cutting ring reamer being measured by micrometer

Industrial manufacturing applications are used to improve the surface quality of cylindrical parts like hydraulic pistons, valves, pump shafts, and others. While machining operations like drilling, turning, and milling come in handy, none of them improve surface finish like burnishing. 

Not only does burnishing improve fatigue and corrosion resistance, but it also increases surface hardness and dimensional accuracy. This is because traditional machining methods are prone to geometrical errors like cylindricity, circularity, and flatness. Apart from the method used for surface finishing, other factors influence the dimensional accuracy of a surface. Let’s look at some of them.

Why Dimensional Accuracy Is Important

The accuracy of the surface dimension refers to the difference between the average estimate and the true dimension of a component. If an accurate method is used to determine a surface dimension, there’s no difference between the real surface dimension and many estimates. When it comes to surface finishing, accuracy is critical because it determines the surface’s overall integrity.

A poor surface finish can cause oil films to rupture at the peak of micro-irregularities, resulting in excessive wear. A good finishing process prolongs a part’s fatigue life and enhances its hardness and residual stress. Precision has to do with the closeness of repeated measurements. Thus, a precise machining method provides similar estimates every time it’s used on the same surface regardless of whether the estimate is accurate.

Surface Finish Dynamics

Another parameter that determines the quality of a surface’s finish is the surface flaws. They can be inherent defects, like blow-holes on the workpiece that develop during the machining process or when exposed to machining. The lay also affects dimensional surface accuracy and its overall integrity. This feature denotes the surface’s predominant direction of the irregularities, and it depends on the orientation of the workpiece.

Material Properties

The material’s ductility affects its overall surface finish. An experiment was conducted to determine the answer to the question, what is a burnishing tool used for? It found that, when the tool is used on more ductile materials, less force is required.

When an aluminum roller sheet is burnished under optimal conditions of 200 N, 0.1 mm/rev, and 400 rpm and compared to an unfurnished specimen, the finished surface increases its yield strength.

The process was also performed on a more ductile material-alloy steel. The result was a slight increase in ductility using significantly lower force (105 N). Another critical factor is surface hardness. Generally, ball and roller burnishing increase surface hardness. Ball burnishing is particularly effective at improving the surface quality depending on the force used and the number of times the tool is passed.

Type of Material

The type of material used also affects dimensional accuracy. Materials made of mild steel, for example, yield less accuracy, as the burnishing force is increased. And while the surface hardness improves, it increases to a maximum of 70 HRB, beyond which it decreases. Conversely, materials made from alloy steel have more tenacity, hence achieving high levels of accuracy regardless of the amount of force used.

Undoubtedly, burnishing gives surfaces better dimensional accuracy and surface quality. However, other features like the types of materials you’re working on, their finishes, and properties affect accuracy. Also, the force applied, the tool size, and speed determine the dimensional surface accuracy. Click here for more information on burnishing tools and how they can help your machining process.