[dustinwassner]

we got an injection mold machine at work and these are the new molds we got. does anyone know how this would be machined? i guess what im struggling to see is how in the second picture these ribs were cut. They have square sides so it could not have been an end mill square or round nose that did it. also, the outer diameter of the cavity changes as it goes lower and along the changing diameter the square edges of the ribs remain perpendicular to the edge. I was thinking if i were to make something like this (assuming the non gradual changing diameter on the bottom section) i would have cut my two mold pieces then put them together face to face and clamped them in a vise, then drilled my hole in the center of them with my point of the drill being on the parting line, then reamed, then ?used a keyway cutter to cut the ribs? anyone know a better way, besides a ball endmill and cnc?

[ekim1956]

The cavity was burned in using EDM as was the gate.
The runner was a simple ball end mill.

[dustinwassner]

is the surface finish what indicates this? i was not aware that edm machines could do such sharp inside corners. i went to a one year certificate program school for machining and we never touched at all on edm, is this learned pretty much by getting a job at a place that has a machine and having on the job training?

[guru]

is the surface finish what indicates this? i was not aware that edm machines could do such sharp inside corners. i went to a one year certificate program school for machining and we never touched at all on edm, is this learned pretty much by getting a job at a place that has a machine and having on the job training?

Yes..That was typical EDM finish surface. To get the sharp inside corners you would first machine A graphite block to match the shape of Cavity, it can be just one big piece of Electrode or you can burn the Ribs on another trode. You would rough machined the Cavity out as much as you can then finish the Cavity on EDM Sinker.

[RomanLini]

Just a thought, it could have easily been machined from the top (the photo top) using an extra-length keyseat cutter, and the 2 mold halves could have been together at the time.

[dustinwassner]

In Response to Roman- I was thinking this but in the second picture you can see how the diameter gradually and smoothly changes and the ribs remain square to the outside of the diameter, not the outside of the whole mold. Im not sure if im seeing how using the keyseat cutter could do this.

Guru- are you saying that first you would take a piece of graphite and actually turn the final shape on a lathe in this case so you have a piece of graphite that is exactly what you want the finished product to look like? and how does this relate to the edm process? is this a necessary step in the process? im not very familiar with it.

for any of you that run edm machines, did you recieve formal training at a school or just on the job?

thanks

[bocko912]

It looks like you have 3 separate inserts. A thin one at the top forming the radius at the end of the part.A center insert which looks like it forms the straight center diameter with some ribs then tapers to the next set of ribs and a third insert that has a taper with some ribs. It looks like they did this so they could machine the details with a short cutter. If you look at the left hand side of your pics you will see a half round detail that looks like it was drilled and reamed. They used this hole to line up both sides of the inserts. I am assuming there is another block that looks the same? Or a male to create a shell?. That same hole is on the right hand side and they are using it as part of the runner. Only the end with the gate was cut with a ball cutter. Everything looks machinable to me but would be very time consuming. I would make 3 electrodes graphite is most common we use copper. 1 rougher .010 to .015 per side undersize from finish detail and 2 finishers .002 to .004 per side. this will give you finish dimension in your cavity after your overburn from the EDM. That to me would be much faster than cutting it but cutting it is possible. Do you have a mold base that this insert fits into?

John

[dustinwassner]

yes there is a mold base, and there is another matching piece. this is an overmold for a cable. i just dont have the knowlege with edm to see this being made but can see how it could be. as far as cnc cutting alone im still not seeing how you would cut the ribs on the smaller lower diameter.

is there any way to tell the material it is made of from these pics alone? i know it is some type of tool steel.

[guru]

Yes bocko912 is right ..there are 3 sections on that Cavity Insert but I think they were part of design change or to make them interchangeable with similar part but with different Ribs.

Insert can be made of 420 stainless steel, you will need to finish all runners, drilled holes, mounting screws and rough out the Cavity as much as you can the heat treat to about 48-52 RC then fin every else after heat treat..should leave grind stock on the Insert block so that you can grind parting line and "dial in" the Cavity.

The upper part can be rough machined using 3D swept, you need to finish machine the shiny area of the ribs and these can be done with 3D swept also, the rest of the Cav will need electrode to go in and fin. I made a quick drawing of Electrode that will burn Ribs area...the bottom will need to be thicker so you could drill some mounting holes ( I just did not want to go back and fix my drawing) you will flip it upside down to burn the Ribs.

If this is your first mold you should learn about shrinkage because you will need to add that to you Cavity dim's.

[dustinwassner]

this is an over mold for a cable. the connector would be hanging off what you see in the mold. the mold fits many different cables because you can swap sections out to make it look like what you need it to.

[bocko912]

Yea I agree the insert idea could be used for insert changes to different styles. I agree with Guru I would make the inserts out of hardened 420 stainless. If you are overmolding with PVC stainless is a must or cavities will degrade from the chlorine gas from the PVC. If you are using Urethane I would still use the stainless that way you will always have an option to go to PVC if you need to. These cavities are still machinable with various cutters and a rotary table on a mill but I would still EDM most of it. It would be faster and cheaper. I would do all the machining Guru stated before heat treat then find an EDM shop by you and have them make the trodes and do the burning.

[dustinwassner]

ok now i have another 2 qurestions

are rotary tables connected to the controller of the cnc and programmed with code? are they essentialy a way to give the machine another automated axis?

and, typically when a mold shop gets a job would they make the electrode, do rough machining on the mold material (in its natural state? soft state?) then get it annealed and then edm it?

[bocko912]

No the rotary table I was talking about is for a manual mill no CNC. CNC W/O rotary table would be faster than manual machining but I would still make trodes and EDM. Yea a mold shop could build you a set of inserts complete and ready to make parts. The EDM process can be done after heat treat no need to anneal and heat treat again.

[SORCHEROR]

its 3 seperate blocks and was machined,even the gate can be cut with a small ball,
personally i would have used one block and cut it all except the ribs,i would EDM those
makes a better mold,but maybe its a cheap prototype

[3D Accuracy]

As other's have mentioned, it appears the insert is laminated in 3 pieces. This was probably done for one of two reasons or even for both reasons.

1) it was the easiest way for the mold maker to cut the cavity given his machine capabilities, and/or

2) the inserts can be interchanged to create a different part/s

Here's a quick explanation on how this was probably done:

- rough mill the 3 laminated inserts for the cavity and core half of the mold
- assemble them together and rough out the cavity geometry by drilling a hole through all the inserts, cut the gate and runners, drill and tap screw holes, any water lines and ejector pin holes (I don't see any on the inserts you show, may be on the other half or the part is hand removed after molding)
- send to heat treat if required unless made of P-20
- grind and fit all the inserts together after heat treat
- make electrodes from round stock using a Harig fixture in a grinder tipped on angle with a sine plate
- individually or while clamped together, separately edm the geometry in both the core half and cavity half inserts, the thin laminated insert doesn't need edm as it's an easy cut
- assemble mold, make parts!

Have a terrific weekend!
Robert
3D Accuracy