July 2021
Linear scale has significant impacts on the machine tool accuracy, since the positioning of the linear axes are controlled by its measurement. This paper presents a novel concept of linear scale design which can provide high thermal stability with low cost. This concept applies two different materials: a steel linear scale attached mechanically on a carbon fiber reinforced plastic (CFRP) tube. Attaching (…)
Variable heat sources in machine tools lead to unsteady displacement fields and hence necessitate temperature control in order to maintain the required positioning accuracy. Adding passive components that redistribute heat through heat storage and heat transport within the machine tool is one approach to compensate for thermal errors. While including latent heat storage components reduces the machine re (…)
The development of a smart sensor is proposed to improve the thermal error compensation model of a multi-spindle automatic lathe. The smart sensor is capable of gathering real-time information about rotating spindle drum temperatures. Thereafter, the temperature obtained by the smart sensor is applied as input to the thermal error compensation model based on the transfer function instead of an indigenou (…)
Heat losses within motor spindles lead to undesired effects such as machining inaccuracies and de-creasing lifetime of the motor and bearings. To reduce thermal loads, complex shaft cooling concepts with costly sealing techniques exist. For this reason, a novel, less costly cooling concept has been de-veloped based on heat pipes with high thermal conductivity and fin-shaped heat exchangers. The de-sign (…)
In most sectors of today’s industry, there is the requirement to manufacture work pieces with accuracy in micron range. However, maintaining this accuracy can be considerably impeded by thermally induced displacements which arise in the production process. Thermally induced errors cause large parts of residual machining errors on modern machine tools. Using climate control systems for whole workshops ca (…)
Thermal errors are one of the major contributors towards positioning discrepancies in machine tools in precision machining. Along with friction and waste heat generated from production processes and internal heat sources, environmental influences around the machine tool create considerable thermal gradients followed by non-linear structural deformations. Efficient quantification of these three contribut (…)
A large amount of the energy produced during grinding is converted into heat. Since not all of the heat can be dissipated by the cooling lubricant, thermally induced displacements in machine components occur, which has a negative influence on the component quality. The generation and distribution of heat is influenced by the change of the grinding wheel topography due to wear.Therefore, the wear mechani (…)
Nowadays, the thermo-energetic design of a machine tool also includes the thermal stabilization of its machine components. In the past, thermal stability was irrefutable connected to minimizing the temperature gradient of machine tools by air conditioning the entire machine or even the factory hall. Today, thermal stability also defines minimal inhomogeneities in the temperature field of the machine too (…)
During machining, most of the thermal sources are resulting from the conversion of mechanical energy during the chip shearing mechanism and the intense frictions between the tool, the chip, and the machined surface. Thermal gradients are high and localized, especially for low thermal diffusivity material like titanium alloys. Moreover, heat rates come close to few million degrees per second in the shear (…)
Thermal effects are the most dominant source for displacements in machine tools and thus work-piece inaccuracies during the manufacturing process. A promising strategy to meet the ever-increasing accuracy requirements is the use of predictive models for, e.g., parameter and design op-timizations or online correction of the thermally induced error at the tool center point (TCP) in the pro-duction process (…)
To control the thermal behavior of machine tools, numerous measures are used today. With the help of thermal machine models, well-founded predictions can be made for the selection and design of these measures. For creation and simulation of thermo-elastic models of structural components and a high effort is still necessary. In the paper, a procedure is presented to reduce this effort. A combination of e (…)
The thermomechanical load on the workpiece surface during the machining process strongly influences its surface integrity and the resulting fatigue strength of the components. In single-lip drilling, the measurement of the mechanical load using dynamometers is well established, but the thermal interactions between the tool and the workpiece material in the surface area are difficult to determine with co (…)
Up to 75 % of the overall work piece error can be caused by the thermo-elastic behavior of the machine tool. Therefore, correction methods based on machine-integrated sensors were intensively researched during the last years, in order to determine the error of the Tool Center Point (TCP) parallel to the process. One of these methods includes the integral deformation sensor (IDS), which detects the defor (…)
This paper analyzes geometrical approaches to optimize the fluid cooling circulation of motorized spindles. The spindle fluid cooling’s effectiveness, efficiency and influence on the machine’s precision are analyzed through observations of the stator temperature, pressure drop and thermal asymmetry, respectively. The observation is based on a validated coupled thermal/fluid mechanical simulation model. (…)
This paper presents a method to quantify and reduce thermal asymmetry of motorized spindles. Thermal asymmetry leads to angular and radial deflections at the tool center point. In contrast to simple thermal expansion issues, these effects are harder to compensate. Therefore, the causes of the asymmetries should preferably be evident in the construction phase. This paper introduces a newly developed math (…)
