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Rubber Mold Design: How to Design Perfect Rubber Mold Part

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Published:  November 11, 2021         Reading Time:  About 3 minutes

Rubber molded products are now an essential part of almost every industry. They are everywhere, from aviation to cars and even in household equipment. The reason for this is not a hard nut to crack. The rubber parts manufacturing process (from the rubber mold design to the actual molding process) is cheaper than the manufacturing process for other types of materials. Also, due to the elasticity of rubber, rubber mold design possibilities are almost limitless. Hence, their widespread use is easily understood.

However, despite the numerous manufacturing possibilities possible with rubber, this doesn’t mean every manufacturing process will succeed. This is because there are set rules to follow when making the rubber product design. Apart from the latter, the rubber mold design is another essential process manufacturers must pay attention to. If they do these two properly, then the production process is on its way to success.

This article will explain the different advantages of applications and advantages of rubber parts, the different rubber parts manufacturing process, and the factors you must never forget when making the rubber mold design.

What are the Advantages and Applications of Rubber Parts?


Apart from the ease of maneuverability due to its natural elasticity, many other properties make it a favorite for making parts. These include:

Low Cost of Production

As a client, you’ll like to minimize the cost of production as much as possible. With rubber as raw material, it is possible to achieve this goal because of the ease of rubber product design and manufacture. While they are not all that cheap, the comparison of their costs to the functions they have makes the production even more cost-effective. However, you can only achieve this when the production process is handled by manufacturing veterans like RapidDirect.

Design Maneuverability

Just as rubber is elastic, rubber mold and product design retain the same properties. There are many possibilities for rubber due to the different molding and bonding methods that designers use during rubber product manufacture. You can also find alternative methods to achieve the same product goal, which means there can be more cost-effective ways to design and manufacture rubber products. By working with us at RapidDirect, we can successfully design your custom rubber products with the most cost-effective methods.

Greater Durability

Metal and plastic parts might tend to lose their functional performance especially if used in machines with high vibrational performance. Rubber parts, especially if custom-made, can take quite a beating due to their natural dampening properties which makes them function for much longer than their counterparts.


For parts with such strength, durability, and elasticity, it is only normal that they have applications in various industries. With the increasing use of multiple materials in manufacturing parts, the use of rubber in making parts has seen a steady increase in popularity. Some of the more popular industries where professionals use rubber products include:

Medical Industry

In an industry that needs equipment that can penetrate the human body without causing damage, rubber products can easily stand up to the task. With materials like catheters and diaphragms, the use of rubber in medical equipment is quite widespread. Apart from this sophisticated equipment, manufacturers also use rubber to make some general-purpose equipment such as gloves, tubes, bottle caps. Also, manufacturers use rubber in making the wheels on hospital beds that assist in the easy movement of patients. These products are all essential medical products used in saving lives.

Electrical Industry

First off, rubber products are popular in the electrical industry due to their insulating properties. Due to their inability to transmit electricity, electrical engineers and professionals use them for protective purposes. Some popular examples include the pantograph insulator, which electrical professionals use in high-transmission power lines. Just as its name implies, it prevents electrical transmission in a highly electrically charged atmosphere. Others include silicon covers which are popular for their use in circuit breakers. Electrical professionals sometimes refer to them as ‘“the heart of the breaker.” Also, we have the multi-way busbar joints used in and gaskets used in junction boxes and enclosures.

Automobile Industry

The automobile industry could arguably be the industry that utilizes rubber parts the most. From their use in their fluid transfer systems to transmission systems and of course, the car tyres, automobiles have a lot of essential parts which use rubber parts. In fact, research has shown that 75% of rubber goes into making tyres. And it’s also a known fact that the automobile industry has a heavy use for tyres. Some other popular parts of automobiles that use rubber parts include automotive antivibration systems, O-rings, and sealants.

