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Machining Polymeric Matrix Composites

Machining composite materials is a rather complex task owing to its heterogeneity, heat sensitivity, and to the fact that reinforcements are extremely abrasive. Conventional machining methods should be adapted in such a way that they diminish thermal and mechanical damage. Fiber-reinforced plastics (FRPís) are characterized by high strength and stiffness at simultaneously low weight, and are superior to metallic materials in many cases. In modern-day engineering, high demands are being placed on components made of fibre-reinforced plastics in relation to their dimensional precision as well as to their surface quality. Therefore, FRPís have replaced conventional materials in various fields of application such as aeronautical, space engineering, biomechanics, mechanical, as well as in other industries because of is own properties. As result of these properties and potentials applications, exists a great necessity to understand the questions associates with the production and machining (Drilling, Milling and Turning) of these materials.

Machining Operations

Drilling 

Milling

Turning

Drilling

Drilling is a frequently practiced machining process in industry owing to the need for component assembly in mechanical pieces and structures.On the other hand, drilling laminate composite materials is significantly affected by the tendency of these materials to delaminate and the fibres to bond from the matrix under the action of machining forces (thrust force and torque).                                                                                            

In this work is presented a study of the cutting parameters (cutting velocity and feed rate) on power (Pc), specific cutting pressure (Ks), and delamination in Carbon Fiber Reinforced Plastics (CFRPís). A plan of experiments, based on the techniques of Taguchi, was established considering drilling with prefixed cutting parameters in an autoclave CFRP composite laminate. The analysis of variance (ANOVA) was preformed to investigate the cutting characteristics of CFRPís using Cemented Carbide (K10) drills with appropriate geometries. The objective was to establish a correlation between cutting velocity and feed rate with the power (Pc) specific cutting pressure (Ks) and delamination factor (Fd) in a CFRP material. Finally this correlation was obtained by multiple linear regression.

 

 

 Type of Delamination on Carbon Fiber Reinforced Plastics (CFRP's)

                                                                                                             

Figure 1 show the evolution of the delamination factor (Fd) at exit with feed for different cutting speed values, for both drills.

Figure 1- Delamination factor (Fd) at exit as function of cutting parameters for both drills

   
 

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Milling

Milling is used as a corrective operation to produce a well-defined and high quality surfaces. Although components made of composite materials are commonly produced net shape, they often require the removal of excess material to control tolerances, so milling is the most practical machining operation for such purpose. The knowledge of cutting mechanisms is indispensable in view of cutting mechanics and machinability assessment in milling.

Milling composite materials presents a number of problems such as surface delamination associated with the characteristics of the material and the cutting parameters used. In order to minimize these problem was done a study with the objective of evaluating the cutting parameters (cutting velocity and feed rate) related to machining force in the workpiece, delamination factor, surface roughness and international dimensional precision in two GFRP composite materials (Viapal VUP 9731 and ATLAC 382-05). A plan of experiments, based on an orthogonal array, was established considering milling with prefixed cutting parameters. Finally an analysis of variance (ANOVA) was preformed to investigate the cutting characteristics of GFRP composite materials using a cemented carbide (K10) end mill

Figure 2 shows the evolution of the international dimensional precision (IT) as a function of the feed, for different cutting speeds.

Figure 2 - International dimensional precision (IT) as function of cutting parameters for both GFRP composite materials

 

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Turning

The quality of surface is an important requirement for many turned workpieces. In the field of engineering, the exact degree of roughness can be of considerable importance, affecting the functioning of a specific component.                                                  

A work was developed with the aim of studying the influence of  the cutting parameters (cutting velocity and feed) on dimensional precision and surface roughness in turning tubes of Fiber Reinforced Plastics (FRPís). A plan of experiments, based on the techniques of Taguchi, was performed machining with cutting parameters prefixed in composite workpiece. An orthogonal array and the analysis of variance (ANOVA) are employed to investigate the cutting characteristics of FPRís (glass fiber-reinforced filament-wound tubes) using cemented carbide (K15) cutting tools. The objective was to establish a correlation between cutting velocity and feed with the surface roughness and the international dimensional precision (IT) in composite workpiece. The correlation was obtained by multiple linear regression. Finally, confirmation tests were performed to make a comparison between the experimental results foreseen from the mentioned correlation.                                                                                            

Figure 3, show the evolution of the surface roughness (Ra) as function of feed.

   Figure 3 - Surface roughness (Ra) as function of feed

 

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MACTRIB - Department of Mechanical Engineering , University of Aveiro

Campus UniversitŠrio de Santiago, 3810-193 AVEIRO, PORTUGAL

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