Academic literature on the topic 'Difficult-to-cut alloy'

Wire Electrical Discharge Machining (WEDM) is a non-traditional machining process widely used for machining difficult-to-cut materials such as titanium alloys. This study proposes an intelligent optimization approach using Adaptive Neuro-Fuzzy Inference System (ANFIS) to optimize WEDM parameters for machining titanium alloy (Ti6Al4V) with coated wires. The key parameters investigated include pulse-on time, pulse-off time, peak current, and wire tension. The results demonstrate that the ANFIS model accurately predicts the optimal parameters, achieving a material removal rate (MRR) of up to 5.22 mm3/min (increased by 15%) and a surface roughness (Ra) as low as 3.60 µm (reduced by 12%). The proposed approach significantly improves machining efficiency and surface quality, reducing the need for costly experimental trials. This study highlights the potential of ANFIS in optimizing WEDM processes for industrial applications, particularly in aerospace and biomedical industries where titanium alloys are extensively used.

Nickel-based alloys are widely used in the aerospace industry, nuclear reactors and the automotive industry. These alloys exhibit excellent physical and chemical properties at high temperatures. However, nickel-based alloys are difficult to machine materials with high hardness and low thermal conductivity, which results in high cutting forces during machining. Additionally, increasing demand for meso-scale components in the industry has opened a door for research in this field. This paper focuses on meso-scale milling of Inconel 718 alloy. Aiming at the problem of high cutting forces, meso-scale milling experiments of Inconel 718 alloy were conducted. Due to its high strength and work-hardening characteristics, proper tool coating and process parameters should be selected. In this work, TiAlN, TiSiN, and nACo coatings were selected. Taguchi’s L9 orthogonal array was employed for conducting experiments in a dry environment. In this paper, feed per tooth, cutting velocity, depth of cut, and tool coatings are considered as input parameters, and their effects on cutting forces are analysed through the statistical technique of analysis of variance (ANOVA) to figure out the most important process parameters.

Additive Manufacturing (AM) offers lots of advantages when compared to other manufacturing processes, such as high flexibility and ability to produce complex parts directly from the Three Dimensional (3D) Computer-Aided Design (CAD) model. Producing highly complex parts using traditional manufacturing processes is difficult, and it requires it to be broken down into smaller parts, which consumes lots of materials and time. If this part needs to have a surface with improved property or a surface made of composite materials, it has to be done by employing another manufacturing process after the parts are completed. AM, on the other hand, has the ability to produce parts with the required surface property in a single manufacturing run. Out of all the AM technologies, Laser Additive Manufacturing (LAM) is the most commonly used technique, especially for metal processing. LAM uses the coherent and collimated properties of the laser beam to fuse, melt, or cut materials according to the profile generated from the CAD image of the part being made. Some of the LAM techniques and their mode of operations are highlighted in this chapter. The capabilities of using LAM for surface modification of metals are also presented in this chapter. A specific example is given as a case study for the surface modification of titanium alloy (Ti6Al4V) with Ti6Al4V/TiC composite using laser material deposition process – an important LAM technology. Ti6Al4V is an important aerospace alloy, and it is also used as medical implants because of its corrosion resistance property and its biocompatibility.

Additive Manufacturing (AM) offers lots of advantages when compared to other manufacturing processes, such as high flexibility and ability to produce complex parts directly from the Three Dimensional (3D) Computer-Aided Design (CAD) model. Producing highly complex parts using traditional manufacturing processes is difficult, and it requires it to be broken down into smaller parts, which consumes lots of materials and time. If this part needs to have a surface with improved property or a surface made of composite materials, it has to be done by employing another manufacturing process after the parts are completed. AM, on the other hand, has the ability to produce parts with the required surface property in a single manufacturing run. Out of all the AM technologies, Laser Additive Manufacturing (LAM) is the most commonly used technique, especially for metal processing. LAM uses the coherent and collimated properties of the laser beam to fuse, melt, or cut materials according to the profile generated from the CAD image of the part being made. Some of the LAM techniques and their mode of operations are highlighted in this chapter. The capabilities of using LAM for surface modification of metals are also presented in this chapter. A specific example is given as a case study for the surface modification of titanium alloy (Ti6Al4V) with Ti6Al4V/TiC composite using laser material deposition process – an important LAM technology. Ti6Al4V is an important aerospace alloy, and it is also used as medical implants because of its corrosion resistance property and its biocompatibility.

