微结构模芯的精密磨削及其在微注塑成形中应用

针对微结构聚合物元器件的批量化生产与制造效率低等问题,采用精密修整成V形尖端的金刚石砂轮,在自润滑性和脱模性良好的钛硅碳陶瓷模芯表面加工制造出形状精度可控的V沟槽阵列结构,然后利用微注塑成形工艺将模芯表面的V沟槽阵列结构一次成形复制到聚合物表面,高效注塑成形制造出倒V形阵列结构的聚合物工件。分析了微模芯的表面加工质量与形状精度,研究了熔体温度、注射速度、保压压力、保压时间等微注塑成形工艺参数对微结构聚合物注塑成形角度偏差和填充率的影响。实验结果表明:通过微细磨削加工技术和微注塑成形工艺可以高效率、高精度地制造出规则整齐的微结构注塑工件,注射速度对微成形角度偏差的影响最大,保压压力对微成形填充率的影响最大,微结构模芯的微细磨削形状精度值为4.05μm,微成形的最小角度偏差和最大填充率分别为1.47°和99.30%。     

Surface microstructure replication in injection molding

In recent years, polymer components with surface microstructures have been in rising demand for applications such as lab-on-a-chip and optical components. Injection molding has proven to be a feasible and efficient way to manufacture such components. In injection molding, the mold surface topography is transcribed onto the plastic part through complex mechanisms. This replication, however, is not perfect, and the replication quality depends on the plastic material properties, the topography itself, and the process conditions. This paper describes and discusses an investigation of injection molding of surface microstructures. The fundamental problem of surface microstructure replication has been studied. The research is based on specific microstructures as found in lab-on-a-chip products and on rough surfaces generated from EDM (electro discharge machining) mold cavities. Emphasis is put on the ability to replicate surface microstructures under normal injection-molding conditions, i.e., with commodity materials within typical process windows. It was found that within typical process windows the replication quality depends significantly on several process parameters, and especially the mold temperature. For the specific microstructures, evidence suggests that step-height replication quality depends linearly on structure width in a certain range.     

Mold surface roughness effects on cavity filling of polymer melt in micro injection molding

Micro injection molding presents many challenges in the injection-molding community. When the dimensions of the part (and thus the cavity of the mold) are small, micro-scale factors such as mold surface roughness may play an important role in the filling of polymer melt. This paper investigates the effects of mold surface roughness on cavity filling of polymer melt in micro injection molding. A disk insert, which has two halves with different surface roughness but with the same roughness mean lines, was used in the investigations. The ratio of flow area of the rougher half with the total flow area of the molded part is used to evaluate the significance of surface roughness effect. The experimental results revealed that mold surface roughness does resist the cavity filling of polymer melt in micro injection molding. For the limited range of injection rate investigated, it is not significant on the surface roughness effects. The increase of mold temperature will decrease surface roughness effects. The change of melt temperature within the range allowed by the process is insignificant for surface roughness effects.     

Development and machining performance of a textured diamond cutting tool fabricated with a focused ion beam and heat treatment

This paper presents the fabrication method and machining performance of a textured diamond cutting tool. To improve the machining performance, a texture was fabricated on the rake face of the diamond tool with a depth of 43 nm and width of 1.8 μm by utilizing a focused ion beam (FIB) followed by heat treatment. In addition, a FIB-induced non-diamond phase that adversely affects the machining performance was removed. A machining experiment using aluminum alloy and nickel phosphorus was conducted to evaluate the proposed method. A significant decrease in friction was observed at the tool–chip interface after texturing. This corresponds to a reduced cutting force, which indicates that the machining performance of the tool was improved by texturing. The magnitude of the effect depends on the shape and direction of the texture. The textured tool was able to machine a surface topography similar to that with a non-textured tool, which indicates that the texture effect can be obtained while maintaining the quality of the machined surface by fabricating the texture far from the cutting edge.     

Influence of inclusion contents on the micro-machinability of three plastic mold steels

For the manufacturing of micro molds, usually, the same sort of materials is used as for conventional machining. However, phenomena that occur when the depth of cut approaches the cutting edge radius have to be considered. This paper presents experimental investigations on tool life tests of micromilling processes. TiAlN-coated cemented carbide tools are applied on three different mold steels for plastic injection molding. The influences of two different types of inclusions are explored on tool wear, cutting forces, chip formation, burr formation, and surface finishing of the machined specimens.     

