Tip of the Day 136: Positive Volume and the Zero Line

Over the years we have been challenged to explain why we show “Volume / Injection” as a value that goes up as the material is injected into the mold. The simplest answer is that “Systematic Molding” means thinking from the plastic’s point of view inside the mold rather than inside the machine. We want to show how much material you have put into the mold (a positive number) rather than how much is left in the barrel.

This means that we start the volume curve at the machine’s shot size setting: the point where the screw was when the screw motor stopped. Thus the decompression after recovery (“suck-back”) shows up as a negative number.

As an attempt to help visualize this I have created a video that shows the screw position in relation to the Cycle Graph volume curve. The cycle graph is rotated so that the tip of the screw lines up with the volume curve.

https://www.youtube.com/watch?v=sxAwHaiT_Sg

A second video shows the same thing mirrored so that the screw traverse is in the direction it is when viewed from the operator side of the press. In both videos the plastic is going into the mold above the dashed zero volume line.

https://www.youtube.com/watch?v=nFxRNrNH2yY

Tip of the Day 107: Copying Changes Log to Laptop

A question came up right away after the last tip: How do I get the change log for viewing with Excel?

With a laptop and a crossover cable use Data Extractor first. This sets up the proper network connections and then lists the IP address at the top of the list of molds.

Once you know the IP address of the eDART™ you can just open Windows file Explorer type in the web address with the log-in like this:

ftp://root:evintea@192.168.1.1/e-dart/logs/

Replace the 192.168.1.1 with the IP address of your eDART.

Once you hit [Enter] on Explorer it will open the logs as an FTP connection. You can then right click over “changes_…csv”, click “Copy” and then go to another part of your computer and paste the file there. Then open the file and view it. It comes in sorted by date by you can sort by type of change, mold name etc.

It may even be possible to open the changes log directly by double clicking on the eDART‘s change…csv file. Excel prints a lot of nasty messages about why it can’t write there and such but it may eventually open the file.

Tip of the Day 106: Viewing the Change Log on the eDART™

When the eDART is networked to a server or EDM and the ftp backups are running it creates a “logs” folder on the server. In that folder are the change logs named “changes_node.csv” where the node number is the eDART‘s node number. These are easily read using Excel and you can sort by change, date / time, mold and a lot of other things.

But some customers have asked whether they can view that change log on the eDART. The answer is “yes”. But you will be reading between the commas in the .csv (“comma separated values”) format. We are working on plans for a better method of change reporting. Until we develop such software you can use the steps below to look at the log on the eDART.

Caution:

Before turning this loose to those not authorized be sure the eDART security is set up to prevent casual editing of this change file.

Also, be sure to click “Exit”, NOT “Save and Exit” if the editor asks when closing the file. This will prevent saving any accidental changes.

Tip of the Day 105: Software Installs Wait for Job Stops

It came to our attention that some did not know about this feature. It became available in Release 8.2 (July, 2007).

When you get a new release, an optional software tool or a patch you use the “edart_installer.exe” provided with it to load the software over the network. This places the install files in the temporary folder on the eDART™. Our full release software (e.g. 8.6) does not install itself because that would automatically stop the job with possibly disastrous results. So the files lurk in /tmp until a restart.

Generally customers have done the download (eDART_installer) and then run around the plant stopping presses and restarting eDARTs. As of release 8.2 the software provides a message that pops up when you stop the job saying that it has found new software to install. This lets the installs take place at natural breaks in jobs.

You can teach the operators and technicians that, if they stop the job and see that message they are free to accept the install. Then, after you have loaded all of the eDARTs in the plant with the new install it is simply a matter of letting time pass until every eDART has had a job end at least once and been restarted.

Detail:

The message reads as follows:

New software Release 8.6 has been sent to this eDART.

Do you want to restart the eDART now to install it?

Of course the release number is different each time.

Tip of the Day 77: Where do the Alarm Levels Come From?

 As most of you have seen when you “Add an Alarm” (or warning) to the “Alarm Settings” tool on the eDART it will automatically put in “Above” and “Below” (high and low) levels. When the value goes above the “Above” or below the “Below” then the parts will be rejected by the part diverter.

How does the Alarm Settings tool pick those levels?

