Jean-François Chatelain

A balancing technique for optimal blank part machining

A balancing technique for casting or forging parts to be machined is presented in this paper. It allows an optimal part setup to make sure that no shortage of material (undercut) will occur during machining. Particularly in the heavy part industry, where the resulting casting size and shape may deviate from expectations, the balancing process discovers whether or not the design model is totally enclosed in the actual part to be machined. The balancing process requires a measurement dataset of the blank part to be balanced as well as a computer-assisted design (CAD) solid representation of the design model. A preferential constrained alignment algorithm calculates the proper compensation, or fixture offset, for any type of geometry to eliminate any possible shortage of material if possible, or orient the unavoidable area of missing material for appropriate rework. The alignment is an iterative process involving nonlinear constrained optimization, which forces datapoints to lie outside the nominal model under a specific order of priority. The Simplex method of direct search is used to solve the optimization process at each iteration. Two different artificial objective functions are implemented and compared for the balancing problem, a logarithmic and a least-squares formulation. The technique is applied to the balancing of a wiggle and a hydroelectric turbine blade. Results show that the balancing process under the logarithmic formulation converges faster than with the least-squares expression and is also more appropriate to balance the stock allowance for proper machining of the part.

A comprehensive analysis of cutting forces during routing of multilayer carbon fiber-reinforced polymer laminates:

Analyzing cutting forces during detouring of carbon fiber-reinforced polymer laminates at high cutting speeds is problematic as the recorded signal can be distorted due to resonance of the measuring system. In addition, excessive tool wear can render signal interpretation difficult. In the present study, a fully controlled experimental protocol is used to investigate the instantaneous cutting forces when milling carbon fiber-reinforced polymer laminates in a bid to avoid signal distortion and limit the tool wear effect. A polycrystalline diamond tool was selected for the experiments in order to limit the effect of tool wear on the recorded signals. The fiber orientation influences principally the cutting force amplitude, which varies nonlinearly with the feed. Based on this experimental data, a high-order mechanistic force model in terms of feed per tooth was proposed to predict the cutting forces. The tooth-to-tooth run-out was measured and included in the model, and the model was validated for different feeds, speeds, and number of plies. A good consistency between simulated and measured forces was observed. For the proposed model, the estimation error was approximately ±12.5%.

Experimental investigation of the cutting temperature and surface quality during milling of unidirectional carbon fiber reinforced plastic

The surface machining of carbon fiber reinforced plastics materials is a challenging process, given the heterogeneity and anisotropic nature of composites, which, combined with the abrasiveness of the fibers, can produce some surface damage and extensive tool wear. The cutting temperature is one of the most important factors associated with the tool wear rate and machinability of these materials, which are also affected by the mechanical and thermal properties of the workpiece material and the cutting conditions. In this work, the cutting temperature, cutting forces, and composite surface roughness were measured under different cutting conditions for the end milling of unidirectional carbon fiber reinforced plastics. Cutting speeds ranging from 200 to 350 m/min; a feed rate of 0.063 mm/rev; fiber orientations of 0, 45, 90, and 135°; and a 0.5 mm depth of cut were considered. The results show that the cutting speed and fiber orientation have a significant influence on the cutting temperature and cutting forces. The maximum and minimum cutting forces and temperatures were achieved for fiber orientations of 90 and 0°, respectively.

An innovative software architecture to improve information flow from CAM to CNC

Abstract Over the years, machine tool evolution has allowed faster equipment, using new configurations, to manufacture parts that were almost impossible to machine in the past. Despite this tremendous evolution in machine and control technologies, the metalworking industry is still using the old ISO 6983 G-Codes programming interface to control the motion of these machines. This programming interface is not the most flexible or most appropriate for use by new open-architecture machine controllers and object-oriented high-level machining interfaces such as ISO 14649 (STEP-NC). This work proposes an innovative language, the ‘Base Numerical Control Language (BNCL),’ which is based on a low-level simple instruction set-like approach. The architecture is designed around two concepts: the BNCL virtual machine, which acts as a virtual microprocessor, and the BNCL virtual hardware, which is an abstraction of the machine tool. The language is characterised by its simplicity and flexibility, two qualities that are critical in a market in which the capabilities and performance of machines are constantly improving. The proposed architectural concepts are validated through various computer simulation and physical tests, including performance throughput, trajectory driving, and CNC controller extension capabilities.

