Cold Mold Research Articles

Residual Stress Reduction Technology in Heterogeneous Metal Additive Manufacturing

Metal additive manufacturing (AM) is a low-cost, high-efficiency functional mold manufacturing technology. However, when the functional section of the mold or part is not a partial area, and large-area additive processing of high-hardness metal is required, cracks occur frequently in AM and substrate materials owing to thermal stress and the accumulation of residual stresses. Hence, research on residual stress reduction technologies is required. In this study, we investigated the effect of reducing residual stress due to thermal deviation reduction using a real-time heating device as well as changes in laser power in the AM process for both high-hardness cold and hot work mold steel. The residual stress was measured using an X-ray stress diffraction device before and after AM. Compared to the AM processing conditions at room temperature (25 °C), residual stress decreased by 57% when the thermal deviation was reduced. The microstructures and mechanical properties of AM specimens manufactured under room-temperature and real-time preheating and heating conditions were analyzed using an optical microscope. Qualitative evaluation of the effect of reducing residual stress, which was quantitatively verified in a small specimen, confirmed that the residual stress decreased for a large-area curved specimen in which concentrated stress was generated during AM processing.

Choice of materials properties and of shell molds structure by investment models

The paper presents a mathematical model optimizing the choice of material and morphological structure of the shell mold (SM), which has the highest resistance to cracking when pouring liquid metal into it. To solve this problem, the theory of small elastoplastic deformations and the heat equation, as well as proven numerical methods, were used. The objective function min – max was constructed from control variables characterizing the properties of the molding material of the shell. The process of heating an axisymmetric shell mold was considered when pouring liquid metal into it. The resistance of the shell form was estimated by the stresses arising in it. An algorithm for solving this problem was compiled. Using numerical schemes and program complexes developed in previous studies, an algorithm for solving the optimization problem was constructed and the values of control variables were found in which the shell mold does not break even in the presence of a rigid process – pouring steel into a cold shell mold. Analysis of the influence of weight of each of the found parameters on the value of the constructed objective function is given. Using a mathematical experiment, the morphological structure of the shell mold was studied. The shell mold of five layers is considered. The corrected system of equations makes it possible to take into account the properties of the layers made of different materials. Calculations were performed when the layer of the shell mold from material found by optimization occupies different positions in its cross section. In this case, the remaining layers of the mold are made of traditional ceramics. The optimal location of this layer was found. It is shown that the presence of several layers with the found properties does not affect the increase in crack resistance of the shell mold.

Common cold among young adults in China without a history of asthma or allergic rhinitis - associations with warmer climate zone, dampness and mould at home, and outdoor PM10 and PM2.5

This paper studied associations between reported common cold and home dampness and mould, cleaning habits and ventilation, climate and outdoor air pollution in China among young adults without asthma or allergic rhinitis. Parents of children attending day care in eight Chinese cities answered a questionnaire on their health and home environment (75% response rate). We restricted the population to subject without asthma or allergic rhinitis (N = 37,275). Temperature and air pollution data was obtained from monitoring stations. Associations were estimated by multilevel logistic regression. Totally 12.5% reported common cold (≥3 colds) and 1.6% frequent common cold (≥5 colds) in the past 12 months. Female gender (OR = 1.53; 95% CI 1.37–1.71), residents in southern China (OR = 1.89; 95% CI 1.16–3.07) and living in homes with water leakage (OR = 1.32; 95% CI 1.16–1.50), mould odour (OR = 1.48; 95% CI 1.28–1.72), indoor mould (OR = 1.47; 95% CI 1.28–1.70), condensation on window panes (OR = 1.42; 95% CI 1.32–1.52) and damp bed clothing (OR = 1.19; 95% CI 1.11–1.28) were associated with common cold. Having many signs of dampness increased ORs. Daily cleaning (OR = 0.91; 95% CI 0.85–0.97) and mechanical ventilation in kitchen or bathroom (OR = 0.75; 95% CI 0.64–0.89) were protective. Higher mean ambient temperature (OR = 1.11 per °C; 95% CI 1.02–1.21), PM10 (OR = 1.17 per 10 μg/m3; 95% CI 1.14–1.21) and PM2.5 (OR = 1.28 per 10 μg/m3; 95% CI 1.20–1.37) were associated with common cold. The association with particulate air pollution was stronger in southern China. Similar associations were found for frequent common cold. In conclusion, indoor dampness and mould, a warmer climate and PM10 and PM2.5 can be associated with reported common cold. Further intervention and prospective studies are needed to verify causality of observed association in this cross-sectional study.

