Before starting, let’s specify which sector we are referring to when we talk about Cold Forming, to make no mistakes later on. In this case, it makes reference to the technology which from a wire or metal wire rod produces mainly Fasteners. The equivocations begin when we confuse shaping the metal wire rod in cold with forming sheet metal, because certain people use the denomination Cold Forming to refer to the metal stamping sector.
Within the family of the Fasteners, most pieces are produced by Cold Forming. The pieces which are most common are screws and nuts. Apart from these, the range of pieces produced is vast, with pieces which combine geometry and holes. The producers of Fasteners basically count on clients from the automobile sector, but also supply to other sectors like: wood and furniture, household appliances, plumbing, electronic components…
Apart from the denomination cold forming, the terms cold forging and cold heading are also used.
One of the main characteristics of Cold Forming is its high productivity. This high productivity comes from the cold headers, because they are designed to work totally automatically. To obtain this total automation, the system of wire coil feeding is important, but above all, the key is in the transport system which makes the forged pieces pass on by themselves from one phase to another. Different possibilities exist for transport; the most complex and special is transport through transfer.
Every cold formers has its own work capacity, referring to the diameters of the wires which are to be worked on, the quantity of pieces produced per minute and the length of the pieces which can be formed. There are many types of machine on the market; each type is focussed on a certain type of pieces: machines for very small pieces (the smallest can work with wire of a diameter of around 1mm) which are usually the fastest (they can work at about 600ppm maximum). The biggest are around 35 to 40mm, these being at the same time the slowest (80ppm maximum).
The following is a summary of the principal virtues of Cold Forming, when compared with other technologies:
1.- High productivity. The example in the photo shows the high number of pieces which can be produced by cold forming, at the same time that it shows a similar one produced by machining.
2.- The final product will be better if it has been produced by Cold Forming. What is this due to? To the fact that the piece obtained by Cold Forming progresses from station to station, under the forces of compression which make the layers of the material reproduce the outlines of the places through which they have passed. Furthermore, in other kinds of technologies the fibres are destroyed or minimized, but not here. All this means the tensile strength, the hardness and the fatigue resistance of the final products are better. The elongation and compression of area will on the other hand logically be worse.
Piece formed in Cold.
Distribution of resulting layers from different technologies.
3.- The accurate dimensions of the final products and the final coat are usually very good. The repeatability of pieces is exceptional.
4.- In the Cold Forming process the production of scrap or surplus material is minimized. For many products the surplus is zero. Surplus material will only occur in pieces with a passing hole or in pieces with a perimetral cut, and furthermore in limited quantities. In comparison with other technologies the difference is abysmal. From an environmental point of view this quality is very important.
5.- From the combination of these virtues, another one arises: the low cost per unit of the pieces produced. Even so, to be able to specify the exact price of the final product, you must take several factors into account: the complexity of the piece to be produced; the quantity of pieces which the client’s order contains; and whether the piece is suitable to be produced by cold forming…
The photo attached reflects the great difference which exists between recurring to cold forming or machining, in the case of one particular piece, when referring to surplus material and the huge initial piece required.
Apart from the virtues, it is a good idea to list the main limitations. The limitations come from the point of view of:
1.- The impossibility of producing certain types of pieces by cold forming. There may be diverse reasons for this: the geometric complexity of the piece, the size of the piece… During the last few years, pieces which it was previously thought impossible to produce through this technology have been produced, of course within some limitations.
2.- If the production of pieces is to be profitable, the quantity of pieces produced must be high, first because you work with high cost machines, high cost tools and with high machine preparation times, when changing from one type of piece produced to another.
3.- Materials which are not adequate for cold forming. In this sense too, progress has been made, but some materials haven’t shown a good enough behaviour. Nowadays, various kinds of steels are used in the forming process; some types of stainless steels are also included in spite of being a complicated material to shape; aluminium; copper; tin…
Cold Forming is closely associated with other technologies related to this activity, technologies which will importantly influence in the production process of the final product.
Wire drawing is an important stage in the preparation of the wire rod which is to be formed. Wire drawing is in itself a concrete step in the preparation, a step in which the wire rod is gauged to a concrete diameter as a reduction in the diameter of the wire is produced when it is stretched by a line. Apart from the step mentioned, the preparation of the wire rod includes many stages, stages which the wire drawing companies take care of, or in other cases the wire drawing divisions which are found within certain cold header companies. The stage in which the oxide layer from the steelwork is eliminated is important, as are also the additives which are added to the steel in different stages: phosphate and soap. During the preparation, annealing treament is applied to the material to maintain its moldability.
THREADING BY LAMINATION
Many formed pieces have a zone which in a latter stage should be threaded. Threads are usually obtained from the company which has formed the pieces through threading machines that in turn produce threading by lamination. When threads are obtained by lamination, you recur to a type of thread which is full of advantages. What advantages? On the one hand you maintain the optimal structure obtained by the arrangement of the fibres and because you are laminating you don’t waste material, but there are certain zones of the material which are compressed, forming the angles of the thread, while the other part expands. The other advantage is the great speed of production, because these machines are capable of threading a large number of pieces per munte automatically.
There is the possibility of buying cold headers which come with integrated threading, as well as pointing machines. Companies which are looking for flexibility in production usually prefer to keep the threading machines separate.
HEAT TREATMENTS AND COATINGSAfter being formad the majority of pieces usually go through later stages in which they are treated thermically to improve their propertiers and later coated to improve their performance under conditions of rust and oxidation. It’s clear then that we are referring to two types of industries which are very close to Cold Forming.