Effect of Tool Wear on Quality of Carbon Fiber Reinforced Polymer Laminate during Edge Trimming

Polymer matrix composites, particularly carbon fiber reinforced polymers (CFRPs) are widely used in various high technology industries, including aerospace, automotive and wind energy. Normally, when CFRPs are cured to near net shape, finishing operations such as trimming, milling or drilling are used to remove excess materials. The quality of these finishing operations is highly crucial at the level of final assembly. The present research aims to study the effect of cutting tool wear on the resulting quality for the trimming process of high performance CFRP laminates, in the aerospace field. In terms of quality parameters, the study focuses on surface roughness and material integrity (uncut fibers, fiber pull-out, delamination or thermal damage of the matrix), which could jeopardize the mechanical performance of the components. In this study, a 3/8 inch diameter CVD diamond coated carbide tool with six straight flutes was used to trim 24-ply carbon fiber laminates. Cutting speeds ranging from 200 m/min to 400 m/min and feed rates ranging from 1524 mm/min to 4064 mm/min were used in the experiments. The results obtained using a scanning electron microscope (SEM) showed increasing defect rates with increased tool wear. The worst surface integrity, including matrix cracking, fiber pull-out and empty holes, was also observed for plies oriented at -45 degrees. For the surface finish, it was observed that for the studied cutting length ranges, an increase in tool wear resulted in a decrease in surface roughness. Regarding tool wear, a lower rate was observed at lower feed rates and higher cutting speeds, while a higher tool wear rate was observed at intermediate values of our feed rate and cutting speed ranges.

Analysis and modelling of cutting forces during the trimming of unidirectional CFRP composite laminates

CFRPs are increasingly employed in the aircraft industry thanks to their high strength and high rigidity both properties that make them difficult-to-machine materials. Cutting parameters must therefore be selected with care; otherwise, damaged parts will ensue. The present study investigates the instantaneous cutting forces at play when trimming CFRP laminates. An experimental setup is proposed for changing the cutting parameters during trimming operations. The instantaneous cutting forces were recorded at high sampling frequencies, and then analysed and modelled. From the investigation, it was found that for the machined laminates, the fibre orientation does not significantly influence the profile of the tangential and radial forces; however, it influences their amplitude. To confirm that, machining tests were performed on aluminium alloy sheets. These tests allowed a comparison of the behaviour of an isotropic material with that of an orthotropic material. The comparison allowed the localisation of non-linearity sources. Employing these observations, it was demonstrated that the average thrust and feed forces vary non-linearly with the feed. Thus, a third-degree polynomial model was introduced to describe this variation. This mathematical description allowed a high-order mechanistic model to be built, simulating the instantaneous cutting forces for different feeds, speeds and fibre orientations.

On the effect of Johnson Cook material constants to simulate Al2024-T3 machining using finite element modeling

Finite element modeling (FEM) of machining has recently become the most attractive computational tool to predict and optimize metal cutting processes. High speed computers and advanced finite element code have offered the possibility of simulating complex machining processes such as turning, milling, and drilling. The use of an accurate constitutive law is very important in any metal cutting simulation. It is desirable that a constitutive law could completely characterize the thermo-visco-plastic behavior of the machined materials at high strain rate. However, there exist several constitutive laws that are adopted for machining simulation, the choice of which is difficult to make. The most commonly used law is that of Johnson and Cook (JC) which combines the effect of strains, strain rates and temperatures. Unfortunately, the different coefficients provided in the literature for a given material are not reliable since they affect significantly the predicted results (cutting forces, temperatures, etc.). These discrepancies could be attributed to the different methods used for the determination of the material parameters. In the present work, three different sets of JC are determined based on orthogonal machining tests. These three sets are then used in finite element modelling to simulate the machining behavior of Al 2024-T3 alloy. The aim of this work is to investigate the impact of the three different sets of JC constants on the numerically predicted cutting forces, chip morphology and tool-chip contact length. It is concluded that these predicted parameters are sensitive to the material constants.Copyright

