When considering coating line productivity, equipment is often the first focus.

The number of coating booths.
Drying oven length.
Conveyor speed.
Spray gun performance.
The number of operators.
Paint drying characteristics.

These are certainly important.
However, coating line productivity is not determined by equipment capacity alone.

In actual workplaces, productivity may be lost at a more fundamental level.

Products are difficult to hang.
Loading fixtures takes time.
Hanging leaves fixture marks on coated surfaces.
Surface preparation liquid does not drain readily.
The workpiece heats up slowly in the drying oven.
Interiors cannot be fully coated because coating takes place after assembly.
Color or product changes cause major interruptions for setup.

These are not simply coating equipment problems.
They arise because product design, fixture design, assembly sequence, and production planning are not suited to the coating process.

Improving coating line productivity requires reviewing the complete sequence of loading, transport, surface preparation, drying, unloading, and inspection, as well as paint application.

1. A coating line involves more than application time

When discussing coating processes, attention tends to focus on spraying time.

However, work before and after application accounts for a substantial share of an actual coating line’s operations.

• Prepare products
• Load them onto fixtures
• Perform surface preparation
• Drain off water
• Dry
• Transport to the coating booth
• Apply the coating
• Allow flash-off
• Bake
• Cool
• Unload from fixtures
• Inspect
• Repair
• Pack

Even if spraying alone becomes faster, overall line productivity will not improve if loading and unloading remain slow.

Fixture changes, color changes, product changes, and setup time are particularly significant losses in high-mix, low-volume production.

Coating line productivity must be considered as a flow that includes the work before and after coating, rather than application alone.

2. A lack of hanging holes alone can reduce line capacity

For suspended coating, stable hanging of the substrate is fundamental.

However, when a product lacks suitable hanging holes or hanging locations, the shop floor has to improvise ways to hang it.

This shop-floor ingenuity can actually impose a considerable burden.

A lack of hanging holes causes the following problems.

• Loading takes time
• Hanging methods vary between operators
• Products swing
• Fixture marks appear on coated surfaces
• Important surfaces remain uncoated
• The hanging orientation makes surface preparation liquid difficult to drain
• Products are unstable in the drying oven
• The risk of falling increases

On a coating line, a difference of just a few seconds in loading time per item becomes a large difference over a day.
Inconsistent hanging also causes variations in film thickness, missed areas, fixture marks, and drying condition.

Hanging holes may appear to be a minor design feature.
In coating processes, however, they are an important condition affecting quality and productivity.

3. Good fixtures reduce operator workload and stabilize quality

Fixtures are more than tools for supporting products.

Good fixtures support coating process quality and productivity.

Good fixtures meet the following conditions.

• Hold products securely
• Do not obstruct surfaces to be coated
• Position products so surface preparation liquid drains readily
• Hold products in an orientation that facilitates drying
• Allow operators to load and unload easily
• Minimize problems from fixture marks
• Resist deformation during repeated use
• Easy to clean
• Require little setup during product changes

Poor fixtures, by contrast, force the shop floor to cope continually with small difficulties.

Difficult to load.
Difficult to unload.
Heavy.
Products swing.
Some surfaces become difficult to coat.
Paint accumulates on fixtures.
The previous color remains.
Products are scratched.

Under such conditions, operator workload increases and quality is unstable.

Fixture design is part of equipment design and quality design.

4. Deciding where fixture marks appear is also a design issue

Suspended coating requires contact between fixtures and products.
It may therefore be difficult to eliminate fixture marks completely.

What matters is where the fixture marks appear.

Fixture marks on important appearance surfaces require rework or recoating.
Marks on functional surfaces may affect assembly or performance.
A fixture contact point in an area requiring rust prevention may also become a starting point for rust.

The following points must therefore be checked during product and process design.

• Where may fixtures contact the product?
• Can appearance surfaces be avoided?
• Can functional surfaces be avoided?
• Is the location easy to repair?
• Does it pose a rust-prevention risk?
• Can products be hung consistently at the same location?

Fixture marks should be considered at the design stage, rather than dealt with ad hoc on the shop floor.

5. Assembly sequence changes the difficulty of coating

Even for the same product, coating difficulty changes substantially depending on whether coating takes place before or after assembly.

