Horst Brünnet

Selecting Manufacturing Process Chains in the Early Stage of the Product Engineering Process with Focus on Energy Consumption

Manufacturing process chains describe the concept of how the transformation of a raw material into a finished product is achieved. Within the planning phase of the process chains not only technical and economic requirements must be met but also ecological aspects need to be considered, e.g. the energy consumption during the production phase. The aim of this chapter is to illustrate how the energy consumption of process chains can be considered in the early stage of the planning phase. It provides an overview of the methods that are available to describe and predict the energy demand of consumers in process chains. The presented method is based on planning data like characteristic power consumption parameters of manufacturing equipment and related time parameters. It aims at predicting the energy consumption per product. The data is needed for predictive assessment of alternative process chains and to assess the impact of energy consumption during the production phase in life cycle considerations. Finally, this chapter presents an example for the energy-aware design and selection of a preferred process chain from several alternatives. By this it is illustrated how the presented heuristic approach can be applied.

Modeling and Measurement of Residual Stresses along the Process Chain of Autofrettaged Components by Using FEA and Hole-Drilling Method with ESPI

The incremental hole-drilling method is a well-known mechanical measurement procedure for the analysis of residual stresses. The newly developed PRISM® technology by Stresstech Group measures stress relaxation optically using electronic speckle pattern interferometry (ESPI). In case of autofrettaged components, the large amount of compressive residual stresses and the radius of the pressurized bores can be challenging for the measurement system. This research discusses the applicability of the measurement principle for autofrettaged cylinders made of steel AISI 4140. The residual stresses are measured after AF and after subsequent boring and reaming. The experimental residual stress depth profiles are compared to numerically acquired results from a finite element analysis (FEA) with the software code ABAQUS. Sample preparation will be considered as the parts have to be sectioned in half in order to access the measurement position. Following this, the influence of the boring and reaming operation on the final residual stress distribution as well as the accuracy of the presented measurement setup will be discussed. Finally, the usability of the FEA method in early design stages is discussed in order to predict the final residual stress distribution after AF and a following post-machining operation.

Full Exploitation of Lightweight Design Potentials by Generating Pronounced Compressive Residual Stress Fields with Hydraulic Autofrettage

Internally pressurized components in hydraulic systems are subjected to high mechanical stresses. In case of dynamic pressure profiles this may lead to fatigue and hence a limited lifetime. This is particularly the case for fuel injection systems in combustion engines. Components of diesel injection systems in automobiles are popular examples for these demands. They have to withstand pressures of 2,200 bar and higher for at least 250,000 km. The increasing usage of high-strength materials and higher wall thicknesses will lead to a dead end as the weight and the complex manufacturing will tie up costs and resources. Autofrettage is a manufacturing process with high potential for the lightweight design of highly stressed hydraulic components. By considering the same wall thickness and applying optimal parameters, the fatigue strength may be increased by a factor of 3.5. If transferred to lightweight concepts wall thickness reductions as well as cost and resource savings by more than 45 % may be realized. However, from the manufacturing perspective the Autofrettage process poses some challenges. This paper presents results from Finite Element simulations and experiments and discusses the interaction between manufacturing processes with respect to residual stresses and deformations. The scientific findings may be used to tear down barriers in the application of Autofrettage and to optimize process chain layouts. It also serves to make a significant contribution to weight reduction in car manufacturing and other high performance hydraulic applications. Abbreviations: AF : Autofrettage; AFM : Abrasive Flow Machining; ECM : Electro-Chemical Machining; FEA : Finite Element Analysis; K-ratio : outer to inner radius ratio; L = length of the cylinder (mm); pAF : Autofrettage pressure (bar); pWP : working pressure (bar); piY : pressure to initiate yielding at the bore (bar); Ra : roughness average (μm); Rz : average maximum height of the roughness profile (μm); RPM : Revolutions Per Minute (1/min.); ri : inner radius (mm); ro : outer radius (mm); ρ : density (kg/dm3); σVM : von Mises equivalent stress (MPa); σy : yield stress (MPa); σt : tensile stress (MPa); σY : yield strength (MPa); SF : Safety Factor;

X-Ray Diffraction Measurements and Investigation of the Stress Relaxation in Autofrettaged AISI 4140 Steel Thick Walled Cylinders

