Die Design Fundamentals. Vukota Boljanovic
is approximately 0.003 to 0.006 inch (0.07 to 0.15 mm) in diameter in short wavelength lasers. The distance between the nozzle and the material is approximately 0.2 inch (5 mm). The material thickness at which cutting or processing is economical is up to 0.4 inch (10 mm). The resulting heat energy created by the laser melts or vaporizes materials in this small-defined area, and a gas (or a mixture of gases), such as oxygen, CO2, nitrogen, or helium, is used to blow the vaporized material out of the kerf. The beam’s energy is applied directly where it is needed, minimizing the heat’s effect on the zone surrounding the area being cut.
There is almost no limit to the cutting path of a laser. The point can move in any direction. Small diameter holes that cannot be made with other machining processes can be done easily and quickly with a laser. The process is forceless. The part keeps its original shape from start to finish.
This method is ideal when production quantities or prototypes do not justify producing tooling for stamping or die cutting.
Lasers can cut at very high speeds. The speed at which materials can be processed is limited only by the power available from the laser. Laser cutting is a very cost-effective process with low operating and maintenance costs and maximum flexibility.
4.2.2 Square Shearing
Large, straight-sided blanks are produced in the shear by cutting sheets into strips, then cutting the strips to required lengths or widths. Blanks larger than 8 by 10 inches (203 by 254 mm) and composed primarily of straight sides are ordinarily produced by shearing because of the high cost of large dies.
Blanks cut in a modern shear can be held to an accuracy of 0.005 inch (0.125 mm). Four factors govern shearing accuracy:
•The shear must have sufficient rigidity to withstand the cutting load without deflection or spring.
•Knife clearance must be set correctly and proper rake selected to reduce twist, camber, or bow. Rake is the angle of the upper knife in relation to the horizontal lower knife of the shear. Twist is spiraling of the strip; it is more severe in soft, narrow, or thick strips than it is in hard, wide, or thin strips. Camber is curvature along the edge in the plane of the strip whereas bow is curvature perpendicular to the surface of the strip.
•Good gaging practice must be followed.
•The sheet must be held down securely while shearing occurs.
For producing square and rectangular blanks shown in the upper illustration of Figure 4.2, the sheet is first cut into strips to length A of the blanks. The strips are then run through the shear again and cut into blanks having width B. Here is the method of listing operations on the route sheet:
Figure 4.2 Rectangular blanks sheared from wide and narrow strips.
•Operation No. 1. Shear to length (A)
•Operation No. 2. Shear to width (B)
When the grain of the material must run lengthwise of the blank for extra stiffness, the sheet is cut into strips to width B of the blanks (Figure 4.2, lower illustration). The strips are then run through the shear again and cut into blanks having length A. On the route sheet, operations are listed as follows:
•Operation No. 1. Shear to width (B)
•Operation No. 2. Shear to length (A)
4.2.3 Triangular Blanks
Triangular blanks (Figure 4.3) are produced by shearing square or rectangular blanks, then splitting them to produce two blanks. In the upper illustration:
•Operation No. 1. Shear to length (A)
•Operation No. 2. Shear to double width (B)
•Operation No. 3. Split (C)
Although operation No. 2 states “Shear to double width,” this does not mean that the strip is to be cut twice the width of a single blank. It simply means that the square or rectangular blanks are to be made wide enough so splitting will produce two full blanks.
Figure 4.3 Triangular blanks made by shearing rectangular blanks sheared from wide and narrow strips.
For running strips the narrow way (Figure 4.3, lower illustration), operations are listed as follows:
•Operation No. 1. Shear to width (B)
•Operation No. 2. Shear to double length (A)
•Operation No. 3. Split (C)
4.2.4 Angular Edge Blanks
Wider blanks having one angular edge (Figure 4.4) can be produced by the same method employed for triangular blanks. For the upper illustration:
•Operation No. 1. Shear to length (A)
•Operation No. 2. Shear to double width (B)
•Operation No. 3. Split (C)
The function of some blanks renders it necessary to run them the narrow way (Figure 4.4, lower illustration). Operations are then as follows:
•Operation No. 1. Shear to width (B)
•Operation No. 2. Shear to double length (A)
•Operation No. 3. Split (C)
Figure 4.4 Angular edge blanks made by shearing rectangular blanks sheared from wide and narrow strips.
Added cuts
One or more extra cuts may be required to complete the blanks (Figure 4.5). Here is the order of operations for the blank in the upper inset:
•Operation No. 1. Shear to length (A)
•Operation No. 2. Shear to double width (B)
•Operation No. 3. Split (C)
•Operation No. 4. Trim (D)
In the lower illustration:
•Operation No. 1. Shear to width (B)
•Operation No. 2. Shear to double length (A)
•Operation No. 3. Split (C)
•Operation No. 4. Trim (D)
4.2.5 Parallelogram Blanks
Blanks in the shape of an angular parallelogram (Figure 4.6) are produced by shearing with the strip positioned at an angle to the shear blade. For the wide strips, upper illustration:
Figure 4.5 Blanks produced by added cutting of angular edge pieces.