Machining

WHAT IS MACHINING?

Machining (German: Zerspanen) is a manufacturing method that involves the shaping of the machine element, which is pre-designed and constructed and whose manufacturing process is determined, by subjecting it to cutting operations on Machining machines suitable for the manufacturing process, by means of specified cutting tools. Machining is carried out by creating tension on the workpiece with the relative movement of the cutting tool and / or workpiece relative to each other.

+ Machining Methods: These are production methods that are shaped by moving chips. Turning, milling, planing, shaping, grinding and honing processes are examined in this group.

1. Machining Methods
Chip removal is a complex physical process based on elastic and plastic deformation, where actions such as friction, heat generation, chip breakage and shrinkage, deformation hardening of the workpiece surface, cutting tool wear are observed [Akkurt].

Machining is a chip forming process. Although the purpose of the process is to bring the metal to a certain shape and size, this process must be done in a way that ensures proper chip formation. Machining: This is a dynamic technology involving many different disciplines such as materials, chemistry, statics, heat, etc.

In the chip removal process, when the cutting tool is pressed on the workpiece with a certain force and pressed in the direction of the force, the material starts to flow after elastic and plastic deformations. As soon as the stresses exceed the rupture limit of the material, a certain surface layer, called a chip, is separated from the workpiece.

The factors affecting chip removal are:
+ Cutting tool life span (T)
+ Cutting speed(V)
+ Chip depth(t)
+ Feed amount(f)
+ Cutting angles(KA)
+ Vibration(Vi)
+ Coolant()
+ Tool/workpiece material pair(TM)
+ Cutting tool radius(r)

If these are expressed functionally; F(T,V,f,t,t,KA ,Vi,TM,r)=0

Machining technology is constantly evolving, driven on the one hand by advances in materials and manufacturing strategies and on the other by developments in the tooling industries. This development will bring along the development of modern tool materials, cutter geometries and tool detection methods, and more and more economical production alternatives will emerge in the field of manufacturing.

In the field of machining, the aim is to determine the most suitable cutting parameters for the most economical production and ideal tool life. This process, which is completely dependent on the tool-workpiece material pair, cutting conditions, machine tool and cutting tool, is extremely difficult.

2. Principles of Chip Moving Systems
In machine tools, the basic principle of shaping parts by removing chips is that the final shape of the workpiece is obtained by machining the relevant material. The excess in the raw part is removed by "chip moving" with the tool connected to the machine tool. Chip removal from the material is ensured by the contact of the tool cutting edge with the workpiece surface and in this impact zone, the chip moving energy is transmitted from the machine where the chip is removed to the workpiece. For this reason, the triangle between "Machine Tool-Tool-Cutter (Tool)-Workpiece Material" must be established very well and the variables that shape this relationship, which we call "cutting parameters", must be evaluated well.

Machine Tool-Tool-Workpiece relationship: The impact movements required in chip removal take place in two or three axes "from the workpiece, tool or both". These movements appear as rotation and shifting. Figure 1,2 clearly shows these effects and the way in which they appear on lathes, milling machines and shaping machines, which are very widely known machine tools. Movements occur in three different ways. They are cutting, feed and chipping (approach).

Tools provide machining production are classified in three ways in terms of their working characteristics.
a. According to the chip removal method: Lathe, Milling, grinding, Planing, Shaping
b. According to Control Methods:
+ Manual control,
+ Automatic control: Mechanically and numerically controlled machines
c. Universal and single-purpose machines according to purpose


3. Chip Removal Model and General Concepts
The study of the physical aspects of chip removal is the basis of metal removal theory. Other investigations such as wear, life, temperature, force, energy, friction, etc. are based on chip removal theory.

During chip removal, the establishment of the relationship between machine tool-tool-workpiece requires a good understanding of the "cutting" event. Although the cutting edges of the tools used in the machining of metals and metal alloys are sharp enough, they encounter considerable stresses during chip removal. For this reason, a lot of research has been done to determine the ideal angles (ideal tool geometry) that will facilitate cutting and the appropriate value cross-section that the tool can withstand.

The first study was done in 1851 by Finnie Cocquilhat to calculate the work in drilling. In 1873, Hartig created cutting work rulers and published them in a book. The first studies on chip shaping were carried out by Time in 1870 and the French scientist Teresca in 1873. In 1881, Mollock emphasized the effect of friction on the tool surface, arguing that the method used for cutting the material is essential in chip formation. Based on the properties of partially formed chips, he identified the types of chips. He investigated the effect of the tool tip and cutting fluids on the cutting method and examined unbalanced cutting methods that lead to undesirable results. Much of his work has been influential enough to lay the foundation for today's modern theories.

However, the most influential work on cutting mechanics, as it is widely used today, was put forward by Taylor after 1900. Taylor compiled about 26 years of experiments and investigations and analyzed the effect of cutting parameters and tool material on tool life during machining operations. In principle, he developed empirical formulas that allowed him to apply the most ideal cutting conditions. With the methods he developed, he increased the productivity in the organization he worked for up to 500% under the conditions of the day. It is noteworthy that the principles he put forward are still in use today. Taylor's other most important discovery was the ability to control the tool wear rate with the temperatures generated at the tool and cutting edge. In 1941, Ernst and Merchant developed these principles further, and the mechanics of chip formation (cutting) were refined. These principles, known as Merchant principles, are also widely used today.

Scientists such as Tresca, Hartig, Finnie, Mallock, Taylor and Merchant have contributed to the development of metal cutting technology. If we ere to explain cutting process based on their principles:

"Cutting" is the separation of the cutting tool and the material like a knife. The cutting edge of the tool is formed by the intersection of two surfaces under a certain angle. The sharpened cutting edge is forced symmetrically within the material body, as in bread cutting, and is also moved parallel to the cutting edge within the body. The cut material body is forced into two parts by the cutting tool surfaces. The sharpened cutting edge will ensure that the body is cut with very little force and the parts are less rough.