Part shrinkage anomilies from stereolithography injection mould tooling

The use of stereolithography (SL) tooling allows plastic parts to be produced by injection moulding in a very short time due to the speed of mould production. One of the supposed advantages of the process is that it provides a low volume of parts that are the same as parts that would be produced by the conventional hard tooling in a fraction of the time and cost.However, this work demonstrates different rates of polymer shrinkage are developed by parts produced by SL and conventional tooling methods. These revelations may counter the greatest advantages of the SL injection moulding tooling process as the parts do not replicate those that would be produced by conventional hard tooling.This work identifies the different shrinkage that occurs in mouldings produced by an SL mould as compared to those produced from an aluminium mould. The experiments utilise two very different types of polymers and two mould geometries, which are processed in the same manner so that the heat transfer characteristics of the moulds are isolated as the only experimental variable.The work demonstrates how the two mould materials exhibit very different rates of expansion due to the temperature profiles experienced during moulding. This expansion must be compensated for to establish the total amount of shrinkage incurred by moulded parts. The compensation is derived by a mathematical approach and by modelling using finite element analysis. Both techniques depend upon knowledge of the thermal conditions during moulding. Knowledge of these thermal conditions are obtained by real-time data acquisition and simulated by FEA modeling. The application of the findings provide knowledge of the complete shrinkage values relating to the mould material and polymer used which would enable the production of geometrically accurate parts.     

基于SL原型的电弧喷涂快速模具工艺研究

介绍了使用光固化成型件作为母模进行电弧喷涂快速制模的关键工艺,包括光固化成型件制作、母模制备、金属型壳制备、背衬制作、脱模以及后处理等。工艺具有母模制备灵活、制模工艺路线短、易脱模和金属型壳表面质量高等优点。根据工艺路线,制备了1副用于注射成型的Zn-Al合金快速模具,验证了该工艺在实际工程中的应用。     

Rapid tooling analysis of Stereolithography injection mould tooling

Increasing competition in global markets is exerting intense pressure on companies to trim their product cycles continuously. As delivery times and costs of tools are on a downward trend, the modern tool manufacturer is under pressure to produce tools quickly, accurately and at a lower cost. Reducing the time to produce prototypes is a key to speed up the development of new products. Rapid tooling (RT) with particular regard to injection mould fabrication using rapid prototyping (RP) technology of Stereolithography (SL) may lead to savings in cost and time. In this paper, SL is used to directly build rapid injection mould tools for short run production. SL tools have been evaluated to analyse the maximum number of successful injections and quality of performance. SL epoxy tools were able to resist the injection pressure and temperature and 500 injections were achieved. The tool failure mechanisms during injection are investigated and tool failure either occurs due to excessive flexural stresses, or because of excessive shear stresses.     

Rapid manufacturing of metal components by laser forming

This overview will focus on the direct fabrication of metal components by using laser-forming techniques in a layer-by-layer fashion. The main driving force of rapid prototyping (RP) or layer manufacturing techniques changed from fabrication of prototypes to rapid tooling (RT) and rapid manufacturing (RM). Nowadays, the direct fabrication of functional or structural end-use products made by layer manufacturing methods, i.e. RM, is the main trend. The present paper reports on the various research efforts deployed in the past decade or so towards the manufacture of metal components by different laser processing methods (e.g. selective laser sintering, selective laser melting and 3-D laser cladding) and different commercial machines (e.g. Sinterstation, EOSINT, TrumaForm, MCP, LUMEX 25, Lasform). The materials and applications suitable to RM of metal parts by these techniques are also discussed.     

