Parallel

Pat your head and rub your tummy

We discover that our two hands can be simultaneously doing different tasks at a young age. This seems to be forgotten when many die cast cells are set up. Yes it is easier to plan a process in a sequential manner. Unfortunately it is difficult to be competitive when the casting cell operates in a sequential fashion.

Early in my career I was charged with automating an entire plant. This plant specialized in making some of the most difficult castings in the game. In most cases it was necessary to achieve the same cycle time that the best cast operators could achieve to make good quality parts. This forced me to micro analyze how a manual die caster could beat the robots. It turned out that they learned how to jump the gun

Running an automated die casting cell is about synchronizing the moving elements.

Die Cast machine clamp — Shot — Die — Extractor — Ladle — Spray robot

It is difficult to win a relay race if you wait every time that you are supposed to pass the baton.

keep all of your moving element busy
  1. Pretip of the ladle cup and pouring directly into the sleeve starts at die face touch results in the pour half complete at die lock and no wait for metal run to complete down the launder.
  2. Subcore pulled at end of dwell
  3. Slides open during die open
  4. Extractor reaches through a window in door starting 4 inches before die full open (I leave both doors closed)
  5. Sprayer partially advances during extract
  6. Slides close during spray
  7. Sprayer completes return home during die close
  8. Subcores close during pour

In this era of Mega presses, automated casting cycle time is even more critical to realizing a profit. It is also fortunate that casting quality improves with reduced cycle time as long as the dwell and spray time is unchanged. As you look at your own casting operation be aware that some of your competitors understand parallel action.

60 Second Rule

One two three four five six seven eight nine ten eleven… all the way to the 60 second rule. Coworkers think I am crazy when they hear me counting out loud to sixty. This is a success habit. I am impatient. Counting out loud keeps me from turning the power back on too soon. It is also a good training tool because people ask what I am doing.

In our electronic age many of the controls are computer operated. I installed the pictured 200 amp motor soft start on my 3500 ton die cast machine because I wanted to free enough power to run oil heaters. Lightning strikes. About 12 times per year it hits the power grid within 5 miles of the die casting plant. Usually trips out this motor soft start computer with a fault code. Enter the 60 second rule. The soft start error happily resets if you leave it off for the 60 second rule. Also applies to the crane drives, the CNC machining centers, Gun drills, Just about every piece of equipment with an embedded computer. The residual power must drain to force a reboot. Count to 60 out loud before you call the service technician.

Counter Bore

The old addage “If the only tool you have is a hammer, every problem is a nail” Eliminating sharp edges fit into the same category “if the only tool you have is a chamfer ever corner is at a 45 angle” Imposing a one size fits all solution to a problem creates sub optimum results. This discussion is about adding counter bores to your design arsenal.

Machined 45 degree chamfers work very well when both adjacent surfaces are machined. In the picture you see a yellow 45 chamfer on the corner from the mounting surface to the bore. This was machined into the plates. On the opposite end of the bore a counter bore replaced the chamfer. This counter bore is on the corner between a unmachined face and the bore. The counter bore was created by interpolating the bore roughing cutter. This resulted in a uninterrupted cut by the fragile finish bore cutter which solved a cutter chipping problem,

Cast counter bore are used when a machined surface connect to a cast chamfer. The counter bore solve the tolerance issue and insures that the chamfer diameter is never oversize.

Having a Ball

Little kids naturally understand how easily balls move around. They have a blast “swimming” through a sea of balls in a ball pit. For those of us that have not experienced that pleasure, the motion of a mass of ball is not intuitive. This is probably why it is sometimes hard to explain the benefit of creating a spherical grain structure.

Rheocast aluminum is a bunch of tiny balls

Many die cast practitioners only have experience making small castings. This is because 800 ton die cast machines are what was historically found in die casting plants. Todays casting purchasers have discovered the cost advantage of combining multiple casting into one. According the castings have become larger. As always one of the challenges is getting the metal to the far end of the part before it solidifies. This is usually accomplished by rapid injection. As the fill path becomes longer it become necessary to use faster injection speeds. Faster injection speed causes flash and venting problems. I would rather use finesse. Rheocast metal with a spherical structure can be injected at 1/3 of the speed taking advantage of the way balls flow smoothly past one another. Any kid in a ball pit would understand this.

