Sheet metal fabricated parts can be produced by many processes. The two broad methods are CNC metal fabrication and metal stamping.
To understand where each comes into play, you must first understand what each is, and what the differences are.
CNC metal fabrication
Sheet metal fabricated parts are those which are typically produced without the use of a stamping dies (sometimes referred to as “hard tooling.”) CNC metal fabrication is ideal for prototyping and small to medium production runs (<20K annual quantities.)
In its simplest form, the most basic equipment consists of shears, modular tooling such as C-Frame Pierce-All® to pierce holes, slots, etc., and press breaks to do the bending.
Moving to automated technologies, it is replaced by Computer Numerically Controlled (CNC) punch presses (often called a “Strippit”), CNC Lasers or CNC Punch/Laser Combination machines, followed by bending if required using CNC Press Brakes.
CNC laser machine
CNC punch/laser machine
CNC press break machine
How it works
Full sheets are placed on either a CNC Laser or Punch Press machine, where the same features could be punched or cut, and also knockouts, shallow forming* and sometimes tapping could potentially be done, and the entire perimeter of the part punch or cut from the sheet.
*such as extrusions, flanges, louvres and other shallow forming, whose heights are limited by each machine’s specifications.
Some tooling may be required for custom hole sizes, shapes, or forms, but it is usually not too expensive, ranging from $50-150 for a simple punch and mating die to perhaps $1500-$2000 for complex forming tools.
A CNC Laser can only cut, but can also cut both intricate shapes due to no tooling requirement, as well as large cut-outs, that might otherwise require punching forces (tonnage) that exceed the CNC punch press’ capabilities.
A CNC Punch/Laser combination machine can achieve both of the above; pierced holes, formed features, and intricate and fine cutting without tooling.
The fully pierced and cut pieces would then be bent if/as required using a CNC Press Break, where programmable and moveable back gauges and stops permit the workpiece to have multiple bends done, often at different bend heights and angles to meet the drawing requirements. These typically require no tooling, or limited tooling, such as small matching punches and bushings for the piercing, and male & female press break tooling for the bending. Most metal fabrication shops have an arsenal of these to suit a wide variety of such requirements, so the customer should bear little or no tooling cost.
Part costs are commensurate with the time it takes to cut parts from each sheet, how they nest within the sheet (which establishes how much material it takes to produce each part), and if/what secondary operations are required such as bending, which consists primarily of labor.
Metal stamping
Metal stamping is done using mechanical or hydraulic presses of increasing tonnage, and one or more metal stamping dies used to form many or all features of a sheet metal part. It is ideal for mid to high volume production OR small parts that can’t be safely handled by CNC processes that require repeatable tolerances.
Dies can cost from $3,000 to $200,000 (or more), depending on part size, complexity, and to what degree of part completion the die will yield.
Small parts that aren’t complex can often be fully produced (i.e., no secondary or subsequent operations) in a progressive die which has the lowest ROI. Larger parts typically involve higher die costs, which can grow exponentially with part complexity.
Metal stamping die setup
The key advantages in having a die that can fully produce a part are high production rates, and in a single operation, and relatively low labor costs resulting in the lowest possible unit cost, provided volumes can justify/amortize the tooling cost and provide an acceptable ROI.
One way to reduce die costs is to produce the part without all required features, which removes some die complexity, thus die cost. To complete the part, either secondary operations or dies (often simpler and less costly dies) can be used to complete the part. Alternatively, secondary operations without dies (e.g. bending in press breaks) can sometimes be employed to complete the part. This however comes with added labour expense due to multiple operations and part handling.
Where your supplier has one or more existing dies to make an acceptable variant of the part you require, or if any of those dies can be modified to do so, you may be able to obtain what you need with little or no tooling expense, and low part cost since the part is made as a metal stamping. This can also be beneficial in the case of a new product where the design is either not stable enough, or unknown volumes may not be able to justify the expense of a die.
Hybrid manufacturing
This is where Metal Stamping and Metal Fabrication become seamless, through a supplier that offers both capabilities; CNC fabrication and metal stamping, ideally with a great many open tooled (supplier owned or non-proprietary) dies that you may be able to benefit from.
- Progressive dies that blank out the part, but do only limited or no bending because volumes could not justify such a complex die. In such situations, parts may be made in two steps; the blank done in a less costly die, followed by CNC bending. Unit part cost may be higher than a fully progressive die, but tooling costs will be reduced.
- Capitalize on a supplier’s existing item that is produced in a die, but have it customized or modified to suit your requirements using their CNC equipment. For example, your supplier has a die that can produce a pan or yoke with a limited range of hole sizes. They may be able to make that part without any hole, and then mount that part on their CNC laser or punch press to cut your custom hole. Better yet, if they have a CNC Punch/laser Combination machine, they may be able to cut holes without any tooling, (including irregularly shaped holes), and add the many other features previously discussed, all in the same secondary operation.
The difference between a CNC shop that has say laser and punch machines without stamping capabilities and one with is that the former as quantities increase, that CNC shop will be content to keep making the part in their usual fashion, unable to offer more cost effective alternatives.
By contrast, working with a hybrid manufacturer that offers both CNC fabrication and stamping capabilities, they have no problem telling you, their customer, if/when you are wasting money and tying up their flexible machine making an item which can be more economically made by metal stamping, at which point they would suggest that you invest in a die that would rapidly pay for itself in reduced unit costs. This can also free up their flexible CNC machine to produce your lower-mid volume production parts; which is what such machines are best designed for.
It’s important to be open and flexible when working with your supplier; the more you do so, the more likely they are to potentially make use of existing dies and/or find the most economical solution given your product volumes.
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