Integrating detailed features into a spray formed rapid tooling
Method of integrating detailed features into a spray formed rapid tooling includes the steps of making a model of a desired tool and constructing a ceramic pattern as the inverse of the model.
The method also includes the steps of locating at least one detailed feature insert on the ceramic pattern and thermally spraying metal material against the detailed feature insert and ceramic pattern to form the desired tool and embedding the detailed feature insert into the desired tool.
It is known to make a spray formed rapid tooling. In spray forming, a master model of a desired tool is produced using a free form fabrication technique. This master model is then used to create a ceramic pattern which is the reverse of the desired tool to be produced. The resulting ceramic pattern is the receptor onto which metal is sprayed to form a deposit in the shape of the desired tool.
Typically, the spray forming process uses a wire-arc spraying. In wire-arc spraying, electric current is carried by two electrically conductive, consumable wires with an electric arc forming between the wire tips. A high-velocity gas jet blowing from behind the consumable wires strips away the molten metal which continuously forms as the wires are melted by the electric arc. The high-velocity gas jet breaks up or atomizes the molten metal into finer particles in order to create a fine distribution of molten metal droplets. The atomizing gas then accelerates the droplets away from the wire tips to the ceramic pattern where the molten metal droplets impact the ceramic pattern to incrementally form a deposit in the shape of the desired tool. The completed desired tool is then mounted and used to produce parts in conventional stamping, die casting, or molding process.
The formation of a totally functional spray formed rapid tooling depends upon the incorporation of many subtle design and functional features. These details can be very fine or small as well as embedded on the surface or at some depth in the desired tool.
Finely detailed features which are embedded at some depth require a very thick deposit to properly anchor the features. It is also problematic to spray around deeply embedded features which are “hidden” because voids can result. Formation of voids is due to limitations of the spray and the wide spray pattern of the typical thermal spray process. In addition, thermal spray particles are not self leveling and therefore do not fill voids. These voids may become crack or stress initiation sites of the desired tool.
Detailed features which can cause voids in spray formed rapid toolings are grouped into two categories as thin/deep and blind. A thin/deep detailed feature has an opening that is too narrow and thus prevents spray steam particles from penetrating to the bottom of the feature in the ceramic pattern. Typical aspect ratios for a thin/deep detailed feature are greater than 1:1 depth: smallest opening dimension. Common examples of thin/deep detailed features include stiffening ribs and baffles. A thin/deep detailed feature is long and has a depth that is greater than the narrowest width dimension. A blind feature may also be small but it is deep relative to width of its opening.
Although the above process for making a spray formed rapid tooling has worked well, it suffers from the disadvantage that very fine and deeply embedded detailed features must be machined into the spray formed rapid tooling after the spray process is completed. This machining process is both laborious and time consuming. Another disadvantage is that the thermal spray coatings are heavily oxidized and the detailed features can only be ground or electro discharge machined (EDM) into the spray formed rapid tooling which is time consuming because the electrodes must be as finely detailed as the detailed features and is costly. Therefore, there is a need in the art to integrate detailed features in a spray formed rapid tooling that would otherwise need to be machined into the tool.
Accordingly, the present invention is a method of integrating detailed features into a spray formed rapid tooling. The method includes the steps of making a model of a desired tool and constructing a ceramic pattern as the inverse of the model. The method also includes the steps of locating at least one detailed feature insert on the ceramic pattern. The method further includes the steps of thermally spraying a metal material against the detailed feature insert and ceramic pattern to form the desired tool and embedding the detailed feature insert into the desired tool.
Processing your request, Please wait....
