The subject of the mechanical design is the creation of new and better machines and the improvement of existing machines. New or better machines are more economical in terms of the total cost of production and operation.
What is Machine Design?
The design process is long and time-consuming. From the study of existing ideas, new ideas must be invented. Ideas are studied in view of their commercial success and embodied in the form of drawings. When creating these drawings, attention should be paid to the availability of funds, people, and materials necessary to successfully implement new ideas into actual reality.
Designing mechanical parts requires a good knowledge of many disciplines, including mathematics, engineering mechanics, the strength of materials, mechanical theory, workshop processes, modeling & drafting.
Mechanical Design Classification
Mechanical design can be categorized as:
Adaptive design: In most cases, the designer’s work involves adapting existing designs. This type of design does not require any special knowledge or skills and can be attempted by designers with normal technical training. The designer makes only minor changes or modifications to the existing design of the product
Development design: This type of design requires considerable scientific training and design skills to transform existing designs into new ideas by employing new materials. In this case, the designer starts with an existing design, but the final product can differ significantly from the original.
New design: This type of design requires a lot of research, technical skills, and creative thinking. Only designers with sufficiently high personal qualities can work on new designs.
Designs can be classified according to the methods used:
- Rational design: This type of design relies on a mathematical formula of mechanics principles.
- Practical design: This type of design relies on empirical formulas based on practice and past experience.
- Industrial design: This type of design relies on the production side of manufacturing each machine part in the industry.
- Optimum design: This is the optimal design for the given objective function under the given boundary conditions. This can be achieved by minimizing unwanted effects.
- System design: This is the design of complex mechanical systems such as automobiles.
- Element design: This is the design of every element of the mechanical system, including pistons, crankshafts, and connecting rods.
- Computer-aided design: This type of design relies on the use of computer systems to help create, modify, analyze, and optimize designs.
General Mechanical Design Considerations
The following are general considerations when designing mechanical components.
Type of Load and Stress due to Load
Loads can act on mechanical components In many ways, thereby increasing internal tension.
Movement of Parts or Kinematics of a Machine
The successful operation of a machine is highly dependent on the simplest arrangement of parts that produce the desired motion. Motions in any parts are:
- Linear motion, including unidirectional and reciprocating motion;
- Curvilinear motion, including rotation, vibration, and monotone.
- Constant speed;
- Constant or variable acceleration;
It is important that designers have sufficient knowledge of material properties and their behavior under working conditions. Some of the important material properties are strength, durability, flexibility, weight, heat and corrosion resistance, castability, weldability or hardenability, machinability, electrical conductivity, etc.
Parts – Shape & Size
Shape and size are optional. You can use the smallest feasible cross-section, but you can be sure that the stresses introduced in the design cross-section are safe enough. To design the shape and size of a mechanical part, we need to know the forces that the part must withstand. It is also important to anticipate sudden or shock loads that can lead to failure.
Frictional Resistance and Lubrication
There is always power loss due to friction resistance and it should be noted that the starting friction is higher than the running friction. Therefore, it is important to pay special attention to lubrication issues for all surfaces Rolling bearings, sliding bearings, rolling bearings, etc. that move in contact with other objects
Convenient and Economical Features
During design, the operating characteristics of the machine should be carefully considered. Start levers, control levers, and stop levers should be arranged for easy handling. Wear adjustments must be made using various jigs and their placement so that the alignment of the parts is maintained. If parts of other products need to be replaced or replaced due to wear or damage, they should be easily accessible and, where possible, the need to remove other parts for this purpose should be taken care of. The economic operation of machinery used for production or material processing should be examined to see if it has maximum capacity consistent with the production of good work.
Use of Standard Parts
The use of off-the-shelf or off-the-shelf parts goes hand in hand with cost, as the cost of an off-the-shelf or off-the-shelf part is a fraction of the cost of a similar made-to-order part. Standard or off-the-shelf parts should be used whenever possible. Parts for which samples such as gears, pulleys, and bearings already exist and parts for regular stock such as screws, nuts, and pins to choose from. There should be as few screws and studs as possible to avoid delays due to changing drills, reamers, and taps and to reduce the number of wrenches required.
Safety of Operation
Some machines are dangerous to operate, especially those that are speeded up to ensure maximum production speed. Therefore, any moving machine parts in the vicinity of the operator are considered an accident hazard and can cause injury. Designers should therefore always provide safeguards for operator safety. Safety devices must never impede machine operation.
Designers should be aware of their employer’s workshop limitations so that they do not have to work in a separate workshop. You may need to plan and supervise workshop operations and design methods for casting, handling, and machining special parts.
The number of items or machines you manufacture will affect your design in several ways. Engineering and manufacturing costs called fixed or overhead costs, are spread over the number of items manufactured. If only a few items are manufactured, the extra cost is not justified unless the machine is large or specially designed. Ordering small quantities of products cannot overwork the workshop process, so designers should limit their specifications to standard parts as much as possible.
Cost of Construction
Item construction cost is the most important consideration involved in construction. In some cases, the high price of an item may well cause it to be quickly excluded from further consideration. If an item is invented and testing of handmade samples shows it to have commercial value, it can justify spending significant sums of money on designing and developing automated machinery to manufacture the item. Commodity trading can sell in bulk. The designer’s goal is always to minimize manufacturing costs.
Machines and structures must be assembled as a unit before they can function. Larger units often have to be assembled and tested in a workshop before being transported to their location of use. The final installation location of each machine is critical and the designer must anticipate the exact location and on-site equipment for assembly.
General Procedure for Mechanical Design
There are no hard and fast rules for designing mechanical parts. Or you can try the problem in different ways. However, here are the steps to fix the design problem:
- Recognition of need: First, fully describe the problem and state the need, goal, or purpose of designing the machine.
- Synthesis (Mechanisms): Select a mechanism or group of mechanisms likely to produce the desired motion.
- Analysis of forces: Find the force acting on each link of the machine and the energy transmitted by each link.
- Material selection: Choose the best material for each member of your machine.
- Design of elements: Determine the size of each part of the machine by considering the forces acting on the part and the allowable stress of the materials used. Note that each element must not bend or deform beyond tolerance.
- Modification: Resize the elements to match previous experience and judgment for ease of fabrication. Modifications may be required for manufacturing considerations to reduce overall costs.
- Detailed drawing: Create detailed drawings of each component and assembly of the machine with full specifications of the proposed manufacturing process.
- Production: Components according to drawings are manufactured in workshops. A flow chart of a general approach to mechanical design is shown in Figure 1.1.