Just looked up tribology.....So i'd better watch out for the composition for brackets and mounts etc...... On a side note how many who voted "I'd cast it if I could" have looked deeper into casting?
Cast it it makes sense!
Buy a billet from the shop!
I'd cast it if I could!
Re: improper heat treat vs improper alloys
Take 4150 and harden and draw it to an Rc58 (easy to do).
Take O6 tool steel and H/D it to same spec hardness. Again easy to do.
When you compare the scuff resistance of O6 to 4150 when subjected to high loads and marginal lubrication, HUGE difference and that occurs even though the parts are of the same hardness.
Hardness and tribology are NOT interchangeable properties. Neither is harness and the tensile and fatigue properties.
Although 6061 and 2018 have comparable properties (after all, to some folks they are both heat treatable aluminum), they are NOT interchangeable should you be in the market for an alloy for forged pistons.
In some cases, metal that "rusts, sinks and is magnetic" is quite adequate for an application. However, for other situations, you better be more specifice with the alloy and the H/T specs.
Just looked up tribology.....So i'd better watch out for the composition for brackets and mounts etc...... On a side note how many who voted "I'd cast it if I could" have looked deeper into casting?
Keith
It all depends on the application. If it is a seriously stressed part that will see high cyclic loads, on which someones safety depends, beware of using melted down drink cans in your back yard wood burning furnace.
But if you are making junk jewelry, toys, or art objects, I say go for it..........
I have never been keen on the idea of buying premium heat treated billet or plate stock, just to turn 90% of it into metal shavings, just to turn up a dumb spacer for something.
Do it yourself primitive back yard metal casting can be very useful. But as Clint Eastwood said in the movie Dirty Harry, " A man should know his limitations".
Hi Warp, 100% agreement.
Depending on your integrity and reputation in the tendering industry, if the customer specifies XYZ material to condition XX and you supply a mixture of Coke cans and old gearbox castings, then your reputation will go before you and you won't be trusted in the industry.
On the other hand, where the item is not particular, it is still important to get the customer's signature to the contract which will specify the requirements.
Material cost is always a prime factor when it comes to deciding how much a job will cost, when everything else is equal.
The problem only becomes one when YOU recommend a certain material for the job, based on getting the cost down against another tender.
For example, a hypothetical customer requires a set of vice jaws for a milling vice and in order to cut costs you decide to use mild steel, case hardened to .75mm depth.
In this job the case hardening failed because the base material being mild steel was unable to support the hard skin which cracked and flaked off.
The material, depending on the cost, should have been either tool steel or nickel chrome steel suitably case hardened.
This happened to me, because the milling vice I bought second hand had a set of soft jaws that had been chewed to bits over time.
I just happened to have some mild steel bar that might do the job, and so made a set up and had them case hardened .75mm (.030") and ground.
They worked beut, untill I gripped a bit of round hard material, and so we have a set of jaws indented near the middle.
When I get a round tuit I'll make a new set, one of these days.
Ian.
Oh yes, professional integrity and business reputation not to mention ethics, (along with Iso traceability) are these days, extremely important to the professional manufacturer and fabricator that desires to stay in business. That goes without saying.
I can identify more with the amateur racer, hobbyist, or hot rodder building his own "stuff" out in the back shed. This is more where the "cast it if I could" mentality reigns, and it can with caution be very practical.
Why would you risk life and limb dealing with molten metals and toxic fumes ?
Why would you spend countless hours designing and building machines that could easily be purchased ?
Why would you spend your meager savings on homebuilt untested gizmos ?
Why do you squander ALL of your free time doing this stuff ???
Because it's fun.
I'm impressed, a whole thread about Aluminium casting including a few moans about porosity but no mention of de-gassing.
Anyone interested should seriously consider buying a book on home foundry work, with correct selection of source metals & using a relatively cheap commercial crucible you can produce reasonable results for a wide range of parts applications.
A man who knows his current limitations does not have to be one incapable of further research to push back those boundaries,
Regards,
Nick
I guess it really depends upon what use you have for the part as casting alloy's have quite different properties to processed billets. Also depends upon what finish you want. Most foundries here in the UK will only take a job if it is a large run of parts and they can charge for tooling ( huge sums of money ), some places will do one off's in sand but still charge an awful lot, you see it requires real skilled workers to do that and it's a workforce that is shrinking rapidly ( they really don't teach it anymore ).
I was in the position of needing castings a few years ago and in the end it was easier and cheaper to build a furnace, burner and buy all the tools needed and teach myself how to do it (steep learing curve). Now I get the odd request from the foundry suppliers that I buy the raw materials & consumables from.
Converting the current furnace to oil and then I expect to be able to do small iron castings.
----------------------------------------------------------------------
On the subject of what alloy to use, you use exactly what the customer wants ( you buy it along with the tracability and analysis reports ), anything else scrap or second hand stuff is for ornamental use only, failing that you will need a damn good lawyer.