Nary a Drop to Drink

Both Air Fins and Tower reject Heat

Water water everywhere but nary a drop to drink. A well known line from the poem – “The Rime of the Ancient Mariner,” by Samuel Taylor Coleridge. The mariner was bemoaning the lack of fresh water in the middle of the ocean.

Die casting got its start in the Great Lakes section of North America. There we have a treasure trove of fresh water left to us by the last ice age. Since fresh water was so plentiful and inexpensive it was natural to use a evaporative cooling tower to accomplish cooling of the die and machine hydraulics. As the majority of die casting moves away from this region this is no longer true. Many regions of the world have times of the year where there is water shortages. We really want avoid making a choice between drinking to survive and running the die cast plant to make an income.

The die casting industry is now at a cross road. New structural castings in new alloys are emerging as the dominant product. Record tonnage machines are being installed world wide to meet the demand. At the same time new die casting technologies are being invented and implemented to solve the challenges imposed by the new alloys. Historically we added iron to the die casting alloy to combat soldering. This was helpful at the expense of a less ductile casting. More precise temperature control of the die is needed to avoid soldering when casting the new structural alloys without the iron content.

Evaporative spray cooling is the historic die cast die cooling method evolving from a plentiful free water supply. Current die cast innovators are discovering that it is easier to achieve the required die surface temperature stability using internal thermal passages in the die. Other new die manufacturing technologies such as 3D printed conformal cooling inserts make this possible. Minimum lubrication water free spray release techniques such a Lubrolene are emerging to match.

This represents an opportunity for the die casting industry to make a “green” contribution. Using air fins for rejecting the heat from hot water die cooling eliminates the scale which is the bane of tower cooled water die cooling. Scale control is very important when using conformal inserts that with cooling passages that are tough to descale. Water free spray release not only reduces VOC emissions but the elimination of evaporative spray cooling prevents the humidity build-up that makes the die casting plant feel like a jungle. I will drink to that. (We will have the fresh water we need to do that)

Fire

Die Cast Machine Hood
Hoods substantially reduce smoke

Five years after I installed these hoods, I happened to be in the area and stopped in to talk with the supervisors of this plant. It turns out one of the hoods caught fire. An employee was driving in after dark and he was sure that a dragon had landed on the roof and was breathing fire into the stratosphere. They were complaining about the only damage that they immediately needed to fix which was the fabric sock between the duct and blower on the roof. I asked them if the roof caught on fire which is what normally happens. Flat roofs on northern die cast plants have 3 inches of foam insulation under a rubber membrane. I said good. The fiberglass insulation without paper around the duct at the roof penetration worked as planned. I asked if the duct pipe fell down. No but it bent a little when it turned orange hot. I said good, the slip joint just below the roof let the duct grow as it got hot. They admitted that they thought I was crazy when I enforced these protective design measures during installation.

P20

The Mini-van used the Common AC Compressor

At the beginning of my HPDC career, the demise of Dohler Jarvis, who invented pressure pins, resulted in the transfer of the dies for the pictured AC front cover to the Chrysler casting plant where I worked. In a panic we not only needed to learn to run these die with pressure pins, but also needed to avoid Dohler pressure pin patent infringement. Many years later I was working with a small air conditioning compressor rebuilder who needed replacement front cover castings. It turned out that mini-vans had a heavy duty cycle that caused the front mount ears to break off of this casting at about 125,000 miles. The normal strategy of buying replacement castings from the original casting supplier was not possible because Chrysler wanted to sell complete replacement air conditioning compressors.

