## 2 Materials and Methods
### Manufacturing Technology Project
#### 2.1.2 Design of the Cutting Blade
It is the radius of bend at which the permanent deformation occurs in the outermost fibres of the bent cross section on the tension side. When using the values of the radius of the bend larger than this value, the bend would be flexible and the material would be straightened out after unloading again. The largest allowable bend radius:  
\[r_{\text{max}}=\frac{s}{2}\ \cdot\ \left(\frac{E}{R_{\text{e}}}-1\right)=\frac{ 0.6}{2}\ \cdot\ \left(\frac{210000}{550}-1\right)=114.25\ \text{mm} \tag{3}\]  
Figure 5: Side view of the designed movable cutting blade of the oscillating cutter. where \(s\) (mm) is the thickness of the bent material, \(E\) (MPa) is the modulus of elasticity in the tension of the bent material, and \(R_{\mathrm{e}}\) (MPa) is the significant yield point of the bent material. For both bends, the designed shape of the cutting blade (Figure 5) was calculated according to Equation (4) the minimum length of the bent arm. The minimum length of the bent arm:  
\[a_{\mathrm{min}}=2\;s=2\;\cdot\;0.6=1.2\;\mathrm{mm} \tag{4}\]  
In the designed shape of the cutting blade (Figure 5) the calculated value of Equation (4) is not lower. The springback after bending will take effect by increasing the bending radius and decreasing the bending angle. The springback after bending arises due to the elastic stress accompanying each cold forming. It is enhanced when the material is harder and when the bend radius is greater (it is reduced as the bend angle increases). The springback can be limited or excluded by the plastification of the bend area, which leads to the reduction or exclusion of the elastic deformation area. The springback angle after bending:  
\[\beta=\mathrm{arctg}\left(0.375\;\cdot\;\frac{l}{k\cdot s}\;\cdot\;\frac{R_{ \mathrm{e}}}{E}\right)=\mathrm{arctg}\left(0.375\;\cdot\;\frac{11.22}{0.44 \cdot 0.6}\cdot\;\frac{550}{210000}\right)=2.4 \tag{5}\]  
where \(\beta\) (\(\lx@math@degree\)) is the springback angle, \(l\) (mm) is the distance between the outer rigging of the bending die, \(k\) (-) is the coefficient indicating the position of the neutral layer depending on the ratio of \(r/s\) (for \(r/s=1\) is \(k=0.44\)), and \(r\) (mm) is the inner radius of curvature in the bending area and thickness \(s\) (mm) of the blank for bending. At both bends in the designed shape of the cutting blade (Figure 5) the springback will be identical and, due to it, even after springback, the parallelism of the blade section that serves as the holder with the cutting part of the blade maintained, which is important for functionality. In the design of the bent part, the following technological principles were kept:  
* The axes of both bends were designed perpendicular to the direction of rolling of the material. * The axes of both bends have directions perpendicular to the part contour. * Small bending radii were chosen to reduce the springback. * Greater springback of the material is also prevented by the choice of bending technology by embossing. * For the blank during bending to not move in the bending tool, the blank is established and fixed in the initial position by two locating pins with the use of positioning holes around the circumference of the holder part of the cutting blade. * Pre-made positioning holes around the circumference of the holder part of the cutting blade will not be deformed during bending because the condition is kept that their boundaries lie at least at a distance of \(a=s\) from the bend area.