JNTU B.Tech III MACHINE TOOLS Previous Question Paper (August - 2022 - R13)

The ASA (American Standards Association) system defines tool geometry relative to the tool shank, making it highly practical for setting up tools on machine tools. It uses a coordinate system where the tool shank base is the reference plane. Conversely, the ORS (Orthogonal Rake System) defines tool geometry relative to the cutting edge and the direction of the resultant cutting velocity vector, making it superior for theoretical analysis and research into cutting mechanics.

Key differences include:

• Reference Plane: ASA uses the tool base; ORS uses the orthogonal plane perpendicular to the cutting edge.
• Rake Angle: ASA defines rake angles relative to the shank axes; ORS defines them based on the chip flow direction.
• Application: ASA is used for tool manufacturing and shop-floor grinding; ORS is used for analyzing chip formation and force components.

A sketch would show the tool shank aligned with the X-Y-Z axes for ASA, while for ORS, the coordinate system is rotated to align with the cutting edge and the normal to the rake face.

Machinability is a relative property of a work material that indicates how easily it can be cut by a tool under specific machining conditions. It is not an absolute physical constant but is evaluated based on factors such as tool life, surface finish achieved, power consumption, and the ease of chip disposal.

Its importance is significant for the following reasons:

• Economic Efficiency: High machinability allows for higher cutting speeds and feeds, which directly reduces production time and manufacturing costs.
• Tool Life: Materials with good machinability cause less abrasive and adhesive wear on the cutting tool, leading to longer tool life and fewer interruptions for tool changes.
• Surface Integrity: It ensures that the final product meets dimensional tolerances and surface finish requirements without excessive post-processing.
• Power Consumption: Materials that are easier to machine require less cutting force, thereby reducing the energy demand on the machine tool and minimizing machine vibrations.
• Process Planning: Understanding machinability allows engineers to select the optimal cutting parameters, tool materials, and lubricants during the process planning stage.