Metal Stamping vs CNC Machining: How To Choose The ...

20 May.,2024

 

Metal Stamping vs CNC Machining: How To Choose The ...

Manufacturing process selection is intertwined with part design and the quantity required. Two of the most commonly used processes are metal stamping and CNC machining. While in some applications it’s clear from the outset which is right, in many other cases a good argument can be made for using either. Here’s a look at the pros and cons of each and some tips for choosing the right method for your design and volumes.

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Metal Stamping Basics

Stamping is an umbrella term for a set of processes used to turn sheet metal into 2D and 3D shapes. Blanking and drawing operations cut and stretch or deform it in two or three dimensions, respectively.

Stamping operations are performed by tools mounted in a press. Typically, a punch and a die are brought together to blank, bend, and stretch the sheet metal to the shape required. Additionally, piercing can be configured if required. In high-volume operations coiled sheet is continuously fed into the press where progressive tools produce the finished form in a series of steps.

Pros and Cons of Metal Stamping

Stamping’s advantages include:

  • High material utilization

  • High production rate

The principle limitations are:

  • Restricted to thin material (many stamping operations consider ¼” (6mm) the upper limit although

    Lutco can stamp thicknesses up to 0.375”

    (9.5mm).)

  • Usually requires complex tools that must be specially made for each part to be produced

  • Not all materials have sufficient ductility for stamping

  • Material springback limits the tolerances that stamping can maintain

CNC Machining Processes

Machining processes cut metal away from a solid bar, tubing, billet, or casting to produce the shape required. Machining processes are generally either prismatic, meaning the workpiece is fixed, or cylindrical, where the workpiece rotates. Milling is the prime example of a prismatic process that cuts straight planes while turning and grinding to produce cylindrical workpiece geometries.

CNC — Computer Numerical Control — refers to how the machine tools are controlled. In a CNC machine, each axis of motion is driven by a motorized spindle. These spindles (there may be several) are controlled by a computer program that moves each one to produce the required geometry.

Pros and Cons of CNC Machining

The principal advantages are:

  • Yields complex 3D parts and can hold very tight tolerances on critical features

  • All metals can be machined (although some may require specialized cutting tools and conditions)

  • Cutting tools are mostly inexpensive consumable items (there are exceptions)

  • Good control over surface finish

Major limitations of CNC machining are:

  • Material utilization, (which is dictated by part design,) can be low

  • Production rate is limited by metal removal rate (which can be low on some materials)

  • Machined parts may need to pass through multiple machines and setups (again, this is design-dependent)

What to Consider When Choosing Metal Stamping or CNC Machining

Four factors to consider are:

  • Quantities required

  • Part geometry

  • Part tolerances

  • Material

How Quantities Impact Manufacturing Process Selection

Metal stamping is much faster than CNC machining and would be preferred were it not for the time needed to get a press ready to run. Depending on tooling size and complexity, this setup time can run into hours. 

In comparison, CNC machines have quicker setup times, although a part program must first be produced using the CAD file.

A second consideration is tooling cost and lead time. In a process that can take weeks, press tools are constructed from very hard grades of tool steels. Lutco often uses electro-discharge machining (EDM) before being ground and polished to the required form. In contrast, CNC machine tools generally use disposable cutting inserts that are kept on the shelf ready for use.

Part Geometry Effects

Some complex shapes cannot be stamped. Engine blocks and cylinder heads are examples, and many housings and valve bodies would also fall into this category.

Some stamped parts may go through secondary machining operations. This is often to achieve specific dimensions or tolerances on particular features as well as surface finishes.

Machining imposes fewer limitations on part geometry. There is however always a requirement for the cutting tool to have access to the feature being machined, and for relative motion between the two.

For both stamping and machining, process constraints may mean that a part must be assembled from several components.

Part Tolerance Impacts

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Precise stamping tools and tight control over material quality have greatly improved the consistency of stamped parts but tight tolerances remain challenging. CNC machining is capable of maintaining tighter tolerances and might be used as a secondary process for specific features.

Material Properties

Metals need ductility if they are to be stamped without cracking. Sometimes this can be put in through heat treatment but many very hard metals just aren’t suitable. Thickness is another limitation as thicker sheet needs far more force to pierce and deform. This requires bigger machines and more robust tooling.

