Dynamic Rock-Breaking Process of TBM Disc Cutters and Response Mechanism of Rock Mass Based on Discrete Element

Rock-breaking efficiency of full-face rock tunnel boring machine (TBM) is closely related to the performance of the disc cutter and the characteristics of the rock mass. In the point of view of mesomechanics, the particle flow code (PFC) is used to establish a numerical model of the rock mass and the disc cutter, and the process of TBM disc cutter intrusion into the rock mass is analyzed. The dynamic response mechanism and crack evolution process of the rock mass under the action of the disc cutter are studied on the basis of micromechanics, and the relationship between the rock mass crack, penetration, and cutting force during the intrusion of the disc cutter is revealed. The sensitivity analysis is carried out on the confining pressure conditions and the influence parameters of the disc cutter spacing. The results show that the rock breaking by disc cutter undergoes the transformation characteristics of compaction, shearing, and tension failure modes, and the failure process of the rock mass is the joint action of tension and shear. In the whole process of rock breaking, the disc cutter has the phenomenon of repeated loading-unloading alternation and leaping rock breaking; after the penetration of the disc cutter reached 9.0 mm, penetration creaks begin to appear on the surface of the rock mass; the penetration was obviously reduced with the increase of confining pressure, and it is mainly the penetration cracks on the surface; after the disc cutter spacing reaches 100.0 mm, there is no penetration crack between the two disc cutters. The research conclusion can provide a reference for the disc cutter optimization design.

Prediction of the number of consumed disc cutters of tunnel boring machine using intelligent methods

Purpose. Disc cutters are the main cutting tools for the Tunnel Boring Machines (TBMs). Prediction of the number of consumed disc cutters of TBMs is one of the most significant factors in the tunneling projects. Choosing the right model for predicting the number of consumed disc cutters in mechanized tunneling projects has been the most important mechanized tunneling topics in recent years. Methods. In this research, the prediction of the number of consumed disc cutters considering machine and ground conditions such as Power (KW), Revolutions per minute (RPM) (Cycle/Min), Thrust per Cutter (KN), Geological Strength Index (GSI) in the Sabzkooh water conveyance tunnel has been conducted by multiple linear regression analysis and multiple nonlinear regression, Gene Expression Programming (GEP) method and Support Vector Machine (SVM) approaches. Findings. Results showed that the number of consumed disc cutters for linear regression method is R2 = 0.95 and RMSE = 0.83, nonlinear regression method is – R2 = 0.95 and RMSE = 0.84, Gene Expression Programming (GEP) method is – R2 = 0.94 and RMSE = 0.95, Support Vector Machine (SVM) method is – R2 = 0.98 and RMSE = 0.45. Originality. During the analyses, in order to evaluate the accuracy and efficiency of predictive models, the coefficient of determination (R2) and root mean square error (RMSE) have been used. Practical implications. Results demonstrated that all four methods are effective and have high accuracy but the method of support vector machine has a special superiority over other methods.

The Assessment of the Maximum Heat Production and Cooling Effectiveness of Three Different Drill Types (Conical vs. Cylindrical vs. Horizontal) during Implant Bed Preparation—An In Vitro Study

The aim of this experimental study was to verify thermal diffusion differences, by measuring the maximum temperature achieved with different drill shapes. Synthetic bone blocks of type I density made from solid rigid polyurethane (PUR) foam were used to perform the drilling procedures. The experiment was conducted at three different rotation speeds: 800, 3000 and 5000 rpm. Conical drills (with and without an internal cooling hole) were compared with horizontal drills and disc drills. The temperature during drilling for implant bed preparation was estimated with the use of thermocouples and an infrared (IR) camera. The temperature during drilling with disc cutters for lateral basal implants did not exceed 33 ∘C and the temperature decreased in proportion to higher drill speed. The results indicate that the tested design is safe and will not cause bone overheating.

