4. Additive Manufacturing and Hybrid Production

Introduction and Context

Additive manufacturing (AM) is a production approach in which a component is created by adding material, usually layer by layer, from a digital model. It differs fundamentally from subtractive manufacturing, which removes material from a workpiece, and from forming processes, which reshape bulk material through pressure, heat, or tooling. The significance of AM is not merely that it can produce complex shapes. Its strategic value lies in linking product design, materials engineering, production planning, supply-chain configuration, and digital manufacturing into one integrated system.

AM is especially valuable when products are geometrically complex, produced in small quantities, customized, difficult to machine, or required quickly. Typical applications include lightweight aerospace structures, patient-specific medical devices, conformal cooling channels for tooling, customized fixtures, dental products, and spare parts produced near the point of use. Nevertheless, AM is not universally superior. Build rates, material costs, surface quality, dimensional accuracy, certification requirements, and post-processing may make conventional processes more economical for high-volume production.

Hybrid production combines additive processes with subtractive machining, forming, joining, inspection, or other operations. A hybrid machine may deposit material and machine it in the same setup, or a production system may integrate separate AM and conventional stages. Hybridization addresses an important practical reality: additive processes create shape freedom, whereas conventional processes often provide superior precision, surface finish, and productivity. Effective production management therefore requires selecting and coordinating processes rather than treating AM as a complete replacement for established manufacturing.

Learning Objectives

After studying this chapter, the reader should be able to:

1. Explain the operating principles and applications of major additive manufacturing process families.

2. Compare material extrusion, vat photopolymerization, powder-bed fusion, directed-energy deposition, and binder jetting.

3. Apply design-for-additive-manufacturing principles and explain the role of topology optimization.

4. Evaluate materials, post-processing, quality assurance, qualification, and economic factors in AM.

5. Explain how hybrid manufacturing combines additive and conventional processes.

6. Identify managerial, technical, regulatory, ethical, and operational risks in AM deployment.

7. Recommend an appropriate AM or hybrid-production strategy for a given manufacturing situation.

From Digital Geometry to Physical Product

An AM process begins with a three-dimensional computer-aided design model. The model is converted into a manufacturing representation, commonly an STL or 3MF file, and then oriented, supported, and sliced into layers. Process parameters such as layer thickness, energy input, extrusion rate, scan strategy, or binder quantity are assigned. The machine creates the part, after which support removal, cleaning, heat treatment, surface finishing, machining, inspection, and documentation may be required.

This workflow is often described as a digital thread because information flows from design through production and quality verification. The digital thread is valuable only when data are controlled. Version errors, incorrect units, unsuitable tolerances, damaged files, or unapproved parameter changes can cause defects even when the machine operates correctly. Consequently, AM management includes configuration control, material-lot traceability, machine calibration, software validation, and secure transfer of production data.

A useful distinction is between process capability and design freedom. Design freedom refers to the range of geometries that can be manufactured. Process capability refers to the repeatability, accuracy, productivity, and material performance achieved in actual production. A machine may create a complex lattice but still fail to meet the required fatigue life or dimensional tolerance. Good AM decisions consider both dimensions.

The Principal Additive Process Families

Material Extrusion

In material extrusion, a thermoplastic filament or pellet is softened and forced through a nozzle. The nozzle follows a programmed path, depositing roads of material that fuse with previous roads. Common materials include polylactic acid, acrylonitrile butadiene styrene, polyamide, polyether ether ketone, and fibre-reinforced polymers. In some systems, more than one nozzle deposits build and support materials.

Material extrusion has relatively low equipment cost, simple material handling, and broad accessibility. It is widely used for prototypes, jigs, fixtures, educational models, architectural forms, and selected end-use parts. Its limitations include anisotropic strength, visible layer lines, thermal warping, nozzle blockage, and comparatively modest resolution. Build orientation strongly influences mechanical performance because bonding between layers may be weaker than strength within a deposited layer.

Production decisions should therefore consider chamber temperature, bed adhesion, cooling rate, raster angle, infill pattern, layer height, and support strategy. For engineering polymers, environmental control and drying of hygroscopic materials can be essential.

Vat Photopolymerization

Vat photopolymerization selectively cures liquid photopolymer resin using light. In stereolithography, a laser traces the required cross-section; in digital light processing, a projected image cures an entire layer or a substantial portion of it. The process can provide fine detail, smooth surfaces, and high visual accuracy.

