aluminium, magnesium

& gravity casting process

February 04, 2024

Aluminium, Magnesium & Gravity Casting Process

Aluminum is one of the most interesting materials, along with carbon, for designing an ebike frame. Less common but not without interest, magnesium is now found in some bicycle brands. Its presence is currently exceptional due to its rarity, but it's possible that soon we may see this material in many ebike models.

My self-balancing scooter, Segway Ninebot, is made of magnesium, and I've had it for six years. It has encountered several impacts on the road, and the body frame has held up very well against the shocks. However, one handle is broken.

There is a magical aspect to creating a monobloc e-bike frame. Our bicycles are typically made up of multiple parts assembled by welds.

If one can be surprised by the refinement of the design of aluminum frames for e-bikes, with no visible welds, this smooth appearance increases confidence in their strength compared to visible and sometimes unsightly welds. Therefore, I researched in detail the techniques used by Chinese foundries to achieve this result.

Among the visited sites, those of CNC Machining, Sunrise Casting and Ming Ming stand out, with the latter being one of the most informative regarding the step-by-step manufacturing process.

Which alloy for an ebike ? AluminIum or Magnesium ?

Magnesium or Aluminium, both materials have their merits, and the choice often depends on factors like weight, cost, and specific performance requirements.

Aluminum Bike Frame:


Gravity Permanent Mold Casting or Die Casting are also widely used for aluminum frames.


Aluminum is lightweight, corrosion-resistant, and can be cost-effective to produce.


The aluminum casting process involves melting the metal and pouring it into the mold, ensuring proper cooling for structural integrity.

Magnesium Bike Frame:


Gravity Permanent Mold Casting or Die Casting are common methods for magnesium frames.


Magnesium offers a good strength-to-weight ratio, making it lightweight and durable.


Magnesium requires careful handling due to its reactivity, and casting it involves specific techniques.

What is the difference between gravity casting and die casting ?

Both gravity casting and die casting are permanent mould casting using moulds made of steel materials. In gravity casting, molten metal is poured from a crucible into a mould by using the force of gravity, instead of using the pressure from gases, vacuums or centrifugal forces.

In contrast, die casting relies on pressure to inject molten metal into the mould. This process is the most common approach in permanent mould casting.

Step-by-step Aluminium Gravity Casting Process

In the realm of aluminum die casting, the process unfolds through a meticulously orchestrated series of steps, especially crucial when crafting bespoke components tailored to specific industrial needs. Here's a detailed breakdown of the steps involved in this intricate process :

Review of e-bike's brand Specifications:

The journey commences with a comprehensive review of the e-bike's brand 2D drawing and a 3D CAD model of the desired part. This critical step establishes the foundation for the subsequent phases of the aluminum gravity die casting process.

Creation of 3D Pattern and Prototype Confirmation:

Building upon the initial design, a 3D pattern of the part is meticulously crafted. This pattern serves as the prototype, and its confirmation with the customer ensures alignment with their exact specifications before progressing further.

Development of Reusable Sand Cores and Metal Molds:

With the prototype approved, the next step involves the creation of reusable sand cores and metal molds. These molds will be instrumental in shaping the molten aluminum into the desired form during the casting process.

Completion of PPAP Process:

The Production Part Approval Process (PPAP) is a crucial checkpoint in ensuring the quality and conformity of the manufactured components. This step involves a comprehensive evaluation and validation of the production process.

Melting and Pouring of Die-Cast Aluminum Alloys:

The heart of the process lies in the melting of die-cast aluminum alloys, which are then poured into automatic gravity die-cast machines. This step demands precision and expertise to guarantee the accurate formation of the intended components.

Cooling, Solidifying, and Gate Removal:

Subsequent to the pouring process, the cast aluminum undergoes cooling and solidification. Once the material has taken its final form, the gate, which facilitates the entry of molten metal into the mold, is meticulously removed.

Heat Treatment for Mechanical Properties Enhancement:

To enhance the mechanical properties of the castings, a crucial step involves subjecting them to heat treatment. This process optimizes the material's strength, durability, and overall performance.

