Common Tablet Defects Caused by Worn Tooling | Troubleshooting Guide

Tablet defects cost manufacturers time, materials, and money. While formulation and press settings are often blamed first, worn or damaged tooling is frequently the root cause. Identifying tooling-related defects early prevents batch rejections and production downtime.

This guide covers the most common tablet defects caused by worn dies and punches, how to identify them, and what corrective actions to take.

Sticking and Picking

What It Looks Like:

• Sticking: Tablet material adheres to the punch face, leaving a rough or incomplete tablet surface

• Picking: Small amounts of material are pulled from the tablet surface, leaving pits or marks — especially in embossed areas

Tooling Causes:

• Rough or worn punch tip surface (Ra value increased from wear)

• Damaged or scratched punch tip

• Worn embossing (letters/logos) creating undercuts where material gets trapped

• Loss of coating (chrome, DLC) exposing bare steel

How to Confirm It Is Tooling-Related:

• If sticking occurs on specific stations only → those specific punches are worn

• If sticking occurs on all stations → check formulation first, then tooling

• Inspect punch tips under magnification — worn tips show visible roughness

Corrective Actions:

1. Polish punch tips to restore smooth surface finish (temporary fix)

2. Apply DLC or chrome coating to punch tips

3. Replace worn punches if surface cannot be restored

4. For embossed punches, replace when embossing detail is worn

Capping

What It Looks Like:

• The top or bottom layer of the tablet separates partially or completely from the tablet body

• Appears as a "cap" lifting off the tablet surface

Tooling Causes:

• Worn punch tip edges (bevels worn away, creating sharp edges that cut into the tablet)

• Excessive cup depth from tip wear (changes compression dynamics)

• Worn die bore allowing air entrapment during compression

• Mismatched upper and lower punch tip profiles (one worn more than the other)

How to Confirm It Is Tooling-Related:

• If capping occurs on specific stations → inspect those punches

• Compare cup depth of worn punches vs new punches — if significantly different, tooling is the cause

• Check die bore diameter — worn bores allow air entrapment

Corrective Actions:

1. Replace punches with worn tip edges

2. Ensure upper and lower punch cup depths match within specification

3. Replace dies with worn bores

4. Consider beveled-edge punch tips to reduce capping tendency

Lamination

What It Looks Like:

• The tablet splits into horizontal layers (like pages of a book)

• Similar to capping but the separation occurs within the tablet body, not at the surface

Tooling Causes:

• Worn die bore allowing excessive air entrapment

• Worn punch tips changing the compression profile

• Scored die bore creating friction that disrupts tablet formation

• Misaligned punches (bent barrels) causing uneven compression

How to Confirm It Is Tooling-Related:

• Measure die bore diameters — worn bores are a primary cause

• Check punch barrel straightness — bent barrels cause uneven compression

• If lamination occurs on specific stations, the tooling at those stations is likely the cause

Corrective Actions:

1. Replace dies with worn or scored bores

2. Replace punches with bent barrels

3. Ensure proper die bore taper (slight taper aids air escape)

4. Check and correct punch-to-die alignment

Weight Variation

What It Looks Like:

• Tablets from the same batch have inconsistent weights

• Weight variation exceeds pharmacopeial limits (typically ±5% for tablets over 250mg)

Tooling Causes:

• Worn die bores (different bore diameters across stations = different fill volumes)

• Worn lower punch tips (different cup depths = different fill volumes)

• Inconsistent punch lengths (worn heads = different compression positions)

• Binding punches (scored barrels) not moving freely in the turret

How to Confirm It Is Tooling-Related:

• Weigh tablets from individual stations — if specific stations consistently produce heavy or light tablets, those tooling sets are worn

• Measure die bore diameters across all stations — variation indicates wear

• Measure punch overall lengths — worn heads reduce effective length

Corrective Actions:

1. Replace dies with bore diameters outside tolerance

2. Replace punches with worn tips or heads

3. Ensure all punches in a set have consistent overall length (within 0.02mm)

4. Replace binding punches with scored barrels

Tablet Hardness Variation

What It Looks Like:

• Tablets from the same batch have inconsistent hardness readings

• Some tablets are too soft, others too hard

Tooling Causes:

• Worn punch heads receiving inconsistent compression force from rollers

• Worn punch tips with different cup depths across the set

• Binding punches not reaching full compression position

• Worn die bores allowing different fill volumes (weight affects hardness)

Corrective Actions:

1. Replace punches with worn heads

2. Ensure consistent cup depth across all punches in the set

3. Replace binding punches

4. Address weight variation first (weight directly affects hardness)

Surface Defects (Rough, Dull, or Marked Tablets)

What It Looks Like:

• Tablets have rough or dull surfaces instead of smooth, glossy finish

• Visible marks, lines, or patterns on tablet surface

• Ring marks around the tablet edge

Tooling Causes:

• Scored die bore transferring marks to tablet edge

• Worn or chipped punch tip edges creating ring marks

• Corrosion pits on punch tips transferring to tablet surface

• Worn punch tip surface finish (Ra value increased)

Corrective Actions:

1. Polish punch tips to restore surface finish

2. Replace dies with scored bores

3. Replace punches with chipped edges

4. Improve tooling maintenance to prevent corrosion

Chipping and Edge Defects

What It Looks Like:

• Small chips or fragments breaking off tablet edges

• Rough or crumbling tablet edges

Tooling Causes:

• Worn punch tip edges (bevel worn away)

• Worn die bore edge (chamfer worn away)

• Chipped punch tips transferring defects to tablets

Corrective Actions:

1. Replace punches with worn or chipped edges

2. Replace dies with worn bore edges

3. Consider beveled-edge punch tips for formulations prone to chipping

Troubleshooting Decision Table

Use this table to quickly identify whether a defect is tooling-related:

Key Rule: If a defect occurs on specific stations only, the tooling at those stations is almost certainly the cause. If it occurs on all stations, check formulation and press settings first, then tooling.

Prevention — Maintenance Schedule

The best way to prevent tooling-related defects is a proactive maintenance program:

Conclusion

Most tablet defects have multiple potential causes — formulation, press settings, and tooling. The key to efficient troubleshooting is isolating the cause. If defects appear on specific stations, check the tooling first. If defects appear across all stations, check formulation and press settings first, then tooling.

Regular tooling inspection and timely replacement prevent most tooling-related defects before they cause batch rejections. EMMKAY INDUSTRIES manufactures precision tablet dies and punches designed for consistent performance — contact us when it is time to replace your tooling.