Nickle based super alloy Inconel 718 is a difficult to cut material due to its large mechanical strength and high heat and corrosion resistance with good thermal stability. μ-EDM is a non-conventional micro-machining process that can produce complex micro features in Inconel 718. The material removal mechanism of μ-EDM is extremely intricate and dynamic in nature. This paper aims to develop a 2D axisymmetric heat transient model that can explain the material removal theory during the single spark μ-EDM process on Inconel 718. The solutions of the developed model have been obtained by finite element method (FEM) based software COMSOL Multiphysics 5.6. First, the model is validated with a literature model by incorporating the same machining condition. It has been accomplished that the present model’s crater radius (r′) and depth (h) values are in a close agreement with the literature model. The absolute percentage error for r′ and h between the simulated results of the two models are found to be 1.37 and 4.45 correspondingly. Both the r′ and h are increased with the enhancement of discharge energy (DE). The highest value of r′ and h are found at 7.2 μJ DE followed by 6.05 μJ and 5 μJ DE. It has been established that the temperature has been drastically decreased along both the radius and depth direction after the single spark simulation process. The temperature gradient is found to be more along the radius direction than the depth direction.

High strength, resistance to corrosion, small density and remarkable strength to weight ratio of titanium distinguish it from other metals and is a reason for its use in in renowned industrial setups like bio-medical, automotive, aeronautics, and power generation industries. However, these are considered as difficult-to-machine elements because of less heat conductivity, minimum value of modulus of elasticity, substantial chemical reactivity and elevated temperature strength. Ti-6Al-4V is regarded as major industrial alloy and a focus of research studies. Measurement and analysis of machining forces provides a deep insight into the mechanics of machining and assist in understanding machinability, tool wear / fracture, machining precision, chatter stability, energy, surface quality and temperature. This further helps in finding optimum machinability parameters for different materials. Machining forces are affected by a number of factors including cutting conditions and lubrication / cooling environment. In this research, analysis of milling forces under three different lubrication / cooling environments i.e. Dry, Wet and MQL (Minimum Quantity Lubrication) along with effects of milling parameters during meso-scale milling of Ti-6Al-4V has been conducted. End milling experiments have been performed basing on Taguchi L9 orthogonal array for optimal combination of milling parameters, keeping spindle speed, depth of cut, feed per tooth and cooling conditions as the control factors. Contribution ratios of different milling parameters and lubrication / cooling environment on feed direction forces have been analyzed through ANOVA.

Secant pile walls are increasingly becoming popular groundwater cut-off systems of choice on underground construction sites, as they offer a number of advantages over traditional sheet piling and diaphragm walls. However, some elements of uncertainty surround the design and construction of secant pile walls. Vertical and horizontal installation tolerances are major issues, especially in the case of multi-level basements, as required tolerances are difficult to achieve with deep piles associated with deep basements. In addition, while conventional foundation piles are routinely statically or dynamically load-tested, hard piles in secant pile walls are rarely axially tested and this does not allow for the routine verification of existing design methods and assumptions.

Abstract This is the first time in this country that an opera of mine has been specially produced on television, and I am extremely grateful to Associated-Rediffusion for its enterprise and courage in mounting THE TURN OF THE SCREW1 I am particularly happy that it should have been this opera that was chosen because it is one of my works most close to me, and also the one I feel most suitable for television. Television can do an enormous amount to popularise opera in this country, especially if it avoids the spectacular Grand Opera so beloved by the eighteenth & nineteenth centuries and concentrates on the intimate and concise, which seems to me to belong particularly to the present day. I cannot praise too highly the skill, taste and knowledge shown in adapting this difficult opera for television, especially when coupled with a respect for the score which did not allow one note to be cut.

Undifferentiated connective tissue disease (UCTD) and overlap syndromes both form part of the broad spectrum of connective tissue disease. They are difficult to define, as the boundaries between them and specific diseases such as systemic lupus erythematosus (SLE), systemic sclerosis (SSc), and myositis are often not clear-cut. This chapter gives a broad overview of diagnosis, clinical features, outcomes, and management. Patients with UCTD have clinical and/or serological features of connective tissue disease but do not fulfil the criteria for any one defined disease. Raynaud’s phenomenon and puffy fingers are often the presenting features but there are many possible others, including arthralgia, sicca symptoms, and breathlessness due to pulmonary fibrosis, usually in the context of a positive anti-nuclear antibody (ANA). A proportion of patients evolve into a defined connective tissue disease: in those who do, this is generally within 5 years of onset. Treatment is dependent upon the clinical features: for examplem vasodilators for Raynaud’s phenomenon, or hydroxychloroquine for arthralgia/arthritis. Patients with overlap syndromes have features of more than one defined connective tissue disease. Overlap syndromes are therefore highly heterogeneous as many combinations of clinical and serological features can occur. Mixed connective tissue disease (MCTD) is the overlap syndrome that has been most described and includes overlapping features of SLE, SSc, and myositis in patients who are anti-U1 ribonucleoprotein (RNP) antibody positive. Treatment is of the specific clinical manifestations. Patients with overlap syndromes should be kept under regular review to allow early identification of internal organ involvement.

