3: Additive Manufacturing Methods

Last updated

Mar 18, 2025
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- 2: DFM Guidelines for Specific Manufacturing Processes
- 4: AI and AM Generative Design

Bryan Guns (Northeast Wisconsin Technical College)
Northeast Wisconsin Technical College

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Figure $\PageIndex{1}$ : AI generated picture of a part being additively manufactured

Introduction to Additive Manufacturing

Additive manufacturing (AM), commonly referred to as 3D printing, represents a transformative approach to fabricating components by building objects layer by layer from digital models. Unlike traditional subtractive manufacturing, which removes material from a solid block, or formative methods, such as casting and forging, AM constructs parts directly from raw materials, typically in powder, liquid, or filament form. This chapter provides an overview of key AM methods, their operational principles, and the circumstances under which AM offers advantages over conventional manufacturing techniques.

Overview of Additive Manufacturing Methods

Additive manufacturing encompasses a variety of processes, each suited to specific materials and applications. The American Society for Testing and Materials (ASTM) classifies AM into seven categories, which are summarized below:

Vat Photopolymerization
- Principle: A liquid photopolymer resin is selectively cured by a light source (e.g., ultraviolet laser or digital light projection) within a vat.
- Materials: Photopolymer resins.
- Applications: High-precision components, such as dental models, jewelry molds, and prototypes.
- Advantages: Exceptional surface finish and fine feature resolution.
- Limitations: Limited material range and relatively high cost of resins.
Material Extrusion
- Principle: A thermoplastic filament is heated and extruded through a nozzle, depositing material layer by layer on a build platform.
- Materials: Thermoplastics (e.g., ABS, PLA, PETG).
- Applications: Rapid prototyping, educational models, and low-cost consumer goods.
- Advantages: Low equipment cost and simplicity of operation.
- Limitations: Lower accuracy and slower build times for complex geometries.
Powder Bed Fusion (PBF)
- Principle: A laser or electron beam selectively fuses regions of a powder bed, typically metal or polymer, to form a solid part.
- Materials: Metals (e.g., titanium, stainless steel), nylon polymers.
  - Stainless Steel (e.g., 316L): Corrosion-resistant, used in industrial and medical components.
  - Titanium Alloys (e.g., Ti6Al4V): Lightweight and strong, ideal for aerospace and biomedical implants.
  - Cobalt-Chromium: High wear resistance, common in turbine blades and dental prosthetics.
  - Aluminum Alloys (e.g., AlSi10Mg): Lightweight, used in automotive and aerospace parts.
  - Nickel Alloys (e.g., Inconel 718): High-temperature resistance, suited for jet engine components.
- Applications: Intricate designs unachievable with traditional subtractive or casting methods. Aerospace components, medical implants, and functional prototypes.
- Advantages: High strength and ability to produce complex internal structures.
- Limitations: High equipment and material costs. Slower than mass-production methods like casting or forging.
- Subtypes: Selective Laser Sintering (SLS), Selective Laser Melting (SLM), Electron Beam Melting (EBM), Metal Laser Sintering (MLS).
Binder Jetting
- Principle: A liquid binding agent is selectively deposited onto a powder bed to bond particles, followed by post-processing (e.g., sintering).
- Materials: Metals, ceramics, sand.
- Applications: Metal parts, sand molds for casting, and full-color prototypes.
- Advantages: High speed and ability to process diverse materials.
- Limitations: Parts may require significant post-processing for strength.
Material Jetting
- Principle: Droplets of material (e.g., photopolymers or wax) are deposited and cured layer by layer using UV light.
- Materials: Photopolymers, waxes.
- Applications: Multi-material prototypes, high-detail models.
- Advantages: Superior surface quality and multi-material capability.
- Limitations: Limited mechanical properties and high operational cost.
Directed Energy Deposition (DED)
- Principle: A focused energy source (e.g., laser or electron beam) melts material (wire or powder) as it is deposited onto a substrate.
- Materials: Metals (e.g., titanium, aluminum).
- Applications: Repair of high-value parts, large-scale metal structures.
- Advantages: Ability to add material to existing components and handle large builds.
- Limitations: Lower resolution and surface finish compared to PBF.
Sheet Lamination
- Principle: Sheets of material (e.g., paper, metal, or plastic) are bonded together, typically using adhesive or ultrasonic welding, and then cut to shape.
- Materials: Paper, metal foils, polymers.
- Applications: Low-cost prototypes, architectural models.
- Advantages: Cost-effective for large, simple parts.
- Limitations: Limited structural integrity and material options.

