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GMT MOLDING

What is GMT material?

GMT material is the short name of glass mat reinforced thermoplastics. It is one of the composite that based on thermoplastic resin such as polypropylene or polyamide and reinforced by long glass fiber or continuous fiber. It is available as a plate sheet semi-finished product. The sheets are usually manufactured using a double belt press. Randomly oriented fiber mats made out of chopped or continuous glass fibers are impregnated with melted PP or with PP films in the film stacking process; they were being heated, pressed, and cooled into semi-finished composite.

The cycle time is short, cost of production is low, and material is stable and easy to storage. More important, it resistances to moisture and chemicals, and it also has low density compare to steel.So as soon as it was introduced into market back in 1960 due to its excellent hardness and rigidity, it becomes the most popular alternative material to replace metal in auto industry. Car flooring, seat frame, battery boxes, bumper beams, roofs, engineer cover, are typical products that made by GMT material. It is prized for the great strength and lightweight nature. In fact, the world first hybrid front bumper beam for automobiles was produced by GMT material back in 2014.

The GMT composite material has good dimensional stability and good impact resistance, so it is also used in logistics field, such as tray, pallet. GMT pallet can resist the higher temperature and its load capacity is also more than regular injection molded pallets.

How the GMT parts were made?

To build a GMT part, we will need both GMT raw material and GMT mold.
Because GMT is always being made as a plate shaped semi-finished product, so the GMT plates are delivered to the mold manufacturer in a component specific size. They were cut into certain size and shape in accordance with the product shape and size.

They will be heated in an oven and transferred to the mold by hand or automatic handing robot. When the mold opens again, the part is molded.

As the development of GMT goes, the raw material process can be integrated with mass production of GMT part. Two processes happen at the same time in the same assemble line. It avoids the pre-heating process of GMT molding, As soon as GMT materials were produced, before it get cold, place it into open mold immediately and mold the part right away to reduce the time and cost for production.

上图：上海韩华高新材料生产线

The GMT mold design and molding process allow thickness variation across the part, and allows preserving fiber length and maintains good mechanical properties compared to injection molding. In compression molding, GMT also faces increasing competition form new comers. One typical composite would be long fiber-reinforced thermoplastic, which also known as LFT material. What are the characteristics of LFT/D material and the difference between GMT? We will talk about it next time.

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