Plastic parts are widely used in industry due to their low weight, reduced cost and well-balanced mechanical behavior. In this context, soft tooling has emerged as an alternative, particularly for low-volume production. However, the lower thermal conductivity and mechanical strength of polymers used in 3d printers leads to challenges regarding their durability and long-term performance. To overcome the problems associated with their low mechanical strength, shell molds are usually filled with materials like epoxy resins or low-melting-point metal alloys. However, introducing these materials can cause deformations in the molds during the backfilling process, compromising the quality of the resulting plastic parts. Mold defects are often replicated in the final parts, posing a significant challenge to achieving high precision and quality. One solution to the problems caused by the backfilling process is to mechanically design the mold to withstand the pressures and forces typical of injection molding, incorporating reinforcing elements such as ribs. In this context, this study proposes an innovative approach that uses topological optimization for the application of ribs in polymeric molds, ensuring structural integrity without the need for filling materials. The aim is to achieve sufficient mechanical rigidity to eliminate dependence on filler materials, ensuring mold integrity and part quality. The developed method was compared with traditional techniques widely used in the automotive sector and also considering previous studies about the usage of additive manufacturing on soft tooling. The numerical application ensured the designed ribs met the established criteria, with precise control over parameters like height and volume. The study used polyamide (PA12) inserts manufactured via the Multi Jet Fusion process. The results indicated a reduction of up to 74% in the volume of the ribs compared to traditional techniques, eliminating the need for filler material. This approach improves the process efficiency and eliminates waste. Additionally, the method allows less experienced designers to achieve positive and optimized outcomes.