Moldmakers - grinding vs milling

[PaceToolmaker]

I am just wondering how many toolmakers out there are now squaring blocks in the cnc mill vs squaring mold inserts on the grinder.We have done it in the mill recently for blocks that were too tall for the grinder and just kinda thinking that maybe this approach is more efficient no matter the size of the block.

[RobertELee]

I 've done it on blocks that were to large, and tried to do it on every block, the problem I have found is that it can get real expensive if you need to hold a .0002 tolerance like I regularly had to do. Since the endmill breaks down and chips out, I would have to have a rotation of 3 endmills and keep having to put a brand new one in for the very last pass in order to get straight walls and smooth finishes. Most of the molds I make are 4+ cavity molds and in order to get all of the blocks exactly the same size it is very time consuming to keep having to make offsets when you can grind everything at the same time and have them all come out exactly the same size. It is great if you do single cavity molds though.

[PaceToolmaker]

We mainly build single or 2 cavity molds.Been using a 6 flute .500dia. Fraisa thats holds up extremely well.We have used just this single end mill on several inserts.We are not holding .0002 but the taper is less than .0005.Will do a semi finish cut leaving .007 per side then a finish with the same end mill taking it right to zero.The block is square and to size in less than an hour plus is already setup and on center for hard milling.Is just a different approach as everybody is used to the traditional method of grinding all 6 sides and then going to the mill.

[cadist]

Too expensive to do it on CNC milling, girnding machine does the job very well and cheaply.

[cqualls]

I use to do it on the cnc on a regular basis, used Walter Inserted mills and it worked well.

[kujo763]

We have been doing it successfully in the CNC for quite a while now. 10 flute 3/4 fraisa holding a .0002 with little to no taper. Unless you have really cheap labor in the grinding room they can't compete with a CNC mill.

 

Erik

[mchin-pilot]

Milling,does it all! - sizing,squaring and finish machine cavity in single set up.

 

Can even have a rad on insert profile so no need undercutting the Mold base pockets at the corners.

 

Reliev the bottom portion of Insert before HT- HeatTreatment , then only size the top portion, hence no problem about taperd walls.

[Midwest]

Mill them as much as possible.

 

 

[kunfuzed]

I know nothing about mold making. Why do all six sides need to be so close? Seem like just the "sealing" surface(s) should need it?

 

Just curious.

[RobertELee]

quote:

---

I know nothing about mold making. Why do all six sides need to be so close? Seem like just the "sealing" surface(s) should need it?

 

Just curious.

---

Most of it depends on what the part is and what the part is made out of. Say for instance you have a two cavity mold and the part is being made out of liquid silicone which flashes (the size air gap at which the material will fill) at .0001" or less. If you have a gap between the two cavities of more than the flash point and the runner or a vent runs over that air gap, you will wind up with sticking parts because it will fill that air gap between the two cavitys. Also some parts are just SO critical (ie. medical, military, etc.) that they want zero parting-line showing on the parts so you have to make everything so super tight there is zero chance of the cavities slopping around(but we also need everything to be able to get disassembled). We also put other forms of alignment into the blocks but we want zero chance of movement so there is less wear on all of the alignment surfaces.

 

But for the main reason -- OUR CUSTOMERS ARE JUST INCREDIBLY PICKY!!

[kunfuzed]

I seeeeeee.

 

Thanks for the info!