You go to the mold maker with a drawing and a simple note saying – “matte finish,” “fine texture,” “leather texture,” “no gloss,” or simply “use VDI.” With the instructions, there can even be a photo or physical sample that can also accompany “match this finish.” Looks like the instructions are clear. But for mold makers there are several questions that remain unanswered. So, how to state texture requirements before tooling? You will learn it in this guide.
| Question | Answer |
|---|---|
| How to state texture requirements before tooling? | Give the mold maker clear details about the usage of texture and how the finished surface should look. Add the texture grade or depth, direction, reference sample, and approval requirements in the RFQ. |
Injection Mold Texture – Why Surface Specifications Must Be Defined Prior to Tooling
While making a mold, a pattern or finish is applied to the mold cavity and this is injection mold texture. But the final part can vary from that mold. The changes are due to resin, color, temperature, pressure, and cooling conditions.
- Mold surface finish: It is the inner side or you can say interior of the mold that controls how the final part will look and feel (polished, matte, etc.).
- Mold texture: A fine-grain, leather or geometric pattern is impressed into the steel.
- Finished-part surface appearance: The surface of the finished molded part (Material, Color, Process conditions, Gloss, Illumination, View point).
When we produce an injection moulding, the texture of the steel of the mould surface gets into the plastic of the part. However, the material, color, part temperature, injection pressure and part cooling time can all affect the finish of the part so it will not look exactly like the mould surface.
This finish should be defined prior to making the mold. The time required to polish and retexture the steel to reverse a finish change after a mold has been made is not cost effective.
Why Basic Texture Names Do Not Fully Describe the Finish?
Let’s say you just said to the mold maker, “Leather grain.” That doesn’t explain the type of grain pattern, size of the grain, direction or depth of the grain. Not even when it says to “identify the approved sample by part number or photo and agree on the method.” If the sample is not visually clear it might cause confusion. Also, there ought to be a method agreed on for evaluating the final texture.
So, how to state texture requirements before tooling? Well, a texture specification should clearly identify the standard, grade, pattern, location, or reference sample wherever applicable.
The following table will make it clearer.
| Buyer says | What is missing? |
|---|---|
| Matte finish | Standard, grade, area, acceptance |
| Fine texture | Texture depth/grade |
| Leather grain | Pattern, scale, direction, depth |
| Match sample | Sample identification and approval method |
| VDI finish | VDI grade |
| SPI finish | SPI grade |
How to Write a Tooling-Ready Mold Texture Specification
Here is what your tooling-ready mold texture specification should contain.
1. Define Exactly Where the Texture Applies
First select the surfaces that require texture or polish, such as the A-surfaces, B-surfaces or cosmetic zones. After selection show these spots clearly on the 3D CAD or maybe the 2D drawing. This helps prevent confusion about parting lines, logos or bosses and inserts and also about surface changes.
2. Talk about Texture Kind
Convey the look or pattern of the texture the way you want. Also tell the making technique that you prefer like EDM, laser texturing, blasting, or chemical etching.
The finish grade and a reference of the texture are required by the mold manufacturer.
3. Provide the Standard and Grade
Surface finish standard or grade and a specific texture reference, both are important for the mold maker. For example it can be SPI/SPE or VDI 3400.
Here if you write only “SPI surface finish” or “VDI finish” it will not give clear instructions. So always add the standard and a grade.
For example:
- VDI 3400 N24
- SPI B-2
If you are using SPI and VDI grades just as a direct conversion for each other, that would be a wrong thing. Each of them uses different process methods and they may result in different visual aspects though surface roughness looks almost similar.
4. Give Texture Depth, Pattern Scale, or Geometry Where Needed
For some of the finishes standard grades work well but if you want a special pattern then these don’t give enough details.
For pattern-based mold texture specifications, you should include pattern name or code, scale of pattern, depth of texture, direction or orientation, boundaries and transition areas.
For example:
How to state texture requirements before tooling leather?
The specification for a custom leather pattern may need considerably more information than simply stating a VDI grade.
