Subtractive vs. additive manufacturing title fight — chemical etching vs. electroforming

In this blog post, we discuss and compare two different manufacturing methods: additive manufacturing and subtractive manufacturing. We also zoom in on the most powerful additive and subtractive manufacturing techniques: electroforming; additive manufacturing, and chemical etching; subtractive manufacturing. A heavyweight title fight, so to speak.

Additive manufacturing

Additive manufacturing (AM) refers to manufacturing methods that build up 3D objects by adding materials layer upon layer. Objects manufactured can be of almost any shape or geometry. Materials used can be metal, (thermo)plastic, ceramic, or sometimes even chocolate.

Additive manufacturing can be seen as a ‘from-the-bottom-up’ method. It is also referred to as: additive layer manufacturing, layer manufacturing, additive fabrication, or additive processes/techniques. We discuss electroforming later in this article.

Subtractive manufacturing

Subtractive manufacturing, the opposite to additive manufacturing, is a manufacturing method that entails the removal of materials to produce a component or product. One can look at subtractive manufacturing as a ‘from the top down’ method. Common subtractive manufacturing methods include: laser cutting, CNC machining, electro discharge machining (EDM), micro stamping, water jetting — and, of course, chemical etching:

Subtractive manufacturing method: chemical etching

Chemical etching is a subtractive manufacturing process that selectively removes metal by chemical action. A clean metal ‘blank’ is coated with a light-sensitive photoresist and exposed, through photo film work, to ultraviolet light, which hardens the resist. Unexposed areas are developed away, leaving bare metal which is sprayed with etching solution on both sides, at high pressure. This process accurately removes the resist, and leaves behind burr- and stress-free components. 

Synonyms of chemical etching 

In the industry, chemical etching is also known as:

• Photo Etching
• Industrial etching
• Photochemical etching
• Chemical Milling
• Photo milling
• Photochemical milling
• Photo-Chemical Machining (PCM)

Engineers are advised not to get confused by the synonyms. All these names describe the exact same process manufacturing process.

Materials that can be chemically etched 

Materials suitable for chemical etching include (but are not limited to):

• Stainless Steels: Wide Range of Austenitic, Ferritic and Martensitic Stainless Steels
• Mild Steel, Carbon Steel, Tool Steel, Spring Steel
• Aluminium: Including Aircraft/Aerospace grades
• Molybdenum
• Nickel Alloys: Inconels, Mu-Metal, Alloy 42 (Nilo 42), Invar
• Copper: Including C110 and C101 (Oxygen Free)
• Brass, Phosphor Bronze, Beryllium Copper, Nickel Silver
• Many other materials – please call us to discuss your needs

Key benefits of chemical etching

Chemical etching is an extremely precise process that facilitates the production of a wide range of burr- and stress-free parts in virtually any metal. Tolerances quoted on etched features on parts will typically be +/- 10% of the parts’ thickness.

Let’s look at the other key benefits that chemical etching provides:

• Stress and burr-free parts
• Micron-sized features
• Tight tolerances
• Wide range of materials
• Thicknesses from 25 um to 2 mm
• Round holes, sharp edges, straight or profiled edges
• Rapid prototyping: prototypes can be produced from drawings in a matter of days
• Cost-effective manufacturing
• Flexible tooling allowing easy modifications

Now let’s look into the other heavyweight in the ring: electroforming.

Additive manufacturing method: electroforming

The electroforming process explained

It's important to know that electroforming is an electrodeposition process. Electrodeposition is the deposition of metal onto a conductive object. Two electrodes (a +ve anode and a -ve cathode) are placed in an electrolytic bath containing a solution of metallic salts and a power source of direct current (DC). While the anode dissolves the material, the cathode builds up the material. In other words, metallic ions are converted into atoms which build up onto the cathode surface through a continuous deposit. Therefore, the material can be built up on micro scale accuracy: atom by atom.