The structure of parts produced by stereolithography injection mould tools and the effect on part shrinkage

Stereolithography (SL) tooling for plastic injection moulding provides a low cost and quick alternative to hard tooling methods when producing a small quantity of parts. However, work by the authors has shown that a different rate of polymer shrinkage was experienced in semi-crystalline parts when produced from SL moulds as compared to those from conventional metal tooling methods. Different shrinkage means the parts are not truly the same as those that would be produced by metal tooling and highlights a disadvantage to SL tooling.This work associates the increased shrinkage experienced to a greater percentage crystallinity developed in the parts due to their thermal history during processing. In these experiments the cooling rate, which is imparted due to the heat transfer characteristics of the mould has been identified as the controlling factor of a parts % crystalline content and the cause of shrinkage anomalies.The morphology analysis results show that there is 30% more crystallinity developed in the nylon (PA66) parts produced in SL moulds than those produced from aluminium moulds. The results also reveal different characteristics during thermal analysis that may also be due to the thermal history imparted by the mould.The work utilises the thermal analysis technique differential scanning calorimetry (DSC) to quantify the different levels of crystallinity in the parts. The thermal characteristics of the mould are demonstrated by real-time data acquisition.     

Development and characterisation of direct laser sintering Cu-based metal powder

Direct laser sintering of metal powder is a promising manufacturing process to produce rapid moulds (or rapid tooling) because complex three-dimensional (3-D) metal parts can be created directly from computer-aided design (CAD) data without machining or use of additional tooling. However, material and process are still the crucial issues that restrict its wider adoption although the technology has been introduced more than 7 years. This paper characterises a self-developed Cu-based metal powder used for direct laser sintering. The material system is Cu-based alloy metal powder, which consists of two metal powders: high-purity Cu powder and pre-alloyed SCuP metal powder. The scanning electron microscope (SEM), XRD and energy dispersive X-ray (EDX) analyses show that the bonding mechanism of this process is liquid-phase sintering. The pre-alloyed SCuP metal powder with lower melting point (645 °C) acts as the binder during laser sintering, while the Cu powder with higher melting point (1083 °C) acts as the structure. The element phosphorus in the powder can act as flux to protect the Cu oxidisation. A case study on fabricating the inserts of a mobile phone cover mould was also carried out. The inserts were created in ambient atmosphere at room temperature. The total sintering time is 40 h. Sixty five percent relative theoretical density and average surface roughness R_a 14–16 μm were achieved with negligible distortion and curling. Epoxy infiltration was employed as post-process to improve the density and the strength of the sintered tooling. The mould inserts were used to inject ABS-PC mobile phone cover after polishing. No defects were found after moulding of 500 components.     

快速模具制造技术分析与发展趋势

介绍了直接法和间接法快速模具制造技术,分析了快速模具制造技术的发展趋势和市场需求,指出应加快快速制模技术在我国的研究和应用,满足产品创新和快速制造的市场需求。     

A comparison of rapid prototyping technologies

Until recently, prototypes had to be constructed by skilled model makers from 2D engineering drawings. This is a time-consuming and expensive process. With the advent of new layer manufacturing and CAD/CAM technologies, prototypes may now be rapidly produced from 3D computer models. There are many different rapid prototyping (RP) technologies available. This paper presents an overview of the current technologies and comments on their strengths and weaknesses. Data are given for common process parameters such as layer thickness, system accuracy and speed of operation. A taxonomy is also suggested, along with a preliminary guide to process selection based on the end use of the prototype.     

采用发泡石膏型快速铸造金属模具的研究

尝试用发泡石膏型法快速翻制铝合金模具。首先对模具的加工图进行三维造型及制作LOM母模。采用物理发泡法对石膏浆料进行发泡。形成泡沫状石膏浆料后再灌入芯盒。待石膏硬化后，采用专用装置平稳起模并脱除木芯盒，将得到的石膏型烘干后合型烧注，去除浇冒口、打磨，机加分型面后便可上线生产。浇出的模样表面粗糙度可达Ral.6。尺寸公差可达到0．2mm之内。一般从三维造型到模具交货约需12天的时间，比数控加工提前2－4周，实现了快速制造的目的。可以满足砂型铸造对模具强度、精度和制造周期的要求。     

金属电弧喷涂成型快速制模关键技术与应用

金属电弧喷涂成型制模技术是一种基于"复制"的制模工艺,与传统制模工艺相比,具有制模速度快、周期短、成本低等特点。金属喷涂模具由金属型壳、背衬强化层以及模框等构成,是一种具有梯度材料结构的复合材料模具。关键制模工艺包括:母模制备、金属型壳制造、模框制作、背衬强化层制作、脱模以及后处理等。金属喷涂制模技术可用于制造注塑模具、热成型模具和板料冲压模具等。该文以大型汽车覆盖件模具的快速制造为例进行了详细介绍。     

Consolidation phenomena in laser and powder-bed based layered manufacturing

Layered manufacturing (LM) is gaining ground for manufacturing prototypes (RP), tools (RT) and functional end products (RM). Laser and powder bed based manufacturing (i.e. selective laser sintering/melting or its variants) holds a special place within the variety of LM processes: no other LM techniques allow processing polymers, metals, ceramics as well as many types of composites. To do so, however, quite some different powder consolidation mechanisms are invoked: solid state sintering, liquid phase sintering, partial melting, full melting, chemical binding, etc. The paper describes which type of laser-induced consolidation can be applied to what type of material. It tries to understand the underlying physical mechanisms and the interaction with the material properties. The paper demonstrates that, although SLS/SLM can process polymers, metals, ceramics and composites, quite some limitations and problems cause the palette of applicable materials still to be limited. There is still a long way to go in tuning the processes and materials in order to enlarge the applicability of LM. This is not surprising if one compares it to the decades of R&D work devoted to tuning processes and materials for hot or cold forming, metal cutting (e.g. development of free machining steels), casting and injection moulding (including powder injection moulding: MIM, CIM, etc.).     

快速原型和制造技术的新进展——2001年国际快速原型和制造技术博览会观感

介绍了2001年美国辛辛那提快速原型和制造技术博览会及快速原型和制造技术的新进展。     

Modeling and evaluation of curved layer fused deposition

Fused deposition modeling (FDM), one of the rapid prototyping techniques is a promising technology for rapid manufacture of end use parts direct from CAD files and with the proliferation of cheaper machines, is likely to play a vital role in future polymer processing, challenging traditional processes such as injection moulding in some cases. Research evidence suggests that the road and layer structures would have significant influences on the mesostructure and consequent mechanical behaviour of the resulting polymer part. While adaptive slicing and other deposition schemes have been attempted for different reasons, it is believed that an appropriate deposition scheme is essential to ensure the best inter-road and interlayer connectivity, resulting in a continuous network of polymer chains, as in the case of the traditional processes. The current research proposes the curved layer deposition for FDM, in particular for thin shell-like parts, to ensure fibre continuity. Mathematical models are developed for curved slicing, implemented in a few case studies, parts are printed, and test results suggest marked improvement in the mechanical characteristics of curved layer parts.     

Studies on the reprocessability of poly(ether ether ketone) (PEEK)

Whilst demonstrating desirable mechanical properties, corrosion resistance and the ability to retain structural integrity over extended temperatures, PEEK (poly(ether ether ketone)) remains expensive, restricting broader usage. The reuse and recyclability characteristics of PEEK are therefore commercially important, where the most prevalent manufacturing process for PEEK is injection moulding. This study comments on the reprocessability of PEEK specifically applied to the injection moulding process, comparing the effect of repeated reuse on mechanical properties. Recycled PEEK retains its tensile properties through at least three moulding and regrinding cycles. XRD and DSC measurements confirmed that reused PEEK shows no degradation in crystallinity.     

注射模温度快速响应技术

介绍了用于注射模的模腔表面温度快速响应技术,其中主要介绍了快速温度响应模具的原理和结构 ,并对其中的一些设计问题进行了讨论 ,最后对比了用传统模具和快速温度响应模具分别加工出来的制品 ,结果显示出了快速温度响应模具的优越性     

RAPID MANUFACTURING AND RAPID TOOLING WITH LAYER MANUFACTURING (LM) TECHNOLOGIES, STATE OF THE ART AND FUTURE PERSPECTIVES

Additive processes, which generate parts in a layered way, have more than 15 years of history. These processes are not exclusively used for prototyping any longer. New opportunities and applications in appropriate manufacturing tasks open up, even though the economical impact is still modest.This review starts with the definition of Rapid Manufacturing and Rapid Tooling, dealing only with direct fabrication methods of components. A systematic material dependent classification of layer manufacturing and process oriented metal part manufacturing techniques are proposed. The generic and the major specific process characteristics and materials are described, mainly for metallic parts, polymer parts and tooling. Examples and applications are cited.The paper attempts to understand the state of the art and the prospective, to put questions, to understand limits, to show opportunities and to draw conclusions based on the state of the art.     

Inlfuence of wet activation of used inorganic binder on cyclically refreshed water glass moulding sands hardened by microwaves

The paper presents the research results of using an innovative method to reclaim the waste moulding sands containing water glass. Two of the examined processes are connected with “dry” or “wet” activation of inorganic binder in waste moulding sand mixtures physicaly hardened by microwave radiation. The sand mixtures consisting of high-silica sand and water-glass with average molar module 2.5, were subjected to the folowing cyclical process: mixing the components, compacting, microwave heating, cooling-down, thermaly loading the mould to 800 °C, cooling-down to ambient temperature, and knocking-out. After being knocked-out, the waste moulding sands were subjected to either dry or wet activation of the binder. To activate thermaly treated inorganic binder, each of the examined processes employed the surface phenomenon usualy associated to mechanical reclamation. The study also covered possible use of some elements of wet reclamation to rehydrate waste binder. To evaluate the effectiveness of the two proposed methods of waste binder activation, selected strength and technological parameters were measured. After each subsequent processing cycle, the permeability, tensile strength and bending strength were determined. In addition, the surface of activated sand grains was examined with a scanning electron microscope. Analysis of the results indicates that it is possible to re-activate the used binder such as sodium silicate, and to stabilize the strength parameters in both activation processes. Permeability of the refreshed moulding sands strongly depends on the surface condition of high-silica grains. The wet activation process by wetting and buffering knocked-out moulding sands in closed humid environment makes it possible to reduce the content of refreshing additive in water-glass. The moulding sands cyclicaly prepared in both processes do not require the addition of fresh high-silica sand. The relatively high quality achieved in the refreshed moulding sands alows them to be reused for manufacture of next moulds. Thus, the two proposed methods for cyclicaly processing used moulding sands containing sodium silicate, subject to microwave hardening, are suitable for economic and ecological circulation moulding mixtures.     

Gas-assisted compression moulding of recycled GMT: Effect of gas injection parameters

Gas assisted compression moulding (or GasComp) is a novel process based on the injection of nitrogen gas during a conventional compression moulding cycle, a technique originally introduced in the injection moulding industry.The gas is injected into the molten material at a preset gas inlet point, hollowing out the part and thus assisting the compressive force of the press in generating material flow. This paper presents gas injection parameter studies on polypropylene based recycled glass mat-reinforced thermoplastic (GMT). The parameters investigated are gas ramp rate, gas injection delay time, and peak pressure. The size of cavity was found to be inversely proportional to gas injection delay time. Rheological instabilities at the polymer–gas interface were observed; a phenomenon previously noted during the development of gas assisted injection moulding.     

高熔点金属电弧喷涂快速制模工艺研究

综述了电弧喷涂快速制模技术的发展现状,分析了高熔点金属应用于电弧喷涂快速制模中存在的问题。通过实验研究,得出了在母模上铺设随形金属网、辅型喷涂、间隔喷涂和复合喷涂等方法,有效地将高熔点金属用于电弧喷涂快速制模,扩展了电弧喷涂快速模具的应用范围。     

基于反求工程和快速原型的零件／模具制造技术

在反求工程和快速原型技术基础上,分析了基于反求工程和快速原型的快速零件／模具制造技术;采用Unigraphics软件进行三维重建,得到三维实体模型,转化为快速原型制造所需要的STL表面模型,采用LOM成形机制造出原型,与石膏型铸造工艺相结合,最终制造出金属零件／模具。