Use cases ·

Metal sintering process and the use of graphite molds

Starting from powders of different materials as raw materials, these are compacted into molds. Some commonly used materials include tungsten, molybdenum, diamond powder, ceramics and metal powders.  After the compaction process, the parts are subjected to high temperatures to achieve a fusion of the materials.

Metal sintering process and the use of graphite molds

The sintering process, also known as powder metallurgy, has many uses in industry and helps to obtain complex and low-cost geometries.

Starting with powders of different materials as raw materials, these are compacted into molds. Some commonly used materials include tungsten, molybdenum, diamond powder, ceramics and metal powders.  After the compacting process, the parts are subjected to high temperatures to achieve a fusion of the materials.

According to the materials used, it is possible to join the elements without the need to heat up to the melting point of all of them, since in the case of some of them, this can be extremely high. For the sintering of metals we usually work with temperatures between 750 and 1300ºC, depending on the material and its characteristics.

For this reason, we investigated the sintering process and the use of molds and graphite powders in this industry.

What is the sintering process in general?

It is a process that applies pressure and high temperatures to a mixture of material (without the need to reach the melting point of all of them), transforming the precompacted preform into a solid piece with special characteristics.

It should be noted that most of the metallic powders used in the process are iron-based and their main alloying agents are nickel, copper, phosphorus, chromium, etc.

The sintering process encompasses from the pulverization of metals, ceramic materials and others, to the final creation of the part.  This process can be described in four stages:

Raw material

It is aimed at pulverizing the various metal powders and alloying additives. These include ceramic and metal powders such as iron or copper, or alloyed powders such as bronze, brass, steel, among others.

Mixing or Dosing

Depending on the characteristics of the final part, different alloys are mixed to the metallic and/or ceramic powder bases.

It is important to mention that this mixing is carried out by a strict process of dosing and control that determine the mechanical, physical or chemical characteristics of the final part.

Compaction

The powder mixture is placed in the molds by gravity and an axial pressure is applied according to the desired compaction parameters. As a result, a compacted preform is created, which can be manipulated.

Sintering

In general, preforms are subjected to elevated temperatures for a certain period of time, causing the elements to melt. This happens by bonding the particles together or, depending on the compound to be manufactured, by encapsulating the particles in another material.

Advantages of the sintering process

Due to the selection of raw materials, controlled dosage and controlled melting, this process offers certain advantages which are described below:

  • Completely controlled composition.
  • Manufacture of final parts without the need for further work.
  • Manufacture of parts of any material (depending on the type of sintering).
  • Controlled porosity, among others according to the particle size of the raw material (impossible with other methods).
  • Special properties such as extreme hardness and wear resistance can be established.
  • High precision and good surface finish.
  • Large series of parts with close tolerances.

Graphite molds for sintering processes

Having described the sintering process in general, it should be noted that there are variations of this process, where molten material is introduced into a mold previously filled with other elements.

In the case of both processes, graphite sintering molds are excellent for the production of sintered parts due to their resistance to thermal shock, electrical conductivity, hardness and thermal stability.

The production of graphite molds is carried out under traditional machining, e.g. on lathes and milling machines. According to the properties of the sintered part, different grades of synthetic graphite are used, such as iso-molded or extruded.

Some of the characteristics that vary between grades include:

  • The density of material
  • Its porosity
  • Hardness
  • Mechanical strength, among others.

These mold properties influence the surface finish of the part and parameters such as compaction strength, among others.

Some sintered products based on graphite molds include:

  • Diamond cutting tools.
  • Tungsten carbide tools.
  • Special drill bits for tunnel boring machines.
  • Drilling lance tips.

Conclusions

To conclude, the sintering process is characterized by the production of complex parts at a low cost. In addition, it has a low environmental impact, because it consumes less energy than other transformation processes and allows the optimization of raw materials.

At ESGRAF we are specialists in graphite. We have a wide range of iso-molded and extruded grades used in the sintering industry for immediate delivery. Do not hesitate to contact us to offer you a customized solution for your business.