Tool life improvement by peck drilling and thrust force monitoring during deep-micro-hole drilling of steel

An unstable drilling process results from the insufficient supply of cutting fluid and bad chip removal as machining depth increases. These causes of unstable drilling lead to serious problems in micro-drilling. All drills were broken while drilling the first hole in the micro-deep-hole drilling of steel with an aspect ratio over 10, regardless of the cutting conditions. Peck drilling, which utilizes an intermittent feed, is widely used in drilling deep holes. Generally, the one-step feed-length (OSFL) of peck drilling is one and a half times longer than the drill diameter in conventional drilling. An OSFL between one half and twice the micro-drill diameter was used by some workers for micro-drilling. However, this range of OSFL was an arbitrary decision. This paper proposes the peck drilling method using thrust force signal monitoring. The monitoring parameters for peck drilling (MPPDs) are introduced through the analysis of thrust force in both the time and frequency domain. The monitoring system was embodied using LabVIEW. Through this monitoring system, the proper OSFL for stable machining in the deep-micro-hole drilling of steel was determined to be about a tenth of the tool diameter.     

Evaluation of machinability in turning of microalloyed and quenched-tempered steels: Tool wear,statistical analysis,chip morphology

The machinability of microalloyed steel (30MnVS6) and quenched-tempered (QT) steels (AISI 1045 and AISI 5140), at different cutting condition, is presented in the paper. An experimental investigation was conducted to determine the effects of cutting speed, feed rate, hardness, and workpiece material on the flank wear land and tool life of coated cemented carbide inserts in the hard turning process. It was tried that for any test condition the hardness of these steels became almost identical by using appropriate heat-treatment processes. The statistical analysis was used for evaluation of different factors on cutting forces. Chips characteristics and chip/tool contact length were also investigated. The different sections (shear plane, microcrack, thickness and edge) of the chip were examined by scanning electron microscope (SEM). Shear planes and microcracks of the chips in microalloyed steel show that the chips of microalloyed steel are regular and discontinuous. Crater wear of the tools was studied by using video microscope in turning process. The results showed that the tool life and machinability of the microalloyed steel is better than the QT steels at identical cutting condition.     

Tool steels for cold working dies

The effect of the main alloying elements (Cr, W, Mo, Ni, Mn, Si) and carbon on the properties of die steels used for cold deformation of metals is considered. Steels heat-treated for primary and secondary hardness are studied. The problems of ensuring maximum values of the impact toughness, strength characteristics, and fatigue limit at optimum content of alloying elements are discussed. __________ Translated from Metallovedenie i Termicheskaya Obrabotka Metallov, No. 6, pp. 3–9, June, 2006.     

Study on the machinability of resulfurized composite free-cutting steels

The machinability of S, S-Ca, S-RE, and S-RE-Ca system resulfurized composite free-cutting steels were investigated, where RE is rare earths, mostly cerium. The experimental results showed that in the low cutting speed range (≤35 m/min), the S-RE system free-cutting steel had better machinability than the others and that the S-RE-Ca system free-cutting steel exhibited the best machinability at high cutting speeds. A protective layer capable of preventing diffusion wear was formed on the rake face of a P30 tool when S-RE-Ca system free-cutting steel was machined in the cutting speed range of 120 to 160 m/min.     

Tool life and surface integrity aspects when drilling and hole making in Inconel 718

Drilling is one of the most important processes in aerospace manufacture and is often the last operation performed. When combined with the fact that holes amplify any in service stresses a significant demand for high surface integrity and production process security is created. In contrast to other machining processes there are relatively few publications regarding the drilling of nickel-based superalloys.

Following a brief review on the general machinability of Inconel 718 a series of experiments examining the tool life/wear of various commercially available drills, recommended for use on nickel-based superalloys, is detailed. In addition a comparison of the resultant hole integrity produced by drilling alone is compared to that obtained using reaming and a relatively new technique of mill boring.

The main conclusion is that when using commercially available drills the resulting hole quality is not sufficient to meet the requirements of the aerospace industry and therefore secondary processing is required. Mill boring with a standard milling tool appears to have significant potential for improving productivity and reducing costs compared to reaming.     

Predictive machinability models for a selected hard material in turning operations

In this paper, empirical models for tool life, surface roughness and cutting force are developed for turning operations. Process parameters (cutting speed, feed rate, depth of cut and tool nose radius) are used as inputs to the developed machinability models. Two important data mining techniques are used; they are response surface methodology and neural networks. Data of 28 experiments when turning austenitic AISI 302 have been used to generate, compare and evaluate the proposed models of tool life, cutting force and surface roughness for the considered material.     

