Diecasting foundry managers who are successful with vacuum, are very enthusiastic about its benefits.
But, most vacuum methods are much less effective and reliable than ZVAC.
To be effective like ZVAC, vacuum diecasting techniques must minimise permeability of dies, maximise gas vent flow areas and have consistently reliable function.
Listed below, are some successful and well known companies, that are producing ‘high-vacuum’ die-castings for prestigious high-performance products, or manufacturing the equipment.
By showing these examples, I hope to encourage sceptical foundry managers to try vacuum and point out that the ZVAC method is simple, reliable, effective and economical.
(Note: the links to external pages might expire.)
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PFEIFFER VACUUM GmbH
Glimo N.V.
ASSLAR
Vacu2 MULTI STEP VACUUM DIE-CASTING PROCESS
This is the latest high-tech solution to vacuum diecasting, which Pfeiffer say will revolutionise die casting.
There is a PDF download which describes their technique. It shows and explains how it is superior to the traditional methods which use elaborately constructed valves mounted on the dies, and those which suck aluminium into the shot sleeve.
Their system includes a PLC and a high speed PC based computer, to manage and monitor the many valves, transducers and sequences.
Achieved pressure in the die is extrapolated using computer algorithmes and calculations in real time, not measured directly as in ZVAC method.
Quoting from their published report in PDF format, dated 06_March_2006 (link below):
“All application combinations produced excellent results with respect to the vacuum achieved and the quality of the workpieces.”
“It is still desirable to seal the mold to a certain degree, which benefits both workpiece quality and process stability.”
“Depending upon the application in question, absolute pressures of between 20 and 100 mbar were achieved in the mold.”
“Significant differences in the quality of the castings were able to be evidenced at an absolute pressure of 40 to 50 mbar.”
“There is every indication that in the future, vacuum will be able to be employed profitably, reproducibly and reliably in foundries on a wide scale basis.”
On the down-side, the Vacu2 method still appears to use the old fashioned washboard chill vent die-inserts, which by virtue of their bulk can only provide limited venting flow area, are prone to blocking up and need long heavy feed runners.
Also, there seems to be no peripheral vacuum gallery, so in the Vacu2 method, any lubricant residues on the parting line would be sucked into the mould cavity by the negative pressure gradient towards the centre of the die.
The Vacu2 also sucks air from the die via an extra hole in the shot sleeve, just past the filling hole, and in principle, is similar in to earlier methods:
In the journal ‘Metal Industry’ of 17 August 1962, HK_Barton, described several methods similar to Pfeiffer’s Vacu2
In 1962, in the journal Giesserei, KA Ritter decribed a new method which had both suction from the shot sleeve and a peripheral vacuum gallery around the die cavity with connecting vents. Ref: Vol 48, May 4 1961, pages 260-262. Titled Neue Vakuum-Druckgiesseinrichtung.
One of the weakness in the method was that the vents connecting the die cavity to the vacuum channel were only 0.2mm deep. They would not have enabled sufficiently rapid exhaust of fumes when the metal filled the mold cavity, so negating some benefits of vacuum. It was observations of that phenomena in 1991, which led to the development of the 0.6mm deep multiple parallel ganged ZedVents in the ZVAC method.
Pfeiffer's published PDF files may be obtained form these links, which may get changed.
Web page with links to PDF report ‘ PA0067PE_Vacu2.pdf ’ Multi Stage Vacuum Process
Web page with links to PDF report ‘ PA0059PE_Vacu2.pdf ’ Multi Stage Vacuum Process
link to PDF BROCHURE Vacu 2 ‘ PA0060_PE_Vacu2.pdf ’ -- file size 1.94 Mbt
link to PDF reports ‘Vacu2 PDF’ \PA0067PE_Vacu2.pdf -- file size 225 KByte
link to PDF reports ‘Vacu2 PDF’ PA0059PE_Vacu2.pdf --file size 888KByte
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YAMAHA MOTOR Co. Ltd.
VACUUM DIE-CASTING PROCESS
Named: "Yamaha CF Aluminum Die Casting Technology"
Used for making high performance motor bike parts
This process is PRETTY GOOD... REALLY!
