Balancing material loads

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Balancing material loads

As stated in the last article, the digital laminate definition that consists of the spatial information of the prepreg tows and the process information of the feeds, pressures, etc. needs to be aggregated and transferred to the layup machine. There is one more parameter set that can be modified to change the way, the laminate is laid upon the tooling. As mentioned in the article about end-effectors, tows are grouped into courses which can then be laid 1 after another. The grouping of these courses can be changed to avoid collisions with the tooling and to balance the material loads of the different spools.

Here are some examples with various parameters sets.  

Last Course 1 Tow

Figure 1: In this figure, the tows have been grouped into courses in such a way, that the last course consists only of three tows. If this part is manufactured in series, the corresponding spools would run low faster than the others. Because the machine cannot continue manufacturing while spools are being swapped out, it makes the most sense, to swap as many spools as possible at the same time. To balance the material amounts between the different spools, the courses may be rearranged accordingly. Meaning that for the other plies, the grouping should complement the existing material usage to balance the total amount of material per spool across the laminate. The blue arrow denotes the centerline of the last course, in which only the bottom-most tow is placed. 

Using the so-called “Seed point offset” shifts the starting point of the grouping by a certain number of tows. In our example, the first course contains 16 tows. If the first course were to contain only 8 tows, the last course then was to contain 9, which would shift the last, single tow to another slot. (Slot number 9, instead of slot number 1) This is equivalent to a seed point offset of 8. Since this does not create any additional courses, this parameter is used to optimize the material usage per spool and to avoid collisions at the start and end of the ply. One could also look at the available material before manufacturing and rearrange the courses in such a way that all spools are used corresponding to the material stored. 

Last Course 9 Tows 1

Figure 2: The same tows as in Figure 1, but with a seed-point offset of 8. The first course at the top only contains 8 tows, while the last one contains 9. The blue arrow denotes the centerline of the last course, in which 9 tows are being placed. 

Another parameter that can be used in conjunction is the number of tows that are to be used in a course. Instead of always using the maximum number of spools at the same time, you could also only use the first half. Or the last half. Let us say that on the first 12 spools CFRP material is stored and on the last 4 spools GFRP material for the outer plies is stored. Only the first and last ply shall be made from GFRP – this would then mean, that the first and last ply only use the last 4 spools for manufacturing, while the other plies use the first 12. When you are trying to establish a multi-material process, this parameter controls how to realize it. 

12 Tows

Figure 3: The same tows as before but grouped in such a manner that every course is being placed using the first 12 slots of the end-effector. The blue arrow denotes the centerline of the last course. 

We hope this article gave you a good insight into how the transfer from the coverage generation to digital manufacturing hardware looks like. The following articles will highlight the analyses of the layup and the positioning in the manufacturing cell.

Until then, stay safe and stay tuned. 

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