The Future of Castings?

[Jasonb]

I have mentioned it before a few times about being able to resurrect some of the older designs where patterns have been lost or if they are still knocking about the owner can't find a foundry to cast them. With modern CNC it should be possible to reproduce these castings with the added bonus of none of the usual casting defects such as blow holes, undersize parts, hard spots, over fettling , etc and leaving the builder to do the final work such a sfinishing bores, drilling and tapping of holes etc.

This video of E T Westbury's "Whippet" being machined would be the perfect example if the machining were stopped before the final holes were done, I'm sure they would sell

<a href="https://www.youtube.com/watch?v=IM2YMM8wtDw" target="_blank">http://www.youtube.com/watch?v=IM2YMM8wtDw</a>

And what a set of "castings" may look like



I have enquired about costings but as the company can produce a fully working engine for $499 I should think that the castings would be quite favorably priced compared with what is available in this case from Hemmingway at about $200. If so it would be nice to see some of the "lost" engines from the likes of Wall and Westbury being made available to those who like to build them rather than just the collector of ready to run engines.

[Jo]

Yes CNC milling machines have always been able to reproduce castings.

The problem always was the price of the CNC milling machine but the prices are coming down. One day they will give them away 

Jo

[GWRdriver]

I think the future of castings, model and industrial, is excellent . . . it's the future of foundries which isn't looking so bright.
But that being said, I'll be very interested to see what alternatives the advance of technology and metallurgy presents us with in the future. 

[lohring]

Metal 3D printing is an even better substitute.  Aluminum is still expensive, but I've had apart made in a steel/bronze alloy that was quite inexpensive.  I was quoted a price from Shapeways in that same alloy for a model race boat propeller that was less than a commercial bronze investment cast one.  Both would require finishing and balancing to about the same degree. 

Lohring Miller

[MJM460]

Probably CNC machining, castings and 3D printing will all have a place in the future, with each finding their own niche area.

Shapeways has been mentioned many times on this forum, and I believe others have been mentioned.   And I have learned there is a company in Darwin which also does it, in aluminium and other metals.  I was surprised about the location.  I have visited Darwin many times and enjoyed it every time, but I don’t think of it as a a powerhouse of manufacturing.  However, my grandson did his school work experience there a couple of years ago.  I wondered if he had understood what was being printed, but more recently a TV documentary had a segment on what the company was doing, and they are indeed 3D printing metals.  Definitely a contender when foundries are facing more obstacles to operation.  As it becomes more common, it should become lower cost.  At least everything else seems to go that way.

MJM460

[Busted Bricks]

Many foundries print the molds directly these days - no need to make a pattern. All that is required is a 3D file of the item.

5-axis CNC machining is expensive to have done for small volume production. There is considerable setup time involved and the CAM software is very expensive. However castings aren't exactly cheap either.

[crueby]

Seems from their pricing that places like Shapeways are set up on the print/casting side for jewelry sized pieces - I've priced out some small frame/cylinder pieces a couple times and the costs go astronomical very quickly, though I've had some piping pieces (tees/elbows) cast at a reasonable price.
My question - are there other outfits that will take a 3D design file for a larger part like a cylinder and do a good quality one off print/casting in brass/bronze at a more reasonable price? The technology is changing almost daily, and the prices too.

[Elam Works]

It is easy to get 'techno-dazzled' by CNC and 3D-printing, but it is the underlying approach that one should look at. Popularly known these days under the buzz words additive and subtractive manufacturing. Subtractive manufacturing, or machining - be it CNC or manually turning the handwheels - share the same limitation, access for the material removal process. You have to be able to reach the area desired with your cutting tool. CNC can help with positioning of the work and/or tool in synchronized movements not practical on a manual machine. I do not know about you, but I could never successfully synchronize the movement of two handwheels, let alone three or more axis of movement. Back when I was gainfully employed, I purchased machinery with up to thirteen axis of control. That is even more than I have fingers for to count... CNC has not been around forever, so back in the day they would have used tracers, form tools, pantographs, etc. when multiple axis of movement or complicated contours were needed. Typically production methods, rather than hobbyist methods. 

