Elon Musk once said, “If you don’t make stuff, there is no stuff”. It’s so simply-said, but so true. As a manufacturer specializing in prototyping, we have made a lot of “stuff”, all sorts of “stuff” from every industry imaginable. We are very proud to say that we have gained a lot of experience in making many parts. Yet we have encountered our fair share of trials and errors. 

This article mainly talks about the difficulty to imitate diffusing property during the prototype-development stage.

What is light diffusion?

The dictionary definition of light diffusion is “the scattering of light by reflection or transmission. Diffuse reflection results when light strikes an irregular surface such as a frosted window or the surface of a frosted or coated light bulb. The diffused light seems to wrap around objects. It is softer and does not show the harsh glares of direct light.

We have come across many customers that want to make a part that diffuses light. Behind or underneath the part, there is often a LED light source. Sometimes the part is soft material with certain hardness requirement. Sometimes the material is hard plastic.

How to make parts that emit diffusion lights

To make a plastic part diffuse light, one common way is to add light diffusion agent inside the plastic part during the injection-molding process or vacuum-casting process.

As you can tell from the photo below, “fine particles” are what we call “light diffusion agents”. These light diffusion agents generally are made of nano barium sulfate, calcium carbonate, silica, etc. When examined under a microscope, the diffusion agents are extremely small beads. Base resin can be clear PC, PMMA used for injection molding, or Polyurethane used for vacuum casting.

Another common way to make a plastic part diffuse light is to coat a diffusion agent on the surfaces of the plastics.  For example, after a transparent PC or PMMA or Polyurethane part being made. A thin layer of glass beads (original glass beads are clear) could be blasted on the surfaces of the parts. In this case, glass beads serves as the diffusion agent. Another diffusion agent for this method is to spray clear grained paint, such as VDI36. The following part is a CNC-machined clear PMMA part. After it was being polished clear, VDI36 grained paint was applied.

The difficulty of making diffusing parts

As you might judge from the aforementioned methods to make diffusing prototypes, to make a part diffuse is very simple, the real difficultly is to make a part diffuse the right amount of light you’d like.

Full-Width Maximum (FWHM) and Half Angle (HA) are values generally used to quantify light diffusion and are commonly used to describe the light diffusion capability of plastic under a light source. For FWHM and HA, higher values mean a higher amount of light diffusion.

In a particular project we once had, a client specified the diffusion level FWHM to be bigger than 70°. Although we have made a lot of prototypes imitating the possible diffusion property, we were having difficulty making the part have a diffusion level to be over 70°.

For one thing, different shades of color, different wall thickness, different structures, different percentages of diffusion agents, and even different base plastic will cause a part to diffuse light differently. For example, if we have added a certain amount of diffusion agent in making a part during the urethane casting (or vacuum casting) process and we have met the requirement of the diffusion level desired by the client.

Then the next customer has a different part that wants the same diffusion effect. Even if this different part is only different in the wall thickness, we could use the same ratio of the diffusion agent as before, but we would not have the same diffusion results as before. Many attempts were needed to get the diffusion level right.

When moved on to mass production, the material used for parts of mass production will be different from the material used for prototypes. For instance, PC used for prototypes are block material while PC used for injection molding are plastic pellets. Although they are both called “PC”, they are in fact two different materials. PC plastic pellets have no impurities inside and are more heat-resistant than PC block materials.

Moreover, the methods used to make diffusing PC prototypes are different from that of mass-production (generally injection molding). The diffusion agent could be only coated on the surfaces of PC prototypes. While in injection molding, a diffusion agent is generally added to molten plastic during the molding process. After the parts come out of the mold, the parts will have a diffusion agent inside, which is what PC prototypes couldn’t do.

Conclusion

To conclude, although it is not hard to make prototypes that diffuse light, it will be extremely hard to make prototypes to diffuse a certain amount of light. Additionally, if applying the formula of the diffusion agent used in a prototype, the diffused light emitted by prototypes and parts of mass production will be different.

