Variable frequency microwave processing of thermoplastic composites (original) (raw)
Related papers
1997
Industrial microwave technology for processing polymers and polymer based composites is currently in a state of considerable flux. This paper extends the applications horizon of microwaves in the area of reinforced thermoplastic composites joining, and places emphasis on the development of equipment and facilities aiming at maximising bond quality. It discusses the microwave facility used, including a 0.8 kW variable control power generator operating at 2.45 GHz, waveguide and a tuning piston designed for obtaining a standing wave at the seam of the butted and lapped test pieces. The effect of power input and cycle time on the heat affected zone is detailed together with the underlying principles of test piece material interactions with electromagnetic field. The process of autogenous joining of 33% by weight of random glass fibre reinforced nylon 66, polystyrene (PS) and low density polyethylene (LDPE) as well as 23.3 % by weight of carbon fibre reinforced PS thermoplastic composites is mentioned together with developments using filler materials, or primers in the heterogenous joining mode. The weldability dependence on the dielectric loss tangent of these materials is also described.
Industrial microwave technology for processing polymers and polymer based composites is currently in a state of considerable flux. This paper extends the applications horizon of microwaves in the area of reinforced thermoplastic composites joining, and places emphasis on the development of equipment and facilities aiming at maximising bond quality. It discusses the microwave facility used, including a 0.8 kW variable control power generator operating at 2.45 GHz, waveguide and a tuning piston designed for obtaining a standing wave at the seam of the butted and lapped test pieces. The effect of power input and cycle time on the heat affected zone is detailed together with the underlying principles of test piece material interactions with electromagnetic field. The process of autogenous joining of 33% by weight of random glass fibre reinforced nylon 66, polystyrene (PS) and low density polyethylene (LDPE) as well as 23.3 % by weight of carbon fibre reinforced PS thermoplastic composites is mentioned together with developments using filler materials, or primers in the heterogenous joining mode. The weldability dependence on the dielectric loss tangent of these materials is also described.
One important thing to be studied in the bonding of thermoplastic composite material using microwave irradiation is the effects of microwave energy on the matrix and fibre reinforcement of the composite. In this research, thirty three percent by weight random glass fibre reinforced polystyrene [PS/GF (33%)] is chosen for the study. Microscopy study is used to find out the microstructural characteristics along and around the interface of the welds. The separation distance of the reinforcing carbon filaments was varied and heat transfer in the material during joining was studied. The reasons why the thermoplastic matrix composite materials were weakened by prolonged microwave irradiation were also studied and analysed.
Microwave facilities for welding thermoplastic composites and preliminary results
The Journal of microwave power and electromagnetic energy: a publication of the International Microwave Power Institute
The wide range of applications of microwave technology in manufacturing industries has been well documented (NRC, 1994;. In this paper, a new way of joining fibre reinforced thermoplastic composites with or without primers is presented.
Materials & Design, 2012
The development of natural fiber reinforced polymer composites has received widespread attention due to their environment friendly characteristics over the synthetic fiber based polymer composites. Although, different categories of natural fiber reinforced composites have been developed, their joining has not been explored extensively. In the current article, natural fibers (nettle and grewia optiva) reinforced polylactic acid green composites and polypropylene based partially biodegradable composites have been developed. These composites have been joined with an innovative microwave heating process in the presence of suitable susceptor. Samples have also been joined with the well known adhesive bonding technique for comparison purposes. Joint strength has been evaluated in each case as per standard procedures and results showed that microwave joining provides higher joint strength as compared to adhesive bonding. Microwave heating process has also been simulated with standard multiphysics finite element (FE) software to analyze the microwave heating mechanism. The results of the experimental study are in close agreement with the finite element investigation.
Characterisation of thermoplastic matrix composites using variable frequency microwave
Plastics, Rubber and Composites, 2000
In most industrial microwave processing operations, the frequency of the microwave energy launched into the waveguide or cavity containing the sample is usually fixed. This brings with it inherent heating uniformity problems. This paper describes a new technique for microwave processing, known as variable frequency microwave (VFM) processing, which gets rid of the problems brought about by fixed frequency microwave processing. In VFM processing, microwave energy over a range of frequencies is transmitted into the cavity in a short time, eg 20μs. It is therefore necessary to find out the best frequency range to process a material. This paper describes the process of finding the best range frequency for microwave processing of five different thermoplastic matrix composites using the VFM facilities. The optimum frequency band for microwave processing of these five materials was in the range of 8 -12 GHz.
