## 2 Materials and Methods
### Manufacturing Technology Project
#### 2.1.2 Design of the Cutting Blade  
The aim was to design the sharp scaper blade for the separation of bonded automotive glasses and for use in scraping and removing soft expansion joint silicone, caulking, window paste, and other sealing compounds, cardboard, carpet, rubber, and cutting insulation materials. The designed blade should be super thin and be shaped to allow access to corners and tight spaces. The clamping part of the blade should have the same dimensions and hole pattern as the mass-produced blades for the given oscillating cutter type. The aim was to design an economically viable technology for the production of about 100 pieces of this blade without spot welding from two parts, preferably from a single blank. To design the clamping part of the cutting blade, the mass-produced multimaterial plunge cutting blade with a straight head (Figure 3) was used. This blade has high-speed steel teeth at the tip of the blade. It is suitable for cutting wood, plastic, fibreglass, nails, non-ferrous metals, thin sheet metal, and hardened fillers. The cutting blade consisted of two parts--the blade holder and the blade cutting part, the parts were spot-welded to each other. The thickness of the blade was 0.5 mm and the thickness of the holder was 1.5 mm. Before the design of the forming tool, the shape of the cutting blade was designed. For access to corners and tight spaces, the tapered blade point design with the cutting edge on the lateral sides of the blade (Figure 4) was designed, so it was possible to produce the blade holder and the blade cutting part from one blank piece. Figure 4: The designed shape of the tapered cutting blade consisting of one piece. Figure 3: Multimaterial plunge cutting blade with a straight head consisting of two spot-welded parts. For both bends, in the designed shape of the cutting blade, the smallest recommended internal bend radius at which the material does not break (the tensile stress in the outer fibres must not exceed the tensile strength of the material \(R_{\text{m}}\)) was calculated according to Equation (1). The size of the smallest recommended internal bend radius also depends on the orientation of the bend due to the rolling direction (if the axis of the bend is in the direction of material fibres, the value of \(r_{\text{min}}\) is about \(2\times\) larger than the value of \(r_{\text{min}}\) when the bend axis is perpendicular to the direction of the fibres. Small radii of the curvature in the bend area cause greater deformation and use of plasticity stock, but the parts have lower springback after bending. The smallest recommended internal bend radius:  
\[r_{\text{min}}=\frac{s}{2}\ \cdot\ \left(\frac{1}{\epsilon_{\text{m}}}-1\right)= \frac{0.6}{2}\ \cdot\ \left(\frac{1}{0.33}-1\right)=0.61\ \text{mm} \tag{1}\]  
where \(\epsilon_{\text{m}}\) (-) is the maximum uniform proportional deformation at stress on tensile strength and \(s\) (mm) is the thickness of the bent material. The maximum uniform proportional deformation at stress on tensile strength can be approximately determined from the following equation:  
\[\epsilon_{\text{m}}=\frac{\frac{s}{2}}{r+\frac{s}{2}}=\frac{\frac{0.6}{2}}{0.6 +\frac{0.6}{2}}=0.33 \tag{2}\]  
Based on the calculated value of the minimum internal bend radius of Equation (1) for both bends in the designed shape of the cutting blade, the internal bend radius \(r=0.6\ \text{mm}\) was chosen, that is, the lowest value so that the springback will be small. Validation of the possibility of use of this radius without the formation of cracks on the outer side of the bend was carried out by simulations in the Dynaform 5.2.1 software, which uses the finite element method (see Section 2.2) and subsequently by bending the annealed blank of the cutting blade in a bending tool (see Section 3.3). For both bends in the designed shape of the cutting blade (Figure 5) the largest radius of bend allowed according to Equation (3) was calculated.