Almost every plastic product contains molded text.
Examples include:
- Company logos
- Part numbers
- Date codes
- Material identification marks
- Regulatory markings
- Safety warnings
From a CAD perspective, adding text is simple.
From a molding perspective, text becomes another geometric feature that must:
- Be machined into steel
- Fill properly with plastic
- Release from the mold
- Remain legible after production
Many text-related defects are not caused by the text itself.
They are caused by text being designed without considering how molds are manufactured and how plastic behaves during molding.
Engineering Problem
Poorly designed molded text often creates:
Manufacturing Issues
- Difficult machining
- Excessive EDM requirements
- Laser engraving limitations
- Increased polishing effort
Molding Issues
- Short shots
- Incomplete feature filling
- Flash around lettering
- Trapped air
Quality Issues
- Poor readability
- Rounded edges
- Inconsistent appearance
- Premature wear of fine details
In many projects, text is added late in the design cycle and receives little engineering review.
Unfortunately, small features can create disproportionately large manufacturing challenges.
Root Cause: Text Is a Micro-Feature
Injection molding reproduces the shape of the mold cavity.
This means every letter becomes a miniature molding feature.
For plastic to accurately reproduce text:
- Molten material must flow into the feature.
- Air must escape.
- The feature must cool properly.
- The part must eject without damage.
As letter size decreases, all four requirements become more difficult.
Fine text behaves similarly to thin ribs or micro-features.
The smaller the detail, the more sensitive it becomes to material flow, mold finish, and process variation.
Engineering Reference Data
Raised vs. Recessed Text
In most injection molding applications:
Preferred: Recessed Text
Benefits:
- Better protection against wear
- Less susceptible to damage
- Easier to maintain readability
- More consistent cosmetic appearance
Typical depth:
| Feature | Recommended Value |
|---|---|
| Recessed Text Depth | 0.25–0.50 mm |
| Maximum Practical Depth | 0.75 mm |
Raised Text
Benefits:
- Improved visibility
- Better tactile feedback
- Easier identification in some applications
Typical height:
| Feature | Recommended Value |
|---|---|
| Raised Text Height | 0.25–0.40 mm |
| Maximum Recommended Height | 0.50 mm |
Beyond these values, filling and ejection risks often increase.
Text Size Guidelines
For good readability after molding:
| Feature | Recommended Value |
|---|---|
| Character Height | ≥ 2.5 mm |
| Preferred Height | 3.0–5.0 mm |
| Stroke Width | ≥ 0.40 mm |
| Preferred Stroke Width | ≥ 0.60 mm |
Very small lettering can be molded, but manufacturability decreases rapidly below these values.
Draft Requirements
Every molded letter requires draft.
Without draft:
- Ejection forces increase
- Steel wear increases
- Letter edges degrade over time
Typical recommendations:
| Feature | Recommended Draft |
|---|---|
| Raised Text | 0.5°–1° per side |
| Recessed Text | 1°–3° per side |
| Textured Surfaces | Additional draft required |
As text depth increases, draft requirements become more important.
Font Selection Guidelines
Not all fonts mold equally well.
Recommended:
Good Choices
- Arial
- Helvetica
- Verdana
- Univers
Characteristics:
- Uniform stroke width
- Simple geometry
- Rounded transitions
Avoid:
- Decorative fonts
- Thin serif fonts
- Script fonts
- Sharp internal corners
Simple fonts generally provide better moldability and longer tool life.
Surface Finish Considerations
Texture directly affects text visibility.
Typical guidance:
| Surface Finish | Text Recommendation |
|---|---|
| SPI-A1/A2 Polished | Fine text possible |
| SPI-B Finish | Standard text recommended |
| SPI-C Finish | Increase text size |
| Heavy Texture (MT/VDI) | Increase text depth and size |
As texture depth increases, text must become larger to remain readable.
Mold Engineering Perspective
When reviewing molded text, we rarely focus on the wording itself.
Instead, we ask:
- Can this text be machined efficiently?
- Will the material fill the smallest features?
- Is the lettering large enough to remain readable?
- Will texture obscure the text?
- Can the part eject without damaging the feature?
One common mistake is designing text based on what looks good on a computer screen.
A 0.5 mm-high logo may appear perfectly readable in CAD.
After molding, it may become nearly invisible.
From a mold engineering standpoint:
Readability in production is more important than appearance in CAD.
DFM Quick Review Checklist: Molded Text
1. Text Geometry
□ Is character height at least 2.5 mm?
□ Is stroke width at least 0.4 mm?
□ Are sharp internal corners minimized?
□ Is the text large enough to remain readable after molding?
2. Raised or Recessed Design
□ Is recessed text preferred?
□ Is text depth limited to 0.25–0.50 mm?
□ Is raised text height controlled?
□ Has wear resistance been considered?
3. Draft and Ejection
□ Is draft applied to all lettering?
□ Is draft sufficient for text depth?
□ Will the text eject cleanly?
□ Has steel wear been evaluated?
4. Surface Finish
□ Will texture reduce readability?
□ Is text depth appropriate for the selected finish?
□ Has polishing access been considered?
□ Will logos remain visible after production?
5. Manufacturing Method
□ Can the feature be CNC machined?
□ Is EDM required?
□ Is laser engraving appropriate?
□ Has maintenance and future modification been considered?
Final Thoughts
Text is often treated as a cosmetic feature.
In reality, molded text is a functional molding feature that must be designed like any other engineering geometry.
The best molded text balances:
- Readability
- Manufacturability
- Tool life
- Cosmetic appearance
A logo or part number may occupy only a few square millimeters of a molded part.
Yet it can influence machining strategy, mold maintenance, molding performance, and long-term product quality.
Good molded text is not simply visible.
It is designed to be manufactured reliably.