 mm/s and more. At the same time, the dedicated software reduces programming efforts.