Since MIM technology can guarantee the accuracy and uniformity of material composition ratio, it has become the key to solving new material problems and plays a decisive role in the development of new materials.
In this post, we mainly talk about the precautions for using MIM technology and how to produce quality products by controlling the manufacturing process from the following two aspects:
- Metal powder production methods
- What problems may occur in different procedures and how to fix them.
After reading this post, you can know what kinds of methods are required and improve manufacturing efficiency during the process.
Preparing powder is the first step in MIM. With the development of the powder metallurgy industry, more and more different types of powders are required.
For example, from the viewpoint of the material range, not only metal powder but also alloy powder, metal compound powder are used; In terms of particle size, powders of various particle sizes from coarse powder with a particle size of 500 to 1000 μm and ultrafine powder with particle size of fewer than 0.5 μm are in great demand.
In order to meet various requirements for powders, there are various methods for producing powders. These methods are nothing more than converting metal or alloy in solid, liquid or gaseous state into a powder state.
1.1 Methods for converting solid state metal into powder include:
(1) Mechanical pulverization and galvanic corrosion methods for preparing metal and alloy powders from solid metals and alloys.
(2) A reduction method for preparing metal and alloy powders from solid metal oxides and salts.
(3) Reduction-chemical treatment of metal compound powders from metal and alloy powders, metal oxides and non-metal powders.
1.2 Methods for converting liquid state metal into powder include:
(1) Atomization method for preparing alloy powder from liquid metal and alloy.
(2) Displacement method and solution hydrogen reduction method for preparing metal alloy and coating powder from metal salt solution; molten salt determination method for preparing metal powder by precipitation from metal molten salt.
1.3 Methods for converting gaseous state metal into powder include:
(1) Steam condensation method for preparing metal powder;
(2) Carbon-based thermal dissociation method for dissociating gaseous metal carbon substrates from metals, alloys and coated powders
However, from the essence of the process, the existing methods can be broadly classified into two major categories, mechanical and physical-chemical methods.
The mechanical method is a process in which the raw material is mechanically pulverized and the chemical composition is substantially unchanged; the physical-chemical method is a process of obtaining a powder by changing the chemical composition or aggregation state of the raw material by chemical or physical action.
The MIM process is mainly composed of these steps: feedstock compounding, injection, debinding and sintering. Many problems can occur during these procedures. Next, we will mainly focus on these problems and make some suggestions for solving them.
2.1 Problems in injection and how to deal with them
A. Edge collapse
Edge collapse is generally caused by uneven material density and improper demolding. This problem can be eliminated by improving the pressing method and improving the demolding conditions.
The crack is mainly caused by the wrong mode of demolding and poor pressability of the material. In this regard, it is important to improve the powder compact type and adopt the correct mold release method.
C. Size defects
Excessive mold wear or unreasonable process parameter settings can cause size defects. To avoid such problems, cemented carbide molds should be used and the manufacturing process should be adjusted.
D. Surface scratch
The hardness of the cavity of the mold is low, resulting in partial scratching of the cavity surface. Lubricating oil should be added to avoid this problem.
2.2 Problems in sintering and how to handle them
A. Adhesive carbon deposit
The high density of the sintered part, the unsuitable pre-tropical temperature, the unreasonable furnace temperature setting, and the large mesh belt load will cause adhesive carbon deposition. The countermeasures are: reducing the load, lengthening the pre-tropical zone, and installing a quick-burning device.
B. Granular carbon deposit
When the atmosphere gas moves too slowly, or the exhaust pipe is designed improperly, particulate carbon deposits can exist. It should be improved by increasing the total flow of the atmosphere gas, changing the direction of the atmosphere gas flow and controlling the exhaust pipe ventilation.
C. Severe oxidation
When the atmosphere gas entering the furnace is too wet or the pressure difference between the two ends of the furnace is not suitable, the product is severely oxidized. This requires repairing the source of oxidant during the production process.
In the production process, if air leaks into the furnace or the carbon dioxide content of the atmosphere gas are high, decarburization may occur.
To avoid decarburization, nitrogen and natural gas in the slow cooling zone can be added, or you can control the initial amount of graphite added.
That’s all the quality issues you should know about Metal MIM. We hope it’d be helpful! Don’t hesitate to leave your comments below if you have any question.
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