Asssignment
In this term project, the main parts of a shaper (Figure 1) will be designed. A shaper is a type of machine tool that uses linear relative motion between the workpiece and a single-point cutting tool to machine a linear tool path. Its cut is analogous to that of a lathe, except that it is linear instead of helical. The ram is moved back and forth typically by a crank inside the column. A shaper operates by moving a hardened cutting tool backwards and forwards across the workpiece. On the return stroke of the ram the tool is lifted clear of the workpiece, reducing the cutting action to one direction only.
The electric motor A (1) on the ground drives the flywheel (2) via the belt (3). The flywheel mounted on the shaft (4) rotates at a constant angular velocity and transmits the motion to the crank (6). The crank (6) is attached to the connecting rod (7) by the pin B (9). Similarly, connecting rods and slider (8) are joined by the pin C (10).
Detail drawings of the shaft (4), and pin B (9) are given in Figure 2 and 3, respectively. Electric motor and flywheel system is provided in Figure 4. The bracket welded to the slider is shown in Figure 5.
In the project do the followings in the given order:
A. Draw the free body diagrams of the following parts (neglect inertias):
1. the flywheel, 2. the shaft, 3. the crank, 4. the connecting rod, 5. pin A, 6. pin B, and 7. pin C.
B. Shaft Design
The belt forces can be calculated from the equation F1/F2 = efα, where f is the coefficient of friction and α is the angle of wrap, shown in Figure 4.
1. Draw the shear force and the bending moment diagrams of the shaft.
2. Design the shaft for fatigue loading. Use distortion energy theory and Soderberg criteria in the design. Note that the shaft is machined. The flywheel and the cranks are fixed to the shaft with sled runner type of keys.
Hint: Note that the magnitude of reaction forces acting on the shaft is a function of the crank angle. You may design the shaft as if the loadings on the shaft changes between 0 and the value corresponding to the maximum torque case (Figure 1). In reality, for the critical locations, you need to plot the bending moment with respect to the crank angle and angular position of the shaft and determine the critical point (crank angle and angular position) from the 3D plot. At the maximum torque position, θ12 = 100º and θ13 = 135º. For the maximum torque position, the value of the maximum torque applied by the belt to the flywheel is T = 45.7 Nm and the reaction forces on the pin (pin located on the disk and shown as red in Figure1) are Fx = 1160 N Fy = 205 N.
C. Connecting Rod Design (CB)
The angular position of the crank at the start-up can attain any angle. Note that the value of the start-up torque does not significantly depend on the initial crank angle. This is because the motor characteristics mainly determine the start-up torque. The cross section of the rocker is hollow square and the ratio of a side of the square to thickness is given in the dataset.
D. Pin Design
Determine the diameter of the pin B and specify an appropriate fit for the pin. Design the pins for static case (start-up position). Use maximum shear stress theory.
E. Weld Design
Find the size of the welds between the connecting rod and bracket welded to the slider considering fatigue loading.
F. Make an engineering drawing of the following parts:
1. The Shaft
2. The Pin B
3. Details of the weld section
The technical drawings should:
- be prepared using CAD tools and be scaled, and
- contain the tolerances in the pin design.
|
Materials (Steel HR)
|
Set 1
|
|
Material of the shaft
|
1040
|
|
|
1035
|
|
Material of the connecting rods and bracket
|
|
Material of the pin B
|
1060
|
|
Geometric Parameters
|
Set 1
|
|
al (mm)
|
500
|
|
hl (mm)
|
200
|
|
CB (mm)
|
350
|
|
DI (mm)
|
270
|
|
Ll (mm)
|
100
|
|
L2 (mm)
|
300
|
|
L3 (mm)
|
550
|
|
L4 (mm)
|
55
|
|
L5 (mm)
|
25
|
|
L6 (mm)
|
85
|
|
L7 (mm)
|
310
|
|
L8 (mm)
|
420
|
|
L9 (mm)
|
250
|
|
L10(mm)
|
370
|
|
Lll (mm)
|
50
|
|
L12(mm)
|
60
|
|
r / d of fillets on the shaft
|
0.15
|
|
d2/d1
|
1.1
|
|
Design Specifications
|
Set I
|
|
Speed ratio of the flywheel and the electric motor
|
16
|
|
Factor of safety
|
2
|
|
Reliability
|
0.95
|
|
Ambient temperature (°C)
|
25
|
|
Coefficient of friction between the belt and the flywheel
|
0.30
|
|
Side to thickness ratio in the rocker
|
6
|
Attachment:- Design - assignment.pdf