When should I choose sheet metal instead of injection molding?

The selection of the appropriate production process can greatly influence the product quality, production cost, lead time and scalability in modern manufacturing. Sheet metal fabrication and injection molding are the two most popular techniques used in the manufacturing process. Both are common processes in various industries including automotive, electronics, aerospace, medical devices and consumer products, but they have unique advantages and applications.

One of the most frequently asked questions in the minds of engineers, product designers and procurement managers is: When does sheet metal make sense when choosing materials for a product?

It will depend on production volume, materials required, design complexity, development time and budget. This guide details some of the primary differences between sheet metal fabrication and injection molding and can assist you in deciding when to use sheet metal for your next project.

Understanding Sheet Metal Fabrication

Sheet metal fabrication is a manufacturing process which makes use of flat metal sheets to create a finished component by following the steps of:

• Laser cutting
• CNC punching
• Bending
• Stamping
• Welding
• Surface finishing

Common materials include:

• Stainless steel
• Aluminum
• Carbon steel
• Copper
• Brass
• Galvanized steel

Fabrication is a common application in sheet metal for enclosures, brackets, chassis, cabinets, electrical boxes, machine housings and structural parts.

Understanding Injection Molding

Injection molding is a manufacturing technique that uses a custom-made mold to inject molten plastic under pressure. The plastic freezes into the desired shape when it is cooled down.

Common injection molding materials are:

• ABS
• Polycarbonate (PC)
• Polypropylene (PP)
• Nylon (PA)
• PEEK
• TPU

Injection molding is commonly used for:

• Consumer electronics housings
• Automotive interior components
• Medical device parts
• Plastic containers
• Household products

Injection molding is very efficient for large volume production, but has a high initial tooling cost.

Choose Sheet Metal for Low to Medium Production Volumes

The low and medium volume production aspect of sheet metal fabrication is one of the major benefits.

In order to produce parts using injection molding, the equipment needs to be expensive and the tools can range from a few thousand dollars to hundreds of thousands of dollars depending on the complexity of the part. This tooling cost is recouped in large production runs.

In sheet metal fabrication, however, minimal tooling is needed. CAD files can be used to produce most of the parts directly by CNC equipment.

Best Production Range for Sheet Metal

• Prototypes
• 10–10,000 units
• Custom products
• Small batch manufacturing

Best Production Range for Injection Molding

• 10,000+ units
• Long-term mass production
• High-volume consumer products

If your production quantity is uncertain or relatively small, sheet metal is usually the more economical option.

Choose Sheet Metal for Faster Prototyping

In today's competitive manufacturing world, speed to market is essential.

In the case of sheet metal fabrication, manufacturers may be able to make a prototype within days. No moulding has to be done, design files can go straight into production.

Benefits include:

• Faster product validation
• Reduced development cycles
• Lower engineering costs
• Quicker design iterations

Before starting the production of an injection molded part, the design and manufacture of a mold, along with testing and validation, are necessary. It can be weeks or months before this process occurs.

Sheet metal manufacturing offers much faster turnaround time for companies creating new products.

Choose Sheet Metal When Design Changes Are Expected

Product designs change in the process of development.

Once production has started, changes can often be made to sheet metal parts by changing cutting programs or bending parameters.

Examples include:

• Changing hole positions
• Adjusting dimensions
• Adding mounting features
• Modifying bend angles

By contrast, injection molding tools are not easily and cheaply modified. Simple design changes can mean changes to the mold or even new tools.

Sheet metal is more flexible and less risky than other materials for projects that will be continuously being changed during design.

Choose Sheet Metal for Superior Strength and Durability

Metal parts are typically stronger than plastic parts.

Sheet metal parts offer:

• Excellent load-bearing capacity
• High impact resistance
• Better fatigue performance
• Greater dimensional stability

Industries frequently selecting sheet metal include:

Industrial Equipment

Machine frames, cabinets and structural supports must be made of strong materials and be able to resist harsh operating environments.

Electrical Enclosures

Sensitive electronics are housed in metal enclosures for protection and durability.

Aerospace Components

Aluminum sheet metal has a great strength to weight ratio.

Automotive Applications

Sheet metal is still used in many structural automotive parts due to the strength and safety properties.

When mechanical strength is important, such as for an application, sheet metal may be a better option.

Choose Sheet Metal for High-Temperature Environments

Plastic materials, like any materials, have temperature restrictions.

Some injection molded plastics can warp, melt or break down at high temperature.

Sheet metal materials can withstand:

• High operating temperatures
• Thermal cycling
• Outdoor environmental exposure
• Industrial processing environments

Applications include:

• Electrical cabinets
• HVAC systems
• Industrial machinery
• Power distribution equipment

When heat resistance is critical, sheet metal provides superior performance.

Choose Sheet Metal for Better EMI and RFI Shielding

Electronic products are sometimes subjected to electromagnetic interference (EMI) and radio frequency interference (RFI) protection.

The sheet metal is a good material for:

• Server enclosures
• Telecommunications equipment
• Medical devices
• Industrial control systems

For comparable shielding performance, plastic injection molded parts usually have to be coated or otherwise enhanced with conductive coatings or inserts.

Sheet metal can be used to design and reduce extra costs of the process.

Choose Sheet Metal for Sustainable Manufacturing

Conscientious manufacturing factors are becoming more and more relevant.

Sheet metal fabrication provides a couple of benefits to the environment:

High Recyclability

Materials such as steel and aluminum are among the most recycled materials worldwide.

Reduced Material Waste

Modern CNC cutting systems optimize material utilization.

Long Product Lifespan

Metal components often last significantly longer than plastic alternatives.

Circular Economy Support

Recycled metal can be reused repeatedly without substantial degradation in quality.

Companies seeking environmentally responsible manufacturing solutions often favor sheet metal fabrication.

When Injection Molding Is the Better Choice

Although sheet metal has many advantages, injection molding remains the superior option in certain situations.

Injection molding is generally better when:

• Production volumes exceed 50,000 units annually
• Complex organic shapes are required
• Lightweight plastic components are preferred
• High cosmetic surface quality is essential
• Extremely low per-unit cost is needed for large-scale production

Products such as smartphone cases, consumer packaging, toys, and household goods are often ideal candidates for injection molding.

Sheet Metal vs Injection Molding: Quick Comparison

Conclusion

Whether to opt for sheet metal fabrication or injection molding depends on the product's requirements, the production volumes, budget, and timeframe.

When it comes to prototyping, low to medium production runs, design variations, high strength, high temperature resistance, or EMI shielding, sheet metal fabrication is the preferred option in general. It provides outstanding flexibility, reduced initial investment and quick time to market.

Injection molding, on the other hand, is more economical for producing large quantities of parts in which the cost of tooling is distributed over thousands or millions of parts.

For many manufacturers, it is not a matter of which process is the universal best, but rather which process fits best the technical and commercial objectives of the project. By assessing production needs upfront in the product development process, companies can save money, speed up product development, and improve overall manufacturing results.