Hollowing Parts for 3D Printing: Complete Design Optimization Guide

Although 3D printing offers unprecedented design freedom compared to traditional manufacturing methods, this doesn't mean that designs cannot be further optimized prior to production. Hollowing, also known as coring, represents one of the most common and effective optimization methodologies in additive manufacturing, requiring a sophisticated understanding of material properties, structural mechanics, and manufacturing constraints to achieve optimal results.

The strategic application of hollowing techniques enables engineers and designers to strike an optimal balance between strength, weight, cost, and dimensional stability across diverse aerospace, automotive, and industrial design applications. Understanding the nuances of part hollowing becomes critical when transitioning from prototyping to production manufacturing, where material efficiency directly impacts project economics and environmental sustainability.

Understanding Part Hollowing Fundamentals

Hollowing or coring is the systematic process of modifying a part by strategically removing internal material while preserving critical structural elements. The primary benefits of hollowing include reduced material cost, decreased part weight, shortened print time, and improved dimensional accuracy through more uniform wall thickness distribution.

Parts with uniform wall thickness cool more evenly during the manufacturing process, significantly reducing the buildup of internal stress in specific locations that can cause warping and dimensional deformation. A well-designed 3D printed part utilizes the minimum material necessary to meet the strength requirements of its intended application while optimizing for manufacturing constraints and economic considerations.

Design Complexity and Manufacturing Economics

Although hollowing a part can increase geometric complexity, additive manufacturing processes do not impose additional costs for complex geometries—in fact, costs typically decrease due to reduced material consumption. This fundamental characteristic of 3D printing enables designers to implement sophisticated internal structures that would be impossible or prohibitively expensive with traditional manufacturing methods.

The economic impact of part hollowing becomes particularly significant in production environments where material costs represent a substantial portion of total manufacturing expenses. Advanced hollowing strategies can achieve material savings of 30-60% while maintaining equivalent or superior mechanical properties through strategic reinforcement placement and optimized wall thickness distribution.

Preparing Parts for Additive Manufacturing

Successful part hollowing requires careful consideration of multiple interdependent factors that influence both manufacturing feasibility and final part performance. The optimization process must account for structural requirements, material properties, manufacturing constraints, and post-processing considerations to achieve optimal results.

Structural Analysis and Load Requirements

The primary consideration when hollowing a part is maintaining adequate structural integrity to meet loading and bending requirements for the intended application. Excessive material removal can significantly compromise part strength, but strategic reinforcement along stress concentration points enables strength preservation while eliminating redundant material.

Strategic rib placement in hollowed parts provides directional strength while maintaining material efficiency.

Perpendicular rib configurations enable multi-directional load resistance while optimizing material distribution.

After material removal, parts should undergo comprehensive analysis through finite element simulation or physical testing of printed prototypes to validate loading and bending performance. Based on this analysis, engineers can strategically add walls and ribs (beam elements) to stiffen the part in directions of anticipated bending or loading while maintaining overall material efficiency.

Critical Design Considerations for Hollow Parts

When designing hollow parts for additive manufacturing, several critical considerations must be addressed to ensure successful production and optimal part performance. These considerations include drain hole placement, internal corner radius optimization, and material removal accessibility.

Strategic drain hole placement ensures complete removal of trapped material from internal cavities.

Internal Corner Optimization and Stress Concentration

Automatic shelling and hollowing tools frequently generate sharp internal corners that create stress concentration points under mechanical loading. Abrupt geometric transitions should be avoided wherever possible, as they significantly reduce part strength and can lead to premature failure under operational loads.

Sharp internal corners create dangerous stress concentration points.

Generous fillets eliminate stress concentrations and enhance structural integrity.

Smooth transitions using generous fillet radii can be more self-supporting during the printing process, enabling greater orientation flexibility and reducing support structure requirements. Once a part is hollowed, all sharp internal corners should be systematically reviewed and smoothed using appropriate fillet tools with radii proportional to the wall thickness and anticipated loading conditions.

Comprehensive Case Study: Manufacturing Jig Optimization

This detailed case study demonstrates the systematic optimization of a manufacturing jig designed for aerospace applications. The optimization process illustrates best practices for reducing material consumption, weight, and print time while maintaining functional performance requirements.

Original solid manufacturing jig design prior to optimization showing areas for material reduction.

Wall Thickness Optimization Strategy

The first critical decision in part optimization involves selecting appropriate wall thickness based on the selected manufacturing process and material properties. Minimum wall thickness requirements vary significantly between technologies, and thicker walls may be necessary to achieve required mechanical strength for the intended application.

For FDM processes, which exhibit weakness concentrated along layer boundaries, shearing strength in the Z-axis is proportional to the surface area of interlayer bonding. SLS processes produce more isotropic parts with different failure modes, enabling thinner walls without compromising structural integrity. Material datasheets provide comprehensive mechanical property data essential for informed wall thickness decisions.

2mm wall thickness: Maximum material savings with minimum strength.

3mm wall thickness: Optimal balance of strength and material efficiency.

4mm wall thickness: Enhanced durability for demanding applications.

5mm wall thickness: Maximum strength retention with moderate material savings.

Advanced Reinforcement Strategies

After initial hollowing, structural analysis revealed that several functional features could potentially fail under operational loads due to inadequate material support at connection points. To mitigate shearing risks, generous fillets were added at the base of these features where they connect to the main structure, resulting in significant improvement in shear strength.

Section view illustrating strategic fillet placement to eliminate stress concentration points at feature connections.

Because this manufacturing jig experiences loading from multiple directions during operation, the design was further reinforced with ribs oriented in two perpendicular axes. The added ribbing was strategically sized shorter than the outer walls, as full height was not required to resist bending in those axes. This conservative approach to material placement achieved additional material reduction while maintaining structural performance.

Final optimized design with strategic internal ribs providing multi-directional strength while minimizing material usage.

Alternative Filling Strategies

Advanced applications may benefit from post-printing filling of hollow cavities with alternative materials such as two-part resins, epoxies, or foam cores. This approach enables the use of lower-cost or specialized materials with desirable properties while avoiding the warping and material costs associated with printing completely solid parts.

Post-printing filling enables hybrid material properties while maintaining the benefits of hollowed design.

Comprehensive Cost Analysis

The economic impact of part hollowing varies significantly across different additive manufacturing technologies, with material cost reductions ranging from moderate to substantial depending on the specific process and material system employed. The following analysis demonstrates cost implications across major 3D printing technologies.