Applications include dental models, hearing-aid shells, casting patterns, prototypes, microfluidic components, and customized products. However, uncured resin must be handled carefully, and parts normally require washing and post-curing. Many photopolymers are sensitive to ultraviolet exposure, temperature, and moisture, and their long-term mechanical properties may differ substantially from those of conventional engineering plastics. Resin waste, worker exposure, and disposal are significant management considerations.

Powder-Bed Fusion

Powder-bed fusion selectively fuses regions of a powder layer using thermal energy. Polymer systems commonly use selective laser sintering, while metal systems include laser powder-bed fusion and electron-beam powder-bed fusion. A new powder layer is spread over the previous layer and the cycle is repeated.

Powder-bed fusion can produce intricate internal channels, lattices, and assemblies with reduced need for support structures. Metal laser powder-bed fusion is used for aerospace, medical, tooling, and high-performance engineering components. Electron-beam systems operate in a vacuum and are particularly associated with certain metals and high-temperature applications.

Important variables include powder size distribution, powder morphology, energy density, scan speed, hatch spacing, layer thickness, thermal management, and atmosphere. Defects may include lack of fusion, keyhole porosity, balling, residual stress, distortion, and unmelted powder trapped in internal passages. Powder reuse requires defined controls because repeated thermal exposure, contamination, oxidation, and particle-size changes can affect performance.

Directed-Energy Deposition

Directed-energy deposition (DED) feeds metal powder or wire into a melt pool created by a laser, electron beam, or arc. The deposition head moves relative to the workpiece and builds, repairs, or adds material to selected regions. Unlike powder-bed fusion, DED is well suited to large components, repair work, graded materials, and addition onto existing parts.

DED is used for repairing turbine components, adding features to forgings, producing large near-net-shape parts, and applying wear-resistant or corrosion-resistant material. It generally offers higher deposition rates and larger build volumes than powder-bed systems, but its surface finish and dimensional accuracy are usually less refined. Machining is therefore commonly required. Process monitoring of melt-pool temperature, geometry, acoustic emissions, and deposited height can help control quality.

Binder Jetting

Binder jetting selectively deposits a liquid binder onto a powder bed. The powder is not melted during printing. The fragile “green” part is subsequently cured, depowdered, and usually sintered; metals may require debinding before sintering. Since the printing stage does not directly melt the material, binder jetting can achieve relatively high throughput and avoid some thermal distortion associated with melting.

The main challenges are shrinkage during sintering, dimensional prediction, green-part handling, density control, and powder-binder compatibility. Binder jetting is attractive for batch production of complex parts where the economics of high-speed printing and furnace processing are favourable. It requires robust process models linking printed dimensions to final sintered dimensions.

Comparing Processes for Production Decisions

No process family should be selected solely on the basis of geometric complexity. A production manager should examine material requirements, annual demand, part size, tolerance, surface finish, mechanical loading, certification, tooling cost, lead time, labour, post-processing, and environmental conditions.

Material extrusion is economical for prototypes and fixtures, but may be unsuitable for highly loaded or appearance-critical parts. Vat photopolymerization is preferred for detail and smoothness, but material durability and resin handling may limit end-use deployment. Powder-bed fusion supports complex polymer and metal parts with strong geometric freedom, although equipment and powder costs are substantial. DED is attractive for large parts and repair, but usually requires machining. Binder jetting can provide scalable batch output, but sintering introduces shrinkage and process-control challenges.

The appropriate comparison is therefore not machine against machine but production route against production route. A fair comparison includes design, printing, supports, cleaning, heat treatment, machining, inspection, scrap, labour, facility requirements, inventory, and the cost of delayed delivery.

Design for Additive Manufacturing

Design for additive manufacturing (DfAM) changes the designer’s question from “How can this conventional part be printed?” to “What product architecture best exploits the selected process?” The principles include:

• Consolidating several components into one part where assembly reduction is valuable.
• Designing internal channels, lattices, graded structures, and organic forms that conventional processes cannot easily create.
• Orienting parts to control strength, support volume, thermal distortion, and surface quality.
• Designing escape holes and powder-removal routes for enclosed cavities.
• Maintaining suitable wall thicknesses, clearances, overhangs, and radii for the selected machine.
• Locating critical surfaces so they can be machined or inspected.
• Incorporating datums, sacrificial features, and allowances for shrinkage or machining.

