Wall Taper Research Articles

Localized sinking electrochemical machining of pre-shaped convex structure on revolution surface using specifically designed cathode tool

Counter-rotating electrochemical machining (CRECM) is an effective method for machining thin-walled revolving parts with complex structures. However, it is difficult to achieve a desirable uniform straight sidewall during the CRECM of isolated convex structures with variable cross-sectional profiles, so a subsequent local machining process is necessary. In this paper, a localized sinking ECM method is proposed to locally machine a pre-shaped convex structure by CRECM. A mathematical model is established to analyze the anode shaping process. In addition, a special cathode tool is designed to control the junction mark between the subsequent dissolution regions and the surrounded non-machined areas. The simulation and experimental results indicate that the sidewall profiles of the convex structure can be improved remarkably. In lateral view, convex side wall taper is reduced from 21.81° to 3.05°, In front view, convex side wall taper is reduced from 6.45° to 0.28°, Furthermore, the junction mark can be effectively controlled to within 0.07 mm.

Endocrown Feasibility for Primary Molars: A Finite Element Study.

To study the possibility of using pediatric endocrowns to restore the second primary molar using three-dimensional (3D) finite element analysis. A 3D finite element model was built for a pediatric mandibular molar, starting with laser scanning a naturally extracted tooth. The access cavity had an elliptic shape with 6 mm width, 4 mm height, and 2 mm depth with a wall taper angle of 5 degrees.Two materials (Zr and E-max) were tested for the endocrown and two cementing materials (glass ionomer and resin cement) with 20 to 40 μm thickness. Twelve case studies were reported within this research as the applied load of 330 N was tested with three angulations vertical, oblique at 45 degrees, and laterally. Twelve linear static stress analyses were performed. The resultant stresses and deformations' distribution patterns did not alter much, and values were within the threshold of physiological tolerance. Deformations were negligibly changed with changing endocrown and cement materials. In contrast, endocrown stresses indicated zirconia endocrown would have a long lifetime, while E-max one will have a relatively short lifetime. Analysis results indicated that bone was negligibly affected by changing endocrowns and cementing materials. Both tested endocrown materials can be used safely. Zirconia endocrowns may have a much longer lifetime than E-max.

A novel chairside technique to assess the interocclusal clearance and abutment axial walls during tooth preparation.

The importance of a judicious and unerring abutment tooth preparation in the field of prosthodontics has always been paramount. It is not uncommon for many clinicians to face challenges during laboratory fabrication of fixed prostheses, caused due to inappropriate occlusal clearance and over axial wall taper of the abutment tooth. With evolving technologies and methods, the modus operandi for attaining such tooth preparation is varying; however, every technique has its own shortcomings. The technique mentioned in the article is cost-effective as it uses modified Heister mouth gag forceps to achieve the desired objective of evaluating the prepared abutment morphology three-dimensionally with minimum chairside time.

Influence of weld joint geometry and strength mismatch on load bearing capacity of API pipeline

The load bearing capacity of pipeline weld joints with varying wall thicknesses and strength mismatch was assessed using finite element analyses. The structural integrity of API X65-API X80, API X42-API X65, and API X42-API X80 weld joints was investigated under tensile, internal pressure and bending load.Pipe joint combinations with an outer diameter of 762 mm (30 inches) had wall thickness ratios of 1.22, 1.54, and 1.89. The pipe joint's end face with different wall thicknesses was machined with a taper angle of 4°∼45° along the longitudinal direction of the low strength and thick pipe.According to parametric studies, the tensile strength and moment of a pipe joint with a wall thickness ratio less than 1.5 were unaffected by the wall thickness ratio and taper angle; however, those of a pipe joint with a wall thickness ratio greater than 1.5 were significantly reduced at low taper angles. The wall thickness ratio and taper angle had no effect on the failure pressure of the pipe joint with different wall thicknesses.

