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Die Casting News

Part 2/4 - Die Casting Porosity Causes and Solutions

Posted by Hill and Griffith Company on Mar 7, 2019 2:13:25 PM

By Tim Cowell, Hill and Griffith Company, Technical Director

Gas Porosity (Runners)

The next location of trapped air is likely to be in the runners. Any sharp corners, high or low ejector pins, or small to large area changes in the metal flow path in the runner system will cause air entrapment. The main rule is that the runner has smooth, rounded corners, that it has ever decreasing area from the plunger to the gate, and that the ejector pins be flush. How much problem will a low ejector pin cause? It is very likely that it will not be noticeable on any given casting, but there is absolutely no question that it adds porosity to the casting somewhere, it is just a question of whether it is a quality issue for this particular casting.

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Tags: Die Casting, Die Casting Lubricant, Tim Cowell, Die Casting Porosity

Part 1/4 - Die Casting Porosity Causes and Solutions

Posted by Hill and Griffith Company on Feb 27, 2019 5:44:03 PM

By Tim Cowell, Hill and Griffith Company, Technical Director

Gas Porosity

Porosity is the biggest problem in die casting.

There are two basic types of porosity

  • Gas Porosity
  • Shrinkage

It is critical that the individuals who are responsible for solving defects determine the kind of porosity before trying to correct it. Each takes a completely different corrective action, however they can look similar. This presentation will show examples of the two primary types of porosity. Generally, a porosity defect should be examined under 5 to 10 power magnification as a minimum. Also, it is usually better to fracture a casting to look at porosity rather than cutting it. Pay particular attention to the geometry (shape) of the porosity.

The high gas content prevents heat treating or welding because it makes the strength unpredictable. Gas porosity is round and generally smooth, although it can be flattened to some extent by pressure. The actions taken to reduce gas porosity will be reviewed, but in general they are not the same as the actions for reducing shrink porosity.

There are three major sources of gas porosity for die castings:

  • Trapped air
  • Steam
  • Gas from lubricant

Any turbulence in the metal movement that allows some air bubbles to be trapped in the metal will mean that these bubbles will be there when the casting is solidified.

  • Air can be trapped in
  • Shot Sleeve
  • Gating System
  • Die Cavity

Gas Porosity (Shot Sleeve)

By the time the metal reaches the gate, the metal flow should be atomized, however, it is vital that efforts be made to reduce turbulence as much as possible during the time frame the metal is flowing to the gate. Starting with the shot sleeve, this presentation will review potential sources of trapped air and possible corrections. The first step is to maintain the same pour rate and shot delay time - this is especially important if the fill percentage is below about 50%. When the fill is less than 50%, a wave is generated by the pouring action, and this wave travels back and forth from the parting line to the shot tip.

If the wave is met by the tip as it moves forward, then extra splashing and sloshing is generated, and this captures some bubbles. However, if the tip is started forward just after the wave has been reflected from it, then the tip “chases” the wave, and this will give the best chance for minimizing air entrapment. The timer that sets the time delay between the end of pour and the start of shot will determine when the tip starts forward in relationship to this wave.

The next phase of the shot profile will be the critical slow shot speed (CSS) - this will be the speed that minimizes the trapped air during the slow shot phase. This speed is calculated from the formula:

Where k = 71 for mmps (inch system). This speed will minimize the air trapped in this portion of the shot.

The following settings should be considered important when trying to reduce air trapped in the shot sleeve. While one of these settings may not seem to be important by itself, there are interactions and it’s recommended they be repeated as close as possible once a good setting is found.

  • Pour rate
  • Delay time before shot
  • Slow shot acceleration
  • Pour hole speed
  • Change over point from pour hole speed to slow shot speed
  • Slow shot speed
  • Fast shot start point

We'll continue next week with die casting porosity caused by runners.


What are die casting release agents?

Die casting lubricants are designed to produce castings without defects such as soldering, staining or porosity. Too little application of lubricant can cause the part to stick to the die "Soldering." Too much can cause discoloration of the die casting "Staining." Too much lubricant in specific areas of the mold is only one of the many reasons for "Porosity." Proper use of die casting release agents combines an exact type, amount and time of application determined by careful observation and analysis.


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Tags: Die Casting, Die Casting Lubricant, Tim Cowell, Die Casting Porosity

NADCA - Die Casting Operator Training Webinar Series

Posted by Hill and Griffith Company on Feb 20, 2019 3:12:39 PM

The die casting industry depends on the skill of the machine operator for efficient production of high-quality products.

The effective machine operator understands the basic function of the process, the proper care of the die casting machine, die setup, recognition and control of basic casting defects, and the procedures that ensure his/her personal safety.



The North American Die Casting Association has created an eleven part webinar series geared towards educating operators on the do's and don'ts of running a die casting machine. Signing up for all eleven parts of this series will also grant you access to these courses through the NADCA Online Education System, which allows you to view the recordings, pdf's and support material for a full year.