In fact, it is probably better than any except ZVAC, the rudiments of which were first publicly distributed in 2000.
Like me, Yamaha recognise the importance of peripheral seals and large vacuum valves. Their method was developed and published around 2002, after acquiring their own foundry.
But, and it’s a big BUT; it does have the valve on the die, similar to the Toshiba and Royobi methods.
And, because there is no peripheral vacuum gallery, die lube residues on the parting face will be drawn into the mold cavity by the vacuum just as the metal enters, and so cause porosities.
Yamaha also put seals on their die ejector pins. Their process upgrade is shown in thier release dated July.
But, they do not seem to seal the internal assemblies of the die. However, they do seal the sleeve where it abuts the bolster, which leaves leaks via water pipe holes through the bolster, still a very real potential problem.
So my technique still has a number of significant advantages, especially in that my technique also lubricates the ejectors.
Quote from their web page:
“This new method makes it possible to manufacture aluminum parts with the high efficiency of high-pressure die casting, and with strength and stretchability equal to gravity casting.
Also, this has made it possible
to produce the kind of large but thin aluminum die-cast parts that were difficult under the conventional die casting methods.
Furthermore, since this new method enables the mass production of cast aluminum parts designed for extreme thinness and more complex curves, it will suggest new design standards for cast aluminum parts.”
see website ‘Innovation Details Released Feb 2002’
‘“Yamaha CF Aluminum Die Casting Technology” developed, making possible the mass production of large but thin aluminum die-cast parts’
see website ‘Innovation Details Released Jul 2002’
Fine Catec Co., Ltd. Yamaha’s diecasting company
see website ‘Innovation Details Released Jan 2001’
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SUZUKI Motor Bikes
The main frames of the latest models, SV-650S and SV1000S, the are made from welded vacuum diecastings.
In the publicity for this Super Bike, there are many prominent references to the benefits obtained by using high vacuum diecasting technology: lighter weight, greater strength and rigidity.
The links below show some of the best trade publications.
Quote from Motorcycle Daily website:
The all-new, aluminum-alloy truss-style frame is constructed using a single-precision die casting, high-vacuum mold process. This is another technique that creates cast frames that have some of the properties of forging. High-strength castings can now reduce weight and increase rigidity (where needed) in a significant step forward for motorcycle chassis design.
see www.motorcycledaily.com
The page shows the High Vacuum Diecast Frame
From publicity by www.motorcycle.com:
Bikes SV-650S and SV1000S, feature ‘lightweight aluminum truss-style frame(s) constructed with high-vacuum die-cast
process for more consistent strength and fewer individual welded sections’
see www.motorcycle.com 2005: Suzuki Line-up
From announcements by Suzuki GB:
‘Due to arrive in UK showrooms in January 2006, Suzuki’s GSR600 is the naked middleweight sports-bike in which modern art meets race technology.’
‘Using the very latest vacuum die-casting technology, Suzuki engineers were able to create an aluminium-alloy frame and a swing-arm that, despite its pure, seamless surface, offers impressive, class-leading rigidity.’
see where ‘art meets race technology’
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MITSUBISHI MOTORS CORPORATION
Mitsubishi is another Japanese company at the forefront of using high vacuum die casting technology, and realising big savings in car chassis weight and process costs.
The links below connects to one of their reports published in 2004, in PDF format titled :
‘New Technologies Report Number 16’,
‘Development of Mitsubishi “i” Body’
I recommend any one interested in their own future in diecasting, should download the file and read it very carefully.
And, as you read it, you might wonder how ZVAC method can obtain equally good results at much less tooling cost and effort.
Quoting from Mitsubishi’s report:
The high-vacuum die-casting method was employed, by which the amount of gas mixing with the molten aluminum could be reduced and thus high welding stability was ensured.
In addition, this method enabled the material thickness to be minimized for further lightness<end quote>
This is a very modest statement of the actual benefits that diecasters can derive from high vacuum.
The link below, gets a PDF report, or you could search Google (.jp for Japanese) using same title or key words ' mitsubishi motors aluminium chassis vacuum die casting '.
