Powder metallurgy is a very important production technique that is used in the metal industry commonly. There are various kinds of metallic parts are produced with powder metallurgy techniques. In here, you can find information about;
- The general process characteristics of powder metallurgy technique,
- Advantages and disadvantages of powder metallurgy over other metal shaping processes.
- Materials and part characteristics of the products of powder metallurgy process.
What Is The Powder Metallurgy Process?
Powder metallurgy techniques consist of the required tooling to press the metals which are in the form of very very small particulates. These toolings are the shaping dies and the pressing mechanisms such as hydraulic pistons.
The metal powder is put inside the shaping dies to fill the cavity inside the dies. Then the high amount of pressures are applied with the pressing machines. With these pressing forces, dies are heated to temperatures right below the melting temperature of the metal. This step of the powder metallurgy technique is called sintering.
Devising the sintering step of the whole process is the most important part of the powder metallurgy.
Advantages Of The Powder Metallurgy Techniques
In terms of dimensional control, powder metallurgy techniques are superior to other conventional metal shaping processes.
Powder metallurgy processes can be automated to adapt the processes to a serial production manner.
Net shapes or near net shapes from metals can be produced with the powder metallurgy techniques. So, the requirement of additional shaping processes is eliminated.
Porous metal parts can be produced with the nature of the metal powders. With this porosity, oil impregnated parts such as bearing can be produced easily.
Waste material is very low compared with other conventional metal shaping processes. Over 97% of the starting materials are used in the part production.
With powder metallurgy techniques, different types of metal alloys can be produced such as cermets.
Parts from some metals can not be produced with the conventional metal shaping processes. With powder metallurgy techniques, these metals can be used to produce parts. For example, tungsten filaments are produced with powder metallurgy technologies.
Disadvantages Of The Powder Metallurgy Techniques
Handling and storing the metal powders can be troublesome in the manufacturing site.
In general, the tooling and equipment required for the powder metallurgy techniques can be expensive. So, powder metallurgy techniques are suitable for high production rates.
Powder forms of metals are expensive compared with the bulk form of metals. This fact adds extra cost to the production of parts.
Shape restrictions are very important because of the low flowability of the metal powders through lateral channels. And some allowances must be provided to de-attachment of the produced part from the sintering die.
For complex geometries, density throughout the sintered part may vary.
Metals Are Used In Powder Metallurgy Techniques
In the conventional powder metallurgy techniques in the metal industry, the most used metal powders are iron, aluminum, and steel. Copper and nickel metal powders are used in powder metallurgy techniques.
In the production of refractory products, molybdenum and tungsten metal powders are used.
Physical Characteristics Of The Metal Powders
Characteristics of the powders that are used in powder metallurgy techniques are very important for the process design steps. First of all, the metal powders must be classified. This classification is generally made by different screens that have different meshes. With these meshes, metal powders classified into different shapes and sizes. These different shapes and sizes of metal powders show different physical characteristics, which are very important for the powder metallurgy processes.
Internal structures of the metal powders are also very important. Generally, these internal structures are defined as open pores or closed pores.
Metal powders that have external pores between particles are called open pores. These open pores are very important for the penetration of the fluids. Lubricative characteristics are very important for the.
If the metal particles have internal voids, these voids are called the closed pores. These closed pores do not have any effect on the physical characteristics of the powders. But they can affect the density measurements of the parts.
Interparticle Friction Of The Metal Powders
This is a very important characteristic of the metal powders that are used in powder metallurgy. If the interparticle friction between metal powders is high, the flowability of the metal powders is very low. If the flowability of the metal powders is low, this means, the ability of the metal powder to fill the mold cavities is very low. This is a negative effect.
If the interparticle friction is low, this means the flowability of the metal powders is high in the mold cavities. So, this is a desired physical characteristic of the metal powders.
Interparticle friction can be measured with a very basic experiment. If the metal powder is spilled through the narrow funnel, there will be a cone-shaped structure on the ground. The bottom corner angle will give the idea about the interparticle friction of this metal powder.
If this angle is high, interparticle friction is high. If this angle is low, interparticle friction is low.
Measurement Of Packing Factor And Porosity Of The Metal Powders
These terms are very important both for the metal powders are used in powder metallurgy techniques and the metal powders. But first, two of terms must be defined;
- True density; If the produced metal part by a powder metallurgy technique were produced from solid metal, this will be the true density.
- Bulk Density: When the metal powders are poured inside a mold, this loose state of the powders that are filling the mold cavity will give the bulk density.
If the bulk density is divided by the true density, the obtained result is the packing factor. In general applications, the packing factor is between 0.5 and 0.7.
Porosity also can be found, if the packing factor value is subtracted from 1.
So, this is the general information about the powder metallurgy techniques in the metal industry.
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