Microform Precision divides our cosmetic requirements into four categories: A, B, C and D.
A is the highest cosmetic finish, requiring the most effort to attain. Similarly, D is the lowest cosmetic requirement, and is the fastest and cheapest option. For most applications, either B or C is an advisable choice. Selecting the appropriate cosmetic class for your application will help ensure an aesthetically pleasing finish, without unnecessary increases to time and cost. Below are a series of relevant excerpts from Microform Precision's cosmetic inspection criteria.
Class A: The Class A finish is the highest quality finish Microform Precision can provide. It is often specified for high visibility surfaces such as control panels, front covers, etc. in which the Customer demands the highest quality appearance. This Class is for surfaces that are of such prominence that imperfections will tend to degrade the public image of the product.
Class B: The Class B finish is a quality finish with only minimal imperfections. A Class B finish is the most common finish for exterior surfaces. It is normally specified on surfaces such as external covers, panels, and parts that are fairly prominent.
Class C: The Class C finish allows more imperfections than Class A or B. Class C is often specified for interior surfaces not readily visible, surfaces that will be covered by another part when assembled, or surfaces which the Customer feels do not need to meet a high cosmetic finish. This Class is generally used for parts or surfaces which are not viewed after installation or viewed only for service.
Class D: The Class D finish might be used when cosmetic appearance is not important. With a Class D finish, all imperfections are permissible provided they do not impair the function, safety, structural strength, environmental, electrical or dimensional requirements of the part; part is usually never viewed.
Viewing Time and Distance
|Class A||12 inches||6 sec / 12″x12″|
|Class B||16 inches||4 sec / 12″x12″|
|Class C||16 inches||3 sec / 12″x12″|
|Class D||24 inches||2 sec / 12″x12″|
What is the level of imperfections allowed in the different classes? This chart below explains what cosmetic criteria can pass in each class.
* Refers to Painted, Powder Coated or Plated surfaces only.
** Not applicable to Class D provided functionality of part is not impaired.
|Imperfection||Maximum allowable per 12″ x 12″ section|
|Class A||Class B||Class C||Class D|
|Blister*||3 x .010||5 x .010||5 x .020||**|
|Burr||None||None||10% of material thickness||**|
|Chip*||None||None||1 x .030||**|
|Crater||3 x .010||5 x .010||5 x .020||**|
|Dent||None||None||1 x .030||**|
|Ding||3 x .010||5 x .010||5 x .020||**|
|Grainy Coating/Orange Peel*||Minimal||Light||Moderate||**|
|Gouge||None||None||1 x .030||**|
|Mar||3 x .010||5 x .010||5 x .020||**|
|Pinhole||3 x .010||5 x .010||5 x .020||**|
|Pit||3 x .010||5 x .010||5 x .020||**|
|Scratch||3 x .010x.125||3 x .010x.25||Moderate||**|
|Specks||3 x .010||5 x .010||Moderate||**|
|Stress Marks (Forming)||Minimal||Light||Moderate||**|
Definitions of Imperfections
To better understand the cosmetic criteria, and how we are judging the quality assurance, here is a definition list of the various imperfections. Each cosmetic class has a different tolerance for these imperfections. Class A being the most stringent, and Class D being the most lenient.
Abrasion: A surface imperfection that removes or displaces material, characterized by its large width and length relative to its depth.
Bleeding: This defect is the discoloration created by the diffusion of coloring material through an applied coating from the substrate to the surface of the coating.
Blister: The raised bumps in the surface, caused by air or solvent vapors forming within or under the coating.
Burr: Raised, rough, or sharp edges inherent in cutting operations such as shearing, blanking, punching and drilling. Burrs will usually snag or tear a cleaning cloth.
Chip: This defect is defined as the loss of adhesion and the removal, usually in small fragments, of the surface coating resulting from impact by hard objects: similar to a mar, ding, or nick.
Color Variance: A difference in hue or color from the specified color.
Corrosion: This defect is caused by chemical reaction with hot humid air or any other solvent.
Crack: A thin break (splitting) in the coating or sheet metal.
Crater: This type of defect is characterized by a cup-shaped depression or cavity in the coated surface. Sometimes confused with pinholes, craters begin as blisters with the depression formed as the gas forming the blister escapes before surface hardening.
Dent: A surface depression caused by a blow or pressure from another object. Dents have no characteristic size or shape.
Ding: An impression or depression formed on the surface with impact from another hard object.
Die Mark: This type of defect is an indentation, depression, or line that occurs in the same location of every part due to a die, mold, tool and so forth.
Dirt: This defect often appears in the form or irregularly distributed dust particles, usually appearing burnt and black. These particles have no common shape or size and may appear long in shape much like tiny hairs. Dirt and smudges may be removed by simple cleaning procedures.
Discoloration: Any change from original color.
Fracture: This defect is characterized by a tear, separation, or pulling apart from metal.
Grainy Coating / Orange Peel: This coating defect is characterized by the presence of irregularly shaped, angular or round protrusions evenly spread over the area of concern.
Gouge: A gouge is characterized as a scratch of wider width.
Mar: This is coating scraped with no color change.
Pinhole: Sharp, round or irregularly shaped depressions — randomly distributed over a surface and may range in size from those barely visible to those the size of a pin-head. These defects will sometimes have a residual varnish or some other solid in their centers surrounded by a hollow, halo-like space.
Pit: A pinhole bigger in size is called a pit.
Run: A run is generally a long, narrow, linear band of discoloration on a finished surface.
Rust: Rust is the visible manifestation of corrosion of the iron or iron alloys. This defect is usually seen as a reddish brown coating, composed mostly of hydrated iron oxides formed on iron or its alloys, as a result of exposure to humid surroundings.
Scratch: A scratch may be described as a roughly linear break in a surface produced by external influences. Scratches vary greatly in length and depth. A characteristic common to all scratches is that they are thin relative to their length.
Smudge: A dirty mark or smear appearing as a run. Smudges usually can be wiped off the surface.
Specks: Small particles of dust or debris embedded in the surface material. Specks may not be able to be removed by simple cleaning.
Stain: This type of defect is generally brown in color and appears as runs. Stains can usually be wiped off the surface.
Streaking: This defect characterized by long narrow marks, smears, or undesirable bands of color in or on the surface. Streaking cannot usually be felt and in many cases may be wiped off the surface.
Stress Marks (Forming): This type of defect usually occurs at the sharp corners and characterized by stress cracking due to deformation.
Tooling Marks: This type of defect is an indentation, depression or line that occurs in the same location of every part due to tooling.