Wrinkling is a common defect that occurs during the drawing process in metal forming. It refers to the formation of undesirable surface irregularities or wrinkles on the drawn part. Several factors can influence the tendency for wrinkling, and among the given options, the decrease in the holding force on the blank (option C) is the correct answer.

Explanation:

Wrinkling occurs when the material in the blank undergoes excessive thinning and deformation during the drawing process. It is characterized by the formation of localized compressive stresses, which cause the material to buckle and form wrinkles. The tendency for wrinkling can be influenced by various factors, such as material properties, process parameters, and tooling conditions.

1. Material properties: The formability of a material plays a significant role in the tendency for wrinkling. Materials with low ductility and high strain hardening tend to exhibit a higher tendency for wrinkling. This is because they have a limited ability to deform plastically without failure.

2. Process parameters: The process parameters, such as the drawing speed, blank holder force, and lubrication, can affect the tendency for wrinkling. Higher drawing speeds and lower blank holder forces generally promote wrinkling, as they increase the likelihood of material instability and localized deformation. On the other hand, proper lubrication can reduce friction and improve material flow, thereby reducing the tendency for wrinkling.

3. Tooling conditions: The design and condition of the drawing die and punch also influence the tendency for wrinkling. The shape and clearance of the die can affect the material flow and distribution of stresses, which can either promote or suppress wrinkling. Additionally, the condition of the punch, such as its surface roughness, can affect the frictional forces and material flow during the drawing process.

Among the given options, the decrease in the holding force on the blank (option C) promotes the tendency for wrinkling. The blank holder force is applied to hold the blank during the drawing process and prevent it from wrinkling. When the holding force is decreased, the material is more likely to buckle and form wrinkles due to insufficient restraint. Therefore, a decrease in the holding force on the blank increases the tendency for wrinkling.

In summary, the decrease in the holding force on the blank promotes the tendency for wrinkling in the drawing process. Other factors such as material properties, process parameters, and tooling conditions also affect wrinkling, but in this case, the decrease in the holding force is the most significant factor among the given options.