Appearance is the first quality the customer sees

When discussing the quality of coated products, attention tends to focus on functions such as adhesion, rust resistance, chemical resistance, heat resistance, and weather resistance.

These are certainly very important.
However, when a customer receives a coated product, test data are not the first thing they see.

The first thing they see is its appearance.

Does the color match?
Is gloss consistent?
Are there particles or contaminants on the surface?
Is there sagging?
Are there scratches?
Is the surface finish attractive?
Are repair marks inconspicuous?

An unusual appearance makes the customer uneasy even if there is no functional problem.

Is this factory’s quality control reliable?
Could there also be problems in areas I cannot see?
Does quality vary between lots?

Appearance is therefore the customer’s starting point for assessing a company’s quality level.

This is why coating appearance is more than a cosmetic matter.
Appearance is the first quality the customer sees.

Appearance can cause rejection even when function is satisfactory

In industrial coating, a film can fulfill its intended functions but still be rejected because of appearance issues.

Examples include the following.

• Rust protection is sufficient, but uneven color is noticeable
• Adhesion is satisfactory, but gloss is unstable
• Film thickness is within specification, but the surface is rough
• Heat resistance is sufficient, but dirt nibs are noticeable
• Coating film performance meets requirements, but repair marks are visible
• There is no problem in use, but the customer’s appearance criteria are not met

The shop floor may consider such products functionally acceptable.
From the customer’s perspective, however, appearance is also part of quality.

Japanese manufacturers in particular tend to have high appearance-quality requirements.
For automotive parts, home appliances, building materials, machine parts, housing equipment, and office equipment, slight appearance differences can lead to customer complaints.

The coating forms the final surface of the product.
Its appearance therefore shapes the impression of the whole product.

Why visual inspection is difficult

Visual inspection is a very difficult process.

This is because much of the judgment is made by the human eye.

For example, inspectors may reach different conclusions about the same coated product.

Inspector A sees no problem.
Inspector B finds it slightly concerning.
The customer rejects it.

Such situations are not unusual in coating workplaces.

Variation in visual inspection can result from the following.

• Differences in inspector experience
• Differences in sensitivity to defects
• Different lighting at inspection locations
• Different viewing angles and distances
• Fatigue associated with inspection time of day
• No reference sample
• No limit sample
• Customer and internal standards that do not match
• Unclear defect classifications
• No retained inspection records

Quality judgments will not stabilize if visual inspection is left solely to individual intuition.

Visual inspection therefore needs standards, training, samples, records, and an improvement system.

Visual inspection must not depend on particular individuals

Experienced inspectors provide valuable expertise.
However, relying solely on that expertise makes the shop floor vulnerable.

For example, the following problems arise.

• Decisions cannot be made without a veteran inspector
• New inspectors’ judgments are unstable
• Standards differ between day and night shifts
• Judgment becomes stricter only when the customer is present
• Defects are found, but cause analysis does not follow
• Reliance on inspector intuition fails to lead to process improvement

The purpose of visual inspection is not only for inspectors to look for defects.

Its true purpose is to consistently assess the appearance quality the customer requires on the shop floor and reproduce it in the process.

Visual inspection therefore needs to be managed as a system rather than relying on individuals.

Requirements for stable appearance quality

The following elements are needed to stabilize appearance quality.

1. Reference samples

A reference sample defines the target accepted-product standard.

It provides a reference for color, gloss, surface texture, feel, and finish condition.
Without a reference sample, inspectors can only judge using their own intuition.

Reference samples allow customers, sales, quality staff, and the shop floor to use the same standard.

2. Limit samples

Reference samples alone may be insufficient.

Some variation occurs in mass production.
Limit samples are therefore needed to show what is permissible and where rejection begins.

Examples of limit samples include the following.

• Color difference limits
• Gloss difference limits
• Permissible dirt nibs
• Permissible sagging
• Permissible scratches
• Surface roughness limits
• Permissible repair marks
• Limits on contaminant size and quantity

Limit samples make it easier to reduce differences in judgment between inspectors.

3. Inspection conditions

Appearance changes with viewing conditions.

The same product may look different in color and gloss under different lighting.
Surface texture and scratches also look different at different viewing angles.

It is therefore important to define inspection conditions.

Check the following conditions.

• Inspection location
• Lighting conditions
• Inspection distance
• Inspection angle
• Inspection time
• Background color
• Product orientation
• Inspection timing
• Elapsed time after drying

Visual inspection results will not stabilize without defined inspection conditions.

