In today’s conditions, the most important weapon in creating a market is the machines that are suitable for the demands and will reveal the work to be done more quickly and efficiently. Therefore, determining the function of the machine is the first task to be solved in the design.
Mehmet Özgür Eroğlu
Project and Sales Consultant/ Proje ve Satış Danışmanı
The generation of a machine roughly goes through these stages: imagining the machine, drawing a sketch, forming its elements, making the mechanism work, sizing the elements, making assembly and production drawings, forming the prototype of the machine and making tests on it and producing the decided machine.
Design and construction should be considered together, where the latter means placing elements.
In today’s conditions, the most important weapon in creating a market is the machines that are suitable for the demands and will reveal the work to be done more quickly and efficiently. Therefore, determining the function of the machine is the first task to be solved in the design. The work of the machine must be determined exactly and precisely.
One of the most difficult tasks in design is to assemble the basic ideas needed for the machine to function. We can call this a design synthesis. Many systems can be developed for a machine to perform a function, and it is very important to decide on this issue. Finishing the final work requires a significant amount of knowledge.
Next is to make a draft design, select the materials and analyze them. Although making a draft design is not as difficult as design synthesis, it requires significant technical know-how and experience. The designer must have technical knowledge such as stress formulas, material properties, production methods. When a satisfactory design is reached, analysis is possible. When the design is satisfactory, production can be started. Most of the time, the prototype that emerges as a result of the design is insufficient due to reasons such as inability to fully provide the function, insufficient or lack of material, not obtaining a satisfactory result, and the design phase starts from the beginning. The design process lasts until a satisfactory result is reached.
We can list the steps of machine design as follows:
Technical specifications, customizedrequests.
Determination of the working principle
Preforming alternatives (kinematics in accordance with the basics
Feasibility analysis (economic and technological)
Shaping (according to general requests)
Assembly and detail pictures
While following these steps, we always have to do technical and economic analysis. Elements that fulfill a function and have their own calculation and shaping principles are called machine elements. And in design, knowledge and experience about machine elements are needed the most.
More than one design formation is needed to shape the entire design of a machine. Machines can be shaped with many different designs such as welded construction, the design of parts produced by casting, the design of parts produced by metal cutting, the design of rolling and plain bearings, the design of sealing components. Lightness of the design, suitability for fatigue and resistance, being as simple as possible and forming a safe machine are the principles to be followed.
Welding is commonly used in places such as various machine bodies, pipelines, containers used in storage works, steel construction buildings, which are manufactured by combining flat rolled plates and profiles. Due to the ease of production of welded parts, it is often preferred to casting and forging works. Particularly, it is preferred because the parts to be manufactured in small numbers are less costly than the casted and forged parts. Welding is used in unalloyed steels with low carbon content (0,25%). Welding seams of high carbon and alloy steels can become hard and brittle.
When designing the materials to be welded, ready-made or standard semi-products should be preferred in the first place. These semi-products should be weldable. Simpler weld shapes need to be found. Overlapping of the welding seams must be avoided. Thick parts and thin parts must not be welded without pre-treatment. The production of parts must be simplified. Thin edges that will burn during welding should not be included. During welding, the parts must be saved from damages in relation with welding. Methods of increasing the strength of welded parts should be considered.
DESIGN OF PARTS MADE BY CASTING
Casting is a non-alternative manufacturing requirement for parts to be produced in large numbers, parts that are difficult to shape with other manufacturing methods, and very heavy and large parts. So the designer must be familiar with the basics of casting rules. The strength of cast parts is weaker than parts produced by rolling and forging. During casting, voids or cracks may occur in the part or the microstructure may be damaged. While all steels can be produced by casting, most cast parts are made of cast irons. Due to the high melting point of the steels, their fluidity in the mold is low, and besides their shrinkage is also high.
Some of the issues that the designer should pay attention to in casting parts and design rules can be listed as follows:
Wall thickness and strength of casting must be calculated
Must be able to be molded, must have a slope or conicity to remove from the mold
Shrinkage in cast parts must be taken into account
Sharp corners and change in sudden profiles must be avoided
There must be material accumulation in the casting parts
The formation of gas pockets in the casting parts must be prevented
Consideration must be given to the design of the casting edges and the flange shaping
Rigidity must be considered in large casting parts
DESIGN OF PARTS MANUFACTURED BY MACHINING
Machining phase of machine parts is the most important part of production. 70% of the production cost is about machining. Some of the methods needed to increase machining efficiency are: reducing machining time; minimizing disassembly and assembly time; making a good production plan so that the bench doesn’t remain idle; sequential operations; preparing parts in a way that is easy and less processed. There are some methods that can be done for these. Some of these are facilitating the process by making sectional designs instead of single piece, avoiding unnecessary tolerances, avoiding cascade processing surfaces, designing simple machinable holes, making easy designs for easier machining.
LIGHTNESS IN MACHINE DESIGN
Lightness is very important in machine design. It provides fuel economy especially in moving machines such as automobiles, airplanes and trains. And it saves material in stationary machines. It reduces cost in machines. The cost is of great importance, especially in machines with mass production. Nonetheless, the strength, rigidity and safety of the machine must not be neglected for the sake of and cost reduction. In order to meet the weights of the machines, the weighting factor has been defined. The weighting factor is calculated by the ratio to the power of the machine.
There are several methods used to reduce machine weight. These methods can be used such as choosing the appropriate profile (such as using steel pipe instead of a solid shaft), providing lightness by changing the shape, and providing lightness with material selection.
DESIGNING ACCORDING TO FATIGUE
90% of mechanical damage is due to fatigue. Most of these damages are affiliated to design defects. A small part is also caused by metallurgical error. Fatigue is caused by the formation, progression, and fracture of the crack. Fatigue cracks usually start in areas of stress concentration. In particular, the designer should avoid shaping that may cause stress concentration. To illustrate, we can solve this by giving elliptical, round or conical shapes to the thick part in front of the shoulder, or by making an additional shoulder and distributing the tension, since it is not possible to open a radius to prevent piling up on the bearing or pulley shoulders.
DESIGN OF ROLLERS AND BEARINGS
Roller and bearing selection is of vital importance for the rotating parts (rotor) of the machines. Along with the correct bearing, we need to choose the bearing to carry the movement and load distribution in the best way. The fitting of the rollers or bearings to the shoulder must be done precisely and completely. The corner radius of the rollers and the corner radii of the shaft shoulders must be compatible with each other. Fixed bearings must withstand both axial and radial force. The free bearing, on the other hand, must only withstand the radial force. If one of the bearings is not free, both bearings are subjected to axial loads due to thermal expansion and this shortens the bearing life.
Below are a few fundamental rules needed to simplify machine design:
The number of parts should be as few as possible.
Parts should be easily dismountable and mountable.
Redundant components must not be used.
Standard manufactured parts should be preferred to special productions.
Symmetrical shapes simplify production.