DfAM is process-specific. An overhang acceptable in one material-extrusion system may fail in another, while a metal powder-bed part may require support because of heat flow and residual stress rather than simple geometric collapse. Design rules must therefore be validated against machine, material, parameter set, and orientation.

Topology Optimization and Generative Design

Topology optimization mathematically distributes material within a defined design space subject to objectives and constraints. Typical objectives include minimum mass, maximum stiffness, reduced compliance, controlled natural frequency, or thermal performance. Constraints may include stress, displacement, buckling, manufacturing direction, minimum feature size, and connection regions.

The resulting organic geometry is not automatically a production-ready design. It must be interpreted by engineers, converted into manufacturable surfaces, checked for load cases not included in the model, and validated through simulation and physical testing. Generative design extends the idea by exploring multiple solutions under specified performance and manufacturing constraints. These tools can reduce weight and material use, but they also raise issues of software verification, explainability, design ownership, and responsibility when automated recommendations are accepted without adequate engineering review.

Materials and Material Qualification

AM materials include thermoplastics, photopolymers, metals, ceramics, cementitious materials, composites, and biomaterials. Material selection must consider not only nominal composition but also feedstock form, particle size, moisture, thermal history, additives, reinforcement orientation, and post-processing.

A printed part is a process-dependent material. Its properties may vary with build direction, location in the build chamber, thermal history, parameter set, and surface condition. Therefore, material datasheets alone do not establish part performance. Qualification typically involves material characterization, machine calibration, parameter development, coupon testing, dimensional evaluation, defect analysis, and repeatability studies.

For safety-critical products, qualification may require documented procedures, approved suppliers, traceable material batches, non-destructive testing, witness specimens, process monitoring, and statistical evidence of consistency. Standards and regulatory expectations differ by sector, but the underlying principle is common: the organization must demonstrate that the complete manufacturing process—not merely the digital design—can repeatedly produce compliant parts.

Post-Processing and Inspection

Post-processing is part of the process plan, not an afterthought. Common operations include support removal, depowdering, washing, curing, debinding, sintering, stress relief, hot isostatic pressing, annealing, shot blasting, tumbling, chemical smoothing, coating, and CNC machining.

For metal AM, heat treatment can reduce residual stress and modify microstructure. Hot isostatic pressing may reduce internal porosity, but adds cost and may alter dimensions. Machining provides accurate datums and critical surfaces, while abrasive or chemical finishing may improve appearance and reduce roughness. The selected sequence matters: machining before heat treatment may lead to dimensional changes, whereas machining after treatment may improve accuracy but increase tool wear.

Inspection methods include coordinate-measuring machines, optical scanning, computed tomography, ultrasonic testing, radiography, metallography, surface profilometry, and in-process monitoring. Inspection planning should focus on critical-to-quality characteristics rather than merely generating large quantities of data. Process monitoring is useful only when signals are linked to defect mechanisms and when the organization has rules for accepting, rejecting, or reviewing builds.

Economics and Production Planning

AM economics are often misunderstood because the absence of tooling is mistaken for low total cost. A realistic cost model includes machine depreciation or leasing, material, energy, labour, software, build preparation, supports, failed builds, post-processing, inspection, facility controls, certification, and inventory effects.

AM is generally strongest economically when tooling would be expensive, demand is uncertain, product variety is high, customization is valuable, or the cost of delay is significant. It may be weak for simple, high-volume parts that can be produced efficiently by injection moulding, stamping, casting, or machining. Break-even analysis should compare total route cost as a function of quantity, not just printing cost per hour.

Production planning also differs from conventional scheduling. The planner must consider build nesting, orientation, thermal interaction between parts, powder or resin utilization, post-processing batch size, furnace capacity, machine availability, and inspection bottlenecks. A machine can appear highly utilized while the overall system remains constrained by cleaning, heat treatment, or certification.

Hybrid Production: Combining Strengths Rather Than Choosing Sides

Hybrid manufacturing integrates additive deposition with subtractive machining or another conventional process. In one common arrangement, material is deposited onto a substrate, rough-machined, deposited again, and finish-machined. Other arrangements use AM to create a near-net shape followed by conventional machining, or use AM to repair a high-value component and restore its original geometry.

