ã€China Aluminum Industry Network】 Abstract: With the development of aluminum profile technology, the quality requirements for aluminum profiles are getting higher and higher. This article explains the concept of aluminum profile plane quality, the concept of plane clearance and flatness, and the relationship between the two. Keywords: Deviation, Plane Clearance, Flatness With the development of aluminum profile technology, the quality requirements for aluminum profiles are also increasing. The flatness of the profile plane is one of the required quality indicators. The requirements for the aluminum profile plane are stipulated in the aluminum alloy building profile standard GB5237, and the plane gap in the product size deviation is the requirement for the plane. Plane gap refers to: the 25mm long ruler leans against the concave surface of the profile in the width direction, and measures the large gap value (F1) between the ruler and the concave surface of the profile. The value (F1) is any 25mm width of the profile. Plane gap; the ruler with a length greater than the width of the profile is leaned against the concave surface of the profile and the larger gap value (F) between the ruler and the concave surface of the profile is measured. As shown in Figure 1, the value (F1) is the profile in the Plane gap over the entire width. Plane gap is what we usually say flat surface, the smaller the gap, the flatter. The index of the plane gap is the size requirement of the section, rather than the shape (shape), as shown in Figure 1. What about the overall shape? In the standard, the degree of bending and twisting are specified. See Figure 2 and 3. The gap values ​​h and T in the figure are as small as possible. If it is 0, it means that there is no distortion. Of course, this is a theoretical result, and in fact there must be deformation. So there is no specific term describing the unevenness of the overall product, and there is flatness. Flatness refers to the deviation of the macroscopic relief height of the substrate from the ideal plane. The tolerance zone is the area between two parallel planes whose distance is the tolerance value t. As shown in Figure 4, the product's flat surface is uneven and is placed on the datum plane. The lower point is on the datum plane. The distance from the higher point to the datum plane is the flatness. Relative to the previously mentioned plane clearance, bending degree, and twist degree, the general understanding is that flatness is a comprehensive embodiment of plane gap, bending degree, and twist degree. Nowadays, on the market, industrial products are marked with flatness on product drawings because of the particularity of their use, which places higher requirements on the product quality of the profiles. Lear Aluminum Company's products are aluminum template series products and computer board series products, the flatness of 0.4mm to 1.0mm range, see Figure 5. It needs to be mentioned that the flatness of the product is originally mostly used for the precision requirements of machining, and there are few fields for using extruded aluminum. Products with flatness requirements usually have shorter delivery lengths than architectural aluminum profiles, such as computer board profiles, with a delivery length of 362 mm.