Bab_3.pdf

WHAT IS SURFACE TEXTURE???

Is defined as a degree of finish conveyed to the machinist by a system of a symbols devised by a Standards Association.

Modern technology has demanded improved surface finishes to ensure proper functioning and long life of machine parts.

SURFACE TEXTURE TERMS AND DEFINITIONS

FLAWS

defects, are random irregularities, such as scratches, cracks, holes, depression, seams, tears or inclusions.

These defects can be caused during the machining or production process such as moulding, drawing, forging, machining, holes cause by air bubbles during casting, crack and tears by forging and drawing process.

LAY

Lay or directionality, is the direction of the predominant surface pattern.

Caused by the machining process and it is usually visible to the naked aye.

ROUGHNESS

Closely spaced, irregular deviation on scale smaller than that of waviness.

Caused by the cutting tool or the abrasive grain action and the machine feed. Roughness may be superimposed on waviness.

WAVINESS

Recurrent deviation from a flat surface, much like waves on the surface of water. It is measured and described in terms of the surface between adjacent crests of the waves (waviness width) and height between the crests and valleys of the waves (waviness height).

Caused by the cutting tool or the abrasive grain action can be caused by: - deflection of tools, dies or the work piece - force or temperature sufficient to cause warping -uneven lubrication - vibration - any periodic mechanical or thermal variations on the system during manufacturing operations.

STANDARD SYMBOLS TO DESCRIBE SURFACE TEXTURE Maximum roughness height (m) Minimum roughness height (m)

Lay symbol (lay perpendicular to the line representing the surface to which the symbol is applied)

Maximum waviness height (mm) Maximum waviness width (mm) Maximum roughness width (mm)

SYMBOLS FOR SURFACE ROUGHNESS

SURFACE ROUGHNESS

The Arithmetic Mean Value, Ra •Formerly identified as AA for arithmetic average or CLA for center-line average. • based on the schematic illustration of a rough surface.

The Root-Mean-Square Average, Rq

Formerly identified as RMS

Maximum Roughness Height, Rt # defined as the height from the deepest trough to the highest peak. # indicates how much material has to be removed in order to obtain a smooth surface by polishing or others.

USING A SURFACE TEXTURE COMPARATOR