Categories of size effects

Self Cite

The limits of the processing window for deep drawing, collected in a deep drawing diagram, are affected by material behavior, process parameters and size effects. A size effect, more specific a density effect, explains the changes in forming behavior of foils with respect to the forming limit, denoted by the limiting drawing ratio. It is shown that it occurs in so called Tiffany structures. The changes in the tribology in deep drawing have an influence on the clamping limit of the processing window. The changes are induced by changes of the drawing speed. They can be explained by the lubricant pocket model only if one takes the temperature dependence of the viscosity of the lubricant into account.

Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Effects on the deep drawing diagram in micro forming

Vollertsen

2011

Self Cite

“…Furthermore, there are structure defects which result from constant structural properties, for example a constant topography, for different workpiece sizes. A detailed description of these three categories is given in [2,3].…”

Section: Introductionmentioning

confidence: 99%

Influence of scaled undeformed sections of cut on strain rate, cutting force and temperature

Denkena

León

Köhler

2010

In machining processes, a decreasing undeformed chip thickness leads to an increase in the specific machining forces. This effect is commonly known as the scaling effect in chip formation. In the literature, several reasons for this effect are discussed. One approach focuses on the increase in the strain rate due to a decrease in the undeformed chip thickness. The increase in the strain rate leads to a hardening effect of the machined material which results in higher specific cutting forces. However, it has not been definitely proven that this is the cause of the scaling effect in chip formation. This paper describes an approach for examining the influence of the strain rate on the scaling effect. Firstly, FE-simulations have been carried out to gain knowledge about the strain rates in the center of the shear zone. By means of these simulations, cutting speeds which lead to constant strain rates in the center of the shear zone have been determined for a broad range of chip thickness. In a second step, experimental investigations have been carried out using the simulated cutting speeds and chip thicknesses. The chip formation processes and the machining forces have been analyzed with constant strain rates and different chip thicknesses as well as with a constant cutting speed. The main result of these investigations is that the strain rate has only a minor influence on the specific cutting forces. It is shown that the temperature in the shear zone decreases with a decrease in the chip thickness. This leads to lower thermal softening of the material and thus to higher specific cutting forces.

“…The most recent one was proposed by Vollertsen [1] and tries to give a general definition and a systematic order for size effects. He proposed that ''size effects are deviations from intensive or proportional extrapolated extensive values of a process which occur, when scaling the geometrical dimensions''.…”

Section: Introductionmentioning

confidence: 99%

Analysis and simulation of size effects in micromilling

Biermann

Kahnis

2009

In this paper the influence of a downscaling of the tool diameter and of the machining parameters on the milling process is analyzed. Starting with an analysis of the cutting edge radius of the tools, the influence of the downscaling on the process is determined by analyzing the surface quality and the cutting forces. The simulation system NCChip, which has been developed at the ISF, is used to simulate the cutting forces when using small tool diameters. This simulation is also used to predict the cutting forces for more complex engagement conditions, like increasing radial immersion or milling of a slot pocket. Additionally, the effects of a downscaling on the tool deflection are analyzed, and strategies to reduce these effects are investigated.