To ensure a quality cast is achieved, it is important to inspect the patterns for leaks or imperfections before you begin processing it.
Visual Inspection: Upon arrival of your pattern, you should perform a visual inspection. Carefully look over the pattern for surface flaws or cracks that may have occurred during shipping. These will cause defects, such as inclusions to the casting. The pattern should have rigid or stiff surfaces. Inspect the pattern for any solid sections. If there are solid walls over about 0.050" thick that are larger than about a ½ inch square, it may be cause expansion and shell cracking in autoclave or flashfire burnout. Of course, it will not be possible to inspect for solid sections after the pattern is shelled so it is important to do it now.
Dimensional Inspection: In order to produce a dimensionally correct casting, it is imperative to know the dimensions of the pattern. Measure and record critical dimensions. 3D Systems On Demand will provide inspection reports of extents dimensions, or at your request, any critical features/dimensions from drawings if provided or otherwise, features selected at their discretion. . Remember, however, that the pattern will include allowances for metal shrink, therefore don’t compare the pattern dimensions you measure to the desired dimensions on the final metal casting. As a general rule, it is good practice to require that the pattern does not contribute more than 50% of the tolerance of the finished casting. Any unacceptable dimensions should be reviewed with the supplier to determine cause and pattern replacement if required.
Leak Inspection: It is critical that the QuickCast pattern be completely sealed and leak proof to prevent slurry from flowing into the internal structure, causing an inclusion or other casting defect. Perform this leak check upon receipt – before doing any addition of wax gates, and again just before introducing the pattern to the shelling process. The pattern should have been vacuum tested by your supplier before shipment. However, the foundry will need to verify with a vacuum test to ensure that the pattern was not damaged in shipment.
If the pattern does not have a tube or port to attach a vacuum hose, you will need to add one, or you may prefer to use a soft rubber tip on your vacuum hose that can be placed over the hole left and marked on the pattern by the supplier. If adding a tapered port to fit onto your vacuum hose, bond the port over the marked hole.
Using a hose attached to the port on the pattern and an automotive vacuum leak tester or other pump draw a vacuum on the pattern to 10 in of mercury (250 mm of Mercury). Too much vacuum may damage the pattern, crushing it. If the vacuum holds and does not leak, the pattern is indeed properly sealed. A vacuum leak will indicate there is a hole somewhere in the pattern.
To find a hole, use a low pressure regulator to blow 1-10 psi (7-70 kPa) into the port on the pattern. Too much pressure will damage the pattern, blowing it apart. Find the hole by feeling or listening for escaping air. Additionally, the part may be submerged in liquid - escaping bubbles will identify the area with a leak. Alternatively, a solution of dishwashing soap and water can be brushed onto the part.
Seal any leaks using the Checking for Holes or Leaks section found in the QuickCast Post Processing Guide. Repeat the vacuum test to verify the pattern is totally sealed.
Storing the Pattern: If the pattern will not be used immediately, store it in a cool, dry environment, away from ultraviolet sources. Continued exposure to ultraviolet (sunlight and fluorescent lights both have high UV contents) will change material properties over time and may make the pattern unusable. In addition, most SLA resins will absorb moisture over time, which can affect both dimensional accuracy and stiffness. Storing the part in a sealed black plastic bag with desiccant is recommended.
Prolonged storage may require re-checking dimensions and leaks on the pattern.
Include desiccant with your QuickCast style pattern in a sealed bag.