I was also working with a small start-up rheocasting casting plant at that time. The higher ductility 356 semi-solid material was a natural choice to solve the ear breakage problem. The rheocasting process is very effective at making freon tight castings. The only remaining problem was coming up with a casting die at an affordable piece cost. We no longer had the 1,000,000 + annual volume to justify spending $250,000 on a 4 cavity die

Unit Die Body Shared by Many Cavities

Because our total manufacturing volume was estimated to be only 50,000 pieces, we elected to make a single P20 cavity in a unit die. This was copied from the strategy we use for creating dies for prototype castings. The dies for making the original part were cut from the original wood patterns. Thus the part print lacked all of the dimensions needed to CAD create a complete 3D model. We found a complete casting from cavity 31 and used it

to create a 3D CAD model. Since the sample was a machined part we chose and added in machine stock to make a model for the casting. Selected surfaces that were originally machined were made as cast taking advantage of the reduced heat check of the rheocasting process. We omitted the original pressure pin substituting a gate cut off with a cold saw such that the shot biscuit would serve as a pressure pin. Interestingly it was unnecessary to impregnate this casting even though the air conditioning compressor rebuilder already was geared up to impregnate the other castings that he bought and machined.

Front Load

This starter nose casting uses only front load cores

Core pins are normally used to solve the short life expectancy associated with near net cores. A good example is a starter nose casting. Because starters are high volume and unchanged from year to year they are very low cost margin products. Core pins create features such as chamfers that would normally be machined to achieve the required manufacturing cost. Very little wear can be tolerated on a core that is creating a feature that otherwise would be machined. This explains the short core life.

On many larger parts it is possible to incorporate holes for traditional core pins without encroaching into the thermal passages. On a part like a starter nose adding traditional cores messes up the die cooling on the ejector side of the die. I even worked for a guy who tried building a die for this part without cores. Front load cores can be installed on top of the thermal passages. In addition to solving the cooling issues it became possible to renew a broken core without pulling the die from the machine. This is very effective when you approach core renewal as a preventative maintenance activity replacing cores before they break.

Its Snowing

“Snow” doesn’t beautify a interior

Snow for Christmas day like we had this year is wonderful. It makes the world seem clean and bright. “Snow” inside a die cast plant just makes a mess. Yes we all know that die cast dies require venting to work properly. The trick is to vent out the gas without venting out the aluminum. It is the vented aluminum that we in the die cast community call “snow”

For those practitioners who have not invented a strategy for controlling snow, it is discovered after the die is put into service. At that point in time the production demand for parts prevents implementing proper fixes. Been there. Just because it is not possible to completely fix the die at that time, doesn’t mean that it is not possible to do something to get better results. In all cases vent features on the die increase the frontal area of the molten metal. The applied pressure multiplied by the frontal area determines the tonnage required. It really starts to “snow” when the applied pressure exceeded the tonnage of the machine because the die blows open. Die vents need to be attached at the last place to fill. Do a short shot to determine where that is. Vents attached to earlier places in the fill only bleed off metal that should have been available to fill porosity at the far end. In many cases a line of weld can block these off or undercuts can stick the overflow into the die filling the unneeded vent.

Every cavity replacement for dies prone to “snowing” includes a redesign of the vent system. Waffle style vents achieve vent path shut off using less frontal area. Zig zag vent shut off works for other dies that are not as close to consuming the available machine tonnage. The knowledge gained from this Kaizen activity makes it possible to launch “snow” free new jobs out of the box.

More is Better?

When you are choosing materials to create a chiller block- more heat conductivity is better. Beryllium copper has 5 times the heat conductivity of H13. Fast freezing of the aluminum creates the crumbly shut off that makes chill vents work. Somewhat messy as the leading crumbs fill the casting machine pit. When choosing the main insert material, more heat conductivity may not be better. Most customers do not wish to buy crumbly parts. Otherwise we would make all of the inserts out of beryllium copper. Fortunately H13 has poor conductivity. It makes it possible to get the molten metal to the far side of the mold before it freezes. Interestingly a thermocouple drilled into a H13 insert to 6mm from molten metal does not rise in temperature until almost one full cycle time has elapsed.

A few proponents of conformal cooling have chosen to over simplify. A die does not run faster simply because more is better. Quickly making good quality parts occurs when proper choices are made. In a 390 alloy (740C cast temp) valve body heat is a problem. An Anviloy ( 3 times the conductivity of H13) roto pocket sub insert proved to be more effective than a conformal cooling sub insert. ( Having tried both) The scale in the water passages of the Anviloy sub insert could be drilled out each run such that the casting quality did not deteriorate with die age.

OLYMPUS DIGITAL CAMERA

However I believe more is better when it comes to the Nanaimo bars that my Canadian wife makes for me. I can even put up with the fact that they crumble.