Croft Additive Manufacturing Limited was approached by its sister company Croft Filters Limited to assist in the development of a new product range that combines additive manufacturing (AM) and conventional materials. Croft Filters manufactures bespoke metal filters for many industrial sectors. One of the major challenges for filtration is to deliver the filtration level (aperture size) and sufficient strength whilst retaining a maximal open area to deliver efficient filtration.
For example, last chance filters, which are commonly made from solely woven wire mesh, delivers high open area but with reduced overall strength. For most filter media whose filtration portion is formed from shaped woven wire mesh, the woven wire mesh used must have sufficient strength to support the final shape of the filter in its final format. This is usually achieved through the mesh wire diameter having sufficient strength to be formed into the shape, however this decreases the size of the apertures. Another solution is to add a perforated support layer, which increases the pressure drop across the filter and reduces filtration efficiency.
Croft Filters sought an innovative solution designed to increase strength and stability of mesh only, woven wire filters, through the addition of localised supports.
Traditionally, mesh is cut and formed into a cone with the help of a jig, it is then spot welded along the seam. A cone filter manufactured from Stainless steel 316L mesh holds its shape but can easily be distorted by operator and operation. Additionally, wire ends are free and not held in position, which may affect the aperture size and shape of the final product.
Croft AM investigated whether conventional wire mesh can be added to a metal 3D printing build platform and then build thin layers of melted material in and on the woven wire mesh that would act as supports for strength in the final filter.
Stainless steel woven wire mesh was spot welded onto the build plate to secure the mesh in position. Layers of SS316L metal powder were then added to the build plate and the filter support areas were melted by the laser according to the CAD design. Initial trials demonstrated the need to tailor the laser power and duration in order to prevent destruction of the mesh. The mesh and supports are then removed from the AM buildplate. The filter body and ends are cut out, and then formed again using another jig. This method ensures that the mesh shape is cut without distortion of the mesh, and the ends of the mesh are held in place. Finally, the support material seam, end and fixings are laser welded to create the quality, improved performance products.
The EXOstructure filters can be made in a number of shapes and the support structures added to the woven wire mesh in specific patterns to suit the design of the filter. Extra support structures can be added to suit operational pressure requirements. The addition here of a metal support frame around the edges of the woven wire mesh firstly secures the loose ends of the wires, holding them in place thus preventing loose wires from being dislodged during operation, and secondly delivers solid edges for welding into the final shape for the main filter body, ends and fixings. The mesh filter shape is strengthened and retains its shape during operation. In addition, the area of the supports added here is less than that of a traditional perforated filter support therefore maximum open area of the mesh is obtained delivering a greater filtration efficiency.
Further studies are ongoing to include finer wire and thicker wire mesh through the optimisation of build parameter settings.
This innovative manufacturing process enables a variety of different ends and fixtures to be secured to the filter mesh more easily and with greater precision. The EXOstructure filters can be manufactured to a more consistent specification than the previous manufacturing process.