Question

r Engineenng eratures in the rim by around 313 K compared with earlier piston designs. The piston's steel skirt is much more rigid than the aluminum skirt in smaller deformation and allowing for designs with tighter clearances tin harmful exhaust emissions) from the piston. This design has been shown to reduce piston termn results in a more stable piston with less oil consumption (thus further r which are machined prior to welding. The process used to join these components is inertia friction welding (Section 12.9) which has the following advantages in th Monosteel pistons are produced from two forged componen application: .The process leads to well-controlled, reliable, and repeatable high-quality Friction welds are continuous and do not involve any porosity, thereby . The welding process is fairly straightforward to optimize, the main process S. producing a high-strength weld that seals the oil gallery variables being energy (or spindle speed for a given flywheel) and contact pressure The friction welding process does not require any operator intervention or expertise, as it is entirely machine controlled. Although the capital investment is significant compared to other welding technologies, weld quality (and the ability to weld this application) is significantly more favorable The Monosteel piston shown in Fig. 12.62 was produced on a 250-ton force capacity inertia friction welder, using a peripheral velocity of 7.5 m/s, and a con tact pressure of 140 MPa (see Fig. 12.30). As can be seen, the weld zone contains the optimum flash shape (see Fig. 12.31), which is removed from the exterior p ton surface by a turning operation (Section 8.9.1), after which the piston cycle times are typical but can be higher or lower depending on piston size. been in high-volume production since 2003 Source: Courtesy of D. Adams, Manufacturing Technology, Inc., a skirt is nds ground (Section 9.6). Production takes place at relatively high rates; 40-60 secon The Monosteel piston has been applied to multiple engine platforms an ke Federal Mogul, Inc and K. Westbr In plane-strain upsetting, the frictional stress cannot be higher than the shear yie stress, k, of the workpiece material. Thus, there may be a distance a in Fig. 6.4 where a transition occurs from sliding to sticking friction. Derive an expression for in terms of a, h, and μ only. Plastics, Rapid Prototypi Carbon fibers 300 200 glass fbers fibe 200 Shon glass fioers 100 Short glass fibers 10 20 30 40 Reinforcement (%) Carbon fibers 0 10 20 30 40 Reinforcement (%) 400 F 30 - 300 n fibers 20- s fibers 200 Long gla Long and short glass fibers Short glass fibers 100 0 10 20 30 40 Reinforcement (%) 0 10 20 30 40 Reinforcement (%) URE 10.19 Effect of the percentage of reinforcing fibers and fiber length on the properties of reinforced nylon. Note the significant improvement with increasing ber reinforcement. Source: Courtesy of Wilson Fiberfill International. however, include the ability to press-in the bearin top face, which provide identification and orientati paction also permits use of a much smaller compact ing (horizontal bolt holes), with associated cost savings and the features of engines. Sour for assembly. U ss than for “flat" pres- pri . In.adıTor"fla the 38 flat orientation; thus, the use of upright compaction was inev tures of the MBCs produced by this method include reces sible to compact ssed bolt-hole boses,a to incorporate a engine's rear MBC has several features that would be impossihlatio pal rectangular oil-drain hole, vertical side grooves, a double arch Once the desired fatigue strength was achieved, the ZM833 matcrial used to produce actual MBCs that were then subjected to severe engine testing in both engines. It was found that the cast-iron engine block generall a tured before the P/M cap cracked. Often, several engine blocks had to be to obtain a fatigue-test point, but eventually an S-N curve (see Fig. 2.26) was erated for the P/M material so that a safety margin could be determined. The was proven to be a robust design by repeated successful fatigue testing ing 1.8 times the most severe running conditions predicted for the engi oil seal, and a raised-arch feature for improved strength Material ductility is a functional benefit, since it is possible to induce in a very brittle material during press-fit installation. The ZM833 P/M matenal the following properties: (a) density of 6.6 g/cm3, (b) tensile (c) hardness of 70 HRB, (d) modulus of elasticity of 107 GPa; t developed for this application has a lower modulus of elasticity iron, resulting in significantly lower initial tensile stresses in hig of the MBC, (e) tensile elongation of 3 to 4%, which compares iron, at 0.5%, and that for ductile iron, typically at 3%, and (nal bending the P/M alloy's fatigue endurance limit, as determined by flexural be bens tests, was intermediate between those of the gray and du the gray iron's level. he P/M mateni at it was

Answer 1

The sheor stress at the intrfoce okue to rct can be expressed as up However the Shear stress cannet exceed the yie on ne strain shear stress , k, of the materal which, for pla :S Y/ The pressure curve is given by equation in the limit we have oY 2u (a-2) Hence 2Ju DM Nate that, as expected the magnitude of x decrears as u decreases Hourver, the pressures must be sufficiently high to cause sticking, that is, the a ratio must be high, h. for ex aunple, Let a-to u then for 2 and for u04