Machining solutions for scroll compressors – Precision takes shape
MAPAL draws from its knowledge about components and the market to deliver optimal machining solutions to the automotive industry in the field of electromobility. Global developments, trends and drivers are incorporated into its solution portfolio for focus components like the scroll compressor.
The global automotive market will continue to develop in the coming years, with the biggest growth taking place in the realm of electric vehicles. As the share of hybrid and battery-power cars increases, so does the share of vehicles with scroll compressors. This part is used to increase the pressure of the refrigerant in the thermal management system, which keeps the temperature of batteries in check, among other things. These have to be cooled in the summer and heated in the winter. The two spirals, orbit and fixed scrolls, form the heart of the component. They move eccentrically to one another so that the refrigerant is compressed between the spirals towards the centre.
MAPAL has defined the scroll compressor as a focus component in the field of electromobility: It has very high demands with respect to the machining quality and is required in large quantities. With specifications that are sometimes less than 20 µm, the form of the scroll spirals and perpendicularity have very tight tolerances. A surface finish with an average roughness depth in the single micrometre range is required for the flawless functionality of both spirals in relation to one another.
The machining process to manufacture the scrolls involves milling the surfaces of the spiral shapes as well as the top and base surfaces. The pre-machining process already comes very close to the final contour. A stepped milling cutter provides the finish for the face surface and spiral shapes during the fine machining that follows. In a single stroke, the tool moves inwards, turns around at the innermost point with the smallest radius, and then moves outwards again along the other side of the spiral shape. Special radii and transitions between the face surface and spiral call for extremely precise contours on the milling tool.
Long tool life despite extreme sharpness
A cutting edge for milling must be selected that can both provide the required precision of form and achieve a long tool life. A MAPAL finish milling cutter can manage more than 2,000 parts made of the aluminium alloys AlSi1 and AlSi12, which are the most prevalent currently. For pre-machining, the specialists in Aalen ensure that as little material as possible remains but as much as needed to ensure safe processing. The milling cutter machines the surface using low force, rather than pressing and deforming it.
Above all when it comes to finishing, there are many solution options available, which can be deployed based on requirements. MAPAL proceeds schematically in their project design according to the basic, performance or expert classification. “Basic” solutions are standard tools which can be used to produce and test initial prototypes. At the “performance” level, special tools with contour geometries for the component come into play. In addition to precise contour machining, the “expert” solutions concentrate above all on the longest tool lives for maximum processing efficiency for large series. Special coating is used here. A tool with three cutting edges and diamond coating represents the top of the line for aluminium alloys with high silicon content.
As a full-range supplier, MAPAL maps the entire process including cycle time calculation and cutting data. The tool package includes not only the milling cutter for machining the spirals but also all the other tools for the compressor. The tool manufacturer offers the corresponding clamping device depending on the machine and spindle connection – the hydraulic chuck HSK-E is the first choice here.
Thanks to its knowledge of the market, MAPAL can keep an eye on future developments. New refrigerant specifications in the EU could result in the widely used R1234yf coolant being replaced with propane or CO2. CO2 in particular has substantial effects on the component: the displaced volume becomes much smaller and the pressure increases significantly. Current developments thus point to the use of grey cast iron or spheroidal cast iron as the material of choice for the scroll spirals, which would correspondingly affect the machining process and tool concept. With its wide range of products and technology expertise, MAPAL is ideally positioned to react to these developments quickly and offer application-specific process solutions.