微注射成形制品质量影响因素分析

在不同工艺条件下进行聚合物和粉末微注射成形试验,制得微米级的聚丙烯和二氧化锆陶瓷微结构,微型腔采用感应耦合等离子深槽刻蚀技术在硅模具镶块上加工。分析微注射成形工艺及硅模具对微结构的填充、尺寸精度及表面质量的影响。不合理的工艺参数容易导致微结构出现填充不足、表面粗糙、气孔等缺陷,提高模具温度和注射压力以及注射前模具抽真空有利于微型腔的填充,模具抽真空还可以改善微结构件的表面质量。深槽刻蚀后的硅模具表面粗糙度为0.31 μm,填充完好的聚丙烯微结构及陶瓷微结构素坯表面粗糙度不再受注射工艺参数的影响,其值近似于刻蚀后的硅模具,亚微米级粉末的使用可以明显改善烧结后陶瓷微结构的表面粗糙度。     

The design and optimization of micro polycrystalline diamond ball end mill for repairing micro-defects on the surface of KDP crystal

Micro-milling is a promising approach to repair the micro-defects on the surface of KH₂PO₄ (KDP) crystal. The geometrical parameters of micro ball end mill will greatly influence the repairing process as a result of the soft brittle properties of KDP crystal. Two types of double-edged micro ball end mills were designed and a three-dimensional finite element (FE) model was established to simulate the micro milling process of KDP crystal, which was validated by the milling experiments. The rake angle of −45°, the relief angle of 45° and the cutting edge radius of 1.5–2 μm were suggested to be the optimal geometrical parameters, whereas the rake angle of −25° and the relief angle of 9° were optimal just for micro ball end mill of Type I, the configuration with the rake angles ranging from 0° to 35°, by fully considering the cutting force, and the stress–strain distribution over the entire tool and the cutting zone in the simulation. Moreover, the micro polycrystalline diamond (PCD) ball end mills adopting the obtained optimal parameters were fabricated by wire electro-discharge machining (WEDM) and grinding techniques, with the average surface roughness Ra of tool rake face and tool flank face ∼0.10 μm, and the cutting edge radius of the tool ∼1.6 μm. The influence of tool's geometrical parameters on the finished surface quality was verified by the cutting experiments, and the tool with symmetric structure was found to have a better cutting performance. The repairing outlines with Ra of 31.3 nm were processed by the self-fabricated tool, which could successfully hold the growth of unstable damage sites on KDP crystal.     

Cutting force reduction and surface quality improvement in machining of aerospace duralumin AL-2017-T4 using carbon onion nanolubrication system

In machining of very high precision Duralumin AL-2017-T4 for aerospace applications, the shape varieties of the product lead to many different complicated shapes to be developed. The computer numerical control (CNC) milling machine facilities provides a wide variety of parameter set-up, making the machining process on the Duralumin AL-2017-T4 excellent in manufacturing complicated special products compared with other machining processes. However, the demand for high quality and fully automated production focuses attention on the cutting process, which are partial determinant of the quality of surface and affects the appearance, function, and reliability of the products. The key solution is to increase the effectiveness of existing lubrication systems in the machining process in order to improve product quality as it could reduce the friction component at the tool–chip interface. For further improvement, introducing the nanolubrication system could reduce the cutting force and produce much better surface quality as the rolling action of billions units of nanoparticles at the tool–chip interface could reduce the coefficient of friction significantly. In this study, carbon onion has been used as nanoparticle mixed with ordinary mineral oil at different concentrations to investigate the cutting force reduction and the surface quality improvement of CNC end-milling machined Duralumin AL-2017-T4. From the results, with using of carbon onion nanolubricant, the cutting force and surface roughness values are reduced by 21.99 and 46.32 %, respectively, compared with the case of using ordinary lubrication systems. This can be attributed to the tribological properties of carbon onion, which reduces the coefficient of friction at the tool–chip interface during the machining process.     

