Composite five-door is generally hot composite structure. Most manufacturers door core material into two: one for Chinese fir timber; two for the perforated plate.The first Chinese fir timber manufacturers are most often used in the keel structure, and a lot of people would think as long as the keel is not good, that is core to do, this is only a one-sided argument that there is hollow keel place is not good, are jerry-building, is not true. In fact, the use of the keel is more scientific and reasonable, each object has his performance, by the surrounding environment factors such as temperature changes, wood will Expansion and Contraction . Keel room is not easy to deformation, and indeed the whole of the door core material is easily deformed, because it does not void; have one point from a mechanical perspective, the keel structure, reduce stress, but also a kind of deformation good measure.