Types of Manufacturing Processes Used in Making Rubber Products

Just as mentioned earlier, there are various processes involved in the rubber parts manufacturing process. In most cases, the rubber product design determines which of these manufacturing processes will be suitable for part production. Each of these production techniques has its advantages, making them specialized for making different types of rubber products. Fully understanding each of these processes helps make the best choice for which to use in your production process in terms of costs, level of technicality involved, and suitability with the production at hand. While there are quite a few of them, we’ll discuss the popular processes which involve molding: injection molding, transfer molding, and compression molding.

Injection Molding

an illustration of the process of rubber injection molding
The rubber injection molding process

This is similar to the plastic injection molding process. However, the rubber injection molding process involves much more heating. The process involves the machinist heating the material into a flowing state. Then, they inject the material under pressure from the heating chamber through a series of channels (known as sprues or runners) into the mold. The heating unit and injection unit are also two separate components, with each having its own controls.

An extruder component can also serve as the heating unit in this process. As long as the designers and manufacturers get the mold design and other components of the machining process right, the rubber injection molding process doesn’t usually take much time. Automation is also a common feature of this process, which speeds up the lead time. At RapidDirect, we can handle all types of injection molding processes regardless of the desired materials.

Compression Molding

an illustration of the rubber compression molding design
The compression molding process

This method is the oldest and also the least cost-intensive. In this process, the raw rubber is formed into a large mass (known as a blank). The machinist then places this blank into the mold and heats it to cure and shape it. Now, this is where the design of the mold for rubber parts is an important factor. Due to the need for curing, the heating time can take a while.

However, this depends on the thickness of the mold walls. Hence, the designer makes the rubber mold walls proportionate to the amount of time wanted for heating. Therefore, the heating time can vary from minutes (for thin walls) to hours (for thick walls). This method is suitable for production using raw materials with bad flow properties and high viscosity. However, the process can be quite time-consuming. Electrical insulators, seals, and silicone wristbands are examples of rubber products made using this rubber part manufacturing process. 

Transfer Molding

the rubber transfer molding process
The transfer molding process

This rubber part manufacturing process aims to counter the long heating time involved in compression molding. The process also involves using a blank, which is loaded into the mold and distributed into the different cavities. However, before distribution into the cavities, the rubber undergoes some preheating. This process reduces the curing time of the rubber and increases its flow properties, hence allowing it to fill the cavities easily. However, the molds here are the most expensive and complicated. Hence, the rubber mold design here should be handled by experts only.

At RapidDirect, we specialize in different types of molding processes; hence, your rubber mold design and rubber product manufacture are guaranteed success.

Each rubber part manufacturing process is suitable for manufacturing different rubber parts. Hence, having a good understanding of each will help decide which one is the best option for your part production.

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Factors You Should Never Ignore When Designing Rubber Parts

One mistake an engineer should never make when manufacturing a custom-molded rubber part is to use less-than-standard parts. While this might seem to have a lower cost in the short term, it ends up in spending more than the budgeted cost. However, when you use good parts, they improve the rubber part’s longevity and functional performance. However, the type of parts used wouldn’t even matter if the design is not top-notch. Hence, this shows just how important the design of both the mold for the rubber parts and the product is in a rubber part manufacturing process (or any type of part).

Below are some factors you should never forget when designing a rubber part:

1. Questions Checklist

When designing a rubber part, there are some essential questions you have to answer to know the best way to design and manufacture the product. These questions include:

  1. What is the function of the part?

In rubber parts, their functions could include absorbing vibrational energy, sealing a fluid container (hence must be impermeable to the fluid), serving as a passage mechanism for the fluid, or providing structural support. These are just a few examples of the functions of rubber parts.

  1. What properties must the part have?

The desired properties of the rubber parts are quite important when determining the materials to use and how to structure the parts. Examples of desired properties in rubber parts include resistance to changes in physical properties in the presence of fluids or heat or the ability to elongate without losing its elastic property.

  1. What is the environment in which the part will function?

The environment in which the rubber part will function will also determine how the designer will structure the part. Some examples of environments where manufacturers use rubber parts include sunlight, wet areas, chemical solvents, in areas of dynamic stress where the part could face deformation.

After answering these questions, you should have a clear vision of the function of the rubber part and how the part will achieve this function. Also, final remarks on the structure of the part will be made at this stage.

