Cutting force estimation in sculptured surface milling

Cutting force milling models developed up to now are mostly used for planar milling using end-mills. Only a reduced number of models applying ball-end mills have been developed. Furthermore these models usually only consider horizontal surface machining, even though the main application of ball-end mills is sculptured surface machining. This article proposes a model that is able to estimate the cutting forces in inclined surfaces machined both up-milling and down-milling. For this purpose a semi-mechanistic model has been developed that calculates the cutting forces based on a set of coefficients which depend on the material, the tool, the cutting conditions, the machining direction and the slope of the surface.A coordinate transformation has been included in order to consider the slope milling case with different cutting directions.The model has been tested on two materials, an aluminum alloy Al7075-T6 and a 52 HRC tool steel AISI H13. Validation tests have been carried out on inclined planes using different slopes and different machining directions.The results provide errors below 10% in most of the cases and both the value and shape of the predicted forces adjust the measured cutting force.     

Quality improvement of ball-end milled sculptured surfaces by ball burnishing

In this paper, the use of the ball burnishing process to improve the final quality of form tools (moulds and dies) is studied. This process changes the roughness of the previously ball-end milled surfaces, achieving the finishing requirements for plastic injection moulds and stamping dies. Ball burnishing can be easily applied in the same machining centres as those used for milling. In this way, both lead times and production costs can be dramatically reduced.

Both the burnishing system and its main parameters are taken into account, considering their influence on finishing. Workpiece surface integrity is ensured due to the surface smoothing effect of process and the associated cold working. Examples of different materials, machined surfaces, and industrial applications are explained, with respect to the maximum and mean surface roughness achieved.

The main conclusion is that using a large radial depth of cut in the previous ball-end milling operation, together with a small radial depth during burnishing can produce acceptable final roughness. Savings of production times are high, as burnishing is applied using the maximum linear feed of the machine, while milling must be made at moderate feeds. Moreover, ball burnishing NC programming is less critical and needs less care in its definition than CAM for milling.     

Modeling of the geometry built-up by coaxial laser material deposition process

Coaxial laser material deposition (also known as laser-cladding process) is being used for selective material deposition on complex parts since the 1990s. Its main applications include coatings, rapid manufacturing, or high added value part repairing. The main advantages of the coaxial laser-cladding process are the high-quality bonding interface between added and substrate material, excellent mechanical behavior, and high precision of the resulting geometry in comparison with conventional welding processes. Moreover, the laser-cladding process involves low-heat input, which leads on minimum thermal distortions and reduced heat-affected zone. Thus, high responsibility components like aeronautic turbine parts, tooling for die and mold industry or medical implants, among others, can be processed with laser cladding. This paper presents a laser material deposition process model for the estimation of the geometric characteristics of added material layers, including the prediction of the 3D shape of single and multiple clads and considering overlapping effect, which is the common situation on industrial applications. The model only needs the typical process parameters as the laser power, substrate material, powder material and size, etc. The model has been applied to different laser material deposition strategies and validated for two different materials (AISI D2 and Inconel 718) by experimental testing, obtaining good agreement between estimated and measured values. Finally, a case study for a turbine engine fixture is presented as a possible application. Therefore, the proposed algorithm can be applied for estimating the resulting geometry of the laser-cladding process and predict the optimum laser-cladding strategy, number of layers, and distance between layers before programming the operation.     

Process planning for reliable high-speed machining of moulds

A method of generating NC programs for the high-speed milling of moulds is investigated. Forging dies and injection moulds, whether plastic or aluminium, have a complex surface geometry. In addition they are made of steels of hardness as much as 30 or even 50 HRC. Since 1995, high-speed machining has been much adopted by the die-making industry, which with this technology can reduce its use of Sinking Electrodischarge Machining (SEDM). EDM, in general, calls for longer machining times. The use of high-speed machining makes it necessary to redefine the preliminary stages of the process. In addition, it affects the methodology employed in the generation of NC programs, which requires the use of high-level CAM software. The aim is to generate error-free programs that make use of optimum cutting strategies in the interest of productivity and surface quality. The final result is a more reliable manufacturing process. There are two risks in the use of high-speed milling on hardened steels. One of these is tool breakage, which may be very costly and may furthermore entail marks on the workpiece. The other is collisions between the tool and the workpiece or fixtures, the result of which may be damage to the ceramic bearings in the spindles. In order to minimize these risks it is necessary that new control and optimization steps be included in the CAM methodology. There are three things that the firm adopting high-speed methods should do. It should redefine its process engineering, it should systematize access by its CAM programmers to high-speed knowhow, and it should take up the use of process simulation tools. In the latter case, it will be very advantageous to use tools for the estimation of cutting forces. The new work methods proposed in this article have made it possible to introduce high speed milling (HSM) into the die industry. Examples are given of how the technique has been applied with CAM programming re-engineered as here proposed, with an explanation of the novel features and the results.     

Evaluation of the stiffness chain on the deflection of end-mills under cutting forces

This study presents the investigation of the stiffness of the system formed by the machine-tool, shank and toolholder, collet and tool. Cutting forces induce the deflection of the system, and consequently an error appears on the machined surface.Comparing values obtained from cantilever beam models applied to the cutting tool, analytical or FEM, with those experimentally obtained, large differences have been observed, which in some cases are more than 50%. For this reason, we have proceeded to evaluate the stiffness of each of the existing elements between the machine bed and the tool tip. Thus, deflections of the machine-tool, toolholder and toolholder clamping in the spindle, tool clamping in the toolholder, and tool itself, were measured experimentally under the effects of known forces.The final application is the ball-end milling of complex surfaces, an operation commonly performed in the finishing of moulds or forging dies, where errors of more than 70 μm are not unusual. A great part of this error comes from the deflection of the machine-tool assembly, spindle, shank and tool, due to the high cutting forces of the high speed machining of tempered steels. Cutting forces can be estimated using a semi-empirical approach, and from here some values of probable errors may be taken into account to check if the CNC programs are sufficiently adapted. However, a previous study of the deflection chain in the cutting process is needed, as is presented in this work.Results show that stiffness of the slender and flexible tools is 15 times lower than that of the machine and toolholder system. But this correlation is only 5–7 times lower for shorter and thicker tools.     

