Freeform powder molding: Process development, analysis and distortion compensation

摘要

Substantial product development time reductions and cost savings have been realized by employing mechanical part Rapid Prototyping (RP) technologies to convert CAD solid models into physical parts. Increasingly demanding applications require structural strength metal and ceramic components, in a wide variety of materials and having high dimensional accuracy, at competitive costs. Powder-based manufacturing techniques appear well-suited to meet these needs if tooling independence and dimensional control issues are successfully addressed.;A new patented RP process known as Freeform Powder Molding (FPM) has been developed which uses a second powder rather than hard tooling to define part shape. Conventional powder consolidation methods are employed to realize a solid component after a multi-powder matrix is constructed. Controlling material placement rather than energy offers economic advantages while enabling fabrication using a wide variety of materials which may even be mixed within a single part. Locally uniform shrinkage can be quite significant when acting on uncompacted powder or powder-binder mixtures as in FPM and several other powder-based RP technologies. This can lead to part distortions when active on geometrically complex shapes.;Geometric distortion compensation, where a "pre-distorted" geometry is determined that negates the effects of process induced distortions, is explored as a means to achieve dimensional control in the RP setting. A distortion compensation methodology is developed which uses observations of macro-scale test samples to determine predictive model parameters by optimization. An iterative distortion compensation algorithm is implemented to develop the required initial geometry given a desired final geometry, and a finite element model capable of predicting the shape change caused by processing is implemented for use in this algorithm.;Results presented demonstrate the complete path from CAD solid model to metal part using the layer-wise additive FPM approach. Distortion compensation is also implemented and successfully applied to a complex shape that experiences substantial distortion during processing.