JEC COMPOSITES MAGAZINE - Issue #103 - March 2016 - 72

joining

Fig. 2: Surface topology and roughness of a sand blasted+LST metal surface

- IJ: glass fibre reinforcement (twill weave, 47% fibre volume
content) polyamide 6 (GF/PA6) or polypropylene (GF/PP)
and steel (DC01, 1.0330).
- LJ: GF/PA6 and aluminium (AlMg3)

Surface structuring
In order to generate form closure between the polymer and the metal
surface, different structuring methods were investigated (see table 1).
All the mentioned techniques generally improve the joint's strength
compared with degreasing. However, the most promising technologies are sand blasting (low cost), laser surface texturing, and sand
blasting + PLST (both very efficient).
Sand blasting (SB) is a well-established, cost-effective process suitable
for different types of materials and parts with complex geometries.
SB uses an abrasive to increase surface roughness and remove contamination and rust. In this study, fused aluminium oxide (250-355
µm) was used as an abrasive and the following roughness values were
produced (Rz):
- Aluminium: x: 26.28±2.81 µm, y: 35.36 ± 1.36 µm

Fig. 3: Surface topology and roughness of laser-structured steel surface

- Steel: x: 17.84±1.96 µm, y: 24.17± 1.07 µm
SB was also combined with punctual laser surface texturing (PLST)
operated at a high feed rate and frequency to generate high-precision
micro-holes with burrs inside. The treated surface and the resulting
roughness are shown in figure 2.
Another fast and efficient technology is structuring with an ultrashort pulse laser. It melts the surface of the metal and generates
vapour, which ejects the molten metal. As a result, a pattern of melt
accumulations along grooves is generated. Steel specimens were
treated with a coarse and a fine zigzag-shaped structure. Surface scans
and images of the two different structures and their roughness (Rz)
are shown in figure 3.

Joining technologies
IJ is based on the ability of electromagnetic fields to induce eddy
currents in a conductive part placed in a field generated by an induction coil. According to Joule's first law, a current flowing through a
conductor causes the conductor to heat up. This effect can be used

Tab. 1: List of investigated surface structuring methods

Method

Structuring effect

Cost

Speed

Flexibility

Strength
improvement

Sand blasting

Increases surface roughness through the use of an abrasive

Low

Medium

High

Average

Laser surface
texturing

Melts the surface of the metal and generates
a pattern of melt accumulations along grooves

High

Fast

High

Sand blasting
+ PLST

Combines sand blasting for micro-texturing and punctual
laser surface texturing for bigger crater-shaped holes

Very high

Medium

High

Water jet

Stream of water at very high pressure to erode the material

Average

Medium

High

Average

Laser remelting

Repetitive local heating with the laser beam above the
melting temperature without removing the melted material

High

Slow

Average

Average-high

Laser cladding

Fusion of a pre-deposited powder layer with the laser beam

High

Slow

High

Average-high

Electro discharge
machining

Rapidly recurring current discharges between
two electrodes that remove the material of the surface

Average

Slow

Low

Low-average

Knurling

Lathe rolled into the material to create a crisscross pattern

Low

Fast

Average

Low

Drilling

Cutting process that uses
a drill bit to cut a hole of circular cross-section

Low

Fast

High

Very sensitive to
material properties

72 jec composites magazine / No103 March 2016

Table of Contents for the Digital Edition of JEC COMPOSITES MAGAZINE - Issue #103 - March 2016