Undifferentiated connective tissue disease (UCTD) and overlap syndromes both form part of the broad spectrum of connective tissue disease. They are difficult to define, as the boundaries between them and specific diseases such as systemic lupus erythematosus (SLE), systemic sclerosis (SSc), and myositis are often not clear-cut. This chapter gives a broad overview of diagnosis, clinical features, outcomes, and management. Patients with UCTD have clinical and/or serological features of connective tissue disease but do not fulfil the criteria for any one defined disease. Raynaud’s phenomenon and puffy fingers are often the presenting features but there are many possible others, including arthralgia, sicca symptoms, and breathlessness due to pulmonary fibrosis, usually in the context of a positive anti-nuclear antibody (ANA). A proportion of patients evolve into a defined connective tissue disease: in those who do, this is generally within 5 years of onset. Treatment is dependent upon the clinical features: for example vasodilators for Raynaud’s phenomenon, or hydroxychloroquine for arthralgia/arthritis. Patients with overlap syndromes have features of more than one defined connective tissue disease. Overlap syndromes are therefore highly heterogeneous as many combinations of clinical and serological features can occur. Mixed connective tissue disease (MCTD) is the overlap syndrome that has been most described and includes overlapping features of SLE, SSc, and myositis in patients who are anti-U1 ribonucleoprotein (RNP) antibody positive. Treatment is of the specific clinical manifestations. Patients with overlap syndromes should be kept under regular review to allow early identification of internal organ involvement.

Abstract The ASTM G 48 test evaluates an alloys resistance to pitting and crevice corrosion using severe test conditions. Unlike most other ASTM standards which are cut and dry in their test procedures, this standard has loop holes which allows test-to-test and laboratory-to-laboratory variation which makes comparison of data difficult. Modifications are often used to improve the standard, but these are not adopted universally. This paper identifies the problems associated with using G 48, and the impact these problems have on evaluating high-alloy stainless steels. Recommendations to correct these problems to standardize the test are made. Attention to the use of electrochemical measurement techniques for improved reproducibility are discussed.

Abstract Nickel-based alloys represented by Inconel are materials with excellent high-temperature characteristics, and are widely used in the aerospace industry, such as aircraft and rocket engine parts. On the other hand, it is known as a typical difficult-to-cut material. Furthermore, in machining and electric discharge machining (EDM), the machining speed is slow and tool or electrode wear is a big problem. Meanwhile, electrochemical machining (ECM) using electrochemical reaction is not affected by the hardness of the material, does not generate a heat-affected layer on the workpiece surface, and has no tool wear. So, it is considered that ECM is suitable for machining difficult-to-cut materials. Therefore, in this study, focusing on the nickel-based alloy Inconel718 (Alloy718), we conducted a machining experiment using NaNO3 aqueous solution by wire ECM using a thin wire (mainly tungsten) as a tool electrode, and investigated the ECM characteristics. Wire ECM can be machined like wire EDM, and high-efficiency machining is possible by using a pulse power supply. As a result, it was found that increasing the voltage, electrolyte concentration, electrolyte supply pressure, and diameter of wire increases the current flowing between the electrodes and has the effect of promoting machining. In addition to simple cutting, the possibility of being effective not only for grooving but also for cutting complex shapes was shown.

Electrical Discharge Micro Drilling (EDMD) is considered as one of the most effective method for machining difficult to cut and hard materials like titanium alloy. However, selection of process parameters for achieving superior surface finish, higher machining rate and accuracy is a challenging task in drilling micro-holes. In this paper, an attempt is made to optimize micro-EDM process parameters for drilling micro holes on titanium grade 19 alloy. In order to verify the optimal micro-EDM process parameters settings, material removal rate (MRR), electrode wear rate (EWR) and over cut (OC) were chosen as the responses to be observed. Pulse on time, pulse off time, electrode diameter and current were selected as the governing process parameters for evaluation by Taguchi method. Nine micro holes of 300 μm, 400 μm and 500 μm were drilled using L9 orthogonal array (OA) design. Optimal combination of machining parameters were obtained through Signal-to-Noise (S/N) ratio analysis. It is seen that machining performances like material removal rate and overcut are affected by the peak current whereas electrode wear is affected by peak current and electrode diameter. Morphology of the micro holes has been studied through SEM micrographs of machined micro-hole.

