Preventing coating problems through coating planning and the 4M approach

Are you treating coating as just a task?

When a coating problem occurs, the factory floor may start by asking, “Was the application method wrong?”, “Was the paint unsuitable?” or “Was there a problem with the operator’s skills?”

These are, of course, important checks.

To stabilize coating quality, however, we need to take another step back.

The question is, “What kind of coating film should we have been producing in the first place?”

Coating is more than applying paint to a product. It is a process that gives the product surface the required appearance, protection, durability and functionality.

What coating actually creates is the coating film formed on the product surface, rather than the paint itself.

CoatureVietnam starts from this principle when examining coating problems.

The purpose of coating extends beyond adding color

Coating is sometimes seen as a task for adjusting color and gloss.

In industrial coating, however, its role goes beyond appearance.

For example, coating can serve the following purposes.

• Creating the required product appearance
• Protecting metal from rust
• Protecting the substrate surface
• Providing heat resistance or chemical resistance
• Providing functions relating to wear, sliding or electrical insulation
• Providing performance suited to the product’s service environment

Coating is therefore a process that adds value to a product surface.

When considering coating quality, the important question is not only which color to apply. The purpose the coating film must serve needs to be clear.

Does the coating prioritize appearance? Does it prioritize rust protection? Does it require special functions such as chemical resistance or heat resistance?

Different purposes require different paint, film thickness, surface preparation and drying conditions.

Selecting good paint alone does not produce a good coating film

When coating problems occur, the thought may be, “Would changing the paint solve it?”

Paint selection is, of course, important. Paint that does not suit the workpiece or required performance can cause poor adhesion, inadequate drying or insufficient durability.

Using good paint does not, however, guarantee a good coating film.

Coating film quality is determined by a combination of conditions such as the following.

• Workpiece material and surface condition
• Condition of surface preparation
• Compatibility between paint and thinner
• Thinning ratio and viscosity
• Application method
• Film thickness
• Drying and curing conditions
• Spray booth and oven capacity
• Operator skills
• Inspection criteria and control methods

Coating quality is created by the entire process, as well as the paint.

Paint is an important material for creating a coating film. However, the final film quality changes according to the application method, equipment and conditions used with that material.

Coating film assurance means producing a film that meets performance requirements

The concept of coating film assurance is one of the first things to clarify in coating planning.

Simply put, coating film assurance means producing a coating film that meets the required functions and quality.

For example, it involves the following checks.

• Do color and gloss meet requirements?
• Is the required film thickness achieved?
• Is adhesion sufficient?
• Can the film withstand the service environment?
• Are rust protection and corrosion protection requirements met?
• Is there any concern regarding the expected service life?

Even if the finish looks good after coating, insufficient adhesion can cause peeling during use. Even if the color matches, insufficient film thickness can mean inadequate rust protection or durability. Good paint may fail to deliver its intended performance if drying conditions are unsuitable.

Coating planning therefore needs to begin by clarifying what the coating film must assure.

Coating film control means reducing variation to produce consistent films

The next important concept is coating film control.

Many conditions change every day on the coating floor.

Air temperature, humidity, paint condition, thinning ratio, viscosity, spray conditions, drying conditions, equipment condition and operator judgment can all vary. If these changes are left uncontrolled, the finish will not be consistent, even with the same paint.

Coating film control means understanding these variable factors and making the resulting film as uniform as possible.

This requires controlling the conditions that affect the result, rather than looking only at the result itself.

Examples include the following.

• Specifying the thinning ratio
• Measuring viscosity
• Measuring film thickness
• Checking drying temperature and time
• Recording the paint batch
• Standardizing operating conditions
• Keeping records that allow causes to be traced when defects occur

Weak coating film control makes it difficult to trace causes when defects occur. In contrast, recorded conditions make it easier to identify what changed.

Coating planning is process design, as well as paint selection

Coating planning means more than deciding which paint to use.

Proper coating planning considers the following points together.

• Purpose of coating
• Required coating film performance
• Workpiece material, shape, quantity and weight
• Surface preparation method
• Coating system or application process
• Paint and auxiliary materials to be used
• Thinning conditions
• Film thickness
• Drying and curing conditions
• Coating equipment
• Operator skill level
• Inspection criteria
• Safety
• Working environment
• Response rules when defects occur

Selecting the paint alone does not complete the coating plan.

For example, high quality requirements combined with insufficient equipment capacity force the factory floor to overextend itself. If the application method or fixtures do not suit a complex workpiece shape, uneven film thickness or missed areas become more likely. If the equipment cannot reproduce the drying conditions, coating film performance will not be consistent.

Coating planning connects materials, methods, equipment, people and control criteria to produce the required coating film consistently.

Checks for coating planning using the 4M approach

CoatureVietnam organizes coating plans from the 4M perspective.

Material: materials

Under Material, we check paint, thinner, surface preparation chemicals and repair materials.

What matters is more than whether a material is good on its own. It must suit the workpiece, application method, drying conditions and required performance.

Even with the same paint, an unsuitable thinner affects drying behavior and the finish. When switching from imported paint to a locally sourced product, checks must cover adhesion, drying behavior, ease of achieving film thickness and application workability, as well as color.

Method: methods

Under Method, we check application methods, surface preparation, thinning ratio, viscosity, film thickness, drying conditions and inspection methods.

Different methods produce different coating films, even with the same materials.

Operators judge thinning differently. Spray distances differ. Film thickness checks use different criteria. Decisions about drying time are unclear.

Quality cannot be consistent under these conditions.

Application methods need to be defined as standard conditions, rather than relying only on workplace experience.

Machine: equipment

Under Machine, we check spray booths, spray guns, ovens, conveyors, fixtures, exhaust equipment and surface preparation equipment.

Having the equipment is not enough. We need to check whether it functions adequately for the workpiece shape, quantity, required quality and production takt time.

Insufficient oven capacity may prevent adequate curing. Unstable exhaust makes appearance defects from mist or dust more likely. Unsuitable fixtures create areas that are difficult to coat, resulting in missed areas or uneven film thickness.

Man: people

Under Man, we check operator skills, training, judgment criteria and workload.

Coating readily depends on human judgment and feel. The skills of experienced operators are very important.

However, a process whose quality depends only on one particular skilled operator cannot be described as stable.

What matters is creating conditions that help operators do good work consistently, rather than blaming them.

Work standards, training, inspection criteria, records and decision rules for abnormalities help create a coating process that is less dependent on individuals.

Coating planning issues commonly encountered in Vietnamese factories

In some Vietnamese factories, work begins before the coating plan has been fully defined.

Examples include the following issues.

• The purpose of coating has not been clearly shared
• Customer requirements are conveyed only as paint names or color names
• Workpiece material and surface condition have not been adequately checked
• Surface preparation conditions and application conditions are considered separately
• Film thickness and drying conditions are not recorded
• The process depends on operator experience
• Equipment capacity does not match required quality
• There are no records for tracing causes when defects occur
• Purchasing, quality assurance, production engineering and the factory floor have different understandings
• The Japanese head office and Vietnamese factory understand quality requirements differently

These may seem like separate problems, but in some cases they actually arise from inadequate coating planning.

To prevent coating problems, first clarify the purpose of coating and the required coating film, then check the 4M factors.

Basic questions for coating planning

When reviewing a coating process, starting with questions such as these makes it easier to organize the issues.

Purpose of coating

• Is this coating intended for appearance, protection or adding a function?
• Which quality characteristic matters most to the customer?
• Will the product be used indoors or outdoors?
• Are there special requirements such as heat resistance, chemical resistance or rust protection?

Required coating film

• Is the required film thickness clear?
• Are there acceptance criteria for appearance, adhesion and durability?
• What scope of coating quality needs to be assured?
• Are quality criteria shared with the customer?

Materials

• Is the reason for selecting the current paint clear?
• Are the thinner and thinning ratio standardized?
• Are paint batches and storage conditions controlled?
• When considering an alternative paint, do you also check compatibility with the process?

Methods and equipment

• Are surface preparation conditions standardized?
• Are drying temperature and time recorded?
• Can the current equipment consistently produce the required quality?
• Are there any problems with the booth, oven, fixtures or conveying?

People and management

• Are there standard work instructions?
• How are new operators trained?
• Does quality vary between operators?
• Are decision criteria clear when defects occur?
• Are there records for tracing causes when quality varies?

These questions are intended to understand the coating process correctly and find a starting point for improvement, rather than blame the factory floor.

How CoatureVietnam can help

CoatureVietnam does not treat coating problems as simply mistakes on the factory floor.

We check coating processes from the 4M perspective and review the coating plan itself to help create processes that are less likely to develop problems.

Paint Voyager

We propose paint and auxiliary materials suited to the required coating film, workpiece, application method and drying conditions. Our focus is compatibility with the process, as well as supplying materials.

Coat Visioner

We make the condition of the coating process visible and organize information on film thickness, operating conditions, defect trends and equipment status. We identify improvements through records and observation, rather than feel alone.

Work standards and process control

We support defect reduction, standardization, operator training and the development of inspection criteria. We aim to create consistent coating processes that do not depend excessively on operator experience.

Coat Systemizer

We support the design of the entire process, including coating lines, spray booths, ovens, conveying, surface preparation, exhaust and operator movement. We aim to create equipment and processes that improve quality, productivity and safety together.

Coating the Future with Science and Care.

Coating processes need science.

It is important to make paint, film thickness, viscosity, drying conditions, equipment capacity, operating conditions and defect trends visible, organize causes and implement improvements that can be reproduced.

Coating processes also need care.

Avoid overburdening operators. Reduce the burden of rework and recoating. Provide a safe, comfortable working environment. Create conditions where quality is consistent and people on the factory floor can work positively.

CoatureVietnam sees coating as more than selling materials.

Organizing coating processes scientifically, reducing the burden on the people who work in them and increasing the value of manufacturing operations: this is what coating improvement means to us.

Summary

Preventing coating problems requires more than responding after defects occur.

First, clarify the purpose of coating and the required coating film. Then check materials, methods, equipment, people and control criteria together.

Coating quality cannot be maintained through factory floor effort alone. It needs to be designed, controlled and improved as a process.

If coating defects, quality variation, rework or recoating are issues in a Vietnamese factory, start by checking what kind of coating film you should be producing.

That is the first step in preventing coating problems.