FRAMEWORK OF THE COLD FORGING PROCESS
Cold forging is an important and historic process in the portfolio of products that ETMA manufactures for its clients. The first machines were installed in the early 1970s and since then it has not only grown, offering more production volume with more machines, but it has also evolved technically, with more complex machines that make it possible to produce more elaborate parts with tighter tolerances.
For this new article, we spoke with Miguel Queirós, an engineer that works as a sales technician at ETMA, to find out more about this manufacturing technology. We will first analyse forging in the context of ETMA’s production and understand how forged parts are made, what the advantages and disadvantages are compared to other processes and what type of parts can be made. In future articles we’ll focus on the more technical aspects of the process, then on part design and the manufacture of forging tools and, finally, we’ll present an article on different applications and examples of parts obtained by this process.
How was cold forging developed at ETMA and how does it fit into the company’s installed capacity?
In the early 1970s, ETMA produced curtain track systems. To assemble various subassemblies of these products screws were needed, which were obtained from sub-suppliers. ETMA’s founder, Mr. Mário Rodrigues da Costa, spotted a business opportunity here and decided to invest in forging machines, thread rolling machines and nicking machines, which enabled the company to start producing screws in-house. Later, this capacity was offered to clients, in order to produce special screws according to their drawings and specifications.
What does the forging process consist of?
It consists of a process of plastic deformation of a volume of metallic material. This is important from a sustainability point of view: the process, in most cases, does not generate waste, because it only changes the shape of the material being worked on.
At ETMA, this process is carried out using the cold method, as the machined parts are small. The forging process can also be carried out hot, usually for large parts, since heat reduces the resistance of metallic materials to deformation. But this is not the case at ETMA.
Regarding cold forging, its main advantages are as follows:
- Manufacture of components with high dimensional accuracy (in some dimensions);
- Geometries close to the use of the part (near-net-shape);
- Good surface finish of the parts;
- High productive rate;
- Preserves and improves the internal structure of the material.
What do you mean by improving parts? And what are the advantages?
Internally, the constituent atoms of metallic materials are organised into highly oriented and ordered structures called “crystalline structures”. This high level of organisation of matter and, in particular, the resulting atomic bonds between layers are the origin of the mechanical and electrical characteristics and properties of materials. In simple terms, we can say that in forging, the layers of material are preserved together with their intrinsic properties. In addition, the high internal compressions generated by forging eliminate some of the internal defects in these structures, so forging can even improve the properties of materials.
For this reason, there are many high-performance applications where forging is the preferred process to ensure highly responsible parts with the mechanical characteristics required for the job, in particular high mechanical resistance, high ductility, high toughness and high resistance to fatigue. This is why it is a very important process in the global industry for highly resistant mechanical components.
Are there any disadvantages to forged parts?
Absolutely.
Some of them are as follows:
- The process is only applicable to simple shapes;
- Tight tolerances are not achieved in all dimensions;
- Tight final tolerances are obtained in subsequent machining operations.
From an industrial point of view, the main disadvantage is that, for components with complex geometries, additional processing (such as machining) is required to obtain the part. The consequence is an increase in the complexity of internal manufacturing logistics and higher processing costs.
What type of parts are usually made by cold forging? Can any material be forged?
In principle, all metals are forgeable, but those with greater ductility are the best or easiest to forge. At ETMA, we can forge steel and stainless steel, copper alloys (copper, bronze and brass) and aluminium alloys. These are the metallic materials most commonly used in industry.
We use cold forging mainly to make screws. Threads cannot be obtained by forging, so in this process only the fully formed head of the screw and the shank are obtained, and this latter is threaded later on, in an additional thread rolling process.
The parts obtained from cold forging are essentially cylindrical or revolution parts, which can have various diameters, screws, rivets, rotating shafts and bolts.
Thanks to material savings and the low level of waste, this process has been attracting interest from clients in recent years, especially in very high quantity series. In many situations it is possible to replace machining completely, or at least partially, for certain types of parts (mainly shafts and bolts).
In cases where machining for finishing is required, the reduction of machine feed times in the second process is vital to keep costs under control and economically interesting.
For this reason, ETMA recently invested in lathes from the manufacturer Muratec, which are particularly suited to part feeding, rather than the continuous bolt feeding that we use on most production lathes.
Which industries consume the most cold forged products?
The diversity of applications and products obtained by forging is due to the favourable quality-production cost ratio achieved in this manufacturing process. All industries can benefit from these advantages. At ETMA, the main clients for these products are in the automotive, electrical and home appliance industries.
We end this first article highlighting that, at ETMA, the demand for tailored solutions, that comply with the requirements of each client, involves the development (comprised of engineers and specialised technicians) and sales teams, who share knowledge and experience with the client, resulting in synergies that are mutually beneficial.
The following topics will be addressed in the next articles:
Technological aspects of the cold forging process
Design of parts and manufacture of tools
The different applications and examples of parts obtained by cold forging
In the meantime, if you are interested in learning more and, eventually, talking to us about a project, please do not hesitate to contact us.