A numeric investigation of friction behaviors along tool/chip interface in nanometric machining of a single crystal copper structure

The interaction between the tool rake face and the chip is critical to chip morphology, cutting forces, surface quality, and other phenomena in machining. A large body of existing literature on nanometric machining or nano-scratching only considers the overall friction behavior by simply regarding the total force along tool movement direction as the friction force, which is not suitable for describing the intriguing friction phenomena along the tool/chip interface. In this study, the molecular dynamic (MD) simulation is used to model the nanometric machining process of single crystal copper with diamond tools. The effects of three factors, namely, tool rake angle, depth of cut, and tool travel distance, are considered. The simulation results reveal that the normal force and friction force distributions along tool/chip interface for all cases investigated are similarly shaped. It is found that the normal force consistently increases along the entire tool/chip interface when a more negative rake angle tool is used. However, the friction force increases as the rake angle becomes more negative only in the contact area close to the tool tip, and it reverses the trend in the middle of tool/chip interface. Meanwhile, the increase of depth of cut overall increases the normal force along the tool/chip interface, but the friction force does not necessarily increase. Also, the progress of tool into the work material does not change the patterns of normal force, friction force, or friction coefficient distributions to a great extent. More importantly, it is discovered that the traditional sliding model with a constant friction coefficient can be used to approximate the later section of friction distributions. However, no friction model for traditional machining is appropriate to describe the first section of friction distributions obtained from the MD simulation.     

Automated surface finishing of plastic injection mold steel with spherical grinding and ball burnishing processes

This study investigates the possibilities of automated spherical grinding and ball burnishing surface finishing processes in a freeform surface plastic injection mold steel PDS5 on a CNC machining center. The design and manufacture of a grinding tool holder has been accomplished in this study. The optimal surface grinding parameters were determined using Taguchi’s orthogonal array method for plastic injection molding steel PDS5 on a machining center. The optimal surface grinding parameters for the plastic injection mold steel PDS5 were the combination of an abrasive material of PA Al₂O₃, a grinding speed of 18000 rpm, a grinding depth of 20 μm, and a feed of 50 mm/min. The surface roughness R_a of the specimen can be improved from about 1.60 μm to 0.35 μm by using the optimal parameters for surface grinding. Surface roughness R_a can be further improved from about 0.343 μm to 0.06 μm by using the ball burnishing process with the optimal burnishing parameters. Applying the optimal surface grinding and burnishing parameters sequentially to a fine-milled freeform surface mold insert, the surface roughness R_a of freeform surface region on the tested part can be improved from about 2.15 μm to 0.07 μm.     

超声振动和切削液联合作用下的刀刃非物理锐化

超声辅助切削和切削液的联合使用能减小切削力和降低表面粗糙度,试图说明其机理,目的是为开发精密和超精加工技术打下基础。超声辅助切削和切削液的联合使用,从性质上改变了刀刃施加给工件表面的作用力,包括摩擦力和压力：在无切削液情况下,刀刃切入时,前刀面和后刀面施加给被切削面的摩擦力方向是指向刀刃;在有切削液情况下,刀刃切入时,前刀面和后刀面施加给被切削面的摩擦力方向是背向刀刃。背向刀刃的摩擦力,相对于指向刀刃的摩擦力而言,会导致剪切角增大,等效于更锋利的刀刃所产生的剪切角;切削液的存在使得刀刃施加给工件的力更加集中,等效于圆角半径更小的刀刃所能达到的效果;切削液在刀尖部位的压力分布不利于工件表面产生微裂纹。也就是说,超声辅助切削和切削液的联合使用起到了更锋利即更小圆角半径刀刃所起的效果,称之为非物理锐化。     

An experimental study on ejection forces of injection molding

In injection molding, the ejection forces decrease when the surface roughness of mold decreases. However, the ejection forces increase contrary in the area of surface roughness is less than 0.2 μmRa. Several kinds of PVD films are coated on the mold cores to prevent the increasing of ejection forces. Some of these PVD films showed effective prevention of increasing of ejection forces.     

A study of die helical thread cavity surface finish made by Cu-W electrodes with planetary EDM