As a counterpoint, it’s very difficult to hold thin sheet metal pieces for machining; they tend to distort under the clamping loads needed to resist the cutting forces.

Metal Stamping vs. Machining: Which is Right For my Parts?

This usually comes down to quantities and part design. Where possible, designing high production volume parts as stampings minimizes production costs.

The higher material utilization of stamping helps keep costs down. This is particularly important when working with more expensive specialty materials or exotic alloys.

Machining is generally used to produce complex parts that require multiple operations to complete, tight tolerances (in the vicinity of .0001” or 2 ½ um), and control over surface finish.

Lutco: Experts in Metal Stamping and Machining Techniques

Because we use both metal stamping and CNC machining Lutco can offer unbiased advice on which process to design for and select. Combining the experience of our toolmakers, the technical know-how of our engineers, and the latest design and simulation software eliminates potential pain points and helps our customers compete globally. Contact us for more information.

Sheet Metal Stamping Vs. Fabrication

Many of our clients wonder whether metal stamping or fabrication is right for them. Each of these techniques is a good choice for different reasons. Look over the details below to see which method will best serve your needs.

 

Sheet Metal Stamping

 

Sheet metal stamping involves bending, punching, or flanging the object with a stamping press. The stamping is either done in separate parts or through multiple stages. Manual presses are an option but coil-fed press equipment is the industry standard.

 

This method creates formations simultaneously or with progressive die. Sheet metal stamping is typically done when replicating parts in high volume. Precision stamping is done when creating unique products with very specific criteria. Bending and forming with CNC equipment is preferred if you are creating two or three-dimensional objects.

 

 

Many businesses opt for metal stamping because of its cost efficiency. For complex products, precision stamping is a quicker solution than fabrication. Metal stamping is not cost-effective for short production runs but it is invaluable for long runs. 

 

Should You Choose Metal Stamping?

 

Simple products with minimal customizations can be effectively produced via sheet metal stamping. This technique can have benefits over fabrication. Primarily, metal stamping is a cost-effective choice for production runs with mid-to-high volumes. Complex products with some customizations are possible with precision stamping. While the level of control is not as extensive as with fabrication via CNC cutters.

 

However, remember the downfalls…

  • Stamping is typically too expensive for short production runs.
  • It can take far too long to make design changes after tools are already produced.
  • Longer lead times are sometimes required.

Sheet Metal Fabrication

 

Sheet metal fabrication involves cutting, drilling, or welding the object with CNC cutters. Fabrication can involve tapping or thread rolling with a tapping machine. The process might also include folding by striking or with press brakes or folders. After assembling, the separate parts can join together with fasteners or crimped seams, or be welded or riveted together.

 

Customizations are more diverse with fabrication. Lead times are lower for complicated creations. The high level of flexibility with this equipment makes it easy to adjust a design on the fly. Meanwhile, it can sometimes be impossible to make any design changes when using a stamping press. 

 

Many businesses prefer sheet metal fabrication because of the fast design-to-production timeline. Producing prototypes is much easier with fabricating versus stamping. Likewise, with fabrication it is not cost-prohibitive to run a small volume production.

 

Read more about the pros and cons of custom sheet metal fabrication.

 

Should You Choose Metal Fabrication?

 

Complex products with a high level of customization should be done via sheet metal fabrication. This technique can work effectively in ways not possible with a stamping press. A big advantage with metal fabrication is the short lead times. You can make adjustments to your design without messing up your production schedule. Furthermore, metal fabrication is more cost-effective on short production runs.

 

However, remember the downfalls…

  • The amount of labor required will vary depending on your expectations. In the most advanced cases, the cost of labor will be high which should be a consideration.
  • Any odd shapes or complex parts can greatly increase the amount of time that it takes to produce a single unit.
  • Production takes longer and repeating a process is not as easy as it is when stamping the sheet metal.
  • The level of consistency is not as dependable when fabricating as it is with stamping dies.

Conclusion

 

Both sheet metal stamping and fabrication are common practices. The appropriate metal formation method will vary depending on the application. One of these two techniques will be more favorable than the other. It’s important to consider the circumstances when deciding which method you will use to create your product or part.

 

Confused about which option is right for your needs? 

Contact Us for some expert help!

 

Contact us to discuss your requirements of sheet metal stamping press machine. Our experienced sales team can help you identify the options that best suit your needs.