How Are Dumbbells Made? (Manufacturing Process Explained)

All weightlifters, whether home or gym-based, know the importance of dumbbells. They allow you to work out all the major muscle groups and stimulate muscle growth effectively. They also offer greater flexibility than machines or bars and help to improve your coordination and stability, engaging your core and improving your functionality.

Dumbbells offer a whole range of benefits, but most of us don't know the manufacturing process involved in creating them. This guide will answer how are dumbbells made and the different materials used to create one of the most used fitness tools in gyms.

Dumbbells come in all shapes and sizes, but there are two main materials, rubber and cast iron. Here's a quick breakdown of the advantages and disadvantages of each:

Cast Iron Dumbbells 

Cast iron dumbbells have the old school look and feel. They are usually made of one piece of solid metal, though some have grips added. Cast iron is generally used for heavier weights and preferred by serious lifters. They're easier to grip and less likely to slip in your hands. These dumbbells are also easier to clean and more durable, so they'll last longer.  

The disadvantage of cast iron is that it tends to be more expensive because of the material and the manufacturing process (we'll come to that in a second). It's also more susceptible to the elements and can get very hot or very cold. This means it isn't always a great option for garage gyms in cold areas. 

cast iron dumbbells

Rubber Dumbbells 

Rubber (or neoprene) dumbbells are the more modern option that have only become popular in the last few decades. Most rubber dumbbells are very similar to cast iron and just have a rubber casing around the outside.

This is sometimes over the metal ends or across the whole dumbbell, including the handle. This gives the benefits of rubber with the weight of metal.  

Rubber dumbbells are often a cheaper alternative because they can use different varieties of metal and don’t need as much work to be done on the outside because there is a thick rubber coating.

They can be made lighter, too, so they're well suited for beginners and often come in smaller weight increments so you can grow stronger at your own pace. They tend to be smaller than traditional iron dumbbells, so they're easier to store, and they don't make any noise if you drop them on the ground.  

Rubber dumbbells don’t tend to go as heavy as cast iron dumbbells and won’t be suitable for heavy lifters. They’re very popular in home gyms because they take up less space and won’t make a loud clang if you drop them.  

man picking up rubber hex dumbbell

How Are Cast Iron Dumbbells Made?  

Cast iron dumbbells offer a range of advantages, but how are they made? Understanding the manufacturing process of these dumbbells can help explain the expensive cost and give you an appreciation of the effort that goes in and why you might choose them: 

The Manufacturing Process 

  • Designing  
    The first step in the process is designing the dumbbell. They come in all different shapes and sizes, and you first need to determine if you want a round, square, or hexagonal shape, or if you just want something completely different. There’s typically a lot of detail on the outside of the dumbbell with writing, logos, or other distinguishing features to set yours apart. All of these factors need to be mapped out and drawn before you move on to the next step. If you're paying to have dumbbells made, you typically use an Original Equipment Manufacturer (OEM) or Original Design Manufacturer (ODM). For an OEM, you'll need to send in a drawing of your design, and they'll go from there. An ODM will design the dumbbell for you, but you'll pay more.   
  • Making Patterns  
    The next step is bringing the design to life by making your pattern. Your pattern is literally a replica of the dumbbell itself, which will be used in the molding. This is usually made of aluminum, and in some cases, there are several parts that are then attached to each other.  
  • Molding Sand  
    To make the mold for iron dumbbells, you use green sand castingThe green sand, which is a naturally bonding wet sand, is poured into a sand flask. The pattern is then pushed down into the sand for a few minutes and then pulled out. What you're left with is a perfect mold for the dumbbells, which can then be used to give your dumbbells the perfect shape.  
  • Casting  
    This is the interesting part which involves a lot of hot metal. First you take your cast iron which is usually examined using a spectrometer for metal to look at the components. If it meets the grade, it is exposed to temperatures of 2200 Fahrenheit (1204 degrees Celsius) until it becomes liquid. It’s then poured into the mold created in the sand flask in the previous step so that it fills the cavity and forms your roughcasting. This is then left for 8-10 hours to cool completely before you can collect the roughcasting. A sandblaster is used to remove the excess green sand from the roughcast, and it can then be passed onto the next step.
  • Machining  
    This is where the roughcast becomes a proper dumbbell. It’s milled, smoothed, drilled, and coated so it is smooth and exactly fits the design from the first step. There is typically a machine process for all of this, but there are sometimes several different machines used. The result is a finished, smooth, even dumbbell ready for testing.  
  • Testing   
    Once the machining is complete, the dumbbells will be inspected and tested. It will be checked for any visible damage, cracks, holes, or other defects which will impact performance. It will also be weighed to make sure it's correct and checked, so there's a good protective coat over the outside. Once it passes this quality control, it can be shipped out to the user.  
  • Packing  
    Finally, the finished dumbbell is packed up and sent out, ensuring there’s enough protective packaging material to prevent any damage on route. 
man doing renegade rows with cast iron dumbbells

How Are Rubber Hex Dumbbells Made?  