Blowing Kinetics, Pressure Resistance, Thermal Stability, and Relaxation of the Amorphous Phase of the PET Container in the SBM Process with Hot and Cold Mold. Part II: Statistical Analysis and Interpretation of Tests.

The technology of filling drinks without preservatives (such as fresh juices, iced tea drinks, and vitaminized drinks) is carried out using hot filling. Mainly due to the production costs and lower carbon footprint, polyethylene terephthalate (PET) bottles are increasingly used in this technology. In this paper, the main aim is to describe and interpret the results of statistical analysis of the influence of the temperature of the blow mold in the SBM (stretch blow molding) process and the method of hot filling on the macroscopic and microscopic bottle properties. The macroscopic bottle properties were defined by the thickness profile, pressure resistance, thermal stability, and the coefficients of blowing kinetics. In addition, the influence of the SBM process on the microscopic PET material properties (in the bottle) relative to the microscopic preform properties was analyzed. The microscopic properties were defined by the degree of crystallite, density, and relaxation of the amorphous phase of the PET material. For this purpose, response surface experiments were performed for the two analyzed factors, i.e., the temperature of the blow mold and the method of hot filling. The sample size was investigated to determine the minimum number of repetitions (number of bottles in the measurement series) required to achieve acceptable measurement uncertainty. The research conducted shows that, despite fulfilling the postulate of acceptable measurement uncertainty, in terms of the power of ANOVA (analysis of variance) in DOE (design of experiment), the accepted number of bottles in the measurement series is too small. The tests of the bottle material density, material crystallite, and relaxation of amorphous phase relative to the preform material density, material crystallite, and relaxation of amorphous phase show that microcavity effects occur during the deformation of the PET material, and that these are associated with the orientation of the microstructure. The blow kinetics study shows that there is a gradient of flow of the bottle material over the thickness of the bottle wall during blowing, and it has been deduced that the air temperature between the blow mold and the wall of the blown bottle has an impact on the kinetics of blowing the bottle.

Blowing Kinetics, Pressure Resistance, Thermal Stability, and Relaxation of the Amorphous Phase of the PET Container in the SBM Process with Hot and Cold Mold. Part I: Research Methodology and Results.

The technology of filling drinks without preservatives (such as fresh juices, iced tea drinks, vitaminized drinks) is carried out using hot filling. Mainly due to the production costs and lower carbon footprint, polyethylene terephthalate bottles, commonly called PET, are increasingly used in this technology. In this paper, the main aim is to describe the statistical analysis methodology of the influence of the temperature of the blow mold in the SBM process and the method of hot filling on the macroscopic and microscopic bottle properties. The macroscopic bottle properties were defined by the thickness profile, pressure resistance, thermal stability, and the coefficients of blowing kinetics. Moreover, the influence of the SBM (stretch blow moulding) process on the microscopic PET material properties (in the bottle) relative to the microscopic preform properties was analyzed. The microscopic properties were defined by the degree of crystallite, density, and relaxation of the amorphous phase of the PET material. For this purpose, response surface experiments were performed for the two analyzed factors (independent variables), i.e., the temperature of the blow mold and the method of hot filling. The sample size was investigated to determine the minimum number of repetitions (number of bottles in the measurement series) required to achieve acceptable measurement uncertainty. The research conducted shows that despite fulfilling the postulate of acceptable measurement uncertainty, in terms of the power of ANOVA (analysis of variance) in DOE (design of experiment) the accepted number of bottles in the measurement series is too small. The tests of the bottle material density, material crystallite, and relaxation of amorphous phase relative to the preform material density, material crystallite, and relaxation of amorphous phase show that the microcavity effects occur during the deformation of the PET material, and that these are associated with the orientation of the microstructure. The blow kinetics study shows that there is a gradient of flow of the bottle material over the thickness of the bottle wall during blowing, and it has been deduced that the air temperature between the blow mold and the wall of the blown bottle has an impact on the kinetics of blowing the bottle.

