Final answer:
Product thickness in pressure-bubble plug-assisted vacuum forming is controlled by pressure differentials (option C) created by vacuuming one side of the heated plastic sheet while applying pressure on the other with a plug. While thermal expansion and viscosity are important factors in the process, they do not directly control thickness. Material shrinkage affects the final dimensions but is not used for thickness control during forming.
Step-by-step explanation:
The control of product thickness in pressure-bubble plug-assisted vacuum forming is primarily through C) Pressure differentials. This process involves heating a plastic sheet until it becomes pliable, then using a vacuum to draw it into a mold where a plug assists the forming process. The thickness distribution is influenced by how the material stretches during this process.
When the heated plastic sheet is stretched over the mold and plug, the material thins out, which is where the pressure differential comes into play. The vacuum removes air pressure from one side of the sheet, while air pressure on the other side coupled with the plug pushing the material, forces it into the desired shape. The difference in pressure between the two sides assists in determining the final thickness of the product.
Thermal expansion can influence the process but does not directly control thickness in this context. However, it's essential to account for thermal expansion because it can affect the initial size of the material and the final product. If materials expand differently, thermal stress can develop, causing distortions or defects in the material.
The plastic sheet's viscosity is also a critical factor; a malleable, yet not too fluid consistency is necessary for proper forming. Adjusting temperature controls viscosity to some extent. Material shrinkage occurs as the product cools and solidifies, affecting overall dimensions but is not used to control thickness during the forming process.