You'll see why the parting line matters in the next bit where Ill show how a flange is made. The water flange is a bit more complex in the fact that it has a void in the middle for the coolant to flow through. Therefore a sand core has to be installed in the mould to prevent the alloy filling up the mould totally and the flange ending up as a solid lump of alloy with no hole through it. Flange in question is the plastic one found on the end of the 8v head which always likes to leak, Im going to make up a few alloy ones for that reason. Its easier to describe with a few diagrams first before I move onto the real deal so you'll get an idea of what it looks like in cross-section. Cross-section photos aren't possible in real life so I hope this helps with the process your going see when your looking at the actual mould and casting photos. Heres a picture of said flange, Im sure you'll recognise it! And here it is in a simple drawing And a cross-section drawing, the light line showing the water way inside, the black bit in the middle being the void that has to be hollow. So, keeping that in mind its easy to see that a mould is needed to cast the outside shape, and a sand core is also needed for waterway in order to install inside the parent mould in order to ''keep out'' the alloy from that bit. Onto how its done, a timber copy of the flange is turned on the lathe in timber, the timber blank used to make the copy is first glued from two pieces of timber with a piece of paper separating the two pieces. That way once turned the timber flange is easy enough to split in halves along its centre line. The flange is then turned up on the lathe but with the addition of a spigot either end, like so shown below.(The timber pattern is solid) Next, a copy of the internal void, or waterway inside flange is turned up, again, with the extra length or spigots either end. The flange pattern is then split along the paper glue line and is mounted up into the mould boxes(flasks) Both halves are separated with a 3mm thick sheet of steel separating the top and bottom flask also, the halves locate on this sheet using positioning pins show in red, that way both halves are exactly opposite each other. The top and bottom flasks are then filled and packed with casting sand. The top flask is then lifted off carefully, this is where the draft angles of the part are important so that the part does not interlock in the sand. The part is then lifted out of the sand contained in the bottom flask. Putting the two flasks back together again the void can be seen that the pattern has left. Next, the inner timber pattern for the core shape(shown below again) is transferred to to the same shape but this time made in sand. This transfer from timber to sand is done using a core box, ill cover this later. With the mould open again the sand core is now installed inside the parent mould, its now clear why the spigots are need on the timber flange pattern, the sand core hangs or sits on these inside the main mould. A sprue and riser are formed in the top mould in order to feed the mould with the molten alloy, a few 1mm vent holes are also made using a bit of wire. The sprue is used to fill mould and also acts as a reservoir for the mould as the mould fills and also feeds the mould after the pour is complete and as the part cools if any shrink occurs. The riser is not needed on some pours, its function is to indicate when the mould is full as the molten alloy rises up this meaning the mould is filled and pouring can stop. A ''gate'' is also made at this time from the base of sprue into mould cavity, its size and cross-section depends on part complexity, wall thickness, and material being poured. The mould is then filled Once solid the mould is knocked out and the part removed from the sand, the sand can be re-used many times. This sounds like a long process but its very quick, the mould and core can all be made very fast once you have patterns to strike them off. For more complex cores of a bigger area a special sand can be used which cures when Co2 gas is passed through it, a core 600mm long can be made this way then and can remain unsupported without collapse inside the main mould. Once the part is removed the sprue and riser remain on it, it would look something like below These are then cut off and ground at the area where the gate was feeding part. The gate location on the bracket can be seen clearly inside the red circle
So, you can now see how a core is used to create a void within the part to be made. Granted the water flange is pretty simple as thats open either end and the core can be ''hung'' inside the mould pretty easy. But on an intake manifold or other part such as a cylinder head where the core is totally contained a different method has to be used. On the water flange it was possible to hang the core from either end as the space inside exited out either end so that made core positioning pretty basic. There are other ways to hang internal cores inside moulds on parts that have no holes through them to the outside. Take the manifold below, the plenum chamber for all intensive purposes is a sealed box, therefore the core used inside it at the time of pouring has to be suspended some way, and in the correct location in order for all the plenum walls, and runners to be of the correct thickness/position. If we look a bit closer things become apparent, notice the frost plugs used to close the holes that the core has been suspended on. Its the very same principal as the flange core, but a different shape. Spigots are also incorporated on the plenum core which are needed to hold the core in the correct place and at the correct height. These holes formed by the location spigots are then closed off after the part is finished by inserting frost plugs into them. Or, in the case of the other end of this manifold a breather pipe has been inserted into the spigot hole. This solved the problem that end and saved