I plan to create a dozen prototype items that use a platform made from 1.5mm thick mild steel sheet. The bit I need advice on is how to punch out the tabs as shown in this link.
Even when I had a fly press, I would have taken that to a company that advertised itself as doing sheet metal work. I had the tools to punch the holes, but would have had to buy the ones needed to punch the tabs. However both are something a specialist sheet metal working company should have in their workshop.
Possibly: steel punch D-shaped, held at an angle on the sheet metal, over rubber, hit with hammer?
(There's a name for this procedure which I forgot...)
Or get it laser/waterjet-cut, but not DIY.
Thomas Prufer
sheet metalwork is all about accurate punches and dies and very tight alignment Unless you have a milling machine you wont be able to make your own die sets.
Unless you have some kind of press you wont be able to align them.
The cost of all this makes it utterly uneconomic for one offs or prototyping. You would do better drilling and filling holes and brazing the tabs on.. The working of the flat bed to give it an edge and ribs could be done with lots of painstaking hammering
Guess why people are using 3D printers
OK, laser jet to cut out the tabs sounds good, so my questions would be:-
The consensus is that it outside the realms of DIY so I guess I am now looking for recommendations for a small sheet metal forming business that can do it for me. 50 years ago the Midlands would have had thousands of such businesses but nowadays it's all so different.
+1 for laser cutting. A few years ago I needed a 10mm thick steel plate cut to a complex shape. This was done by a local steel supplier with a laser cutter. I just supplied a hand drawn sketch of what I wanted. The whole job cost around £100 including around 0.5m^2 of steel plate.
John
i don't think SendCutSend operates outside the USA, maybe search for equivalent UK services?
This says ~1mm for waterjet:
Really depends on the equipment they have.
If the shapes are complex then that would help. On the other hand a dimensioned drawing with basic shapes like lines and (half) circles and similar may be as quick for them to CAD up as to interpret your input file, unless you can use the same software they use.
The advantage of you doing the CAD is you can print out a copy on 1.5mm cardboard (or paper stuck to cardboard) and hand cut it to confirm that it fits with the rest of your design. You can also send them that so they have a physical golden model to work from (avoids problems like dimensions being interpreted as mm instead of inches, or whatever)
I would send them a sketch to begin with and ask what they would prefer.
Theo
Just how small series is it?
Because a drill and a fine metal blade in a coping saw will make those cuts on
1,5 mm sheet metal... might that be enough for a few one-off design iterations?Saw, sawblades, v-board --- looks like well under under 20 on eBay.
Thomas Prufer
Most laser cutters will accept Corel Draw, or HPGL type files.
The problem is you need a bug fuckoff laser to cut that thickness of metal, A 60W CO2 ain't gonna work. And those cost money, and wont make the bend.
That piece is designed to be stamped - probably on a progressive die machine - in tens of thousands. If you wanted to laser it, you wouldn't start with that design.
If it were me, I'd redesign it as 3D print of several plastic parts that would be glued together like an Airfix kit.
Or mould it out of glass fibre.
+1
If there are good reasons why it needs to be metal, it is possible to 3D print metal. You end up with something that looks more like a casting than a pressed sheet, so you need to account for that (it will be thicker). They either do it by laser sintering of a metallic powder, or a lost-wax process (3D print in soft plastic, make a mould out of sand, pour molten metal into the mould which melts away the plastic).
Whether that comes in more or less expensive than laser/waterjet cut sheet metal rather depends on your subcontractor. For 3D printing there are firms like Shapeways who have a service which is fairly streamlined (send them file, select material, pay, wait N days, part arrives) whereas for local engineering firms it may be a more manual process which adds to the costs.
The maxim is to select materials based on the tooling you have at your disposal, rather than select the materials first and then look for the tooling.