Effect of cutting tool lead angle on machining forces and surface finish of CFRP laminates

Abstract Machining is one of the most practical processes for finishing operations of composite components, allowing high-quality surface and controlled tolerances. The high-precision surface milling of carbon fiber-reinforced plastics (CFRP) is particularly applicable in the assembly of complex components requiring accurate mating surfaces as well as for surface repair or mold finishing. CFRP surface milling is a challenging operation because of the heterogeneity and anisotropy of these materials, which are the source of several types of damage, such as delamination, fiber pullout, and fiber fragmentation. To minimize the machining problems of CFRP milling and improve the surface quality, this research focuses on the effect of multiaxis machining parameters, such as the feed rate, cutting speed, and lead angle, on cutting forces and surface roughness. The results show that the surface roughness and cutting forces increase with the feed rate, whereas their variations are not uniform when changing the cutting speed. Generally, a lower surface roughness was achieved by using a lower cutting feed rate (0.063 mm/rev) and higher cutting speeds (250–500 m/min). It was also found that the cutting forces and surface roughness vary significantly and nonlinearly with the lead angle of the cutting tool with respect to the surface.

Machining analysis of unidirectional and bi-directional flax-epoxy composite laminates

Natural fibers, and more particularly, flax fibers, have a considerable potential as replacements for synthetic fibers. These fibers are of significant economic and environmental interest because they are natural products, are biodegradable, and unlike synthetic fibers, are entirely recyclable. They are also less expensive than synthetic fibers, less abrasive for machining, and their specific properties (strength-to-weight ratio) are comparable to those of glass fibers. Consequently, they thus provide economic and environmental benefits for companies. Unfortunately, machining knowledge with respect to this kind of material is low, and research in this domain has barely begun. The objective of this study is to describe the machinability of unidirectional and bidirectional flax/epoxy composites and to analyze the influence of cutting parameters and fiber orientation on cutting forces and surface finish. Milling tests were performed on unidirectional composite laminates with two different tools. The results show that the surface finish and cutting forces depend largely on the feed rate, and to a lesser extent, on the cutting speed. The PCD cutting tool, with a zero helix angle, showed the best performances as compared to the CVD cutting tool, which had a different geometry. The former provided a better surface finish, a lower delamination factor, and lower cutting forces. The material was found to be easy to machine and low abrasive, since no tool wear was observed following the cutting tests. Finally, it was found that an intermediate feed rate value and a high cutting speed were the best of all parameters tested for achieving a low cutting force level, low surface roughness, and high throughput.

Issues and Challenges in Robotic Trimming of CFRP

Thanks to their adaptability, programmability, high dexterity and good maneuverability, industrial robots offer more cutting-edge and lower-cost than machine tools to bring molded Carbon Fibre Reinforced Polymers (CFRPs) parts to their final shapes and sizes. However, the quality of CFRP parts obtained with robotic machining must be comparable to that obtained with a CNC machine. In addition, the robot itself has to be very stiff and accurate to provide the same consistency and accuracy as their machine tool counterparts. If the robot is not sufficiently stiff, chatter, overall vibrations and deviations in shape and position of the workpieces will occur. Furthermore, during robotic machining of Carbon Fibre Reinforced Polymer, the anisotropic and highly abrasive nature of CFRPs combined with the higher cutting forces and the lower stiffness of the robot, lead to numerous machining problems. Therefore, robotic machining of CFRPs stills a big challenge and need further research. In this position paper, a methodology has been developed and implemented to identify, understand and quantify the machining errors that can alter parts accuracy during high speed robotic trimming of CFRPs.