There are times in the economic cycle where it would be nice to have additional casting business to fill empty machine capacity. This usually means taking over an unprofitable job at the same selling price. In many cases it will require creative die design to make the difference. I have pictured an example. A four cavity 900 ton die without slides made the pictured freon tight casting. Annual volume was a couple million which would fill a couple machines. This part was being run at a competent competitive plant at a loss due to poor yield. The OEM could not accept a price increase or changes to the part design. The competitors dies being run were designed from standard die detail hardware and cores.

The competitors dies used a core pin to form the inside of the nose of the casting. This pin overheated because it was short and buried deep in the cover insert such that it is difficult to spray. Water cooling this standard H13 core as suggested by my boss was not the answer. H13 does not accept a high thermal gradient. H13 cores or inserts with water closer than 19mm to molten metal usually split. A water cooled H13 core split on the 4^th shot after it was implemented.

Enter exotic material. Maraging steel (Marlock was the first widely used example) tolerates a higher thermal gradient than H13. Inserts and cores can be implemented with water as close as 6mm to molten aluminum. Incorporating the percolator head and retaining bar into the core created enough heat transfer surface within the core. {Conformal 3D printed cores also use maraging steel for the same reasons}

Massively cooled finger segments only solve part of the problem. With massively cooled

finger segments it is easy to over cool. This sometimes can be solved by using hot oil within the core. Because hot oil only has 1/2 the heat transfer capability of water it would not work on this finger segment. Because we purchased our Buhler casting machines with cooling water timers, this was the most effective solution. The cooling water flow could be shut off before the finger segments become too cold. (the four finger segments (1 per cavity) were piped into a separate zone) You will also notice that the chosen finger segment detail has a lot of extra size which serves as a storage reservoir for heat.

I am the first one to avoid inventing custom details. The wheel is round and does not need to be reinvented. Finger segments emerge as one area where creative design can change the casting yield. Taking over jobs that are unprofitable at a competitor plant only help your bottom line if you can make them profitable. Custom finger segments improve both yield and cycle time changing profitability.

Most die casters realize that it is necessary to have the die at the right temperature to make good castings. This is partially true. The temperature of most of the die really does not matter. Process temperature control only applies to die surfaces when they touch molten metal. The good news is that the instruments for measuring the process significant temperatures on the die surface are both accurate and affordable
It would be convenient if a constant uniform die temperature yielded the best casting results, Unfortunately the opposite is true. Commercially acceptable scrap rates only occur when a thermal pattern is implemented. I suspect this is why casting plants specialize in certain types of castings. They can embed their die thermal design experience in new jobs such that they are running profitably sooner.
It is easy to be overwhelmed by the amount of temperature data that a tool such as an infrared camera can generate, The picture shown on this post is an infrared temperature scan of one side of a structural casting die. The die surface temperature in the picture varies between 66 and 221C in this die region. Actually I was in the process of increasing this range to simultaneously reduce poor fill (hotter die) and reduce soldering (colder die)
Most die casters use a water based release agent. When water based lube is used, die surface temperature in metal contact areas must be above 100c which is the boiling point of water. The ejector die around ejector pins usually must be less than 205C to avoid ejector pin seizing. This is a normal struggle area because the majority of the heat added solidifying metal ends up in the ejector die. Cover dies end up too cold because the shrinkage of the metal during solidification creates a gap which blocks further heat transfer between the part and the cover dies about half way through dwell. Hot oil is commonly used in cover die thermal passages because the cover die surface temperatures can be between 100C and 375C
It has been only recently that simulation software has be able to predict steady state die surface temperature. This is the starting point for engineering thermal passages to achieve desired temperatures. Up to this point control of die surface temperature was left to the caster who sprayed the die

A customer was talking to his carpenter. ” How do you explain your great reputation? ” The carpenter answered “I inherited my hammer from my father who was also a carpenter” The customer replied ” Your dad has been dead for many years. Are you sure it is his original hammer? The carpenter answered ” It has had 7 new handles and 3 new heads but it still is his original hammer”

Die casting dies that make castings with complicated precision shapes like transmission valve bodies also wear out like hammers. Die casters who are serious about making a profit realize that it is not necessary to replace the complete die every time a portion wears out. This is even easier it the original die design has the segmented design to enable partial renewal. Most dies have replaceable core pins. Better dies also are segmented such that worn sections in front of the gate can also be renewed. Skilled casting die designers use self cleaning features as part of their designs so that hand manicuring of segment flash lines is avoided.

The die casting engineer is at the receiving end of customer venting when part quality suffers due to a lack of venting. Virtually all aluminum die castings dies require venting. This is related to the vaporization of the organic release agents used. These agents vaporize when the aluminum fills the cavity creating a gas barrier between the molten aluminum and the mold. This vaporization creates 500 psi (34 bar) gas pressures at the middle of the fast shot event. Vacuum can reduce that pressure by 15Psi (1 bar) but does not eliminate the need for rapid venting.

Vent elements with moving valves have a greater flow rate when open. This style is less popular because the larger flow rate is lost because the start of valve close must be triggered early to insure that the valve is closed before the molten metal arrives. Waffle style vents are the most popular. The lack of moving parts improves their reliability. The biggest challenge is choosing vent materials that resist exposure to molten aluminum without wear or soldering. As our industry develops a successful formula for structural body castings we see an evolution away from vacuum to waffle plates that are double the historic size and have H13 inserts for the first few waffles. This is related to the fast (6 m/s) fill speeds and hot metal temperatures. Thin wall castings with long fill path lengths use faster shot speeds like the big magnesium dash panel frame castings.

This post is not about the best way to remove rusted in bolts that retain the inserts in the holder. Die casters who are running dies that are constructed using metric bolts have enough practice to teach me more efficient ways. The hot steamy die cast running environment is perfect for generating enough rust to seize a bolt in one casting run

In North America most die casters still use coarse thread cap screws to secure inserts within the holder. This is because they spin free even when rusted in. Yes it is going to take a 10 ft pipe and possibly lifting with the crane. This is more time efficient than drilling. My first experience with metric bolts was a European transfer die. Converting this die to US coarse bolts was the right answer for a single die. Converting an entire plant of metric secured dies is cost prohibitive.

I did not know of a good solution until I worked building Japanese designed excavators. They use soft Loctite on all bolts because it becomes impossible to drill out rusted in metric bolts in the field when service is required. The same Loctite is effective on preventing metric bolt seizing in die cast dies

All gates are not created equal. The flow from some gates is blocked by the shape of the casting in front of them. In the attached example the center gate was effectively blocked by a step in the part shape in front of it. The simulation appears to allow metal to enter the part through the center gate. A short shot demonstrated that this was not true. The process was fixed by a tuning of the casting shape

Gates are effective when 50 mm of straight air path exist in front of them. #Soldering and #erosion occur when this is not true.