Development of Mitsubishi “i?Body (English version)
Development of Mitsubishi “i?Body (Japanese version)
From URLs:
http://www.mitsubishi-motors.com/corporate/
about_us/technology/review/e/pdf/2004/16E_07.pdf
http://www.mitsubishi-motors.co.jp/corporate/
technology/review/pdf/2004/16J_07.pdf
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HONDA ACURA AUTOMOBILES
Honda are using high vacuum diecasting technology to make subframe chassis elements. The technique combined with hydro-forming has led to savings of 39.6 lbs.
Quote from HONDA ACURA Media Newsroom Technology Reports:
The RL front and rear aluminum subframes are composed with members made
by high temperature bulge forming and high vacuum die casting. Both
manufacturing techniques result in significantly lighter units than
would be possible with either aluminum hydroform or steel hydroform
processes.
see reports titled:
‘2005 Acura RL Chassis’
‘2006 Acura RL Chassis’
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GIBBS VACUUM DIE-CASTING PROCESS
Gibbs’s use their own ‘Vacuum High Pressure Die Casting’ process to make high integrity components for automotive and consumer products
The method combines vertical shot sleeves with totally surrounding the die cavity in a peripheral vacuum groove, to create an elegant solution to the cold chamber process.
The technique was patented by Glen R. Morton in 1961 and became known as the Vert-A-Cast or Vertacast process.
Glen Moreton also pioneered the use of vacuum to fill the shot sleeve.
See US Patents: 1,058,439 1965, and 2,977,649 1961.
Key points made by Gibbs about their process:
- Reduces gas porosity
- Produces die castings that can withstand high temperature
- Is being extended world wide
see website
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RYOBI VACUUM DIE-CASTING PROCESS
Used for making automotive, power tool and jetski parts
RYOBI have been using vacuum for many years, and have a policy to equip every diecasting machine with their own developed process, which seems less sophisticated than Yamaha’s, in that they do not appear to seal the die or sleeves.
RYOBI have named their technique the ‘RNC PROCESS’ (Ryobi NEW CASTING).
on their website they say:
‘Ryobi has originated die casting system to stably produce heavy wall products that require high strength and to enable them to undergo T6 heat treatment, which we call RNC Process.
RNC Process can reduce gas inclusions, shrinkage and scattered chill structure with use of laminar flow filling and RSV vacuum system that Ryobi developed.’
At a Bühler organised symposium in Switzerland in 1995, Mr Morris C. Rowlett, President and CEO of Ryobi Diecasting (USA) Inc., spoke at length on the advantages of vacuum.
He said that vacuum was used on every one of their diecasting machines, world wide.
The reason for doing so, being that “vacuum makes the process rugged”; enabling the diecasting process to produce good parts over a wider range of parameter variations than the standard process.
see website
The process used by Ryobi was patented by Messrs: Yamauchi, Noriyoshi; Ishida, Hitoshi; Kawai, Kazuaki; Mizukusa, Yasuyuki; in 1989.
see United States Patent 4986338
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VACURAL BY MÜLLER WEINGARTEN AG
The Vacural method looks like a British method patented by Aubrey R Mills, in 1961; patent number 928,063.
This is another valve on die method, which also sucks metal from the furnace into the shot sleeve (cylinder / magazine).
Müller say that their process allows the reliable production of:
- highly ductile structural and chassis components
- thin-walled, weldable chassis components
- coatable surface parts
see website: Vacuum diecasting Method
see website: Diecasting machines
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ALCOA AUTOMOTIVE GmbH
Alcoa Vacural Die Casting (AVDC)
and
Alcoa Vacuum Die Casting (AVDC) Process
Alcoa use their AVDC method at their plant at Soest, Germany, for manufacture of automotive body configuration parts; notably, for very expensive prestige high performance cars.
The AVDC method is based on Müller Weingarten’s Vacural vacuum die casting system, which Alcoa say they have developed, without expanding on details; but probably by adding seals as used in the ZVAC method.
Vacural is another valve on die method, but it also sucks metal from the furnace into the shot sleeve (cylinder / magazine).
Structural, chassis and spaceframe die-cast components require high ductility and freedom from porosity or flow defects. That function conformance in die cast parts, can only be met by using relatively high vacuum techniques such as AVDC or ZVAC.
Applies to casting such as:
- thin-walled parts 1.6 to 2.0 mm thick
- weldable chassis components for WIG, MIG and laser welding processes
- coatable surface parts
- large area, thin spaceframe parts up to 20 kg
For cars such as:
- Ferrari 360 Modena
- Ferrari 612
- Chrysler Crossfire
- Audi A8
- Jaguar XJ350
Using equipment such as:
- diecasting machines with locks 750 to 4,100 ton
see website: Alcoa AVDC Vacuum diecasting Method
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HITACHI HI-VACUUM DIE-CASTING
Hitachi say: “HIVAC-V' is our new casting method which improved our original vacuum die-casting. This process produces thin wall and high strength suspension and body components.”
see website: Hitachi HI-VAC method
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TOSHIBA MACHINE CO., LTD.
Die Casting Machine Division
Quote from Mr Daisuke Fujimaki, Mr Shokou Kubota and Mr Takaaki Katoh,
about new Vacuum Unit. Published in 2002
Recently, the demand for reducing the weight of automotive parts has been growing with the environmental issues in its background. Furthermore, the demand has been upgraded from the parts for accessories or suspension-related parts to even higher-quality die cast parts that can be welded on aluminum body structures. To meet this demand, we have achieved casting the high-quality die cast parts with the super-high-speed-injection die casting machine and the new vacuum device working together.
see website: Report on TOSHIBA HI VACUUM
A PATENT BY TOSHIBA FOR A VACUUM POPPET VALVE
United States Patent 4787436
Assignees: Toshiba Kikai Kabushiki Kaisha (Tokyo, JP)
INVENTORS: Ozeki, Mamoru; Tsuda, Akihico;
A PATENT BY NIPPONDENSO Co FOR A VACUUM POPPET VALVE
United States Patent 4586560
Assignees: Nippondenso Co., Ltd. (Kariya, JP)
Ikeya, Seizi; Tabuchi, Tsuyoshi;
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THURNER VACUUM DIE CASTING METHOD
Patented by Hans Thurner 1984
United States Patent 4463793
Assignees: Bayerisches Druckguss-Werk Thurner KG (Markt Schwaben, DE)
This is another valve on die method, with some attempt to draw air from leaks around inserts and seal ejector pins. The patent does not show any platen or slide way sealing.
There are two vacuum valves in series, one for applying the vacuum to the die, and one to stop molten metal getting into the vacuum pipe.
Setting of switches and timers, speeds of response of hydraulic valves and amount of ladled metal, are critical to the function of this method, it works on the knife edge of success and failure.
The metal blocking valve is actuated by a hydraulic piston, which is driven by oil from a spring centred spool valve which is actuated by a solenoid operated pilot valves.
There are a couple of optional operational modes for the valve, which is supposed to complete its closing stroke as the die is filling, during high speed fill phase! (So, plenty to go wrong there then.)
The patent acknowledges that metal can get into the valve, and when it does, removal of the poppet for cleaning would be very time consuming.
There is no reference to monitoring vacuum achieved in the die before or during injection.
I’ve had requests for help prevent molten metal getting into the valves of this method.
The potential client sought FREE consultancy help with view to replacing the hydraulic piston which actuates the poppet, with an electrical solenoid!
Big companies seem to like buying into this method because of its patented gadgets, and it seems that once committed, they are reluctant to heed the requests of the guys on the foundry floor, to get something more reliable, easier to run and more effective.
My conclusion |:-( This method is expensive, temperamental and unreliable.
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IDRA-PRINCE Inc ®
Sell a vacuum pump unit and ‘add-on’ valves which fit in the die
Quoting from their website, they say:
OMC/Prince Vacuum Die Casting Systems by IdraPrince removes nearly all air and gasses from the die cavity and shot sleeve. This allows the die caster to produce higher quality, leak tight, or T6 heat treatable parts.
A die with this method was exhibited at METEF, Brescia. It was obvious that it would be less effective and reliable than the Thurner method, which is by its own patent admission, could be prone to failure.
