April 07, 2020

Formability of beryllium copper strip

Formability involves the material being able to bend into the desired geometry. There is no crack or failure to complain about an ability. Beryllium copper strip moldability depends on a number of variables, including alloys, state, bending direction, the strip thickness and width, and a molding method.
The unheated beryllium copper (Brush, Alloys 3, 10, 25 and 165) is the easiest to shape during the manufacturing process, and the finished parts can be heat treated to a very high level of strength. Excellent combination of formability and highest strength. In the field of use where intense molding is not required, factory-strengthened beryllium copper alloys (Brush, Alloys 165, 190, 290, 3, 10, 174) are the most cost-effective, and these materials are heat-treated by Brush Wellman. The optimum formability is ensured under the condition that the strength level is satisfied, and since the customer does not need cleaning and heat treatment after the parts are formed, they can effectively reduce the manufacturing cost.
R/t Ratio The ratio of the formability (R/t) of a material is expressed by the ratio of the bend radius (R) to the strip thickness (T). This value determines the small bend radius that can be formed without failing. A larger R/t ratio indicates lower formability. Because of the large bending radius required. Thus, when the R/t value is not zero, it means that the material does not fail around a sharp corner (zero bend radius). As far as the ductility of a material is concerned, the formability mainly depends on the strength of the alloy. When the strength of the alloy is increased by cold rolling or factory strengthening treatment, moldability is lowered (R/t ratio is increased), and moldability becomes anisotropic (directional)
Longitudinal and lateral bending
As shown in Figure 1, it is referred to as longitudinal or transverse bending, depending on their orientation and the direction of strip rolling. The anisotropy or directionality of the strip is a result of the texture effect of cold rolling. When such anisotropy occurs, the formability in the longitudinal direction (good bending direction) is superior to the transverse direction (poor bending direction).


Jintian Company tested the formability of the strip using a semi-guided bending test method similar to the method of ASTM E290. The fastening device for inspection consists of a 90o punch. The punching blade has a different radius, and the 0.5 hour (12.7 mm) wide strip to be inspected is forcibly pressed into the V-shaped block with a punch, as shown in Fig. 2.

After bending, the sample was observed under a magnifying glass of 10 to 30 X to check that the surface of the crack was a convex surface of a radius. If no crack was observed, the sample passed the test of this radius. Subsequently, the radius of the punch is reduced, and another strip sample is taken and tested. This step is repeated until a crack occurs on the surface of the sample. The crack does not need to penetrate the thickness of the sample to break. The R/t ratio is determined by dividing the minimum bend radius that causes visible cracks by the thickness of the strip. Fig. 3 is a graph showing the formability of a strip having a thickness of 0.05 (1.27 mm) or more as disclosed by Jintian Company. A strip having a thickness of less than 0.015 (0.38 mm) is more moldable.

After bending, the surface forms a "skin" structure that sometimes appears to be broken. This soft structure is not a crack, but a straight-like surface change of the material's deformation. The appearance of the skin is affected by many factors, including: cold rolling reduction, grain size and direction of bending. As a result of the appearance of the skin, the formability of the material cannot be accurately determined. Evaluating materials in this way is very subjective.
The elements of design are a given use case and there are many factors that must be considered when determining the most appropriate material. With the improvement of the state, the strength and hardness of beryllium copper increase, and the plasticity and formability decrease, and the parts can be molded without the highest state of cracking. It is the state that should be selected. This state can be shaped and effectively ensure the design. reliability.
The natural characteristics of the forming direction (comparison of the good and bad directions of the bend) can add extra flexibility to the design, ie the effective use of the material.
The use of Jintian's information on the formability of materials is intended to guide the selection of the appropriate state for a particular use case. If the inner angle of a bend is relatively blunt, a smaller radius than the recommended value can be used. If the internal angle is sharp, a larger bending radius is required. The quality of the bend is again affected by the molding method used. Proportion, taking several steps to complete the bend, instead of completing the bend once, or wrapping the material along the bend radius, will produce a tighter bend than the value indicated by R/t. Similarly, the width of the strip also affects the quality of the bend, and the narrow strip is better formed than the width. When the ratio of the width of the strip to its thickness is less than about 10:1, the formability is improved.

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