Titanium and Ti alloys are popular materials used in aviation and biomedical field due to their excellent strength-to-weight ratio and corrosion resistance properties. Micromilling is a common mechanical machining process used in the production of microscale features. The micro-tool has very low stiffness and even small forces can lead to catastrophic tool failure. High speed micromachining can be used to address the issue because of lower chip loads at higher rotational speeds. Consequently, high speed micromilling can be used for micromachining of hard metals/alloys which are difficult to accomplish at lower speeds. Nowadays high speed micromilling is gaining popularity due to its high material removal rate and good surface finish. In many cases, the machined product does not need an additional finishing process. However, the burr formation in the mechanical machining process is the most important problem which becomes more critical for a microscale feature. Removal of micro-size burr is much more difficult than its macro counterpart. The current work is focused on the characterization of the burr formation in high speed micromilling. Influence of various process parameters, viz., spindle speed, feed rate, depth of cut, tool diameter and number of flutes of the micromilling tool has been analyzed on the burr size and on the quality of the machined surface via measuring the surface roughness.

Duralumin sheets are strong, hard, light weight and heat treated alloy of Aluminum, widely used by different sectors such as automobile, marine, aircraft and satellites. Many a times those applications demand complex shapes and intricate profiles with stringent design requirements which are not completely achieved by conventional sheet cutting methods. Laser cutting has capability of quality cutting with above requirements in thin sheetmetals. But highly reflective and thermally conductive sheetmetals like Duralumin pose difficulty in achieving quality cuts by laser beam. The kerf taper always occurs in laser cut specimen due to inherent converging-diverging profile of laser beam. The optimization of kerf taper and other cut qualities such as surface roughness, heat affected zone and recast layer formation in difficult-to-laser-cut sheetmetals like Duralumin or Aluminium alloy has become recent research interests. The aim of present research is to optimize kerf taper in pulsed laser cutting of Duralumin sheet using hybrid approach of ‘design of experiment (DOE)’ and ‘artificial intelligence tool’ such as genetic algorithm. The empirical model for kerf taper has also been proposed with the discussion on parametric effect.

Electrochemical micromachining process is one among the successful micromachining technique, which uses the electrochemical energy and is recognized for machining difficult-to-cut materials. One such material is Nimonic 75 alloy, which is used to make gas turbine components. In this study, an effort has been made to machine micro-hole profiles in Nimonic 75 with a thickness of 500 μm using two different electrolytes. A combination of sodium bromide, hydrofluoric acid and ethylene glycol has been chosen as the first electrolyte, while the second is a combination of sodium chloride and sodium nitrate. Solid tungsten carbide of diameter 500 μm is used as the tool in each case. For layout of experiments, Taguchi orthogonal array was chosen with following input parameters namely voltage, micro-tool feed rate and duty cycle. Performance characteristics such as material removal rate, overcut and conicity have been assessed for each electrolyte. Experimental results have shown that the first electrolyte yields lower values of overcut (OC) and conicity, whereas the second electrolyte gives higher material removal rate (MRR). Further, the optimal combinations of process parameters have been found by implementing the TOPSIS procedure and the results were found to be in good agreement with the experimental outcomes.

Inconel 718 alloy is used extensively in aerogas turbines and this alloy is most difficult to machine and highly prone to dimensional instability after machining. Such detrimental phenomenon poses enormous problem in engine assembly and affect structural integrity. This paper highlights the systematic research work undertaken to study the plastic deformation characteristics of Inconel 718, effect of process variables on machined surface, subsurface and dimensional instability. Also illustrated the technique developed for simultaneous optimization of several process variables such as cutting speed, feed, depth of cut, rake angle and tool nose radius, to control the residual stresses and dimensional instability, within the acceptable tolerance band of the component. Prediction equations were developed for residual stress, dimensional instability, tool life, surface finish and material removal rate. Predicted data were validated experimentally. This paper also presents the qualitative and quantitative data on dimensional instability with specific case studies of jet engine components and clearly illustrates the approach followed to develop technique to control such detrimental effect.

