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Fiber composite materials such as GRP (glass fiber reinforced plastic) and CFRP (carbon fiber reinforced plastic) are relatively new in engineering and industrial design. Both can often be processed more precisely than metals and are therefore popular alternatives to stainless steel and others. Also because both polymers are very light and yet particularly robust. From these contents you can find out why GRP and CFRP need special tools for cutting and grinding in post-processing and what the fiber is all about. You can also read why congestion when processing fiber-reinforced plastics is a welcome waste product and how dirt can be removed from CFRP and GFRP
GRP and CFRP
The optimal solution for small batches and prototypes
Glass and carbon-reinforced plastics are semi-finished products and are processed by various manufacturing methods, such as fiber injection molding, manual lamination or the so-called resin injection molding process (RTM for resin transfer molding). The applied resins protect the fibers from external influences and preserve the shape of the part or component. Unlike metals, which need almost no machining after processes such as deep drawing, both CFRP and GFRP require intensive post-processing. In terms of efficiency, it can be said (albeit very generalized) that fiber-reinforced plastics are less expensive for small batch or one-off production, while mass production is more cost-effective for components made of metals.
Plastic - a truly versatile material
Use in shipbuilding is one of the most popular applications, especially for GRP – engineers appreciate its good formability in lightweight construction for ships of all types. Whether custom laminates, individually fabricated hulls or masts and other superstructures: in shipbuilding, where weight and strength are equally important, GRP and CFRP are indispensable. A professional like you is certainly long familiar with the positive aspects of the good formability of both polymers. GRP and CFRP are particularly attractive when it comes to the individual design of enclosure solutions. Engineers in the aircraft industry, for example, attach particular importance to increasing stiffness and strength. CFRP is the main material used here, as it allows for very lightweight construction and thus energy efficiency. Incidentally, wind turbine designers also appreciate this property. And since anything that is lightweight moves in a more energy-efficient manner, CFRP components are also increasingly being used in many areas of the automotive industry.
Machining fiber-reinforced plastics is a challenge. The reason: inhomogeneity of the material and significantly different properties of the fiber and matrix. In addition, the fiber is very abrasive, so high tool wear is inevitable. As polymers, both substances have poor thermal conductivity. Therefore, pay attention to heat dissipation and, ideally, cooling during processing. This is the only way to avoid negative effects such as thermal expansion or high clamping pressures.
When processing CFRP and GFRP, certain risks arise, especially when working manually and not by machine, due to the particulate dust that is produced when the polymers are cut and ground. These dusts not only increase the risk of explosion and fire. Inhalation should also be avoided by wearing personal protective equipment and a suitable mouth and nose mask. Good protective equipment also prevents your skin from being subjected to GRP / CFRP exposed areas.
Cutting of fiber-reinforced plastics: End of life cycle
If you want to saw fiber-reinforced plastics, the first step is to de-laminate the cut surface, taking into account the possible inclinations of the material. Make sure there is sufficient cooling. The tool you use depends on the desired result: If you just want to separate the two materials to e.g. get rid of it, all you need is a saw. For contour cuts and fine work, specific tools are required, especially diamond tools, with which the cuts can be made even more precisely.
Both CFRP and GRP have a tendency to fray, so choose your tools carefully and consult experts if necessary.
GRP and CFRP grinding
When components are manufactured from fiber-reinforced plastics, they are usually produced as close as possible to their final form. In terms of machining processes that produce chips, such as grinding for example, the volume of chips tends to be quite low. In most cases, CFRP and GRP are only deburred, side milled, drilled or cut. With regard to pressure and processing speed, the following applies:
- During machining, whether deburring, abrasive grinding or coarse pre-cleaning, pay attention to slow speeds and moderate contact pressure and carefully check beforehand which type of plastics are used – thermoplastics react differently to duoplastics. In both cases fiber-reinforced plastics have a highly abrasive effect – rapid wear of sanding and cutting tools is characteristic.
- For this reason, make sure that the quality of the tools is good and use diamond tools (electroplated or PCD-tipped), for example. Its wide chip evacuation channels facilitate the machining of fiber-reinforced polymers, as well as milling cutters with special geometries.
- Look at the tools for aluminum machining. Like aluminum, CFRP and GRP must be lubricated. Open pore grinding tools, tools with abrasive coatings and SiC grain with good cutting properties are therefore a good choice for clean machining, even with composite materials.
- Never forget your personal protective equipment, because polymer particles pose a health hazard to you and your employees.
GRP and GFRP welding
Unlike metals, fiber-reinforced plastics cannot be easily welded by conventional methods. Laser bonding methods for fiber-reinforced composites are gaining increasing acceptance, but are currently only used in research. Today, form-locking or form-locking bonding is one of the established industrial processes. Fiber-reinforced materials are glued, riveted or bolted in mass production.
GRP and CFRP polishing: why powder is not necessarily a waste material
Polishing means very fine sanding and requires tools and abrasives that close even the smallest pores on the surface of GFRP and GRP. In the process, part of the abrasion evaporates, while the other fills the pores and grooves on the surface of the fiber-reinforced plastics. Further sealing can be achieved with wax.
Cleaning of GRP and CFRP
As a professional knows: especially with fiber-reinforced plastics, the boundary between cleaning, care and polishing agents is not always easy to determine. Some additives are ground and thus remove dirt, while others are ground less and seal the surface. When GRP and CFRP are cared for, the transition from cleaning to polishing and sealing of fiber-reinforced plastics is seamless. Depending on the component and fiber, a wide variety of tools and abrasives are used, using individual contact pressures and rotational speeds.