Hybrid production offers several benefits. Additive deposition can place material only where needed, while machining establishes precision. A single setup can reduce workholding errors and improve positional accuracy. Hybrid systems may also create conformal cooling channels, repair worn regions, or manufacture large components more quickly than powder-bed systems.

The challenges include machine complexity, software integration, calibration between coordinate systems, tool accessibility, thermal effects, chip and powder contamination, and higher capital cost. Process planning must determine where additive deposition ends and machining begins. Allowances must be provided for machining, and the deposited material must have sufficient integrity for subsequent cutting.

A practical hybrid route often follows this logic: establish a reliable substrate; deposit material with monitored parameters; perform intermediate inspection; rough-machine to remove distortion or excess material; apply heat treatment if required; finish-machine critical surfaces; and complete dimensional and material verification. The best route is determined by functional requirements, not by the novelty of hybrid equipment.

Applied Case: Hybrid Repair of a High-Value Turbine Component

Background

The following is an illustrative case. A maintenance organization receives a nickel-alloy turbine component with localized wear in a region that is expensive and time-consuming to replace. The original component has complex geometry and a controlled material specification.

Situation and Problem

Conventional repair would remove the damaged region, fit a replacement insert, weld it, and machine the surface. This approach requires specialized fixtures and may introduce joints or distortion. The organization considers laser DED followed by CNC machining. The repair must restore geometry, maintain metallurgical integrity, and provide evidence suitable for customer and regulatory review.

Analysis

Engineers first identify the damaged volume using scanning and compare it with the nominal CAD model. They define a deposition boundary, select compatible feedstock, and establish a qualified laser power, travel speed, powder-feed rate, and shielding-gas condition. Thermal simulation indicates that uncontrolled heat accumulation could distort the component. The process plan therefore includes controlled deposition paths and intermediate cooling. Because the repaired surface is functionally critical, machining allowances and inspection datums are incorporated into the deposition design.

Approach and Solution

The component is cleaned, fixtured, and scanned. DED adds material in successive passes while monitoring melt-pool behavior and deposited height. After deposition, the part receives an approved heat treatment. CNC machining restores the final profile and surface finish. Dimensional inspection compares the repaired region with the digital model, while non-destructive testing checks for cracks, lack of fusion, and unacceptable porosity. Material certificates, machine settings, operator qualifications, inspection results, and software versions are retained in the production record.

Outcome

The route avoids manufacturing an entirely new component and reduces the amount of material removed compared with producing a replacement from a larger billet. Its success depends not simply on deposition speed but on the qualification of the complete repair process. If inspection had been postponed until the end, a hidden defect could have made all subsequent machining and heat treatment wasteful.

Learning Points

The case demonstrates that DED is particularly valuable for high-value repair and feature addition. It also shows why AM must be integrated with scanning, machining, heat treatment, inspection, configuration control, and documentation. In regulated applications, repair approval is a systems problem rather than a machine-capability problem.

Risks, Governance, and Professional Responsibilities

Common technical failures include warping, delamination, porosity, residual stress, inaccurate shrinkage prediction, poor support removal, and inadequate surface finish. Operational failures include untrained operators, uncontrolled parameter changes, weak powder handling, insufficient maintenance, and bottlenecks in post-processing. Economic failure often results from ignoring inspection, failed builds, facility requirements, or low equipment utilization.

AM also creates governance concerns. Digital design files may be proprietary or safety-critical and require access control, version management, encryption, and cybersecurity safeguards. A copied or modified file may produce a counterfeit or unsafe part. Organizations should define who approves design changes, machine parameters, material substitutions, and release decisions.

Worker safety involves powders, resins, lasers, ultraviolet radiation, heated surfaces, fumes, compressed gases, and rotating equipment. Risk assessments, ventilation, personal protective equipment, spill procedures, fire controls, and waste-disposal systems are essential. Environmental evaluation should include energy use, powder or resin waste, support material, cleaning chemicals, and the possibility that lightweighting or local production reduces transport and inventory impacts.

Professional responsibility requires engineers to avoid presenting an attractive printed geometry as proof of functional performance. Designs must be validated against actual loads, environments, failure modes, and lifecycle requirements. Automated design tools support professional judgment; they do not replace it.

