1. What is design?
Wallpaper is a design. You may be wearing clothes designed by a “designer”. The appearance of a car is “designed”. Obviously, the term design covers a wide range of meanings. In the example above, design is primarily about designing the appearance of an object. In the case of a car, for example, many aspects of it are involved in design. For example, its mechanical internal components (engine, brakes, suspension structure, etc.) all need to be designed. When designing machinery, engineers are perhaps better able than artists to show a certain degree of artistry.
2. What is mechanical design?
Mechanical design is the study of how to create machinery so that it works safely, reliably, etc. The definition of a machine is: an assembled system of parts that can transmit motion and energy in a predetermined and controlled manner. Or more simply: a system that controls forces and motions.
The basic function of a machine is to do useful work, and machines more or less involve the transfer of energy. Here, we are most concerned with forces and motions. A machine generates motion and forces when energy is converted from one form to another. The engineer’s task is to analyze and calculate these changes in motion, force and energy in order to determine the size, shape and materials required for each of the relevant parts in the machine. This is the essence of machine design.
When a designer needs to design a part of a machine, he or she must first understand that the function and performance of any one part depends on many other related parts in the machine. Therefore, here we are trying to design the whole machine, not simply each part individually. To do this, we must make use of statics, dynamics, material mechanics (stress analysis) and material properties.
3. What is the ultimate goal of mechanical design?
The ultimate goal of mechanical design is to determine the size and shape of the components (machine parts) and to select suitable materials and manufacturing processes so that the designed machine can perform its intended function without failure. This requires the designer to be able to calculate and predict the forms and conditions of failure for each part and then prevent it from failing by design. This requires stress and deformation analysis for each part. Since stress is a function of external load and inertia forces, as well as a function of part geometry, force analysis, moment analysis, torque analysis, and system dynamics analysis must be performed before stress and deformation can be calculated.
If a machine to be designed has no moving parts, its design task becomes much easier, because only static analysis is then required. However, if a machine does not have moving parts, it is not a machine (because it does not meet the definition of a machine above); it is actually a structure. And, of course, structures need to be designed to prevent failure. In fact, large external structures (such as bridges, buildings, etc.) are also subjected to dynamic loads caused by wind, earthquakes, traffic, etc., so they must be designed to take these operating conditions into account as well. If the machinery is moving very slowly and the acceleration is negligible, then a static analysis of it is sufficient. However, if the machinery has significant acceleration, a kinetic analysis must be performed, where the accelerating parts will be “victims of their own mass”.
In a static structure, such as the floor of a building, which is designed to support weight, the safety factor of the structure can be increased by adding appropriate dispersion materials to the structural elements. Although this makes the addition heavier (adds “dead” weight), if properly designed, the floor may carry more “live” weight (payload) than before without failure. However, for a dynamic machine, increasing the weight (mass) of the moving parts may have the opposite effect, i.e. reduce the safety factor, allowable speed or effective load capacity of the machine. This is because the load that generates the stress is the inertial force from the part, and we can use Newton’s second law, F = ma, to estimate its magnitude. Since the acceleration of a mechanical moving part depends on its kinematic design and operating speed, increasing the mass of the moving parts increases the inertial force on these parts, or else one has to reduce their operating speed to avoid increasing the inertial force. Even though one can increase the strength of a part by increasing its mass, this increase may be greatly reduced or even offset by the increase in inertial forces.
In summary, we are faced with a dilemma in the initial stages of mechanical design. Usually, the motion process of the machinery is determined before the size of the part is sized. The external loads acting on the machinery are called external loads. Note that in some cases, the external loads on the machinery will probably be difficult to predict, for example, the external loads on a moving car. When the designer cannot accurately predict the external loads on machinery (e.g., potholes, hard turns, etc.), statistical analysis of empirical data gathered from actual tests done for design purposes can provide some information.
Also, when the acceleration of the motion is known, but the mass of the moving part is unknown, the resulting inertial force is yet to be determined. This needs to be obtained by iteration, i.e., constant repetition, or return to a previous state. To do this, we need to design tests that use the mass characteristics of the test device (such as mass, center of gravity position and rotational inertia) to perform dynamic force analysis to determine the forces, moments and torques acting on the part, and then use the geometry of the cross section of the test device to calculate the stresses. Usually, the accurate determination of all loads on machinery is the most difficult thing in the design process. If the loads are known, the stresses can be obtained by calculation.
Most likely, in the first test, we will find that our design material cannot withstand the current stress level. Then, in order to achieve a viable design, we must redesign the part by changing the shape, size, material, manufacturing process, or other factors (this is called iteration). Often, it is difficult to achieve success without several iterations of the design process. Note that a change in the quality of a part also affects the forces acting on other parts connected to it, resulting in other parts needing to be redesigned as well. This is the design of related parts.
Design can be fun and frustrating at the same time. The general approach to design problems is not fixed and much of it requires creativity, which naturally leads to multiple solutions. For example, you can see that there are many different makes and models of new cars to choose from. Obviously they vary greatly, but you will certainly have your own opinion of which cars are better and which are worse. In addition, the ultimate goal varies from design to design. A four-wheel drive car design will have different goals than a two-seat sports car design (although other examples of cars may include features of both).
It is important for the beginning designer to expand his or her horizons. Don’t try to design in the incorrect way of looking for the “right answer”; there is no such thing as the “right answer” to many problems. Instead, be bold! Try some disruptive designs. Then, test that design through analysis. Don’t be disappointed if you find that the design doesn’t work; through it, you’ve learned something about the problem that you didn’t know before. Failure is the mother of success! We can learn a lot from a wrong design and can make the next design solution better. This is why iteration is said to be important for successful design.
Computers are an essential tool for solving modern engineering problems. By using computer-aided engineering (CAE) software, design problems can be solved faster, more accurately and rationally. However, the results are based on the good quality of both the engineering model and the data used. Therefore, if the designer has a good understanding of the model