Reducing distortion in a spray formed rapid tooling
Reducing distortion in 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 building a thermal model of the desired tool from a solid model of the ceramic pattern and applying thermal boundary conditions to the thermal model based on known conditions.
The method also includes the steps of running the thermal model to produce a temperature distribution of the desired tool and determining any temperature deviations in the temperature distribution above a predetermined value. The method further includes thermally spraying a metal material against the ceramic pattern to form the desired tool if there are no temperature deviations in the temperature distribution above the predetermined value.
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.
During the spray forming process, the spray formed rapid tooling may have a varied temperature distribution across the ceramic pattern and each layer thereof. This can result in distortion of the spray formed rapid tooling as shrinkage of the sprayed metal occurs. Recently, there has been a need to create the spray formed rapid tooling geometrically accurate. To accomplish this, a number of trial spray runs are conducted to determine ideal spray parameters to obtain a uniform temperature distribution.
Although the above process for making a spray formed rapid tooling has worked well, it suffers from the disadvantage that trial spray runs have to be conducted to determine the spray parameters for spraying the spray formed rapid tooling. Another disadvantage of the above process is that the spray parameters are achieved by trial and error. Yet another disadvantage of the above process is that to scale between different sized tools with different geometric features, estimation occurs which is undesired. Still another disadvantage of the above process is that the trial spray runs and estimation are time consuming and result in significant development costs for a spray formed rapid tooling.
Accordingly, the present invention is a method of reducing distortion in a spray formed rapid tooling. The method includes the steps of making a model of a desired tool, constructing a ceramic pattern as the inverse of the model, and building a thermal model of the desired tool from a solid model of the ceramic pattern. The method also includes the steps of applying thermal boundary conditions to the thermal model based on known conditions. The method also includes the steps of running the thermal model to produce a temperature distribution of the desired tool and determining any temperature deviations in the temperature distribution above a predetermined value. The method further includes the steps of thermally spraying a metal material against the ceramic pattern to form the desired tool if there are no temperature deviations in the temperature distribution above the predetermined value.
One advantage of the present invention is that a method is provided of reducing distortion in a spray formed rapid tooling. Another advantage of the present invention is that the method has greater probability to create spray formed rapid toolings accurately the first time. Yet another advantage of the present invention is that the method eliminates conducting trial spray runs to determine the spray parameters, resulting in a shortened product development cycle time. Still another advantage of the present invention is that the method reduces the estimation required to scale parameters between different sized tools with different geometric features. A further advantage of the present invention is that the method reduces development costs.
Other features and advantages of rapid tooling will be readily appreciated as the same becomes better understood after reading the subsequent description taken in conjunction with the accompanying drawings.
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