In vacuum forming, webbing is caused by which factor?

• A. Moulds placed too close together
• B. Moulds spaced widely apart
• C. Moulds with excessive draft
• D. Moulds that are too simple

Answer: (A)

Webbing happens when the heated plastic sheet is drawn into narrow gaps between adjacent moulds by the vacuum. If moulds are placed too close together, the sheet between them is pulled through the tight space, forming thin bridges of plastic that connect the moulded features instead of producing clean, separate parts. When moulds are spaced widely apart, there isn’t a small gap for the sheet to bridge, so webbing is much less likely. Excessive draft mainly affects how easily the part releases and the edge shape, not the formation of bridging between moulds. Moulds that are too simple don’t create the conditions needed for bridging either.