Effect of abutment tooth geometry on the accuracy of 2 intraoral scanners

Aim: The aim of this in-vitro study was to evaluate the effect of abutment tooth geometry on the accuracy of two intraoral scanners. Methodology: The study was conducted using maxillary typodont. Six full coverage crown preparations were performed on central incisors, 1st premolars and 1st molars with known axial wall taper (6o and 12o) using dental parallelometer. Highly accurate table-top scanner (Identica T500) was used to obtain reference scan to the typodont. Two intraoral scanners (3shape Trios 3 and Medit i500) scanned the typodont 13 times to obtain total samples of prepared teeth (n=39) for each group. All scans were exported in standard tessellation language (STL) format. Measurements of trueness and precision for respective tooth preparation were evaluated using reverse engineering software for superimposition and deviation analysis. Comparison between groups was performed by using One-Way ANOVA test followed by Tukey`s Post Hoc test and Independent t- test. Results: Statistical analysis showed no significant difference in trueness between the two intraoral scanners. Trueness values were 39.9 µm and 41 µm for Trios 3 and Medit i500. Trios 3 was significantly more precise (23.6 µm) compared to Medit i500 (34.7 µm).

Femtosecond Laser for Cavity Preparation in Enamel and Dentin: Axial Wall Taper Related Factors.

Background and objective: Femtosecond laser (fs-laser) is a novel tooth preparation tool. After cavities were prepared by fs-laser, their axial-wall taper is closely related to the retention force and success of restorations, while the taper after preparation by fs-laser is not clear yet. This study aimed to explore the value of the taper after fs-laser tooth preparation and the effect of laser fluence, scanning line spacing, and scanning layers on taper. Materials and methods: Twenty cavities with a width of 0.5 mm were prepared by an fs-laser both in enamel and dentin to obtain the axial-wall taper (No. PKUSSIRB-201949124). To study the effects of three parameters of fs-laser, five different laser fluence were set as 1.56, 3.13, 4.69, 6.25, and 7.81 J/cm2 of five cavities. Scanning line spacing was set as 6, 12, 25, 30, 40, and 50 μm of six cavities and the scanning layers were 5, 10, 25, 50, 75, 100, 200, 300, and 400, respectively, of nine cavities. Laser pulses irradiated perpendicular to the tooth and the scanning path was controlled via a vibratory mirror. The taper was measured with a laser confocal microscope. Curves of the taper versus different parameters were drawn. Results: There was a significant difference in taper between enamel and dentin. Overall, the taper decreased gradually with the increase of laser fluence. The optimal taper obtained was 20.53° ± 0.28° in dentin and 38.71° ± 0.46° in enamel when the corresponding fluence was 6.25 J/cm2. In comparison, the scanning line spacing has little effect on the taper. The scanning layers significantly affect the taper, which decreased dramatically as scanning layers increased within 75 layers and does not change considerably as it was beyond 100 layers. Conclusions: Reasonable selection of laser fluence, scanning line spacing, and the number of scanning layers can optimize the cavity taper by fs-laser.

A Comparison of Convergence Angles of Crown preparations in an undergraduate programme at a Tertiary Institution

The retention of indirect dental restorations is of concern for clinicians as it influences the success of clinical outcomes. Retention and resistance are dependent on many factors including the convergence angles of the opposing axial wall tapers. Adequate axial wall taper is important in crown preparation to improve physical retention and increase resistance of the restoration. Aims and objectives To determine and compare the convergence angles (CA) of KaVo® teeth prepared for full coverage crown restorations by fourth year dental students in a preclinical fixed prosthodontics module in a five year dentistry training programme. Methodology Crown preparations produced by fourth year dental students at Sefako Makgatho Health Sciences University (SMU), South Africa, over a period of 3 years were included in this study. These preparations were digitally captured using CAD-CAM imaging technology. The images were analysed in ImageJ® software to determine the mesio-distal convergence angles. Statistical analysis was undertaken using SPSS ver. 27 for Windows. Results The overall mean convergence angle of 15.38° ± 6.68° was computed for n=75 crown preparations. ANOVA revealed a significant difference (p<0.05) in the CA among the three cohorts (2017: 16.87° ± 6.94°; 2018: 17.23° ± 6.13°; 2019: 12.02° ± 5.86°). A reasonable proportion of dental students n=25 (33%) achieved the recommended CA of 6° to 12°.ConclusionThis study indicates that with objective evaluation tools, it is possible to improve on the intended guidelines for crown preparations during undergraduate teaching and training in pre-clinical Fixed Prosthodontics.

