Definitions: Understanding: plural of understand, comprehension, knowing, Graph: a display of data in composite or visual display showing a range

Within many injection molding machines today, the controls also have the capabilities of displaying data in a graphic form. One of those graphs may be the injection phase of the process. It is a great tool to master and in the past one had to actually employ some sort of processing monitor to generate this data. One key to understanding the graph is to know the rate that it monitors at, though from a generic point this is not critical unless one has very critical parts/ process than knowing how many points per second it picks up may become critical as to understanding.

These are great tools and one need be aware of what they are looking at to see what is going on.

The following things need to be understood:

1. does the graph run right to left or left to right
   1. Note that many machine manufactures run screens differently. While it is important to know which direction it is running from an observation point it makes no difference in data presented.
2. What are the data points one is reviewing
   1. This means is it pressure, speed, time or what?
   2. Are they clearly defined
   3. Is there a scale
   4. Can the scale be modified, meaning can it be expanded
3. Is the data real time or last cycle
   1. This is in regards to when is data posted to graph.
   2. Some machine manufactures post in real time other may post after cycle is completed.
   3. Is there any smoothing of data, meaning does the machine process average or generate a smooth out graph?
   4. What is the data rate? This means how many points a second are looked at.
4. What units are being displayed
   1. In many cases they are set but in a few and as new software and capabilities become more common it is possible to change units.
5. Can the data or cycles be overlaid, saved, and printed.

Example Pressure curve

The above example is showing the pressure gradient of the injection screw on a machine from start of injection through pack / hold. The red line is the pressure and the bottom or horizontal represent time. (This is an example only for explanation) the process / graph is read form left to right. The left side would be a scale showing pressure.

As can be noticed there are no reference points on this graph as to what the units are and it is just for display to illustrate what might be a pressure curve. It is showing how the pressure goes up and then down to a stable level position for a period of time.

Explanation in reading graph from a few set points:

1. A This is the start point of filling typically a 0-0 point, meaning pressure is 0 and time is 0.
2. B This is the transfer point (of fill) on this graph and also a peak of injection fill pressure.
3. C This is the bottom of drop off from filling to the start of packing/holding pressure.
4. D Packing / holding pressure and is in this example flat.

In reading the graph it is simple to see that what is going on in that as the screw comes forward (point A to Point B) the pressure raises as resistance to fill increases, and when the transfer point is reach (peak B) the screw switches to a pack/hold mode with reduced pressure/ speed to finish off completing the packing of the part. This is why there is a drop in the realized pressure; both pressure and speed of screw are decreased, in a typical pack and hold situation. The last horizontal section is the pack / hold which shows a stable pressure.

The example shows an ideal or example of what basically happens during the injection phase of the molding operation. It is important for a processor to understand their machine and which way it reads and how to adjust the scale, graph settings and anything that can affect the graphing of the injection phase of the process.

In following segments further detail and possible issues well be explored.

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17042013.01