Christopher Müller

Compact Air Bearing Spindles for Desktop Sized Machine Tools

In this paper two new small and lightweight spindles for the implementation in desktop sized machine tools are introduced. In both spindles, the tool shaft with a micro tool on the tip (e.g. micro end mill, micro pencil grinding tool or Electrical Discharge Machining (EDM) electrode) works directly as a rotor and is supported by aerostatic bearings. The spindles are driven via air turbines and reaches high rotational speeds in combination with high rotational accuracies. One spindle was implemented in a desktop-sized machine tool and used for micro machining of titanium and brass. With the high rotational speed of the spindles very high material removal rates can be achieved. Thus, the productivity of the micro machining process is enhanced.

Recent Developments in Desktop-Sized Machine Tools

The miniaturization of components and the functionalization via micro structures demands for flexible and economic manufacturing processes. Micro machining, i.e. micro milling and micro grinding can meet these requirements. In this paper, desktop-sized machine tools and their components that were developed at our institute are presented. With those machine tools, micro tools can be machined and used in one clamping, allowing for increased machining quality. Grooves milled with such machine tools achieve a bottom surface roughness below 10 nanometer.

MONOPOLISTIC LOCATION CHOICE IN A TWO-SIDED HOTELLING MODEL

We analyse the optimal location choice of a monopolistic firm that operates two arbitrarily located platforms on a two‐sided market. By extending the traditional Hotelling framework, we show that the optimal platform locations are equivalent to the one‐sided benchmark if both sides are either restricted to single‐ or multi‐homing. In the mixed case (one side single‐homes, the other one multi‐homes), the optimal platform locations are in line with the respective symmetric case. If the monopolist is restricted to choosing the same location on either side of the market, the optimal locations are determined by the relative profitability of the market sides.

Welfare Effects of Water Pricing in Germany

The observed two-part tariff price structure (consisting of a lump-sum price and linear marginal price) for drinking water in Germany does not reflect the cost structure reported in the literature. Recovering marginal costs from a sample of 251 German counties, we see that there are positive price-cost margins, while lump-sum prices are too low. A price structure readjustment along welfare economic principles (marginal cost pricing, lump-sum price ensures cost-recovery) would increase the mean consumer surplus by 0.037% of the local GDP or €2.129 million per county, assuming a share of 15% variable costs in total costs.