Picosecond laser machining of ceramic matrix composite

In recent years, there has been increased interest in using silicon carbide (SiC) based ceramic matrix composites (CMC) materials for aero-engine applications; however, both conventional and non-conventional machining of SiC CMC is challenging. Ultrashort pulse laser machining is evolving as an attractive option for materials like SiC CMC; however, the current understanding is based only on low-power lasers, whose removal rate is not in-line with the industrial requirements. This paper presents the results of 300 W picosecond laser machining of SiC CMC. The laser machining characteristics of SiC CMC were investigated at high average power and discussed in detail. A 300 W picosecond laser can be used to achieve a material removal rate of ∼230 mm3/min (0.76 mm3/minW) for a machining depth of 2 mm in SiC CMC, however, irrespective of the laser parameters a wall taper of ∼7° was observed over the sides of the slots that need to be addressed.

High-Throughput Picosecond Laser Machining of Aerospace Nickel Superalloy

This manuscript discusses the experimental results on 300 W picosecond laser machining of aerospace-grade nickel superalloy. The effect of the laser’s energetic and beam scanning parameters on the machining performance has been studied in detail. The machining performance has been investigated in terms of surface roughness, sub-surface thermal damage, and material removal rate. At optimal process conditions, a picosecond laser with an average power output of 300 W can be used to achieve a material removal rate (MRR) of ∼140 mm3/min, with thermal damage less than 20 µm. Shorter laser pulse widths increase the material removal rate and reduce the resultant surface roughness. High scanning speeds improve the picosecond laser machining performance. Edge wall taper of ∼10° was observed over all the picosecond laser machined slots. The investigation demonstrates that high-power picosecond lasers can be used for the macro-machining of industrial components at an acceptable speed and quality.

A Mathematical Model of Laser Drilling with Laser Absorption in the Plasma

Despite being an accurate process with high processing speed, laser drilling suffers from several drawbacks including wall taper, recast layer and spatter. Hence, in order to improve the process efficiency and achieve the good hole quality, it is crucial to have a precise model which can be used as a tool to relate the process parameters to the process output. In this paper, an analytical model of laser drilling is developed. The governing equations are established from the energy equations at the solid-liquid and liquid-vapor interfaces. Absorption of laser energy in the plasma and an additional energy generated from the exothermic reaction are also included in the model. Aiming at simplifying the model, a constant value of the plasma absorption coefficient of the laser beam is employed. Validation of the model is done by comparing with the available experimental data. It is concluded that the recommended value of the plasma absorption coefficient for low carbon steel drilling is 0.2.

Picosecond laser machining of tungsten carbide

Hard materials such as tungsten carbide (WC) are extensively used in cutting tools in high-value manufacturing, and the machining of these materials with sufficient speed and quality is essential to exploit their full potential. Over the last two decades, short (nanosecond (ns)) and ultra-short (picosecond (ps); femtosecond (fs)) pulse laser machining has been evaluated by various researchers and proposed as an alternative to the current state-of-the-art machining techniques for advanced materials like WC, which include mechanical grinding and electrical discharge machining. However, most of the established/existing research on this topic is based on low power lasers, which may not be adopted in industrial production environments due to its low material removal rate. This paper presents the results of a fundamental study, on using a 300 W picosecond laser for the deep machining of tungsten carbide. The influence of various laser parameters on the geometric precision and quality (surface and sub-surface) of the ablated area was analysed, and the ablation mechanism is discussed in detail. Laser pulse frequency and scanning speed have minimal effect on ablation rate at high power levels. The surface roughness of the ablated area increases with the ablation depth. At optimal conditions, no significant thermal defects such as a recast layer, micro crack or heat affected zone were observed, even at a high average power of 300 W. The material removal rate (MRR) seems to be proportional to the average power of the laser, and a removal rate of around 45 mm3 per minute can be achieved at 300 W power level. Edge wall taper appears to be a significant issue that needs to be resolved to enable industrial exploitation of high power ultra-short pulse lasers.

Influence of Preparation Type and Tooth Geometry on the Accuracy of Different Intraoral Scanners.