Using tailored temperature variations to obtain flawless forming of multi-stacked unidirectional prepreg

In this article, tailored temperature zones are used to obtain improved quality during rapid, high pressure forming of multi-stacked unidirectional prepreg. Particularly in aerospace applications, commonly used forming processes for multi-stacked unidirectional prepreg are often considered a bottleneck in production since the forming cycle requires both heating and cooling ramps and consequently takes long time—often about 1 h. It is possible to speed up the process by using elevated pressure and temperature. However, higher pressure and temperature also increase the influence of pressure gradient-driven, in-plane material movement (squeeze flow). This typically appears as radius thinning when forming a C-spar geometry on a male mold. Decrease of lay-up temperature will decrease radius thinning, but due to obstructed interply slippage, instead bending-induced wrinkles appear on the spar flange. In this article, tailored temperatures at the radius and in the flange area are introduced by using a hot lay-up and a cold mold. The results show that temperature differences of 6℃–10℃ between the radius area and the flange edge of the lay-up decreases radius thinning while still avoiding bending-induced wrinkles. Except from the radius temperature also the stacking sequence and the choice of prepreg system showed a significant influence on the radius thinning.

Hereditary Effect of the Structure of the Charge on Density, Gas Content, and Processes of Solidification of an Al–Si–Cu Alloy System

The effect of the structure of the initial charge density in liquid and solid states, as well as on the temperature–time parameters of the process of solidification of the AK6M2 alloy (Al–6% Si–2% Cu), is shown. To obtain a coarse-crystal charge (C charge), part of the melt is crystallized in ceramic forms in a sand backfill with a cooling rate of ~0.5–1.0°C/s. The fine-crystal charge (F charge) in the form of thin ingots weighing 0.2–0.3 kg is obtained by crystallization of the melt in cast-iron cold molds with ~5.0–10°C/s. Further, the charge billets are separately melted, re-refined and degassed, and the samples are poured to determine the gas content and density in the liquid (dL) and solid (dS) states. It is established that structural information from the original charge of the alloy is stable in the solid–liquid–solid system. Direct thermal analysis is used to find that the melt obtained from the F charge hardens at low temperatures: the decrease in liquidus temperature tL is 3°C; the temperature of the beginning of solidification of the eutectic is reduced by 10°C, and the temperature of the end of solidification of a eutectic is 3°C in comparison with the melt of the C charge. At the same time, the formation of α-Al and eutectic dendrites in the melt from the F charge occurs 0.4 and 0.6 min more quickly, respectively. The results obtained on the Paraboloid-4 installation show that a smaller number of pulses throughout the studied temperature range passes through the melt from the F charge, which confirms its increased density when compared to the alloy from the C charge. Thus, for the melt from the F charge, the values of the degrees of compaction were –ΔJl ~ 278.66 and –ΔJe ~ 129.83 imp/s and, for the melt from the C charge, –ΔJl ~ 302.9 and –ΔJe ~ 163.47 imp/s. The values of the phase-transition temperatures determined by anomalies on the temperature dependence Jt practically coincide with the results of direct thermal analysis. The main technological recommendations of management by structural information in aluminum alloys are formulated from the position of the phenomenon of structural heredity.

Hereditary effect of the charge structure on Al-Si-Cu alloy density, gas content and solidification processes

