Everything You Need To Know About Metal Prototype FabricationCharles Leveillee
In 2019, the number of patents submitted to the U.S. Patent and Trademark Office totaled 606,562. In less than 20 years, U.S. Patent applications have doubled.
Are you getting overwhelmed with the thought of prototyping and think 3D CAD design is enough to apply for a patent? There are hundreds of reasons why you should prototype. There are thousands of reasons more why skipping the prototype phase is a bad idea.
Keep reading to know the ins and outs of metal fabrication and why you need it.
Why Make a Metal Prototype?
The reasons for using a metal prototype, or another material, are up to you. Most prototypes are not built to provide any actual mechanical functionality. They might not even be the proper size of the object if it has micro- or nanofeatures.
Instead, they could be for marketing, brainstorming, display at a conference booth, or some other reason.
Whether 3D printed or not, a metal prototype will have:
- Better aesthetics
- Closer-to-life test results
- More ease to move to into mass-production
- Give better mechanical or function
- Manufacturing challenges in a similar material
- Cost savings over plastic in certain applications
If your end product is 3D printed in metal or cast, you could have a similar experience with plastic. If you are doing some CNC work on your end-product manufacture, you’ll get a clearer picture of the final product by working in metal.
Plastics are only “inexpensive” due to their ability to gain complex shapes through molds and casts. That doesn’t mean that raw material prices won’t be high because your prototype construction material is plastic.
Best Metals for the Job
If you’re deciding on a metal prototype, the two most common metals to use are aluminum and steel. There are situational reasons to use titanium, chrome alloys, magnesium, copper, and other alloys or metal elements.
For example, titanium has corrosion-resistant without adding nickel, as you must do for steel. It also has one of the highest strength-to-density ratios and a high melting point. It’s not very electrically or thermally conductive and is a weak paramagnetic material.
Nickel can cause allergic reactions, asthmatic attacks and is magnetic at room temperature.
Aluminum, on the other hand, is lightweight but quite soft and not particularly strong. Using it in place of steel to keep the prototype light might make it fragile. It’s also an excellent electrical conductor — only pure silver, copper, and gold performs better.
Otherwise, you’ll have to test a mechanical or functional prototype with the same materials the end-product will have at the same size.
Considerations to make in metal prototyping are magnetism, electrical conductance, durability, and cost.
Why Consider Prototyping With Additive Manufacturing?
Additive manufacturing processes are bursting onto the scene and getting more popular (and cost-effective) every day. Many people think of 3D printing as a plastic thermoset or thermoplastic process, but you can 3D print metal as well.
What makes 3D printing an additive process is that you’re building using the raw material instead of removing material or casting it in a mold. You’re adding the material used to create your part.
Metal 3D printing prototyping is a valuable new form of component manufacture, not only a fad. It’s a technology with the ability to create complex geometries at sizes that have been, until now, impossible. It’s also a technology that promises ultra-lightweight components and systems without sacrificing strength.
There are tons of names thrown around when it comes to metal 3D printing, along with catchy acronyms and abbreviations. It can quickly get very confusing.
Powder-fed systems are called:
- Directed energy deposition
- Laser metal deposition
- Laser cladding
This system is an exact automated deposition system. Thickness varies from 0.1mm to more than a millimeter.
Powder-bed systems are known as:
- Direct Metal Laser Sintering or DMLS
- Selective Laser Melting or SLM
- Laser CUSING
- Electron Beam Melting
The list of common metals that can be used in these systems is growing every day. Metals and alloys for precision metal prototypes include:
- Stainless steel alloys
- Titanium alloys
- Precious metals (gold and silver)
- Copper alloys
- Cobalt alloys
- Aluminum alloys
- Tool steels
That covers almost all common rapid-prototyping materials and production materials. Even Inconel and Hastelloy prototyping are possible for high corrosion environments.
Magnesium alloys have proven difficult to work with, but researchers gain traction with this material every day.
3D Printing With Powder-Fed Metals
Powder-fed systems resemble laser marking in many ways.
In laser marking and etching, a laser travels over a designated area and physically changes the optical qualities of the material in the heat-affected zone (HAZ). Some metal and laser combinations require marking material, and the laser bonds the material to the atoms in the HAZ.
In powder-fed 3D metal printing, the powder is directed in a jet toward the HAZ created by a laser. Also, as in laser etching and other welding processes, a shielding gas can create better welds, prevent contamination, and reduce unwanted chemical reactions.
All these ideas combined create a perfectly bonded metal structure, built layer by layer along the laser path.
An innovation, called “Laser Engineered Net Shaping,” or LENS, powder delivery system is an exciting variation of this technology. This technology allows us to add material to existing parts. This repairs existing expensive parts or mold toolings or can even add physically bonded coatings with high precision.
