Maoliang Wu, Wanhua Zhao, Yiping Tang, Dichen Li and Bingheng Lu
Stereolithography (SL) is a kind of rapid prototyping technology which uses the laminate manufacturing to fabricate parts. With the development of RP, some new RP processes have…
Abstract
Stereolithography (SL) is a kind of rapid prototyping technology which uses the laminate manufacturing to fabricate parts. With the development of RP, some new RP processes have boomed rapidly. Compact prototyping system (CPS) is a kind of novel stereolithography method which utilizes conventional UV light as the light source. After transmitting by optic fiber and focusing through lens set, the light is intensified and can be used to cure the photopolymer. Compared with the laser SL prototyping apparatus, this apparatus has unique characteristics on its driving system and light path system. Discusses the characteristics and corresponding consequences of the driving system and light path system, and analyzes the light energy distribution and the corresponding line shapes. Since each layer is constructed from a serial of lines, the scanning parameters, especially scanning speed and hatch gap, will influence the overall light intensity which determines the layer thickness, section shape and ultimately the prototyping accuracy. The driving system, due to the non‐uniform moving speeds, could cause the shape error of the lines. A light shutter, keeping the light only illuminating on resin surface within given curing areas, is employed to solve this deficiency.
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Zhengying Wei, Yiping Tang, Wanhua Zhao and Bingheng Lu
This paper describes the rapid development process for emitter which is the key part in water‐saving irrigation device. The design of labyrinth‐channel in emitters, the generation…
Abstract
This paper describes the rapid development process for emitter which is the key part in water‐saving irrigation device. The design of labyrinth‐channel in emitters, the generation of process‐oriented structural CAD model, the building of emitter prototype and its integrative experimental model based on RP are introduced in detail. The emitter prototypes can be directly applied to irrigation experiments and production practice, and hence the rapid development of drip irrigation emitters can be realized.
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Yiqing Wang, Wanhua Zhao, Yucheng Ding, Zhongyun He and Bingheng Lu
The purpose of this paper is to detect and control the liquid‐level of stereolithography apparatus precisely.
Abstract
Purpose
The purpose of this paper is to detect and control the liquid‐level of stereolithography apparatus precisely.
Design/methodology/approach
A brightness‐variable laser source is adopted to remove the computational error of divider and a closed‐loop circuit is set to measure the terminal voltage directly proportional to the output current of photosensitive devices. It employs a sinking‐block device to control the liquid‐level.
Findings
The precise calibration result of this detecting device indicates that the resolution of the liquid‐level detection can reach ±1.5 μm.
Originality/value
This sinking‐block style liquid‐level control device can allow for the liquid‐level wave reduced from ±45 to ±15 μm.
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Yiqing Wang, Yucheng Ding, Wanhua Zhao, Zhongyun He and Bingheng Lu
The purpose of this paper is to show how to precisely control the liquid resin coating thickness in stereolithography (SL).
Abstract
Purpose
The purpose of this paper is to show how to precisely control the liquid resin coating thickness in stereolithography (SL).
Design/methodology/approach
A vacuum adsorption coating equipment and technology are developed to precisely control the liquid resin coating thickness in SL. Dual‐electrode device is used, so adsorption can be precisely controlled and the electrode polarization can be avoided.
Findings
It turns out that the apparatus can control coating thickness effectively, and thickness uniformity is increased remarkably, which induces the standard deviation thickness decrease from 0.00547 to 0.00243 mm, and efficiency of rapid prototyping production increase by 53 percent.
Originality/value
The paper demonstrates that the apparatus can control coating thickness effectively.
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Guangshen Xu, Wanhua Zhao, Yiping Tang and Bingheng Lu
To satisfy the demands for rapid prototyped small‐size objects with intricate microstructures, a high‐resolution stereolithography (SL) system is developed.
Abstract
Purpose
To satisfy the demands for rapid prototyped small‐size objects with intricate microstructures, a high‐resolution stereolithography (SL) system is developed.
Design/methodology/approach
This novel SL system consists of a single mode He‐Cd laser, an improved optical scanning system, a novel recoating system and a control system. The improved optical system consists of a beam expander, an acoustic‐optic modulator, a galvanometric scanner and an F‐θ lens; the recoating system consists of roller pump, resins vat with an integrated high‐resolution translation stage and part building platform and a scraper. Experimental studies were performed to investigate the influences of building parameters on the cured line width and depth.
Findings
With the SL system, a laser light spot with a diameter of 12.89 μm on the focal plane and resin layers with a thickness of 20 μm have been obtained. The experimental results indicate that cured depth and width increase with the ratio of laser power to scanning speed, and cured line with a width of 12 μm and a depth of 28 μm was built, which showed the capability building microstructures with this new SL system.
Research limitations/implications
The building area limited to 65 × 65 mm, is smaller than that of current SL system.
Practical implications
Small objects with intricate microstructures can be fabricated with the SL system.
Originality/value
The high‐resolution SL system provides a solution to the problem that has hampered the progress of SL process into a high resolution ranges below 75 μm.
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Zhengying Wei, Yiping Tang, Wanhua Zhao and Bingheng Lu
The paper aims to summarize the design theory for labyrinth channels of water saving emitters.
Abstract
Purpose
The paper aims to summarize the design theory for labyrinth channels of water saving emitters.
Design/methodology/approach
On the basis of extracting the structural parameters of labyrinth channels in water saving emitters, the hydraulic performance experiments on the integral emitters fabricated with higher resolution rapid prototyping technology are performed. Then, using multivariable linear regression, formulas of pressure versus flow rate and regression plots for different emitters are induced.