Relationship between machinability index and in-process parameters during orthogonal cutting of steels

Temperature and plastic strain maps were obtained during orthogonal cutting of two steels with different machinability indexes using a high-speed dual-spectrum (visible and infrared) and visible spectrum cameras, respectively. Surface and internal temperature were compared by simultaneous measurements with a thermal camera and thermocouples embedded in the flank face of the cutting tool. A cause–effect relationship between the machinability index and the analyzed in-process variables is determined. This will help with developing a practical tool for the scientific design of different machinability index materials, as well as an alternative method to time-consuming and expensive standardized machinability tests.     

A search for a short term test to assess the machinability of stainless steels

The paper describes four short term tests that were used to assess the machinability of stainless steels. Three of the tests, such as power bandsaw, slot milling, and turning, involved metal removal, while the fourth was based on the criterion of critical accumulated damage (CAD). Only the latter (CAD test) ranked the machinability of stainless steels consistently with the results of a long term automatic screw machining test. The critical accumulated damage can be assessed very easily from a compression test and this seems to be a short term test that could be used to assess the machinability of stainless steels.     

Tool wear in friction drilling

This study investigates the tool wear in friction drilling, a nontraditional hole-making process. In friction drilling, a rotating conical tool uses the heat generated by friction to soften and penetrate a thin workpiece and create a bushing without generating chips. The wear of a conical tungsten carbide tool used for friction drilling a low carbon steel workpiece is studied. Tool wear characteristics are quantified by measuring its weight change, detecting changes in its shape with a coordinate measuring machine, and making observations of wear damage using scanning electron microscopy. Energy dispersive spectrometry is applied to analyze the change in chemical composition of the tool surface due to drilling. In addition, the thrust force and torque during drilling and the hole size are measured periodically to monitor the effects of tool wear. Results indicate that the carbide tool is durable, showing minimal tool wear after drilling 11,000 holes, but observations also indicate the progressively severe abrasive grooving on the tool tip.     

Savings of rolled stock with the use of steels with good machinability

Conclusion The technology of a wide range of new modern structural steels with good machinability was worked out and their production was started, and their principle physical, mechanical, operational, and technological properties were investigated. Experience at the largest engineering plants showed that the use of such steels yields substantial savings of material and labor resources including savings of rolled stock equal to the amount of easily machinable steels used.Research Institute of Metallurgy, Chelyabinsk. Translated from Metallovedenie i Termicheskaya Obrabotka Metallov, No. 12, pp. 20–23, December, 1987.     

Tool wear condition monitoring in drilling operations using hidden Markov models (HMMs)

Monitoring of tool wear condition for drilling is a very important economical consideration in automated manufacturing. Two techniques are proposed in this paper for the on-line identification of tool wear based on the measurement of cutting forces and power signals. These techniques use hidden Markov models (HMMs), commonly used in speech recognition. In the first method, bargraph monitoring of the HMM probabilities is used to track the progress of tool wear during the drilling operation. In the second method, sensor signals that correspond to various types of wear status, e.g., sharp, workable and dull, are classified using a multiple modeling method. Experimental results demonstrate the effectiveness of the proposed methods. Although this work focuses on on-line tool wear condition monitoring for drilling operations, the HMM monitoring techniques introduced in this paper can be applied to other cutting processes.     

Optimization of carburizing steels for drilling tools within grade chemical composition

Results of optimization of the chemical composition of steels 15N3MA and 14KhN3MA with the use of standard methods of statistical analysis of “composition-properties” data arrays with the aim of ensuring the required level of properties in commercial production are presented. It is possible to attain a specified set of properties by optimizing the alloying within grade composition.     

Identification of thrust force models for vibratory drilling

Among the scientific problems in drilling, determining thrust forces for any drill geometry and any workmaterial remains an issue. This question is especially critical in the context of the self-vibratory drilling (SVD) technology, since thrust force governs the trajectory of cutting lips. In order to predict the dynamical behaviour of the self-vibratory drilling head (SVDH), a numerical simulator has been developed in the laboratory. In order to predict the relevant behaviour of the SVD operations, a good accuracy of the thrust force model is highly necessary. The aim of the paper is to propose an experimental methodology to identify a thrust force model for one pair “drill–workmaterial” depending on the uncut chip thickness. This methodology proposes to divide cutting edges into several parts in order to define the local contribution of this part to the macroscopic thrust force. Local models are identified during the penetration of the drill. From a limited number of experiments with various feeds, it becomes possible to identify all the coefficients of an accurate thrust force model.