Rapid Prototyping:EVT Engineering Validation

Engineering Verification Test (EVT) is a crucial stage in transitioning from functional prototype to manufacturability verification. Unlike PoC, Visual Prototype, and Functional Prototype, EVT focuses not on "whether the function can be achieved," but on "whether it can reliably enter mass production engineering." This stage ensures that the product structure, materials, processing methods, tolerance systems, fit accuracy, and safety standards meet mass production requirements, while verifying that the design can withstand long-term use in real-world environments.

CNC machining plays a central role in the EVT stage: CNC prototypes typically replace earlier injection-molded, die-cast, and sheet metal parts, undertaking engineering-level functional verification tasks. Due to their high precision, stability, and ability to provide small-batch, rapid parts, CNC prototypes have become one of the most important data sources in EVT verification.

This article will systematically outline the engineering goals of EVT, application strategies for CNC components, testing priorities, supply chain integration logic, and common risks, helping companies establish standardized and engineering-oriented verification processes.

Objectives of EVT: Establishing a Baseline for Engineering Manufacturability and Reliability

EVT is a crucial threshold for a product to enter subsequent DVT (Design Verification Test) and PVT (Production Validation Test), primarily addressing three major engineering objectives:

1. Verifying the Manufacturability of the Engineering Design

Including but not limited to:

Whether the wall thickness meets machining/mold limitations

Whether chamfers, radius corners, and draft angles are reasonable

Whether the machining path is feasible

Whether key structures possess stable and repeatable machining capabilities

Whether CNC machining can effectively simulate future mass production solutions

2. Verifying Structural Strength, Durability, and Safety

EVT requires the execution of systematic engineering tests, including:

Static mechanical testing (strength, bending, impact)

Dynamic testing (fatigue, vibration)

Heat conduction/heat dissipation verification

Environmental testing (high and low temperatures, humidity, corrosion)

Safety standard verification (especially electrical and structural safety of electronic products)

3. Confirming that the engineering solution can serve as a basis for mass production

EVT A crucial question must be answered: Can the current engineering design directly proceed to mass production process development?

If the answer is no, then EVT (Engineering Virtualization) needs to continue iterating until the structural design, materials, and processing requirements meet mass production standards.

Core Application Scenarios of CNC Components in the EVT Phase

In EVT testing, most engineering parts are still manufactured using CNC machining, rather than the final mass production processes (such as injection molding, die casting, and metal molds). The logic behind this includes: shorter lead times, high precision and stability, ease of design modification, and the ability to simulate the real structures of most metal and engineering plastic parts.

1. Extensive Use of Metal Structural Components

During the EVT phase, metal components are typically fabricated directly using CNC machining, such as:

Aluminum alloy frames, support frames

Stainless steel shafts, guideways, structural components

Steel load-bearing components, connectors

These components bear the responsibility of strength, load-bearing capacity, and fatigue testing, therefore they must be machined using engineering materials (e.g., AL6061, AL7075, SUS304/316, 45# steel, etc.).

2. Precision Verification of Motion Components

Motion systems represent the structural component with the highest engineering risk, including:

Sliders, gears, supports

Hinges, shafts, lead screw assemblies

Friction and clearance verification of guideway systems

CNC functional-grade components can achieve machining accuracy of ±0.01–0.03 mm, making them the most reliable method for verifying motion performance during the EVT phase.

Verification of Assembly Clearance, Fit, and Screw Hole Accuracy

CNC prototypes consistently maintain the flatness of assembly surfaces, the coaxiality of holes, and the accuracy of threaded holes, enabling accurate testing during the EVT stage for:

Assembly interference

Fastener torque stability

Match surface tolerance stacking

Displacement deviation caused by dynamic vibration

These tests provide crucial inputs for subsequent mold design and mass production process development.

Key Validation Items for EVT: Systematic Verification of Engineering Parameters

EVT involves numerous engineering validation projects, making it one of the most densely tested phases in the entire product lifecycle.

1. Mechanical Validation: Strength and Fatigue

Key aspects include:

Static load strength testing

Bending/compression/tensile testing

Stress concentration analysis

Fatigue life testing of hinges and rotating structures

Failure mode assessment of structures under extreme external forces

Permanent deformation assessment of materials under repeated loading

CNC structural components can fully demonstrate the true mechanical performance of metallic materials, avoiding misjudgments due to material instability.

