Metal Injection Molding: How Spark OES can Help

Metal injection molding (MIM) has become an indispensable metal fabrication technique since its initial demonstration in the 1930s. MIM involves the creation of small metal shapes by fusing metal powder.

This enables the formation of intricate shapes with minimal waste, resulting in reduced costs. The final components are nearly 100% dense, providing superior strength compared to die-casting, improved tolerances over investment or sand casting, and more intricate shapes than traditional machining techniques.

MIM has been in mainstream production since the 1970s, when it was employed for manufacturing dental orthodontic brackets, watch cases, and firearms.

However, MIM technology has now advanced to produce intricate components for high-performance applications, such as dental implants, artificial joints, pacemakers, and jet engines.

The Importance of Certification and Chemical Analysis

Similar to other metal-forming processes, the composition of the initial powder governs the composition and specifications of the finished component in metal injection molding.

The presence of impurities can have an impact on the performance and longevity of the part, and the component must meet local, state, and federal statutory requirements. Chemical analysis is pivotal in ensuring that components meet customer specifications, internal quality control, and statutory requirements.

In metal injection molding, there are three primary methods of alloying: elemental, pre-alloy, and master alloy. The type of starting powder chosen relies on the alloying method, which can be pre-mixed or blended manually to achieve the correct composition.

For the elemental method, powders of individual elements must be mixed in the proper ratios to obtain the desired composition following alloying.

The pre-alloy process can use a powder that precisely matches the final alloy specification's composition.

The master alloy approach employs an elemental powder with the addition of specific alloying components.

The majority of MIM stainless steel components and some low-alloy steel components are produced in this manner. For instance, a MIM component made of 316L stainless steel is generated by combining one part of a 55Cr38Ni7Mo master alloy with two parts of carbonyl iron powder.

It is crucial to authenticate the composition of raw powders before molding to ensure maximum yield and minimal scrap.

Due to the complexity of the alloying process, the finished components' composition must also be checked before shipping to ensure high quality and performance.

This is particularly critical for components produced for essential applications, such as medical implants or jet engine parts. This is where spark optical emission spectroscopy (OES) is helpful.

OES: A Trusted Technique for Sensitive Applications

Optical emission spectroscopy is a reliable analysis technique for verifying the composition of MIM parts.

This method is known for its high accuracy and precision, making it a popular choice for sensitive applications such as melt control, tramp, and trace element detection in metal fabrication facilities globally.

Spark OES spectrometers are used across the entire metal fabrication process and supply chain, from analyzing trace elements in scrap metals and controlling incoming materials to metallurgical process control and quality control of finished goods.

Using OES for MIM Parts

To ensure a reliable OES measurement, a clean, flat, and planar surface is required at the point where the OES measurement head makes contact with the sample. Depending on the material composition, the sample surface is ground or milled immediately before taking a measurement.

As MIM fabricated components are typically small in size, the area of the measurement site is reduced using a special spark stand plate to minimize the size of the hole in the plate, which leads to accurate results.

If the sample's shape is rather complex, a special sample adapter may be necessary to ensure the sample is held correctly.

Controlling the carbon content in metal components is crucial, as even small variations in carbon concentration can impact the microstructure and mechanical properties of the finished part.

It is especially important to monitor the carbon content in MIM components because the binder used is carbon-based and must be completely removed during the de-binding stage.

The OE750 is a ground-breaking instrument designed with a new optical concept that delivers reliable results for all elements within metals, including gasses.

Although only typically available from more expensive instruments, the OE750 offers this level of performance at an affordable price.

Innovations such as the use of dynamic CMOS detectors and direct coupling of the optics to the spark stand provide the OE750 with the necessary optical resolution for demanding metal injection molding applications. 

Thus, the analytical performance of the OE750 offers an easy and cost-effective solution for controlling carbon content.

This information has been sourced, reviewed and adapted from materials provided by Hitachi High-Tech Analytical Science.

For more information on this source, please visit Hitachi High-Tech Analytical Science.

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