Hydraulic autofrettage is a manufacturing process that induces favorable compressive residual stresses and is especially suitable for the treatment of internally pressurized components. If autofrettage is not the final treatment applied, the application of post-machining or other cold working processes can lead to a relaxation and redistribution of the stresses induced by the autofrettage process. In this paper, comprehensive X-ray diffraction residual stress measurements were performed and the influence of the applied autofrettage pressure and post-machining on the resultant residual stress vs. depth profiles was investigated. Introduction It is well known that compressive residual stresses are favourable because they act to close existing cracks in components and prevent the generation of new ones. When a component experiences inservice loading, applied tensile stresses will be shifted by the compressive residual stress (RS) field, if present. If the compressive RS field is of sufficient magnitude, the final stress state may still remain locally compressive despite the superimposed applied tensile stresses. There are several processes that are able to induce high magnitude compressive RS; e.g. shot peening, deep rolling and laser shock peening. The autofrettage (AF) process is especially suitable for treating internal geometries, e.g. components of the common rail diesel injection system. It leads to a beneficial and pronounced compressive RS vs. depth profile [1, 2] and several authors report an extension in fatigue life for components treated with this process [3, 4]. Its principle can be explained as follows [5]: when applying AF, a low-viscosity hydraulic medium is used to rapidly over-pressurize the treated component. If the resulting stresses exceed the yield strength of the material, then elasto-plastic deformation will result. Typically, the inner surface of the treated component deforms plastically while the outer surface of the component remains only elastically deformed. After releasing the AF pressure, the elastically deformed region of the component strives to return to its original state but is prevented from doing so by the inner plastically deformed region. This inhomogeneous deformation leads to the generation of compressive RS on the inner region of the component. This compressive region is compensated for with tensile stresses on the outer region of the component. The AF pressure is the most important processing input parameter and changing it leads to different RS vs. depth profiles in the part [6]. It has been shown that the AF process not only induces RS but also results in concomitant macroscopic shape deviations [7]. When high dimensional accuracy of the treated component is required, it may be necessary to perform a post-machining operation that could result in a redistribution and/or relaxation of the RS induced by the AF process. As such, the following paper presents investigations that include: pre-machining, autofrettage and post-machining. Residual Stresses 2016: ICRS-10 Materials Research Forum LLC Materials Research Proceedings 2 (2016) 335-340 doi: http://dx.doi.org/10.21741/9781945291173-57 336 X-ray diffraction (XRD) is an established, generally applicable, and time-proven method for near surface (up to 0.025 mm) RS measurements [8]. Accompanied with an electropolishing procedure, it offers the possibility to investigate RS at depth. In the presented paper, XRD techniques were employed to measure the RS vs. depth profiles in thick walled cylinders that were treated with different AF pressures and partially post-treated using a reaming operation. Due to the geometric constraints inherent to the specimens, they were sectioned in half to enable XRD based RS measurements on their inner diameter (ID). To account for the relaxation and redistribution of the RS induced by the AF process as a result of axial sectioning, strain gauges were applied to the inner and outer diameters (OD) of the specimens’ surfaces prior to cutting. The strain gauges were then monitored during the sectioning process and the results obtained were used to correct the measured stresses for the effect of sectioning. Since the XRD technique samples a relatively thin surface layer, material removal techniques were applied so as to obtain the full through wall thickness RS profile. To this end, electropolishing techniques were employed and the resulting stress relaxation was corrected for using the analytical methods proposed by Moore and Evans [9]. Experimental setup The samples used for the experiments are thick walled cylinders, manufactured from high strength AISI 4140 steel (hardened at 840 °C and tempered at 610 °C). Two measurement points (MP1 and MP2) were chosen to characterize the different treatment sequences on both sides of the thick walled cylinders. The process and measurement chains are shown in Table 1. Table 1 – Process and measurement chains for the thick walled cylinders Samples were prepared by first boring (n = 200 1/min, vf = 1 mm/s) an inner diameter of 9 mm, using a HSS twist drill. The cylinders were then treated with AF pressures ranging from 2000 to 9500 bar. The treatment with 2000 bar did not lead to a plastification of the cylinders’ surface and RS was therefore not generated; the cylinders treated with an AF pressure of 2000 bar are thus considered to be untreated. A reaming operation (n = 200 1/min, vf = 0.6 mm/s) to an inner diameter of 10 mm was then performed on the right side of the cylinder leaving the left half of each cylinder MP1 MP2 Process and measurement chain Process parameters Residual Stresses + + Rolled Hardened at 840 °C Tempered at 610 °C Present, unknown Randomly distributed + + HSS twist drill Length: 125 mmm n = 200 1/min, vf = 1 mm/s, ID = Ø 9H12 + + Autofrettage pressure levels: P = 2000, 8000, 8500, 9000 and 9500 bar + HSS – E 6 blades reamer n = 200 1/min vf = 0.6 mm/s OD (up to middle) = Ø 10H7