Cold forging machines are capable of manufacturing precise metal parts for automotive, aerospace, railway and heavy vehicle industries, among others. In this post, we will explore the several advantages of this technology in comparison with traditional machining manufacture and the design considerations that must be taken in order to smoothly transfer our designs from machining to cold forging . The devil is in the details. 

What are the advantages of cold forging?

Cold forging is a high-speed process that consistently meets the required resistance values and geometry accuracy of the components, making it a very suitable process for high volume productions.

These machines are fed with room temperature steel rod coils of a given diameter (sometimes even other non-circular geometry) which is then sheared, transported and shaped progressively in various steps by applying pressure using precisely shaped toolings.

Many times, we associate cold forging with standard screw geometries; however, it is possible to obtain highly complex parts that would otherwise require machining centers to complete them.

Cold formed parts can be finished with heat treatments, simple secondary machining operations, thread or groove rolling, and coatings.

The following advantages can make you consider transferring your production or supply of components from machining to cold forging:

Cost-effective

Both cold forging and machining are viable processes for different applications and needs. When the production volume reaches around 100,000 parts per year, we can start considering whether the geometry of our part can be cold formed. The initial investment in tooling development will be easily compensated by the savings in material and part cost when manufacturing in large volumes. The repeatability and speed of cold forging make up for the necessary production costs. Depending on the geometry, smaller annual volumes may also easily pay off.

Reduced lead time

Cold forging machines work at 100-150 parts per minute (that’s around 2 parts per second!), whereas machining lathes require longer times to finish the component with a higher dependency on the part geometry (1-2 parts per minute can be usual). Some geometries can be challenging to obtain by cold forging and a secondary machining operation may be necessary, however, we still have savings compared to machining the whole component because of the speed and the amount of material used, which takes us to the next advantage; scrap savings.

Less scrap

Cold forging is a sustainable process since the material is deformed instead of cut. This means that when we shear a portion of the coil, the whole blank is used as part of the final component. When the blank is progressively pressed into the dies, the initial shape can enlarge or reduce its diameter, adjust the length of different portions of the part and include other geometries such as hexagonal heads or sockets. Think of it as pressing a portion of Play-Doh inside a die, its shape will change but the amount of material is constant. Without a doubt, the metallic materials we cold forge are not as soft as Play-Doh, which implies several limitations in terms of material deformation, and the geometry progression must fulfill certain rules.

When a hollow part is needed, a small portion of the part (called slug) must be cut, generating some scrap.

However, when machining a part, the initial material required must be at least the size of the biggest diameter and length of the final component, in order to cut the desired shape out of it. You can imagine this as a marble sculpture from where you take lots of material out of before revealing the final product.

Mechanical properties and geometry accuracy

With the right choice of material and thanks to the work-hardening effect, secondary operations such as heat treatments can be avoided, bringing a competitive part with the expected properties into the market.

The accuracy achieved in a cold-forged part enables finishing parts without the need for additional processes and is suitable for many applications; automotive, general industry, off-highway… It all depends on the geometry of the component, but we know that lengths can meet tolerances of ±0,10mm and many diameters ±0.02mm. This level of precision in diameters is consistently achieved due to the excellent surface finish. In fact, we have been able to develop parts where secondary grinding operations for diameters have been eliminated thanks to the precision of cold forging.

So, are my components suitable for cold forging?

Now that we know more details about the advantages and applications of cold forging, it is time to consider whether it is feasible to cold form the parts we currently manufacture by machining. This way, we will have lower-cost parts due to high production speed that improves the lead time of the part and reduced scrap. This will allow us to offer more competitive solutions in a market like the automotive industry, where it is increasingly difficult to stand out.

Material deformation is the key to designing a suitable process for the geometry and characteristics of the final component. Therefore, it is possible that the design of the machined component must be slightly adapted to continue meeting its functions and requirements while optimizing the process for cold forging.