Abstract Titanium alloys are widely used as mechanical components, since they have superior properties such as high strength-to-weight ratio. They are regarded as difficult-to-cut materials. Their low thermal conductivity increases the temperature near the cutting edge, which causes excessive tool wear during cutting. Recently, many studies on cryogenic machining have been conducted. Cryogenic machining has emerged as an environmentally friendly alternative to traditional emulsion coolants. In this study, the rake face temperatures of cutting tool in the turning of titanium alloy under dry, soluble coolant, cryogenic carbon dioxide coolant and liquid nitrogen coolant conditions were measured to clarify the effect of coolant on cutting temperature. Turning tests were performed using a precision lathe. Tool insert was made by a translucent alumina. A small hole was drilled into the tool insert. An infrared radiation pyrometer with an optical fiber was used. The optical fiber was inserted into the hole. During chip formation, the infrared rays, radiated from the tool-chip interface and transmitted through the cutting tool, were accepted and transmitted by the optical fiber. The effects of cryogenic coolant on the rake face temperature were investigated. The rake face temperatures under carbon dioxide cooling and liquid nitrogen cooling were approximately 60 °C and 90 °C lower than that in dry cutting, respectively.

Abstract Electric Discharge Machining (EDM) is one of the leading non-conventional machining processes used to machine hard-to-cut materials in wide range of industrial, biomedical, automotive, defense and aerospace applications. EDM is a controlled spark generation process, which is usually used for machining of difficult to cut materials. In this study, experiments were performed on Titanium Alloy (Ti6Al4V) using thin-film multi-wall Carbon Nanotubes (MWCNT) coated electrode and uncoated aluminum electrodes. Morphological and structural investigations of MWCNT coating were performed using Scanning transmission electron microscope (TEM) and Raman spectroscopy. All experiments were designed with Taguchi’s L16 orthogonal array. Each experiment performed under different condition of current, gap voltage and pulse on time. MRR, TWR, SR and OC are studied for each experiment. It was observed that MWCNT coated electrode gives better surface roughness, higher material removal rate, and lower tool wear rate. The experimental result showed that MRR increased by 14.15%, tool wear rate decreased by 23.40%, surface roughness reduced by 22.14 % and overcut reduced by 23.43 % respectively as compared to uncoated aluminum electrodes. All performance responses improved with thin-film MWCNT coated electrode due to magnificent electrical conductivity and chemical stability of CNT. Analysis of Variance (ANOVA) carried out to understand significant process parameters and its contribution in mentioned response variables. Multi-Wall CNT shows better results at high temperature and prevents the tool wear rate. The surface roughness of Ti6Al4V improved with MWCNT coated electrode and it was evident with scanning electron microscope (SEM) images of workpiece. Comparative study of coated and non-coated gives new development of novel electrode tool for electric discharge machining processes.

Abstract The machining of difficult-to-cut materials, such as nickel-based alloys and high-alloy steels, is usually assisted by cutting fluid. In addition to the commonly used flood cooling, high-pressure cutting fluid supply offers great potential for further increasing tool life and process reliability. Although the positive effect of high-pressure cooling has been confirmed in a large number of studies, the relevant cutting fluid setting parameters such as nozzle cross-section area and supply pressure, and their influence on the process results have so far been insufficiently investigated. Against this background, a prototype tool holder was designed and additively manufactured in this work. The tool holder allows to vary the nozzle cross-section area without changing the cooling channels and the inclination of the nozzles. Experimental results revealed the optimal cross-section area of the rake face nozzle for the investigated process. It was also shown that although flank face cooling is necessary for the turning process, improper setting of the flank face nozzles can lead to a reduction in tool life.

