Many real castings require cast holes that are not aligned with the mould direction. If the feature can be created on a pin that is less than 60mm in diameter a subcore is a good design choice. This is especially true if axis of this core needs to be skew; Many die caste struggle with subcores because they are not any easy to operate as regular core pins

ISSUES

1. HEAT REMOVAL

Subcores are effectively separated from the insert thermal passages. My subcores have 25mm rear diameters such that they contain a cascade The core cycle is timed to pull out of the casting as soon as possible. I add a second PLC to run the cores when faced with casting machines with OEM program locks

2. LUBRICATION

The subcore quickly seizes to the operating bushing if the running gap is not lubtivcated. Installing a pressurized lube pump to force grease into the gap only results in stained castings. The back side of my running fit is atmospheric vented. My lube reservoir in the die is filled once per day

3. SEIZING

I have not been able to eliminate the wear that causes a subcore to seize. My designs enable quick removal of the subcore cartridge and bushing without die removal. The bushing is 2/3 pre split on the back side to make removal and recovery of the subcore pin easier

4. BLOW BACK

Some brands of die cast machines do not maintain core hydraulic pressure during the shot. I manifold mount pilot check valves directly on the subcore cylinder to fix this. Even though many machines come with pilot checks on the core valve stack the hoses flex too much for this to be useful.

Creating a high pressure casting die design for the new 8000 ton machines would be a lot easier if you could just upscale a die design for a 4000 ton machine. The ejector pins would have twice the diameter and length. Unfortunately they would also have twice the sliding fit gap. Molten aluminum has the same properties independent of machine tonnage. It happily penetrates gaps that are twice as large. Aluminum in the gap around ejector pins effectively seizes them. This limits the maximum ejector pin diameter when casting 380 alloy to 11mm. Less fluid primary alloys like 356 can work with pins up to 15mm diameter.

Ejector pins in 8000 ton dies must deliver the same force per pin as pins in 4000 ton casting dies. Because buckling limits the maximum force that a pin can deliver. They cannot be longer than the pins used in a 4000 tin die. This strategy works well for the 8000 ton castings with shallow relief. Taller parts require more complicated designs to keep the ejector pins from buckling.

I like the position to win strategy used by Bear Bryant football coach of the University of Alabama. Because heat check increases the force on ejector pin, a pin that worked on a new die will buckle unexpectedly. Adding set screws to enable rear removal is no help whatsoever. Rear set \screws only work removing unbent pins (never the case) Whats worse is the replacement pin will buckle again almost immediately because the heat check that caused the pin failure is still there. Getting back to position to win. I initially drill the ejector pin clearance holes in the holder for threading such that a brass head hex head bolt can be easily added as a guide bushing. A column guided in the center can deliver 4 times the force. Good die designs have features that enable quick compensation for wear issues.

The discussion of the effect of scale on the die cast process begins with considering the reasons that we design in thermal passages in the die. Benefits of thermal passages can include

Cycle time reduction

Ordering of solidification

More effective die preheating

Refinement of grain structure

Transfer of heat around die

Reduction of poor fill / knit lines

Die solder control

Vent freeze off

Even though it is possible using die spray technique to run many dies without thermal passages, the yield reduction usually makes this an uneconomic choice.

As a young die cast engineer it took a while to understand why a die that started making good parts deteriorated into making scrap. Die casting is a thermal process. Scale build up in the thermal passages within the die upsets that process. And no, you do not need fancy instrumentation to measure the impact of scale build up. I have seen cores for making the fine grain structure needed to create castings with dry seal pipe threads accumulate enough scale to stop the flow in one shift. This was because boiling within the passage deposited the accumulated tower water minerals. Ostrich engineering applies. If you stick your head in the sand, you will not look for the scale build up within the thermal passages in the die.

Once you admit that your die cast process creates scale, it is possible to implement improvements. I have found that the a major reduction in scale formation is possible. Next I rank ordered a list of thermal strategies from worst to best

Tower water- steel pipes-atmospheric outlet pressure

City water- steel pipes-atmospheic outlet pressure

Hot oil-steel pipes-pressurized outlet

Closed loop hot water- stainless pipes- pressurized outlet

Closed loop de-ionized water- stainless pipes-pressurized outlet

(stainless pipes reduce rust build up)

(pressurized outlets control boiling within the die)

Do not feel bad if your plant currently uses a less favourable strategy. I can make a list because I have been there.

One of the early lessons taught to mechanical engineers is that materials deflect under applied loads. I can assure you that there is no shortage of applied loads in high pressure die casting. I thought that a 1000 ton press was massive as a new die cast engineer. Now we see 10,000 ton high pressure die casting presses. When you see the blocks of steel used to make high pressure die cast platens, it is hard to picture them flexing

This discussion is about the flexing of the ejector platen. On a 400ton die casting machine you can pretty much ignore ejector platen flexing. The ejector die itself is rigid enough to bridge across the platen face. On a 4000 ton die cast machine platen flex is an important consideration. The style of clamping mechanism is also a factor. There are four common styles.

Vertical pin axis book links

Horizontal pin axis book links

4 corner links

Hydraulic cylinder 2 platen

It is usually necessary to design the ejector die to match the style of machine clamp. Dies run in machines that they were not designed for are well known for flashing.

Large dies with slides will flash. Even if you are able to blue the die to shut off at steady state temperature, the first shot is not at steady state. Die require 30 to 100 shots to reach steady state even with preheat. Properly designed dies eject all flash every shot. This avoids die damage related to closing on flash. Remember the machine could be applying 10,000 tons on a small piece of flash