Composites Part A: Applied Science and Manufacturing
Accelerated curing of high performance fibre-reinforced polymer (FRP) composites via microwave heating or radiation, which can significantly reduce cure time and increase energy efficiency, has several major challenges (e.g. uneven depth of radiation penetration, reinforcing fibre shielding, uneven curing, introduction of hot spots etc). This article reviews the current scientific challenges with microwave curing of FRP composites considering the underlying physics of microwave radiation absorption in thermoset-matrix composites. The fundamental principles behind efficient accelerated curing of composites using microwave radiation heating are reviewed and presented, especially focusing on the relation between penetration depth, microwave frequency, dielectric properties and cure degree. Based on this review, major factors influencing microwave curing of thermoset-matrix composites are identified, and recommendations for efficient cure cycle design are provided.
Microwave Heating for Manufacturing Carbon-Fiber Thermoplastics
MRS Proceedings, 1990
ABSTRACTTraditionally, polymeric composite parts are heated and consolidated in an autoclave. For large parts, such as transport aircraft fuselages or submarine hulls, size becomes a limiting factor. To overcome this limitation and to reduce labor costs we are developing an automated tape placement process. In this process we build composite parts one layer at a time with tape containing carbon fibers impregnated with a thermoplastic. As the tape comes into contact with the part, we apply heat to melt the thermoplastic and apply pressure to consolidate the tape to the part. To support this effort we have developed a proprietary microwave applicator that is suitable for rapidly heating carbon-fiber composites in an automated tape placement process. Small carbon-fiber/poly(aryl-ether-ether-ketone) parts made using the microwave applicator have interlaminar shear strengths of 100 MPa (14.5 ksi), which is almost equal to the 103 MPa (15.0 ksi) obtained using an autoclave.
Characterisation of Thermoplastic Matrix Composites (TPC) Using Variable Frequency Microwave (VFM)
In most industrial microwave processing operations, the frequency of the microwave energy launched into the waveguide or cavity containing the sample is usually fixed. This brings with it inherent heating uniformity problems. This paper describes a new technique for microwave processing, known as variable frequency microwave (VFM) processing, which gets rid of the problems brought about by fixed frequency microwave processing. In VFM processing, microwave energy over a range of frequencies is transmitted into the cavity in a short time, eg 20μs. It is therefore necessary to find out the best frequency range to process a material. This paper describes the process of finding the best range frequency for microwave processing of five different thermoplastic matrix composites using the VFM facilities. The optimum frequency band for microwave processing of these five materials was in the range of 8 -12 GHz.
Journal of Materials Processing Technology, 2001
Microwave processing of materials is a relatively new technology advancement alternative that provides new approaches for enhancing material properties as well as economic advantages through energy savings and accelerated product development. Factors that hinder the use of microwaves in materials processing are declining, so that prospect for the development of this technology seem to be very promising . The two mechanisms of orientation polarisation and interfacial space charge polarisation, together with dc. conductivity, form the basis of high frequency heating. Clearly, advantages in utilising microwave technologies for processing materials include penetrating radiation, controlled electric field distribution and selective and volumetric heating. However, the most commonly used facilities for microwave processing materials are of fixed frequency, eg 2.45 GHz. This paper presents a state-of-the-art review of microwave technologies, processing methods and industrial applications, using variable frequency microwave (VFM) facilities. This is a new alternative for microwave processing. The technique is geared towards advanced materials processing and chemical synthesis. It offers rapid, uniform and selective heating over a large volume at a high energy coupling efficiency. This is accomplished using a preselected bandwidth sweeping around a central frequency employing frequency agile sources such as travelling wave tubes as the microwave power amplifier. Selective heating of complex samples and industrial scale-up are now viable. During VFM processing, a given frequency of microwaves would only be launched for less than one millisecond. Two facilities were employed during the study. The VW1500 ) with a maximum power output of 125 W generates microwave energy in the frequency range of 6 -18 GHz and the other, Microcure 2100 Model 250 ( ) operates at 6 -18 GHz with a maximum power level of 250 W. The cavity dimension of VW1500 ) was 250 mm x 250 mm x 300 mm and the Microcure 2100 model 250 has a cavity size of 300 mm x 275 mm x 375 mm. Successful applications of the VFM technology are in the areas of curing advanced polymeric encapsulants, thermoplastic matrix composite materials characterisation, adhesive characterisation, rapid processing of flip-chip (FC) underfills, joining reinforced thermoplastic matrix composites materials, and structural bonding of glass to plastic housing. However, there are a lot of factors that have to be considered before employing variable frequency microwave (VFM) irradiation for processing materials. Not all materials are suitable for microwave processing and one has to match the special characteristics of the process. Blind applications of microwave energy in material processing will usually lead to disappointment. On the other hand, wise application of the technology will have greater benefits than have been anticipated. Successful applications of these modern facilities by the authors include the characterisation of glass or carbon fibre reinforced thermoplastic matrix composites, eg 33% by weight glass fibre reinforced low density polyethylene [LDPE/GF (33%)], of primers eg two-part five-minute rapid araldite (LRA), and joining of the above mentioned composite materials with, or, without primers. Such applications are detailed in this paper.