The paper provides the results obtained when studying the initial charge structure effect on the density, gas content and temperature-time parameters of AK6M2 (Al-6%Si-2%Cu) alloy solidification. Coarse crystalline charge billets ( C -charge) were obtained when pouring the melt into ceramic molds with sand filling providing a cooling rate υ охл ~0.5÷ 1.0 °C/s. Finely crystalline charge billets ( F -charge) were prepared by pouring the melt to cold cast iron molds ( υ охл ~ 5÷ 10 °C/s). Charge billets obtained were separately remelted with the same temperature-time conditions, rerefined and degassed with samples taken to determine hydrogen content as well as density values in liquid and solid states. It is established that structural information inherited from the initial charge billets is stable in the solid-liquid-solid system. It was found using direct thermal analysis that the melt obtained from C -charge solidifies with a reduction in liquidus temperature by 3 °С and in the temperatures of the beginning and end of eutectic solidification by 10 °C and 3 °С, respectively, as compared to the melt obtained from C -charge. At the same time, α-Al and eutectic dendrites form in the C -charge melt 0.4 and 0.6 min faster, respectively. The results obtained at the Paraboloid-4 unit showed that the F -charge melt has higher density as compared to the C -charge alloy due to a smaller number of pulses passing through it in the studied temperature range of 750 — 450 °C. Temperature values of aluminum and eutectic dendrite formation determined by J—t temperature relationships (where J is the number of γ pulses, t is the temperature) correlate with the results of direct thermal analysis. General practical recommendations on the purposeful conservation of positive structural information in aluminum alloys are formulated in terms of the structural heredity phenomenon.

Relationship and mechanism between microstructure and property of C70250 copper alloy strip prepared by temperature controlled mold continuous casting

Temperature controlled mold continuous casting (TCMCC) technology was used to fabricate the C70250 copper alloy strips. The influences of solidification microstructure on mechanical and electrical properties of C70250 copper alloys were systematically studied, and the relevant influencing mechanism was discussed. The results show that the microstructure of TCMCC C70250 copper alloy has a large number of fine dispersed Ni2Si phases, small angle grain boundaries and columnar grains with strong [001] orientation. The tensile strength, elongation and electrical conductivity of the C70250 copper alloy are 328 MPa, 40.4% and 24.3% IACS, respectively, which are obviously higher than the properties of the C70250 copper alloys prepared by conventional cold mold casting methods. The tensile strength of TCMCC C70250 copper alloy strip significantly increases due to the dislocation plugging inside the grains, which caused by strong pinning effect of Ni2Si phases during room temperature tensile. Straight small angle grain boundaries and columnar grains with strong [001] orientation significantly reduce the hindering effect of grain boundaries on dislocations. The deformation between and within grains is more uniform, and it is not easy to form high strain concentration, which leads to the increase of plastic deformation ability. The scattering effects of solute atoms and transverse grain boundaries on electrons are significantly reduced due to the precipitated Ni, Si atoms and the high orientation of columnar grain structure, which contributes to the improvement of the electrical conductivity.

INFLUENCE OF METHODS FOR ALTI MASTER ALLOY PRODUCTION ON ITS STRUCTURE AND EFFICIENCY IN ALUMINUM ALLOY MODIFICATION

A comparative study on the effect of methods for obtaining AlTi4 modifying master alloys on the sizes of Al3Ti intermetallics is made. It is found that increasing cooling rates at solidification from 10–15 °C/s (crystallization in a hot cast iron mold, a plate 30 mm in thickness) to 60–65 °C/s (crystallization in a cold cast iron chill mold, a rod 20 mm in diameter, 170 mm in length) reduces the length and thickness of needle-shaped intermetallics almost twice (397×23 to 215×13 μm). At the same time, lower electrical conductivity and higher alloy density in a solid state are observed. Melt modification with 0,5 wt.% magnesium addition causes the formation of homogeneous 98×3 μm fine-needle intermetallics. The addition of magnesium slightly reduces electrical conductivity and density compared with the AlTi4 master alloy crystallized at the same cooling rate (60–65 °C/s). Modification of A97 grade aluminum and AK9ch alloy (Al–Si–Mg system) with the specified master alloys at the same amount of titanium added (0,01 wt.%) exerts hereditary influence on the density and electrical conductivity, and macrograin (A97) and dendrites of aluminium (AK9ch). The maximum modifying effect is provided by the AlTi4 master alloy containing 0,5 wt.% magnesium. When introduced into the alloy, it contributes to the formation of 10 μm aluminum dendrites 1427 pcs/mm2 in total in the alloy structure. When the AK9ch alloy is modified with the master alloy crystallized at cooling rates of 10–15 °C/s, 28 μm dendrites 672 pcs/mm2 in total are formed in the alloy structure. It is suggested to use density and electrical conductivity determination methods for express evaluation of master alloy modifying effectiveness.