5. Mention Texture Direction and Orientation
Direction has a key role in appearance. It matters a lot for a brushed, line, leather or other types as changing the direction will make the part look different.
6. Discuss How the Texture Will Be Approved
It is important to choose the reference and approval methods before the beginning of the tooling. You can use a texture plaque, master sample, molded part, along with the required viewing conditions and allowable variation.
SPI vs VDI 3400 vs Pattern-Based Texture: Which Is Better?
While telling the specifications, the best way to tell mold texture is how well you explain the details. Like you may be defining a surface finish level or you can be showing the actual texture pattern.
Standard references are usually SPI/SPE and VDI 3400. But it is not wise to treat any of these as a complete description of every textured surface.
| Specification approach | Best for | Main advantage | Main limitation |
|---|---|---|---|
| SPI/SPE | Polished/semi-polished finishes | Easy to understand and widely used | Does not describe custom pattern geometry |
| VDI 3400 | EDM-type textures | Common in European tooling | Grade does not fully describe custom visual pattern |
| Pattern reference | Leather/custom/brand textures | Shows the actual pattern and appearance | Requires a reliable reference |
| Physical master sample | Cosmetic-critical parts | Provides the clearest visual reference | Needs a controlled sample/approval process |
Why Ra Alone Is Not Enough to Specify Mold Texture
From the Ra value, you get the idea only about the average roughness; it gives no information about the pattern or the tactile feel. It is important to request a reference or a sample of an approved texture if you want to clearly define the visual texture of the molded part. It is highly possible for the two surfaces to have the same value of Ra but completely different visual patterns, such as linear scratches or pitting. The reason for it is that they also differ in:
- texture pattern and shape
- texture direction or orientation
- process or tooling used
- light reflection characteristics
- tactile feel
Therefore, you cannot rely on a single parameter of arithmetic mean roughness (Ra) to define the cosmetic texture of the surface. For technical documentation in Europe, there is a standard ISO 21920 which covers surface texture specification. But in case of cosmetic or custom textures, it is better to refer to specific roughness requirements together with a pattern, its location, and an approval sample. It also helps to create a quantified requirement for the mold maker and a reference visual appearance.
How Texture Requirements Affect Mold Design and Feasibility
Injection molding texture is a cause of concern before beginning with the mold design and not once you finish with it. This is because the texture you choose will affect draft angles, parting lines, shutoffs, ejection, slides, lifters, and even the overall mold design.
So it is better to review texture requirements during DFM and mold design, before finalizing the tooling details.
Texture and Draft Angle
There is the need for additional draft if you want to release part from the mold properly.
Though there is no recommendation for a specific draft angle for a given texture. But you can consider a number of factors, such as material, texture depth, geometry of the molded part, mold ejection system, texturing process, etc. It’s the mold designer who can evaluate these factors and establish a correct correlation between texture and draft. Here’s worth noting you will get results when checking and evaluation of texture and draft is made during mold design.
Texture Near Shutoffs, Ribs and Parting Lines
The areas of part that are textured near shutoffs, thin walls, ribs, slides, lifters, and parting lines require special attention. These require more draft for easy ejection.
The pattern may not match perfectly where the two mold halves meet, if the texture crosses the parting line. This can create a visible line or noticeable change in the texture. A careful checking during DFM can help find these issues before steel is cut.
Texture and Cosmetic Transitions
At surfaces which have texture, it must flow consistently from one surface to another. If there are any inconsistencies in the transition, it can produce a mismatch of texture, difference in sheen, witness marks, or visible boundaries.
Your drawing should specify where the texture begins and ends and how it is to be transitioned.
Texture and Material
The final appearance of a texture depends on the type of resin, color, content of filler, and molding conditions.
Therefore, the same texture may appear in different ways when the material or color changes. If there is any change in material or color, it would be best to check the appearance of the texture before production.
How Texture Requirements Affect Mold Cost and Lead Time
Texture can have an impact on the cost and lead time of the mold.