To evaluate the influence of preparation design and tooth geometry on the accuracy of scans obtained from three different intraoral scanners (IOS). Full coverage crown and inlay preparations with known axial wall tapers (6ᵒ and 12ᵒ) were performed on typodont teeth using a computer numerical control machine. Reference models were scanned with a highly accurate reference scanner (Ineos X5) and saved in standard tessellation language (STL) format then each IOS (Omnicam, Trios, and i500) scanned each model 10 times. The STL files obtained from the intraoral scanners were compared to the reference models (trueness) and within each test group (precision). Data were statistically analyzed using three- way ANOVA and one- way ANOVA. When comparing trueness values extracoronal preparations (32.30 ± 11.23µm) was significantly better than intra-coronal preparation (59.61 ± 16.42 µm). As for opposing wall taper, one-way ANOVA revealed that the more the convergence or divergence between opposing walls the better is the trueness. Significant differences were observed between the scanners. 3 Shape Trios (35.70 ± 14.12 µm) and medit i500 (44.31 ± 11.41 µm) showed no statistically significant differences. However, both showed significantly better precision results when compared to Omnicam (57.83 ± 22.14 µm). Extracoronal preparations show better trueness and precision in comparison to intracoronal preparations. Trios and i500 have better trueness and precision than Omnicam. Increasing the taper of the axial wall has a direct effect on trueness of scans obtained from the IOS.

A Comprehensive Approach to Design the Copper Mold Tubes for Steel Continuous Casting

In this article, some of the design aspects of mold tubes for continuous casting of steel have been discussed and analyzed. A coupled thermo-mechanical mathematical model based on finite element methods has been presented for computations of basic design parameters of a tubular mold. The basic parameters include tube length, inner wall taper, corner radius, etc. A simulation based on an industrial rectangular mold tube from an integrated steel plant has been performed for better understanding of the basic designing process. From the simulation, it is noticed that the corner area of the solidifying shell loses contact with mold wall causing reheating of the off-corner region and thinning of shell thickness. The performance of the continuous casting process is found to be strongly dependent on inner wall taper.

Volumetric analyses of restorative crown preparations in simulated-premolar and -molar teeth

Crowns or abutments of fixed partial denture tooth preparations to restore natural teeth or implant-supported restorations require tooth or abutment reduction in a tapered format. Low angulations of axial wall taper to the long axis of the tooth or abutment have been shown to increase the restoration’s stability during masticatory function with large occlusal loads. The tooth preparation and luting agent stabilize the restoration during these loading cycles to prevent dislodgement. Restoration dislodgement represents a catastrophic failure of the prosthesis in function. The preparation attributes contribute to prevent displacement failure and reduce luting agent tensile and shear stresses. Low axial wall taper levels increase resistance to rotational displacement. Increasing axial wall angulations produces negative consequences including reduced rotational resistance, reduced surface area and increased volume of remaining tooth structure. These three considerations have been shown to involve three variables: preparation vertical height, horizontal base width from rotational axis and rotational axis vertical height compared to the opposing axial resisting wall. Natural tooth preparations are completed by a restorative dentist with a hand-held high-speed handpiece with cutting instruments within the oral cavity; while implant-supported custom abutments are prepared in a similar manner but machined outside the oral cavity. As a result, the machined abutment is more controlled for ideal taper in inanimate materials compared to the intraoral tooth preparation on human vital tissues. This experimental study will analyze the preparation of simulated-vital tooth premolars and molars for volume loss at ideal and non-ideal axial wall angulations with variation of vertical heights and vital pulpal tissue volumes.

Axial wall angulation for rotational resistance in a theoretical-maxillary premolar model.

ObjectivesThe aim of this study was to determine the influence of short base lengths and supplemental grooves on surface area and rotational resistance in a simulated‐maxillary premolar.Materials and MethodsTrigonometric calculations were done to determine the total surface area with and without supplemental grooves. Additional computations were done to determine the maximum wall angle needed to resist rotation displacement in a premolar‐sized model. Wall heights of 3.0, 4.0, and 5.0 mm were used in the surface area and rotational axis computations. The rotational axis was located on the lingual restoration margin to produce a buccal‐to‐lingual rotational displacement.ResultsTotal surface area decreased with increasing four‐wall taper levels from 2° to 18° and decreasing preparation heights from 5 to 3 mm. Significant surface area improvements were found with the supplemental use of mesial and distal axial grooves compared with the same condition without grooves in all taper levels and preparation height categories. Resistance to rotational displacement was determined to occur at only at very low levels of opposing wall taper angles. The use of supplemental grooves on mesial and distal axial walls significantly improved both total surface area and rotational resistance.ConclusionsThe vertical wall taper angles, preparation heights, and supplemental grooves play a role in resistance form and restoration stability.