Comparison with Traditional Manufacturing

Traditional manufacturing methods, such as machining, casting, and injection molding, have long been the cornerstone of industrial production. These processes excel in high-volume production, offering economies of scale, repeatability, and robust material properties. However, AM introduces distinct advantages that warrant its consideration under specific conditions. The decision to employ AM over traditional methods hinges on several key factors, outlined below.

When to Prefer Additive Manufacturing

Additive manufacturing is preferable to traditional manufacturing in the following scenarios:

Complex Geometries and Customization
- AM enables the production of intricate designs, such as lattice structures, internal channels, or organic shapes, which are impractical or impossible to achieve with subtractive or formative methods. For instance, aerospace designers utilize PBF to fabricate lightweight, topology-optimized components that reduce material use without compromising strength. Similarly, medical implants tailored to individual patient anatomies are efficiently produced using SLM or EBM.
Low-Volume Production and Prototyping
- Traditional methods often require expensive tooling (e.g., molds or dies), making them cost-prohibitive for small batches. AM eliminates this need, allowing rapid iteration of prototypes or production of limited-run parts. Material extrusion and vat photopolymerization are widely used in engineering design cycles to validate concepts before committing to mass production.
Material Efficiency
- Subtractive manufacturing generates significant waste by removing material from a larger block, whereas AM builds parts additively, minimizing scrap. This is particularly advantageous when working with costly materials, such as titanium or cobalt-chromium alloys, common in DED and PBF processes.
Supply Chain Simplification
- AM facilitates on-demand production, reducing the need for inventory storage and long lead times associated with traditional supply chains. For example, binder jetting can produce sand molds directly, bypassing the need for pattern-making in foundry operations.
Repair and Hybrid Manufacturing
- DED excels in repairing high-value components, such as turbine blades, by depositing material onto worn surfaces. This hybrid approach integrates AM with existing parts, extending service life and reducing replacement costs.

Limitations and Trade-Offs

Despite its advantages, AM is not universally superior. Traditional manufacturing remains preferable for high-volume production due to faster cycle times and lower per-unit costs. Additionally, AM parts may exhibit anisotropic properties (direction-dependent strength) and require post-processing (e.g., heat treatment, surface finishing) to meet stringent standards. Material selection in AM is also narrower compared to the extensive range available in conventional processes.

Case Study: Transitioning a Precision Component from Traditional to Additive Manufacturing at Titletown Manufacturing LLC, Green Bay, WI

Background

Titletown Manufacturing LLC, a hypothetical precision metal fabrication and machining company based in Green Bay, Wisconsin, has established itself as a trusted supplier to original equipment manufacturers (OEMs) across the Midwest. Among its product portfolio, the company historically produced a critical stainless-steel valve housing for an industrial pump system used in food processing—a sector prominent in Northeast Wisconsin. Traditionally, this component was manufactured using CNC machining from a solid stainless-steel block, a subtractive process requiring multiple setups, significant material waste, and a lead time of approximately three weeks per batch.

In early 2024, Titletown faced increasing pressure from a key client to reduce costs, shorten delivery times, and accommodate design iterations for a next-generation pump system. This prompted the company to explore additive manufacturing as an alternative production method. After a feasibility study, Titletown selected powder bed fusion (PBF) using selective laser melting (SLM) to transition the valve housing production, leveraging Green Bay’s growing ecosystem of advanced manufacturing support and regional expertise.

The Traditional Manufacturing Process

The valve housing, measuring approximately 150 mm x 100 mm x 80 mm with internal flow channels, was machined from 316L stainless steel billets. The process involved:

Material Procurement: Sourcing 20 kg billets, of which only 4 kg remained in the final part, resulting in 80% material waste.
CNC Machining: Multi-axis milling to create external geometry and internal channels, requiring three setups and custom fixturing.
Post-Processing: Deburring, surface finishing, and quality inspection.
Production Metrics: Each batch of 50 units took 120 labor hours, with a per-unit cost of $180 and a three-week lead time due to tooling and machining schedules.

The subtractive process excelled in high-volume production but struggled with rapid prototyping and design flexibility, limiting responsiveness to the client’s evolving needs.

