The conveniences of our modern world would not exist without metals. They have properties that are useful to engineers and are the building blocks of many of our most important products. They are tough and hard, conduct heat and electricity, and have a high melting point. Because of these great properties, they have found a place in refrigerators, vehicles, televisions, phones, ovens, and many of life’s essential products.
The only truly life changing invention that does not contain metal in it is the fanny pack. (But even those require tools made of metal to manufacture it.) All kidding aside, metals are really useful for finished products, and are also useful in making prototypes. Due to their versatility, working with metals has become increasingly easy as they can be manipulated in many ways.
Here are a few different ways metals can be processed:
One of the most popular ways to turn a block of raw metal into a finished part for a prototype is by machining. Machining is any process that uses a tool or bit to progressively remove small amounts of material to “whittle” the material to a finished dimension. There are many different machining methods, but the two most popular are milling and turning.
Milling is done on a milling machine and uses a rotating cutting tool to cut a block of material that is fixed to a moving bed. Turning is done on a lathe and has the opposite setup where the raw material is the spinning part, and the tool is slowly moved against it to remove the material. Lathes and mills are available in both manual and CNC versions. Manual versions are great for making quick prototypes and modifications as the material can be fixed in the machine and run in just a minute or less. CNC lathes and mills require a CAD file and additional software to create the instructions for where the machine needs to move. However, they can create complex shapes accurately and quickly for complex parts, and they are much better at making large quantities.
The Tormach CNC cutting a detail into a key.
Welding is a process that allows separate pieces of metal to be rigidly attached to each other. There are many different styles of welding and welding machines, but the most common are electric arc welders. They work by using electricity to melt the area around the two adjoining pieces while a filler rod of metal is fed into area to join them.
Once the pieces are cooled, they are very strongly bonded together. One of the biggest caveats to welding is that the materials being welded together need to be of similar metals and similar thickness. Welding can also cause parts to warp. The process dumps a lot of heat into the parts and when they cool they can warp. Parts for prototypes that need accurate features need to be machined after welding to get the required accuracy.
Welding some metal parts for a prototype.
Working with metals is made easy with CNC cutters such as a laser or water jet. A water jet uses high pressure water mixed with an abrasive aggregate to cut through metals, and laser cutting uses a high power focused laser beam to burn through the material. In either case, the cutting head is mounted to a motion platform that can be driven from a CAD file to make accurate cuts. Most water jet and laser cutters can only cut two-dimensional shapes, but there have been innovations in water jet technology that make angled cuts and cuts on round pieces possible.
Both processes produce parts fast, but they both have shortcomings. Laser cutters introduce a lot of heat into the area around the cut, which can at best cause discoloration and at worst cause a degradation of material properties. Parts cut using a water jet are usually submerged in water so heat buildup is not an issue. However, as the jet of water gets wider the further it is from the exit of the nozzle, the edge of the parts starts to taper. Despite these weaknesses, they are still very useful for making prototype parts.
Cutting a gear shaped part for a prototype with the water jet.
3D printing is not just for plastics. Metals, among other types of materials can be 3D printed too. The primary technology used in metal 3D printers is called Direct Metal Laser Sintering or DMLS. DMLS machines have a vat of powdered metal and a laser that solidifies selected areas to build a part. The process is very efficient and the finished parts are over 99% as dense as raw material.
DMLS is great because it uses real engineering metals like aluminum, titanium and stainless steel, and it also allows for intricate shapes to be created that machining processes cannot create, such as internal passageways and undercuts. As amazing as the DMLS technology is, it is still relatively young and is expensive to have done. 3D printing metal is really only viable for small parts that require the material properties of metal.
Photo etching is a way to create highly detailed, yet thin metal parts. Photo etching is a similar process to making photographic prints in a darkroom. A photosensitive laminate is placed over a thin sheet of metal. Then a mask is placed over the laminate and the sheet is exposed to UV light. The sheet is then put in a developer bath and the exposed areas are dissolved away leaving laminate to protect the metal in certain areas. Then it is placed in an acid bath and the unprotected areas of metal are dissolved away leaving the finished part behind.
Photo etching is only possible when working with metals up to .080” thick, but it can be done on just about any type of metal. It does not require special tooling, so iterations of prototype designs can be made cheaply. One of the most common uses for photo etching is to make copper traces for circuit boards, and other small parts for electronics. Photo etching can also be used to make filter screens, gaskets and springs. While specialist groups typically make production parts, DIY kits are available for the home prototype.
A batch of photo etched aluminum parts showing the intricate detail that the technique produces.
Metals are a versatile group of materials and have desirable properties for both prototypes and production products. They can be processed and turned into parts in a variety of ways. Each method has unique equipment requirements, speed and price point, but when properly used can yield robust parts that help make products come to life.