The devil is in the details —this means that considering these details beforehand will allow us to transfer our parts from machining to cold forging without issues and achieve stable mass production in a short time.

It is important to consider that this technology shift brings several advantages, so it is worth reviewing the functionality of the current part, its role in the assembly where it is mounted, and the essential geometric requirements needed in each area.

As you can imagine, the pressures in the cold forging process are very high, since the material deformation occurs at room temperature, and some geometry changes can be considered extreme. However, the deformation itself can heat the material in some cases up to almost 200ºC, so caution must be taken when handling parts that have just come out of the machine.

The tools used in cold forging have highly demanding characteristics to withstand these cyclic pressures, so anything we can do to improve tool life is beneficial for production stability and dimension accuracy, reducing downtime and tooling costs.

Let’s go into detail

At Ecenarro , we have been analyzing our customers’ blueprints for years. Many times, we realize that designs are intended for machined parts, and we proactively indicate the details that must be modified to make them feasible for cold forging. Without a doubt, the functionality of the part must remain just as demanding, but we can identify non-critical areas
where changes are feasible and simulate them before purchasing any tools to verify their potential. This can make the difference between being able to cold form the parts or not, with all the benefits that this entails!

If we consider the following design tips, we can verify whether our machined part is directly “cold-formable” or detect what can be adapted to make it feasible. Are you ready to dive into the details that will successfully translate your designs from machining to cold forging? Here we go!

Exterior edges vs. underfilling:

One of the main mistakes is assuming that the cold formed part will have all edges as sharp as in the machined piece. When machining a part, creating an edge or an external chamfer is easy. In cold forging, however, filling an external edge can sometimes be challenging. Remember that in cold forging, the material fills the molds through pressure, so it struggles to reach external edges. This results in irregular radii or underfilled areas in some of these edges. The geometry of each part must be analyzed, as the values obtained in a stable process can range between 0.3mm-1.5mm.

Using our simulation programs, we can accurately calculate these values before manufacturing any tooling.

*DESIGN TIP: Whenever the edge is not critical to the component’s function, allowing for some underfilling will make it possible to cold-form the part without issues. These underfilled areas, being irregular, are usually defined by ISO 13715, which sets maximum and minimum limits for different axes.

Interior corners vs. radii

When cold forging parts, interior corners are formed by replicating the tooling geometry, which usually includes radii at transitions to make them more robust and capable of withstanding high pressures without deteriorating during the production of hundreds of thousands of parts. In machined components, these geometries are defined by a combination of the tool’s trajectory and its cutting geometry. If a sharp interior corner is required, we will progressively deform that area, starting with larger radii until achieving the final value. However, it is important to consider that very sharp edges weaken cold forging tools and hinder material flow, so we should always try to avoid them when possible. Depending on the part’s geometry, optimal minimum radii can vary between 0.4mm and 1mm, but each case may have different requirements.

Axial vs. radial undercut

In order to ensure a successful assembly of the part, many designs include an undercut or relief groove. In machined parts, this groove is radial, meaning that the radius is reduced in that area to obtain the desired geometry because it is easier to achieve. However, when transferring this geometry to cold forging, a radial undercut becomes a complexity.

Cold forging machines consist of two blocks—one fixed and one movable—so that the parts being transported deform in the same direction as their main axis. A radial undercut would prevent the part from being extracted from the mold, so these cases are easily solved by changing the undercut direction to axial. The function remains unchanged, while making it possible to transition the design to cold forging.

*DESIGN TIP: When you see a radial undercut, remember that it would unnecessarily complicate the cold formed process, whereas an axial undercut brings your part one step closer to being suitable for cold forging.

Stay tuned!

There are several more tips that can help you achieve a successful transition from machining to cold forging, which we will continue sharing with you. This way, you will never look at parts the same way again and will be able to identify critical points in your design to enable cold forging for your components. Remember, this can bring you great advantages and make your product more competitive!