Guru
Introduction
Machining processes are essential in contemporary manufacturing, transforming raw materials into precise components for different industries. Orthogonal cutting and oblique cutting are key techniques that are important for achieving efficiency, surface finish, and tool lifespan in machining operations.In this blog we will study in details about Orthogonal and Oblique Cutting.
Before we delve into Orthogonal and Oblique Cutting we let's take a closer look at metal cutting process.
Principle of metal cutting
- Relative motion between the cutting tool and work piece.
- Tool edge comes in contact with the metal, it exerts pressure on metal.
- Metal severely compressed,causes high temperate shear stress in metal.
- As tool advance, stress in the work piece just ahead of cutting tool reaches a value exceeding the ultimate strength of metal.
- Particles of metal start shearing away and flow plastically along the shear plane.
- It forms segment of chip which moves up alone the face of the tool.
- Cycle of compression, plastic flow and shearing away is repeated.
- It results into from of a continuously flowing chip.
Mechanism of Metal Cutting
The removal of extra material from a metal surface by shearing or cutting action is known as machining or metal cutting. The cutting takes place along a plane, which is known as shear plane. There is a cutting zone; if it is examined carefully, we find that the severe plastic deformation occurs in this zone due to compressive force applied by the sharp-edged cutting tool. The extra material due to this deformation flows over the tool surface, known as chip, and this shearing zone is known as primary shear zone.
During flow of chip on the rake surface of the cutting tool, the temperature of newly formed chip increases due to friction and it gets welded automatically on the rake surface. But, due to compressive force applied by newly formed chip (just after the welded chip) causes secondary shear of the welded chip, and this shear is known as secondary shear. In metal cutting the line generated by the cutting motion is called generatrix and the line formed by feed motion is called directrix.
Definition of Orthogonal and Oblique Cutting
- Orthogonal cutting, also referred to as 90-degree cutting, is when the tool is perpendicular to the workpiece. The cutting edge aligns with the feed motion, resulting in a right angle. It is commonly employed in operations such as turning and facing.
- In contrast, oblique cutting uses a tool tilted at a different angle than 90 degrees from the workpiece surface. It is more intricate than orthogonal cutting and is often seen in milling, shaping, and specific turning tasks.
Orthogonal cutting is a machining process in which the cutting edge of the tool is kept perpendicular to the direction of the tool travel (Figure 5,6).But, in oblique cutting, the cutting edge of the tool is inclined at some acute angle to the direction of the tool travel. There are some fundamental differences in orthogonal and oblique cutting.
Figure 5: Oblique Cutting
Figure 6: Orthogonal Cutting
Differences Between Orthogonal and Oblique Cutting
| Orthogonal Cutting | Oblique Cutting |
|---|---|
| The cutting edge of the tool is perpendicular to the direction of the tool travel. |
The cutting edge of the tool is inclined at some acute angle to the direction of the tool travel. |
| The cutting edge clears the width of the workpiece on either end. | The cutting edge may or may not clear the width of the workpiece on either end. |
| The chip flows over the rake surface of the cutting tool in the direction perpendicular to the cutting edge. The shape of the chip coil is tight flat spiral. |
The chip flows on the rake surface of the tool making an angle with the normal on the cutting edge.The chip flows sideways in a long curl. |
| Only two components of the cutting force act on the cutting edge. | Three components of the forces mutually perpendicular act at the cutting edge. |
| Maximum chip thickness occurs at the middle. | The maximum chip thickness may not occur at the middle. |
| For same feed and depth of cut, the force which shears the metal acts on a smaller area and therefore, the heat developed per unit area due to friction along the tool work interface is more and tool life is less. |
Force of cutting acts on longer area and therefore, the heat developed per unit area due to friction along the tool work interface is more and tool life is less. |
Conclusion
In short orthogonal and oblique cutting are both important in machining, each has its own benefits and obstacles. The decision between them is based on factors like tool life, cutting forces, and surface finish desired for the machining operation. Knowing the variances in these cutting methods helps engineers and machinists make educated choices, improving efficiency and accuracy in manufacturing.