Präzision in Form

MAPAL hat den Scrollverdichter als Fokusbauteil im Bereich der Elektromobilität definiert, da er sehr hohe Anforderungen an die Qualität der Bearbeitung stellt und in hohen Stückzahlen benötigt wird. Mit Vorgaben von teilweise kleiner als 20 µm sind die Form der Scroll-Spiralen und die Rechtwinkligkeit sehr eng toleriert. Eine einwandfreie Funktionsweise der beiden Spiralen ineinander setzt Oberflächengüten mit einer gemittelten Rautiefe im einstelligen Mikrometerbereich voraus.

Im Bearbeitungsablauf der Scrollfertigung werden die Flächen der Spiralformen sowie Grundfläche und Topfläche gefräst. Der Vorbearbeitungsprozess erzeugt bereits eine hohe Endkonturnähe. Bei der anschließenden Fertigbearbeitung übernimmt ein Stufenfräser das Finish der Planfläche und der Spiralform. In einem Zug fährt das Werkzeug dabei nach innen, kehrt am innersten Punkt mit dem kleinsten Radius um und fährt an der anderen Seite der Spiralform wieder nach außen. Spezielle Radien und Übergange zwischen Planfläche und Spirale erfordern dabei äußerst präzise Konturen am Fräswerkzeug.
 

A milling blade 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 cuts 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 three-bladed tool with 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.