4. Defect classification

Defects need to be classified to improve appearance quality.

For example, grouping everything as appearance defects hides the causes.

Appearance defects can be classified as follows.

• Uneven color
• Uneven gloss
• Dirt nibs
• Contaminants
• Sagging
• Solvent popping
• Cissing
• Cratering
• Orange peel
• Scratches
• Uneven film thickness
• Show-through
• Pinholes
• Repair marks
• Dirt
• Drying defects

Defect classification makes it easier to trace the responsible process.

For example, frequent dirt nibs and contaminants call for checks on the coating environment, booth cleaning, filters, surface preparation, and contamination inside the oven.
Frequent sagging calls for checks on film thickness, viscosity, delivery rate, drying speed, and application orientation.
Frequent uneven color calls for checks on stirring, film thickness, the underlying surface, application conditions, and drying conditions.

Classification enables improvement.

5. Inspector training

Inspector training is essential for stable visual inspection.

Inspectors need training in the following.

• How to assess reference samples
• How to use limit samples
• Classification of defect items
• Inspection distance and angle
• Lighting conditions
• Differences between accepted and rejected products
• Understanding customer requirements
• Reporting rules when judgment is uncertain
• How to keep inspection records

Visual inspection is not simply looking carefully.
It is a skill for making consistent judgments based on quality standards.

6. Inspection records and data

Inspection results must be recorded to reduce appearance defects.

Without records, the same problems recur.
With records, trends can be analyzed.

For example, records reveal the following.

• Which defects are most frequent?
• Which products have the most defects?
• Which operators have the most defects?
• Which lines have the most defects?
• At what times are defects most frequent?
• Which paint lots have the most defects?
• Under which equipment conditions are defects most frequent?
• Did defects decrease after improvement?

Visual inspection must not end with inspection itself.
It is important to convert results into data and connect them to process improvement.

Appearance defects will not decrease just by finding them during inspection

Visual inspection is important.
However, inspection alone does not reduce defects.

Inspection finds defects that have already occurred.
What is really needed is a process that prevents them from occurring.

For example, stricter inspection alone is insufficient when dirt nibs are frequent.
Their sources need to be identified.

• Are there contaminants in the paint?
• Are stirring containers clean?
• Are filters appropriate?
• Is there dust inside the booth?
• Are contaminants falling from work clothing?
• Is there dirt inside the oven?
• Are draining and drying after surface preparation sufficient?

For frequent sagging, check the following.

• Is film thickness excessive?
• Is viscosity too low?
• Is paint delivery rate too high?
• Is gun distance too close?
• Is drying too slow?
• Does the application sequence suit the product shape?

For frequent uneven color, check the following.

• Is the paint stirred sufficiently?
• Is film thickness stable?
• Is the underlying color consistent?
• Is the dilution ratio consistent?
• Are drying conditions stable?
• Are there differences in application technique between operators?

Reducing appearance defects requires tracing back to the process cause, rather than merely stopping them at inspection.

Appearance quality through 4M + Management

CoatureVietnam organizes appearance quality through 4M + Management.

Material: Materials

Many appearance defects originate in materials.

Check the following items.

• Paint lot
• Pigment dispersion
• Stirring condition
• Dilution ratio
• Thinner used
• Hardener mixing ratio
• Pot life
• Paint storage condition
• Filter usage
• Substrate material
• Surface preparation chemicals

Appearance quality will not stabilize if material condition is unstable.

Method: Methods

Working methods also greatly affect appearance.

Check the following items.

• Application sequence
• Spray distance
• Gun angle
• Gun travel speed
• Overlap width
• Paint delivery rate
• Air pressure
• Film thickness
• Setting time before drying
• Repair methods
• Inspection methods

Without standardized working methods, appearance varies between operators.

Machine: Equipment

Equipment condition is a major factor in appearance defects.

Check the following items.

• Spray gun condition
• Nozzle and air cap wear
• Paint supply equipment
• Booth cleanliness
• Booth air velocity
• Filter condition
• Oven cleanliness
• Temperature variation inside the oven
• Conveyor and fixture contamination
• Inspection lighting
• Film thickness gauges, glossmeters, and color measuring instruments

Dirty equipment or unstable settings also make appearance quality unstable.

Man: People

People’s skills and judgment are also important.

Check the following items.

• Operator coating skills
• Inspector judgment skills
• Ability to identify defects
• Understanding reference samples
• Understanding limit samples
• Reporting uncertain judgments
• Training history
• Variation between operators

Dependence on people cannot be eliminated completely.
However, training and standardization can reduce variation.