Shot-Blasting for Surface Refinement:

Shot-blasting comes into play to remove contaminants and smooth any rough surfaces. This meticulous refinement process ensures that the final product meets the highest standards of quality and aesthetics.

CNC Machining for Precision Refinement:

The concluding touch involves refining the components further through CNC machining. This step ensures the utmost precision, meeting tight tolerances and providing the finished parts with the desired specifications.

In conclusion: 

The aluminum gravity die casting process is a symphony of precision and craftsmanship, ensuring that the end products not only meet but exceed the expectations of the customer. Each step in this intricate dance contributes to the creation of high-quality, customized components for diverse industrial application ...

Ming Ming official step-by-step Aluminium Gravity Casting Process

source : Ming Ming
Photo credit: Ming Ming

Pattern making & prototyping

After the design is confirmed, the pattern is moulded into a 3D shape by using materials such as wood, clay, and plastic. 3D sand printing is currently also used for this purpose. A sand core prototype might also be made during this stage. The prototypes are then used to produce samples to confirm the design. Some adjustments, based on the sample might be suggested

Creation of the mould

The mould creation starts after the pattern and the sample are finalised and confirmed by the customer.

Reusable metal moulds and sand cores are created. CAD is also used to simulate the casting process, i.e., gating

Coring inside the mould is often also required in order to form desired holes and recesses. Ming Ming uses sand, mixed with thermosetting resin, to make sand cores for such purposes.

Photo credit: Ming Ming

Production Part Approval Process PPAP

A few samples are casted by using the created metal mould and, together with PPAP documents, sent for approval. The mould is ready for mass production.

Mass production: melting of aluminium ingots and automatic pouring process

Metal is melted and then the molten aluminium alloy is poured into the mould under gravity in an automatic device.

Using automatic tilting gravity casting machines, by which the molten metal can flow into the mould cavity smoothly and with low turbulence.

Photo credit: Ming Ming

Remove the gate

After the cast is solidified and cools down, the gate is removed by using a saw.

Heat treatment

Heat treatment after casting is used for improving the mechanical property of casts.

After heat treatment, the quenched cast could show minor deformation. Using gauges to go through a thorough measurement check and then fine-tune the cast, if necessary.

Photo credit: Ming Ming

Shot blasting

This step is for smoothing the rough surface and removing surface contaminants

CNC machining

The final step is to refine cast parts through CNC milling and precision CNC turning so that the final parts will meet the design required by the ebike's brand. CNC milling cuts the parts in different angles and ensures the parts are cut into the desired shape. CNC turning is used for drilling, grooving, and reaming; it shapes exterior and interior of cylindrical, taper, and curved parts.

Magnesium Alloy in Bicycle Frames: Lightweight and High Performance


Magnesium alloy has a density of 1.7, which is only 21% of steel and 60% of aluminum alloy.

Advantages of Lightweight

The lightweight nature of magnesium alloy makes it an excellent choice for bicycle frames.

High Rigidity and Bending Resistance

Magnesium alloy provides high rigidity and bending resistance, enhancing the overall strength of the frame.

Shock Absorption

Magnesium has superior shock absorption properties compared to aluminum, making for a more comfortable ride.

High-Temperature Extrusion Molding

The material’s good processability allows for thin-wall magnesium alloy pipe fittings, reducing vehicle weight.

Environmentally Friendly

Magnesium is pollution-free and easily recyclable.

Load-Bearing Structure

The frame is a critical load-bearing component in bicycles, and choosing a lighter magnesium alloy frame with good mechanical properties contributes to overall weight reduction.

Research and Development

Many countries and institutions invest in researching magnesium alloys for bicycle frames, leading to successful applications in various parts such as handlebars, front forks, rims, and gear systems.

source : cncmachining

Of course, magnesium can also be treated by the gravity casting process, or by die casting, as explained below by SUNRISE

source : SUNRISE
Photo credit: Sunrise Casting

I hope that this brief file dedicated to the manufacturing of frames for our smart e-bikes will provide you with interesting information about the technical aspects surrounding current designs.


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