5.5. Diffusion Welding
The method was found out in the USSR by N.F. Kozakov. It is one of methods of pressure welding. The works 1 (Fig. 5.25) are replaced into vacuum chamber 3, pressed and heated by heater 2. The welding occurs by the mutual diffusion of atoms in the surface layers of the pieces brought in contact.
The advantages of the method are
- the absence of electrodes and fluxes;
- the absence of weld when the same metals are welded;
- the possibility to weld materials which cannot be welded by other methods, for instance, metal and glass, steel and aluminium, etc.
The disadvantages of this method are the following:
- long time of welding (15…25 min);
- welding in vacuum.
Fig. 5.25. Diffusion welding: 1 – works to be welded; 2 – heater; 3 – vacuum chamber
6 Metal cutting operations
Quite accurate workpieces and parts may be produced by the advanced methods of casting, metal forming and welding. But their dimensional accuracy and surface finish are not satisfactory to use them for assembling the machines and devices. Therefore machining still remains and will probably be for a long time the main technique of finishing mechanical treatment.
We can say that machine tool is a mother of all machines, devices and things used by people, because each of them is produced by machine tool. So, machine tool is the basis of human society.
In simple terms a machine tool is a power-driven machine designed to cut or shape metal or other material. From the machine tool flows every object of our industrialized word: automobiles, airplanes, atomic bombs and atomic power plants, washing machines, electric stoves, radio-sets, refrigerators, etc.
6.1. Principles of Cutting and Shaping the Metals
In many cases the desired shape and dimensions of a workpiece are obtained by detaching chips from the material by means of cutting tools. Machine tools shape workpiece by cutting operations (Fig. 6.1). During the sequence of operations workpiece and tool perform certain motions relative to each other.
The process of chip removal is affected by the working motions of the machine tool (formative motions), which are transmitted either to the cutting tool, or to the workpiece, or to the both simultaneously. Working motions of the machine tool include a primary cutting motions and a feed motion (motions). Each of the working motions is specified by its speed or rate.
The primary cutting motion V provides cutting of the chip from the blank at a cutting speed V equal to the velocity with which the chip leaves the work.
The feed motions enable the cutting process to be extended to the whole surface to be machined; it may be longitudinal S1 or transverse St.
In addition to the working motions auxiliary motions are needed to prepare the machine, tool and work for carrying out the cutting process. One of them is setup motion of tool Ss, which, determines the cross-sectional area of the chip, or the thickness t of removed metal.
Fig. 6.1. Schemes of the basic machining operations: a – turning; b - milling;
c – drilling; d – planning; e, f – grinding; g – broaching
A straight-line reciprocating primary cutting motion V is employed in shapers (Fig.6.1d), planers, slotters, etc. This motion can be transmitted either to the tool, as in shapers and slotters, or to the work, as in planers.
The cutting cycle consists of a working stroke Vw during which the tool cuts a chip, and the idle or return stroke Vr, when the tool or work returns to its initial position.
In turning (Fig. 6.la), drilling (Fig. 6.1c), milling (Fig. 6.1b) and grinding (Fig.6.1e, f) the primary cutting motions are rotary motions of work, or of tool. In broaching (Fig. 6.1g) longitudinal feed is absent.
There is no set-up motion in the drilling, so the width of cut is determined by drill diameter.