Digital Manufacturing, Automation, and Emerging Directions

AM increasingly uses machine learning, digital twins, automated build preparation, in-process sensing, robotic deposition, and closed-loop control. Cameras, pyrometers, acoustic sensors, melt-pool monitoring, and layerwise imaging can identify abnormal conditions. The long-term objective is not simply to collect data but to relate process signatures to material properties and part acceptance.

Artificial intelligence can assist with orientation selection, support generation, defect classification, parameter optimization, demand forecasting, and predictive maintenance. However, models may fail when presented with new geometries, materials, or machine conditions. Their use in safety-critical production requires representative training data, validation, human oversight, and records explaining decisions.

Emerging developments include multi-material deposition, recyclable and bio-based feedstocks, larger-format metal and polymer systems, automated robotic cells, in-situ alloy development, distributed spare-part production, and more integrated hybrid platforms. Industrial adoption will depend less on novelty than on repeatability, standards, cybersecurity, repairability, workforce competence, and demonstrable lifecycle value.

Best-Practice Framework for AM Implementation

An organization evaluating AM should proceed through a disciplined sequence:

1. Define the business or engineering problem, including demand, risk, performance, and delivery requirements.

2. Screen candidate parts using complexity, value, customization, lead time, and tooling criteria.

3. Select the process and material together rather than independently.

4. Redesign the part using DfAM, topology optimization where appropriate, and explicit post-processing allowances.

5. Develop and document parameters, orientation, supports, build layout, and inspection requirements.

6. Produce test coupons or representative articles and characterize performance in relevant directions.

7. Qualify the complete process and establish change-control procedures.

8. Model total cost, capacity, labour, post-processing, and supply-chain consequences.

9. Introduce production with traceability, monitoring, non-conformance procedures, and periodic capability review.

10. Improve the system using measured evidence rather than isolated demonstrations.

Chapter Summary

Additive manufacturing produces components by adding material from digital information, while hybrid production combines additive deposition with machining or other conventional operations. The major AM families differ in feedstock, energy source, accuracy, productivity, material behaviour, and post-processing requirements. Material extrusion is accessible and economical for many prototypes and fixtures; vat photopolymerization provides fine detail; powder-bed fusion enables complex polymer and metal parts; DED supports large components and repair; and binder jetting offers a potentially scalable route requiring careful sintering control.

DfAM, topology optimization, and generative design exploit AM’s geometric freedom, but designs must remain compatible with process constraints and validated loads. Material qualification, parameter control, inspection, post-processing, and digital traceability determine whether a printed part is reliable. Economic evaluation must include the entire production route. Hybrid manufacturing is particularly valuable when additive processes provide material placement or geometry and conventional processes provide precision and finish. Successful implementation depends on technical capability, quality governance, cybersecurity, worker safety, professional judgment, and evidence-based production management.

Key Terms

Additive manufacturing: Production of a component by progressively adding material according to digital geometry.

Binder jetting: An AM process that selectively deposits binder into a powder bed, followed by curing and commonly sintering.

Build orientation: The positioning of a part relative to the machine axes and layer direction.

Directed-energy deposition: Deposition of powder or wire into a melt pool created by a focused energy source.

Digital thread: Controlled flow of product and process information across design, manufacture, inspection, and support.

Design for additive manufacturing: Designing products specifically to exploit AM capabilities and accommodate its constraints.

Generative design: Computer-assisted exploration of alternative designs subject to performance and manufacturing constraints.

Hybrid manufacturing: Integration of additive and conventional processes in one coordinated production route or system.

Infill: Internal material pattern used in many extrusion-based parts to balance mass, strength, and build time.

Layer height: Thickness of each deposited, cured, or fused layer.

Material extrusion: AM in which softened material is forced through a nozzle and deposited along programmed paths.

Powder-bed fusion: AM in which selected regions of a powder layer are fused using thermal energy.

Post-processing: Operations performed after printing, such as curing, heat treatment, machining, cleaning, or finishing.

Residual stress: Locked-in stress generated by uneven heating, cooling, shrinkage, or transformation during production.

Topology optimization: Mathematical redistribution of material within a design space to meet defined objectives and constraints.

Vat photopolymerization: AM in which light selectively cures liquid photopolymer resin.

Qualification: Documented demonstration that a defined process repeatedly produces parts meeting specified requirements.

Traceability: Ability to link a part to its materials, design version, process parameters, equipment, operators, and inspection records.