David
( never stop learning )
http://www.steamcastings.co.uk/
Nick is right about fluxing and de-gassing aluminium. Both libraries and book shops seem to be fairly bare of books on home metal casting, it is not a very popular or widespread hobby. These days, internet is probably a much better resource than books anyway.
Back to fluxing and de-gassing aluminium. The commercial foundries have solved all these problems long ago, and commercial products to do this properly are more or less readily available if you inquire. I am still a very raw beginner, but I did finally track down one company with a nearby sales branch called Foseco that supplies castable refractory, and many of the special fluxing and de-gassing agents to the industry. The only real problem being that the quantities available are inconveniently large for the casual small amateur home foundry.
Another approach to this problem, might be to visit a commercial aluminium foundry and ask their advice on specific products to use, and where to get some. They may even give you reasonable sized samples to try.
For small quantities of fluxing and degassing materials, check out:
http://www.budgetcastingsupply.com/
They also have some good deals on crucibles and other foundry related supplies.
It is also a good source for metalcasting information.
I have found over the years all commercial foundries are more than happy to give away "free" advice and indeed materials but then again I am a professional scrounger "give and ye shall receive" I've never charged for my time in my hobbies and never will. Nitrogen is available from "Public houses" aka "bars" and it makes a great difference to the pour. Al is a strange material in that it can dissolve much higher melting metals into itself :shrug: very acidic when liquid.
Keith
It depends on what your working on...
We make rotational moulds. Some of our customers prefer the finish and tolerances you can get with a machine from solid tool, but sometimes it just doesn't make sense to make it from solid. I usually look at the size of the job.. If it has deep cavities that are gonna be difficult to machine then i would make a pattern and have it cast. If the job is relatively shallow with not too many sweeping surfaces then it makes sense to cut out the pattern making process and machine it straight out of a solid block. it all comes down to time.
DC
You cant ask that without giving some sort of job discription. Some jobs are machine form solid and others are clearly cast. it depends on what your working on. the size/difficulty of what your doing etc..
Obviously there are some jobs that fall smack bang in the middle. They can be cast or machine from solid. As i said.... IT DEPENDS ON THE JOB YOUR DOING!!!http://www.cnczone.com/forums/images...es/RAINFRO.gif
:rainfro:
Cast Vs machined, fabricated from machined parts and machined after fabrication are my preferences, making short runs of complex parts is faster by machining as the time to make the pattern needs to be considered. All this talk about aluminium, what about steel? cheap, easy to cut and weld, easy to machine 3 times as stiff as Aluminium, hard wearing, good strength to weight if using low alloy steels, the prehards machine very well. Aluminium has its uses but it can also be fabricated and machined with the right welder and a bandsaw or plasma cutter.
Hi all, one thing a lot of theorisers forget and that is before you can make a casting you must have/make/get a pattern.
Castings don't just happen.
The other thing is once you've made a pattern you must be able to form the mould round it and also be able to extract it from the mould without destroying the mould in the process, which means no long vertical flat sides, tapered sides are required.
All this is very boring, but when all you want is one square shaped part with lots of flat sides and undercuts, plus a few bores here and there, then the casting may be a pain to have to finish off, plus the fact that unless you have a foundry of even the most primitive nature, you will have to send out the pattern, and hope the foundryman will not throw it in the bin.
I won't even mention haveing a core in the casting, as this will seperate the men from the boys like a dead rat at a banquet.
Fabrication gives you the option of making the part in steel which is a lot better for most uses, and the average tool orientated person can become a welder after a bit of practice.
Whichever method is chosen, it is more than likely that the end product will have to be machined.
One of the chief reasons parts would be cast is for repetition purposes and here a well made pattern is absolutely necessary.
Fabrication doesn't lend itself to repetition, unless you like working with an angle grinder doing weld preperations.
There is a meeting point of the methods, and this is called design.
Ian.
The attached image depicts a gantry support. The support is 1 inch thick and 13 inches high. If this were machined from a billet, it would generate about 30 pounds of aluminum chips.
No, I haven't cast it yet. Might be too much for my crucible.
Diplomacy is the art of saying "Nice doggie" until you can find a rock. - Will Rogers
Hi .. Well this is my first post to this forum after lurking for ages. I recently started a blog on my furnace design and the stuff I get up to in my backyard.
I don't have the money to buy a machine capable of machining billet into something usefull... and I haven't seen too much "scrap" billet lying around either, so the next logical step is to try and cast it. I must say melting aluminium is really a LOT easier than I first thought.
I'm trying to use lost foam method to get results and for that I use a cnc machine I built in about an hour using two old dot matrix printers. So just purely from a time standpoint I save a LOT of time machining the "thing" from foam, a cutter moves through it like butter. The 4-jaw chuck I'm working on takes 3 minutes to machine and added together the covering it in plaster of paris and the melting of the aluminium takes around 1 hour.. and if I do multiple parts at once that time really gets used well. So adding all that together I have machining from billet beat for time.
That's why my vote goes for.... cast it!!!
It really is easier than you think!
Check my blog there is a step by step write up of what I do.
http://jvwprojects.blogspot.com/