112.2.4 - CAD/DFM

Inspection Basics

Inspection Tools & Accuracy vs. Precision

There is a key difference between Accuracy vs. Precision:
- Accuracy = How close to a target you are getting
- Precision = How close or consistent your measurements are to one another (AKA repeatability)
When measuring/inspecting products, it is critical that you have PRECISE MEASURING TECHNIQUE
- To test this, you can measure a feature of a part multiple times, and compare the measurements. If they are not identical, then your setup/technique is imprecise and not consistent enough for a proper measurement

Additionally, accuracy & precision are both relative to the tolerances of the thing you are measuring. In general, if something is referred to as having a "low" or "loose" tolerance, it has more room for error. Inversely, if something is referred to as having a "high" or "tight" tolerance, it has less room for error:
- Low Tolerances
  - Example being carpentry/construction work, especially those involving manual processes (ex: +/- 0.1in/1.0mm)
    - Tools that can be used within this range of tolerance include:
      - Measuring Tape
      - General Purpose Rules/Rulers
- Medium Tolerances
  - Example being structural/fabrication work, especially those involving welding processes (ex: +/- 0.01in/0.1mm)
    - Tools that can be used within this range of tolerance include:
      - Analog/Vernier Calipers
      - Precision-Ground Rules/Rulers
- High Tolerances
  - Example being general-purpose (less than "aerospace-grade") Machined parts, requiring a fairly high degree of accuracy (ex: +/- 0.001in/0.01mm)
    - With these tolerances, human measuring can be precise enough to adequate capture measurements correctly, with the right tools:
      - Digital Calipers
      - Analog/Vernier Micrometers
- Extreme Tolerances
  - Aerospace work typically has extremely tight tolerances and therefore requires an extremely high degree of accuracy (ex: +/- 0.0001in/0.001mm, and greater)
    - Tools typically used to measure to these tolerances usually eliminate as much human error as possible, such as:
      - Digital Micrometers
      - Computer-controlled measuring equipment, such as Coordinate Measuring Machines (CMM)
      - Laser or Optical Measuring Equipment
      - Electron Microscopes

Types of Inspection/Testing

Generally speaking, Inspection/Testing of products can be segregated into two broad categories, each with their own distinct processes:
- Destructive Testing (DT) - as its name also implies - damages or destroys the products being tested, and therefore is used most often in Research & Development (R&D) or Scientific applications/environments
- Non-Destructive Testing (NDT) - as the name implies - tests products without damaging/destroying them, as is the most common inspection/testing done in Manufacturing applications/environments

Destructive Testing (DT) Processes

Hardness Testing - involves applying a hard object to a component and measuring the depth of the indentation in order to determine the component's hardness.
Tensile Testing - involves applying a tensile force to a component until it breaks in order to determine its tensile strength, yield strength, and ductility.
Bend Testing - involves bending a component until it breaks in order to determine its bend strength and ductility.
Compression Testing - involves applying a compressive force to a component until it breaks in order to determine its compressive strength.
Impact Testing - involves subjecting a component to an impact load in order to determine its impact resistance.
Fatigue Testing - involves applying repeated loads to a component in order to determine its fatigue strength and fatigue life.
Fracture Toughness Testing - involves applying a force to a component until it fractures in order to determine its resistance to crack propagation.
Creep Testing - involves applying a load to a component and measuring its deformation over time at a high temperature in order to determine its creep resistance.
Corrosion Testing - involves exposing a component to a corrosive environment in order to evaluate its resistance to corrosion.

Non-Destructive Testing (NDT) Processes

Dimensional Inspection - the most common inspection process in most product manufacturing environments; verifies that the dimensions of a product or component meet the specified requirements.
Visual/Optical Inspection - examining the product or component for defects or flaws using the naked eye or visual aids.
Functional Testing - verifying that a product or component functions correctly and meets the specified requirements.
Structural Testing - evaluating the strength and durability of a product or component by applying loads or stresses to it.
Environmental Testing - evaluating how a product or component performs under different environmental conditions, such as temperature, humidity, and altitude.
Materials Testing - evaluating the properties of materials used in the manufacturing process to ensure that they meet the required specifications.
Chemical Testing - analyzing the chemical composition of materials used in the manufacturing process to ensure that they meet the required specifications.
Magnetic Particle Testing - uses magnetic fields to detect surface and slightly subsurface defects in ferromagnetic materials.
Liquid Penetrant Testing - involves applying a liquid penetrant to the surface of a component and then removing the excess penetrant. A developer is then applied, which absorbs the penetrant that has seeped into any surface defects, making them visible.
Eddy Current Testing - uses electromagnetic fields to detect surface and slightly subsurface defects in conductive materials.
Ultrasonic Testing - uses high-frequency sound waves to detect internal defects in materials and to measure the thickness of materials.
Radiographic Testing - uses X-rays or gamma rays to create an image of the internal structure of a component. The image is used to detect internal defects that are not visible from the outside of the component.

Inspection Reports

Inspection Reports are formalized documents that detail the results of an inspection of a product or system
- As a basic level, they can ensure that products and systems meet certain standards or specifications
- They may include information about the product or system being inspected, the inspection process and methods used, and the results of the inspection, as well as recommendations for addressing any issues or defects that were identified during the inspection
- Most importantly, inspection reports are often used to identify and resolve problems in the manufacturing process and to ensure that products meet the required standards and specifications

One common type of inspection report is a First Article Inspection (FAI)
- FAI is typically performed on the first production run of a new product or component, or when changes have been made to an existing product or component. The purpose of FAI is to ensure that the product or component is manufactured correctly and meets all of the necessary requirements before it is put into use or mass production.
- During FAI, a trained inspector compares the actual product or component to the engineering drawings and specifications to verify that it meets the required tolerances and specifications. The inspector may also test the product or component to ensure that it functions correctly. If any issues or discrepancies are found during the FAI process, they are documented and corrective action is taken to address them before the product or component is released for use or mass production.

FIT-FORM-FUNCTION (FFF)

It is common to assume that just because a specified dimension is Out of Tolerance (OOT) that the defective product should automatically be rejected/"scrapped". This tracks logically and in high-production environments, is often exactly what happens
However, in higher-quality, lower-volume production (ex: Aerospace Systems; Rockets, Fighter Jets, etc.), defects can happen often throughout the entire production process, and it is not practical for many companies to simply scrap multi-million dollar aircraft for singular defects
- In these situations, when potential defects are identified, they often undergo a more involved inspection process:
- The defective component(s) will be isolated/removed from the production line and further inspected, to determine if the defect can be considered acceptable, reworkable, or rejectable
- When making this determination, oftentimes it comes down to analyzing whether or not the defect(s) considerably affect the Fit, Form, and/or Function of the product:
  - - - FIT
        Does the defect unacceptably negatively impact how the product fits/connects to other mating components/assemblies?
        FORM
        Does the defect unacceptably negatively impact how the product looks or appears? Products can definitely be "too ugly to sell"
        FUNCTION
        Does the defect unacceptably negatively impact the functionality of the product?
    - If, through this process and/or others it is determined that despite its defect(s), the product can be either accepted or reworked to an acceptable standard, the product will be processed accordingly and re-enter the production line

2.4✔ CHECKPOINT

D6 Dice Inspection Report

Using the Inspection Report format and the correct measuring tool(s), inspect your 3D-Printed Die to the tolerances on your Technical Drawing
- Follow best practices!
Once fully inspected, add documentation to your previously-created "D6 Dice" Project page on your portfolio website, including:
- Picture of your completed Inspection Report
- Pictures(s)/Gif(s) of you measuring
- Descriptions/summaries of what you did/learned

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