the use of a plug as the tapping was needed for the brake booster line. If we look at other parts that have enclosed cores such as the manifold the spigot positions used to carry cores can be located too Take a look at the 16v cylinder head below, a core is needed to form the inner waterways around valves and chambers, while this core is pretty complex the basics still apply. And a picture of a water way core for use in a cylinder head(not the core for the above head) You can see the extra spigots on both ends needed to locate it in the main moulds, these spigot holes left behind after casting sometimes become waterways either end of head, or can be capped off. Both are done on the 16v VW head as shown below Spigot/core carrier hole right hand end, milled flat for water flange And the hole the left hand end, machined, and capped with a frost plug The same can also be seen on the engine block itself, here the three spigot holes needed to carry the water jacket core are capped off with frost plugs on the rear of the block A cutaway view of water jacket and a guide as to what shape the jacket core would have been And another showing frost plug removed And an example of what a core needed for water jackets would look like, this is from a 6cyl but the principal is the same, check out the spigots on it needed to position it in the parent mould Another feature of these spigots on the cores is to help expel any hot gasses that build up inside the core at the time of pouring. These hot gases escape out these, through an air hole in parent mould and out to atmosphere. If these were not there, the gas could build up and rupture the casting from the inside out before it had fully cooled. All cores are also given a gas impermeable wash before being installed, this helps direct internal gas out to the areas of the core where the spigots are, these spigot areas are left untreated so the gas can escape. You'll notice above the wash is kept off these areas. To give you a rough idea of what an engine block mould would look like heres a picture of a partially constructed one below, granted its done as a sketch but you can see the holes along the face of the red sand mould where the water jacket core would hang once assembled. You can easily see that a more complex part requires multiple sand moulds and cores to be integrated together in order to form the final mould. Anyway, more about cores and how they are made later on. ---------------------------------------------------------------------------------------------------------------------------------- Next up a run-down on the flasks and the parting plate. They are pretty basic, but vital non the less. You could make these very easy if you wanted to, later I'll be making a bigger set for an Intake manifold but these ones are perfect for small castings. I picked these up years ago at a car boot sale with the intent of doing all this, hard to believe Im only getting round to it now. The guy I bought them off thought they were grates from a stove............I told him ''Yes, they must be'' and handed him 20. The drawings I did above pretty much sum them up but a few pictures and a quick run down on them wont go astray. They are made of alloy, very strong, and have two integrated positioning pins to locate the top flask exactly onto the bottom flask. The precision of these pins is vital in a good casting, if there is play, the top half wont locate on the bottom half exactly and a step at the parting line in the finished part will be very noticeable. Luckily for me, these are quality items and no more than .25mm play exists, just enough to make removal of top half easy. The guide pins do need a bit of a shine up and oiling but thats pretty easy to do. Here they are below, in the assembled position, notice the large corrugations in the walls of the flasks to hold sand in place, remember, these are open top and bottom. And in the open position. A view from the side in the closed position. And again from the side in the open position. A closer look at the guide pins, one side has a round pin, the other a hex pin, this way the top can only go on the bottom one way. And the hex pin, slightly larger in size than the round pin. The hex pin socket is also adjustable clockwise or anti-clockwise so any play can be compensated for. -------------------------------------------------------------------------------------------------------------------------------
Next, onto the parting plate and how its made. Originally I was going to make this from steel, but given the fact that steel isn't transparent it could make taking photos or explaining stuff awkward, so, I went with some 12mm acrylic sheet. Once a size was taken I cut it out on the table saw, I left a bit of extra all round the edges to make it easier to grip it when removing it. Chop chop. After that I gave all edges a run with the electric planer, they were a bit rough after the saw and Im going to be handling this plate a fair bit. And a bevel to remove sharp corners. Job done. Now onto the holes, these have to be pretty exact too in order for the plate to slip down onto guide pins. Transfer measurements to plate and scribe them out. Bore guide holes Like so. Next up, 3mm bit in the router to inscribe the word ''up'' on plate, that way installing it upside down by mistake will never happen. You could use a marker but, I doubt it would stay on there too long. Parting plate installed, mould in the closed position. And a view from the side. Drawing I did earlier below it showing proposed set-up as shown now for real in photo(Pattern omitted). (more to follow)
Sorry Just let me know now and then if it reads ok, Ill try my best to ''try'' and explain it in steps that make sense, but having said that, Ill prob forget something and have to double track Plus, Im no story writer Brian
Must have been cos there were so many pictures and i skimmed through it. It makes sense after taking time to read it.
