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Mold Texturing: How to Add Desired Finishes to Plastic Parts

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Don’t leave the finish on your product open to interpretation by your mold fabricator! We help you get to grips with the mold texturing that results in the finish on your injection molded plastic parts. We explore how to specify the textures you require, technical considerations such as Ra values and draft angles, possible texturing methods, and more.

 

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General points to get started with mold texturing.

These points roughly cover the ‘why’ of mold texturing to add finishes to your product:

  • Consider the purpose and function of the finish/texture for your product – the product may need a texture to make it non-slip or to be very slick and shiny, and textures may also be chosen for purely aesthetic reasons. Think about why you are adding a texture in each specific place. For example, an iPad case needs to look good, but the texture needs to make it easier for the user to grip the case and protect the iPad from being dropped.
  • Select the right texture/finish for your needs – consider the depth and scale of the texture, i.e. how deep and rough it is on the product, and also the pattern of the texture itself which could be anything from a brushed finish to alligator skin!
  • Be aware of the cost of application – highly complex textures could add a lot of cost to the tooling which might make the project unworkable financially, so research the textures and find a balance between what you need and what it will cost.
  • Choose molding processes to maintain consistency – you want to make sure that your products all have a consistent texture across batches, so you should select the right type of texture application, mold design, and processes to enable that as rough or smooth, it can be hard to get products out of the mold depending on their finish. (02:55)

 

Rules of thumb for mold design with textures in mind.

Don’t forget to add draft angles to your 3D CAD models for the mold as these are crucial for being able to eject the parts from the tooling. These draft angles are extremely small spaces that stop the part from being jammed inside and scuffing the texture upon removal. A helpful analogy here is children making sandcastles with a shaped bucket…these buckets were always at an angle to allow the compacted sand to be released easily. The angle required to be built into the mold varies depending on the type of texture being used, with lighter textures requiring smaller draft angles and rougher/heavier textures requiring steeper ones.

Here are some examples and approximate draft angles required to maintain the integrity of the textures being applied:

  • A lighter texture would be something like a brushed or lightly stippled texture of 0.001″ – 0.005″ or 0.0254 to 0.127 mm depth. A draft angle of 1 – 2 degrees is typically sufficient.
  • A medium texture might be a leather or woven fabric effect of 0.005″ – 0.010″ or 0.127 to 0.254mm depth. A draft angle of 3 – 5 degrees is usually suggested.
  • A heavier texture can be wood grain and complicated geometric designs of 0.010″ – 0.020″ or 0.254 to 0.508mm depth. Draft angles here are the steepest, requiring at least 5 – 10 degrees. (07:59)

 

5 Common mold texturing methods.

  1. Sanding and Polishing – The traditional method of manually adding textures to the metal mold tooling, is still used to some degree in every toolmaking workshop today. It is time-consuming and labor-intensive and is done by skilled technicians who can polish the metal to a mirror finish suitable for smartphone cases and other items that need a high gloss finish.
  2. EDM Spark Erosion – Electrical sparks erode the tool’s surface in the shape of the electrode that is in contact with it. It is typically used for adding logos, shapes and pockets, rather than textures.
  3. Media Blasting – Typically sand, metal, or grit particles are blasted onto the metal tooling by a skilled operator to create the texture. This common, quick, and easy method is often used to add simpler, more uniform light/medium textures to tooling for products like grips for tool handles and sports equipment, and decorative finishes on appliances.
  4. Chemical Photoetching – This newer method is not the industry’s go-to method in terms of popularity and it can be used to create even complex and heavy textures in a wide variety of styles. A photoresist film is added to the area to be textured and then UV light cures it, chemicals are applied which etch the exposed areas, and then it is washed away leaving the texture etched into the tooling’s metal surface. For complex patterns like animal prints, geometric shapes, and other intricate textures, it’s a great option, as well as being fast, accurate, and uniform (in comparison to the more manual processes seen earlier, like sanding and polishing). This may be used for watch dials, textured grips on electronics, anything with a leather finish, luggage, and even auto parts like dashboards (both of the latter two require large and uniform patterns).
  5. Laser Etching – The most expensive method, also useful for large, uniform, and complex textures in products that are mass-produced on a very large scale, such as the automotive industry and where high accuracy is required such as the medical industry. A computer controls a laser beam to etch the desired texture onto the tooling and very intricate textures can be added, hence why it is used for medical devices that need to be biocompatible. (14:58)

Key benefits of Chemical Photoetching mold texturing.

Since the chemical photoetching process is the most popular method of mold texturing, let’s look at its key benefits:

  • Precision and detail are second to none.
  • It’s extremely versatile and it can add patterns to steel, aluminum, nickel, and even plastics.
  • The textures created are very durable.
  • It’s cost-effective today.
  • Consistency is good as the outcomes from this process are easy to control and repeat. (27:46)

 

Texture Roughness: Ra Value and Mold Tool Textures.

The Ra value helps us measure the peaks and troughs of a texture, i.e. how rough it is. The Ra value is the average distance between the peaks and troughs of the surface of the tooling in this case.
Ra is measured in micrometers (µm). The lower the Ra value, the smoother the surface is, and vice versa. For example, a fine wood grain texture may have an Ra value of 5-10 microns, whereas a stippled grip texture may be 20-30 microns.

As with almost any aspect of a new product, you should seek to specify your textures’ Ra values on your drawings for the mold fabricator so you get your expected results and leave no room for interpretation by the supplier. (30:30)

 

Using mold texture books to help specify your texture/s.

A mold texture book is a physical reference book with hundreds of small plates demonstrating the different surface finishes/textures you can choose from for your product. There are a few options (all including largely similar textures to select):

  • Yick Sang Texture Book (Classic Version): Features 240 unique texture plaques with four-digit codes. (Sofeast sell these to our customers on request).
  • LW Texture Book: Offers a variety of textures, including geometric, organic, and natural patterns.
  • Plastipol Mold Tech Texture Book: Provides a comprehensive guide to textures achievable with specific mold technologies.

When designing the product and specifying your textures, you can refer to the book and the precise texture/s you desire in your technical specifications and drawings that are received by the tooling fabricator, again, to avoid any guesswork on their side. (34:27)

You can see an example of the Yick Sang mold texturing book below (courtesy of yicksangltd.com):

yick sang mold texturing book

Some examples of typical textures from the Yick Sang texture book.

 

These examples go from smooth to rough:

  • YS1286: Mirror Finish: A super smooth and reflective surface, perfect for high-gloss products like phone cases or kitchen appliances.
  • YS1629: Crocodile Leather: A realistic crocodile skin texture, perfect for adding a luxurious touch to handbags or shoes.
  • YS1754: Bamboo Grain: A subtle bamboo grain pattern, ideal for creating a natural and organic feel for tableware or spa products.
  • YS1815: Diamond Grid: A raised diamond grid pattern for excellent drainage and ventilation, perfect for food containers or shower mats.
  • YS1204: Herringbone: A classic herringbone pattern for adding visual interest and a touch of tradition, ideal for architectural elements or furniture.
  • YS1457: Paisley Swirl: A swirling paisley pattern, perfect for adding a unique and eye-catching element to jewelry or decorative pieces.
  • YS1783: Geometric Maze: A raised geometric maze pattern, adding a playful and modern touch to packaging or toys. (37:29)

 

Summary.

When deciding on your mold texturing you need to choose a relevant surface finish, look at how it is applied to the tool, and understand the overall picture of why this texture is best here, its cost implications, its functionality, aesthetics, and if the product can feasibly be designed with that texture. Investing in a texture book is a great idea to help you select and specify your textures. (43:20)

 

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