 Silicone molds – those nifty and convenient shapes or mold boxes that can be used to prepare just about any item.

Now, when it comes to making a silicone mold, there are multiple approaches that can be adopted.

In this article, we focus on industrial applications for making silicone molds using methods such as vacuum casting. This is contrary to more DIY or hobbyist approaches to silicone mold making, for say crafting items at home.

Instead, here we concentrate on the creation of silicone mold prototypes particularly for plastic items.

Making a silicone mold: which way is better

Now, typically when it comes to the preparation of silicone molds for more large-scale purposes, there are two approaches that are used most commonly.

First, you have silicone injection molding, and secondly, there is vacuum casting.

Both methods have their pros and cons, and below, we will delve briefly into each of them

Injection molding

As the name suggests, this is a molding process where the raw melted plastic material is injected into the mold.

Advantages:

• Greater flexibility in terms of the materials that can be used.
• Equal flexibility on colour choices.
• Reasonably high level of accuracy.
• Low wastage: even the leftover materials can often be reused.

Disadvantages:

• Not cost-effective for low volume output.
• Initial setup cost can be rather high.
• Relatively longer lead time for output delivery.

Vacuum casting

As the name suggests, this is a silicone molding technique that involves vacuum.

Advantages:

• Low initial setup cost.
• Shorter lead time.
• Especially suitable for making smaller batches of products such as silicone prototypes.
• Ideal for making large size plastic parts.

Of course, vacuum casting to create a silicone mold has its set of shortcomings too:

• For large volume orders, this method may not be suitable.
• Detailing in more intricate items might be minimal.

Having enlisted the pros and cons of both methods, it would now be a lot easier to choose between the two:

1. Injection molding is preferred when more detailing is required.
2. For low volume silicone prototypes, vacuum casting makes maximum sense.
3. For swift turnaround times, again vacuum casting proves ideal.

How to make a silicone mold by vacuum casting

The use of vacuum, viz. a space that is completely void of matter, is at the core of making silicone molds this way.

The process starts by typically deploying two different molds – one at the top, and the other at the bottom.

The raw material is mixed separately and then placed inside the mold. Vacuum pressure ensures firm casting inside the chamber. Final casting is commonly done inside an oven to ensure complete and even curing.

Now, notwithstanding some of the minimalistic deficiencies in the process of making silicone molds by vacuum casting that we had referred to previously, it continues to be one of the most sought after ways in which silicone molds are made – for all the advantages that we had enlisted above.

Accordingly, in this section we go into greater detail about this process of making silicone molds.

Bear in mind that for the large part, the reference here would be in terms of urethane casting, viz. a casting process where additives, curatives, or polyurethane resins are poured into silicone molds for fabricating a variety of different plastic items.

First Step – Master Crafting

The first step to making a silicone mold by vacuum casting involves the master crafting process where digital renders are initially prepared using systems like CAD. With their help, 3D solids are made, often using 3D printing or CNC machining.

Once completed and checked for accuracy, we move on to the next step.

Second Step – Preparing the Molds

The second step involves preparing the silicone molds using liquid silicone. The casting box in this instance is usually half filled with liquid silicone and heated till it is completely cured.

Even after this initial curing process, additional curing is done in an oven, as we had referred to previously. While timelines may vary, the usual drying process takes around 16 hours.

Once fully dried, the two halves of the mold (as mentioned earlier) are cut to remove the finished master output.

Third and Final Step – Preparing Additional Copies from the Master

With the master output ready in the previous step, it is now all about preparing additional copies from it. At this juncture, the empty cavity inside the mold would be accurate enough to create precise replicas of the master, to the extent that materials other than plastic (say a blend of steel metal, among various feasible possibilities) can also be deployed.

Herein, one of the key advantages of making silicone parts by vacuum casting comes to the fore – the fact that silicone molds in this instance can be used repeatedly, at least 20 times or more, to continually create copies of the master.

