One of the key elements of metalworking is shaping the being worked. Using the example of steel, the particles within the metal are arranged in a formation known as a lattice. This is a regular alignment of particles and gives the steel an extremely high tensile strength, however when this alignment is heated up to an extreme temperature -- around 2,600 Fahrenheit -- the particle alignment begins to destabilize and the metal begins to melt, making it much easier to mold into whatever shape you desire.
Heating metal before shaping it is an expensive procedure but it is usually necessary in order to induce movement into a piece of metal that would otherwise resist or snap. However, as metals are ductile and can be hammered flat, some thinner metal objects can be manipulated at room temperature. The science behind this centers on the atomic bonds within a metal; these bonds are as such that the outer electrons of an atom can move freely, giving the atoms delocalized cohesion. This means that atoms can dislocate to relieve any stress that is applied. This process, and the process of shaping heated metal, straddles the boundary between physics and chemistry; it displays the physical considerations of how a substance reacts under heat and pressure as well as the chemical explanations of why these reactions occur.
A common way to apply a finish to a piece of worked metal is by electroplating. This involves connecting a piece of freshly worked metal to the negative terminal of a power pack, attaching a piece of graphite carbon to the positive terminal and placing both ends in an electrolyte solution. When the power pack is turned on, the positive ions in the electrolyte solution are attracted to the negative metal -- known as the cathode in this process. They attach to the piece of negative metal and form a uniform plating effect. The positive graphite terminal -- or anode -- corrodes away. This is an example of the application of chemistry to metalworking.
In metalworking, two pieces of metal are often joined together by welding. Welding is a process in which two pieces of metal are actually physically bonded together rather than simply attached via some sort of adhesive. This makes the resulting bond far stronger. What occurs is that intense heat is applied to each side of the bond, melting the metal into an amorphous mass. This gives it plasticity rather than rigidity and allows the two sides to combine when the joint is pushed together. The joint remains under pressure until cooling begins to happen and the joint fuses. The welding process straddles the two scientific disciplines of chemistry and physics.