But there are going to be areas of a casting that you cannot reach; under cuts and cored passages for example. There are way around this certainly. Simplification of features to eliminate the undercuts and cores, or building up (fabrication) from multiple pieces. That is a workaround. You accept the compromise because you want to avoid the difficulty and expense of the pattern making and foundry process. The issues also apply to 3D printing: the difficulty being the need for a 3D CAD model and the expense being the printing process. As noted by others, the latter has been making great strides. More folk are learning 3D CAD modeling and 3D printing cost have continued to drop.

So that aside for the moment, there are some parts that lend themselves to subtractive manufacturing (machining) and some that lend themselves to additive manufacturing (casting or printing). You can convert a design for one into the other, but you give up some of the benefits of the original design. Simple parts are the most successful to convert, as usually they were not designed for one process or the other, other than the manufacturer just used whatever was easiest for them, or the most cost effective. That is, production requirements rather than design requirements.

So I think castings will never go away. If you have internal features or undercuts they can be integral with your casting. You pour the metal in and viola, all things going well, you have your part. Subtractive machining cannot do that. But what about the problem of getting small quantities of castings, or just one casting? Well to some extent 3D printing can help, but it is a compromise too. Instead of a pattern, you have to prepare a 3D model; both have up-front 'costs'. 3D printing is slow compared to casting - a lot slower. As the fidelity of 3D printing improves, the speed gets slower. This is both a function of smaller deposition (or fusion, in metal printing) and a thinner layer thickness to get that higher fidelity. But as foundry cost continue to go up and printing costs come down, they might converge. There is the distortion issue. With castings you have distortion, but it is a general overall shrinkage as the metal solidifies. Problems only occur when the casting is poorly designed and the shrinkage is uneven. With 3D printing the material is solidified in layers which imparts internal stress to the part. They want to curl in the direction of the build. Like castings you can mitigate it somewhat by designing around it, but it is always there. 

At the moment, I have not seen any additive manufacturing processes that can rival the surface finish of a decent investment cast part, or even a good sand cast part. The striations of the 3D printing process are visible. If you are willing to sand the part or use filler, then that does not matter. I have used the 3D sand mold printing method to have parts cast for a vintage motorcycle. The original castings were lightly polished, so sanding the striations away was not an issue; I did not need an as-cast surface. And while the castings were not cheap (about $2600US each) getting two done was cheaper than the cost of the intricate pattern and core that would have otherwise been required. And as a bonus, no core shift to worry about! Had four parts been required, a traditional pattern and core boxes would have been more cost effective.

Will 3D printing ever match the finish of nicely as-cast part? No, there are physical limitations. With 3D printing based on extrusion processes, you are limited by the size of the blob of liquid material you can extrude. That tends to be a function of the material you are using. The thermoplastics used by the majority of desktop printers tend to be the coarsest layering. I see marketing claims down to 0.005 to 0.008" layering but I think it is more like 0.010 to 0.015". UV cure acrylics, using an inkjet like process, are good for about 0.005" thick layers at best. Maybe they have gotten a little better since the Eden Objet 350V printer I use to have access to. Then you have the stereolithography processes that (marketing) claimed were good down to 0.0005". Alway the tradeoff is the smaller the resolution the longer it takes to print.

However, these are all plastics, and generally with casting one is talking about metal. 3D metal printing lays down a bed of metal powder than then uses energy (a laser or electron beam) to fuse the powder together. Similar to printing plastic, the fidelity is a function of smaller energy beam size and smaller particle of powdered metal. And similar, the higher the fidelity the slower the build. Some years ago they reached the limit of minimal powder size. The issue is when the metal powder gets to the point of being like talcum powder or dust, it just tends to float around in the build chamber (and these chambers are usually under vacuum) rather than settling down on the build layer. They had just at that time managed to half the industry standard beam size for lasers in half (I forget the size, but this was going back about ten years ago) which was a big jump forward for fidelity. The powder then became the limiting factor. Short of artificially enhanced gravity, the process had it reached its practical limit. The parts coming of that generation of machines still have visible striations. Do not get me wrong, it was good, and a vast improvement over what had come before in even just the previous ten years.