Coating after assembly may appear simpler to manage because the product can be processed in its finished form.
However, paint may have difficulty reaching interiors and gaps after assembly.

Assembly can also create structures that allow surface preparation liquid to enter but prevent it from draining.
In such cases, rust or blistering may develop some time after coating.

Coating individual parts before assembly, on the other hand, makes application and surface preparation easier and facilitates internal rust prevention.
However, it increases the risk of damage during subsequent assembly and the effort needed to manage parts.

The better option must be decided for each product.

Points to check are as follows.

• Will areas remain uncoated after assembly?
• Is internal rust prevention required?
• Can surface preparation liquid drain out?
• Is drying easy?
• Will assembly after coating cause scratches?
• Will parts management become excessively complicated?
• Which option provides greater overall line productivity?

Assembly sequence is an important design condition directly linked to coating quality and productivity.

6. Orientations that retain surface preparation liquid cause problems in later processes

Surface preparation may include degreasing, cleaning, chemical conversion treatment, and water rinsing.
These are important for stabilizing coating quality.

However, an unsuitable hanging method or orientation makes surface preparation liquid and water difficult to drain.

Retained liquid causes the following problems.

• Drying defects
• Rust
• Poor adhesion caused by residual chemicals
• Blistering
• Discoloration
• Cissing in the coating film
• Liquid seeping out later

Closed-pocket structures, pipes, joints, and internal spaces with few openings require particular attention.

It is not enough for surface preparation liquid to enter.
Drainage and drying must also be considered.

When designing fixtures and choosing hanging orientations, the flow of surface preparation liquid should therefore be checked as well as the surfaces to be coated.

7. Drying oven performance is also affected by workpiece orientation and fixtures

Drying oven performance is not determined only by its setpoint and length.

In practice, the workpiece temperature rise changes with substrate material, sheet thickness, shape, hanging arrangement, fixture heat capacity, and loading density.

For example, thick parts heat slowly, while thin parts heat quickly.
Large, heavy fixtures may absorb heat and affect the workpiece temperature rise.
Densely packed products create areas that hot air cannot readily reach.

As a result, different parts may reach different curing conditions even in the same drying oven.

Insufficient drying leads to poor adhesion, undercuring, insufficient chemical resistance, gloss defects, and discoloration.
Overbaking leads to discoloration, gloss changes, and substrate deterioration.

To stabilize drying conditions, the actual workpiece temperature must be checked, as well as the oven setpoint.
The influence of fixtures and hanging arrangements on drying quality should also be examined.

8. Fixtures and production planning are important on lines with frequent color and product changes

Color and product changes occur frequently in high-mix, low-volume production.

If fixtures differ substantially between products, cleaning takes a long time, or paint losses during color changes are high, productivity drops significantly.

Cleaning during color changes can be a particularly heavy burden in powder coating.
In solventborne coating as well, inadequate cleaning of hoses, guns, cups, and tanks causes color contamination.

Lines with frequent color and product changes need to check the following points.

• Can fixtures be standardized for shared use?
• Can loading changeover time for each product be shortened?
• Can the color-change sequence be improved?
• Can similar colors be produced together?
• Is the equipment configuration easy to clean?
• Is there an SOP to prevent residues of the previous color?
• Are there rules for first-piece inspection after a color change?

Coating line productivity depends on reducing setup time as well as the speed of coating an individual item.

9. Organize hanging arrangements, fixtures, and assembly sequence through the 4Ms

Problems involving hanging holes, fixtures, and assembly sequence become clearer when organized through the 4Ms.

Material: materials

Check whether substrates and paints suit the hanging arrangements and drying conditions.

• Is the substrate sufficiently heat-resistant?
• Are differences in sheet thickness excessive?
• Does the substrate suit the paint’s drying conditions?
• Does the structure tend to retain surface preparation chemicals?
• Does the fixture material adversely affect coating or drying?

Method: methods

Check hanging methods, coating sequence, assembly sequence, and surface preparation methods.

• In which orientation should the product be hung?
• Where should fixture contact points be located?
• Should coating take place before or after assembly?
• Is the color-change sequence appropriate?
• Does the method allow surface preparation liquid to drain?
• Does the orientation facilitate drying?

Machine: equipment

Check fixtures, transport systems, booths, drying ovens, and surface preparation equipment.

• Are the fixtures stable?
• Do products swing during transport?
• Are products easy to coat inside the booth?
• Does workpiece temperature rise adequately in the drying oven?
• Can liquid drain out in the surface preparation equipment?
• Are fixtures easy to clean and maintain?

Man: people

Check operator workload, safety, and differences in skills.

• Is loading and unloading difficult?
• Are heavy items being handled in a way that places excessive strain on operators?
• Do hanging methods differ between operators?
• Are difficult-to-coat areas being compensated for through operator skill?
• Are working postures comfortable?

10. Management perspective: feed information from the coating shop floor back to design

Problems involving hanging holes, fixtures, and assembly sequence sometimes cannot be resolved on the shop floor alone.

Even if the coating shop floor finds a product difficult to coat, the same problem will recur unless this information reaches design and production engineering.

A system for feedback from the coating shop floor to design and production engineering is needed.

For example, sharing the following information is useful.

• A list of parts that are difficult to hang
• Areas prone to missed coating
• Structures from which surface preparation liquid drains poorly
• Areas where fixture marks cause problems
• Products that take a long time to load and unload
• Materials and sheet thicknesses prone to drying defects
• Products with high losses during color or product changes
• Tasks operators find burdensome

Applying this information to subsequent designs and process improvements allows the coating line to improve gradually.

Feedback from the coating shop floor is not mere complaint.
It is important information for improving process design.

11. Particular points to check in factories in Vietnam

Factories in Vietnam may commonly face the following coating line productivity issues.

• Fixtures are handmade on the shop floor
• Hanging methods are not standardized for each product
• Hanging methods differ between operators
• Processing takes place in an orientation that drains surface preparation liquid poorly
• Shop-floor effort compensates for structures that are difficult to coat
• Coating after assembly makes internal rust prevention difficult
• Frequent color changes require long cleaning times
• Previous colors remain on fixtures and cause color contamination
• Workpiece temperature in the drying oven is not checked
• Shop-floor problems are not fed back to design

These issues may be improved by reviewing fixtures, hanging arrangements, assembly sequence, and production planning, even without installing or replacing coating equipment.

When reviewing a coating line, CoatureVietnam considers it important to assess not only equipment capacity, but also whether the products suit the line.

12. Coating the Future with Science and Care

Hanging holes, fixtures, and assembly sequence may appear to be minor shop-floor details.

However, they have a major influence on coating quality and productivity.

Products that are easy to hang can be handled faster.
Stable fixtures reduce film thickness variation.
Orientations that drain surface preparation liquid prevent rust and blistering.
Hanging arrangements that facilitate drying prevent undercuring.
Comfortable working postures reduce operator strain.

This is precisely what CoatureVietnam means by bringing science and care to coating.

Science means examining hanging arrangements, fixtures, workpiece temperature, film thickness, and drying conditions logically.
Care means building systems that stabilize quality without putting excessive strain on operators.

Coating line productivity is not determined by equipment capacity alone.
Quality and productivity can improve substantially by considering product design, fixtures, assembly sequence, surface preparation, drying, and operator movements together.

Practical checklist

Check the following points concerning coating line productivity and quality.

• Does the product have suitable hanging holes?
• Does the hanging location avoid affecting appearance and functional surfaces?
• Is loading onto fixtures easy?
• Do hanging methods differ between operators?
• Are there any areas where fixture marks cause problems?
• Are products processed in an orientation that allows surface preparation liquid and water to drain?
• Are there parts that would be better coated before assembly?
• Are there areas that remain uncoated when coating takes place after assembly?
• Are drying differences caused by different materials and sheet thicknesses checked?
• Is workpiece temperature checked?
• Are setup times for color and product changes known?
• Can fixtures be standardized for shared use?
• Are fixture cleaning and maintenance standardized?
• Is coating shop-floor feedback communicated to design and production engineering?

CoatureVietnam’s perspective

Improving coating line productivity requires considering hanging holes, fixtures, assembly sequence, surface preparation, and drying conditions as well as coating equipment.

CoatureVietnam supports coating quality and productivity improvements in factories in Vietnam through on-site process reviews, review of fixtures, transport and drying conditions, and reduction of operator workload.

Improving a coating line is not simply about applying paint faster.
It means establishing a process in which the shop floor can produce stable, reproducible quality without excessive strain.