Strength Test Method Design And Experiment Research Of Laser Transmission Welding Of Plastics

Comparing with the traditional plastic connection methods such as adhesive,hot-melt welding, friction welding and ultrasonic welding, laser transmission welding(LTW) has distinct advantages, and it has been widely used in manufacturing ofautomobile spare parts, medical equipments, and electronic packaging fields. Domesticresearches in this field are mainly concentrated in the experiment parameters, absorbentand numerical simulation. However, there are few studies on the research of weldingquality evaluation, especially specification of welding strength test method. Therefore,starting research on the strength test method in LTW of plastic has significant meaning.The contents of this specific research are as follows:1. According to analyze the present LTW joint strength test method, we found thatthere is an additional force moment generate at the welding position during the testprocess. The additional force moment will cause the deflection of weld seam, thus theloaded tensile force could be analyzed into two forces by resolution, i.e. the shearingforce of periphery and the release force of normal. Eventually make the test by thedestructive power of deviating from the real joint shear force value.2. Propose new joint strength test methods of LTW plastic, including double-lappedwelding shear strength test method and tensile strength test method. Pressure equipmentwas designed corresponding with the two test methods, respectively.3. Tensile strength test method is operated based on the experimental design. Theresults showed that: in the experimental parameter range, tensile strength of the samplehas the anti increased with energy density. PMMA sample has the maximum weld tensilestrength28.634MPa, which reached47.5%of the basic material; In PP weld tensilestrength test, most of the samples tensile strength are in the range of17.2%～26.8%to thebasic material, when the energy density is1.731J/mm2, the weld joint reached maximumtensile strength9.144MPa.4. Single-lapped LTW of PMMA/ABS plastics experiment and shearing strength testwere operated based on the design. The results showed that, in the shearing strength testof single-lapped specimens, there is an obvious deflection of the weld joint. When thethickness of PMMA is2.0mm, the deflection angle φ reached maximum4.8°, When the sample length is70mm, φ got minimum of2.4°. The influences of PMMA thicknessand sample length on φ are in the similar range of2.4°~4.8°. According to the form ofdestruction of the weld samples, we found that the conventional method withsingle-lapped weld could not get an accurate assessment of the shear strength in LTW ofplastics.5. Double-lapped LTW of PMMA/ABS plastics experiment and shear strength testexperiment were taken. The results showed that, when the H (thickness of PMMA) is1.5mm, the (shear strength of double-lapped weld joint) is no less than15.781MPa,when H=2.0mm, is no less than12.754MPa and when H=3.5mm, is no less than16.539MPa. Under the condition of L (specimen length) is70mm, the actual measuredshear strength of the specimen is14.265MPa,when L=40mm, is no less than21.406MPa, L=50mm, is no less than23.908MPa, L=60mm, is no not less than19.991MPa. In the shear strength test of double-lapped weld joint experiment, there is nodeflection of the weld joint. So, we reach the conclusion that, double-lapped weld methodin LTW of plastic can measured the shear strength of welded joint accurately.