Answer:

It looks at the previous 20 values for the alarm you are setting and picks levels that are the “mean ±4.5 x standard deviation”.

For those of you not familiar with statistical terms, don’t panic. Here’s the skinny on it.

In statistics “standard deviation” as a number that is computed from a set of values by running those values through an equation. The value that pops out (abbreviated with the Greek letter sigma, ó ) tells you how much the set of values vary among themselves. The larger the number the more “fuzzy” the data (on a Summary Graph, for example). The word “mean” is just another word for the average.

Thus when you add an alarm to the Alarm Settings tool it computes the average value and the standard deviation value for the previous 20 shots. It then multiplies the standard deviation by 4.5, adds it to the average and sets that as the high level alarm (“Above”). It subtracts standard deviation from the average and sets that as the low level alarm (“Below”). It does the same thing with warnings except that it uses mean ± 3 x ó for the levels.

The graphic below explains this by using the Statistics window to show where the values come from. The Statistics tool is not required to add alarms, just to show statistics after the fact.

Notes, Cautions and Warnings

• Always wait for the process to be stable 20 shots before adding alarms. Otherwise the startup variation will be used to compute standard deviation and the values will be wild and useless.

  (We have completed a prototype of a tool for Alarm Settings that postpones the setting of alarms until the process stabilizes)

• After the values are first chosen the Alarm Settings tool never changes the levels. You can do that by simply changing the numbers in the “Level” column or using the sliders on the Summary Graph.
• The number of shots and the number of “sigmas” (standard deviations) for both alarms and warnings can be changed by clicking the “Adjust Selected Levels” button on the Alarm Settings’ “Settings” menu. The 20 shots and 4.5ó and 3ó values are chosen from general experience and practice.
• Note that the alarm levels that are first picked do NOT represent any specific part characteristics. They are simply a way of capturing changes in the process. To determine whether a part is good or bad at a specific value you need to do a correlation study.
• You may use the statistics tool to choose alarm levels different than the ones that the Alarm Settings tool has picked. If you have put the +N*Stdev and -N*Stdev values up and have the “Data Range” set to “Summary View” you can zoom in to the portion of the Summary Graph that you think is most representative of the process. Then read the values and enter them for the alarms. You can change the sigma multiplier at the lower right.

Tip of the Day 76: Stable vs. Whole Hold Pressure

 As mentioned in Tip #74 you can pick two different hold pressure summary values that represent hold pressure: Average Value / Stable Hold Pressure or Average Value / Hold Pressure. Each has a particular use. Here is a graphical description of how the eDART computes the two values.

 

Note that Average Value / Hold Pressure is computed correctly when the fill volume is set.

The two values are not dramatically different. This is because the extra increase in the average value over the slow transition at transfer is somewhat negated by the slowly declining hold pressure slope at the end of hold (the two pink areas). So the average value and stable value are similar. If the pressure dropped quickly at the end of hold the the Average Value / Hold Pressure would be significantly greater than the Average Value / Stable Hold Pressure.

 Average Value / Stable Hold Pressure

Use this value to study whether someone has set the machine’s hold pressure setting to the proper process setting or not. This value only considers the flat part of the hold pressure curve and ignores droops or oscillations at transfer to hold or at the end of hold.

Average Value / Hold Pressure.

Use to determine whether the hold pressure as seen by the plastic may differ from machine to machine because of differences in the way the machine transitions to hold. This is not a precise measure of what the plastic sees because of the compression in the runner system. However if Average Value / Hold Pressure differs on the same mold template from one machine to another it should alert you to the fact that you have differently performing machines and may need to make a process adjustment to match between the two.

Additional Information

The graph below shows the difference in the two values if the hold sequence goes off when the machine ends injection earlier.

Here is an example showing three different problems.

1. Fill volume not set => hold comes on too early and includes the velocity controlled packing pressure in the Average Value / Hold Pressure.
2. The eDART cannot compute an Average Value / Stable Hold Pressure because the oscillations during hold are too great and the pressure is never stable. The value may come and go from shot to shot if the oscillations get lower on one shot and worse on the next.
3. If you have multiple hold pressures (profiled hold) then the eDART may not be able to determine which profile is the real Stable Hold Pressure.

Tip of the Day 70: Levels and Folders