The Flowform flow-hole and thread-forming screw enables a fully automated joint that is accessible from one side. With its polygonal tip geometry, the Flowform screw forms a flow hole and a thread that can accommodate a metric screw in the event of a repair.

With the Flowform Plus, a further development of the established Flowform, the company is now responding to growing customer requirements. The automotive industry is focusing on weight reduction against the backdrop of ever decreasing_{CO2 emissions}. Thinner and higher-strength steels or aluminum are increasingly being used and mixed construction is on the rise. But the screw must also guarantee a reliable connection under changed boundary conditions. In short, the flow form had to be further developed to meet these new requirements.

"Depending on the sheet thickness, the application limit for joining steel applications with the conventional Flowform was a maximum of 600 MPa, with the Flowform Plus it is 1,000 MPa," says Heiko Miller. He is project manager for the further development of the Flowform Plus at Arnold Umformtechnik. Compared to the conventional Flowform, the dimensions have been reduced from 5 mm diameter and 20 mm length to 4 mm diameter and 20 mm length. Depending on the head and length, the conventional Flowform 5 weighs around 4 g, while the new Flowform Plus 4 weighs around 3 g. Extrapolated to the number of screws used in the body, this is significant: with 500 elements, the weight saving is 500 g with almost the same performance. In addition, the geometry of the flowform tip has been optimized and the heat treatment process adapted so that the performance of the connection remains almost the same.

Joining point validation provides safety

But when is the Flowform Plus the right joining element? Feasibility studies are carried out in the sheet metal joining laboratory using original material, for example. Here, the strength values for the bond and the limits for failure are determined. A joining point test goes into a little more detail: Here, the user has already defined certain material pairings. In addition to a recommendation, specific values are also expected here, for example which strength values are achieved at a joining point.

In principle, the Flowform Plus is designed for higher-strength steel sheets and thicker sheet combinations. "By using aluminum components, thicker joint combinations with several layers can also be created. In the past, this meant that the top and middle layers of three-layer joints were pre-punched. According to Arnold Umformtechnik, the use of Flowform Plus now allows thicker material combinations of up to 7.5 mm to be joined without pre-punching, depending on the joining materials," explains Miller.