Direct and indirect extrusion both use a stationary die and press ram to apply pressure to a billet. Indirect extrusion is much simpler because the billet remains stationary in relation to the container. This eliminates friction and ensures that the amount of work performed is constant. However, there are some drawbacks to indirect extrusion.
Backward extrusion

Aluminum extrusion with aluminum extruders has several advantages over direct extrusion. Indirect extrusion requires less force and friction, but it cannot produce very long extrusions. Nevertheless, many manufacturers combine both processes. The following are a few of their benefits.

Indirect extrusion can yield more consistent work and temperatures across the entire length of the extrusion. It also produces profiles with greater consistency in dimensions, grain structure, and mechanical properties. However, this method is not without its drawbacks. First, it requires the removal of the as-cast surface layer, removing dirt and oil from the billet. Second, it is necessary to support the die during extrusion. Third, the die is not as large as in the direct process.
Problems with lubrication

In the indirect extrusion of a carbon nanotube, lubrication has been a crucial issue to consider. The absence of lubrication has been shown to cause sleeve fractures and longitudinal grooves in the extruded rods. The authors suggest lubrication with carbon oil or boron nitride sprays to improve the flow of material and to maintain the sleeve integrity.

Lubricants can reduce friction and ensure a smooth process. Some lubricants can be applied to the billet surface using a fat-sulphur mixture. Other lubricants, such as zinc phosphate coating, are also available. Glass is also a good lubricant, especially at high temperatures. It can be applied to the billet surface by rolling or dipping.
Drawbacks of indirect extrusion

Indirect extrusion has many benefits, but it also has a few drawbacks. It is not as flexible as direct extrusion, and the size of the stem limits the cross-sectional area of the finished extrusion. This method can also lead to the appearance of a product that has impurities, which can negatively impact its finish appearance.

Indirect extrusion reduces friction and requires lower loads during the extrusion process. It also produces more consistent profiles, grain structures, and mechanical properties than direct extrusion. However, it has some drawbacks, including the need for die support, and reducing the size of the profile.
Results in higher quality

Direct extrusion is a more efficient method for making parts, especially if you need to produce a large number of parts in a short time. The advantage of this method is that the tooling cost is 80-90% lower compared to other processes. Furthermore, it is better suited to producing parts with complex cross-section forms, such as T-slots, grooves, and undercuts.

Direct extrusion reduces filament travel time. Since the extruder is mounted directly above the hot end, the filament travels through a very small distance. This reduces the amount of filament friction and makes the extrusion process more efficient. This leads to better quality prints with fewer oozing and stringing.
Hydrostatic extrusion

Indirect extrusion involves moving the punch opposite the billet. This eliminates friction, and the forces required to move the press are smaller. The hydrostatic method uses a container filled with fluid that transmits the pressure from the press to the billet. This eliminates friction and the resulting increased ductility in the product.

It is particularly useful when large strains are required, such as in the case of high-strength materials. This method also minimizes surface damage, as it imparts a uniform force to the proximal end of the device. In addition, it is useful for high-strength materials, because it allows the parts to be easily removed from the die without worry of them recovering their shape.