Management: Management

A management system is needed to stabilize appearance quality.

Check the following items.

• Clarification of customer requirements
• Establishment of internal standards
• Reference sample management
• Limit sample management
• Defect classification tables
• Inspection records
• Defect rate compilation
• Improvement activities
• Recurrence prevention
• Standard updates
• Agreements with customers

Appearance quality is not solely a shop-floor issue.
Sales, quality, production engineering, the shop floor, and managers need shared standards.

Visual inspection issues likely at factories in Vietnam

The following issues are considered likely at factories in Vietnam.

• Visual inspection depends on veteran inspectors
• Reference samples are old
• No limit samples are available
• Lighting at inspection locations is unstable
• Acceptance criteria differ between inspectors
• Defect classifications are unclear
• Inspection records are not retained
• Customer and internal standards do not match
• Defects are stopped at inspection without feeding back into process improvement
• Operators do not understand the causes of appearance defects

These are not individual inspector problems.
In many cases, the inspection system is inadequate.

CoatureVietnam can help transform visual inspection from work that relies on people’s eyes into a quality assurance process supported by standards and training.

Steps to stabilize appearance quality

The following sequence is effective for stabilizing appearance quality.

Step 1: Check customer requirements

First, determine the level of appearance quality required by the customer.

• Which appearance defects matter most?
• What is the permissible range?
• Is a reference sample available?
• Are limit samples available?
• Are inspection conditions defined?
• How are functional quality and appearance quality prioritized?

Unclear requirements here cause misunderstandings later.

Step 2: Define internal standards

Using customer requirements, establish criteria that can be applied internally.

• Accepted-product samples
• Defect samples
• Limit samples
• Defect classifications
• Acceptance criteria
• Inspection locations
• Inspection methods
• Recording methods

Standards make shop-floor decisions easier.

Step 3: Train inspectors

Creating standards alone is insufficient.
Inspectors need training to make judgments using the same criteria.

Training is effective when it uses defect samples as well as accepted products.
Looking at physical samples helps everyone understand what to examine and where rejection begins.

Step 4: Record inspection results

Always record inspection results.

Records reveal defect trends.
They also allow past conditions to be checked when a customer complaint occurs.

Step 5: Improve the source

When visual inspection finds a defect, trace back to its source.

Stopping defects at inspection alone does not reduce them.
Identify the cause in materials, methods, equipment, people, or management, and connect it to process improvement.

Visual inspection connects customer satisfaction with shop-floor improvement

Visual inspection does more than find defective products.

It is an important process for understanding customer quality requirements and reproducing them consistently on the shop floor.

A well-organized visual inspection system can be expected to provide the following benefits.

• Fewer customer complaints
• Stable outgoing quality
• Reduced judgment differences between inspectors
• Improved operator training
• Visible defect causes
• Reduced rework labor
• Shared quality standards with the customer
• Faster shop-floor improvement

Appearance quality is not only for the customer.
It also helps create a system that makes shop-floor decisions easier and less uncertain.

This also relates to CoatureVietnam’s guiding principle, “Coating the Future with Science and Care”.

Science means addressing appearance quality through standards, samples, records, and data, rather than intuition alone.
Care means creating an environment where operators and inspectors can make decisions without uncertainty.

How CoatureVietnam can help

CoatureVietnam can provide the following support for coating appearance quality.

• Organizing appearance defect items
• Supporting the use of reference and limit samples
• Standardizing inspection conditions
• Inspector training
• Creating visual inspection SOPs
• Creating defect classification tables
• Developing inspection record formats
• Supporting color, gloss, and film thickness control
• Checking booths, ovens, and equipment condition
• Analyzing causes of appearance defects
• Proposing recurrence-prevention measures
• Aligning customer and internal standards

Paint alone cannot always solve coating appearance problems.
Materials, processes, equipment, people, and management need to be examined together to stabilize quality.

Summary

Coating quality is not judged by function alone.
Customers perceive quality through appearance, including color, gloss, surface texture, contaminants, scratches, sagging, and unevenness.

Leaving visual inspection solely to intuition produces inconsistent judgments.
Reference samples, limit samples, inspection conditions, inspector training, records, and improvement activities are therefore needed.

Appearance quality is built into the process, as well as safeguarded through inspection.

The following perspective matters.

Appearance is the first quality the customer sees.
This is why it must be safeguarded through standards and systems rather than intuition.