Brass Casting Defects

But this sounds like a wonderful application for Six Sigma.

Probably, my first question would be - what changed?

I assume the process was working better and has now become worse (was in control and now is out of control).

If that is true, start looking over your data and see what has changed that may correlate to the results you are getting. However, correlation is not causation, so proceed carefully and always doubt the findings until they are proven rock solid.

Make a detailed drawing or flowchart of the process to manufacture the product and look at all variables that control the process (temperature, humidity, brass stock, etc). Don't overlook even the smallest thing. You can go back over the list and rank them for criticality, but don't discount the possibility that something that seems trivial really is not! Look for changes that may have occurred that may drive a change in the product quality.

If the process was never in control and has been producing bad parts from the get-go, then you should consider a design of experiments to understand what variables control the process, the degree of control each variable has, and any interactions between the variables that may generate unexpected results.

If you do not have anyone that is six sigma trained you might look for a consultant that is. It would be a help if someone understands the casting process, but the training (six sigma) will give you a broad spectrum of tools to track down what is going wrong and is probably more valuable than expert domain knowledge of casting.

Even when you find the problem, chances are you can improve the process a lot more by applying diligent record keeping and statistical analysis to ferret out variables that should be further tweaked. Six sigma is really an on-going process a lot like gardening. A bad garden needs a lot of work up front to get it to where you want it, but you will need to keep tending it on a regular basis. The good news is the regular tending is a lot less effort than the fire fighting mode you are in now. What is more important is that you are almost assured you will never be in a fire fighting mode again. That means more profit.

Good luck!!!

I realise that six sigma is proprietary, but it is a pity that the above post was anonymous, because the process is good.

I lost my login information. I guess I should just create a new one.

For that matter I wish my name was Howard, then I could create a new ID called Anonymous Howard.

Nevertheless, was there something specific you wanted to know regarding Six Sigma?

"Six Sigma" as a training/certification protocal may be proprietary, but the information and methods he described are not, although the "Six Sigma" people may want you to think so.

Control Charts, especially those relating to a process mean and deviation ("x bar and r", "x bar and s") have been around for decades. Almost any college statistics book or manufacturing processes book will include a section on that. It is usually referred to as Statistical Process Control, or SPC. The basic goal of SPC is to keep the mean value within control limits set by the Standard Deviation of the process, usually within plus or minus 3 SD's, or a "Six Sigma" spread. There are other charts that can be kept as well, for example P charts, which are used to control things that can be counted rather than measured.

"Design of Experiments" is also known as Taguchi Methods, after the Japanese professor who initially formulated them. This is becoming common learning in Engineering schools as well.

I learned both of these methods in the late 1970's and early 1980's, including taking an in-plant course from Phillip Crosby's Quality College in "Zero defects" management, which espoused the now famous concept of the "Cost of Quality". Crosby wrote the 1979 book "Quality is Free" and was a disciple of the famous W. Edwards Demming. Demming went to Japan to teach statistical methods and quality improvement in the 1950's after American industrialists, who were fat, dumb, and happy at the time, basically ignored him and his teachings. The Japanese revered this American and his teachings so much, the annual quality improvement award is called the Demming Prize.

I later had follow up training at another company in the 90's when practically the same methods were called "Total Quality Management" or TQM.

So, I learned and practiced "Six Sigma" long before there was any such certification. Now, if I want to be certified and my current employer does not sponsor me, I would have to take leave and spend my own money to become a "Black Belt".

I also have a BS in Engineering Management, including courses in Production Management, Manufacturing Processes, and Quality Management, as well as graduate studies in Industrial Engineering (Statistics, Robotics, etc.) and earned an MBA at night.

Unfortunately, "Six Sigma Black Belt" is the magic key that opens many job opportunities.

I feel a little like the guy in the alley confronted by a would-be mugger claiming, "I have a Black Belt in Karate", to which the would-be muggee replies, "I have a Smith & Wesson in my pocket." Which would you rather have in that situation?

Nice post! Good history lesson, too.

