materials Article Dimensional Analysis of Workpieces Machined Using Prototype Machine Tool Integrating 3D Scanning, Milling and Shaped Grinding Piotr Jaskólski 1, Krzysztof Nadolny 1,* , Krzysztof Kukiełka 1 , Wojciech Kapłonek 1 , Danil Yurievich Pimenov 2 and Shubham Sharma 3 1 Department of Production Engineering, Faculty of Mechanical Engineering, Koszalin University of Technology, Racławicka 15-17, 75-620 Koszalin, Poland; [email protected] (P.J.); [email protected] (K.K.); [email protected] (W.K.) 2 Department of Automated Mechanical Engineering, South Ural State University, Lenin Prosp. 76, 454080 Chelyabinsk, Russia; [email protected] 3 Department of Mechanical Engineering, IK Gujral Punjab Technical University, Jalandhar-Kapurthala Road, Kapurthala, Punjab 144603, India; [email protected] * Correspondence: [email protected]; Tel.: +48-943-478-412 Received: 11 November 2020; Accepted: 9 December 2020; Published: 11 December 2020 Abstract: In the literature, there are a small number of publications regarding the construction and application of machine tools that integrate several machining operations. Additionally, solutions that allow for such integration for complex operations, such as the machining of shape surfaces with complex contours, are relatively rare. The authors of this article carried out dimensional analysis of workpieces machined using a prototype Computerized Numerical Control (CNC) machine tool that integrates the possibilities of 3D scanning, milling operations in three axes, and grinding operations using abrasive discs. The general description of this machine tool with developed methodology and the most interesting results obtained during the experimental studies are given. For a comparative analysis of the influence of the machining method on the geometric accuracy of the test pieces, an Analysis of Variance (ANOVA) was carried out. The obtained results show that for four considered features (deviations of flatness, vertical parallelism, opening dimensions, and opening cylindricality), no statistically significant differences were detected. For the evaluation criteria, the probability level p exceeded the assumed confidence level α = 0.05 and ranged from p = 0.737167 to p = 0.076764. However, such differences were found for two others—a dimensional deviation between flat surfaces (p = 0.010467) and horizontal parallelism deviation (p = 0.0)—as well as for the quality of the machined surface defined by four surface texture parameters: Ra (p = 0.831797), Rt (p = 0.759636), Rq (p = 0.867222), and Rz (p = 0.651896). The information obtained by the ANOVA will be useful for the elimination the weaknesses of the prototype machine tool, further analysis of technological strategies, and to find possible benefits of integrating machining operations. Keywords: dimension accuracy; shape accuracy; 3D scanning; milling; shaped grinding; complete machining 1. Introduction There is a significant increase in the share of variable curvature surfaces, as presented by Yang et al. [1–3], in various types of engineering structures, such as: dies, molds, stamping dies, turbine elements, and decorative, design, and utility products. Designing such elements’ surfaces is not difficult thanks to the use of computer-aided design (CAD) and computer-aided manufacturing Materials 2020, 13, 5663; doi:10.3390/ma13245663 www.mdpi.com/journal/materials Materials 2020, 13, 5663 2 of 18 (CAM) systems. Such systems can be used to create complex parts, but in many cases, the surfaces of the parts after the milling process require grinding and precise smoothing to achieve specific quality requirements of the finished product. These operations are carried out on separate machine tools, which differ in their control. During the production of parts, for which several machining operations have to be performed, there are timeouts due to retooling, positioning, and clamping of parts in several different machine systems. Moreover, each subsequent clamping reduces the dimensional and shape accuracy resulting from the change of machining base. To attempt to solve this important problem in modern manufacturing, so-called complete machining (integrated machining) carried out, which integrates high-accuracy 3D scanning and Computerized Numerical Control (CNC) machining. The 3D scanning was carried out to obtain spatial information about the scanned object (points cloud) and generate a CAD model. Based on such a model, the control program for a CNC machine tool equipped with multiple tool heads and a single workpiece clamp was prepared. The technical solution ensuring the possibility of complete machining is a platform that connects a 3D scanner and a CNC machine tool, supported by appropriate computer software. Integrated machining systems have been successfully developed for over thirty years and are used in many fields of modern science and technology. Examples of some of them are given in Table1. Table 1. Integrated machining systems and their fields of application. Integrated Methods Area of Application