[laka]

Our company has been given an RFQ for many parts called 'Orifice plates.' They are water-jet cut from 1/8" thick SS sheet. They require various bore sizes which must be +/- 0.001", and also need chamfers on the bore. Flatness, finish, and tolerances are all very important. I'm just looking for some ideas on how to make these cheaply. I'm thinking a turning center would require many different sets of soft pie jaws to prevent the material from bending in when machining the bore.

Just curious if anyone has any suggestions, or knows how other companys make these parts. (They are widely used in the natural gas field, and are made by many suppliers.)

PDF example (handle not required on our parts)
http://www.mac-weld.com/Orifice-Plat...fice-Plate.pdf

Thanks

[MonoNeuron]

I think the easiest way would be to use a punch and die then just chamfer the hole to the desired depth.
regards,
The Neuron.

[ctate2000]

You did not give hole sizes. The +/- .001 should not be a problem. What size is plate? We need a little more info to make good suggestions.

[ViperTX]

If you're looking for flatness and finish at most any value but "close to flat" punch and die will not work, unless you do a post punch operation....surface grinding....

[dertsap]

flatness is an issue , are you going to send them to the grinder first , its 1/8 plate and the pdf shows 1/8 thickness ????
,the bores can be easily interpolated on a decend vmc , simple pin locators on a plate with a couple clamps would probably do it

[JPMach]

Send them to me for the bores!

I second what dertsap said

JP

[handlewanker]

Hi, as I see these parts, they are inserted in between the flanges of a pipeline and serve to regulate the flowrate of whatever passes through the pipe, probably gas or oil, to cause back pressure on the supplier's facility.
I would get the outline cut with an abrasive waterjet process, and then
A good punch and die should produce the bore size without too much problem, and the chamfer to remove the burrs and smooth the flow, and if required bring the bore to the .001" tolerance, can be done in the lathe.
If the batch volume is small, then a purely lathe operation would do, but if it was significantly large, about 150 batch size per month for a 3" bore, then a punch and die with a 30 ton press would be required.
The press size would be determined by the maximum hole size to be punched out, and a 6" lathe would handle the blanks for chamfering.
As far as flatness is concerned, it's the wad that is punched out that distorts, and the plate that is supported on a flat die face will remain flat.
A punch operation will produce any hole size you want,in one hit, ask any toolmaker.
You would also need a batch size of at least 1000 parts to justify making a punch and die and buying in a press to allow payback in 2 years.
Ian.

[Geof]

They are flow metering orifices. When the fluid is flowing whether it is gas or liquid there is a pressure difference across the orifice plate. This can be used to calculate the rate of flow through the orifice. Tight tolerances are needed on thickness, flatness, bore and chamfer size because these all influence the pressure difference.

[handlewanker]

AHH SO! day light, couldn't think what they were for otherwise.
Is this something like a venturi principle?
Ian

[Geof]

AHH SO! day light, couldn't think what they were for otherwise.
Is this something like a venturi principle?
Ian

Yes, same principle, all based around Bernoullis' theorem. If you wanted to spend a lot more money you could use a venturi; aother option is a Pitot Tube*. The orifice plates can be selected for different pressure and flow rates and for different fluids.

*I think this is the name...it is used to get airspeed on aircraft and I think a version is used on boats.

[ViperTX]

Well I have yet to run into a punch and die...that fit so perfectly that a burr was not present on the piece being punched......

[handlewanker]

Hi viper, I know what you mean. The problem occurs when the clearance between punch and die is increased to allow for sloppy set-up and even sloppier die making.
Given that a die will drag a small piece of metal down with it if the clearance is too much, then the obvious answer to the ill informed is to make the clearance almost nill.
In a perfect world this is ideal, like cutting paper circles with a paper punch.
The problem starts at the die-set. This little device ensures that the die and punch are in as perfect allignment as can be, and overcomes the wear in the press ram.
If the punch has a perfect allignment with the die then no clearance beyond a sliding fit would be required.
But the toolmaker knows that after he has made the tool it will not be in perfect allignment for long due to wear and tear on the guide mechanism.
So he adds a bit of insurance in the form of increased clearance, so that the tool will give a decent life.
The life of the tool is determined by how long the shear edge of the two faces last, and too little clearance will "nip" the edge of punch and or die and so heavy burring will occur and early tool failure.
Ask any toolmaker to make you a punch and die and stipulate that no clearance must be added, and that the tool set-up must last a long time and see what he says.
Two conflicting design requirements, and he would not put his reputation on the line for early failure.
Depending on the volume required, if it is small then die clearance can be reduced and the tool carefullyset-up.
However if the volume is large then it would be asking a lot to expect the running clearances in ram, die-set, and tool deflection, to not affect the cutting edge.
Incidently, the punch does not "cut" the blank from the metal sheet, it shears it by the proximity of the punch edge to the die edge.
To clarify this statement, draw a cross section of the tool at 10:1 ratio.
If you place the circle for the punch on the circle of the die and seperate the two by the material thickness, then draw a line from punch corner to die top edge you will see how much shear the metal blank will have and how much metal in the clearance will get dragged down to form the burr.
However at the end of the day the part is going to be chamfered anyway, so burring will not be a problem.
What will be a problem is:- if the metal being punched is not clamped firmly enough, then the plate will rise up and distort as the punch goes through.
A spring loaded clamp on the punch will prevent this.
The spring being in the form of a thick rubber disc surrounding the punch and backed up by a collar on the punch.
A normal die set-up would have a punch in a holder in the ram and a die with a stripper plate to stop the material rising up with the punch after punching.
Usually some distortion of the part, a small amount of dishing at the hole, will occur, and is allowable depending on the part requirements.
The flatter the part is required to be, the more complicated and dearer the tool will be.
If the subsequent punch operation is to the best design criterior, and distortion still occurs then the next operation will necessitate surface grinding, using a vertical spindle type grinder with a large diam stone, such as is used to face cylinder heads.
Ian.