Two electroforming methods explained

Depending on the material used and the size of the substrate — and thanks to the electric charge in combination with the time span — the electroforming process makes it possible to control ampere seconds, minutes or even hours (and therefore the thickness of the formed material) extremely accurate. This level of control makes it possible to create the product in a desired thickness at micron accuracy.

The thickness of the plated part brings a new challenge to the table. To control the shape of the product, metal is grown onto a patterned surface: the substrate. Two different methods with different outcomes can be applied: electroforming overgrowth and electroforming thick resist.

Plating defined: electroforming overgrowth

A light sensitive coating is applied on a conductive surface. Artwork, film or glass-tooling is used to expose the light sensitive coating. The coating will polymerise where it is exposed to UV light.

After developing the light-sensitive coating the mandrel with conductive and nonconductive areas is ready for electroforming. Metal will grow over the photoresist and size of the apertures is defined by the overgrowth of the electroforming process. The accuracy of the product is therefore defined by the plating process. Check out this video for animated explanation of the overgrowth process.

Photo defined: electroforming thick resist

In some cases, it is desired to make the product thicker. This is when the thick resist method is applied. The mandrel surface is masked off with photoresist except for the hole area in the pattern. You don't grow over, but build the metal within the shape, resulting in a pattern with a cylindrical hole shape. Thus in this case accuracy is defined by the photolithographic process. Check out this video for an animated explanation of the thick resist method.

Materials that can be electroformed  

The material that is most widely used for the creation of micro-precision parts through electroforming is nickel. Nickel is predominantly used because of its versatility and physical and mechanical properties that it possesses.

But what if you’re fabricating a metal part that is in constant contact with human skin, for instance, as seen in medical applications?

You can utilize full plating and metal finishing with materials as: Gold, Silver, Copper, Chromium, Nickel, Palladium Nickel, and Tin (bright or matt).

Key benefits of electroforming

Electroforming’s uniqueness is that you can grow metal parts atom by atom, providing absolute accuracy and high aspect ratios. Here are some other major benefits:

• Significant cost reduction
• Large scale production and high replicability
• Ultra-precision metal parts (products where the standard deviation of the most critical feature is only ~0.1 µm on that single part are no exception)
• No additional tooling (costs)
• Freedom of design
• Short lead and delivery times
• Creation of multi-layer metal parts
• Creation of components with very specific contour shapes
• Straight and burr-free side walls
• Local variation in material properties

Engineers who are looking for low-cost, flexible tooling that takes prototypes to industrial scale production in a short timeframe should definitely consider electroforming and chemical etching. Of course, for engineers and manufacturers to choose the technique that’s most suitable for their application, a comparison is recommended. It’s time for the heavyweight title fight:

Additive vs. subtractive manufacturing title fight — chemical etching vs. electroforming

We start off by comparing the two manufacturing techniques on run time and precision:

Comparison on run time and precision

As you can see, electroforming has the upper hand when you purely compare the techniques on run time and precision. There is, however, an important distinction to be made, and it has to do with cost-effectiveness:

Comparison on cost-effectiveness

When you require nickel as a material, electroforming will most likely be more cost-effective than chemical etching.

But when you do not necessarily require nickel parts, but have multiple options like nickel and stainless steel, costs of electroformed products are likely to be slightly higher than those of etched materials. Other factors like volume, precision, and the desired shape of the contours of your product may influence your decision.

Generally, the rule of thumb is: the higher the precision, the higher the price. So when tolerances are less important, the material is predetermined, and the manufacturing costs of this material forms a boundary condition (price aspect), chemical etching wins the fight. When micron precision, hole geometry/shape, and high repeatability are the main consideration factors, electroforming is definitely your go-to technology.

To learn more about the Electroforming technology, download the Whitetpaper Electroforming.  

Selecting the right manufacturing technique for your product

If you want to find out which micro-precision manufacturing technique is right for your application, speaking with one of our engineers might be a good idea. They will be happy to go over the parameters of your project with you and help you find the right solution. Don’t hesitate to reach out — we’re here to assist!