Always consider the manufacturing process when designing a part. Forging, casting, and machining can all be used to produce metal parts, but the costs and resulting mechanical properties will differ significantly.
The application dictates the properties needed in each component, and the quantities required influence process economics and lead time. Strength, toughness, and low mass are often priorities, while the expense and time required to produce tooling factor into piece costs and delivery dates.
In some cases, a design team may start with machining as a means of quickly producing samples, but later switch to casting or forging. Although expedient, this can lead to poorly optimized designs that are heavier, larger, or more expensive than necessary. Alternatively, it may require the part to be redesigned, which can affect development timelines and product launch dates.
A better strategy is to compare these three processes during the design phase, select the one that yields the optimal product or components, and incorporate the necessary time and cost into the project plan.
Best Use Cases for Forging Over Casting
Both forging and casting are near-net shape processes that minimize secondary machining and require dedicated tooling. Casting can produce more complex geometries than forging, and with more internal chambers and passages. However, there are many applications where forging offers significant advantages, including better strength, higher impact and fatigue resistance, fewer defects, and faster production rates.
Strength/Integrity
Forging yields stronger parts than casting because it optimizes grain structure. Stronger parts can also be lighter as less metal is needed. These properties make forging a better process for automotive components used in applications from light vehicles to heavy trucks and trailers.
Impact/Fatigue Resistance
Forged parts are tougher than those made by casting by virtue of the grain flow and cold working that take place during processing. Applications benefiting from the higher impact and fatigue resistance produced by forging include components for agricultural machinery and forestry equipment, railroad components, and parts for firearms.
Material Defects
Turbulent flows during casting can entrain air bubbles, which can become porosity in the final piece. Likewise, cold shuts can result where metal flows around obstacles and joins back up. Additionally, segmentation can occur in complex alloys during solidification. These defects are difficult to predict and costly to inspect. In anticipation of quality losses, it’s customary to overproduce, which is wasteful.
In contrast, through a combination of recrystallization and compaction, forging results in highly homogeneous material, making it appropriate for parts used in applications involving pressure, like those in chemical processing equipment and other industrial machinery.
Production Rates/Speeds
Casting involves melting, pouring, solidification, and breakout or mold release, as well as material analysis and other quality control checks, which can further slow the process. Comparatively, impression die forging is a stable, repeatable process requiring billet heating, followed by shaping in the die. Because there are fewer steps involved, the process is much faster than casting, which is especially useful when parts are needed urgently.
Best Use Cases for Forging Over Machining
While capable of high precision and excellent surface finishes, machining processes are slow and subtractive. This makes them costly and wasteful, which is why they are generally best minimized. However, the major strength of machining is that minimal tooling is needed, which minimizes both lead time and tooling costs.
Despite these strengths, forging is the better choice for high-volume production, waste minimization, enhanced mechanical strength, and reduced lead time.
High-Volume Production
Machining processes handle one part at a time on costly machine tools. The greater the volume of metal to be removed, the longer each part stays on the machine. Forging is a much faster process by virtue of using dedicated tooling and shaping the entire part in one step or a linked series of steps. Consequently, forging is the better choice for applications such as automotive components (suspension and drivetrain) and parts used in construction and civil engineering.
Waste Minimization
While forged parts often need some limited secondary machining, the volume of material removed is small compared to machining from billet or bar. The disposal of chips resulting from machining is becoming increasingly difficult and expensive; however, a bigger problem arises when machining higher-value alloys, such as some stainless and alloy steels. In such cases, the volume of metal cut away can be more expensive than the material content of the finished part!
Applications where waste minimization is a priority are found in the production of complex parts like those used in aerospace. Higher production volumes, such as those in automotive component production, can also benefit from the reduced waste associated with forging.
Mechanical Strength
Parts machined from bar or billet lack the grain flow that forging creates. Forged parts are, therefore, significantly stronger, which increases durability and can allow component mass reduction. Important applications that need forging rather than machining are found in aerospace and motorsport, and to a lesser extent, in firearms and automotive component manufacturing.
Lead Time Reduction
The speed advantage of forging over machining results in shorter lead times from order to delivery. This is especially important for situations where customers require changes at short notice, as can happen in automotive component manufacturing, or when there’s a focus on supply chain and inventory management.
See If Forging Is Right for Your Project
Founded in 1967, Trenton Forging is a U.S.-based company dedicated to satisfying customers through innovation and urgency. We deliver approximately 3.5 million forged parts annually to customers across various industries, including automotive, railroad, and defense.
If you need or are designing metal components, selecting the optimal production process should be at the forefront of your thinking. Forging isn’t right for every project, but there are many situations where it provides the best combination of mechanical properties and cost. Contact us today to speak with one of our experts.