Rubber hex dumbbells are made using a very similar process to cast iron dumbbells but with a few extra steps. They are typically made with pig iron and natural rubber, but it’s important not to use any other type of rubber as this could be toxic. 

These dumbbells are generally cheaper because there’s less metalwork needed, and the rubber cover will hide some imperfections. Here’s a quick breakdown of the manufacturing process:

The Manufacturing Process 

  • Designing  
    You start by completing the design of the dumbbell to determine exactly how you want it to look and feel. You need to determine the weight, any logos or branding, and also how you want the rubber to encase the dumbbell. Typically, with hex rubber dumbbells, you'll want to cover the whole weight, but you can just cover each end if you prefer. Within this design phase, you need to determine how thick the rubber casing around the dumbbell should be. Typically, this is 0.3-0.7cm thick, but some heavier weights may want a slightly thicker coating. Once you've finalized the look, feel, and specifics, you can make your pattern. 
  • Making Patterns  
    Once you have a finalized design, an aluminum pattern is created, just like in the cast iron dumbbell manufacturing process. This should only cover the metal elements of the design and not the rubber. Otherwise, it will be too thick. With rubber dumbbells, you'll need to create a shell. This is the space the rubber coating will take up and should be the thickness around the dumbbell which you agreed in the design phase. Once you have both of these, you can start the molding process. 
  • Molding  
    Once you've finalized the pattern, you need to create the mold. This is the same process as cast iron dumbbells, and green sand is poured into a flask with the aluminum pattern pushed in to create your mold.  
  • Casting  
    For hexagonal rubber dumbbells, pig iron is melted to create the base to which the rubber is applied to. This is heated to 2200-degree Fahrenheit, poured into the mold, and left to cool for 8-10 hours. Once cooled, you are left with a roughcast which can be sandblasted to remove any excess green sand.
  • Machining  
    The metal then needs to be smoothed around the edges so the rubber coating can be applied evenly. It doesn’t need as much treatment or filing as cast-iron dumbbells because it won’t be visible, so this is a less intensive piece of work.  
  • Melting The Rubber  
    Rubber can typically be used several times by heating and reshaping. For dumbbells and weights, it’s best to use natural ‘virgin’ rubber, which is being used for the first time. It will generally last longer and be easier to use than older rubber. The rubber is heated to 356-degree Fahrenheit (180 degrees Celsius) until it is liquid. It should then pour into the shell mold created earlier in the process so the metal dumbbell can be dipped into it.  
  • Dipping The Dumbbell  
    The cast dumbbell should be dipped into this shell and coated with melted rubber to create your finished dumbbell. Leave for 6-8 hours until the rubber is evenly coated and completely solid again.  
  • Testing 
    Once you have a finished hexagonal rubber dumbbell, it needs to be checked for any imperfections or cracks around the outside. The rubber should have formed an even seal around the weight with no lumps or bumps around the edges. The dumbbell should then be checked, so it's the correct weight before it’s ready to be sent.  
  • Packing  
    The dumbbell is now ready to be packed up and sent out. They are usually grouped together into sets, and packaging material is used to help prevent any damage in transit.  
rogue fitness rubber hex dumbbells

Which Dumbbell Is Best For Workouts? 

It can be difficult to decide which dumbbell is best, but it all depends on you and how you will use it. A rubber dumbbell is quieter to use and often smaller. They can be durable as the rubber gives extra protection, but they are less comfortable to hold. Cast iron dumbbells give the real rustic feel and are very durable. They feel good in your hand and can support very heavy lifting.  

If you’re a serious lifter, you’ll probably prefer the cast iron dumbbells. If you have limited space and you’re just starting out, then you’ll probably prefer the smaller rubber dumbbells. 

Let's not forget to mention adjustable dumbbell sets. This type of dumbbell set is great for home gyms as they save space and allow you to change weight on the fly.


People Also Ask (FAQs)

Why are dumbbells hexagonal? 

Hexagonal dumbbells are the modern alternative to rounded ones and offer one key advantage; they don't roll. If you have an uneven floor, this can be really useful and stops them from rolling away between sets.

Why do iron dumbbells feel heavier? 

Iron dumbbells have a greater density than rubber dumbbells which can make them feel heavier. This is all psychological, though; they won't actually be heavier.

Are cast iron dumbbells more durable? 

Yes, cast iron dumbbells are more durable and should last longer, even if used heavily.

Are rubber dumbbells toxic? 

Rubber dumbbells should be made from natural rubber, which is non-toxic, so no, rubber dumbbells aren't toxic.


Conclusion

Dumbbells are a great tool to help you work out effectively, and there's a lot of different styles available. Rubber and cast-iron dumbbells are both popular choices, and the manufacturing process isn't too different. 

Even though rubber dumbbells have an extra step, they're actually simpler to make and require less precision, so they can end up being cheaper. Hopefully, this guide has explained how these dumbbells are made and helped you determine which is the best choice for you.