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Rated Load Mechanical Operation
Prototyping Situation
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In this, the most common prototyping situation, we simply want to build a part to see how well it performs in normal operation. The objective is not to determine failure loads or life. Loads will remain within the rated load of the device.
Key Material Properties
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The primary material property that controls performance in this situation is stiffness. Since most plastic parts are stressed in flexure as opposed to tension or compression, the appropriate material property is flexural modulus. (To see a comparison of flexural modulus for common rapid prototyping materials, click here)
The second key material property is some measure of strength of the material. There are several to choose from, but flexural yield strength is the most appropriate for this situation. (To see a comparison of flexural strength of common rapid prototyping materials, click here)
Approximation Requirements
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How close must we approximate the material properties of an injection-molded plastic to be able to simulate them?
We believe that flex modulus must be within 20% of that of the injection molded plastic. That way, deflections will be within 20% of those in actual use.
Flexural strength of the SLA resin must be greater than 50% of that of the target plastic material. The design typically includes a factor of safety of 2 or more so that occasional overloads will not result in failure. Since in our prototyping situation, loads are limited to rated loads, we do not need to accommodate the design overload.
Selection Chart
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The chart below plots flexural modulus against flexural strength. Each of the SLA resins is plotted as a point on that chart. A shaded rectangle surrounds each point, which represents the range of material properties that that resin can approximate as determined by the approximation requirements above.
The chart also includes several common injection molded plastics. If a plastic falls within a shaded rectangle, that resin for this prototyping situation can then adequately approximate it.
If you would like a chart made like the one above that lists the plastics used in your company, contact Tom Mueller
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