In the manufacturing industry, most engineering products are synchronized between two or more components, which work together to provide their main functions. However, achieving this goal requires an understanding of the different types of fits used in mechanical engineering.
In this article, we will discuss different types of coordination in engineering. After reading this article, you will understand what fits are and the types of fits used in mechanical engineering.
What Is An Engineering Fit?
Engineering fit is a mechanical assembly in which two mating components are permanently or temporarily connected together. The term ‘fit’ refers to the amount of mechanical clearance or physical contact between mating components.
Fits are based on shafts or holes. The hole is whether the internal feature of the part is cylindrical, while the axis is whether the external feature of the part is cylindrical.
For hole based systems, the size of the hole remains unchanged while changing the axis to determine fit. On the contrary, it applies to shaft based systems where the shaft size remains unchanged, and the hole size will change to determine the fit.
Please note that CNC turning services are a precision machining method that can manufacture shafts with specific dimensions, making it easier to obtain the required fit.
If the part fits closely and the joint can bear the load, it is a interference fit. On the other hand, the characteristic of transitional fit is that the joint bears sufficient force to maintain contact but cannot withstand high loads. The third type, clearance fit, has a small gap between the mating components that allows them to rotate or slide freely.
Types Of Fits
There are various types of commonly used combinations in engineering applications. Choosing the appropriate fit for a specific application depends on the required accuracy and the magnitude of the force or load to be applied.
Clearance Fit
Clearance fit allows for loose fit, where free movement is important and requires a certain amount of clearance. We see that the gap fit requirement elements should be able to slide in and out without obstacles, and can be loosely guided for alignment without requiring strict accuracy. Examples of clearance fits may include bolts/shaft holes, where one component can freely slide through another feature.
Due to this clearance, the parts in the clearance fit have a certain degree of freedom (motion). For example, the pin and frame in the pivot joint use a clearance fit, allowing the two components to move independently of each other while maintaining locking in place.
The common gap range in these engineering collaborations is+0.025mm to+0.089mm.
Interference Fit
The interference fit will be much tighter than the clearance fit. The high friction force tightly fixes the mating surfaces together. Therefore, interference fit is also called friction fit.
The tightness of interference fit comes from its negative clearance. This means that the mating surfaces are pressed into each other. In other words, the mating surface undergoes inward deformation under contact pressure. For example, in a hole and shaft system, the hole is actually smaller than the shaft in a interference fit. Force the shaft into the hole by hydraulic press or hammer (another name for interference fit).
In addition, another common method of creating interference fit is shrink fit. In this technology, one of the parts is cooled or heated, causing it to contract or expand (respectively) enough to instantly turn a negative gap into a positive gap. After positioning the components relative to each other, the temperature returned to normal. The resulting thermal shrinkage/expansion forms a tight interference fit
Generally, the clearance of interference fit is -0.001mm~-0.042mm. Once joined, this will create a relatively solid alliance that requires significant force or potential machine operations to decouple.
Transition Fit
The transition fit is between the clearance fit and the interference fit. When accurate alignment is crucial, a transitional fit is required, and the mating parts must be connected with higher accuracy. You may also see these called sliding fits or push fits. There will still be a larger gap than a pressure/interference fit, but it will be much smaller and excess gaps or movement in the joint should be eliminated.
Transition fit is very useful for accurately positioning parts during assembly operations. It limits their relative motion while also preventing extreme mechanical stress. The mechanical interference/gap in the transition fit is between+0.023mm and -0.018mm.
How To Choose Suitable Fit For Your Projects
Application
According to your needs, there are different types of accessories suitable for different purposes. By examining the precision and tolerance attributes displayed by different types of fits and suggested features of products, you should determine the appropriate fit for the project.
Budget
Before deciding on the appropriate type of product that suits you, you should understand your budget. For example, using a fit with stricter tolerances will cost more than normal. Therefore, you must carefully weigh your choices. The best choice is to provide the correct tolerances required to perform its functions while reducing product development costs.
Tolerance
You must understand the concept of product tolerance in order to choose the appropriate fit type for such products. You must specify what you want. In addition, you must also answer some questions, such as do you want the components to rotate one full turn or do you want them to be tight?
Another thing you need to pay attention to is tolerance relaxation, which is the total maximum or minimum tolerance for a specific measurement. For example, you must pay attention to the aggregation of different component tolerances to form a single product. If the resulting tolerance is very high, this is very important.
In engineering, improper use can have serious consequences. The small gap or space between two components can lead to friction, wear, and tear, ultimately leading to failure. Excessive clearance or space can lead to vibration, noise, and energy loss. Therefore, achieving perfect fit is crucial in many engineering applications. Each type of fit has its own advantages and disadvantages, which must be considered when selecting the best fit for a specific application.