Transition to Additive Manufacturing

Titletown partnered with a regional AM service provider to adopt SLM, a PBF method using a laser to fuse 316L stainless steel powder layer by layer. The transition process included:

Design Optimization: Designers redesigned the valve housing using topology optimization software, reducing weight by 15% (from 4 kg to 3.4 kg) and enhancing flow efficiency by integrating conformal internal channels—features infeasible with CNC machining.
Material Shift: Stainless steel powder was sourced, with unused powder recycled within the SLM system, reducing waste to less than 10%.
Production Setup: An SLM machine with a 250 mm x 250 mm x 300 mm build volume was utilized, allowing four housings to be printed per build cycle.
Process Execution: Printing took 18 hours per cycle, followed by heat treatment to relieve residual stresses and wire EDM to remove parts from the build plate. Surface finishing ensured compliance with food-grade standards.
Production Metrics: A batch of 50 units required 90 hours of machine time plus 20 hours of post-processing, reducing total labor to 110 hours. Per-unit cost dropped to $150, and lead time shrank to one week.

Outcomes and Benefits

The shift to AM yielded several advantages:

Cost Reduction: A 16.7% decrease in per-unit cost ($180 to $150) due to lower material waste and streamlined production.
Lead Time Improvement: Production time reduced by 67% (three weeks to one week), enabling just-in-time delivery.
Design Flexibility: The ability to produce complex internal geometries improved pump performance, increasing client satisfaction.
Sustainability: Material efficiency rose from 20% to over 90%, aligning with Green Bay’s emphasis on sustainable manufacturing practices.

Challenges Encountered

The transition was not without hurdles:

Initial Investment: The SLM machine and training required a $500,000 upfront cost, amortized over multiple projects.
Process Validation: Ensuring mechanical properties (e.g., tensile strength, corrosion resistance) met industry standards necessitated extensive testing, delaying full-scale adoption by three months.
Volume Limitation: SLM’s slower build rate made it less economical for batches exceeding 200 units, prompting a hybrid approach for larger orders.

Strategic Decision and Future Implications

Titletown adopted AM for low-to-medium volume production (up to 100 units) and prototyping, retaining CNC machining for high-volume runs. This hybrid model maximized flexibility while leveraging existing infrastructure. The success of this transition positioned Titletown as a regional leader in AM adoption, attracting new clients in aerospace and medical device sectors seeking similar capabilities.

Looking forward, Titletown plans to invest in multi-material AM systems to further enhance component functionality, capitalizing on Green Bay’s manufacturing talent pool and proximity to technical colleges like Northeast Wisconsin Technical College (NWTC) for workforce development.

This case study demonstrates how a Green Bay-based manufacturer successfully transitioned a traditionally machined component to additive manufacturing, achieving cost savings, faster delivery, and design innovation. It underscores AM’s value in low-volume, high-complexity applications, offering a blueprint for other regional firms navigating the shift from traditional methods.

Case Study, Real-World Example: General Electric's LEAP Engine Fuel Nozzle Transition to Additive Manufacturing

Background

General Electric (GE) Aviation, a global leader in aerospace manufacturing, historically produced fuel nozzles for its jet engines using traditional manufacturing methods. One such component, the fuel nozzle for the LEAP (Leading Edge Aviation Propulsion) engine, developed in collaboration with CFM International, was originally fabricated through a complex subtractive and assembly process. In 2012, GE began exploring additive manufacturing to enhance performance, reduce costs, and streamline production, culminating in the successful transition of this component to AM by 2016. This case is widely regarded as a landmark in the adoption of AM for production parts.

The Traditional Manufacturing Process

The original LEAP engine fuel nozzle was a precision component made from a cobalt-chromium alloy, designed to inject fuel into the combustion chamber with high efficiency. Traditionally, it was manufactured as follows:

Casting and Machining: The nozzle comprised 20 individual parts, cast separately using investment casting, followed by CNC machining to achieve precise tolerances.
Assembly: These parts were brazed and welded together, requiring skilled labor and extensive quality control to ensure structural integrity and leak prevention.
Production Metrics: Each nozzle required approximately 40 hours of manufacturing and assembly time. For a batch of 100 units, the process generated significant scrap (up to 30% material waste) and cost $250 per unit, with a lead time of four weeks due to tooling and assembly schedules.

This method, while effective for high-volume production, limited design flexibility and resulted in a heavier component, impacting engine efficiency.