An experimental research study intended for the application of a planetary electrical discharge machining (EDM) process with copper-tungsten (Cu-W) electrodes in the surface micro-finishing of die helical thread cavities made with AISI H13 tool steel full-hardened at 53 HRC is presented. To establish the EDM parameters’ effect on various surface finishing aspects and metallurgical transformations, three tool electrode Cu-W compositions are selected, and operating parameters such as the open-circuit voltage (U ₀), the discharge voltage (u _e), the peak discharge current (î _e), the pulse-on duration (t _i), the duty factor (τ) and the dielectric flushing pressure (p _in), are correlated. The researched machining characteristics are the material removal rate (MRR—V _w), the relative tool wear ratio (TWR—?), the workpiece surface roughness (SR—Ra), the average white layer thickness (WLT—e _wl) and the heat-affected zone (HAZ—Z _ha). An empirical relation between the surface roughness (SR—Ra) and the energy per discharge (W _e) has been determined. It is analysed that copper-tungsten electrodes with negative polarity are appropriate for planetary EDM die steel surface micro-finishing, allowing the attaining of good geometry accuracy and sharp details. For die steel precision EDM, the relative wear ratio optimum condition and minor surface roughness takes place at a gap voltage of 280 V, discharge current of 0.5–1.0 A, pulse-on duration of 0.8 μs, duty factor of 50%, dielectric flushing pressure of 40 kPa and copper tungsten (Cu20W80) as the tool electrode material with negative polarity. The copper-tungsten electrode’s low material removal rate and low tool-wear ratio allows the machining of EDM cavity surfaces with an accurate geometry and a “mirror-like” surface micro-finishing. A planetary EDM application to manufacture helical thread cavities in steel dies for polymer injection is presented. Conclusions are appointed for the planetary EDM of helical thread cavities with Cu-W electrodes validating the accomplishment as a novel technique for manufacturing processes.     

EFFECT OF PROCESS PARAMETERS AND TOOL SHAPE ON THE MACHINABILITY OF A PARTICULATE FILLED-POLYMER COMPOSITE MATERIAL FOR RAPID TOOLING

This paper presents the results of an experimental study on the effects of machining parameters (cutting speed, feed, depth of cut) and tool shape on chip formation, surface topography, resultant cutting force and surface roughness produced in flat and ball end milling of the Ren Shape-Express 2000™ aluminum particulate filled-polymer composite material. This material is shown to exhibit a brittle-to-ductile transition in chip formation with decreasing cutting speed. The transition is explained by the strain-rate sensitivity of the polymer matrix and is found to correlate well with a corresponding change in the surface roughness. The absence of clear feed marks on the milled surface explains why molds made from the composite material require less hand polishing than machined metal molds. The influence of cutting conditions and tool shape (flat end vs. ball-nose) on the cutting force, surface roughness, and workpiece breakout are discussed and relevant comparisons with conventional metal and polymer machining are made.     

Surface generation modeling of micro milling process with stochastic tool wear

Micro milling is widely used to manufacture miniature parts and features at high quality with low set-up cost. To achieve a higher quality of existing micro products and improve the milling performance, a reliable analytical model of surface generation is the prerequisite as it offers the foundation for surface topography and surface roughness optimization. In the micro milling process, the stochastic tool wear is inevitable, but the deep influence of tool wear hasn't been considered in the micro milling process operation and modeling. Therefore, an improved analytical surface generation model with stochastic tool wear is presented for the micro milling process. A probabilistic approach based on the particle filter algorithm is used to predict the stochastic tool wear progression, linking online measurement data of cutting forces and tool vibrations with the state of tool wear. Meanwhile, the influence of tool run-out is also considered since the uncut chip thickness can be comparable to feed per tooth compared with that in conventional milling. Based on the process kinematics, tool run-out and stochastic tool wear, the cutting edge trajectory for micro milling can be determined by a theoretical and empirical coupled method. At last, the analytical surface generation model is employed to predict the surface topography and surface roughness, along with the concept of the minimum chip thickness and elastic recovery. The micro milling experiment results validate the effectiveness of the presented analytical surface generation model under different machining conditions. The model can be a significant supplement for predicting machined surface prior to the costly micro milling operations, and provide a basis for machining parameters optimization.     

Fundamental investigation on partially overlapped nano-cutting of monocrystalline germanium

Molecular dynamics simulations on partially overlapped nano-cutting of monocrystalline germanium with different feeds are carried out to investigate the surface topography, cutting force and subsurface deformation. The results indicate that the side-flow material piling up on the edges of tool marks is a decisive factor for the surface topography with the machining parameters in this study, ignoring the tool wear and machining vibration. In the partially overlapped nano-cutting, the lateral force is more affected by nominal depth of cut than by pitch feed with the value of feed being in some range. The atomic sights on the subsurface deformation show that the thickness of deformed layer after machining is much thinner than that after single cut with the same nominal depth of cut. Laser micro-Raman spectroscopy and cross-sectional transmission electron microscopy are used to detect the subsurface deformation of monocrystalline germanium after eccentric turning. The crystalline structure with defects rather than the amorphous germanium is observed in many areas of machined surface. Both molecular dynamics simulation and experimental results indicate that the amorphous-damage-less and even amorphous-damage-free machined surface can be achieved by partially overlapped nano-cutting.     

