Influence of the nitrided layer thickness of dies made of two types of tool steel used in hot extrusion of valve forgings made of nickel–chromium steel on the durability of these tools

The study constitutes an analysis of the durability of dies used in the first operation of producing valve forgings from chromium–nickel steel (NCF 3015) for motor trucks. The average durability of the dies (subjected to standard thermal treatment and nitriding) in this operation equals about 800 forgings. To perform an in-depth analysis of the effect of the nitrided layer thickness (0.1 mm and 0.2 mm) and the tool material (W360 and QRO90) on the possibilities of increasing the die durability, complex studies were carried out, which included: a macroscopic analysis combined with 3D scanning, microstructural examinations using a scanning microscope and a metallographic microscope, as well as hardness measurements. A minimum of three tools were tested for different variants, and for each of them, one representative die was selected for detailed examinations. The research showed the presence of abrasive wear, thermo-mechanical fatigue and traces of adhesive wear as well as plastic deformation on the surface of the working impressions. Also observed was the effect of the extruded material sticking to the tools (high friction and the presence of intermetallic phases in the extruded material) and the forging being blocked in the smallest section of the die, which is a critical factor causing a production shutdown and the necessity of tool replacement. The highest mean durability equalling 2600 forgings was obtained for the dies with a lower carbon content and a higher content of vanadium and the nitrided layer thickness at the level of 0.2 mm. The lowest mean durability (after one forging item) was recorded for the dies made of steel with a higher carbon content and a higher chromium content, forming less stable compound carbides and the thickness layer at the level of 0.1 mm.

Application of Selected Reverse Engineering Procedures Based on Specific Requirements

The paper describes a solution of reverse engineering tasks using the equipment of the laboratory of the Technical University in Zvolen. The first task was linked to evaluation of a wear rate of the tool used to for mulching and elimination of unwanted wood or weed vegetation. The obtained data will be used as a base line for determination of the time interval for the tool replacement. We developed a prototype of components and their drawing documentation for a single-purpose machine for cutting barley. We created the 3D model using the method of photogrammetry. The finished drawing documentation and prototypes were handed over to the company KRUP. Finally, we identified the most suitable procedures for creating a model of a part with a complex shape. We tested the techniques of editing the point cloud processing, as well as of smoothing the surfaces and automating the creation of partial geometric elements of the model. Based on the properties of the component, which is the starting point of the entire reverse engineering process and from the achieved results, we set recommendations for the selection of appropriate procedures.

Process Monitoring in a Flexible Manufacturing Cell through Data Analytics and a Visualisation Tool

With the need of more responsive and resilient manufacturing processes for high value, customised products, Flexible Manufacturing Systems (FMS) remain a very relevant manufacturing approach. Due to their complexity, quality monitoring in these types of systems can be very difficult, particularly in those scenarios where the monitoring cannot be fully automated due to functional, safety and legal characteristics. In these scenarios, quality practitioners concentrate on monitoring the most critical processes and leaving out the inspection of those that are still meeting quality requirements but showing signs of future failure. In this paper we introduce a methodology and visualisation tool based on data analytics that allows the practitioner to anticipate out of control processes and take action. By identifying a reference model or best performing machine, and the occurring patterns in the quality data, the presented approach identifies the adjustable processes that are still in control, allowing the practitioner to decide if any changes in the machine's settings are needed (tool replacement, repositioning the axis, etc). An initial deployment of the tool at BMW Plant Hams Hall to monitor a focussed set of part types and features has shown a reduction in scrap of 97% throughout 2020 in relation to the monitored features compared to the previous year. This in the long run will reduce reaction time in following quality control procedure, reduce significant scrap costs and ultimately reduce the need for measurements and enable more output in terms of volume capacity.

Adjusting Mechanical Properties of Forging Dies Produced by Ausforming

Due to high thermo-mechanical loads, tools used in hot forming operations need a high resistance to different damage phenomena, such as deformation, cracking and abrasion. They are exposed to cyclic thermo-mechanical stress conditions, which leads to tool failure and subsequent tool replacement during cost-intensive production interruptions. To increase wear resistance, forging tools can be produced in the metastable austenite area. Forming of steel below the recrystallisation temperature, also known as “ausforming”, offers the possibility to increase strength without affecting ductile properties. This is due to grain refinement during forming. In this study, the thermo-mechanical treatment ausforming will be used to form the final contour of forging dies. For this purpose, an analogy study was performed where a cup-preform is ausformed, which represents the inner contour of a highly mechanically loaded forging die. It is investigated to what extent a fine-grained microstructure generated in the last forming stage can be achieved and how it influences the tool’s performance. The hot-working tool steel X37CrMoV5-1 (AISI H11) was used as workpiece material. To achieve optimal properties, process routes with tempering temperatures from 300 °C to 500 °C and global true plastic strains of φ = 0.25 and φ = 0.45 were examined. The results were evaluated by pulsation tests, metallographic analysis and hardness measurements of the formed parts. Optimal ausforming parameters were derived to produce a high performance forging die.