ПОРОШКОВЫЙ МАТЕРИАЛ НА ОСНОВЕ МЕХАНОХИМИЧЕСКИ АКТИВИРОВАННОГО СТРУЖКОВОГО ПОРОШКА Д16, С ДОБАВЛЕНИЕМ ФЕРРОТИТАНА

The PURPOSE of the paper is determination of the influence regularities of mechanochemical activation parameters on the particle size and properties of hot-deformed powder materials (HDPM) that are based on activated chip powder D16 with the addition of ferrotitanium. METHODS. Combined mechanochemical activation of chip D16 and ferrotitanium was carried out in the saturated aqueous solution of boric acid (SASBA) in a planetary ball mill SAND-1 at different processing times and grinding rates. The particle size distribution of charge followed by its processing in a hand mixer was studied and the agglomeration parameter was determined. The resulting charge was divided into fractions; one part was mixed with aluminum powder; subjected to cold moulding followed by short-term heating and forming. Hardness, ultimate shear strength and ultimate bending strength of hot-deformed powder materials were also determined. RESULTS AND THEIR DISCUSSION. 3D spline models of the activated chip powder (ACP) yield dependence on grinding time and rate have been constructed. Introduction of 30% saturated aqueous solution of boric acid of the charge weight into the grinding media provides better grinding estimated by the amount of yield of the activated chip powder. Using Rosin-Rammler equation the correspondence to the normal distribution law has been revealed for the particles of this charge. The integral curves of particle size distribution after the mechanochemical activation and manual processing have been constructed. CONCLUSIONS. The optimal parameters of mechanochemical activation are determined. They provide a higher yield of the activated chip powder. The resulting charge is characterized by a minimum average particle sizes and the increased value of the agglomeration parameter. The obtained materials have increased values of the ultimate shear strength (249 MPa), hardness (102 HRE) under the bending strength of σ b = 179 MPa. An improved technology is proposed for the production of hot-deformed powder materials based on mechanochemically activated chip powder with the addition of ferrotitanium.

Development of Crystalline Morphology and Its Relationship with Mechanical Properties of PP/PET Microfibrillar Composites Containing POE and POE-g-MA.

The main goal of this research is to study the development of crystalline morphology and compare it to various mechanical properties of microfibrillar composites (MFCs) based on polypropylene (PP) and poly(ethylene terephthalate) (PET), by adding a functional compatibilizer and a non-functional rubber in two different steps in the processing sequence. The MFCs were prepared at a weight ratio of 80/20 PP/PET by twin screw extrusion followed by cold drawing and injection moulding. The non-functionalized polyolefin-based elastomer (POE) and the functional compatibilizer (i.e., POE grafted with maleic anhydride (POE-g-MA)) were added in a fixed weight percentage at two stages: during extrusion or during injection moulding. The morphology observations showed differences in crystalline structure, and the PP spherulite size was reduced in all MFCs due to the presence of PET fibrils. Their relationship with the mechanical performances of the composite was studied by tensile and impact tests. Adding the functional compatibilizer during extrusions showed better mechanical properties compared to MFCs. Overall, a clear relationship was identified between processing, structure and properties.

Premature melt solidification during mold filling and its influence on the as-cast structure

Premature melt solidification is the solidification of a melt during mold filling. In this study, a numerical model is used to analyze the influence of the pouring process on the premature solidification. The numerical model considers three phases, namely, air, melt, and equiaxed crystals. The crystals are assumed to have originated from the heterogeneous nucleation in the undercooled melt resulting from the first contact of the melt with the cold mold during pouring. The transport of the crystals by the melt flow, in accordance with the socalled “big bang” theory, is considered. The crystals are assumed globular in morphology and capable of growing according to the local constitutional undercooling. These crystals can also be remelted by mixing with the superheated melt. As the modeling results, the evolutionary trends of the number density of the crystals and the volume fraction of the solid crystals in the melt during pouring are presented. The calculated number density of the crystals and the volume fraction of the solid crystals in the melt at the end of pouring are used as the initial conditions for the subsequent solidification simulation of the evolution of the as-cast structure. A five-phase volume-average model for mixed columnar-equiaxed solidification is used for the solidification simulation. An improved agreement between the simulation and experimental results is achieved by considering the effect of premature melt solidification during mold filling. Finally, the influences of pouring parameters, namely, pouring temperature, initial mold temperature, and pouring rate, on the premature melt solidification are discussed.

