Effect of tool finishing on ejection forces for injection moulded parts made using direct metal laser sintered tools

With the continuing development of Rapid Prototyping technologies, there has been a move into areas of Rapid Tooling. This takes advantage of the shorter lead times and lower costs associated with the production of tooling, particularly for injection moulding. This paper analyses the effectiveness of using direct metal laser sintering to produce injection-moulding tools, in terms of the force required to eject a part from a tool. Different levels of finishing were applied to test tools, and the results show that in some cases the forces required to eject parts from direct metal laser sintered tools were comparable with those from machined tools.     

Predicting stereolithography injection mould tool behaviour using models to predict ejection force and tool strength

The work reported involved Finite Element Analysis (FEA) modelling of heat transfer in a stereolithography (SL) tool and then performing a series of experiments to measure true heat transfer in the tool. The results from the practical measurement of heat transfer were used to validate and modify the FEA model. The results from the modified FEA model were then used to predict the tensile strength of the tool at various stages after injection of the thermoplastic melt. Previously developed equations to predict ejection forces were used to estimate the ejection forces required to push the moulding from the SL core. During the practical experiments the true ejection forces were measured. The combination of predicted tool strength and ejection forces were intended to be used a basis for to determine whether certain SL tool designs will fail under tension during part ejection. This would help designers and manufacturers to decide whether SL tooling is suitable for a specific application. The initial FEA heat transfer model required some modifications and the measured ejection forces were higher than the predicted values, possible reasons for these discrepancies are given. For any given processing conditions there was an inherent variance in the ejection forces required however longer cooling periods prior to ejection resulted in higher ejection forces. The paper concludes that, due to the variations in required ejection forces, a reliable tool to predict tensile failure will be difficult to produce however improved performance may be gained by adopting processing conditions contrary to those recommended in the current process guidelines.     

Hybrid moulds: A case of integration of alternative materials and rapid prototyping for tooling

Hybrid moulds with mouldings blocks made with epoxy composites are being used in injection mouldings of precision parts. In the last decade developments were made in view of applying these production series of thermoplastics injection mouldings. This paper reviews some of the outcomes of research activity on specific issues of manufacturing and utilisation of these tools. Most of the results refer to moulding blocks produced in epoxy composites that were manufactured using the vacuum casting technique. Some references are also made to rapid tooling techniques based on laser sintering.     

Flexural strength of fused filament fabricated (FFF) PLA parts on an open-source 3D printer

Fused filament fabrication (FFF) has been widely used to develop prototypes as well as functional parts owing to its capability for creating parts with complex geometries in a short time without the specific requirement of tooling. The mechanical properties of parts produced by FFF exhibit 70%-80% of the mechanical properties of parts produced by injection molding. The mechanical properties of FFF-produced parts are primarily dependent on the selection of various process variables. The mechanical properties of the part can be enhanced through the proper selection of process variables. In the present experimental investigation, the effects of the process variables, viz. raster angle, layer height, and raster width on the flexural properties of FFF-printed polylactic acid (PLA) is studied. The result shows that flexural strength is primarily influenced by layer height followed by raster angle. The sample printed with 100-μm layer height and 0° raster angle exhibits a higher tensile strength. Further, the microscopic examination of the deformed specimen is performed to understand the mode of failure. Specimens printed at different raster angles show different modes of failure.The full text can be downloaded at https://link.springer.com/article/10.1007/s40436-018-0237-6     

Principles of design for laminated tooling

The emergence of rapid prototyping over the last 7-8 years has had a revolutionary effect in many companies undertaking new product design. Currently, the emphasis has moved from rapid prototyping to rapid tooling. Use of laminated tooling for sheet metal working has already been proved and some work has also been undertaken to build laminated tooling for moulding plastics. Laminated tooling is relatively rare at the moment and as more tools are built using this technique the benefits and limitations will become more clear.     

Application and modelling of hybrid stereolithography injection mould tooling

The use of stereolithography (SL) to make injection moulding tools has been shown previously to be an efficient way of producing rapid tools for simple geometries, aiming at small lot sizes with an acceptable degree of accuracy. This paper highlights the unexplored potential of using SL inserts in hybrid tools using practical experiments and FEA mould filling models. The practical experiments reveal problems incurred by uneven flow as a result of differential thermal conductivity between dissimilar mould materials in a hybrid tool. The FEA flow models confirm that this uneven flow would be anticipated when using finite element analysis (FEA) software. A further FEA stress analysis predicts that catastrophic mould failure will be expected under some conditions and these reflect the results found in the practical experiments. The use of a homogeneous SL tool eliminates the issues caused by uneven mould filling but results in thermal distortion of the female mould. Ultimately, a SL tool backfilled with low melt point alloy provides a solution that eliminates the problems of uneven filling and thermal distortion.     