A Note about Silicone Rubber

While talking about making silicone molds, it would only be apt that we delve briefly into silicone rubber.

Remember that irrespective of the method you use for making these molds – injection molding, vacuum casting, or any other, the fundamental raw material will remain the same, viz. silicone rubber.

Due to its pliability, durability as well as its unique ability to withstand extreme temperatures, silicone rubber finds frequent usage globally, for a number of diverse applications.

Silicone Molding is the right choice for Low-Volume Plastic Parts Production

When it comes to producing smaller batches of plastic items – say prototypes for larger orders that are to follow, silicone molding proves to be the ideal choice.

A major reason for this is the reusability factor; the same silicone mold can be used over and over again for at least 20 to 25 times (possibly even more) to create accurate replicas of the item in question.

This has a direct relation with costs since it helps keeping them in check. Of course, it leads to enormous time savings too!

An additional benefit is the ease with which silicone can be stored for prolonged periods. This proves especially helpful when production might have to be halted.

Getting Started with Silicone Mold-Making for your design

While there are multiple approaches that can be adopted for making a silicone mold, vacuum casting proves to be the right choice for the production of smaller batch silicone prototypes.

In this article, we have vividly described how to make a silicone mold by vacuum casting.

As you would have noted, the steps to be followed are fairly simple in nature. Notwithstanding a more industrial level of production which is not akin to any DIY or homely approach to silicone mold making, the method we have outlined proves easy to follow and implement.

Have you recently come up with a custom part design, or do you need to manufacture a part with special requirements? If so, the next steps are to hire a manufacturer, send over your 3D computer-aided design (CAD) file, receive a fair product quote, and manufacture your product, right? Not exactly.

The truth is that a lot can go wrong if your product is not correctly designed for manufacturing from the onset. For instance, you might incur huge manufacturing costs or defects that render your product useless. Therefore, there are several things and design tips that you must first understand before creating your 3D CAD and reaching out to that manufacturer.

This article covers all of these and more. It will serve as a guide to help you prepare for your project quote.

Understand the Manufacturing Process

Understanding the manufacturing technology and process a manufacturer will use to fabricate your product helps you create product designs you can easily fabricate with that technology. For instance, CNC machining and 3D printing ㅡ two of the most popular manufacturing methods today ㅡ have different modes of operation and suitability for different custom product design scenarios.

CNC machining is a subtractive manufacturing process. That means it involves removing portions of material from a workpiece (using cutting tools) until the desired product is formed. It utilizes computer numerical control (CNC) technology to automate the movement of the cutting tools and workpiece to create the desired product. In contrast, 3D printing is an additive manufacturing process. It involves adding portions of material layer by layer until the desired product is formed.

The CNC machining process is ideal for creating complex custom product designs featuring angled cuts, cavities, off-center holes, and other complex features. While 3D printers can equally create these parts, you have limited material options (plastics and a few metals). Therefore, choosing 3D printing over CNC machining makes sense for certain plastic prototypes or complex parts.

Learn more: CNC Machining vs. 3D Printing

Some Design Guidelines for Custom CNC Machining

Here are some helpful design guidelines to help you achieve high-quality parts and reduce your manufacturing costs.

#1 Cavities

You should design cavities and pockets to have a depth that is less than four times the cavity width. This is because end mill tools have limited cutting length, so you might experience tool deflection and vibration when fabricating cavities with a smaller depth-to-width ratio.

Figure 1: Designing cavities

However, if your product design requires a larger depth-to-width ratio, you will need specialty cutting tools, which might incur additional manufacturing costs.

#2 Wall Thickness

Thin walls are prone to vibration during CNC machining, which lowers machined parts’ achievable tolerance and accuracy. Therefore, as a rule, you should design metal parts to have a minimum wall thickness of 0.8 mm, while plastic parts should have a minimum wall thickness of 1.5 mm.

