Archive for March, 2010
What’s your style?
Do you know how you sound to others? Your style can seriously affect your communication effectiveness.
Narcissism: They see everything from their own perspective. The only reason they tell anyone their point of view, is to have the audience tell them how great they are.
Arrogance: They try to inflate their own ego by diminishing that of others.
Status Seekers: They need to be seen as very important people. They drop names and their achievements into the conversation. They are insecure and rarely impress anyone.
Jargon Addiction: These people use professional terminology. The alienating language usually backfires. Simple language that your audience can easily understand is always better.
Adjective Impairment: These people cannot say that they really like anything, instead they remain neutral. They rarely inspire anyone.
Soft Speaking: Speaking in a soft voice is manipulative and is all about getting more power in the conversation.
Speaking Verrry Slowly: These people talk very deliberately, by the time they get to their point, the audience has drifted off.
Missing the Point: Asking questions that completely miss the point.
Banality: Trying to make a connection by asking questions that you are not really interested in the answers. Be genuine, ask an interesting question, or be silent.
Stress Relieving
Microstructurally, stress relieving does close to nothing. It is simply a way of relieving internal stresses by use of thermal energy. Internal stresses strain the atomic structure. Increasing the temperature allows these stresses to dissipate. Higher temperatures allow this process to occur quicker, but using too high a temperature or for too long will further transform the hard martensite phase and soften the temper. That’s why it’s best to ensure the stress relief temperature is below the tempering temperature to avoid further softening.
You could effectively stress relive at a lower temperature than you do, but it would take much longer.
Alternate ways to stress relieve include the use of ultrasound, which allows residual stress dissipation by physically vibrating the atomic structure, letting stress dislocations move and disappear (self cancel with other dislocations, or blend into grain boundaries) – hence stress relieve.
The traditional way and simpler is to vibrate the atomic structure by using thermal energy.
Either way, the net result is atomic structure vibration, dislocation movement, and stress relief.
Who are today’s heros?
Who Are Todays Heroes?
It’s really unfortunate that a formerly useful word has now been virtually lost from the English language as a result of several years of sloppy useage by the media. The word is “hero”.
“Hero” is a simple enough word. Easily understood, It usually used to referred to someone who had performed a heroic act, an act of bravery. Usually the saving of another’s life at considerable risk to his own.
I think we began losing the true sense of the word at about the time of the first Gulf War when all of the several thousand American participants began to be referred to as “Gulf War Heroes”. This misuse spread to eventually include all Canadian or American troops serving, or who have served, offshore in any capacity, and for any length of time.
The unfortunate thing is that there really are many brave men who by any standard qualify for a definitive word that separates them from the rest. “Hero” is now far from adequate.
Fill the container as much as possible!
Remember the three basic rules of productivity. Fill the container as much as possible, empty it as fast as possible, and do it as often as possible. In other words, container utilization, ram speed and contact time.
If the Extrusion ratio is in the right range of 40 – 50 then it should be possible to utilize most of the container length most of the time. Cut length at the saw will restrict using full length billet most times but you should be able to operate within 75% all times.
An opportunity does exist for most presses to increase the container length usually by approx 3 ins. There’s usually enough available daylight to do this
QR Container Controls Liner Temperature
- There is plenty of strong evidence from metal flow studies (even the old plasticine experiments and then the work of Valberg and others in the 90’s) that clearly illustrates the frictional effect of the container wall during direct extrusion. Reducing the container temperature with reference to the billet temperature will only enhance that effect.
- The frictional effect helps collect billet skin and enriched surface layers (plus contaminants) and allow this material to accumulate into the rear of the billet and be discarded in the butt. Admittedly some of this accumulated garbage will flow into the extrusion interior – but for many commodity 6063 type extrusions where the emphasis is more on surface finish, this is quite acceptable.
- Recent studies show that not all the billet skin flows backward with typical container/billet temperature differences of around 70F, but some actually seeps forward and cause some surface finish issues on the extrusion. Maintaining this delta T or higher minimizes the risk of forward flow of billet skin and helps maintain an acceptable surface finish. (I very much doubt forward flow can be totally controlled and avoided – there are too many other secondary factors at work also – edge distance of die aperture to container, press alignment, butt shear, dummy block performance etc.).
- An additional benefit using a colder container liner compared to the incoming billet temperature, relates to partial chilling of the billet, offsetting some of the extrusion deformation temperature gain towards the end of the extrude cycle. This effectively compliments the benefits of a taper heated billet (colder back end) and thus helps achieve isothermal extrusion conditions and maximize extrusion speed.
- With indirect extrusion the situation is quite different. First there is no container/billet friction and billet surface has a much higher tendency to flow forward. Heat loss into the closure block at the back of the container, typically means the container temperature has to be controlled – at least at the back end – ideally higher than the incoming billet temperature, or at least as close to as possible. This allows the extruder to optimize indirect extrusion productivity by maintaining maximum extrusion speed throughout the entire live cycle.
Therefore, with direct extrusion the container should be designed to run around 70F below the billet temperature. Less delta T for longer live cycle times (e.g. hard alloy extrusion). Using a QR container with the front zones closer to the incoming billet temperature (say only 20F below) and the back zones approx 70-100F colder than the front is clearly advantageous.
For indirect extrusion, target the container temperature to be close to the billet temperature, with the back end zones hotter by around 70F if at all possible (QR container technology can do this)..
Die Evacuation: Fast, Efficient and Reliable
David Purdy will be presenting this paper at Cast Expo/10, Orlando on Tuesday March 23 at 8:30 AM
ABSTRACT
No one would deny that the use of vacuum in high-pressure die-casting has brought about crucial improvements in quality. Castool and VDS have devoted considerable effort to developing reliable high-speed vacuum shut-off valves with very high performance.
For high integrity casting, where high quality castings with low porosity are required, a high-speed secure vacuum valve is the best solution.
INTRODUCTION
Vacuum pressure die-casting makes it possible to produce high-quality thin-walled parts with predictable and repeatable mechanical properties. The successful use of vacuum requires fast and accurate control of the vacuum valve, and precise timing of its cut-off.
The vacuum valve must be fast, efficient and reliable.
THE VACUUM LEVEL
There are three essential requirements for an appropriate vacuum system.
• Vacuum tank with a large volume relative to that of the die cavity to ensure rapid evacuation, a high
level of vacuum in the die, and effective elimination of impurities, dirt and so on after the shot.
• High vacuum in the tank should be at least one millibar.
• Good sealing throughout the system (die and shot end system) to keep air leaks to a minimum.
CRITERION FOR THE CHOICE
The criterion is the level of vacuum in the die cavity just as the metal enters, at the end of the slow movement of the shot piston (just over a second after the piston begins to move). The best way to determine this is to measure it directly, comparing evacuation devices of a comparable size for the casting weight. The size of the high-speed valve is dependant on the critical evacuation section. This is the smallest section that the exhausting gas passes through. The smaller the evacuation section, the longer is the evacuation time. For a valid comparison, the measurement has to be made with valves having the same critical evacuation section, with a machine set up for high vacuum tightness.
VDS has a laboratory test bench, which was built to optimize the design of its valves. The equipment permits the evacuation of gas volumes from 0.1 to 40 liters, and directly measures the pressure in the die cavity as well as that at the valve. The measurements have been performed for a large number of casting shot-weights, performing the evacuation in an extremely tight die and shot sleeve. Precise absolute pressure transducers and a high-speed data acquisition system are used to measure and record the pressures.
CHILL VENT VERSUS ProVac VACUUM VAVLE
A chill vent is a device made of two half blocks designed to allow very fast heat removal, to force the molten metal to freeze quickly. The cavity between the two half blocks is narrow (at most 1 mm) and wide. It is also wavy, to increase the surface area and the heat transfer. The structure itself of the chill vent therefore prevents the easy passing through of the gas.
This is not the same for a high-speed vacuum valve.
In a typical case, the tests were made for a 4 kg shot-weight part (evacuation volume of 3 liters), comparing the ProVac® Plus 2000 vacuum valve and a chill vent, each one having the same critical evacuation section of 60 mm2.
Comparing their performances, the VDS valve can evacuate 3 liters of gas to achieve a cavity pressure of 100 mbar in just 1.3 seconds, whereas the chill vent did not attain this level of vacuum even after the unacceptably long time of 2.5 seconds. This result is highly significant in relation to casting quality. The die cavity pressure with the valve also fell to 50 mbar after 1.8 seconds.
In a further test, a bigger chill vent was used, with twice the evacuation section of 120 mm2. It took 1.55 seconds to reach 100 mbar, 20% longer than the valve. Of course using so large a chill vent for such a small shot weight would be quite impractical in reality, (large vacuum channels and loss of metal, very high projected surface, higher price, poor process repeatability and so on).
It is difficult to predict what is happening in the die during the evacuation, since the pressure is normally only measured at the vacuum valve or chill vent, and therefore the measurement of the evacuation will show approximately the same behavior for both evacuation devices in spite of huge differences in evacuation performance.
Generally speaking, a chill vent takes two to three times longer to evacuate the die than a high-speed valve. This remarkable difference in evacuation capability is the result of the higher airflow resistance of the chill vent compared to that of the vacuum valve.
Vacuum measurement in a valve – a valid measurement
When the aspiration piston closes the aspiration hole, the hole for the measurement of vacuum is closed at the same time. The last pressure before the closure is the measured level of the vacuum, and this value is recorded and stored.
Vacuum measurement in a chill vent – an invalid measurement
At the moment when the die cavity is sealed off from the vacuum by the solidified aluminum between the two chill vents half blocks, the manometer remains directly coupled to the vacuum tank. The recorded measurement of the pressure therefore bears no relation to the vacuum in the die.
PRACTICAL CONSIDERATIONS
Design and use
i. For easy and quick maintenance, the VDS valve mechanism is made of a small number of large components
ii. The VDS mechanism is designed for low friction, with suitable low-wear materials.
iii. VDS uses a valve with a reliable mechanism. Mechanisms and their reliability differ greatly from one valve to the other. A careful risk analysis of the closure mechanism makes it possible to determine what the failure potentials are, and if the valve is reliable.
iv. Adequate vacuum runners must be cut into the die from the casting parts or overflows to the vacuum valve. To ensure the best evacuation, the runner sections should be dimensioned adequately. The main runner section, the sum of the side runner section and the total gate section should all be similar to or slightly bigger than the critical evacuation section.
v. The valve runners should guarantee reliable closure. The shape of the vacuum channels strongly affects reliability. Incoming metal at very high speed shows an atomized metal front. The front should be directed towards a “security zone” where it is imprisoned, and then should be conducted as late as possible near the evacuation piston. Such an arrangement can much reduce the incidence of failures.
vi. The vacuum channels should be cut on the ejector-side of the die according to a special shape for high security. VDS strongly recommends cutting the vacuum channels on the side opposite to that carrying the closure mechanism. This ensures that the heat removed from the liquid metal will mainly escape without disturbing the high precision mechanism.
vii. VDS uses a long and powerful blow out procedure. The blow out serves two purposes, the first being to cool the valve’s internal mechanism and the second to clean it. Therefore it is recommended to use a strong flow of air during blow out, and to maintain it throughout the whole die lubrication operation.
viii. The valve should be thermally cycled as is done for the die. It is recommended to spray the valve during the die release agent spraying phase. At each production cycle the amount of heat carried into the valve has to be removed just as it is for the die, in order to ensure steady state casting operations.
viiii. The shot sleeve should be thermally and dimensionally stable to provide a reliable seal, and an absolute minimum amount of lubrication applied in all vacuum installations.