Banco de la República is celebrating its 100th anniversary in 2023. This is a very significant anniversary and one that provides an opportunity to highlight the contribution the Bank has made to the country’s development. Its track record as guarantor of monetary stability has established it as the one independent state institution that generates the greatest confidence among Colombians due to its transparency, management capabilities, and effective compliance with the central banking and cultural responsibilities entrusted to it by the Constitution and the Law. On a date as important as this, the Board of Directors of Banco de la República (BDBR) pays tribute to the generations of governors and officers whose commitment and dedication have contributed to the growth of this institution.1 Banco de la República’s mandate was confirmed in the National Constitutional Assembly of 1991 where the citizens had the opportunity to elect the seventy people who would have the task of drafting a new constitution. The leaders of the three political movements with the most votes were elected as chairs to the Assembly, and this tripartite presidency reflected the plurality and the need for consensus among the different political groups to move the reform forward. Among the issues considered, the National Constitutional Assembly gave special importance to monetary stability. That is why they decided to include central banking and to provide Banco de la República with the necessary autonomy to use the instruments for which they are responsible without interference from other authorities. The constituent members understood that ensuring price stability is a state duty and that the entity responsible for this task must be enshrined in the Constitution and have the technical capability and institutional autonomy necessary to adopt the decisions they deem appropriate to achieve this fundamental objective in coordination with the general economic policy. In particular, Article 373 established that “the State, through Banco de la República, shall ensure the maintenance of the purchasing power of the currency,” a provision that coincided with the central banking system adopted by countries that have been successful in controlling inflation. In 1999, in Ruling 481, the Constitutional Court stated that “the duty to maintain the purchasing power of the currency applies to not only the monetary, credit, and exchange authority, i.e., the Board of Banco de la República, but also those who have responsibilities in the formulation and implementation of the general economic policy of the country” and that “the basic constitutional purpose of Banco de la República is the protection of a sound currency. However, this authority must take the other economic objectives of state intervention such as full employment into consideration in their decisions since these functions must be coordinated with the general economic policy.” The reforms to Banco de la República agreed upon in the Constitutional Assembly of 1991 and in Act 31/1992 can be summarized in the following aspects: i) the Bank was assigned a specific mandate: to maintain the purchasing power of the currency in coordination with the general economic policy; ii) the BDBR was designatedas the monetary, foreign exchange, and credit authority; iii) the Bank and its Board of Directors were granted a significant degree of independence from the government; iv) the Bank was prohibited from granting credit to the private sector except in the case of the financial sector; v) established that in order to grant credit to the government, the unanimous vote of its Board of Directors was required except in the case of open market transactions; vi) determined that the legislature may, in no case, order credit quotas in favor of the State or individuals; vii) Congress was appointed, on behalf of society, as the main addressee of the Bank’s reporting exercise; and viii) the responsibility for inspection, surveillance, and control over Banco de la República was delegated to the President of the Republic. The members of the National Constitutional Assembly clearly understood that the benefits of low and stable inflation extend to the whole of society and contribute mto the smooth functioning of the economic system. Among the most important of these is that low inflation promotes the efficient use of productive resources by allowing relative prices to better guide the allocation of resources since this promotes economic growth and increases the welfare of the population. Likewise, low inflation reduces uncertainty about the expected return on investment and future asset prices. This increases the confidence of economic agents, facilitates long-term financing, and stimulates investment. Since the low-income population is unable to protect itself from inflation by diversifying its assets, and a high proportion of its income is concentrated in the purchase of food and other basic goods that are generally the most affected by inflationary shocks, low inflation avoids arbitrary redistribution of income and wealth.2 Moreover, low inflation facilitates wage negotiations, creates a good labor climate, and reduces the volatility of employment levels. Finally, low inflation helps to make the tax system more transparent and equitable by avoiding the distortions that inflation introduces into the value of assets and income that make up the tax base. From the monetary authority’s point of view, one of the most relevant benefits of low inflation is the credibility that economic agents acquire in inflation targeting, which turns it into an effective nominal anchor on price levels. Upon receiving its mandate, and using its autonomy, Banco de la República began to announce specific annual inflation targets as of 1992. Although the proposed inflation targets were not met precisely during this first stage, a downward trend in inflation was achieved that took it from 32.4% in 1990 to 16.7% in 1998. At that time, the exchange rate was kept within a band. This limited the effectiveness of monetary policy, which simultaneously sought to meet an inflation target and an exchange rate target. The Asian crisis spread to emerging economies and