Laser machining of WC-Co green compacts for cutting tools manufacturing

Nowadays, conventional machining of WC-Co green compacts is used in industries in order to achieve desired dimensions, complex geometries and good surface quality. However, conventional machining presents some problems, namely tool wear, tool breakage, chatter, vibration and deflection besides mechanically induced damage to the compact. Laser machining is a promising approach to machine WC-Co green compacts, since it is performed without contact and allows great flexibility for producing several geometries, high material removal rate, good surface quality and precision, also for complex shapes. It also allows the production of details smaller than 0.2 mm, hardly manufactured by conventional machining, due to the brittle nature of cutting tools of very small dimensions. Due to the abovementioned reasons, laser machining presents a great potential for lowering the production costs of cemented carbide tools.This work addresses the laser machining of WC-Co green compacts, using a Nd:YAG laser and performing different strategies and combinations of laser parameters to obtain different types of profiles (grooves, areas and specific geometries).Results showed that an effective laser machining of WC-Co green compacts is attained when using laser power of 3 W, scan speed of 128 mm/s, 8 passages and line spacing of 0.08 mm. These parameters were effective for obtaining around 800 μm depth geometries, where the addition of a finishing step (1.5 W, 256 mm/s and 8 passages) improved the quality of the edge of the machined geometry. The laser machined compacts were sintered using a SinterHIP process and no undesirable phases were detected, as eta-phase or graphite.     

Quality optimisation for laser machining under transient conditions

Quality improvements in laser machining have been achieved by a newly developed model-based optimisation strategy. The specific aims of such efforts are to assure machining quality right up to boundaries or pre-machined sections, which are inherent in intricate part geometry. Such boundaries frustrate heat-transfer and result in bulk heating of the workpiece. This in turn leads to a degradation of the machining quality. In order to achieve such optimisation, transient heat-transfer is modeled. Close inspection of the laser–workpiece interaction zone reveals that the machining front exhibits dynamic behaviour, and such mobility plays a significant role in temperature determination. Non-linear parameter adaption profiles are generated via the optimisation strategy in order to stabilise the machining front temperatures. Currently, trial-and-error based experimentation is needed in order to improve machining quality in such regions. Thus model-based optimisation has the added benefit of reducing this step whilst leading to an optimal solution. Experimental results are presented and it is demonstrated that such process manipulation can lead to significant quality improvements.     

面向制造业的先进生产模式CIMS的发展趋势

论述了现代集成制造系统(CIM／CIMS)组成体系及其主要研究内容，分析了现代集成制造系统的发展趋势，阐明了现代集成制造系统是制造业企业获得良好社会效益和经济效益的先进生产模式之一。     

A hybrid machining center for enabling new die manufacturing and repair concepts

This paper presents an analysis of a scanner-based laser cladding process and its integration into a hybrid machining center. After deducing a robust set of process parameters from experiments for scanner-based cladding which reliably yield defined geometries, we present an automation architecture to encapsulate the hardware that is specific to this process. We then describe a planning approach in CAM software to facilitate using the scanner-based cladding process within a planning framework for milling processes. After introducing a hybrid laser tool which enables new stabilizing process possibilities we conclude with an approach to combine all these findings into a seamless machine concept of which we present a prototype.     

Picosecond laser machining of tungsten carbide

Hard materials such as tungsten carbide (WC) are extensively used in cutting tools in high-value manufacturing, and the machining of these materials with sufficient speed and quality is essential to exploit their full potential. Over the last two decades, short (nanosecond (ns)) and ultra-short (picosecond (ps); femtosecond (fs)) pulse laser machining has been evaluated by various researchers and proposed as an alternative to the current state-of-the-art machining techniques for advanced materials like WC, which include mechanical grinding and electrical discharge machining. However, most of the established/existing research on this topic is based on low power lasers, which may not be adopted in industrial production environments due to its low material removal rate. This paper presents the results of a fundamental study, on using a 300 W picosecond laser for the deep machining of tungsten carbide. The influence of various laser parameters on the geometric precision and quality (surface and sub-surface) of the ablated area was analysed, and the ablation mechanism is discussed in detail. Laser pulse frequency and scanning speed have minimal effect on ablation rate at high power levels. The surface roughness of the ablated area increases with the ablation depth. At optimal conditions, no significant thermal defects such as a recast layer, micro crack or heat affected zone were observed, even at a high average power of 300 W. The material removal rate (MRR) seems to be proportional to the average power of the laser, and a removal rate of around 45 mm³ per minute can be achieved at 300 W power level. Edge wall taper appears to be a significant issue that needs to be resolved to enable industrial exploitation of high power ultra-short pulse lasers.     