Review Questions

Short Answer Questions

1. What distinguishes additive manufacturing from subtractive manufacturing?

2. Why does build orientation affect the performance of an extrusion-based part?

3. State two important controls in powder-bed fusion.

4. What is the purpose of post-processing in AM?

5. Define hybrid manufacturing.

Long Answer Questions

1. Compare material extrusion, vat photopolymerization, powder-bed fusion, DED, and binder jetting in terms of feedstock, strengths, limitations, and applications.

2. Explain the principles of design for additive manufacturing and discuss why design rules are process-specific.

3. Describe how topology optimization can support lightweight product design and identify the engineering checks required before production.

4. Discuss the technical and economic factors that should be included in an AM production-route decision.

5. Explain how qualification, inspection, traceability, and change control support reliable AM production.

Analytical / Application Questions

1. A firm needs 200 customized polymer housings annually, each with internal channels and a six-week delivery requirement. Evaluate whether powder-bed fusion, material extrusion, or conventional moulding is the most appropriate route and justify your decision.

2. A metal DED repair shows dimensional accuracy but intermittent lack-of-fusion defects. Develop a structured investigation covering materials, parameters, thermal management, monitoring, and inspection.

3. A company proposes purchasing a hybrid AM-CNC machine for high-value tooling inserts. Construct a decision framework that includes design opportunity, capacity, post-processing, skills, total cost, qualification, and cybersecurity.

22. Multiple Choice Questions with Answers

Question 1

Which process is most directly characterized by depositing softened material through a nozzle?

A. Material extrusion

B. Vat photopolymerization

C. Binder jetting

D. Powder-bed fusion

Correct Answer: A. Material extrusion

Question 2

A major production concern specific to binder jetting is the need to control dimensional change during which subsequent operation?

A. CNC roughing

B. Sintering

C. Laser scanning

D. Support welding

Correct Answer: B. Sintering

Question 3

Why is machining commonly combined with directed-energy deposition?

A. DED cannot deposit material on existing components

B. Machining improves the dimensional accuracy and surface finish of deposited material

C. Machining converts photopolymer resin into metal

D. DED requires machining to create the powder bed

Correct Answer: B. Machining improves the dimensional accuracy and surface finish of deposited material

Question 4

Which design decision most directly supports powder removal from an enclosed powder-bed-fusion cavity?

A. Increasing raster angle

B. Adding suitable escape holes

C. Reducing inspection frequency

D. Eliminating all datums

Correct Answer: B. Adding suitable escape holes

Question 5

Topology optimization primarily seeks to do what?

A. Distribute material to meet defined performance objectives and constraints

B. Replace all physical testing with software output

C. Increase material use regardless of loading

D. Guarantee a defect-free build without qualification

Correct Answer: A. Distribute material to meet defined performance objectives and constraints

Question 6

Which statement best explains why AM material datasheets alone may not establish part performance?

A. Printed parts are unaffected by process parameters

B. AM properties can depend on orientation, thermal history, location, and post-processing

C. Datasheets apply only to subtractive processes

D. AM materials have no measurable mechanical properties

Correct Answer: B. AM properties can depend on orientation, thermal history, location, and post-processing

Question 7

In an AM economic analysis, which item is most likely to be incorrectly omitted?

A. Post-processing and inspection costs

B. The colour of the CAD interface

C. The historical age of the product designer

D. The number of pages in the machine manual

Correct Answer: A. Post-processing and inspection costs

Question 8

What is the principal purpose of qualification in safety-critical AM production?

A. To demonstrate that the complete defined process can repeatedly produce compliant parts

B. To prove that every geometry can be printed on every machine

C. To eliminate the need for traceability

D. To replace material certificates with visual inspection

Correct Answer: A. To demonstrate that the complete defined process can repeatedly produce compliant parts

Question 9

A company needs to repair a localized worn region on an expensive metal component and then restore a precise final profile. Which route is most appropriate?

A. Vat photopolymerization only

B. DED followed by heat treatment, machining, and inspection

C. Binder jetting without sintering

D. Material extrusion followed by resin washing

Correct Answer: B. DED followed by heat treatment, machining, and inspection

Question 10

Which is a central governance risk associated with AM digital files?

A. They cannot be copied or modified

B. Unauthorized changes may produce counterfeit or unsafe parts

C. They eliminate the need for configuration control

D. They are unrelated to product quality

Correct Answer: B. Unauthorized changes may produce counterfeit or unsafe parts