A new IDRA vacuum unit trialed by a client could only achieve 68 mbar abs (1 psi) when pumping down the receiver, so there was not the slightest possibilty of getting below 50 millibar in the die.
see website 1:
see website 2:
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ALLPER AG ®
sell Multi-Vac ® ‘add-on’ Valve block type units.
The best vacuum that I ever saw with one of these units in production, after cleaning a die and providing ideal conditions, was 85% full vacuum, i.e. 150 mbar abs! That is not very good, and would only have effect of halving the diameter of gas porosities. The client had asked me how to improve their vacuum method. Nowadays, they are using ZVAC.
see website:
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VDS®SA ( Vacuum Diecasting Service )
VDS SA sell ProVac ® ‘add-on’ Valve block type units, and provide free technical assistance; which one would expect, considering the cost and reliability of their equipment.
see website:
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Hodler-Optivac ®
One of the first to put a metal stream activated poppet valve on the die, and which led to the methods of Fonderex, VDS and ALLPER
In carefully prepared and controlled tests on a die equipped with a Hoddler-Optivac valve and unit, researchers from BNF Metals Technology Centre, measured maximum vacuum attainable in the cavity of only 34%, i.e. 670 millibar absolute, or 9.7 psia; equivalent to 66% of the air remaining in the die.
The tests were conducted in 1982, and in the BNF report number R427/T1, they conclude that the vacuum Hoddler-Optivac valve method made only 0.1% reduction of porosity and gave no significant improvement to surface finish.
And to achieve those results consistently, BNF add that the valve has to be maintained on a regular basis as recommended by the manufacturer, as blockages of the valve with grease and powdered metal occurs.
The researchers also comment on the runner to the vacuum valve acting as a giant overflow, which in itself would account for some of the reduction of porosity.
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FONDEREX ®
Fonderex make and sell SUPERVAC ® and similarly named add-on Valve block type units, which have valve poppet closure initiated by pressure of the metal against a sensor in the valve.
Their complicated and sophisticated PLC based control gear provides lots of alerts for the possible failure modes, such as: when metal gets in the poppet valve, when the valve jams open or closed, or when there are massive air leaks, or the tiny filter gets clogged with wax and flash, etc.
The vendors of these units alude to ‘high vacuum’ without sealing the dies. But unless sealed, once in production, dies leak a lot, and any vacuum effect is reduced to assisted venting, and the vacuum channel to the valve provides a massive overflow.
In this method, without sealing the die, the vacuum 'seen' by the metal can vary from OK to inadequate.
That is why the latest ‘high vacuum’ techniques now being used by Japanese automotive companies have valid grounds for thier claims, because they use flexible seals at all potential leak pointsand valves with massive flow areas. Just like the solution applied by the ZVAC method, in 1990.
Two clients are now using ZVAC on their dies in place of Fonderex's valves, but still use their old vacuum pump and tank units to generate the vacuum pressure.
see website:
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J.L.J. Technologies, Inc.
Mr John L. Jorstad is a highly respected and authoritative consultant specializing in the technology of light metal casting, with over 36 years of senior level experience at Reynolds Metals Company. He is now President of J.L.J. Technologies, Inc. Richmond, VA,
In his report to the International Conference on Structural Aluminum Casting in 2003, titled 'High Integrity Die casting Process Variations', Mr Jorstad said the following about vacuum diecasting processes.
“Several versions of moderate level vacuum die casting are currently practiced (Hodler-Optivac? Thurner? Verticast? etc.); the process seemingly most often associated with high integrity structural castings is the high vacuum Vacural?process offered by Mühler Weingarten of Germany.”
“...some vacuum systems (or the way in which some systems are employed) achieve only a partial vacuum (perhaps 60 to 80%) and provide little more than excellent positive venting; they do, in fact, significantly improve the fill and integrity of resulting parts, but may not make parts that can be solution heat treated without blistering.”
“The goal of high vacuum die casting, such as Vacural? is to virtually eliminate the atmosphere in the shot system and die cavity and thus make parts that are sound, heat treatable and have predictable and reliable mechanical properties. To accomplish this, the shot and die cavity system must be well sealed to avoid drawing in ambient air while under high vacuum.”
