Introduction
Metal forming is one of the most important industrial processes for transforming sheet metal into useful products. Metal forming processes involve applying force to a piece of sheet metal to shape it into the desired form. One of the most common metal forming processes is called folding, which is a process that involves bending a sheet of metal along a straight bend line to form an angle between the two panel sides. Folding is widely used in the fabrication of sheet metal components, such as sheet metal cabinets, air conditioning ducting, and automobile body components.
Folding processes produce a variety of parts with varying levels of complexity and cost. Despite its numerous benefits, folding can be difficult to perform due to the presence of folds on the sheet surface. Folds on the sheet surface are a common problem that can lead to quality issues, reduced part yield, and lower production efficiency. Consequently, it is important to understand the causes of folding and the various methods available for avoiding or minimizing them.
Causes of Folding
Folding of sheet metal occurs when the sheet material is bent at an angle greater than its elastic limit. In sheet metal forming operations, the sheet material is subjected to a certain level of force which, when exceeded, can cause it to deform. This process can happen if the sheet material is over-formed, or if it is stretched beyond its elastic limit. As the sheet material is stretched, it will begin to form folds due to the different rate of stress applied along the length of the sheet.
Folds on the sheet surface can also occur due to improper tooling and process design. If the tool geometry is not appropriate, it can cause the sheet material to bend at a higher angle than the desired one, causing folds to form. Additionally, the use of incorrect process parameters, such as a higher-than-necessary forming pressure, can lead to unnecessary stretching and folding of the sheet.
These factors can be further compounded by other issues, such as the materials thickness and mechanical properties, which can cause folds to form due to uneven force distribution or material deformability. For example, thicker materials are more prone to folding over thinner materials, as they are more likely to form bulges when bent. The mechanical properties of the material can also play a role in the folding issue, as certain materials may be more prone to spreading when formed.
Methods of Minimizing or Avoiding Folding
While it is impossible to completely eliminate folding, there are various methods that can be employed in order to reduce or minimize its occurrence. First, it is important to ensure that the sheet material is not stretched beyond its elastic limit. This can be done by properly selecting the tool geometry and forming parameters, such as the forming pressure and die radius, to ensure that the sheet will not be overly stretched and deformed.
It is also important to use the correct tooling for the material being formed. Tools that are too sharp or too blunt can cause the sheet to deform in an undesired way, resulting in the formation of folds. Additionally, it is important to check the clearance between the tools and the sheet material to ensure that the sheet is not being pulled or stretched during the forming operation.
Finally, the material being formed should be chosen in such a way that its mechanical properties are taken into consideration. For example, materials that are prone to spreading when formed, such as aluminum, should be used with caution, as they are more likely to form folds when bent.
Conclusion
Folding is a common problem that can occur in metal forming operations, leading to quality issues, reduced part yield, and lower production efficiency. It is important to understand the causes of folding and the various methods available for avoiding or minimizing them. These methods include properly selecting the tool geometry and forming parameters, using the correct tooling for the material being formed, and using materials with the appropriate mechanical properties. By employing these measures, it is possible to reduce or minimize the occurrence of folding in metal forming operations.