Study thermo-mechanical properties of polyester composite reinforced by ceramic particles, SiC

Development of the Polymer Composites with natural fibers and fillers as a sustainable alternative material for some engineering applications, particularly in aerospace applications and automobile applications are being investigated. Lightweight and biodegradability and low cost Polyester composites are synthesised with an addition of Silicon carbide (SiC) particles by varying weight percentage (0, 3, 6, 10, 13, and 16 wt. %) respectively by using hand- layup technique followed by cold moulding. The prepared specimens were cut according to ASTM standard to determine hardness, impact strength, bending distortion and thermal conductivity properties. Afterward, the thermal and mechanical properties of all the unfilled and particulate filled composites are also evaluated for structural applications, i.e., hardness, impact strength, bending distortion, are determined with the change in filler content to notice the behaviour of composite material subjected to loading in addition to thermal conductivity property. Thermo-mechanical properties of the material are measured with the help of testing machines above according to their ASTM. It is found that the strength properties are greatly influenced by addition of this ceramic filler. Also shows that the thermal and mechanical properties of SiC-filled polyester composites are better than unfilled base composites

Dynamic local temperature control in micro‐injection molding: Effects on poly(lactic acid) morphology

Microinjection molding is one of the most efficient processes for wide‐scale production of thermoplastic polymer microparts. The injection molding process with a cold mold suffers from drawbacks, that is, the premature solidification, caused by the small thickness and large temperature difference between the surface of the mold and the incoming polymer. In this work, an original and versatile system to dynamically control the local temperature of the cavity surfaces in microinjection molding was developed. The system was used to investigate the effects of rapid variations of the temperature of a 200 μm thick cavity on the reachable flow length and study the morphology of microinjection molded parts of poly(lactic acid). For the rapid mold temperature control, electrical resistive thin components are located very near the surface of the impression to change the temperature by some tens of degrees per second. This study also demonstrates that the system is able to influence the final morphology of the part with a semicrystalline thermoplastic material. Changing the annealing time and temperature, the effects on the morphology of the part, in the mold and immediately after the injection, were investigated by microscopy analysis and X‐ray diffraction. POLYM. ENG. SCI., 58:586–591, 2018. © 2017 Society of Plastics Engineers

Numerical Simulation of Temperature Field and Microstructure of a Wide Copper Plate during Warm Mold Continuous Casting

Wide plates are mainly prepared through traditional cold mold continuous casting technology. A problem is cracking which caused by the non-uniform temperature field in solidification. Warm mold continuous casting is a new technology. Warm mold continuous casting of wide copper plate (section 500mm×12mm) was studies. Temperature field, solid/liquid interface and microstructure were analyzed by ProCAST software. By simulation, the optimal processing parameters: withdrawing speed was 60-80 mm/min, and the temperature of copper melt, mold and cooling water were 1200°C, 800-900oC and 20 oC, respectively. The temperature field in the width direction of the copper plate broad face was uniform, and the temperature decreased uniformly along the withdrawing direction. The temperature difference between center and edge was within 10 oC, and the temperature difference between narrow and broadfaces was within 25oC. Microstructure of plate contained ‘bamboo-like’ grains along the withdrawing direction.