Download full report as PDF document:
from www.moderncasting.com
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ADD_ON VACUUM VALVE METHODS: COMMENT
Vacuum valve-block type methods usually have the valve bolted to the top of the die so that they can be removed for unblocking, which can happen several times a day.
Sometimes the valve blocks are spring loaded so that their faces touch, even when the die bolster faces are held apart by flash debris!
Generally, these 'add-on' valve block methods do not have any seals to prevent leaks, which can occur via the many small gaps and paths available for air to enter the die cavity. Hence, the level of vacuum can be disappointing and variable, and very dependant on the condition of the die, its slideways, ejectors, etc.
The performance of these and similar devices marketed by companies like ALLPER, VDS and FONDEREX, is limited by their need to restrict the flow in the vacuum channels in their valve blocks, in order to create sufficient back pressure to trigger the valve closure.
During production, unsealed dies can leak heavily, and with this type of device, the flow areas of the vacuum valve channel can be exceeded by the total of leak areas arising from assembly clearances and contamination on die faces and slide abutments. The result of which is that the level of vacuum can vary widely, with consequent wide variation of part quality.
These add-on methods also ignore measuring the actual vacuum pressure in the mold cavity, and instead monitor the pressure in the connecting pipe. This configuration produces an overstated indication of vacuum in the die, where it matters.
Because these devises have to respond extremely quickly, to avoid metal entering their innards, they frequently get blocked up.
Thus instead of vacuum making the diecasting process rugged, as is the experience of Ryobi and others with more reliable methods, these add-on valve block methods actually make the process more fragile and unreliable, which accounts for most of my requests for help, coming from foundry guys who have been handed the task of making them work.
And on costs; these add-on valve blocks are very expensive, and some dies have to have two!
And, costs don't end there: you will also be advised to carry a spare valve block, so that it can be swapped while you unblock a valve choked with frozen metal.
For the cost of just one of these valves, you could equip an entire foundry with a simple, reliable high vacuum system.
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BNF (British Nonferrous Metals Research Association)
The Hoddler vacuum test and others, led BNF to pioneer a new method with a peripheral vacuum gallery, which in a series of foundry based tests through 1983, gave very encouraging results.
The original work of BNF (also BNF-RA) was the foundation for my development of the ZVAC technique in 1990, which took the peripheral vacuum gallery concept, and combined it with peripheral seals to dies and slides, internal sealing, sealing ejectors and plungers, and application of my new and unique massive Zed (Zee) Vents.
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COMPARING METHODS
Comparing these methods we see that the latest big trend amongst the modern developments, is to seal the dies.
Only by sealing dies on all identifiable leak paths, can ‘Hi-Vacuum’ be achieved.
Features like the following must be sealed.
- shot sleeves (cold chamber magazines)
- slide ways
- parting face
- ejector pins
- insert mating faces
The latest valve-on-die vacuum methods get rapid vacuum pull down, by using big valves connected to the cavity by simple deep and wide channels, with large flow areas.
The old methods have long narrow vacuum vent channels, often with throttle restrictions to create back-pressures for triggering vacuum valve closure. They often have metal wasting overflows at each corner of the vacuum channel.
The old methods also take molten metal very close to the outer edge of the die bolster, this can leads to dangerous flash excursions, especially where the valve blockes are held together by springs, as in the ALLPER method.
Methods with long small vacuum channels have slow cavity vacuum pull down.
Some vacuum methods deceptively show vacuum upstream from the valve, where pressure drop through the valve and leaks into the dies have less influence on indicated vacuum pressure.
Pfeiffer mention that the old valve-on-die methods have vacuum monitoring between the valve on the die and the pump, which indicates best vacuum when the valve is actually blocked!
All the promoters of the methods which have molten-metal-contacting vacuum valves on the dies, recognise that metal aften enters the valve and have strategies for:
- minimising down time needed to unblock the valves
- alarm systems that stop production when the valves get blocked and stop working.
The ZVAC method:
- can have massive vents which stop metal flow close to the die cavity, without overflows,
- can give extremely fast vacuum pull down in the mold,
- can measure vacuum pressure directly in the cavity or metal feed gate,
- is much lower cost than any commercial gadget based vacuum diecasting equipment and is very reliable.
