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Fall 2015, Vol. 11, No. 2

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InsideCWMv112-thumb

  • CWM Addresses Critical Industry Issues to Congress
  • CWM and A-Dec Flash Their Pearly White Castings to Take Home the IMA Award
  • High School Student selected for Summer Internship Program
  • CWM Employee Has Deep Roots in Civil Rights History
  • 2015 Annual Summer Picnic Luncheon
  • CWM Uses GoPro in Training
  • Perspectives: Bill Baraglia Celebrates 46 Years with Chicago White Metal
  • 35th Annual Golf Outing Recap
  • Continuing Equipment Investments

  Inside CWM Newsletter, Vol. 11, No. 2pdf-icon

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?

die casting engineering dc2 image

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.

LED-Light-Housing-Magnesium-Die-Casting-Part

 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!  

Many Places for Mini: Miniature Zinc Die Castings

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A group of miniature zinc die casting components shown are projects that CWM has worked on over the years.

Miniature zinc die casting is a precision die casting process which addresses the need for smaller component production.  The process is similar to conventional hot chamber die casting, but has the ability to produce castings with faster cycle times, tighter tolerances, and minimal value-added operations.  It can also be an economical replacement for other processes such as screw machine or stamping.

These miniature parts can be cast with great precision in comparison to larger die castings.  

This electronic whiteboard part is a miniature zinc die casting from CWM.  This image compares the size of the part with a quarter.

Thin walls, minimal flash, and ability to produce complex geometries are among the benefits of choosing miniature die casting for smaller parts.  Miniature die casting can be used in many different industries such as: medical, military/government, electronics, computers & peripherals, lawn & garden, alternative energy, telecommunications, global positioning services (GPS), lighting, consumer products, automotive, and many others. n also be an economical replacement for other processes such as screw machine or stamping.

 

A miniature zinc die cast part for a handheld bar code scanner is compared against a quarter.

Using four-slide machines and single cavity tools, cycle times are significantly faster than conventional die casting, yet still offer great accuracy and repeatability.  With a single cavity tool, tolerances of +/- .001 of an inch are possible on select features. This becomes a crucial advantage as die cast parts get smaller, as costly secondary machining can be avoided.  If larger volumes are required, it is not uncommon to utilize multiple cavity tooling.

For more information on miniature zinc die casting, visit our Mini Zinc Die Casting Page or e-mail us at sales@cwmtl.com.

NEW and FREE Download:  A Quick Overview of 10 Different Miniature Zinc Die Castings!

OEMTechBrief47-10-Mini-Zinc-Die-Casting-Case-StudiesFor more information on Miniature Zinc Die Casting, check out the rest of this article today by downloading our newest document!  This article gives a brief overview on 10 CWM Case Studies, specific to Miniature Zinc Die Casting.  Register and download today!

Register for or log into your account at dc2.cwmdiecast.com.  This resource for design assistance is at NO COST TO YOU and is entirely FREE to use.  Download PDF documents, past webinar presentations, and other resources that will prove useful in the die cast engineering process.

For additional resources online to assist with the engineering design of your die castings, you may also access our FREE Die Casting Design Center (DC2) for webinars, case studies, and other documents pertaining to all things die casting.

Aluminum vs. Magnesium vs. Zinc: Alloy Properties in a Nutshell

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Aluminum, magnesium, and zinc are the most common alloys used in the die casting process.  Aluminum and magnesium are considered to be relatively “lightweight” metals, and zinc alloys are a preferred metal to use in the miniature die casting processes and applications requiring thinner walls.

Deciding which alloy is best suited for a specific application of a die cast part is usually based on the design specifications – the alloy usually provides physical and mechanical properties that fit the end product application.  It is important for a product designer seeking a die casting supplier to understand each type of alloy being offered and what benefits are involved.

Aluminum Die Casting Alloy

Metal Die Casting Worker is hand filing an aluminum component at the parting line.

Aluminum is by far the most frequently used alloy in die casting.  The most common aluminum die casting alloy is A380, which offers the best combination of material properties and castability.  Aluminum alloy die castings are used in a wide variety of industries.  It is common to see this alloy in electronics, communications equipment, automotive components, gear cases, lawn mower housings, hand and power tools, and many other products.