Integrated cut and place module for high productive manufacturing of lithium-ion cells

A main reason for the high costs of lithium-ion cells is the complexity of the assembly process. Especially, creating the cell stack is an inefficient process due to an immature handling and aligning of the limp electrodes and separators. This paper focuses therefore on the methodical development of a functionally integrated assembly module that combines cutting and handling of electrode sheets to increase stacking accuracy, process reliability and productivity. Based on an analysis of requirements and functions, a technical solution has been identified and will be illustrated. At the end, the realized module is described and its performance is proven by experimental validation.     

高速加工的CAM技术与模具加工

论述了高速加工的特点及技术要求，给出了高速加工的实现方法－基于材料贸量的加工。指出贸量加工不仅是实现高速加工的有效方法，而且是智能加工的技术基础。     

Energy-efficient manufacturing on machine tools by machining process improvement

This paper aims to provide information on process improvement for energy-efficient manufacturing. A machine tool has the highest rate of energy consumption among plant equipment. There are effective ways to reduce energy consumption of machine tools such as reducing required energy, shutting down the power to standby equipment, and shortening the cycle time. This paper introduces several approaches for process improvement such as optimizing the cutting conditions and the inclination angle of the tool in 5-axis machining. Minimizing the use of fluid and using control functions are also shown to be effective.     

Visualization of electro-physical and chemical machining processes

This paper aims to visualize spatio-temporal phenomena in electro physical and chemical processes in order to understand machining mechanisms and to achieve a technological breakthrough. In situ measurement methods to visualize the time evolution of stress, strain, temperatures, fluid velocities, and species density distributions, together with 2D or 3D images of the workpieces being processed are summarized. Applications of these methods to fundamental studies on electrical discharge machining, electrochemical machining, laser processing and additive manufacturing are introduced. Signal recording and processing technologies and real time monitoring enabling closed-loop feedback control are also discussed.     

Water-assisted laser thermal shock machining of alumina

A combined experimental and computational approach was undertaken to investigate water-assisted laser cutting of 96% pure alumina specimens through controlled thermal shock fracture mechanism. A low-power CO₂ laser (<300 W) was used for localized heating and scribing of alumina samples followed by water quenching to induce thermal stress cracking. In order to elucidate the cutting mechanisms and identify the regime of processing conditions suitable for controlled fracture, laser cutting experiments were performed under two different environments: water-assisted laser cutting and dry laser cutting. Temperature profiles of the heat-affected zones were obtained using thermocouples and data acquisition system. Finite element analysis was applied to predict the temperature and thermal stress distributions developed during both water-assisted and dry laser cutting operations. Temperature histories of the samples recorded during cutting were compared with numerical model predictions to determine heat transfer parameters associated with wet and dry laser cutting of alumina samples. Both experimental data and numerical analysis indicate that water quenching makes a substantial difference in thermal stress distribution, which governs the ability to control the fracturing of alumina. This in turn, resulted in better control of cutting and higher feed rates than previously reported in laser machining of alumina.     

On-machine three-dimensional monitoring technique using machining laser

An on-machine three-dimensional monitoring system has been developed that uses machining YAG laser as a source of light for monitoring. In the monitoring stage, the output of the laser is decreased. The reflected light from a workpiece is taken out with a beam sampler on the way of the optical system, and observed by CMOS image sensor. This system can measure both Z-direction depth and the position of X–Y-direction. Because the same laser and the optical system are used, the system has no gap of an optical axis between the measurement and the machining, and also has no limitation of viewing angle. Every three-dimensional shape which can be machined by laser beam can be measured. In this paper, system configuration, monitoring technique and the experimental results are described.     

