Driver roll speed influence in Ring Rolling process

Ring Rolling is an advanced local incremental forming technology to fabricate directly precise seamless ring-shape parts with various dimensions and materials. To produce a high-quality ring different speed laws should be defined: the speed laws of the Idle and Axial rolls must be set to control the ring cross section and the Driver roll angular velocity must be chosen to avoid too high localized deformation on the ring cross section. Usually, in industrial environment, a constant rotation is set for the Driver roll, but this approach does not guarantee a constant ring angular velocity because of its diameter expansion. In particular, the higher is the ring diameter the lower is its angular velocity. The main risk due to this constrain is the generation of a non-uniform ring geometry. An innovative approach is to design a Driver Roll speed law to obtain a constant ring angular velocity. In this paper a FEM approach was followed to investigate the Driver roll speed influence on the Ring Rolling process. Different Driver roll speed laws were tested starting from a model defined in an industrial plant. Results will be analyzed by a geometrical and physical point of view

Laser decoating of DLC films for tribological applications

Damaged DLC coatings usually require remanufacturing of the entire coated components starting from an industrial chemical de-coating step. Alternatively, a complete or local coating repair can be considered. To pursue this approach, however, a local coating removal is needed as first operation. In this context, controlled decoating based on laser sources can be a suitable and clean alternative to achieve a pre-fixed decoating depth with high accuracy. In the present study, we investigated a laser-based decoating process executed on multilayered DLC films for advanced tribological applications (deposited via a hybrid PVD/PE-CVD technique). The results were acquired via multifocal optical digital microscopy (MF-ODM), which allowed high-resolution 3D surface reconstruction as well as digital profilometry of the lasered and unlasered surface. The study identifies the most critical process parameters which influence the effective decoating depth and the post-decoating surface roughness. In particular, the role of pulse overlap (decomposed along orthogonal directions), laser fluence, number of lasing passes and assist gas is discussed in text. A first experimental campaign was designed to identify the best conditions to obtain full decoating of the DLC + DLC:Cr layers. It was observed that decreasing the marking speed to 200 mm/s was necessary to obtain a sufficient pulse overlap and a nearly planar ablation profile. By operating with microsecond pulses and 1 J/cm2 (fairly above the ablation threshold), less than 10 passes were needed to obtain full decoating of the lasered area with an etching rate of 1.1 μm/loop. Further experiments were then executed in order to minimise the roughness of the rest surface with the best value found at around 0.2 μm. Limited oxidation but higher Ra values were observed in Ar atmosphere

Laser Surface Texturing to Realize Micro-grids on DLC Coating: Effect of Marking Speed, Power, and Loop Cycle

In the present study, laser surface texturing was tested with the aim of improving the tribological properties of a diamond-like carbon (DLC) coating. Two experimental campaigns were designed to realize different micro-grids, and to study the effect of marking speed, laser power, and loop cycle. The grid profiles obtained were analyzed using a digital microscope and a laser probe system to measure the track cross section. At the end of the experiments, the authors identified a good-quality track obtained by imposing a marking speed of 300 mm/s, a power of 0.5 W, and one loop cycle. For the identified condition, the presence of defects (such as cracks) on both the coated surface and at the substrate/coating interface was analyzed. Furthermore, the coating nanohardness, adhesion to the substrate, and wear behavior in dry condition were investigated. The results underline how laser texturing can improve the DLC wear behavior (wear tracks lower than 30%) without considerably affecting the other tested coating properties

Ring Rolling speed rolls optimization to improve ring quality and reduce production time

In this paper, an analysis of the production time reduction as a function of the Idle and Axial rolls speed law in a Ring Rolling process was examined. Starting from an industrial case study, the authors defined a new milling curve able to produce a better ring quality with lower loads. From this result, the authors tested the effect of the production time reduction till the 40% of the initial one. The Ide roll velocity was varied in a range between 0.71 and 1.13 mm/s while the Axial roll between 0.35 and 1.70 mm/s. Geometrical and load parameters have been taken into account to compare the results achieved. The authors identified in the external ring diameter and in the Idle roll maximum load the most critical parameter to control; in particular, a break-even point was determined in order to select a set of rolls speed laws able to produce a good quality ring with lower production time (about 20%) and lower loads (about 10 %). In this research both experimental and numerical approaches were followed

Overview of Current CAT Systems

The paper surveys the current status of the models for representing, manipulating and analyzing dimensioning and tolerancing data behind the major computer-aided tolerancing (CAT) systems, now commercially available. The solid models and tolerance models that these systems adopt, and their implications for the successful integration of CAT and CAD/CAM are discussed. There are two main purposes. First, the attention is focused on the theoretical backgrounds of every CAT system analyzed, for understanding its limits and its usefulness in design and manufacturing practice. The other purpose is to present a comparison among these systems to support the designer and the manufacturing engineer, as well as the researchers, in the choice of the system will be more proper to everyone. Finally, the research work that remains to be carried out, to improve the future CAT systems and their integration with CAD/CAM is sketched out