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Tags: Die Casting, Metal Casting, Die Casting Plunger Lubricants, Aluminum Die Casting Process, Die Casting Release Agent, Die Casting Defects, NADCA

Die Casting - Surface and Gas Porosity Defects

Posted by Hill and Griffith Company on Feb 13, 2019 10:57:59 AM

NADCA EC-515 Die Casting Defects Course Review, Basics for controlling die casting defects - By Dr. Steve Midson

Gas porosity is the biggest single problem in die casting. High gas content prevents heat treating or welding and makes strength unpredictable.

  • There are three major sources of gas porosity for die castings: Trapped air, Steam, Gas from lubricant
  • Gas porosity is round and generally smooth, although it can be flattened to some extent by pressure
  • The actions to reduce gas porosity, in general, are not the same as the actions for reducing shrink porosity
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Tags: Die Casting, Metal Casting, Aluminum Die Casting Process, Die Casting Release Agent, Die Casting Defects, NADCA

NADCA Video News: Die Casting Defects - Inclusions, Leakers and Cracks

Posted by Hill and Griffith Company on Feb 6, 2019 1:45:04 PM

The material presented in this video are some highlights from the North American Die Casting Association’s online webinar - Die Casting Defects - Inclusions, Leakers and Cracks.

This course discusses various types of inclusions and corrective measures to minimize inclusions. In addition, causes of leakers and corrective measures are presented. Lastly, the various causes of cracks in die castings are discussed.



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Tags: Die Casting, Die Casting Process Improvement, Die Casting Process Evaluation, Die Casting Process, NADCA Video Highlight, Die Casting Surface Defects

Die Casting Process Evaluation Checklist

Posted by Hill and Griffith Company on Jan 30, 2019 2:34:34 PM

Regular reviews and benchmarks are important for successful die casting process evaluations

The Hill and Griffith Company offers this helpful Die Casting Process Evaluation Form to submit your input.
 
On-site process surveys, casting defect investigations, product testing, tooling start-up programs, statistical process controls are available.
 
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Tags: Die Casting, Die Casting Supplies, Die Casting Release Agent Application, Die Casting Process Improvement, Die Casting Lubricants, Permanent Mold Coatings, Die Casting Process Evaluation

NADCA Video News Update: Alloys for High Integrity Die Casting

Posted by Hill and Griffith Company on Jan 24, 2019 5:09:18 PM

The material presented in this video are some highlights from NADCA’s online webinar - High Integrity Die Casting: Alloys for High Integrity Die Casting.

In this webinar all aspects of aluminum high integrity die casting alloys will be covered: from AA numbering, basic metallurgy, the role of alloying each element, impurities and their impact on part quality and properties, ... all the way to different alloy families and existing alloys currently used or under development, with their advantages and disadvantages, current and potential applications as well as achievable properties (using different heat treatments) with each of them.

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Tags: Die Casting, Die Casting Process Improvement, Die Casting Process Evaluation, Die Casting Process, NADCA Video Highlight, Die Casting Surface Defects

NADCA Video News Highlight: Die Casting Defects - Flash, Solder, and Other Defects

Posted by Hill and Griffith Company on Jan 16, 2019 2:17:34 PM

The material presented in this video are some highlights from NADCA’s online webinar

This course is focused on the causes and corrective measures related to a number of defects including: blisters, sinks, solder, flash, erosion, out-gassing, and cold flakes.

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Tags: Die Casting, Die Casting Process Improvement, Die Casting Process Evaluation, Die Casting Process, NADCA Video Highlight, Die Casting Surface Defects

NADCA Video News: Die Casting Defects - Shrinkage Porosity

Posted by Hill and Griffith Company on Jan 9, 2019 4:12:11 PM

Shrink porosity can also be reduced by metal pressure.

"With the high pressure die casting process, we use intensification in all of these processes whether it's called the whole time in zinc, whether it's intensification in aluminum and magnesium, we're using those high pressure features to fill those voids.

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Tags: Die Casting, Die Casting Process Improvement, Die Casting Process Evaluation, Die Casting Process, NADCA Video Highlight, Die Casting Surface Defects

Engineering Die Casting Dies: Dimensional Repeatability - NADCA Video Highlight

Posted by Hill and Griffith Company on Jan 2, 2019 10:09:26 PM

Define what the customer wants and use a standard approach to what the die casting process can achieve.

The material presented in this video are some highlights from NADCA’s online webinar – Engineering Die Casting Dies: Dimensional Repeatability. This looks at defining what the customer wants and gives a standard approach to what the process can normally achieve, with such things as dimensional tolerances and flatness. It covers defining what your plant can achieve on a day-by-day basis using a small amount of math.

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Tags: Die Casting, Die Casting Process Improvement, Die Casting Process Evaluation, Die Casting Process Modeling, Die Casting Process, NADCA Video Highlight, Die Casting Surface Defects

 


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