Application and modelling of hybrid stereolithography injection mould tooling

The use of stereolithography (SL) to make injection moulding tools has been shown previously to be an efficient way of producing rapid tools for simple geometries, aiming at small lot sizes with an acceptable degree of accuracy. This paper highlights the unexplored potential of using SL inserts in hybrid tools using practical experiments and FEA mould filling models. The practical experiments reveal problems incurred by uneven flow as a result of differential thermal conductivity between dissimilar mould materials in a hybrid tool. The FEA flow models confirm that this uneven flow would be anticipated when using finite element analysis (FEA) software. A further FEA stress analysis predicts that catastrophic mould failure will be expected under some conditions and these reflect the results found in the practical experiments. The use of a homogeneous SL tool eliminates the issues caused by uneven mould filling but results in thermal distortion of the female mould. Ultimately, a SL tool backfilled with low melt point alloy provides a solution that eliminates the problems of uneven filling and thermal distortion.     

Spritzgießen keramischer Bauteile

Powder injection moulding of ceramic parts Powder injection moulding is a parts production technology that combines the advantages of plastics injection moulding with the materials properties of ceramics. It makes possible the production of complex shaped parts for high production numbers. Almost all possibilities of parts design used in plastics injection moulding can transfered to ceramics. Paying attention to the special properties of highly filled thermoplastics and the well known rules for parts and tools construction, new parts can be realized in short development times. This article will have a closer look at the parameters for injection moulding, at rules for design of ceramic parts and the corresponding tools as well at a never debinding technology.     

Optimum part deposition orientation for multiple objectives in SL and SLS prototyping

In the present work an attempt has been made to achieve minimum average part surface roughness (best overall surface quality), minimum build time and support structure for stereolithography (SL) and selective laser sintering (SLS) processed parts by determining optimum part deposition orientation. A conventional optimisation algorithm based on a trust region method (available with MATLAB-7 optimisation tool box) has been used to solve the multi-objective optimisation problem. It is observed that the problem is highly multi-modal in nature and a suitable initial guess, which is used as an input to execute the optimisation module, is important to achieve a global optimum. A simple methodology has been proposed to find out the initial guess so that global minimum is obtained. Finally the surface roughness simulation is carried out with optimum part deposition orientation to have an idea of surface roughness variation over the entire part's surface before depositing the part. Case studies are presented to demonstrate the capabilities of the developed system. The major achievements of this work are consideration of multiple objectives for the two rapid prototyping processes, successful use of conventional optimisation algorithm available with MATLAB to handle multiple objectives and development of graphical user interface-based system.     

Squeeze moulding makes prototypes to simulate SMC parts behaviour

Before undertaking the manufacture of steel tooling for fabricating new SMC (Sheet Moulding Compound) parts it is important to ensure that the projected part will meet the required mechanical specifications. The manufacture of prototypes by the squeeze moulding technique is a good answer to this requirement. Such prototypes are representative of the mechanical behaviour of the considered SMC part. They can be obtained at moderate cost and within a reasonable time time span.In this articlethe basis of the technique will be established, and an example of its commercial application, the manufacture prototypes for the Chevrolet Citation bonnet, will be described. The comparison of the behaviour of parts made in SMC and parts made by squeeze moulding is also presented.     

The measurement and analysis of micro bonding force for electroplated CBN grinding wheels based on response surface methodology