wow, seriously impressive and informative thread. i design injection moulded stuff for a living which is pretty similar so know all about the headaches involved in draft angles and undercuts! thanks for taking the time to take all the pics and write it up!
Really? Nice one, thats a real interesting job id say You'll be right at home so in a while on the head thread as in order to eject the water way core from the core box Im having to install manual ejector pins Oh the joys!! Brian
No, not yet, wanna give a rundown first on the basics, so that itll be easier to concentrate on the head build than explaining why Im doing things whichever way. Thats the plan anyway
@ cepris, I looked at it, but no Im not going to, I think a while is needed to get up to speed on controllers, etc, its pretty new yet, but nice. So onto the making the pattern for the flange. Im going to make the pattern double so I'll get two flanges per pour, I could make it four but Im going to stick with two for the smaller flasks for the time being. Here is a rough cross-section sketch of how the finished pattern will look once turned. Remember this is for forming the shape of the main mould(s) and will be split after turning and both halves fixed either side of the parting plate. So, onto the making the timber blank, I chose an off-cut of walnut I had because it was handy and near the size I need. Any type timber can be used for this, but, It has to be one that cuts pretty good and turns easy on the lathe, soft wood for example is less able to hold fine detail. I measured off-cut thickness and set the rip fence to double that and cut two pieces. Chop chop. Cut. Now, onto the glue up. Remember, a piece of paper gets glued between them in order to re-split them after turning, both halves mount either side of parting plate. Normal water based Pva, nothing fancy. Lay paper down on top of one, and drop the other onto it. Like so. Ill be able to mount that in the lathe once it has fully dried tomorrow. Back to the flange for a second, a closer look shows the parting line from factory, which in this case will also be the position of paper/centre line on my pattern blank. Ill be turning up the blank to make the double flange pattern once its dry.
yep, heard of Airfix kits? i design them stuff like spitfires are much easier to draw on paper than to model accurately on CAD! ejector pins are the bane of our lives, theyre fine on everyday consumer stuff like remote control housings where the pins can go on the inside of the assembled product, but often we have parts where both sides have to have loads of moulded detail and ejector pin marks are the last thing you want in the middle of it all.