Cutting processes of carbon fibre reinforced polymer (CFRP) material generate significant energy in the form of heat which can be detrimental to final surface and sub-surface quality. By artificially changing the temperature of the workpiece to simulate cutting temperatures, thermal effects on friction metrics can be understood. Feed rate and CFRP pre-heating for macro and nanoscale open loop pin on pla (…)
Progress in improving the accuracy of metal-cutting machines is inextricably linked and driven by deeper knowledge gained through the study of thermal processes and effects occurring in machines, which can be used to manage them. This led to the dominance of temperature errors in the balance of machine accuracy, the share of which changed from 20-30% to 70% during the period from 1950 to 2020, which is (…)
The calibration of machine tools or industrial robots needs high precision 3-dimensional coordinate measurements. Common available systems still have the need of ambitious and time extensive processes to fulfill the requested requirements. Therefore there is a strong request for fully automated systems that allow an autonomous and easy to handle procedure for 3D volumetric deviation measurements. This e (…)
In metal additive manufacturing, a metal material is melted by a concentrated heat source such as a laser. Therefore, thermal deformation occurs in the fabrication, which causes deterioration of shape accuracy and crack of the workpiece. In this study, a method to systematically reduce the thermal deformation was discussed. The mechanism of thermal deformation caused by stacking and lining up the bead w (…)
The cooling with cutting fluids is a complex process in manufacturing, since chemical, mechanical and thermal phenomena occur simultaneously. The experimental methods developed so far do not allow for a direct observation of the coolant flow during machining, which limits the understanding of the cooling mechanism. The main aim of this paper is the investigation of convective heat transfer between cutti (…)
Inconel 718 as one of the most common nickel-base alloys is mainly characterized by its high-temperature strength. Thus, in particular drilling is subject to high tool wear due to high thermomechanical loads on the cutting edges. To reduce those effects an alternative process design of discontinuous drilling was developed which contains a periodical interruption of the machining process with the aim of (…)
When analyzing machine tools it is observable that despite sufficient cooling capacity thermo-elastic deformation of the machine structure is badly compensated due to heat input. The reason is the missing adaption of coolant and heat input into the system structure during the process, resulting in insufficient productivity and quality. In this paper, various system configurations are shown that can be (…)
In this presented work, the main objective is the in-process measurement of the thermal as-is state near the drilling contact zone by means of a sensor-integrated tool for single lip deep hole drilling (SLD). Additionally, the mechanical quantities feed force and drilling torque are evaluated. The process monitoring is essential to optimize the surface quality as well as the subsurface properties such a (…)
Static and dynamic stiffness [N/m] determine the ability of solids to resist constant and variable loads. Both elastic characteristics of a machine tool effect their quality assessment. Thermal stiffness (comprising heat stiffness and temperature stiffness) [W/µm] is a key accuracy indicator of the machine tool's ability to resist temperature influences. The proposed method creates the thermo-physical s (…)
Temporally and spatially unstable thermal conditions lead to transient or inhomogeneous thermo-elastic behavior of workpieces during manufacturing or geometric inspection. Temperature monitoring by means of sensors consign transient temperature fields, but do not yield information about the heat flow acting as thermal boundary condition, which is a relevant input parameter for nearly any thermal simulat (…)
The paper presents a numerical simulation of thermal induced tool displacement during milling oper-ation. An unidirectional finite element model is developed which consists of two sections. A CFX model and a thermal transient model. With the aid of CFX module, the conjugated heat transfer be-tween milling tool and coolant fluid is described. The result of these efforts is the body temperature field of t (…)
Continuous rotation of spindle bearings and motor cause thermally induced structural deformations and thermal growth, which is one of the main reasons for machining errors. A positive feedback loop between bearing preload and heat generation causes preload variations in spindle bearings. These preload variations demonstrate a nonlinear transient behavior until the gradual expansion of outer bearing ring (…)
During machining occurring losses conduct into the machine tool and lead to deformations that im-pair the machining accuracy. Thus, high effort is invested into the compensation of thermo-elastic er-rors. One new approach is to use the information extractable from part programs in combination with CNC controller systems to forecast occurring losses in terms of a look ahead function. The method al-lows t (…)
Achieving high workpiece accuracy is a long-term goal of machine tool designers. There are many causes of workpiece inaccuracy, with thermal errors being the most dominant. Indirect compensation (using predictive models) is a promising strategy for reducing thermal errors without increasing machine tool cost. A modelling approach using thermal transfer functions (a dynamic method with a physical b (…)
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