Sheet metal fabrication is one of the widely used manufacturing technologies. It involves deforming worksheets into desired parts and products across industries. You can utilize several sheet metal fabrication techniques, such as cutting, bending, stamping, blanking, coining, punching, welding, riveting, etc. However, considering possible defects in fabrication processes is key to achieving precise and structurally intact parts.
Burrs, spring-back, cracks, surface roughness, and several other sheet metal defects influence the performance and accuracy of fabricated parts. Furthermore, we will elaborate on some common defects under various fabrication methods, their cause, and strategies for prevention.
Stamping is one complex and detailed sheet metal technique, which creates diverse shapes by executing many metal forming techniques in a single setup, cutting, punching, bending, etc.
The following are some common sheet metal stamping defects;
Rough Edges and Burrs
The cutting edges of metal sheets can produce rough edges and burrs due to improper cutting forces and worn cutting tools. In the case of laser cutting, the incompatibility of sheet thickness and laser power creates these sheet metal defects. To avoid this, maintain the quality of the cutting tool and adjust the cutting clearance,
Material Tearing or Cracks
The excessive metal-forming forces by punches result in over-deformation, tearing, and cracks in the stamped parts. Therefore, it is essential to calculate and use optimal cutting or forming forces based on the type of forming method to avoid this.
Buckling
Buckling, also known as “wrinkles” is caused by the uneven pressure distribution into the sheet while executing the punches and other pressure-exerting mechanisms. It is important to control the forming force, die-punch alignment, and punch surface parameters.
Die Failure
The die failure happens by either breakage or excessive deformation of the die material. The main reason is again the forming pressure/force, lack of die maintenance, and selection of inappropriate die & work material combinations.
Sheet metal forming is a broad term, including different techniques that form raw sheets into desired parts with deformation, including bending, stamping, punching, cutting, etc. Some sheet metal forming defects are the same as the stamping defects, like rough edges, material tearing, etc.
Let’s discuss the defects under different forming techniques
Shear Cutting Defects
The shear cutting of sheet metal can create rough edges, burrs, and edge twisting. The common causes of these sheet metal defects are dull or worn cutting blades, and improper cutting angles, cutting force imbalance.
Sheet Metal Bending Defects
“Springback” is one of the key bending defects, also associated with stamping and other forming processes. Metal sheet tends to regain their original position after deformation ( by a certain %). It means a portion of the deformation goes back into the initial position. It affects the dimensional accuracy of formed sheet metal parts. Therefore, it is essential to calculate and consider the during the design phase.
Springback as sheet metal bending defect
Furthermore, you can calculate the spring back factor (k) using the following mathematical expression;
Sheet Metal Deep-Drawing Defects
Earing, wrinkling, and material tearing are the major sheet metal defects associated with the deep-drawing process. The earring defect refers to an uneven height around the rim of the drawn part. The main reason is neglecting the work and die materials compatibility.
The following are the five general tips to avoid the common defects;
1. Compatibility of Die and WorkSheet Material
The die and punch materials should be tougher, rigid, and durable than the worksheet. If the die material fails to exert the punching pressure, it causes deformation and failure. For example, forming of stainless steel sheet requires HSS or carbide dies.
2. Optimize the Sheet Metal Fabrication Variables
Depending on which fabrication methods are used for the sheet metal parts, choose the optimal parameters, including deforming forces, punching speed, angle, bend radius, clearance, etc. Here you need to consider the work material properties like tensile strength, formability, ductility, elongation, plastic deformation, etc.
Subsequently, simulation of fabrication processes in computer software helps to identify the possible defects due to improper forming variables.
3. Material Handling
It is important to protect the raw sheets and formed sheet metal parts’s surface from dent and abrasion. For this, the handling should be done with soft padded or film supports.
4. Real-Time Process Monitoring
Any error in the process execution of sheet metal fabrication techniques can also cause the defects in final parts. So, use real-time monitoring with a feedback mechanism to monitor and adjust the process.
5. Springback Compensations
As mentioned before, it is one of the main dimensional defects in sheet metal fabrication. You need to maintain a slightly high accuracy to complete this.