Maintenance
Since not only gas but also dirt, die release agent, and ash have to be evacuated through the evacuation device a certain amount of maintenance is needed. A high-speed valve has high precision moving parts, and VDS recommends carrying out maintenance after 5000 shots to prolong valve life and ensure product consistency (but there have been many instances of customers’ successfully putting off maintenance until more than 20,000 shots).
THE VAMP – PROCESS MONITORING ENSURES GOOD AND REPEATABLE QUALITY
Measuring the pressure in the die is normally extremely difficult, and it may significantly increase the costs of the process, so that in practice it is hardly ever done. VDS has solved this problem with a new advanced analysis system called the Vacuum Analyzing and Monitoring Processor (VAMP).
The VAMP is a microprocessor-supported deep level analysis and control tool for monitoring and optimizing cavity evacuation. In addition it is a tool to help in diagnosing some general characteristics of the die-casting process.
The embedded computerized system is permanently connected to pressure sensors for high precision measurements and to a complete database consisting of laboratory-measured pressure curves.
The VAMP uses either a Siemens or Allen Bradley CPU for advanced analysis of vacuum-curves, suction capacity and pollution control, monitoring and determination of leaks in the die and in the shot sleeve.
The results of the VAMP analysis are stored both in forms of characteristic values giving a summary of the main characteristics for the shot, and also in the form of complete evacuation curves. The user can log more than 20 years of operating results on the hard disk. Results can be reviewed easily to highlight improvements in quality or changes in the die-casting process.
THE VAMP – DETERMINING PRESSURE IN THE DIE WITHOUT AN EMBEDDED SENSOR
The VAMP does more than analyzing and monitoring. In the heart of its main program there is a consistent database of laboratory-measured vacuum curves. This database was built up by making a comprehensive series of tests similar to the one which make it possible to predict the die cavity pressure from that measured at the valve or the chill vent. The tests were carried out for all sizes of ProVac® valves with or without vacuum channels, and for a variety of shot weights, and the relation between measured pressure and in-die pressure described mathematically with respect to each one of these parameters. The VAMP uses the database to predict the variation through time of the die cavity pressure from that of the measured pressure at the valve or the chill vent. The procedure is as follows:
• VAMP assumes that the vacuum runners have been cut into the die according to VDS recommendations, which means among other things that the critical evacuation section will be located not in the runners, but in the valve. If this is not so, then the evacuation speed will be lower by an indeterminate amount than that predicted from the database.
• The program calculates the prediction using the database and the mathematical relations.
• The validity of the prediction is verified by checking if the first derivative with respect to time of the measured pressure is plausible. This slope is related to the volume of gas to evacuate and to the leaks of the die and shot-sleeve. Were the vacuum runners for example to be closed by a jam, then this slope would be very much steeper than it could possibly be in relation to the shot-weight.
The VAMP first shot-pattern shows among other things the predicted pressure in the die cavity, which is a vital indicator of quality in vacuum pressure die-casting.
THE VAMP – MANY OTHER HELPFUL TOOLS
The VAMP – Vacuum Analyzing and Monitoring Processor can be very helpful for improving quality in die-casting. They are for example zooming on curves, overview of minima and history, determination of characteristic values (slopes etc.), alarms adjustable on different levels for optimal production monitoring, users’ “ideal curves” for comparison and alarms, monitoring of the leaks in the die and shot-sleeve, advanced checks of the evacuation capacity, distribution of the VAMP-windows on the Local Area Network…
CONCLUSION
Castool and VDS’s advanced high security high-speed valves help the die-caster on his way towards high quality and a secure and repeatable die-casting process.
For high integrity casting, where high quality casting with low porosity as well as repeatability in the process and evidence of the optimal fabrication are required, a high-speed secure vacuum valve is the best solution.
