Laser beam machining (LBM) is one of the most widely used thermal energy based non-contact type advance machining process which can be applied for almost whole range of materials. Laser beam is focussed for melting and vaporizing the unwanted material from the parent material. It is suitable for geometrically complex profile cutting and making miniature holes in sheetmetal. Among various type of lasers used for machining in industries, CO2 and Nd:YAG lasers are most established. In recent years, researchers have explored a number of ways to improve the LBM process performance by analysing the different factors that affect the quality characteristics. The experimental and theoretical studies show that process performance can be improved considerably by proper selection of laser parameters, material parameters and operating parameters. This paper reviews the research work carried out so far in the area of LBM of different materials and shapes. It reports about the experimental and theoretical studies of LBM to improve the process performance. Several modelling and optimization techniques for the determination of optimum laser beam cutting condition have been critically examined. The last part of this paper discusses the LBM developments and outlines the trend for future research.

/pdf/laser-beam-machining-a-review-kavveu0ges.pdf

Laser beam machining—A review

Machining of Composite Materials

In this paper, a concept of delamination factor F d (i.e. the ratio of the maximum diameter D max in the damage zone to the hole diameter D ) is proposed to analyze and compare easily the delamination degree in the drilling of carbon fiber-reinforced plastic (CFRP) composite laminates. Experiments were performed to investigate the variations of cutting forces with or without onset of delamination during the drilling operations. The effects of tool geometry and drilling parameters on cutting force variations in CFRP composite materials drilling were also experimentally examined. The experimental results show that the delamination-free drilling processes may be obtained by the proper selections of tool geometry and drilling parameters. The effects of drilling parameters and tool wear on delamination factor are also presented and discussed. Cutting temperature has long been recognized as an important factor influencing the tool wear rate and tool life. An experimental investigation of flank surface temperatures is also presented in this paper. Experimental results indicated that the flank surface temperatures increase with increasing cutting speed but decreasing feed rate. Optimal cutting conditions are proposed to avoid damage from burning during the drilling processes.

Some experimental investigations in the drilling of carbon fiber-reinforced plastic (CFRP) composite laminates

Drilling of fiber reinforced plastics: A review

An evenly and smoothly distributed abrasion wear, observed along the entire cutting edge of an uncoated carbide drill bit in drilling CFRPs, is due to the highly abrasive nature of the carbon fibres. A very few researchers have only quoted this wear mode as being responsible for giving rise to the rounding of the cutting edge, or its bluntness. However, this wear feature has seldom been investigated, unlike the conventional flank wear in practice. This paper offers a new approach in unveiling and introducing the cutting edge rounding (CER) – a latent wear characteristic as a measure of sharpness/bluntness – of uncoated cemented carbide tools during drilling CFRP composite laminates. Four different types of drills (conventional and specialised) were tested to assess the applicability and relevance of this new wear feature. Mechanical loads (drilling thrust and torque) were recorded, and the hole entry and exit delamination were quantified. For the utilised tools, the accruing magnitude of CER was also recorded, in parallel with studying their conventional flank wear. Very appreciable correlations between the CER and the drilling loads, and also the quantitative delamination results are observed. Results reveal that this new wear type develops almost similarly for the selected tools and is practically independent of their respective conventional flank wear patterns. Moreover, a distinct, non-zero magnitude of the CER for a very fresh tool state may provide researchers with some lucid information in further studying the results during wear tests, more emphatically. The CER correlations with quantitative delamination results are noticed quite comparable to those of the conventional flank wear via statistical linear regression analyses.

Cutting edge rounding: An innovative tool wear criterion in drilling CFRP composite laminates

Drilling tests were carried out on glass fibre reinforced plastic composites, in order to verify the effect of machining parameters on the cut quality and on the mechanical behaviour of the material under examination. A novel method was adopted to measure the width of the damage zone. The experimental data showed that the width of the damage zone is correlated to the ratio between drilling speed and feed rate, Vr/Vt; in particular, the higher the Vr/Vt value, the better the cut quality. The damage zone decreases to a minimum value for a definite Vr/Vt, beyond which damage zone constant. The tensile strength of specimens with holes is not influenced by the quality of the material at the edge of the hole, whereas the bearing strength suffers a marked reduction with increasing damage zone width when the latter is large. For small damage zone widths, no correlation seems to exist between the bearing strength and the damaged zone.

Effect of drilling parameters on the finish and mechanical properties of GFRP composites

A simple one-parameter thermal model, predicting the maximum feed rate still resulting in a through cut as a function of beam power, focal spot diameter and thickness of worked material is presented and discussed for CO 2 laser cutting of composites. An extensive experimental program, including glass, carbon and aramide fabric reinforced polyester resin was carried out by varying all the parameters involved in the model. An excellent agreement is shown between experimental data and theoretical predictions. In addition, a criterion for cut quality classification, based on kerf geometry and heat affected zone size is formulated to help in selecting the optimum cutting conditions in order to obtain the best cut quality.

G. Caprino

Papers

Effect of drilling parameters on the finish and mechanical properties of GFRP composites

Maximum cutting speed in laser cutting of fiber reinforced plastics