Determination of optimal coordinates for switching processing cycles on metal-cutting machines

Introduction. One of the ways to improve the efficiency of processing on machines is to coordinate the CNC program with the changing properties of the dynamic cutting system. If this takes into account the tool wear and the associated with it changes in the parameters of the dynamic cutting system, then the cutting speed to ensure the minimum wear rate is reduced along the cutting path. The corresponding feed rate is reduced even faster, since it is necessary to ensure a constant deformation displacement of the tool relative to the workpiece. The evolution of the properties of the cutting process (for matching with which the trajectories of the operating elements of the machine are corrected) depends on the power of irreversible transformations of the energy supplied to cutting. This reduces the processing efficiency. Therefore, a new for the considered subject area problem of determining the coordinates of the tool movement relative to the workpiece is formulated, starting from which further processing is economically inexpedient. In this case, it is necessary, after processing the next part, to ensure the replacement of the tool and carry out its changeover. Subject. A metal-cutting machine of a turning group, the trajectories of the executive elements of which are controlled, for example, by a CNC system. The purpose of the work. Mathematical simulation and methods for determining the coordinates at which it is necessary to replace the tool. Method and methodology. The necessary conditions for the optimality of determining these coordinates are proved. Mathematical tools are provided that allow calculating the coordinates at which the given manufacturing costs take the minimum value according to the given trajectories. The probabilistic characteristics of evolutionary trajectories are taken into account. Results and discussions. The analysis of the efficiency of using the technique in industry depending on the cost of the machine and tool together with its replacement and readjustment is given. The proven optimality conditions and the given mathematical tools complement the knowledge about the optimization of controlled machining processes on machines. Conclusions. The results of the study show new options for the organization of tool replacement, aimed at improving the efficiency of processing by software methods using a CNC system.

Physician-Friendly Tool Center Point Calibration Method for Robot-Assisted Puncture Surgery

After each robot end tool replacement, tool center point (TCP) calibration must be performed to achieve precise control of the end tool. This process is also essential for robot-assisted puncture surgery. The purpose of this article is to solve the problems of poor accuracy stability and strong operational dependence in traditional TCP calibration methods and to propose a TCP calibration method that is more suitable for a physician. This paper designs a special binocular vision system and proposes a vision-based TCP calibration algorithm that simultaneously identifies tool center point position (TCPP) and tool center point frame (TCPF). An accuracy test experiment proves that the designed special binocular system has a positioning accuracy of ±0.05 mm. Experimental research shows that the magnitude of the robot configuration set is a key factor affecting the accuracy of TCPP. Accuracy of TCPF is not sensitive to the robot configuration set. Comparison experiments show that the proposed TCP calibration method reduces the time consumption by 82%, improves the accuracy of TCPP by 65% and improves the accuracy of TCPF by 52% compared to the traditional method. Therefore, the method proposed in this article has higher accuracy, better stability, less time consumption and less dependence on the operations than traditional methods, which has a positive effect on the clinical application of high-precision robot-assisted puncture surgery.

A Robust RCSA-Based Method for the In Situ Measurement of Rotating Tool-Tip Frequency Response Functions

Measuring rotating tool-tip frequency response functions (FRFs) is difficult because of the fluted tip geometry. The methods based on receptance coupling substructure analysis (RCSA) can obtain rotating tool-tip FRFs with a few tests. Existing RCSA-based methods require at least one smooth rod for measurement and then mathematically calculate the desired rotating tool-tip FRFs. However, involving the inverse of the experimentally obtained FRFs matrix, these methods are susceptible to the measurement noise in the rotating structure. In addition, the inconsistency between the holder–tool and holder–rod connections is another uncertainty which impacts accuracy. This paper presents a robust RCSA-based method to obtain rotating tool-tip FRFs. It is found that tool-tip FRFs can be calculated from another point FRFs on the same assembly. Then, one point on the smooth cylindrical shank of the tool is selected for measurement. The measured FRFs, along with those from the theoretical tool model, calculate the rotating tool-tip FRFs. Compared with the previous methods, the proposed one does not require inverting the measured FRFs matrix, inherently avoiding amplification of measurement noise. Since the tool replacement is no longer required, in situ measurement is achieved to ensure the same holder–tool connection throughout the procedure. The proposed method is first validated in a numerical case and then verified experimentally by a commercial hammer and laser vibrometer. Both results show that the method is insensitive to the measurement noise and can obtain rotating tool-tip FRFs with considerable accuracy.