The superabrasive (e.g. CBN or diamond) grain dislodgement occurrence on the wheel surface due to insufficient bonding force is the major failure phenomena in the grinding process with electroplated grinding tools. This failure leads to the abrupt increase of load on the immediate grains, accelerating more grain dislodgement on wheel surface. Ultimately, the aggregated grain dislodgement causes the workpiece profile accuracy degradation and catastrophic wheel sharpness loss. Therefore, the provision of sufficient and uniform micro bonding force all through the wheel surface is the critical task in electroplated superabrasive grinding wheel design. Considering the complexity in the micro bonding force enabling factors, e.g. the grain shape, dimensional size, spatial orientation, and bond layer thickness, it is vital to establish the quantitative and comprehensive relationship between these factors with the micro bonding force for optimal electroplated grinding wheel design. In this paper, an inclined micro-thread turning test is developed to measure the single grain micro bonding force. In addition, the finite element model of single CBN grain bonding force is established and validated to simulate the grain dislodgement. Finally, the response surface methodology (RSM) is applied to build the comprehensive correlation of the bonding force with its dimensional size, spatial orientation, and bond layer thickness. Therefore, the optimal bonding condition through regressed prediction model is identified to provide the quantitative basis for the electroplated CBN grinding wheels design, which indicates that the bonding force can be predicted for specific wheel manufacturing parameters and improved by related variable adjustment.     

Effects of gate design and cavity thickness on filling,morphology and mechanical properties of microinjection mouldings

Miniaturized parts weighing up to tens of milligrams represent a large category of microinjection moulded products. Both miniaturization and extreme processing under microinjection moulding cause material to experience high shear rates and high cooling rates, and to have different morphology and final properties from conventional injection moulding. It also makes mould design quite challenging. This study investigates micro gate design (opening and thickness) and cavity thickness (100–500 μm) on filling, morphology and mechanical properties of Poly(ether-block-amide) miniaturized dumbbell parts. It is found that a reduction of gate size has two conflicting effects: increased shear heating increases flow length; increased cooling rate reduces flow length. Filling increases significantly with an increase of cavity thickness. In addition, skin ratio reduces from ∼70% to ∼10%, when part thickness increases from 100 μm to 500 μm. Such oriented skin layer determines molecular orientation and broadly influences Young’s modulus, elongation and yield stress. Natural aging at room temperature induces an increase of modulus and yield stress, and a decrease of strain at break. Mechanical properties of microinjection mouldings are significantly different from conventional injection mouldings and measurement at the microscale is required for successful miniaturized product design.     

Integral approach for production of thermoplastics microparts by injection moulding

Over the last decades, microinjection moulding of thermoplastics has gained a pertinent place on the market of electronic equipment and a broad range of the mechanical aids. However, when size of component drops to the micro-level, the assumptions of the conventional injection moulding cease to describe complex rheological and thermo-mechanical behaviour of the polymer in the microcavity. Miniaturization implies a number of challenges which could only overcome by a series of profound modifications of the conventional injection moulding machine and tools. In the scope of this review, a brief discussion of the strategies applied for adaptation of the conventional injection moulding process to microscale will be introduced. Further, a particular attention will be given to the process/tool/polymer interaction and its influence on the quality signatures of micromoulded parts. In addition an overview of the rheological models of the polymer flow at microcavities and the numerical simulation of the microinjection moulding will then be addressed. Quality evaluation of the micromoulded parts require considering both polymer morphology assessment and final mechanical properties. At microscale, the acquisition of the latter is unlikely by means of conventional mechanical testing, therefore, a brief summary of the mechanical testing for micropolymeric parts will be presented. In order to further evaluate the quality signatures of micromoulded parts an overview of the combined thermo-rheological and structural analysis to link processing history and mechanical solicitations of the part to its short- and long-term performance is also presented here.     

Optimal part deposition orientation in FDM by using a multicriteria genetic algorithm

In rapid prototyping processes, the deposition orientation of the part is very important as it affects part surface quality, production time and the requirement for support structure and hence cost. Depositing the part with thinner slices results in a larger build time. At the same time, if a large slice thickness is chosen, the surface finish is very poor due to stair-stepping. These are two contradicting issues and are tackled by using adaptive slicing. In adaptive slicing, slice thickness is calculated based on local geometry of the computer-aided design model and rapid proto-typing machine specifications. Even though adaptive slicing controls part surface quality by compromising on build time for a deposition orientation, an optimum orientation can further reduce build time and enhance part surface quality. In the present work, an attempt has been made to determine the optimal part deposition orientations by considering two objective functions at a time, namely average part surface roughness (average part surface quality) and build time. The two objectives are minimized simultaneously using a multicriteria genetic algorithm.     

