Hemming implies sheet formation in which each edge of the sheet gets bent or folds over the other part to gain a snug fit. Commonly hemming is suitable to attach one part to another to achieve an improved part look as well as to strengthen the edges of parts. 

In automobile production process hemming serves as a kind of subordinate procedure to accomplish assembling after the sheet gets deeply drawn, trimmed and flanged to connect both sides of parts (external and internal ones) with each other. Examples of such assembled parts are car bonnets, doors, boot lids, dashboards.

Precise hemming is crucial as it has a direct effect on the part look and its facing qualities. Sheet deformation occurring in the hemming operation may bring about variation of dimensions or different part faults. Typical hemming faults may include any split or wrinkle in flanges, sheet overlap at the corners or sheet rolling-in. Thus, using simulation tooling helps to decrease considerably the amount of trials and errors in the try-out as well as manufacturing process. Two types of hemming exist: ordinary die and roll hemming.

While hemming through the ordinary type, flanges get bent along the full extension with a hem tool.

While hemming through the rolling type, the hem roll gets directed by industrial robots to mold flanges.

Ordinary die hemming is proper to produce large quantities of products. While hemming through the ordinary type, flanges get bent along the full extension with a hem tool.

In fact, hemming is a process to form flanges through the hem tool when sheets have got trimmed and drawn completely. Already formed flanges require some processing stages such as pre-hem and finishing hem procedures based upon opening angles of flanges. Production plant for ordinary die hem is rather costly, while cycling time is quite short. 

Roll Hemming

Roll hemming is realized step by step through hem rollers, which are guided by industrial robots. This operation includes pre-hem and finishing hem processes. Rolling hem is featured with use flexibility, besides, tooling cost is considerably low, less than in the case of ordinary die hemming. Yet, the cycling time is longer as the hemming roll goes along a specified path.