There are a number of aluminum alloys used in die casting.  Each alloy has its own unique set of properties.  Aluminum alloys for die casting have superior machining characteristics in comparison to iron, steel, and titanium.  Amongst the other types of aluminum alloys, A380 has better than average machining characteristics.

Aluminum die casting alloy informational sheet from NADCA.

For more information on Aluminum Alloys for Die Casting:
Click Here to Register and Download “NADCA Alloy Data: Aluminum Alloys” White Paper.

 

 

Magnesium Die Casting Alloy

Magnesium alloys are Magneisum die casting used as a Kodak camera housing.the lightest of the commonly used structural metals used for die casting.  Magnesium alloy AZ91D offers the highest strength of all commercial magnesium die casting alloys.  It is also the most widely used.  AZ91D Magnesium is a high purity die casting alloy which offers the following qualities:

–          Excellent Corrosion Resistance

–          Excellent Castability

–          Excellent Strength

Corrosion resistance is achieved by enforcing strict limits on three metallic impurities: Iron, Nickel, and Copper.

Some of the more common applications for magnesium die castings are:

Automotive: cam covers, steering columns, steering wheels, brake and clutch pedals, clutch housings, seat frames, and dashboard supports; Portable tools such as: chain saws, drills, grinders, lawn mowers, string trimmers and pruners; portable electronics such as: projectors, cameras, radar indicators, calculators, and navigation devices; telecommunications equipment, levels; and recreational products such as: snowmobile components, archery bows, spotting scopes, etc.

While there are special precautions to take when machining or grinding magnesium die castings, magnesium alloys machine easily, requiring less power to machine than the other die casting alloys.

Finishing magnesium castings is similar to other alloys and any special treatments and coatings are usually taken into account when considering the end product and application.

magnesium alloys for die casting - information sheet from NADCA.  For more information on Magnesium Alloys for Die Casting: 
Click Here to Register and Download “NADCA Alloy Data: Magnesium Alloys” White Paper.

 

Zinc and ZA Die Casting Alloys

Zinc and ZA alloys are Zinc and ZA Alloys have ingots and recycled zinc, ZA8, Zamak 3 die casting scraps.  commonly used for smaller die castings or die castings that require thinner sections.  Zinc alloys generally allow greater variation in section thickness and can maintain closer tolerances.  The impact strength of zinc die cast components are higher than the other common metal alloys, with the exception of brass.  Also, because Zinc and ZA alloys require lower pressure and temperatures in comparison to magnesium and aluminum alloys, the die life is significantly longer and maintenance is relatively minimal.

Zamak alloys all contain approximately 4% aluminum and a smaller percentage of magnesium to make sure strength, hardness, and corrosion resistance properties can be achieved.

When it comes to miniature die castings, zinc is definitely the route to take.  Miniature zinc die castings can be produced at high volume using special hot-chamber die casting machines that yield castings which are flash-free, with minimal draft and very close tolerances, requiring no secondary trimming or machining.

Zamak #3 is the most common of the Zinc alloys for die casting, offering the best combination of mechanical properties, castability, and economics.  These zinc alloy metals have the ability to produce castings that have intricate details and surface finish at high production rates.

ZA alloys have more aluminum and copper content in them than the Zamak group for several reasons:  higher strength, superior wear resistance, superior creep resistance, and lower densities.  ZA-8 is the sole ZA alloy that can be die cast by the faster hot-chamber process.

Machining characteristics of Zamak and ZA are very good and both alloys have the ability to accommodate high-quality surface finishes when routine guidelines for machining zinc are followed.

zinc, miniature zinc, ZA8, and zamak alloy groups explained in this NADCA information sheet about die casting alloys.  For more information on Zinc Alloys for Die Casting: 
Click Here to Register and Download “NADCA Alloy Data: Zinc and ZA Alloys” White Paper.

 

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magnesium zinc and aluminum die casting engineer at work.

If there are any suggestions to be made to gain more information, it is this:  have that initial discussion with a die casting specialist or engineer regarding the product and its application!  This will increase the understanding from a product design standpoint in order to know what options are available and best for your product.

 

North American Die Casting Association. “NADCA Alloy Data: Aluminum Alloys,” “NADCA Alloy Data: Magnesium Alloys,” “NADCA Alloy Data: Zinc and ZA Alloys.”  NADCA Product Specification Standards for Die Castings. 9th ed. Vol. #402. Arlington Heights, IL: NADCA, 2015. N. pag. Print. NADCA Publication.