significantly affected the Colombian economy. The exchange rate came under strong pressure to depreciate as access to foreign financing was cut off under conditions of a high foreign imbalance. This, together with the lack of exchange rate flexibility, prevented a countercyclical monetary policy and led to a 4.2% contraction in GDP that year. In this context of economic slowdown, annual inflation fell to 9.2% at the end of 1999, thus falling below the 15% target set for that year. This episode fully revealed how costly it could be, in terms of economic activity, to have inflation and exchange rate targets simultaneously. Towards the end of 1999, Banco de la República announced the adoption of a new monetary policy regime called the Inflation Targeting Plan. This regime, known internationally as ‘Inflation Targeting,’ has been gaining increasing acceptance in developed countries, having been adopted in 1991 by New Zealand, Canada, and England, among others, and has achieved significant advances in the management of inflation without incurring costs in terms of economic activity. In Latin America, Brazil and Chile also adopted it in 1999. In the case of Colombia, the last remaining requirement to be fulfilled in order to adopt said policy was exchange rate flexibility. This was realized around September 1999, when the BDBR decided to abandon the exchange-rate bands to allow the exchange rate to be freely determined in the market.Consistent with the constitutional mandate, the fundamental objective of this new policy approach was “the achievement of an inflation target that contributes to maintaining output growth around its potential.”3 This potential capacity was understood as the GDP growth that the economy can obtain if it fully utilizes its productive resources. To meet this objective, monetary policy must of necessity play a countercyclical role in the economy. This is because when economic activity is below its potential and there are idle resources, the monetary authority can reduce the interest rate in the absence of inflationary pressure to stimulate the economy and, when output exceeds its potential capacity, raise it. This policy principle, which is immersed in the models for guiding the monetary policy stance, makes the following two objectives fully compatible in the medium term: meeting the inflation target and achieving a level of economic activity that is consistent with its productive capacity. To achieve this purpose, the inflation targeting system uses the money market interest rate (at which the central bank supplies primary liquidity to commercial banks) as the primary policy instrument. This replaced the quantity of money as an intermediate monetary policy target that Banco de la República, like several other central banks, had used for a long time. In the case of Colombia, the objective of the new monetary policy approach implied, in practical terms, that the recovery of the economy after the 1999 contraction should be achieved while complying with the decreasing inflation targets established by the BDBR. The accomplishment of this purpose was remarkable. In the first half of the first decade of the 2000s, economic activity recovered significantly and reached a growth rate of 6.8% in 2006. Meanwhile, inflation gradually declined in line with inflation targets. That was how the inflation rate went from 9.2% in 1999 to 4.5% in 2006, thus meeting the inflation target established for that year while GDP reached its potential level. After this balance was achieved in 2006, inflation rebounded to 5.7% in 2007, above the 4.0% target for that year due to the fact that the 7.5% GDP growth exceeded the potential capacity of the economy.4 After proving the effectiveness of the inflation targeting system in its first years of operation, this policy regime continued to consolidate as the BDBR and the technical staff gained experience in its management and state-of-the-art economic models were incorporated to diagnose the present and future state of the economy and to assess the persistence of inflation deviations and expectations with respect to the inflation target. Beginning in 2010, the BDBR established the long-term 3.0% annual inflation target, which remains in effect today. Lower inflation has contributed to making the macroeconomic environment more stable, and this has favored sustained economic growth, financial stability, capital market development, and the functioning of payment systems. As a result, reductions in the inflationary risk premia and lower TES and credit interest rates were achieved. At the same time, the duration of public domestic debt increased significantly going from 2.27 years in December 2002 to 5.86 years in December 2022, and financial deepening, measured as the level of the portfolio as a percentage of GDP, went from around 20% in the mid-1990s to values above 45% in recent years in a healthy context for credit institutions.Having been granted autonomy by the Constitution to fulfill the mandate of preserving the purchasing power of the currency, the tangible achievements made by Banco de la República in managing inflation together with the significant benefits derived from the process of bringing inflation to its long-term target, make the BDBR’s current challenge to return inflation to the 3.0% target even more demanding and pressing. As is well known, starting in 2021, and especially in 2022, inflation in Colombia once again became a serious economic problem with high welfare costs. The inflationary phenomenon has not been exclusive to Colombia and many other developed and emerging countries have seen their inflation rates move away from the targets proposed by their central banks.5 The reasons for this phenomenon have been analyzed in recent Reports to Congress, and this new edition delves deeper into the subject with updated information. The solid institutional and technical base that supports the inflation targeting approach under which the monetary policy strategy operates gives the BDBR the necessary elements to face this difficult challenge with confidence. In this regard, the BDBR reiterated its commitment to the 3.0% inflation target in its November 25 communiqué and expects