Table 4.

Summary of the DLP and LCD VPP process modification methods to reduce the separation force.

VPP Methods	Modification Strategy	Noticeable Improvement	Limitations
DLP [69]	Resin vat tilting (using cam follower mechanism)	The separation force is reduced by 20% compared to the pulling-up process when using PDMS as an interface at 0.2 mm/s lifting speed.	The stress distribution in the vat along the tilting axis is not uniform. At the hinge, the stress is minimum and increases away from it. By using this method, the separation force increases by almost 11% compared to the pulling up when using FEP as an interface.
DLP [70]	Resin vat Vibration (using loudspeaker)	The measurement of maximum separation force does not go beyond 200 gm while it reaches up to 500 gm during the normal separation.	The print failure rate is higher than the normal process when the feature size ≤ 300 μm. The reliability of the vibration source needs to improve.
DLP [71]	Resin vat vibration (using piezoelectric actuators)	The reduction in the separation force is around 75% for different cross-section areas compared to the pulling-up process.	The separation time takes longer than the standard process. The printability of smaller dimensions (<10 mm) has not been checked.
LCD [72,73]	Hot lithography (increasing resin temperature)	A significant viscosity reduction in approximately 300 mPa.s can achieve by increasing the temperature from 25 °C to 60 °C.	The mechanical properties of the printed part have a negative effect when the temperature crosses the glass transition temperature of the printed part. The separation force increases beyond the temperature of 35 °C.