Mechanisms and processing limits in laser thermochemical machining

Metallic microparts can be produced with high quality by laser thermochemical machining when the etching liquid is injected coaxially to the laser beam directly into the irradiated area. The basic mechanisms and limits of the process are described. It is shown that the reaction is temperature driven independent of the laser wavelength. A limiting factor is the diffusion of the anions identified by comparing experimentally determined and calculated diffusion coefficients for the reaction products. The machining quality with respect to aspect ratio, edge radius and roughness can be enhanced by increasing the velocity of the etching liquid.     

数控电火花多轴联动斜向加工在模具加工中的应用

介绍了模具加工中运用数控电火花多轴联动斜向加工方法的实例,列出了典型的数控加工程序,并对应用实例的技巧之处作了详细的分析,是模具企业数控电火花加工值得借鉴的加工方法。     

Comprehension of chip formation in laser assisted machining

Laser Assisted Machining (LAM) improves the machinability of materials by locally heating the workpiece just prior to cutting. Experimental investigations have confirmed that the cutting force can be decreased, by as much as 40%, for various materials. In order to understand the effect of the laser on chip formation and on the temperature fields in the different deformation zones, thermo-mechanical simulations were undertaken. A thermo-mechanical model for chip formation was also undertaken. Experimental tests for the orthogonal cutting of 42CrMo4 steel were used to validate the simulation. The temperature fields allow us to explain the reduction in the cutting force and the resulting residual stress fields in the workpiece.     

Thermal effects in laser assisted jet electrochemical machining

The purpose of the laser in laser assisted jet ECM (LAJECM) is to localise machining to specified areas so that precision and the productivity is improved. Temperature is a predominant determinant of this localisation effect and must be carefully monitored to avoid any heat affected zones or spark damage due to electrolyte boiling. This paper investigates the thermal effects in LAJECM on several alloys by temperature distribution modelling and experimental analysis. The laser influence on material micro removal has led to 25 μm deeper cavities with a reflective surface of roughness 20 nm R_a, without any detectable heat affected zone.     

Direct laser assisted machining with a sapphire tool for bulk metallic glass

Bulk metallic glasses (BMGs) are amorphous metallic alloys with high strength and hardness. This paper discusses the machining process of Zr-BMG using a transparent sapphire tool with direct laser assistance. The laser beam passes through the tool and directly heats the workpiece material to improve its machinability. Micro textures were generated on the tool rake face to facilitate chip formation. Reduced cutting forces and improved surface finish were observed with direct laser assistance. The effects of machining speed and laser power on the material deformation mechanism were investigated. A finite element model was developed to investigate the cutting forces.     

Analysis–synthesis of dimensional deviation of the machining feature for discrete-part manufacturing processes

Dimensional deviation analysis has been an active and important research topic in mechanical design, manufacturing processes, and manufacturing systems. This paper proposes a comprehensive dimensional deviation evaluation framework for discrete-part manufacturing processes (DMP). A generic, explicit, and transmission model is developed to describe the dimensional deviation accumulation of machining processes by means of kinematic analysis of relationships between fixture error, datum error, machine tool geometric error, fixturing force inducing error and the dimensional quality of the product. The developed modeling technology can deal with general fixture configurations. In addition, the local contact deformations of the workpiece–fixture system are determined by solving a nonlinear programming problem of minimizing the total complementary energy of the frictional workpiece–fixture subsystem in machining system. Moreover, the deviation of an arbitrary point on machining feature can be also evaluated based on a point deviation model with prediction dimension deviation from the transmission model. The dimensional error transmission within the machining process is quantitatively described in this model. A systematic procedure to construct the model is presented and validated. This model can be also applied to process design evaluation for complicated machining processes.     

CAXA制造工程师在模具表面精加工中的应用

CAXA制造工程师2006对模具表面精加工提供了多种加工方式,虽对同一零件用几种加工方式都能实现,但是加工后的零件表面质量和加工效率却存在一定的差异,以变半径简单曲面加工、多曲面形成的凸模和凹模加工以及模具的两轴半加工为例,对适合不同形状的模具零件的加工方式进行了比较和研究。