What's new
What's new

Sheet metal straightening/flattening plate/die

billzweig

Stainless
Joined
Jun 4, 2015
Location
BC
Looks that this is a completely forgotten tool. Seldom a piece of sheet metal is completely flat and any bends or twists are impossible to flatten - the metal just springs back when pressed between hardened and ground plates on a hydraulic press. And yet there is an easy way to flatten it to 0.0001" or better - or as accurate as the tool itself. The device that was used in production of precision instruments like clocks, counters etc was a flatting plate. This is a hardened and ground steel plate with a pattern of miniature pyramids. Once pressed into the sheet metal, the sheet metal surface undergoes a controlled plastic deformation and comes completely flat and work hardened with a fine pattern of dots on one surface.
I've seen this in in the past, but cannot find this tool anywhere, I am not even sure how to call it. Any suggestion will be appreciated.

strighenning-plate.jpg
 
Last edited:
I have seen metal with the indents in the past. Thanks for telling me why they were there.
 
You might use "planishing" as a search term.

I saw this a lot on aerospace and video equipment (of the reel-to-reel vintage) along with a yellow chromate finish. Not so much recently, but maybe I've just been exposed to fewer precision components. :)
 
You might use "planishing" as a search term.

I saw this a lot on aerospace and video equipment (of the reel-to-reel vintage) along with a yellow chromate finish. Not so much recently, but maybe I've just been exposed to fewer precision components. :)


Thanks, will try.
 
Searched quite a bit and can't find much at all about this tool/process.

To roll your own what kind of spacing/height for the little pyramids?
 
Searched quite a bit and can't find much at all about this tool/process.

To roll your own what kind of spacing/height for the little pyramids?

I too was contemplating making it myself. I would start with a thick hardened and ground steel plate and run it on a surface grinder with a formed wheel to create the pattern. I have seen various forms of indents and grid spacing of the pattern - some of this depends on the material, thickness etc. but for the small parts I need I would go for 1 mm grid and about 0.15 mm high points. In most cases the sheet metal is pressed between two of those, but I have seen one sided patterns as well.

plate.jpg closeup.jpg
 
I found a published paper on this process and came up with another search term. Apparently the Japanese call this "waffle die flattening" in English when they aren't calling it sheet metal planishing.

The paper suggests the pitch between indenting diamonds should be about the thickness of the material.

Added in edit: Here and here a US source uses the term "stippling the blank".
 
I found a published paper on this process and came up with another search term. Apparently the Japanese call this "waffle die flattening" in English when they aren't calling it sheet metal planishing.

The paper suggests the pitch between indenting diamonds should be about the thickness of the material.

Added in edit: Here and here a US source uses the term "stippling the blank".

Thank you! This is the first time I see this mentioned in print. Indeed my instinct was that the pattern grid should be close to the thickness: my sheet metal parts are about 1 mm thick.
"Waffle die flattening" and "sheet metal planishing" searches however did produce any results. Planishing is almost exclusively used as a term for a process of shaping metal into formed parts, and waffle got me a lot of information about Belgian waffles. I also tried "Stippling" but this is mostly a technique in artistic etching and engraving. So I am loosing hope of finding a commercial supplier of this tool, though I've seen it many years ago. I will have to find the time to make the "waffle plates" myself.
 
What you have is called stippling. The tools are normally custom made for the application. Just a piece of hardened tool steel that has been ground to produce the pattern of pyramids.

Tom
 
What you have is called stippling. The tools are normally custom made for the application. Just a piece of hardened tool steel that has been ground to produce the pattern of pyramids.

Tom

Thank you, Tom. I'll keep a search for stippling plate, but likely will make it myself. Still, surprising that no one offers this useful tool, as there is really hardly an alternative when it comes to flattening small, precision sheet metal parts.
 
Yeah, there doesn't seem to be a lot that's not buried under tons of unrelated craft topics. For instance, that "regaining flatness" article is one of the the two I linked above.
 
Nice find JP. Now the holy grail would be a table of pressure for adequate stippling. I wonder how much it's a function of the amount of stress or a function of thickness. Seems like that sort of knowledge is in the mechanical engineering academic literature or the watchmaker folk wisdom. Now I've said it I'll try to go look in the former.
 
I would think that accurate pressure is not an issue. In the initial stage, when the indentations are pressed into the metal, the pressure will increase gradually as it happens. When the flat part of the die makes contact with the the full surface, there will be a sudden and significant jump, this will indicate the end of the process. you do not want - and there is no need to press the part beyond that. What requires more understanding is the depth of the indentations. This will depend on the material, the thickness and possibly other factors.
 
Fair enough. I guess the size of the part and point density will determine how much pressure you need to form the points but you're right, it should be a self limiting process.

I did briefly look at Web of Science and didn't see anything but some of my search terms got me to a bunch of papers around the subject of, "Ayurvedic herbal medicine and lead poisoning" so that was amusing.
 
What about a roller plate straightening machine?

What I need is to flatten small, machined components, typically 1-2 mm thick and usually no bigger than 60x40mm. It is not about flattening the whole sheet of metal. Even when starting with a flat sheet, often there is distortion in the finished part.
 
What I need is to flatten small, machined components, typically 1-2 mm thick and usually no bigger than 60x40mm. It is not about flattening the whole sheet of metal. Even when starting with a flat sheet, often there is distortion in the finished part.

I have seen plates as small as about 100mm square straightened on a roller plate straightening machine. 60 x 40 does seem undo-able. If I had to do the little diamonds, I would cut them on our wire EDM. Similar to making grippers for clamps only sharper.
 








 
Back
Top