2. Reliability Validation: Operational Stability and Environmental Tolerance

Reliability testing is the core of EVT:

High and low temperature cycling (-20°C ~ +70°C)

Constant humidity testing (90% RH)

Salt spray testing (especially important for metallic structural components)

Drop testing, impact testing

Long-term vibration testing

Thermal management validation (heat sinks, metal frames, thermal path analysis)

These validations can uncover hidden mechanical, thermal, and electrical risks.

3. Engineering Feasibility Verification: Matching of Structure and Process

This mainly includes:

Whether the wall thickness meets future mold design standards

Whether chamfers, draft angles, and radius (R-angle) are reasonable

Whether the machining path leads to excessive tool load or machinability

Whether deep cavity structures require special fixtures

Whether there is a risk of shrinkage or warping in subsequent injection molded parts

Whether the CNC prototype can accurately simulate the assembly relationship of future mass-produced parts

4. Safety Regulations Verification (especially for electronic products)

This includes:

Electrostatic shock protection design

Fire resistance rating

Creep distance and clearance

Structural reinforcement and fastener anti-loosening design

Battery structural safety

Grounding reliability of the metal casing

These tests directly determine whether the product can pass future third-party certifications (such as CE, UL, FCC).

Supply Chain Integration: CNC Prototypes as Engineering Basis for Mold Manufacturers and Manufacturing Teams

The EVT (Engineering, Manufacturing, and Transmission) phase is a critical node for supply chain initiation. CNC prototypes, serving as "engineering benchmarks," help mold manufacturers and mass production teams complete the following tasks:

1. CNC Prototypes Assist Mold Manufacturers in Verifying Structural Design

Mold manufacturers need to confirm:

Whether the structure is machinable

Whether hole positions, hanging points, and rib positions are reasonable

Whether the wall thickness meets injection molding/die casting specifications

Whether the assembly structure is easy to implement

Whether the CNC prototype has excessively tight tolerance distribution

2. Using CNC to Simulate Mold Directionality and Draft Angle

Mold manufacturers can verify in advance through CNC prototyping:

Whether there is side core pulling

Whether the draft angle is sufficient

Whether the parting line position is reasonable

Whether there is stress concentration in ribs and boss pillars

By exposing mold manufacturing risks in advance through CNC prototypes, the mold rework rate can be significantly reduced.

3. Assessing the feasibility of mass production processes

CNC prototypes in the EVT phase are also used for:

Verifying whether parts can be milled and turned in the future

Determining whether tolerance requirements exceed the processing capabilities of existing equipment

Verifying the design feasibility of assembly fixtures

Simulating mass production tolerance stacking

Assessing which components are suitable for CNC machining and which are suitable for molded parts mass production

CNC prototypes serve as the "engineering language carrier" for supply chain engineers.

Common EVT Risks and Mitigation Strategies

1. Focusing Only on Test Results Without Recording Test Data

The core value of an EVT lies in its data, not the performance of a single test.

Recommended to establish:

Test Record Sheet

Data Trend Chart

Stress/Deformation Test Log

Assembly Data Sheet (Torque, Clearance, Coaxiality)

ECR/ECO Engineering Change Record

Lack of data will prevent the establishment of a baseline for subsequent DVT testing.

2. Material Differences Between CNC and Injection Molded Parts Lead to Misjudgments

CNC machining typically uses solid materials, while injection molded parts are affected by flow direction, fiber orientation, and shrinkage, resulting in:

Differences in strength

Differences in structural stiffness

Inconsistent assembly clearances

Different heat deformation characteristics

Solutions:

Incorporate small-batch injection/die-cast test molds for cross-validation in the later stages of EVT

Distinguish between CNC and mass-produced part data in the test report

3. Design Failure to Consider Machining Limits

Leading to CNC Machining Inability or Excessive Costs:

Deep cavities

No radius for sharp corners

Insufficient wall thickness

Excessively long tool causing tool vibration

Excessively deep holes without clearance

Best Strategy:

DFM (Design for Manufacturability) must be implemented during the EVT stage

Include the CNC factory and mold factory in the engineering review process in advance

Conclusion: EVT is a Critical Inflection Point for Engineering Maturity

EVT is the critical point that guides a product from "operable" to "manufacturable." It establishes the manufacturability baseline of the engineering design, verifies the performance of structures and materials in real-world environments, and provides core data for mold development and supply chain startup. CNC prototypes play an irreplaceable role at this stage; their precision, stability, and rapid iteration capabilities make them the most reliable carrier for engineering verification.

Only after the EVT stage is fully validated can the product, with stable engineering data, enter the more complex DVT, PVT, and final mass production processes.