2. Selecting Elastic Material

After answering the questions, the next part is choosing the material to use for the part. This is another important aspect as the material used will go a long way in determining how much the part can fulfill its functions. Choosing the best material for any part production means you’ll have to find a suitable material for the intended function, is not too expensive, and has longevity.

In most cases, once you’ve answered the questions above, you should be able to pinpoint the material that will fulfill the intended function. However, if you’re still indecisive about the perfect materials to use, here are some factors to consider:

  • Exposure of the rubber to ultraviolet light and sunlight, which can decompose it.
  • Presence of ozone gas from either natural or artificial sources (e.g., electric motors). Ozone is a contaminant that has adverse effects on rubber.
  • The likeliness of the rubber part to be exposed to the human body either directly or indirectly. You should consider the period of contact.
  • The fluids (either primary or secondary) to which the rubber part will be exposed.
  • The ability of the material to maintain its integrity and functional performance in extreme temperatures.

Elastic Material Hardness

Elastic materials have a scale for their hardness level ranging from Shore A (thermoset rubbers) to Shore D (thermoplastic rubbers). Each scale also has its ratings, e.g., Manufacturers rate the Shore A scale from 20 Shore A to 90 Shore A. The materials commonly used in the rubber parts manufacturing process range from 50 Shore A to 80 Shore A.

While the hardness used for a particular project depends on the application of the part, there are some difficulties regarding the use of some materials. For example, there are some significant difficulties faced when manufacturers attempt to use very softly (<30 Shore A) or very hard (>80 Shore A) rubber materials for the manufacturer of parts with deep undercuts or complex geometry. Here are some suggestions on some material applications:

  • If your rubber part will be exposed to temperature extremes greater than 150 degrees Celsius in an industrial environment, then a fluoroelastomer is a good material choice.
  • Nitrile rubber is an excellent choice for general-purpose applications.
  • If your rubber part will have medical applications and needs to maintain a high level of requirement, then a silicone rubber will be the best choice.

3. Designing Corners and Edges

In rubber product design, sharp corners are generally unacceptable. In most cases, designers break the corner with a radius >0.05 inches. The reason for doing this is that the corners make the rubber mold design and construction unnecessarily difficult. This also increases the cost of manufacturing the mold, hence increasing the rubber part cost price. Apart from the increase in the cost of production, it could also increase the possibility of some parts defects occurring.

However, it is the exact opposite of rubber part edges. Machinists generally prefer rubber part’s edges to be sharp, especially when they intersect with a parting line. This simplifies the rubber mold design and construction. The figures below show what ideal corners and edges should look like.

  • Corners should look round when viewed from the top
rubber part corners
How an ideal rubber part corner looks like
  • Edges should look like a square when viewed from the side
rubber part edges
Illustration of a deal rubber part edge

4. Undercuts

a rubber part with an undercut
An example of an undercut

An undercut is a feature of a part that projects into the main body of the part. One problem with undercuts is that they must not project too deep into the part. If this happens, the part becomes really difficult to remove from the mold. In cases of rubber parts that need these types of undercuts for their functionality, the designers should make the rubber mold design such that the mold opens both vertically and horizontally. Then, when removing the part from this type of mold, the part comes out more easily. This is because the center plate pulls up while the sides slide out. However, the design and machining of these types of rubber molds are more expensive.

a rubber mold design for making undercuts
Rubber mold design for undercuts


While rubber parts can provide you with a lot of structural performance for relatively lower costs, it is essential they are designed properly. The rubber mold and part design must be top-notch if the rubber part will live up to its expected functions. This is why you cannot afford to outsource your rubber mold design to just anyone. You need the best of the best. And that is what RapidDirect offers you.

With years of experience in rubber parts manufacturing under our belt, we can assure you of the best of the best services in designing the mold for rubber parts and machining the rubber parts itself. In addition, we’ll check your proposed mold design for its feasibility for manufacturing while providing cost-effective options to make it even better. To have a glimpse of our excellent services, click on the link below. We’ll be waiting!

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