Surface preparation/polishing, EDM or chemical etching, laser texturing, masking and multiple texture areas, involvement of texture supplier, sample approval and corrections, additional polishing or rework, and even correction of texture issues after sampling can affect the cost and/or lead time of a mold.
Unclear texture requirements or more complex texture can cause delays in the mold production schedule if a texture correction needs to occur after sampling.
The least expensive texture specification is not necessarily the most economical if rework or delays are taken into account.
A Tooling-Ready Texture Specification Example
When a texture specification gives clear instructions to the mold maker, it is considered good.
For example, if you say “Apply leather texture to exterior,” it does not explain any of these – the exact area, pattern, direction, reference, or how the final texture will be approved.
A clear specification would be like this:
- Texture area: A-surface areas indicated on the drawing
- Texture type: Custom leather-grain pattern
- Reference: Approved physical texture plaque/supplier pattern ID
- Standard: VDI 3400 surface finish / SPI, if applicable
- Grade/depth: Based on the approved reference
- Pattern/depth: As defined by the selected texture supplier or approved reference
- Orientation: As shown on drawing
- Non-textured areas: Maintain specified polish/finish
- Draft review: Supplier to confirm texture and draft feasibility before steel cutting
- Approval: First-off molded sample compared to approved physical reference
- Production resin: [Exact resin grade]
The above specification guides the mold maker in a much better way. It fully explains the location of the texture, pattern, and orientation, as well as the process for final approval. Moreover, it also recognizes the need of the mold maker to review the texture draft before finalizing the tool design.
For custom leather patterns or custom grain patterns, avoid specifying an arbitrary depth value (e.g., 150 microns). It would be best to rely on the supplier’s recommended depth and pattern-scale for the selected process.
You can follow the same approach for other custom textures as well.
Texture Specification Checklist Before You Release the Tool
Approve tooling only after checking all texture areas. Here is the quick checklist to do so:
Texture Definition
- ☐ “Mark all textured areas” clearly on the drawing
- ☐ Decide on the required texture or pattern
- ☐ Include the SPI or VDI grade, if applicable
- ☐ Provide a texture reference, pattern ID, or approved texture plaque
- ☐ Decide on the texture depth or pattern size, if needed
- ☐ Define the required grain direction or orientation
Tooling & Feasibility
- ☐ Mark areas to be left smooth or requiring a different injection molding surface finish
- ☐ Check that the draft angles are compatible with the selected texture
- ☐ “Confirm with the mold maker” that the texture is feasible
- ☐ Agree on any steel-safe or tooling requirements before machining begins
Approval & Production
- ☐ If available provide a physical texture sample or reference
- ☐ Agree on inspection and approval procedure for first molded samples
- ☐ Define the exact production resin grade
- ☐ When required identify the texture supplier or pattern reference
Release rule: If the texture requirement can be understood in more than one way, you need to clarify it before steel cutting. It will always be cheaper and faster to correct a missing detail at this stage then having to rework the mold at a later stage.
Conclusion
The goal is to remove confusion before steel is cut. You can do so by defining the appearance, texture, location, depth, direction, and approval reference before the beginning of the tooling. Now, you know how to state texture requirements before tooling.
You can contact CustomMoldHub to help you out!
FAQ Section
What do you mean by T1 sample?
When a newly made injection mold produces a first trial sample, it is a T1 sample. T1 molded samples are compared with the approved physical texture reference.
What are the SPI surface finish grades for injection molding?
Common SPI grades are A, B, C, and D. These range from highly polished to matte finishes as following:
- A-1 to A-3 (high gloss)
- B-1 to B-3 (semi-gloss)
- C-1 to C-3 (low-gloss)
- D-1 to D-3 (matte)
Can two mold textures have the same Ra but look different?
Yes, it can happen because Ra does not describe pattern, direction, depth, or texture geometry. One may have a fine, random texture. Another may have a deep, directional pattern. Their pattern spacing, peaks, valleys, and direction can be different.