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Punching holes in tooled hub forgings

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Hi guys we have been landed with an order for these 10 off for (what we call) pinions, but others call a tooled hub forging. Normally we have just supplied the customer with a solid forged hub, ie no hole up the guts of it.
We would like to go the extra distance, save our customer the hassle of having to bore out the centre. We want to punch it, now I know that there is a guy gets on this forum sometimes that works for Scot Forge in USA, and I know that Scot Forge makes tooled hubbed forgings. I'd like to get in touch with someone who has some experience in punching holes in tooled forgings to give me some pointers on how it is performed and any pit falls to look out for.

I'll attach the drwg as a PDF, all dimensions are in mm.

We have the equipment to forge it, the material is 8620, a case hardening steel, and its a job that we have done before, we have all the dies to forge the hub solid, but we just would like some help putting the hole in the centre.

Ta guys


Metalform pinion Drg 180821S-1.pdf

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Here is what he has to say:


I am not able to jump online and answer this directly right now. If you
don't mind, could you post the following information in response to the

To add a hole to a tool job you use an approach much like you would if
punching at the anvil except that in our case we punch completely
through the forging from one side and out through a die on the bottom.
The tooling is simple, a cylinder with a flat face and straight sides of
the diameter you want to make. There usually is a small step machined in
to reduce drag as the tool moves through the metal. A bolster is placed
beneath the work and the tool is driven through. We keep our tools short
so it is often necessary to have some follower blocks to allow for
punching a hole that is deeper than your tool is tall. Depending on the
equipment capacity and available material you could vary this process by
punching from both sides with tapered tooling, leaving a web in the
center of the hole that is removed in a second operation with a straight
sided punch or your may punch multiple times using two straight sided
tools of two different diameters. It all depends on exactly what you are
trying to accomplish.


And more from me..
I know there was a recent forging study on this as well on lubes used in this use..


I recall and article on forging hubs in this "Forge Mag" as well, but can not find it now.


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This is smaller that you wish to do..and they make more than ten, but perhaps you can draw some ideas

Or this at minute three or so...typical ring rolling piercing that I am sure you know how to do.

I am sure I have seen what you are asking for on a video or series of stills..just can not locate it.
You will either have to have the work done in several heats or make a set of containment dies or specific swages to either keep the shape while forging or reform the shape after piercing.
Obviously for just ten you will have little use for dedicated closed dies to do net shape forging...I think you will have to pierce undersized and still have a bit of boring for your client.

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In looking at your drawing more closely here is what I would recommend:

1. Forge the job to size in a ring tool with a counter bore. Upset your starting stock to create the flange. Be sure to figure and cut the weight very accurately so that you don't form a burr locking the forging into the tool.
2. Flip the job upside down and punch from the small end side with a punch about 25mm smaller than the final forged ID you want.
3. Flip the job back up with the flange side up and run a second punch through, this time of the final ID size. If you used a single snap and ran it from the flange sided first you likely would have a tendancy to drag the ID corner down and create a dish in the face of the flange. By running a smaller and then a larger tool starting from the small OD side and corner drag that does develop will be cleaned up by the second tool since the metal removed by that tool can very easily flow into the hole created by the first tool.

In our shop the flat bottom, straight sided punching tools I described earlier today we call snaps and the tapered punching tools are called punches. A snap typically has its major diameter for length of 2 to 3 inches and the remainder is turned down to a minor diameter about 1" less than the major. For a 6" snap the minimum length in our shop is probably about 6-8 inches. Max length is probably about 10". You really have to be careful that these tools don't get too tall or they can bend or shift and fly out from under the press or hammer. Unless you are trying to concerve weight, I'd use two straight sided snaps. When we are close on weight we will run a tapered punch in from both sides of the work creating a blind hole in each side with only a thin bit of metal between the two holes. A snap slightly larger than the big end of the hole is the use to create a straight sided through hole. This method removes less metal than the normal single snap method, but does take longer.

We make the snaps and bottom bolsters from 4340 or 4330 heat treated to about 363 Brinell. When working with nickel alloys like inconells the tooling should be made from properly heat treated H13. The bolster or bottom die should have a hole no larger than 1/8" (3mm) in diameter than the snap that will pass through it. If you can't or don't want to make a bolster, you can drive the snap through the work against the bottom die like you would if punching on an anvil and then flip the stock and run the snap back through. This will work but it will be harder to make a clean job of it. We do not lubricate our tools for this type of work. I hope this helps.

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Thanks Patrick
That ticks about all the boxes for me, my questions were going to be, do you start punching from the small end or the big, do you use tapered punches or parallel, do you part way punch it with a taper punch then flip it over and come back from the other side with another taper punch, or do you punch almost all the way then just blob punch out the slug from the other side, or do you just blob punch the whole slug out in go into a bolster. Almost all my questions answered in one go, cool.
One question remains if you don't mind, regarding the calcs for material, is the material calculated to take account of the hole, or is it just calculated as a solid hub with the material removed for the hole becoming waste, obviously if you are to blob/slug punch the whole lot out in one go into a bottom tool you would calc to forge a solid hub with the slug becoming waste, but what is the procedure if you are going to taper punch it, then come back with a cleaning punch the right size.



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Thanks for this description Patrick. Is there a blank put in the bottom of the ring tool while upsetting so the slug does not go all the way to the bottom of the ring tool? I would assume that material will extrude up around the punch and up the side of the ring tool?

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In our process there is plenty of clearance below the bottom bushing for the slug and snap to drop out. Our bottom to is loose and is place on the the bottom die by a modified fork truck, but you can scale the concept up or down depending on your needs. In general, when creating a hole with a snap (parrellel sides) you can figure that you slug will be roughly the length of your snap diameter. For short hubs like the one under discussion here you can probably assmume that you will remove about the same weight as if you drilled the ID after forging. If you are punch something substantially taller than the snap diameter, say running a 6" snap through a 30" tall part, you will still only lose a slug about 6" diameter by 6" long. When you use the tapered puncheds followed by a snap I know the weight lost is less, but I am not sure by how much. My rough guess would be something like 50% less waste but you'd have to determine that experimentatlly. As far as extrusion of excess metal, that can happen if you drive a snap against a solid bottom die rather than against a bushing. It can also happen during upsetting of the flange if you're not carefull, but if you pay attention, you will see that happening and correct it before it becomes a problem. I would say that most of our hub jobs are NOT done with plugs in place. We use plugs when we want to use a tool with the ID we need but which has a length longer than we need for the specific job.


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  • 3 months later...

Hi Guys

Just wanted to let the blokes that helped me with this that this job went without a hitch, thankyou espcially Patrick for you insight and also Jim (where ever you may be lurking). I did take some photos of the forgings after we finished them, and I'll have to load them and post them.

Once again thanks guys.




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Hello Forgemaster,

Looks like the job went with out a problem, was wondering what type of equipment and what the tooling look like for this job. Would it be possible to post some picture?


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