Effects of tool deflection in the high-speed milling of inclined surfaces

The present paper looks at the dimensional errors resulting from tool deflection in the high-speed milling of hardened steel surfaces. These errors are measured as the difference between the theoretical surface and the high-speed milling machined using ball-end mills. The effect of various factors on this dimensional error is investigated. First, account was taken of the workpiece material and the slope of surfaces; the values chosen were those normally used in injection mould manufacturing. The workpiece materials were of 30 and 50 HRC hardness, with slopes of 15°, 30°, and 45°. In this manner, results may thus be of utility to the mould and die industry. The selected tools were solid ball end mills of sintered tungsten carbide, coated with TiAIN. These were of various diameters and lengths, and accordingly exhibited various degrees of slenderness. A great value for this latter parameter is a restraint on the potential application of the high-speed milling technique. This is the main reason for this work. Tests were carried out using three machining strategies, namely, upward, downward, and z-level (horizontal), as well as with two cutting types, downmilling (also called climb milling) and upmilling (or conventional milling). In all cases the resulting roughness was also measured. Dimensional errors in several flat slope planes were measured, comparing with those obtained by simulation. The results of these tests have been applied to the prediction of error in the high-speed milling of two industrial parts. Knowledge of error magnitude may be useful when NC programs are prepared for the machining of mould complex surfaces, since it may then be attempted to enhance accuracy. Reference is made to various practical problems that were necessary to resolve in order to achieve measurement errors less than 20 μm in a process as complex as that of high-speed milling in three axes machining centres.     

Improving the high-speed finishing of forming tools for advanced high-strength steels (AHSS)

Forming tools manufacturers have extensively incorporated high-speed milling technology for the finishing of large punch or die tools. The main objective is to achieve a good surface quality directly form machining, without any additional, tedious, manual work. Currently, new advanced high-strength steels (AHSS) are being used for car body parts. In this case, there are two special changes related to the forming tools: a higher proportion of harder surfaces on the working area, and long try-out iterations, due to their great springback. Tempered surfaces and insert blocks harder than 60 HRC are needed to withstand the forming charges with a good working life expectancy. From this, two problems arise with regards to high-speed finishing: first, the deflection of the tool due to the cutting forces, which can produce unacceptable dimensional errors; and second, in the same finishing operation, zones with sharp changes in hardness must be machined with the same CNC program and cutting tool. The key to solving both problems will be the use of newly developed utilities in the preparation stage, and the elaboration of CNC programs using CAM software. In the first case, the deflection of tool is dealt with by a milling model which obtains the values of cutting forces. This model characterises the couple tool/material with six coefficients, which are previously obtained for ball-end milling tools and base die materials. Inputs provided by the CAM user include feed per tooth, and radial and axial depths of cut. The problem of surfaces with areas of different hardness and poorly defined boundaries is solved with a special postprocessor coded in C language. Once the CAM user has defined (on the CAD model) the theoretical boundaries of the tempered areas, the insert blocks or the deposition material areas, this utility includes changes of the programmed feed function in the CNC program. In this paper, these approaches are applied to medium size workpieces with the same features of the actual punch and die for AHSS forming. Results are provided to die manufacturers for application in real forming tools. This technological model of the milling process estimates values of cutting forces and offers manufacturers a reduction of production and lead times.     

Semantic speech recognition in the Basque context Part I: cross-lingual approaches

This work, divided into Part I and II, describes the development of GorUP a Semantic Speech Recognition System in the Basque context. Part I analyses cross-lingual approaches oriented to under-resourced languages and Part II the development of the Language Identification system. During the development, data optimization methods and Soft Computing methodologies oriented to complex environment are used in order to overcome the lack of resources. Moreover, in this context three languages coexist: French, Spanish and Basque. Indeed our main goal is the development of robust Automatic Speech Recognition (ASR) systems for Basque, but all language variability has to be analyzed. In this regard, Basque speakers mix during the speech not only sounds but also words of the three languages which results in a strong presence of cross-lingual elements. Besides, Basque is an agglutinative language with a special morpho-syntactic structure inside the words that may lead to intractable vocabularies. Nowadays, our work is oriented to Information Retrieval and mainly to small internet mass-media. In these cases the available resources for Basque in general, and for this task in particular, are very few and complex to process because of the noisy environment. Thus, the methods employed in this development (ontology-based approach or cross-lingual methodologies oriented to profit from more powerful languages) could suit the requirements of many under-resourced languages.     

Experiments for the selection of sub-word units in the Basque context for semantic tasks

The long term goal of our project is the development of robust ASR systems in the Basque context where coexist French, Spanish and Basque (a minority language). The development of ASR systems involves dealing with issues such as Acoustic Phonetic Decoding (APD), Language Modelling (LM) or the development of appropriate Language Resources (LR). Thus, these applications are generally very language-dependent and require very large resources. This work is focused on the selection of appropriate sub-word units with under-resourced and noisy conditions. Nowadays, in particular, the work is oriented to Basque Broadcast News (BN) due to the interest of digital mass-media as the trilingual Infozazpi radio (situated in French Basque Country). Thus, in order to decrease the negative impact that the lack of resources has in this issue we apply several data optimization methodologies based on Matrix Covariance Estimation and Ontology-based approaches.