This new laser cladding technology is currently under research for a hybrid manufacturing process with 5-axis milling systems.
3D Printing With Powder-Bed Metals
Laser Powder-Bed Fusion is perhaps the highest tolerance class you can predictably reach. This metal alloy 3D printing form is a demonstrably higher tolerance procedure than LMD (Laser Metal Deposition) or EBM (Electron Beam Melting).
That said, LMD that we talked about in the previous section has high tolerance and a bit more freedom.
In powder-bed 3D metal printing, metal alloy powders scrape from a delivery cavity onto the workpiece surface. A laser fuses the powder to create the first “slice.” The workpiece surface drops one desired thickness level, and a new powder layer scrapes across and fused.
Rinse and repeat until the part is finished.
This precise and “simple” operation means that it has more stability since the metal powder physically holds it up. Still, though, stabilizing elements will have to be built into the prototype’s build file and removed after completing the product.
Also, if there are hollow sections in your product, it may be impossible to eliminate the powder.
Casting and Subtractive Manufacturing
A die is a casting method where molten or liquid metal is pushed into a mold under high pressures. The mold is called a die and is used repeatedly to create more pieces.
Plastic injection molding and die molding share a lot of similarities. Both have post-fabrication processes for removing gate material, also called a sprue in the case of injection molding. Die casting is used in almost every industry, from automotive, aeronautics, to food.
To use die casting, you need to make a mold or “tooling.” You can use this tooling repeatedly for sometimes thousands of cycles and make new ones when it wears out. This isn’t a suitable prototyping method for one-offs, though.
Like plastic injection molding, die casting is more suited to hundreds or thousands of runs that use the economy of scale to bring part costs down.
Subtractive manufacturing relies on various fabrication tools such as mills, lathes, CNC machines, drill presses, and more to remove material from a working surface. This is one of the most economical methods for one-off pieces in virtually any material type for prototyping.
Sheet metal prototyping works best with stamping and forming sheet metal instead of purely casting or CNC fabrication. Stamping, cutting, folding, and other processes create complex and beautiful geometries.
For solid parts, Computer Numerical Control machining works exceptionally well. Some complex geometries can’t be mass-produced using molds or dies and need to be either 3D printed or CNC machined.
Solid blocks with a lot of material lacking much internal geometry work best with CNC rather than 3D metal printing. It’s faster and cheaper, leading to quick turnarounds.
Standard CNC machines are:
- Laser cutters, etchers, and markers
- Milling machines
- Electrical discharge machines (EDM)
- Plasma cutting machines
- lathes and turning machines
Some CNC machines work only on X and Y planes, others on all three dimensions, and some have 6-axis capability, which means rotation on two or three planes.
This range of planes different machines work on are:
As mentioned earlier, some of the 3D metal laser-fed devices are now used in conjunction with CNC machines for subtractive manufacturing methods. This means they’re coming up with new hybrid machining methods for expanded capabilities.
Sheet Metal Prototypes
Sheet metal prototypes are another hybrid that often employs 2-axis laser, plasma, or EDM cutting machines.
Once the cutting has been done, various machines will fold, bend, stamp, and otherwise shape sheet metal to your design spec. Sheet metal is very sturdy, despite its appearance.
Neither 3D printing nor 3-axis CNC machines are effective for creating sheet metal parts. For 3D printing sheet metal, there is the disadvantage of time and strength. In the case of 3-axis CNC machines, the obscene cost of part material wastage makes it prohibitive.
Sheet metal is often cold-rolled, giving it superior strength characteristics than cutting across the metals’ grain themselves. This is similar to cold-rolling bolt threads to improve shearing characteristics.
Some of the advantages of sheet metal rapid prototyping are:
- Range of sheet metal selection
- Wears well
- Inexpensive and fast prototyping
Industries that commonly benefit from prototyping using sheet metal prototype fabrication are medical, communication, and low volume part fabrication.
Common Metal Prototyping Challenges
Metal prototyping comes with its challenges. Some of these can be:
- Software conflicts
- Programing errors for the CNC machine or 3D printer
- Downtime due to machine repair
- Difficulty deciding on alloy
- Cost of material
The challenges are not impossible to overcome. The benefits of overcoming these challenges far outweigh going with an inferior product for your prototype.
Your Rapid Metal Prototype Done Right
A metal prototype tends to look better, sell to investors better, and can even cut down on material costs with advanced fabrication methods available today.
Metal prototyping has and will continue to be the primary rapid prototyping method moving forward. Even with plastic 3D printing on the rise, the same principles can and are used in metal 3D printing.
Because of the superior durability, heat resistance, and aesthetic appeal, metal prototypes will almost always win out.
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