With the 3D sand printing, they could use a finer granule sand than they presently are using. Again, the build would be slower but the fidelity increased. Also, the finer the sand the less permeable the mold, and the greater problem of trapping gasses in the metal (porosity.) They do not have the option available to the traditional foundryman of using thin layer of fine sand against the pattern, and then backing it with a course, permeable sand.

I have also used CNC machining to 'fake' cast or forged parts by milling from billet or bar stock. Again, making one or two parts did not warrant the trouble of pattern/foundry work or a die/stamping. I was employed as a CAD modeler and have a CNC machine, so it was a little easier for me versus someone that was transitioning cold from manual machining only background. Had I not had that advantage, I would have manually roughed it out and finished by hand using files or a Dremel tool, fabricated from multiple sub-pieces (examples of both having been featured on this forum in member's build logs) or maybe not have even attempted something so ambitious.   

Cost of metal printing has been touched upon in this thread. I was getting medical devices printed in stainless steel and titanium, and keeping a log to evaluate the cost and results with the view of justifying the purchase a machine for in-house prototyping. Meanwhile we were using outside vendors to do our 3D metal printing for us. The cost was greatly affected by build direction. Adding volume or additional parts in the x-y direction did not have as much impact on time (cost) as in the z- direction. The machine had to sweep across the width of the build table anyway (more or less, there were some slight variations depending on the machine manufacturer's use of a gantry, galvanic mirrors, etc. to manipulate the energy beam that influenced how fast it could cover an area), but they all had to stop and apply and scree each addition layer of powdered metal. Building material in z- was slower than x-y. It behooved one to fill up the tray as much as possible, and orient parts so they lay flat to the build table and had minimal height. Folk that have their own desktop 3D printers will have already discovered this also. Sometimes, build distortion did not allow that. Vendors would try and combine several client's jobs with similar heights, to maximize x-y usage. Nesting a lot of small parts therefore tends to be cheaper than one larger part of the same volume, especially if that one part is taller. 

Ironically the biggest challenge we had was re-training the product development engineers and I cannot say we were entirely succeeded. The production engineers had for years beaten them up over complicated designs to the point they were cowed into the habit of developing the simplest solution for a given problem. Not a bad habit, but the opposite of what you want for designing for additive manufacturing. Complexity adds very little to the build cost, compared to if you were using subtractive manufacturing methods. Since you are paying more per part to have it additive manufactured, you might as well pile on the features. Extra lugs and bosses? Add them! Internal features that would be difficult or impossible to machine? No reason to avoid them! Blind keyways with no runout for the cutter? No problem! Oh, wait, we had plenty of novice engineers that would design those types of features... It is not unlike the process of changing a design from a weldment to a casting. You add features and complexity because it does not cost that much extra and saves you money elsewhere in the manufacturing process.

Well enough rambling on. Just some thoughts to add to the discussion.

-Doug


[fix typo.  26Nov21. -Doug]

[lohring]

The part I was talking about required as much finishing as an investment cast part would have.  The texture of the surface was different, but if you need a polished surface both need post processing.  The shock to me was the cost.  These parts are produced by binder jet printing and tolerances are similar to investment casting.  Aluminum parts are produced by selective laser melting as described above, a more expensive process for the same part.  3D printing is in its infancy and the current processes are primitive. 

In the 1960s when I was involved in a machine shop making mostly large custom milling cutters, one off parts were expensive to make.  We investigated NC machining, but the technology of the time wasn't up to the job.  Fast forward to today and even hobbyists can afford CNC machines and computers to do 3D modeling for them.  The new generations of machinists and engineers will be familiar with the requirements of these new processes.  The old generation, familiar with the requirements for casting, is retiring.

[Roger B]

I think this will always be driven by economics. For high volumes die casting will always be cheap. For lower volumes there will be many competing factors. Additive machining has it's place but so does sand casting and CNC. If every surface is important then CNC probably is best. If it has cavities sand (or investment) casting may be better. Somewhere in between additive machining may be most economical.

As a total Luddite I am 2D cad and manual machines with a vague wish to move to CNC