Well, it dried! The ends are trimmed square. Next, two pieces of 6mm Mdf are screwed either end, these have two purposes, they hold the two halves together in-case they come apart on the lathe, ruining your smile for Christmas, and they also provide positive location for the lathe drive and tailstock centre, if you were to drive them into blank, they would be hitting dead on the glue line and without a doubt would split the blank. With the centres are marked a rough max diameter circle marked. The blank is planed down to match this circle roughly, it saves knocking the corners off it on the lathe. The centres are driven home before mounting. Tail centre. Mounted on my home made lathe! Actually, a lot of people spend thousands on wood turning lathes, why I dont know, all a lathe has to do is turn the blank, and have a solid tool rest, the rest is upto the guy holding the chisels. A couple of seconds with the 25mm skew and its down to round, or round enough for the time being. Basic sizes are transferred off the flange plus a little more for the shrink rule. The marks are then made heavier by turning the lathe by hand to mark all round the blank. You can now see all the particular lines where the various diameters change. When turning a blank like this that has a narrow central diameter all turning or as much as possible is done before the centre diameter is reduced, that way the blank stays solid and whip is minimised. In the next few photos you will see how the various sections are taken to near their final diameter. Here Im turning the larger spigot that the core will hang on. And the portion that the hose will clamp on. Moving onto the spigot area in the centre of pattern. Note, always working towards headstock(left), that way keeping high cross-section to the left of me, ensuring that the blank can always transmit the torque to the area Im cutting without failing. A screw is inserted at this point once centre is turned, that way clamping the two halves together incase of glue line failure, you do not want this blank coming at you. Moving left always and onto the other flange pattern. A quick check on all important dimensions is done and the part is then burnished, this involves holding its own shavings against it in order to shine the part, it works well.
Removed from the lathe the 6mm Mdf plates can be removed either end, and the screw in the centre. A quick datum mark is make before parts are split so you know which way they came apart. Screws removed its given a quick tap, this splits the paper glue line. The waste either end is trimmed off to provide spigots of equal length. A very rough drawing now shows what shape the core cross-section needs to look like. And left down on the parting plate to give you an idea. You can now see the cross-section transformation from the drawing I did earlier, to the part in real life. A small bit of work on the flange area next and that will be the main pattern done. For anyone thinking this was a huge job turning this, its approx 40min lathe time, so, not too bad. (more to follow)
So now the with all the turning done the flange outline can be cut, I marked out the flange shape on a piece of card and transferred it to pattern. Its positioned keeping the parting line in mind and the draft angles, if positioned wrong it would cause the sand to become locked on splitting the mould and ruin the moulds also. Like so, the line is pretty faint.. The two halves are screwed together again for the cutting operation. Quick run around with the coping saw and they are ready for a quick sanding. Done And un-screwed again. Thats that pretty much done, bar mounting them on the parting plate. Next up, making the core, thats pretty handy.
Fascinating read, very interesting to see how its done and looks so simple when someone takes time to explain the processes
Thanks lads, I hope it reads ok and makes some kind of sense Onto the core pattern, Much the same process again, blank of correct size, centres marked, centres driven home, corners knocked off with planer. Next, the main points are marked out on the now round blank. Not forgetting the extra material either end for the ''hanger spigots''. Taking shape, care is needed at curve area to provide sufficient strength and wall thickness on the finished part. Nearly done, diameters are checked and the ends narrowed down with the parting tool to make cutting off waste easier. When held up against main pattern you can now see how the core will look inside the mould. If you look at the plastic flange two dimples can be seen inside, these are clearance for the bolt heads holding flange to head, I have to make two hollows yet in core pattern to ensure there is sufficient material here after the pour for when I counter-bore the bolt holes. I could make the same two dimples in the main pattern doing away for the need to counter-bore, but Ill be boring the flange holes in a jig anyway so its only a matter of using a stepped counter-bore bit. That way, the flange holes are bored, and the clearance around them is also done at the same time using the stepped bit. You'll see that later anyway, its very simple. Some of you may be wondering where the groove for the ''o'' ring is, I chose to omit it for a reason, on some heads pitting can occur at the flange area making sealing a problem when using an ''o'' ring, this way, I can face the flanges flat and use a gasket or sealer, or I can machine the groove with a simple mill jig. That way I have options. If you wanted to mould the groove you could very easily by inserting a removable core on that end, but doing it this way I wont need to. Next up, transferring the core mould to a core box. The core box is basically a box with the shape of the core I just turned inside it. You then pack sand into this box tightly, the box is separated and you then have the core shape replicated, but in sand and ready to place inside mould. (more to follow)
