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Technical article: Molding and welding within the mold

In collaboration with Hummel-Formen and KVT Bielefeld, Engel sets the path for a new kind of process integration. The "joinmelt" process supports hot gas welding directly in the mold. Besides cost savings, it is said that the new process also improves part quality and functional safety.

ENGEL

July 3, 2014

4 Min Read
Technical article: Molding and welding within the mold

In collaboration with Hummel-Formen and KVT Bielefeld, Engel sets the path for a new kind of process integration. The "joinmelt" process supports hot gas welding directly in the mold. Besides cost savings, it is said that the new process also improves part quality and functional safety.

Oil lines and reservoirs are typical examples for hollow composite parts which are conventionally produced using a multi-stage process. In the first stage, the two part halves are injection molded and then, in a second process step outside of the molding machine, they are welded together. This multi-stage process usually requires concessions to part quality. The commonly used vibration welding can lead to flashes along the welding seam. Ultra small particles, so-called "flitter," may appear and peel away, leading to the damage of further functional parts. Using the hot gas welding process would allow a clean and homogenous welding seam, but this process requires absolute plane-parallel joining areas which injection molded parts do not always offer. There is usually a certain degree of warpage during the cooling phase and ejection of the part.

The "jointmelt" process

The "jointmelt" process combines everything in one: injection molding is followed by the welding process, inside the molding machine, without the need to remove the two halves of the part as an intermediate step. This solution, for which a patent is pending, promises potential savings, especially in the automotive industry. It removes the need for additional welding equipment, and part removal and re-insertion are no longer needed, as the finished product can removed directly out of the mold. 

For this process, both halves of the component are injected simultaneously into a single mold. After the cooling phase, the mold is opened; with one half of the part staying in the left half and the other in the right half of the mold. The movable left half of the mold is now positioned so that both parts are opposite each other in the welding position. The heating element is positioned between the cavities and the edges of the component halves are heated. The mold then closes, and the two parts are bonded so that the finished part can be removed when the mold re-opens.

Improving quality and functional safety

Besides the savings potential achievable due to the integration of two manufacturing steps previously performed in sequence, the new process also helps to improve the quality and functional safety of the parts. The fact that both product halves remain fixed in the mold during the welding process avoids issues with warping, and considerably reduces the time to market. The process creates a clean and thin weld which is particularly strong and achieves a superior quality to welds created by legacy techniques with respect to bursting pressure.

According to the company, this new technology is suitable for all thermoplastic materials.

The process developers also see potential for the processing of glass fiber reinforced polyamides as fluid distributing parts for use in engine compartments. In current molding practices these components have always had a visible bulge at the joint, making them prone to friction and reducing the service life of other functional parts, such as the valve tappets. As there is no bulge with the "joinmelt" process, there is additional savings of material and weight. Yet another benefit becomes apparent early in the development phase of new products: freedom of choice with respect to part geometry, as there is no need to take a specific welding direction into account.

Teamwork with specialists from welding and mold technology

Engel developed this new technology in cooperation with two partner companies. The injection molding machine manufacturer has taken responsibility for developing both the machine technology and the software for controlling the integrated process workflow. Hummel-Formen in Lenningen applied for a patent for hot gas welding in the injection mold and has contributed its mold technology know-how to the collaborative project. KVT Bielefeld was responsible for the welding technology in the "joinmelt" project and holds a patent for hot gas welding in a protective atmosphere to ensure a particle-free and highly stable weld. 

Editor's note: The opinions expressed are those of the author.   

www.engelglobal.com

Hummel-Formen

The company employs 250 people at two facilities and is specialized in injection and compression molds for plastics with weights of up to 100 tons. Its service portfolio covers everything from product development through to sample making under volume production conditions. (www.hummel-formen.de)

KVT Bielefeld

The company is specialized in the development and production of plastics welding machines for use in various industries from automotive and domestic appliances through to telecommunications and medical technology. (www.kvt-bielefeld.de)

ENGEL_joinmelt_en.jpeg

Injection molding is followed by the welding process without needing to remove the two halves of the part in an intermediate step. (photo: Engel) 

FB_joinmelt_Bild_1.jpeg

The joinmelt method shows potential when processing glass-fiber-reinforced polyamides for leading components in the engine compartment, such as oil separators. (Photo: KVT Bielefeld) 

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