Visual inspection results

join the two materials. The mechanical resistance and the standard deviation presented by the two seams tested was the lowest of all materials tested.

The Clearweld samples used as the absorber material presented the weakest seams overall. Indeed, it proved necessary to weld more than 10 plates of this material together to obtain 2 specimens capable of being mechanically tested. With the two analyses made, it is possible to conclude that is necessary to increase the concentration of Clearweld to obtain a good seam. Figure 70 presents analysis of the deformation levels obtained from the different samples tested.

Figure 70 Deformation of the PP with different additives on their matrix

All the PP specimens with additives presented lower deformation when compared to the specimen with no additives, the PP sample with 20% of talc registering the higher level of deformation of all the specimens with additives.

In terms of the absorbent additives, the sample with the carbon black as an absorber was the material that presented the higher deformation, overall, when compared to the other additives. At the same time, the specimens that were welded using the carbon black absorber presented the higher levels ofstandard deviation.

welded by laser. The visual inspection was made using a Lupe Stereoscopic Nikon SMZ-10 and a digital camera Olympus DP11 with four times of magnification. Due to the size of the welding path it was impossible to take a photo of the whole seam length and because of this it was decided to present two photos of each of the seams analyzed.

One was taken near the middle of the seam and the other on the edge of the seam; the left-hand side photos shown below are always of the middle section while the right-hand side photos are always of the edge section.

Figure 71 photos of the seam of the weld between PMMA with PC

In figure 71 in the middle section (left) it is possible to discern a small area of bonding between the PMMA and PC (inside the blue circle).

A continuous mixture of the two along the entire seam had been anticipated but this did not happen. The low pressure applied to keep the two materials connected can explain this result. At the same time, the image showed perfect contact between the two materials without the occurrence of any voids. The explanation for this comes from the low thermal levels exchanged between the two materials. In this case, the material that absorbed the laser energy did not exchange the necessary heat needed to form the seam.

The image taken at the edge of the weld path (figure 71 right) reveals a gap between the two materials (highlighted inside the blue circle). This defect is due to the low pressure applied to keep the two plates connected in the welding zone. Defects of this nature will be responsible for the initiation and the propagation of cracks when a load overcome the resistance of the seam.

Figure 72 photos of the weld made between PC with PC

In figure 72 the photos taken of the welding zone of the PC/PC sample are presented. In the photos taken, it is possible to visualize a perfect contact between the two materials leading on to improved seam resistance when external loads are applied.

No voids are discernable throughout the entire seam.

The following paragraphss analyze the PP/PP specimens welded according to table 16.

The first specimen analyzed was the specimen welded with condition 1 of table 16. In the middle section of the weld (figure 73, left) an extensive bonding zone can be readily seen. The zone is clearly visible inside the blue circle. In this case, the material that absorbs the laser has blended well with the transparent material making it possible to obtain a good seam. No voids can be seen along the entire weld path.

Figure 73 specimen welded and injected with condition 1

At the edge, (figure 73, right) of this specimen it was possible to identify a small area of defective bonding between the two materials (blue circle). This defect will decrease the resistance of the seam and it will be through this weak point that a crack propagates when the load limit is overcome.

Figure 74 shows the welding zone of the two PP plates joined with welding condition number two. The specimen analyzed exhibits a very visible mixture zone (blue circle) in the middle of the length of the seam. The zone analyzed does not present any voids, indicating an almost perfect contact between the two materials.

Figure 74 specimen welded and injected with conditions 2

At the edge of the specimen analyzed (figure 74 right) a large amount of burr material (blue circle) was visible. This can indicate two possible problems, the use of more pressure than was needed or too high a laser power. Taking into consideration the absence of voids, the explanation could be the use of a contact pressure higher than needed to join the two materials.

Figure 75 specimen welded and injected with conditions 3

The plates of PP welded with under condition 3 parameters (figure 75, above), showed a high level of mixture between the two materials (blue circle) and no visible voids were found along the weld path.

On the edge of the two plates an overlap of PP with carbon black was visible.

connected during the weld process was applied. All the same, this over pressure can be advantageous because the mixture of more material is promoted, this more intimate level of bonding improving the mechanical resistance of the seam. The bright material discerned is burr material resulting from the steps needed to do this visual inspection.

The PP/PP specimen welded under condition 4 (Figure 76) shows a smaller welding area compared to preceding samples.

Figure 76 specimen welded and injected with conditions 4

Visual inspection reveals perfect contact along the entire length of the seam with no discernable voids. At the edge of the two plates the situation is the same with more or less perfect between the two materials.

Figure 77 specimen welded and injected with conditions 5

For weld condition 5 the images show a perfect contact between the two plates with no visible voids (figure 77). The mixture between the two materials is not so visible along the entire length of the seam, being more pronounced at the edges. At the edge shown an enormous overlap of the carbon black material is seen, this being explicable in light of the use of high pressure to keep the two materials connected during the weld. The results obtaining at the edge of the seam can also stem from the application of high laser

power settings since a combination of high contact pressure with high laser power promotes the mixture of the two materials.

Figure 78 specimen welded and injected with conditions 6

In contrast to many other specimens, the plates welded with weld condition 6 (figure 78), presented a near perfect contact along the entire welding path, the images showing good mixture between the two materials throughout. The most interesting result comes from the image taken at the edge of the plates (figure 78, right). In this case the seam line disappears altogether indicating the formation of a perfect bond between the two materials.

Figure 79 specimen welded and injected with conditions 7.

The specimen welded and injected according to the parameters detailed for condition 7 (figure 79), presented broadly similar results to those detailed for condition 6 above.

Again, a zone of near perfect contact is visible without voids along the entire seam length. The specimen showed a zone of heat propagation, this area being larger on the black material than on the transparent material. Considering the photos, the specimen has more tendencies to break through the black material than the transparent.

On the edge of the specimen (figure 79, right), despite what is seen on the photo the contact between the two materials is good with no discernable voids. The bright material is, in fact, burr material from preparation of the sample.

Figure 80 specimen welded and injected with conditions 8

The last specimen analyzed was the specimen welded and injected under condition number 8 (figure 80). On the middle length of the seam it is possible to see mixture between the two materials and no voids were found during the analysis of the entire seam.

On the edge of the two plates (figure 80 right) mixture between the two materials was not observed. This zone has more tendencies to initiate the propagation of cracks, at the same time showing the need to apply more laser power so as to increase bonding or mixture between the two materials.