Thanks, The S&W analogy about sums it up. When I was doing this kind of stuff it was you said, TQM.

I can't see how six sigma can be proprietary. So many consulting firms support it. Many manufacturing firms use it and train their teams in it. Amazon lists more than 600 books and Google claims more than 26 million pages on six sigma.

Chris: Have you tried high frencey vibration durning the casting process? I was a brass polisher @ Kohler co some 50 years ago and that was a problem then too. Del

Have you degassed your melt? To degas your metal, put a wad of soft paper such as newspaper in one end of the piece of pipe, tamp the pipe full of the sodium hypochlorite powder and put another wad of soft paper in the other end of the pipe. When your melt is up to full pouring temperature or slightly hotter, and wearing face mask, apron, gloves and other protective clothing, thrust the pipe and powder to the bottom of the crucible using tongs or a welded handle, and gently stir. The powder will decompose, liberating chlorine gas that will combine with any hydrogen in the molten metal. **Caution**: Be sure not to breathe any of the smoke that comes off the melt when you do this, as it is poisonous. This will also create a quantity of slag or residue that will float to the top of the molten metal. It may be helpful to cover the molten metal with a layer of powdered charcoal to protect it while melting and after degassing. You will need to skim this off before pouring the casting. Stir the metal when you degas and skim off the slag to insure you have a good mixture of the metals as these may want to separate. If this helps but does not eliminate the bubbles in your casting, get a bigger piece of pipe and use more powder. Be advised that the chlorine will also combine with any zinc in your brass/bronze and will lose excessive amounts of metal if you over-degas.

There are two possible causes 1)you have not double melted your billot of stock metal, this will degass it, you have to increase your pouring temp as well to make sure any gasses formed during the pour are vented, also make sure you pour the metal at a constant rate. Try an increase of 50 Deg Centigrade. Skim the metal before pouring. You must also make sure you don't cool the casting too quickly. You moulds must be preheated to prevent premature cooling of the outer part of the metal which could form a skin that will trap gasses. Try 150-200C Some vibration may help? Make sure the pouring hole is the correct size too small and it won't vent very well, too large and the metal will spill out. Do you use multiple linked moulds or individule moulds? Multiples save time but can cause problems with metal flow. Keeping an even temperature is vital. You do have seperate vent/witness holes don't you? Don't hurry things it does not pay to. It is vital to keep every thing very clean, and free of surface defects. Your steel should be highly polished and grease free. How do you heat your metal? Gas, or electricity? What grade of stock metal do you use it matters. The ratio of zinc to copper is important. Too much zinc can cause blowing.

I was a welder in a non ferrous foundry and had to repair lots of castings. Give a welder a crack at some of them.A good tig man or women can surprize you. Where are you located perhaps we can come to terms.

I had the same problem- simple solution I found was to make magnesium powder or lathe turnings rolled in plaster of paris balls- use minimum of water- about 2" dia.. Let these be totally BONE DRY at your source of heat- not flame hot- the mag will catch fire and flare up in an instant so be careful. I poked a hole in each with about 5" of 3/8" stainless steel rod- put the ball on the rod and shove it to the bottom of the crucible quickly and the fouling gas will be burnt out- it may take 2-3 or more depending on the amount of your melt. I found it also helpful to put about a 1/2" of BONE DRY plaster of paris upon the melt as it works as a seal from outside air entering the melt. You don't say if your using Perma Bond Casting material or what- I assume it is totally clean- not a trace of any other matter can be tolerated in the sand. You may try using a torch to flash-dry the internal cavities. Also you may not have enough Vent's and sized proper-as should be several-do you use a feed riser? configured proper- you must have a good head on the pouring sprew for weight. You may also use a heated red to white hot ramming rod about the size of the neck below the sprew funnel to create the pressure needed for weight- All the above is old hat learned the hard way-But it worked for me. The simple solution is to use a centrifical casting machine-I made one from my junk heap and it worked as good as a high priced factory unit- several thousand $$$$. I am in New Port Richey, FL. Whats ur 20?

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