Findings
The formulas of flow rate versus structural parameters are summarized based on the trapezoid‐type channel unit, and verified through experiments. The relationships between flow rate, pressure and structural parameters of channels are established.
Research limitations/implications
The effect of emitter fabrication error on the flow rate is analyzed, which provides a basis for parameterized structural design and accuracy control in the fabrication of future emitters.
Practical implications
The Q‐H‐n relationship equations are used to design emitters which have flow‐rate errors under both high‐ and low‐water pressure of less than 4 percent. So the Q‐H‐n relationship equation of the emitter is well proven and accurate which can guide the design for the structure of emitters with trapezoid labyrinth channels.
Originality/value
In this paper, a new stereolithography system has been used to fabricate accurately a drip irrigation emitter with a complex microstructure, which cannot be obtained with conventional RP or other manufacturing processes. Compared to other manufacturing process, this new technique has higher manufacturing accuracy and can reduce the manufacturing cost and time. Furthermore, a design theory for labyrinth channels of water saving emitters is established.
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Wurikaixi Aiyiti, Wanhua Zhao, Bingheng Lu and Yiping Tang
To fabricate fully dense components with low costs, a rapid prototyping (RP) system based on micro‐plasma arc welding (MPAW) was developed. The appropriate process parameters were…
Abstract
Purpose
To fabricate fully dense components with low costs, a rapid prototyping (RP) system based on micro‐plasma arc welding (MPAW) was developed. The appropriate process parameters were investigated to build the parts with good mechanical properties and surface smoothness.
Design/methodology/approach
A simplified overlapping model between deposited tracks was established to investigate the relationships among the overlapping parameters, such as the ratio of width to height of the deposited track cross‐section (λ), scan spacing and overlapping ratio. Some ER308L stainless steel parts were built by different overlapping parameters, and the surface smoothness, tensile strength and elongation of the parts were tested.
Findings
The overlapped surface smoothness, tensile strength and elongation of the parts built with larger λ were better than those built with smaller λ. The longitudinal tensile strength and elongation of the parts were better than the transverse data.
Research limitations/implications
The scanning direction obviously affected the tensile strength and elongation of the parts, so the multi‐directional scanning mode should be used to get isotropic parts.
Originality/value
This MPAW‐based RP system provides a solution to build fully dense metal parts with relatively lower costs. The appropriate process parameters can be obtained with the developed overlapping model.
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Chunwei Li, Quansheng Sun and Yancheng Liu
As the service time of bridges increases, the degradation of bending capacity, the lack of safety reserves and the decrease in bridge reliability are common in early built…
Abstract
Purpose
As the service time of bridges increases, the degradation of bending capacity, the lack of safety reserves and the decrease in bridge reliability are common in early built bridges. Due to the defective lateral hinge joints, hollow slab bridges are prone to cracking of hinge joint between plates, transverse connection failure and stress of single plates under the action of long-term overload and repeated load. These phenomena seriously affect the bending capacity of the hollow slab bridge. This paper aims to describe a new method of simply supported hollow slab bridge reinforcement called polyurethane–cement (PUC) composite flexural reinforcement.
Design/methodology/approach
This paper first studies the preparation and tensile and compressive properties of PUC composite materials. Then, relying on the actual bridge strengthening project, the 5 × 20 m prestressed concrete simply supported hollow slab was reinforced with PUC composites with a thickness of 3 cm within 18 m of the beam bottom. Finally, the load test was used to compare the performance of the bridge before and after the strengthening.
Findings
Results showed that PUC has high compressive and tensile strengths of 72 and 46 MPa. The static test revealed that the measured values and verification coefficients of the measured points were reduced compared with those before strengthening, the deflection and strain were reduced by more than 15%, the measured section stiffness was improved by approximately 20%. After the strengthening, the lateral connection of the bridge, the strength and rigidity of the structure and the structural integrity and safety reserves were all significantly improved. The application of PUC to the flexural strengthening of the bridge structure has a significant effect.
Originality/value
As a new type of material, PUC composite is light, remarkable and has good performance. When used in the bending strengthening of bridge structures, this material can improve the strength, rigidity, safety reserve and bending capacity of bridges, thus demonstrating its good engineering application prospect.
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Thenmozhi M. and Aghila Sasidharan
This study aims to examine the effectiveness of governance in state-owned enterprises (SOEs) and explores if board independence enhances the firm value of SOEs in India and China…
Abstract
Purpose
This study aims to examine the effectiveness of governance in state-owned enterprises (SOEs) and explores if board independence enhances the firm value of SOEs in India and China. The study further explores the moderation impact of promoter ownership in enhancing firm value.
Design/methodology/approach
The study is confined to government-owned enterprises in India and China and is based on a sample of 53 central government-owned firms listed in National Stock Exchange of India and 110 state-owned firms listed in Shanghai Stock Exchange of China for the period 2010–2017. A fixed-effect panel regression analysis has been used to examine the effect of board independence on firm value.
Findings
The study found that board independence adds value to the SOEs in India and China and the presence of independent directors (IDs) in the board of SOEs act as better monitors of performance to protect the interest of minority shareholders. Probably, they minimize agency conflict and provide resources to the firm and management. The greater the government shareholdings, the board independence further enhances value of SOEs in India and China.
Practical implications
Compliance with guidelines on IDs in SOEs serves as an effective corporate governance mechanism and the presence of IDs can signal better firm performance. The government promoters align with the IDs in better monitoring of SOE performance.
Originality/value
The study is unique and contributes to the literature by examining the impact of board independence on firm value in the context of SOEs in India and China and also provides insight on the effect of promoter ownership on the effectiveness on board independence.