An investigation on deformation behaviors of energy absorbers for passenger coaches

Thin-walled structures is used commonly as energy absorbers at the front and back of the coaches. These parts should be designed to minimize the damage to the vehicle and prevent the passengers from fatality and/or injury by absorbing the collision energy in railway transportation. In this paper, deformation behaviors of tube like structures with truncated cone under the axial impact load were investigated by means of finite element analysis (FEA). The energy absorbers having tube like structures were modelled at the same weight and have three different wall thickness and taper angle. As a result of FEA, the performances of straight and truncated cone type energy absorbers were compared in terms of energy absorption capacities and an optimization study was done to determine the effects of thickness and taper angle on energy absorbing performances of the members. The analysis of variance in 95% confidence level was applied in order to determine the effects of design parameters on total efficiency (TE). Besides, optimum design parameters for TE were determined by using Taguchi optimization methodology. Thickness was found as the most significant parameter on total efficiency with 60.52% percentage contribution ratio according to ANOVA results.

A clinical study on abutment taper and height of full cast crown preparations.

Dental students at Tokyo Medical and Dental University are taught to prepare teeth for full cast crowns with a wall taper of 2 to 5 degrees and an occlusal clearance of 1.2 to 1.5 mm. However, it is difficult to achieve such an ideal taper. The objective of this study was to examine the abutment taper and height of teeth prepared for crowns by final-year dental students under clinical supervision. To evaluate the degree of taper and height of the prepared teeth, shadowgraphs of 63 working stone dies were traced. The angles and height of the abutments were then measured on the same tracing. Only 12.7% (8 out of 63 abutments) of the prepared teeth fell within the ideal range of 2 to 5 degrees, and the average taper was 9.5 degrees (19.0 degrees convergence angle). The average abutment height varied from 4.8 mm to 6.9 mm and showed a close relationship with the abutment taper. The average taper, 9.5 degrees, of the present study was larger than the ideal taper; however, it was thought to be clinically acceptable as it is difficult to achieve the ideal taper intraorally.

Relative contributions from the ventricle and arterial tree to arterial pressure and its amplification: an experimental study.

Arterial pressure is an important diagnostic parameter for cardiovascular disease. However, relative contributions of individual ventricular and arterial parameters in generating and augmenting pressure are not understood. Using a novel experimental arterial model, our aim was to characterize individual parameter contributions to arterial pressure and its amplification. A piston-driven ventricle provided programmable stroke profiles into various silicone arterial trees and a bovine aorta. Inotropy was varied in the ventricle, and arterial parameters modulated included wall thickness, taper and diameter, the presence of bifurcation, and a native aorta (bovine) versus silicone. Wave reflection at bifurcations was measured and compared with theory, varying parent-to-child tube diameter ratios, and branch angles. Intravascular pressure-tip wires and ultrasonic flow probes measured pressure and flow. Increasing ventricular inotropy independently augmented pressure amplification from 17% to 61% between the lower and higher systolic gradient stroke profiles in the silicone arterial network and from 10% to 32% in the bovine aorta. Amplification increased with presence of a bifurcation, decreasing wall thickness and vessel taper. Pulse pressure increased with increasing wall thickness (stiffness) and taper angle and decreasing diameter. Theoretical predictions of wave transmission through bifurcations werre similar to measurements (correlation: 0.91, R2 = 0.94) but underestimated wave reflection (correlation: 0.75, R2 = 0.94), indicating energy losses during mechanical wave reflection. This study offers the first comprehensive investigation of contributors to hypertensive pressure and its propagation throughout the arterial tree. Importantly, ventricular inotropy plays a crucial role in the amplification of peripheral pressure wave, which offers opportunity for noninvasive assessment of ventricular health.NEW & NOTEWORTHY The present study distinguishes contributions from cardiac and arterial parameters to elevated blood pressure and pressure amplification. Most importantly, it offers the first evidence that ventricular inotropy, an indicator of ventricular function, is an independent determinant of pressure amplification and could be measured with such established devices such as the SphygmoCor.