Roundness Error in Deep Hole Drilling using Twist Drills and Cold Mold Steel 718

Applications: Deep hole drilling is one of the machining processes which currently has been applied in the manufacturing area. The sophistication in some area such as aerospace, automotive, wind energy and nuclear power encourage the application of deep hole drilling. Objectives: In this study the effect of machining parameters on the roundness error during the drilling multiple deep holes of steel alloy using HSS Co5 DH100 straight shank twist drills for deep hole drilling of cold mold steel 718 towards the value of roundness error was investigated. Method: Drilling tests were carried out using a CNC milling machine under three different levels of minimum quantity lubricant (20, 30, 40 ml/hour) by drilling three different levels of depth of holes (65, 70, 75 mm), three different levels of spindle speeds (700, 800, 900 rpm) and three different levels of feed rates (50, 60, 70 mm/min). Findings: It was observed that the minimum value of roundness error obtained when using DoE approach and regression model is when cutting speed (V) is 700 rpm, minimum quantity lubricant (l) is 40 ml/hr and feed rate (f) equals 50 mm/min, depth of hole (d) is 65 mm. ANOVA analysis also proves that the combination of machining parameters obtained is significantly to the roundness error value that results in the roundness error minimum value and F statistic also showed that the model is important at the significance level of 95%.

Two-component injection moulding of thermoset rubber in combination with thermoplastics by thermally separated mould cavities and rapid heat cycling

Two-component injection moulding is a manufacturing process used to combine polymers with different properties within a single product. The process is often used to combine thermoplastics of different colours or to combine thermoplastic elastomers with thermoplastics to create hard and soft areas. In this study, a two-component injection moulding process is proposed for combining thermoplastics with thermoset rubbers. This poses technological challenges since rubbers require a heated mould (160–200 ∘C) for the rubber to vulcanise whereas thermoplastics need a relatively cold mould (20–100 ∘C) for the polymer to solidify. The mould used for this study is equipped with thermally separated mould cavities and allows to reverse the injection sequence of the two materials. It was found that the optimal sequence is to inject the thermoplastic first, followed by rubber, and that the mould temperature at the interface during the vulcanisation of the rubber is a critical process parameter. Too low mould temperatures at the interface result in long vulcanisation times and poor adhesion, whereas higher temperatures at the interface both decrease the vulcanisation time and increase the adhesion strength. However, when the temperature is too high, the adhesion strength decreases again due to gas bubbles at the interface released during the vulcanisation process.

Roundness Error Study in Deep Hole Drilling of Cold Mold Steel 718

Objective: The objective of this study is to investigate the experimental results of roundness error of machined holes using deep hole drilling process. The machining parameters include feed rate (f), spindle speed (s), depth of hole (d) and Minimum Quantity Lubrication MQL, (m). The work piece and tool material used in this study are Cold Mold Steel 718 and High Speed Steel, HSS (5mm diameter) with twist drill bit respectively. After that, to evaluate the quality of holes the roundness error has been used as machining performance. Method: A systematic approached based on Design of Experiment (DoE) was executed using Full Factorial design with added center point. Finding: Analysis of variance (ANOVA) was applied to the results to check the significance of the model. From the ANOVA analysis indicate that the model is significant for a confidence level of 0.05 or 95%.

Effects of picosecond laser repetition rate on ablation of Cr12MoV cold work mold steel

In this paper, the effects of pulse repetition rate on ablation efficiency and quality of Cr12MoV cold work mold steel have been studied using a picosecond (ps) pulse Nd:YVO4 laser system at λ=1064nm. The experimental results of area ablation on target surface reveal that laser repetition rate plays a significant role in controlling ablation efficiency and quality. Increasing the laser repetition rate, while keeping a constant mean power improves the ablation efficiency and quality. For each laser mean power, there is an optimal repetition rate to achieve a higher laser ablation efficiency with low surface roughness. A high ablation efficiency of 42.29, 44.11 and 47.52μm3/mJ, with surface roughness of 0.476, 0.463 and 0.706μm could be achieved at laser repetition rate of 10MHz, for laser mean power of 15, 17 and 19W, respectively. Scanning electron microcopy images revels that the surface morphology evolves from rough with numerous craters, to flat without pores when we increased the laser repetition rate. The effects of laser repetition rate on the heat accumulation, plasma shield and ablation threshold were analyzed by numerical simulation, spectral analysis and multi-laser shot, respectively. The synergetic effects of laser repetition rate on laser ablation rate and machining quality were analyzed and discussed systemically in this paper.