Theo
+10001 I laser cut ply and balsa wood, or thin plastic or card. Not sheet metal. If you have a handy fly press and a box of dies and/or a milling machine, then this is an excellent design. If not I wouldn't touch it
It's also worth considering the quantity required. For 3D printing there's basically no economies of scale: the unit cost is the same for making 1 or
100. The same goes for hand cutting (although you may get quicker over time). For laser cutting, once the job is set up it doesn't take a great deal longer to make a dozen or so more. For plastic injection moulding, the setup is very costly but the items are more or less free once you've done it.Theo
I think I may need to reinforce the original post and extend the information.
The quantity is small because the item can only go into production if it meets the stringent requirements of a government agency. I have to pay all the costs of the laboratory and field tests on each of the prototypes submitted. If one fails in any way, then all testing ceases and I'm out of packet.
If the prototypes all pass, then that opens up the pathway to full production on volumes of 10,000 to possibly 30,000 here and overseas.
The prototypes must be in metal because that is a fundamental requisite. Also, it has to have tabs that can take certain forces.
As a first stage, I have to produce the batch of prototypes and appreciate that the product process in mass production may well be different. In both cases , I guess I would need to have CAD 3D drawings and once that is paid for these could also be used for production.
If it was only one unit I assume it could be done DIY with a die/tool to cut the " U" shaped outline, then lift it vertical to make the tab. But with a batch of 12 and each having 9 tabs in two different sizes that it becomes a big task to get consistency
If this is a 'type approval' process, I think you'd need something that approximates the finished product. In other words you need to design backwards from how the production line will make them, and work out how to make the same item in a smaller quantity.
For example, suppose you're presenting a new car design for type approval. One of those tests is to test the emissions, which means having the production engine in it. It wouldn't do to put in a different engine just because that was easier to deal with in the prototype. But it would be ok to hand-assemble the engine with spanners rather than robots. In other words, the type approval is testing the design, rather than the production engineering of how to build the design economically in quantity, to sufficient quality.
OTOH this might just be a 'proof of concept' stage, in which case it needs to work, but the exact details of the design can change once it is ready to be production engineered. In which case it is ok to cut non-critical corners in the interests of building a prototype. (like a concept car which is not intended for mass production but to test out various ideas)
It sounds like CAD and laser or water cutting (or maybe CNC milling) is the way to go for now, but I'd be looking for someone who knows how the design would be adapted for mass production, so there are minimal changes from prototype to production version.
Theo
A drill for the holes and a Dremel with a cutting disc for the tabs? How many do you need to do?
No. Not if you have to amortise design time.
The same goes for hand cutting (although you may get quicker over
It does. The setup is very quick, the cutting is not. And since it ties up a pricey bit of kit and needs an operators full time attention. £60 an hour is about par for the course.
For plastic injection moulding, the
And the same for die stamping
@Theo You have it spot on and you have helped me clear my thinking. In this case, functionality and efficacy take precedence over the appearance. The testing authority does not issue any detailed specification. They only specify that it must do the task quickly, reliably and consistently time after time. Appearance does not matter in the prototype batch so they can be in bare metal. After approval, for marketing reasons ,they would have to be painted or galvanised for longevity. I tend to agree with your suggestion for laser cutting it provides accuracy and because the tabs have a mix of circular and rectangular holes. Much appreciated.
I had a bespoke metal thing made. Emailed a photo of a pencil sketch with measurements, and got a CAD-drawn PDF back. Said, "yeah, drawing is good" and it went into production, received parts by mail. About two weeks from sketch to parts on table. Cost was *very* reasonable, well under ~7€ a piece for cut and four bends on 1,5 mm stainless, about A4 size, plus taxes and shipping (UPS?). The company will laser-cut, and bend the edges, but maybe not the tabs. But bending the tabs on 12 prototypes is a DIY task. Also, the material will be stainless steel...
I'd estimate the cost to be well under 10 Euro a piece -- but just email them and ask, that's their daily business: snipped-for-privacy@monoflo.de. (Also, they do lots of animal stuff, drinkers, and bespoke piping, and so on -- and "Vet Tech" sounds like you do, too?)
Thomas Prufer
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