Herstellung metallischer Turbinenbauteile nach der PM-Spritzgießtechnik

P/M Injection Moulding of Metallic Turbine Ports The well known injection moulding technique of ceramic components has been modified for the fabrication of metallic turbine parts. Commercially available super alloy powders, mainly Merl-76 and Udimet-700 were used. The following results have been obtained. Super alloy powder <45 µm can be used with PM injection moulding. After containerless HIP-treatment densities near 100% have been achieved. The tensile strength of the parts meet the requirements, when the surface roughness is reduced by mechanical treatment. The oxygen and carbon content in the finally produced parts is relatively high. But the distribution of the non-metallic inclusions is fine and uniform. So high strength values could be obtained.     

The effects of moulding geometry on the structure and mechanical properties of fibre-reinforced polypropylene structural foam mouldings

The influence of weld lines and changes in moulding section thickness on structure and mechnanical properties has been determined for short glass-fibre reinforced polypropylene structural foam prepared using a short-shot moulding procedure at two different melt injection times. Results are discussed in terms of the variability in skin to core thickness ratio, moulding density and fibre orientation obtained in these mouldings and subsequent effects on flexural stiffness and impact energy to failure.     

熔体温度对注塑成型iPP制品结晶形态的影响

注塑成型聚丙烯制品的内部结晶形态对制品的最终性能起着至关重要的作用,而结晶形态的形成对成型条件(尤其是熔体温度)有一定依赖性。文中利用偏光显微镜、小角X射线散射和广角X射线衍射等实验方法,详细研究了熔体温度对注塑成型iPP制品结晶形态的影响。研究结果表明,在实验温度范围内,制品厚度方向形态呈现五层皮芯结构,即冷冻层、过渡层、剪切层、β晶层、α球晶层。随着熔体温度提高,皮层厚度减小;结晶度提高,取向度极大值并无明显变化。     

浅述精密注塑件的设计

简述了在模具设计前,设计塑料件的重要性,详细阐述了塑料件设计的壁厚、脱模角度、产品表面质量、分型面、模具结构可行性和浇注系统等要求的具体内容,总结了注塑件在结构、外观、模具制造工艺、注塑工艺等方面的一些注意事项。     

Optimization of process parameters in fused deposition modelling of thermoplastics: A review

Among the several techniques for additive manufacturing (AM), fused deposition modelling (FDM) is widely used. Fused deposition modelling process uses a thermoplastic material, which is melted and then extruded layer by layer through a nozzle, in order to create a three-dimensional object. As a result of the default setting of process parameters provided by the manufacturers, produced parts normally have a poor surface finish, low mechanical properties, low dimensional accuracy, and increased residual stresses compared to the parts produced using conventional manufacturing processes like molding (casting). Qualities of fused deposition modelled (FDMed) parts are generally affected by process parameters including the layer thickness, extrusion temperature, build orientation, printing speed, raster angle, infill density, raster width, nozzle diameter, and air gap. Increasing infill density, printing temperature, and decreasing print speed and layer thickness lead to increase mechanical strength and improve the surface finish of the printed parts. The optimal process parameters are preferred to achieve superior properties of the parts. This paper reviews the optimal fused deposition modelling process parameters on part qualities for making the stability of used deposition modelled parts for use. Various process parameters are identified in order to obtain desirable qualities in the manufactured parts. Areas for future research are proposed.     

Effect of Processing on Precision of Composite Panels

As the demand for precision composite parts increases, understanding the effects of processing parameters on composite precision is needed. This study is devoted to observing the warping tendency of angles and investigating the effects of the part thickness, tool material, and stacking orientation on the precision of angled composite parts. Composite parts with both concave and convex angles were fabricated with various thickness, tool material, and stacking orientation. It was found that composite angled parts always warped inward. As the part angle decreased, the warp angle decreased. The resin volume fraction gradient induced a further inward warping tendency at convex angles. Rigidity improvement achieved by increasing the thickness overcame this resin gradient effect. The precision at convex angles was, thus, improved. However, the precision at concave angles worsened with increasing part thickness. The tool material was found to significantly affect the part precision at both concave and convex angles. Angled parts fabricated in molds made of advanced composite tools yielded much better angle precision than that fabricated in mold made of aluminum tools. As far as the stacking orientation was concerned, the best precision at a 135° convex angle was achieved with a stacking orientation of [0/90/0/90/0/90/90/0], whereas at a 90° concave angle the best precision was achieved with [90/0]_4Tfor a laminate of 8 plies. A stacking sequence with a [0/90] orientation was found to cause upward warping. This could be used to counterbalance other inherent warping tendencies.