Figure 2: Wall thickness requirements for metal and plastic parts

It’s possible to achieve thinner walls, but it usually comes with additional manufacturing costs.

#3 Holes

You should design holes to have standard diameters. This allows you to use standard drill bit sizes to create these holes and eliminates the need for specialty end mill tools. We also recommend that the depth of the hole is less than four times the end mill’s nominal diameter to minimize tool deflection.

Figure 3: Designing holes

#4 Tolerances

Tolerance is the allowable amount of variation in the size of a machined part that will still allow for it to function properly.

Product designers usually specify tolerances to manufacturers by stating the permissible limits of variation in a physical dimension. You can specify tolerances using the “±” symbol (pronounced “plus or minus”) and accompanied by a value, for example, ±0.05 mm. For instance, say you plan to fabricate a part with two holes (having a diameter of 21 ±0.25 mm), as shown in Figure 4.

Figure 4: Engineering tolerance

In such a scenario, it simply means you permit a deviation of 0.25 mm extra (or less) than your standard diameter value. So, if your manufacturer fabricates a hole with a diameter of 21.25 mm or 20.75 mm, it won’t affect the proper function of your part.

CNC machines are among the most accurate manufacturing technologies, capable of achieving tight tolerances of up to ±0.04 mm. However, keep in mind that tighter tolerance requirements typically result in higher manufacturing costs.

Choose the Ideal Surface Finish

Although the CNC machining process is subtractive, it does a great job of producing parts with excellent surface finishes. The “as-machined” surface finish refers to machined parts coming straight from the CNC machines. These parts retain the accuracy of the manufacturing process and require no additional costs.

Figure 5: As-machined milled part

If your parts require additional post-processing options like anodizing or powder coating, then you can expect a higher project quote from your manufacturer.

Figure 6: Parts with anodized aluminum finish

Parts with powder coated finish

Learn more: Anodized Aluminum Finishes.

Custom CNC Machining: Gensun Can Help

Now that you know a little bit more about custom machining and product design tips, you’d probably agree that your project quote and product development success depends on your product design. That’s why you must work with a manufacturer that looks at your product design and advises you on what’s best for you.

Gensun Precision Machining is a leading provider of custom CNC machining services across Asia. We have a team of highly qualified engineers, technicians, and quality control experts capable of getting your product done right. We keep our customers’ best interests in mind, so use our quoting tool to upload your 3D CAD files, request a quote, and discuss your manufacturing project with our highly qualified engineers.

Learn more about our high-quality CNC machining services.

Note: This article was originally published in Feb 2021 and updated in May 2022

For precision CNC milling services, the right tools are required. Basically, in order to perform precision machining jobs, you need CNC milling machines. These machines are precise, accurate and fast.

We suggest that to providers that offer these services, you outsource the job if you deal in the products of parts. You can use the following tips if you find it harder to choose a good company.

Ask for a work sample

To know more about their services like Aluminum Machining, you should email or call each company As soon as you have got the contact details of the companies. You can get a pretty good idea of their service quality by looking at their work samples or portfolio.

A list of good companies can be made. Ensure from each company, you get a few work samples. Then you can find out which company is the best one by comparing the samples.

Use the web

First of all, business directories must be used. Alternatively, you can use online directories by going online. Usually, orders are received online by them. For more information, you can dial their number and go ahead once you have got the contact details of the company.

Shop around

We suggest that you always shop around In order to get the best deal. You will be able to compare various companies, which is the benefit of getting quotes from several companies. As a result, you will be able to pick the perfect company for Aluminum Machining.

By a company that at an affordable price will deliver the order is the right company. So, highly recommended is shopping around.

CNC milling machines

Make sure quality machines are used by the company. During a personal visit or the phone call, you can find out about their machines. During the phone call, don’t forget to make a note of the details.

For instance, about the brand and model of the machine, you should note down the information. If the machine is high quality or not this way you can easily know.

Check our in-depth guide to better understand CNC milling technology and how it works.

Share this blog: