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Why Your Perfect Mold and Process Produces Imperfect Parts
In 1997 one of the leading causes of plastic part failure was first revealed to the world and recognized by the SPE IMD as one of the most significant discoveries in injection molding. The problem begins in the injection phase of the molding cycle where high shear conditions create viscosity variations of more than 1000%. These variations are non-uniformly and often unknowingly, distributed throughout a mold thus making many part quality defects appear to be a result of random acts of process variation. The phantom-like phenomena impacts every part that is injection molded and affects shrinkage, warpage, mechanical properties as well creating cavity-to-cavity product variations during each molding cycle. This presentation will reveal the source of the problem, how it affects molded parts, where it appears, how to recognize it and how it can be managed.
Advanced Process Controls for Injection Molding
It is possible to control viscosity including shear stress and shear rate, part compression and shrinkage from inside the mold cavity. Utilizing cavity pressure and cavity temperature sensors to detect melt front, target values for these parameters are achieved and more consistent parts are produced.
FINITE ELEMENT ANALYSIS OF HEAT STAKING DESIGN
Staking is a common joining method to assemble similar and dissimilar materials. Ultrasonic staking, hot air cold staking, heat staking, and infrared staking are common techniques used in the industry. Recently, impulse staking and laser staking are also reported. Regardless of the different staking techniques, the concept of staking is to deform a stud or hollow boss to form a button (or mushroom) to mechanically hold two materials together. The varieties of staking design guidelines developed by equipment suppliers possess significant discrepancies. This work utilized finite element (FE) modeling to study the effect of stake geometry on pull strength on a TPO material. Both 2-D axial symmetric and 3-D solid models were constructed to simulate the stake under tensile load. Geometric parameters such as button radius and button height were studied. It was found that mushroom height is the most critical parameter in achieving high retention force. Tall and large button provides highest retention force. However, tall and standard radius button provides compatible retention force and manufacturing advantages.
POLYPHENYLENE ETHER MACROMOLECULES. VII. PERFORMANCE IN T-BUTYL STYRENE/DIVINYL BENZENE RESIN SYSTEM
The optical quality of plastic microlens arrays is verysensitive to the presence of residual stress induced duringthe molding process. In this paper, the effects of aperturestructures on the maximum value of residual stress havebeen investigated. The results from numerical simulationindicate that the geometrical configuration of the aperturecan profoundly influence the levels of residual stress inprecision injection molded microlens arrays. The fiveaperture structures present similar trends to the change ofmold temperature, packing pressure, packing time andcooling time. With regard to melt temperature and flowrate, the trends of maximum value of residual stressexhibit differences with different aperture structures. It isshown that the cooling time has the least effect on theresidual stress. The aperture structure of microlens arraysshould be considered the effects on final quality of productat the initial stage of optical design.
PREPARATION OF POLYPROPYLENE-ORGANOCLAY ANOCOMPOSITES: EFFECT ON THERMAL, MORPHOLOGICAL AND VISCOELASTIC PROPERTIES
In the present work, PP-clay nanocomposites were prepared and the effect of nanoclay content on the properties of the nanocomposite was studied. polypropylene/surface modified clay nanocomposites were prepared via melt blending method in a laboratory mixing extruder (LME) using commercial polypropylene (PP) and nanoclay masterbatch in concentrations ranging from 5 to 15 wt%. The structure and thermal-mechanical features of the nanocomposites were characterized by scanning electron microscopy (SEM), differential scanning calorimetry (DSC) as well as dynamic mechanical analyzer (DMA). For all nanoclays loadings, SEM shows homogeneous dispersion of the nanoclay in the polymer matrix. The DSC curves show a 15% increase in heat of fusion (crystallinity content) up to 5% wt nanoclay loading but then decreased at higher loadings. This is attributed to the nucleating role of the silica particles at low nanocaly content; however, at relatively high loadings, the presence of excessive number of silica particles hinders the motion of polymer chain segments and thus, retards crystal growth. The temperature sweep reveals an increase in storage modulus (G') with increasing nanoparticles content due to the restricted motion of the PP chains as a result of the interaction between the nanoclay and the matrix that depends on the interfacial area shared between the PP and the nanoclay. As the interfacial area increased, the interaction increased, and hence the chains were more restricted. Besides, the estimation of the softening temperature as well as the slope of the flat region of the curves show that the addition of the nonmaterial increases the thermal stability of the nanocomposites as compared to the neat polypropylene.
COMPARING THE RHEOLOGICAL PROPERTIES OF SELECTED POLYOLEFINS USING ROTATIONAL RHEOMETRY TO THOSE OBTAINED FROM MELT FLOW INDEX; A TRILOGY
This paper is the third in a series which was previously presented in ANTEC08(1) and ANTEC09(2). These papers showed different applications of the melt flow index, MFI, equipment. These applications included the temperature and/or shear sensitivity, extrudate (die) swell, melt density, melt strength, thermal degradation, and processability of polyolefins. In the current paper, the relation between the measured values via MFI equipment will be related to the viscoelastic properties measured by rotational rheometer. For example, the extrudate swell will be compared to the elastic properties of some polyolefins. Additionally, the processability will be analyzed via the relationships of viscosity, shear rate, and temperature. Moreover, some molecular structure parameters are indentified and then are used to interpret some of the properties measured by the MFI equipment.
SONOPLAST NEW PROCESS AND MACHINERY FOR MICROPARTS MOLDING BASED ON ULTRASOUND EXCITATION
Injection molding although widely extended as one of the main replication technologies has shown important limitations when applied to the manufacture of plastic parts in the micro and mini scale. The present work describes a new moulding process based on the fusion ofthat has been thermoplastics materials via ultrasounds developed in the Sonoplast European project. First experimental achievements led to an innovative concept of mould and ultrasound moulding machine for the production of plastic parts (micro and mini). In addition the molding process management is simplified and directed by few machine parameters differing from conventional injection molding. The ultrasound molding process is extremely fast and with reduced filling pressures achieves a very good reproduction of the mould micro details. Besides it has been possible to obtain reductions about 50% on sprue volumes (around 0,16 g of plastic per shot) comparing with a conventional microinjection machine. Moreover, process energy consumption and power requirements are between 500 and 1200J and 200 and 500W, respectively. Finally, rheological analysis showed that no noticeable degradation process occurred after processing; equally, tensile testing gave better mechanical performance retention, comparing with traditional microinjection processes.
DEVELOPMENT OF OXYGEN SCAVENGING BIOCOMPOSITES BASED ON PLA AND OXYGEN SCAVENGING NANOCLAYS FOR PACKAGING APPLICATIONS
A new commercial iron-based oxygen scavenging montmorillonite clay (MMT-Fe), was analyzed for its oxygen scavenging capacity. In a subsequent step, it was incorporated by solution casting into PLA to obtain a brown colored nanocomposite sheet with significant oxygen scavenging properties. Since PLA is known to exhibit shortages in barrier properties to gases, which conventional existing nanoclay formulations cannot overcome, the potential of combining the passive barrier properties of nanoclays with a novel functionalization capable of scavenge oxygen from the packaging headspace shows strong potential in high barrier packaging applications of oxygen sensitive products.
MORPHOLOGY AND BARRIER PROPERTIES OF SOLVENT CAST NANOCOMPOSITES OF POLYLACTIC ACID WITH CELLULOSE NANOWHISKERS DERIVED FROM ALPHA PURIFIED MICROFIBERS
PLA nanobiocomposite films containing cellulose nanowhiskers (CNW) were obtained by solution casting. The cellulose nanowhiskers, prepared by acid hydrolysis of microfibers of highly alpha purified cellulose, consisted of nanofibers of typically 60 to 160 nm in length and 10 to 20 nm in thickness. The nanocomposites were prepared by incorporating 1, 2, 3 and 5 wt.-% of the CNW into the PLA matrix. The morphology and mass transport properties of the films were investigated by SEM, TEM, AFM, optical microscopy, OTR and WVTR.
PROCESSING AND PERFORMANCE OF HDPE POLYMER BLENDS INCLUDING POST CONSUMER RECYCLED HDPE
With the rapid increase in the market for recycled polyethylene from various sources, there is an urgent need to quantify the performance of these materials. Blends of recycled high density polyethylene (HDPE) were prepared to obtain specific mechanical properties and MFI. The results show that the MFIs had significant effect on the rheological, mechanical and phase morphology characteristics of the various blends.
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