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Porosity at a Glance

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Die casting is a process whereby liquid metal is injected into a steel die to form a die cast part.  The filling and solidification occurs rapidly under high pressure, and the part “freezes” quickly.   The very nature of this fast-cycling process creates castings that contain some degree of porosity.

What is porosity?

Porosity in a die casting occurs when there is an air pocket that forms because air or gas is entrapped in the metal as it solidifies (gas porosity), or, it is caused by the metal shrinking away from thick sections and toward thin sections, leaving voids in the center (shrink  porosity).

 This indicates gas porosity in a zinc, aluminum or magnesium die cast part. Gas Porosity

The formation of “bubbles” is a sign that the gas is being trapped within the die cast part, which is indicative of gas porosity.  When close to the surface of the casting, these pores can cause surface blisters to form.  A die casting engineer will take a look at venting, gating, lubrication, an increase in time held within the die, and other factors that may contribute to the defect.

This is a picture of shrinkage porosity, which occurs in aluminum, magnesium, or zinc die castings.

Shrinkage Porosity

These pores are larger and irregular in size, occurring in heavy sections of the die casting.  Shrinkage porosity decreases the integrity of the die cast part, especially when machining operations are located in close proximity to the pores.  A die cast engineer will look at the potential of eliminating thick walls and redesigning the section where shrinkage porosity occurs.

Porosity can be influenced by:

–              Material cleanliness

–              Part Design

–              Die Design

–              Metal & Die Temperatures

–              Die Casting Machine Pressure

–              Spray or Mold Release

–              Shot Speed

–              Wall thickness

–              Shrinkage

In order to gain a better understanding of the formation of porosity, a basic knowledge of the die casting process is helpful.

Die Casting 101

Die casting is a process which involves molten metal being placed inside a shot cylinder.  A piston uses a great amount of force and speed to inject the liquid metal into the die that is mounted to a machine.  The machine provides the power to inject the metal and to hold the die shut until solidification occurs, which is aided by using water or oil cooling in the die.   The machine then opens the die and a series of ejector pins, built into the die, move forward to push the part out.

This process is repeated with every die cast part.

CWM die casts all 3 of the most common families of alloy; aluminum, magnesium, and zinc.   We employ state-of-the-art engineering systems to design the dies and develop the process parameters to help make sure that porosity is minimized.

For more information or if you would like to discuss your project further, feel free to contact one of our CWM engineers at sales@cwmtl.com or give us a call at 630-595-4424.

Want to know more about Die Casting Engineering & Design?

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Did this explanation of porosity spark your interest?  Chicago White Metal offers a rich, dynamic resource center for engineers and purchasing managers who are interested to learn more.  Register for or log into your account at dc2.cwmdiecast.com.  This design resource is our gift to you – there is no cost associated with the downloads!  Have unlimited access to our constantly updated library of PDF documents, past webinar presentations, case studies, and other resources that will prove useful in the engineering process of die casting.

CWM and A-Dec Dental win the prestigious IMA Award for Die Casting!

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International Magnesium Association presents Chicago White Metal with the prestigious Magnesium Die Casting Award for Excellence in Design.

Chicago White Metal does it again!  To add to the collection of die casting awards, CWM teamed up with A-Dec to create a part that fulfills and exceeds the high standards and quality of A-Dec’s parts, which ultimately became an award-winning duo.

The International Magnesium Association (IMA) was founded in 1943 with a mission in mind – “promote the use of the metal magnesium in material selection and encourage innovative applications of the versatile metal.”

A-Dec produces high-end dental products with exceptional quality.

This Award of Excellence is an annual award that is given to the company demonstrating an outstanding example of the use of magnesium.  With the rear housing and driver die castings being the first magnesium parts to be used in A-Dec’s LED Operatory Dental Light, the benefit of a decreased mass, ease of movement, and satisfaction of the customer proved to be a winner in itself, even without the award.


 When asked why a magnesium die casting was chosen for this application, a presentation given by Jon Miller a the Closing Banquet said the following:

“Magnesium’s strength-to-weight ratio and thin wall casting capability allowed for a thin-walled, lightweight part, which in turnallowed for a slender, stylish, ergonomic support structure.  Magnesium’s low mass enables the LED light to be easily maneuvered/positioned and minimizes issues with drift, inertia, or vibration.  Magnesium’s ability to dissipate heat allowed for passive cooling of the circuit board and diode connection points.  This means fewer moving parts and helps the unit achieve an estimated 20-year service life.  Magnesium’s ability to be die cast with excellent surface finish, and to readily accept commercial RoHs-compliant pre-treatment and po

magnesium-die-casting-driver-componentswder paint allowed the light housing to have a highly cosmetic appearance, matching the uniformity of the mating molded plastic and painted tubular structure.”

Congratulations to CWM and to A-Dec for amazing teamwork on this magnesium die casting duo!