Transition to Additive Manufacturing

GE adopted Direct Metal Laser Melting (DMLM), a subtype of powder bed fusion, to redesign and produce the fuel nozzle as a single, integrated part. The transition involved:

Design Optimization: Using generative design software, designers consolidated the 20-part assembly into a single geometry, reducing weight by 25% (from 0.9 kg to 0.67 kg) and improving fuel flow dynamics with intricate internal channels—features unachievable with casting or machining.
Material and Process: The nozzle was printed using cobalt-chromium powder in a DMLM system with a build volume of 250 mm x 250 mm x 300 mm. Each print cycle produced two nozzles in 24 hours, followed by heat treatment to relieve stresses and minimal surface finishing.
Production Metrics: A batch of 100 units required 1,200 machine hours (50 print cycles) plus 100 hours of post-processing, totaling 1,300 hours. Per-unit cost dropped to $200, and lead time was reduced to two weeks, as no tooling was required.

Outcomes and Benefits

The shift to AM delivered substantial improvements:

Performance Enhancement: The redesigned nozzle improved fuel efficiency by 15%, contributing to the LEAP engine’s superior thrust-to-weight ratio, a critical factor in aerospace applications.
Cost and Time Savings: Per-unit cost decreased by 20% ($250 to $200), and lead time was halved, enabling faster delivery to customers like Airbus and Boeing.
Material Efficiency: Waste was reduced to less than 10%, as AM used only the material needed for the part, with excess powder recycled.
Production Scalability: By 2020, GE was producing over 100,000 nozzles annually at its Auburn, Alabama facility, demonstrating AM’s viability for serial production.

Challenges Encountered

The transition faced several obstacles:

Certification: The Federal Aviation Administration (FAA) required rigorous testing to certify the AM nozzle for flight, delaying initial deployment by 18 months.
Equipment Investment: DMLM machines cost upwards of $1 million each, necessitating significant capital expenditure, though offset by long-term savings.
Process Refinement: Early builds exhibited porosity issues, requiring optimization of laser parameters and powder quality, adding six months to development.

Strategic Impact and Broader Implications

GE’s adoption of AM for the LEAP fuel nozzle marked a paradigm shift in aerospace manufacturing. The company integrated AM into its supply chain, reducing reliance on external vendors and enabling on-demand production. This success spurred further AM investments, such as the 2021 development of AM-produced turbine blades, and inspired competitors like Rolls-Royce and Pratt & Whitney to accelerate their own AM programs.

This example highlights AM’s ability to replace traditional manufacturing for high-value, complex components, offering superior performance, reduced lead times, and material efficiency. It remains a benchmark for industries transitioning to AM worldwide.

This case study is grounded in documented industry developments, drawing from GE Aviation’s widely publicized adoption of AM for the LEAP engine, as reported in engineering and aerospace literature. It provides a concrete, real-world illustration of AM replacing traditional methods.

Conclusion

Additive manufacturing offers a versatile suite of methods that complement, rather than replace, traditional manufacturing. Designers must evaluate project requirements—geometry complexity, production volume, material properties, and cost constraints—to determine the optimal approach. As AM technologies advance, their adoption will likely expand, reshaping design and production paradigms across industries.

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Case Study: Transitioning a Precision Component from Traditional to Additive Manufacturing at Titletown Manufacturing LLC, Green Bay, WI

Background

The Traditional Manufacturing Process

Transition to Additive Manufacturing

Outcomes and Benefits

Challenges Encountered

Strategic Decision and Future Implications

Case Study, Real-World Example: General Electric's LEAP Engine Fuel Nozzle Transition to Additive Manufacturing

Background

The Traditional Manufacturing Process

Transition to Additive Manufacturing

Outcomes and Benefits

Challenges Encountered

Strategic Impact and Broader Implications

Introduction to Additive Manufacturing

Overview of Additive Manufacturing Methods

Comparison with Traditional Manufacturing

When to Prefer Additive Manufacturing

Limitations and Trade-Offs

Case Study: Transitioning a Precision Component from Traditional to Additive Manufacturing at Titletown Manufacturing LLC, Green Bay, WI

Background

The Traditional Manufacturing Process

Transition to Additive Manufacturing

Outcomes and Benefits

Challenges Encountered

Strategic Decision and Future Implications

Case Study, Real-World Example: General Electric's LEAP Engine Fuel Nozzle Transition to Additive Manufacturing

Background

The Traditional Manufacturing Process

Transition to Additive Manufacturing

Outcomes and Benefits

Challenges Encountered

Strategic Impact and Broader Implications

Conclusion

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