Attributes of feed and tool nomenclature on surface roughness obtainable

ATTRIBUTES OF FEED AND TOOL NOMENCLATURE ON SURFACE ROUGHNESS OBTAINABLE

The quality of surface plays a very important role in functionality of produced part. Surface roughness has received serious attentions for many years. It has formulated an important design feature in many situations, such as parts subject to fatigue loads, precision fits, fastener holes, and esthetic requirements.

The most important measures of surface quality during the machining process is the average surface roughness (Ra). It is generally caused by many machining parameters, such as true rake angle and side cutting edge angle, cutting speed, feed rate, depth of cut, nose radius, machining time etc.

The surface finish of any product depends mostly on the following factors.

(i) Cutting speed

(ii) Feed

(iii) Depth of cut

(iv) Tool nomenclature.

(i) Cutting speed:

The better surface finish can be obtained at high cutting speed. Rough cutting takes place at low cutting speed.

(ii) Feed:

Surface finish will not be good when coarse feed is applied. But a better finish can be obtained in fine feeds. Therefore, increase in feed rate can increase the surface roughness. 

(iii) Depth of cut:

Lighter cuts provide a good surface finish to the workpiece. If the depth of cut increases during machining, the quality of surface finish reduces. Therefore, higher cutting speeds, fine feeds and low depth of cuts are applied to ensure a good surface finish. Usually, it is done in finishing cuts. But, lower cutting speeds, coarse feeds and heavier depth of cuts are applied in rough cutting operations.

(iv) Tool nomenclature:

Various tool nomenclatures such as true rake angle, side cutting edge angle, clearance angle, and nose radius plays role in surface finish. Among these nomenclatures, the nose radius will have more effect on the surface roughness. The surface roughness is directly proportional to the cutting speed and feed rate and it is indirectly proportional to the nose radius. The surface roughness increases with reduction in nose radius.

Calculation of surface roughness:

Ideal surface roughness is a function of only tool feed and geometry. It represents the best possible finish which can be obtained for a given tool shape and feed. It can be shown that the roughness value is closely related to the feed and corner radius (turning cutting tools are usually provided with the rounded corner) by the following theoretical expression:

where

Rmax is the height of (surface roughness) profile; 

f is feed and

r is radius of rounded corner of cutting tool.