it to be reached by the end of 2024.6 Monetary policy will continue to focus on meeting this objective while ensuring the sustainability of economic activity, as mandated by the Constitution. Analyst surveys done in March showed a significant increase (from 32.3% in January to 48.5% in March) in the percentage of responses placing inflation expectations two years or more ahead in a range between 3.0% and 4.0%. This is a clear indication of the recovery of credibility in the medium-term inflation target and is consistent with the BDBR’s announcement made in November 2022. The moderation of the upward trend in inflation seen in January, and especially in February, will help to reinforce this revision of inflation expectations and will help to meet the proposed targets. After reaching 5.6% at the end of 2021, inflation maintained an upward trend throughout 2022 due to inflationary pressures from both external sources, associated with the aftermath of the pandemic and the consequences of the war in Ukraine, and domestic sources, resulting from: strengthening of local demand; price indexation processes stimulated by the increase in inflation expectations; the impact on food production caused by the mid-2021 strike; and the pass-through of depreciation to prices. The 10% increase in the minimum wage in 2021 and the 16% increase in 2022, both of which exceeded the actual inflation and the increase in productivity, accentuated the indexation processes by establishing a high nominal adjustment benchmark. Thus, total inflation went to 13.1% by the end of 2022. The annual change in food prices, which went from 17.2% to 27.8% between those two years, was the most influential factor in the surge in the Consumer Price Index (CPI). Another segment that contributed significantly to price increases was regulated products, which saw the annual change go from 7.1% in December 2021 to 11.8% by the end of 2022. The measure of core inflation excluding food and regulated items, in turn, went from 2.5% to 9.5% between the end of 2021 and the end of 2022. The substantial increase in core inflation shows that inflationary pressure has spread to most of the items in the household basket, which is characteristic of inflationary processes with generalized price indexation as is the case in Colombia. Monetary policy began to react early to this inflationary pressure. Thus, starting with its September 2021 session, the BDBR began a progressive change in the monetary policy stance moving away from the historical low of a 1.75% policy rate that had intended to stimulate the recovery of the economy. This adjustment process continued without interruption throughout 2022 and into the beginning of 2023 when the monetary policy rate reached 12.75% last January, thus accumulating an increase of 11 percentage points (pp). The public and the markets have been surprised that inflation continued to rise despite significant interest rate increases. However, as the BDBR has explained in its various communiqués, monetary policy works with a lag. Just as in 2022 economic activity recovered to a level above the pre-pandemic level, driven, along with other factors, by the monetary stimulus granted during the pandemic period and subsequent months, so too the effects of the current restrictive monetary policy will gradually take effect. This will allow us to expect the inflation rate to converge to 3.0% by the end of 2024 as is the BDBR’s purpose.Inflation results for January and February of this year showed declining marginal increases (13 bp and 3 bp respectively) compared to the change seen in December (59 bp). This suggests that a turning point in the inflation trend is approaching. In other Latin American countries such as Chile, Brazil, Perú, and Mexico, inflation has peaked and has begun to decline slowly, albeit with some ups and downs. It is to be expected that a similar process will take place in Colombia in the coming months. The expected decline in inflation in 2023 will be due, along with other factors, to lower cost pressure from abroad as a result of the gradual normalization of supply chains, the overcoming of supply shocks caused by the weather, and road blockades in previous years. This will be reflected in lower adjustments in food prices, as has already been seen in the first two months of the year and, of course, the lagged effect of monetary policy. The process of inflation convergence to the target will be gradual and will extend beyond 2023. This process will be facilitated if devaluation pressure is reversed. To this end, it is essential to continue consolidating fiscal sustainability and avoid messages on different public policy fronts that generate uncertainty and distrust. 1 This Report to Congress includes Box 1, which summarizes the trajectory of Banco de la República over the past 100 years. In addition, under the Bank’s auspices, several books that delve into various aspects of the history of this institution have been published in recent years. See, for example: Historia del Banco de la República 1923-2015; Tres banqueros centrales; Junta Directiva del Banco de la República: grandes episodios en 30 años de historia; Banco de la República: 90 años de la banca central en Colombia. 2 This is why lower inflation has been reflected in a reduction of income inequality as measured by the Gini coefficient that went from 58.7 in 1998 to 51.3 in the year prior to the pandemic. 3 See Gómez Javier, Uribe José Darío, Vargas Hernando (2002). “The Implementation of Inflation Targeting in Colombia”. Borradores de Economía, No. 202, March, available at: https://repositorio.banrep.gov.co/handle/20.500.12134/5220 4 See López-Enciso Enrique A.; Vargas-Herrera Hernando and Rodríguez-Niño Norberto (2016). “The inflation targeting strategy in Colombia. An historical view.” Borradores de Economía, No. 952. https://repositorio.banrep.gov.co/handle/20.500.12134/6263 5 According to the IMF, the percentage change in consumer prices between 2021 and 2022 went from 3.1% to 7.3% for advanced economies, and from 5.9% to 9.9% for emerging market and developing economies. 6 https://www.banrep.gov.co/es/noticias/junta-directiva-banco-republica-reitera-meta-inflacion-3