For advanced evacuation in high quality die-casting, the use of the Vacuum Analyzing and Monitoring Processor (VAMP) is a major advantage. This computer-assisted system with its embedded sensors, used in conjunction with a complete database built up from laboratory-measured vacuum curves, offers a totally new perspective for improving the pressure die-casting process.
Lessons from the Recent Olympics
1) Keep score. Olympic athletes know how they are doing all the time. They know their results, and their progress and improvement.
2) Have clear goals. Every athlete had a goal. To some, just qualifying to be there was the target, while, for others, a medal – 0r a specific medal, gold – was the obsession.
3) Practice. They practice, practice, practice and practice. They practice in a focused and strategic way to reach their goals.
4) Play to the end. They know where the finish line is, and they do not stop until they reach it. They pick themselves up after falling and continue.
5) They have coaches. It is unheard of not to have a coach. Even though they are among the best in the world, they recognize that they need help to keep them improving their performance.
Culture
Culture lives in one of three states.
The first is barbarism. Barbarians believe that the customs of their village are the laws of nature and that anyone who doesn’t live the way that they live is beneath contempt and requiring redemption or destruction.
The second is civilization. It is the most rare state. Civilized people are able to balance two contradictory thoughts in their minds. They believe that there are truths and that their cultures approximate those truths. At the same time, they hold open in their mind the possibility that they are in error. The combination of belief and skepticism is inherently unstable.
The third state is decadence. Decadents cynically believe that nothing is better than anything else. If they hold anyone in contempt, it is those that believe in anything. Nothing is worth fighting for.
Civilized people fight selectively but effectively.
This is how it (RDX) should work!!
The die runner from the die shop is responsible for delivering the die,
putting it in the scheduling area and entering it into the system as ready,
and its position in the scheduling area.
It’s then up to the operator to call whatever die he needs that is on temp,
and to replace with one from the scheduling area.
The press crew may possibly be down-manned by one, except someone
has to load the bolster and die into the die slide. If it’s a cold bolster,
that can be done at any time – ideally as early as possible after the last
die is taken out of the slide. The new die should be loaded into the slide
during last billet extrusion. It’s possible most times the operator has a
chance to do that, but preferably he should be keeping his eye on the press
controls.
What are your chances of surviving the recession?
Four Responses to a Slowdown
We are able to classify companies and their approaches to managing during a recession into four types.
1) Prevention: they practice primarily defensive moves. They are more concerned than their rivals with avoiding losses and minimizing downside risks.
2) Promotion: they invest more in offensive moves that provide upside benefits than their peers do.
3) Pragmatic: they combine defensive and offensive moves.
4) Progressive: they deploy the optimal combination of defense and offense.
Progressive leaders rarely have a plan when they enter a recession. They encourage their organizations to discover what works and combine those findings in a portfolio of initiatives that improve efficiency along with market and asset development. This agility serves organizations well during a recession.
Some Survival Facts
Research shows that only 9% of companies come out of recession stronger than before than recession.
17% of companies do not survive a recession.
80% of surviving companies do not regain their prerecession growth rate for sales and profits 3 years later.
Firms that cut costs faster and deeper than rivals have the lowest probability – 21% – of pulling ahead of the competition.
Businesses that boldly invest more than their rivals don’t always fare well either. They only enjoy a 26% chance of becoming leaders after a downturn.
About 15% of the growth leaders coming into a recession retain their momentum. 85% are toppled during bad times.
9% of companies flourish after a downturn, doing better on key financial parameters than they did before and out-perform rivals in their industries by at least 10% in terms of sales and profits growth.
These companies master the delicate balance between cutting costs to survive today and investing to grow tomorrow do well after recessions.
They reduce costs selectively by focusing more on operational efficiency than their rivals, even as they invest in the future by spending on marketing, R&D, and new assets.