A Simulation Method for Free-form Milling Cylindrical Gears With Disc Cutters

Free-form milling is a flexible gear machining method that allows using general disc cutters to machine various gear types on a 5-axis machine tool. This paper proposes a two-dimensional simulation method for free-form milling of cylindrical gears with disc cutters. A mathematical model for free-form milling of cylindrical gears with disc cutters is constructed. By analyzing the spatial positional relationships between the cutter and the workpiece, the instantaneous contact line is derived and projected onto the gear end face, and then the projected curves are intersected to obtain the final profile. This calculation method realizes the rapid simulation of the actual cutting condition on the gear end face, which is beneficial to the judgment of machining interference and the analysis of the tooth profile accuracy during the gear machining process.

Development of Optimal Design and Circular Broach Modular Design of Disc Cutters with the Development of a Parametric Model

Cutting tool is one of the most important instruments in production. It is used for machining of different components on machine tools. A material is cut into a chip to incur the desired work piece surface currently used in engineering various cutting tools. The directions of development of structures of metal cutting tools are: higher precision of dimensional and geometrical parameters, the use of new tool materials, cost, and quick. The cutting tools are not only affected by the design of machine, technology of manufacturing of products, but also impact the constructive forms of machine parts. The emergence of mechanical spine, thanks to the pull method. Spine broach can provide high-performance processing spine bore with the required accuracy. The development of heavy machine tools required the creation of new designs of large instruments. The use of mechanical automatic lines also required design tools with high dimensional stability capable of handling the items within the specified tolerance for a certain time. Instruments were developed in the process of renewing the cutting edge of the cutting tools with automatic adjustment; setting up tools on the size of the machine is a device for automatic replacement of worn tool in the process line of the Computer-Aided Manufacturing CAM of the cutting tool special requirements. Equipment must operate with high level efficiency, so to reduce the loss of time resetting of the need to minimal. A cutting tool requires knowledge of the theoretical foundations of design and calculation tools using CAD.

Evaluating the Efficiency of a New Cutterhead Design to Counteract the Drawbacks of Excavation through Very Hard Rocks

The application of appropriate excavation equipment in difficult grounds is of crucial importance and consequently improves the performance of hard rock Tunnel Boring Machines (TBMs). The cutterhead is one of the main components of TBMs which is directly involved in the excavation process, and its design can highly affect the cutting efficiency, the overall balance of the head, the performance of main bearing in long term, and the wear of the whole cutting face and muck buckets. This paper mainly focuses on the significant role of a proper design on the cutting efficiency with reference to a TBM tunneling project. Due to existence of very hard and abrasive rocks on the path of Kerman water conveyance tunnel, a new cutterhead was designed to be applied on a second hand TBM. The new cutterhead contains larger 19-inch disc cutters with a new disc cutter layout. Since the new cutterhead was launched following the excavation of the old one in a specific chainage of the tunnel, the performance of the two cutterheads in pyroclastic rocks could be compared with respect to the cutting efficiency, and lower specific energy values were observed for the new cutterhead which is the indicator of a better cutting efficiency in this geological condition.

Discrete-Element Analysis of the Excavation Performance of an EPB Shield TBM under Different Operating Conditions

This study used a discrete-element analysis to predict the excavation performance of a 7.73 m-diameter earth pressure balance (EPB) shield tunnel boring machine (TBM). The simulation mainly predicted several excavation performance indicators for the machine, under different operating conditions. The number of particles in the chamber and the chamber pressure varied, as the operating conditions changed during the simulated TBM excavation. The results showed that the compressive force, torque, and driving power acting on the TBM cutterhead varied with its rotation speed, increasing as the cutterhead rotation speed rose. The overall compressive force acting on all of the disc cutters and their impact wear increased linearly as the cutterhead rotation accelerated. The position of a disc cutter on the cutterhead had a particularly strong influence, with higher compressive forces experienced by the cutters closer to the center. In contrast, the gauge disc cutters at the transition zone of the cutterhead showed more wear than those elsewhere. The muck discharge rate and the driving power of the screw conveyor rose with increasing screw conveyor and cutterhead rotation speeds. Finally, this study suggests optimal operation conditions, based on pressure balance and operational management of the TBM.