Custom-Designed Coiled Tubing Leads to Success in Extended-Reach Operations

This article, written by Special Publications Editor Adam Wilson, contains highlights of paper SPE 184752, “Vaca Muerta Coiled-Tubing-Operations Success and the Development of Future Extended-Reach Operations,” by I.I. Galvan, Global Tubing; M.M. Nebiolo, R.D. Del Negro, and G.A. Landinez Gomez, YPF; C. Cerne, SPE, ThruTubing Solutions; and A. Sanchez, SPE, and G. Mallanao, Global Tubing, prepared for the 2017 SPE/ICoTA Coiled Tubing and Well Intervention Conference and Exhibition, Houston, 21–22 March. The paper has not been peer reviewed. Advanced horizontal drilling, multistage hydraulic fracturing, and other technologies have helped make the Vaca Muerta shale oil and gas resource economically viable. An option to exploit this resource better is to increase the length of the horizontal section of each well to add hydraulic-fracture stages. Anticipated high angles in deviated well sections, along with the extended horizontal length of the planned wells, formed an expectation that conventional coiled-tubing (CT) designs would not be able to service the new well designs. Using refined, custom-engineered CT-string designs appears to be an economic and efficient solution. Project Overview Increased diameter, strength, and reliability have made CT the preferred cost-effective well-intervention solution in the Vaca Muerta unconventional shale development; however, the maximum lateral reach the CT can achieve during operations is a limiting factor for well optimization. Initially, 2-in. CT strings with a simple wall taper shape were an effective and reliable option to complete wells in the first development stage. However, the need for optimized design and even-larger-diameter CT with enhanced-wall-thickness configurations became apparent when an increase of the well lateral lengths was attempted. CT-String Design Considerations The CT-string designs followed a cooperative process between the operator, the CT service companies, tool providers, and the CT-manufacturing engineers. Tubing forces, buckling occurrence, and lockup depths were analyzed in detail to determine the optimal CT size and string design makeup to ensure the likelihood of reaching target depth (TD) in the planned extended-reach wells. Additionally, hydraulic analysis was performed to compare frictional pressure losses (CT, bottomhole-assembly, and annular) using the optimal flow rates for annular velocities adequate to support sufficient well cleaning. The results from the analysis were used to estimate fatigue accumulation in the CT strings, considering anticipated circulating pressures and surface-equipment (reel and gooseneck arch) dimensions. The primary objective for the new CT-string design is to optimize lateral reach and available weight on bit for post-fracture mill-out operations.

Theoretical axial wall angulation for rotational resistance form in an experimental-fixed partial denture.

PURPOSEThe aim of this study was to determine the influence of long base lengths of a fixed partial denture (FPD) to rotational resistance with variation of vertical wall angulation.MATERIALS AND METHODSTrigonometric calculations were done to determine the maximum wall angle needed to resist rotational displacement of an experimental-FPD model in 2-dimensional plane. The maximum wall angle calculation determines the greatest taper that resists rotation. Two different axes of rotation were used to test this model with five vertical abutment heights of 3-, 3.5-, 4-, 4.5-, and 5-mm. The two rotational axes were located on the mesial-side of the anterior abutment and the distal-side of the posterior abutment. Rotation of the FPD around the anterior axis was counter-clockwise, Posterior-Anterior (P-A) and clockwise, Anterior-Posterior (A-P) around the distal axis in the sagittal plane.RESULTSLow levels of vertical wall taper, ≤ 10-degrees, were needed to resist rotational displacement in all wall height categories; 2–to–6–degrees is generally considered ideal, with 7–to–10–degrees as favorable to the long axis of the abutment. Rotation around both axes demonstrated that two axial walls of the FPD resisted rotational displacement in each direction. In addition, uneven abutment height combinations required the lowest wall angulations to achieve resistance in this study.CONCLUSIONThe vertical height and angulation of FPD abutments, two rotational axes, and the long base lengths all play a role in FPD resistance form.