airplane pressure diagram

Angle of attack (Wing Design Optimization)

The figure to the left shows the vector forces of lift and drag involved with wing airfoil design. The angle of attack represents the angle of the neutral axis of the plane with respect to the angle of the chord axis. The magnitude of the angle of attack impacts the resultant forces experienced by the wing during flight. IIT Kanpur had developed a similar glider design guide and recommended a 3-4° angle of attack. The 4° angle would have necessitated a tool smaller than the minimum tool diameter size available in the machining lab due to the resulting distance between the machined core and the edge of the fuselage being less than ⅛ in, as a result a 3° angle was chosen.

Prototype/Product Design Phase

Three airplane prototypes were designed and 3D printed prior to starting the design of the injection mold. All prototypes incorporated the front nose hook shown in the gallery below as well as included a front and rear slot for the front wing and horizontal stabilizer to slide into respectively.

Fuselage

Horizontal Stabilizer

Wing

mold drawing

Family Mold CAD Drawing/Model

The figure to the left shows the family mold drawing. The gate locations of each cavity are clearly outlined as well as ejector pin locations. Cooling lines run on either side of the mold ensuring none of the ejector pins cause interference.

Moldflow Analysis

Gate locations, runner diameter and depth, as well as gate diameter and depth were decided upon and accurately justified using this approach:

 

Following the Ineos polypropylene processing guide parameters, the runner was the first modified element. The goal was to first balance the runner systems so as to provide simultaneous filling of the multi cavity airplane mold. Once the runners had balanced filling, the gate design was modified. To ensure a minimal pressure loss of the polymer flowing through each cavity, the gate length was originally designed to be 0.040 inches. The land length of the horizontal stabilizer could not follow these design guidelines as the gate diameter needed to go all the way through the surface geometry shown by the figure to the right. By using the MoldFlow analysis software, the land length of the gates were updated to adjust for equivalent cavity balance. The final land length of both the horizontal stabilizer and the front wing gates were 0.045 inches while the fuselage gate land length was 0.075 inches.

moldflow
molecular orientation

Molecular Orientation Analysis

The molecular orientation during fill varied depending on specific locations of the gate. From Figure X, the orientation follows a unidirectional pattern from the bottom of the gate location to the opposite side of the wing shown in yellow. From the figure on the left, the molecular orientation deviates from unidirectional and curves out around the wing slot towards the edge of the airfoil. The chosen gate location allows the molecular orientation to stabilize the wing to the left of the wing slot (section of the wing subject to fail first, outlined in section B). Had the gate location been at the mid-section of the wing, the molecular orientation would have been perpendicular to the orientation shown in the figure to the left. This would have created a more brittle part as the direction of molecular orientation would not run parallel to the length of the wing

TIME FOR SOME MACHINING!

The fuselage section of the mold resulted in the best surface finish. This was due to a flat tool surface (end mill) directly contacting the fuselage cavity upon machining the shaped cavity. As there was no curvature on the top of bottom of the fuselage, the surface finish result was smooth. The horizontal stabilizer and front wing cavity of the mold had a rougher surface finish. This was caused by the airfoil design incorporated into the shape of the wing. By using an ⅛” endmill and surfacing operations in CATIA to extract CNC code, the shape of the airfoil was obtained. Because these surfacing operations were done with a flat  ⅛” end mill, it resulted in small stepover ridges as shown below  in both the horizontal stabilizer cavity and the front wing cavity.

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Mold Cavaties