On the prediction of surface roughness in the hard turning based on cutting parameters and tool vibrations

This research work concerns the elaboration of a surface roughness model in the case of hard turning by exploiting the response surface methodology (RSM). The main input parameters of this model are the cutting parameters such as cutting speed, feed rate, depth of cut and tool vibration in radial and in main cutting force directions. The machined material tested is the 42CrMo4 hardened steel by Al₂O₃/TiC mixed ceramic cutting tool under different conditions. The model is able to predict surface roughness of Ra and Rt using an experimental data when machining steels. The combined effects of cutting parameters and tool vibration on surface roughness were investigated while employing the analysis of variance (ANOVA). The quadratic model of RSM associated with response optimization technique and composite desirability was used to find optimum values of cutting parameters and tool vibration with respect to announced objectives which are the prediction of surface roughness. The adequacy of the model was verified when plotting the residuals values. The results indicate that the feed rate is the dominant factor affecting the surface roughness, whereas vibrations on both pre-cited directions have a low effect on it. Moreover, a good agreement was observed between the predicted and the experimental surface roughness. Optimal cutting condition and tool vibrations leading to the minimum surface roughness were highlighted.     

An experimental work on the effect of injection molding parameters on the cavity pressure and product weight

The injection molding process is one of the most efficient processes where mass production through automation is feasible and products with complex geometry at low cost are easily attained. In this study, an experimental work is performed on the effect of injection molding parameters on the polymer pressure inside the mold cavity. Also, the effect of these parameters on the final products' weight is studied. Different process parameters of the injection molding are considered during the experimental work (packing pressure, packing time, injection pressure, injection time, and injection temperature). Two polymer materials are used during the experimental work (polystyrene (PS) and low-density polyethylene (LDPE)). The mold cavity has a cuboidal form with two different thicknesses. The cavity pressure is measured with time by using pressure Kistler sensor at different injection molding cycles. The results indicate that the cavity pressure and product weight increase with an increase in the packing pressure, packing time, and injection pressure for all the analyzed polymers. They also show that the increase of the filling time decreases the cavity pressure and decreases the product weight in case of PS and LDPE. The results show that the increase of packing pressure by 100 % increases the cavity pressure 50 % in the case of PS and 70 % in the case of LDPE. They also show that the increase of injection pressure by 60 % increases the cavity pressure 36 % in case of PS and 90 % in case of LDPE at an injection temperature of 220 °C. The results indicate that process parameters have an effect on the product weight for LDPE greater than PS. The results obtained specify well the developing of the cavity pressure inside the mold cavity during the injection molding cycles.     

Optimizing end-milling parameters for surface roughness under different cooling/lubrication conditions

The effect of cutting parameters on average surface roughness (Ra) in the different cooling/lubrication conditions, including minimal quantity lubrication, wet and dry cutting, was analyzed in this study. Orthogonal arrays were applied in the design of experiments, and Ti6Al4V end-milling experiments were performed on the Daewoo machining center. The white light interferometer (Wyko NT9300) was used to obtain the 3D profile of machined surface and calculate Ra values. Then, exponential model and quadratic model were proposed to fit the experimental data of surface roughness, respectively. Exponential fit model was employed to determine the significant cutting parameters on average surface roughness. Quadratic fit model was used to optimize the cutting parameters when cutting tool and material removal rate were given. The optimal average surface roughnesses were estimated according to the quadratic model. Finally, the verification experiments were performed, and the experimental results showed good agreement with the estimated results.     

基于VERICUT的虚拟数控加工刀具轨迹优化

虚拟物理数控加工仿真主要研究加工过程中切削力、切削热、机床运动误差、加工系统颤振以及负载变化引起加工结果变化的预测问题,目前已成为虚拟制造最具魅力的地方。通过在VERICUT下的电吹风外壳模盖的虚拟数控加工刀具轨迹优化研究,为复杂曲面零件的加工生产提供了有效参考。