Author(s) Reference 3D scanning (triangulation) + Free-form surfaces and Bradley et al. [4] CNC machining (milling) quadric surfaces (1992) 3D scanning (LDS) + NC Aerospace industry, Liu et al. [5] machining large thin-walled parts (2015) 3D scanning + CNC machining Wu et al. [6] (milling) Small-engineering parts (2014) 3D scanning (SLS) + CNC Galantucci et al. (2015) [7] machining (milling) 3D scanning (ACT) + CNC Orthodontics, Chang et al. [8] machining (milling) orthodontic denture (2006) 3D scanning (triangulation) + Dentistry, Milde and Moroviˇc [9] CNC machining (milling) dental restorations (2016) LDS—Laser Displacement Sensor, NC—Numerical Control, SLS—Slit Laser Scanner, ACT—Abrasive Computer Tomography. Developing the above solutions, over time, allowed their commercialization and implementation as a new class of technological machines in the industry. Examples of such solutions include machine tools: DMG MORI CTX gamma 2000 TC; • DMG MORI LASERTEC 65 3D; • Doosan PUMA SMX3100L. • A CTX gamma 2000 TC (DMG Mori Seiki AG, Bielefeld, Germany) lathe and milling center is a universal machine tool integrating turning, milling, and grinding operations. On this machine tool, it is possible to process elements with diameters of up to 700 mm and lengths of up to 2050 mm. It is equipped with two spindles: one for turning with a maximum speed of 4000 rpm and one for milling with a maximum speed of 20,000 rpm. Additionally, the DMG MORI CTX gamma 2000 TC lathe and milling center offers the possibility of internal and external cylindrical grinding, face grinding, and also allows for the dressing of grinding wheels. Other applications were presented by Bleicher et al. [10]. Whereas the milling center LASERTEC 65 3D hybrid (DMG MORI Seiki AG, Bielefeld, Germany), a hybrid is a machine tool that integrates the possibility of carrying out milling and laser surfacing Materials 2020, 13, 5663 3 of 18 operations in five-axis, The machine has an operating range of 735 mm on the X-axis, 650 mm on the Y-axis, and 560 mm on the Z-axis. It is equipped with a spindle with a maximum speed of 20,000 rpm and a fiber-coupled laser diode of 3000 W. Both described machine tools of DMG MORI are controlled by the COLEOS® system (DMG MORI Seiki AG, Bielefeld, Germany), which allowed us to control the production by monitoring and supervising machining process the workpiece. Some of the applications of the LASERTEC 65 3D hybrid were given by Seidel et al. [11], Bennett et al. [12], Kledwig et al. [13], as well as Soshi et al. [14,15]. The Doosan PUMA SMX3100L (Ellison Technologies, Inc., Santa Fe Springs, CA, USA) lathe and milling center is a machine tool that integrates turning and milling operations in one clamping. On this machine tool, it is possible to process workpieces with diameter up to 660 mm and length up to 2540 mm. It is equipped with two spindles: one for turning with maximum speed up to 3000 rpm and one for milling operation with maximum speed 12,000 rpm. The machine is programmed and controlled by the FANUC control system (FANUC Ltd, Yamanashi-ken, Japan). Specialized machine tools are not always required to integrate operations. There are solutions on the market that allow many types of operations to be performed on a CNC turret lathe with a driven Y-axis. Among the most interesting in this area are the tool holders offered by M.T. S.r.l. (San Giovanni In Marignano RN, Italy): X11 Powered Electrospindle; • Broaching Toolholder; • Driven Gear Hobber; • Laser cutting device for turret lathes. • The X11 Powered Electrospindle by M.T. is a device mounted in one of the slots in the turret magazine of a CNC lathe. It enables grinding, engraving, and drilling operations at high speed. The motor of the device is driven by a system that converts the rotary movement of the driven tool holder into electrical energy driving the shaft. The device is connected to the cooling system in the turret of the CNC lathe, which enables cooling of the electrospindle motor. Moreover, the device has a dedicated system ensuring proper protection of the electrospindle against contamination and coolant during machining, thanks to which it can be installed in CNC lathes without compressed air connections. The X11 Powered Electrospindle by M.T. has a diameter of 42 mm and its maximum speed is 60,000 rpm. The Broaching Tool holder from M.T. is also a tool holder mounted in one of the slots in the turret magazine of a CNC lathe. It is used to perform broaching machining, as a result of which it is possible to make keyway grooves directly on the CNC lathe. The 1:4 reduction factor (1600 rpm, corresponding to 400 tool strokes per minute) allows the machining of hard materials even with limited power available on the driven tool holder. Additionally, the tool holder has a double guide mechanism that increases stability during broaching and lowers the tool during the return stroke, maximizing tool life. Driven Gear Hobber by M.T. is a tool holder designed to be mounted in one of the slots in the turret magazine of a CNC lathe.