MILLING EFFECTIVENESS INCREASE BY MEANS OF HARD-ALLOY COMPOUND END MILLING CUTTERS

The investigation purpose: the effectiveness increase of hard-alloy end milling cutters at the expense of new milling cutter design development conventionally called compound milling cutters. The problem solved during investigation: the reveal of the most efficient fields of compound milling cutter use. The scientific novelty of the work: the formation of a new kind of hard-alloy end milling cutter design, to avoid milling cutter destruction in the place of shank end mounting in the chuck of the machine a shank end is made of structural steel and soldered with a hard-alloy cutting part of the milling cutter. As a result of the investigation it was defined: a) compound milling cutters compete with monolithic milling cutters in accuracy during billet production of parts at a lower cost of milling cutters; b) a compound milling cutter with a diameter of 16 mm and a milling cutter length of 92 mm substitute successfully a monolithic milling cutter by production accuracy and ensures cost reduction of a product by 4%; c) a compound milling cutter with a length of 220 mm as compared with a monolithic milling cutter ensures product cost reduction by 38% and applicable for general aims at engineering enterprises.

Improvement of drilling cutter design

The article describes the design of drilling cutters most commonly used in coal mines in Russia. The area of their application is given versus the type of a drilling machine and hardness of rocks. The implemented research aimed at finding the causes of failure of drilling cutters shows the types of breakdowns of drilling cutters and their causes. A review of the recommendations and modern engineering solutions on increase in the life of rotary drilling tools is given. Percentages of the cutter failure causes over the period from 2010 to 2014 are presented. The main failure cause of cutters is found to be the blunting of the blades of tungsten-cobalt cutting plates. The studies conducted earlier by the authors of the article indicate the possibility of extending the life of a drilling tool by reinforcing its cutting plates with superhard composite materials. In this connection, the use of composites based on cubic boron nitride has been proposed for creating cutting inserts for drilling cutters. The article also describes the study of rock drilling rates with various cutters mounted on hydraulic and pneumatic drilling machines. The obtained information can be used when planning drilling in coal mines. It is shown that the highest drilling rate can be achieved with hydraulic drilling machines equipped with triple cutters. It is found that with the growth of rock hardness on the scale of Professor M. M. Protodyakonov, reduction in the drilling rate of a hydraulic drilling rig with a three-blade cutter occurs more intensively than with a pneumatic drilling rig with a two-blade cutter. It is revealed that at the rock hardness of 10 on the Protodyakonov scale, drilling rates of different design cutters differ slightly. The study was supported by the President of the Russian Federation, Grant for Young Candidates of Sciences—MK-6689.2018.8.

Numerical modeling on drilling fluid and cutter design effect on drilling bit cutter thermal wear and breakdown

The unconventional reservoir geological complexity will reduce the drilling bit performance. The drill bit poor performance was the reduction in rate of penetration (ROP) due to bit balling and worn cutter and downhole vibrations that led to polycrystalline diamond compact (PDC) cutter to break prematurely. These poor performances were caused by drilling the transitional formations (interbedded formations) that could create huge imbalance of forces, causing downhole vibration which led to PDC cutter breakage and thermal wear. These consequently caused worn cutter which lowered the ROP. This low performance required necessary improvements in drill bit cutter design. This research investigates thermal–mechanical wear of three specific PDC cutters: standard chamfered, ax, and stinger on the application of heat flux and cooling effect by different drilling fluids by using FEM. Based on simulation results, the best combination to be used was chamfered cutter geometry with OBM or stinger cutter geometry with SBM. Modeling studies require experimental validation of the results.

Variable Helix Cutter Design to Suppress Regenerative Effect

Regeneration is a major mechanism to generate self-excited chatter vibration in cutting. Variable helix cutters are useful to suppress regeneration. Although simultaneous optimization of pitch/helix angles is significantly important, there is no practical design methodology to optimize the variable helix cutter geometry so far. In order to attain robust regeneration suppression, a new design method of variable helix cutters is proposed in the present study. The pitch angles vary along axial position due to disagreement of the helix angles. Because of this nature, regeneration can be suppressed in a robust manner with respect to changes of chatter frequency and/or spindle speed. The proposed design satisfies robustness against axial depth of cut variations. Optimal pitch/helix angles are formulated on the basis of distinctive relationship between the cutter geometry and “Regeneration Factor (RF)”, which is an index to quantify influence of regeneration in the process. Through analytical investigations, it is confirmed that regeneration can be suppressed effectively by the proposed method, resulting in significant chatter stability increase. Low immersion milling experiment verified significant stability and robustness of the proposed variable helix design.

Design and Experiments of Coaxial Contra-Rotating Sugarcane Base Cutter with Time-Frequency Control

A laboratory-based cutting platform with speed control was developed to investigate the cutting mechanism for the support-cutting of sugarcane. A coaxial contra-rotating base cutter was designed to facilitate sugarcane support-cutting in a laboratory setting. The cutting platform, which consists of two discs with cutting blades, was driven by two variable-frequency electric motors. To manipulate the speed of each motor independently, a time-frequency controller was designed to handle system nonlinearity and to maintain system stability subject to speed variation. To validate the cutter design, a series of idle running tests and cane-cutting tests were implemented using the laboratory-based cutting platform. The results indicated that the rotating speed of the two cutting discs could be adjusted smoothly. The controller capped the overshoot under 1% in the speed step response and kept the fluctuation of the speed difference of the two cutting discs at less than 2.5 rpm. Evaluating the cane quality of support-cutting against free-cutting showed that support-cutting decreased the stubble damage rate from 22.67% to as little as 6.67%. The results also suggested that the time-frequency-controlled cutting platform was feasible for subsequent investigation for a better understanding of sugarcane support-cutting, such as the variation of energy consumption or stubble damage rate with different rotating speed or different blade shape, which will provide constructive suggestions for the future base cutter design. Keywords: Base cutter, Support-cutting, Cutting platform, Time-frequency control.

Optimization model for polycrystalline diamond compact bits based on reverse design

To improve the effectiveness and efficiency of bit cutter design, a new reverse design method is put forward based on the geometry of a polycrystalline diamond compact bit. The polycrystalline diamond compact bit design parameters (cutter parameters and polycrystalline diamond compact bit profile) are calculated based on the data obtained by three-dimensional scanning technology. The main calculation work is realized using MATLAB. Compared with using point cloud data, using the three-dimensional model based on calculated cutter parameters also provides accurate results. Then, the cutter parameters are optimized according to the minimum lateral force principle, minimizing the maximum wear rate principle. The lateral unbalance force of the bit decreases from 7.55%, for the original bit, to 3.17%, for the optimized bit, and the wear of the optimized drill bit is more uniform. The field data show that the optimization models create bits with a longer life and a higher rate of penetration.