Metal Fabrication: A Guide to Manufacturing Metal Parts

Author: Geym

Mar. 07, 2024

Machinery

Take a walk to the nearest park or ball field and look down; that’s not just a bunch of rocks and dirt down there. Every metal known to humankind comes from the ores and minerals found underground. To a manufacturing person, all that stuff under our feet is what rocks our world. Pardon the pun.

Let’s take another walk, this one through the Periodic Table of the Elements. Yes, most of us learned about the elements in high school chemistry class, but it’s probably been a while, so a refresher might be in order.

We’ll zoom through most of it. Hydrogen, oxygen, and argon—gases are exciting to welders and neon sign makers, but unless we’re short of breath after a brisk walk, most of us take them for granted. Without silicon and germanium, computer chip manufacturers would need new jobs. Plutonium is important to bomb makers, as are lead and krypton to those in lighting. To everyone else, the elements are a pretty boring subject.

In between all those rare earths and noble gases, however, sit metals. Aluminum, titanium, iron, and nickel—these are the building blocks of modern society. Without the raw materials trapped in the earth’s crust, and the technology to extract and process those minerals into various alloys, humans would still be living in grass huts and chasing their food with wooden clubs. Protolabs uses a range of metals for its manufacturing services. These can be classified as either hard or soft, with metals like steel and stainless steel on one side of the fence, and brass, copper, magnesium, and aluminum on the other. The last on this list—aluminum—is the most abundant metal in the earth’s crust, and the third most common element after oxygen and silicon. Despite making up 8 percent of the earth’s crust by weight, aluminum is rarely found in its pure metallic form, however, since most of it is locked up in bauxite and other ores.

Soft Metals: Aluminum, Magnesium, Brass, and Copper

Elemental aluminum is soft and highly malleable, making it a poor candidate for mechanical purposes. Instead, aluminum is usually blended with a mix of other elements, including silicon, copper, magnesium, and zinc, then heat-treated to make the strong, lightweight alloys used today in airframes, automobiles, and various consumer products.

Protolabs’ machining service makes parts from two types of aluminum: 6061-T651 and 7075-T651. The T-suffix signifies how the material was processed, in this case mechanically stretched by 1 to 3 percent after heat treatment to eliminate residual stress, thus making it more stable when machined. 6061 aluminum is alloyed with magnesium and silicon, and in its wrought form offers yield strength of 40,000 psi or more. It is very corrosion resistant and weldable given the proper equipment, making it an ideal choice for low-fatigue applications such as structural components in machinery, hydraulic valve bodies, marine, and automotive parts, and most any application requiring robust, lightweight material.

The other horse in Protolabs’ aluminum stable is 7075 aluminum. Harder and stronger than 6061, it offers yield strength nearly twice that of its less robust cousin, but at nearly three times the cost. Its primary alloying elements are zinc, magnesium, and copper. The American military uses 7075 in many of its firearms, connecting rods made of forged 7075 aluminum are used in top fuel dragsters, and the wing spars in Boeing aircraft are made of 7075. It’s tough stuff. In fact, the only place where 6061 wins out is in corrosion resistance, and in parts that need a little more “give” than those made of 7075. Both materials offer easy machining, although 7075 is a bit abrasive.

Another popular lightweight material is magnesium, which is the fourth most abundant element in the earth’s crust. Two-thirds the weight of 6061 and nearly as strong, it is the lightest of all structural metals. Camera and cell phone bodies, frames for power tools, laptop computers chassis—magnesium is a preferred material wherever good strength and low weight is important. In an effort to improve fuel efficiency, automobile manufacturers make extensive use of magnesium in transmission cases, seat frames, and intake manifolds.

Magnesium is most commonly alloyed with aluminum and zinc. It has excellent dampening characteristics, is very machinable, and readily molded or die-cast.

In addition to magnesium’s susceptibility to corrosion, another drawback is its reduced strength at high temperatures, although Volkswagen used magnesium successfully in the crankcase of its air-cooled Beetle engine for more than 50 years. Price-wise, it’s more expensive than aluminum, but this is largely mitigated by the relative ease with which magnesium components are manufactured. Note that Protolabs no longer manufacturers magnesium parts.

Rounding out the soft metal lineup are brass and copper, the kissing cousins of the metal family. Of the two, brass is by far the most versatile. With the exception of environments high in ammonia and some acids, it is extremely weather and corrosion resistant. If you’ve ever replaced a car radiator, soldered a kitchen faucet, or played the French horn, you’ve handled parts made of brass.

Protolabs offers parts machined from C260 cartridge brass, long a favorite for ammunition casings. It contains 70 percent copper and 30 percent zinc, and is considered the most general purpose of all brass alloys. There are literally dozens of brass grades though, all with subtle differences and distinct uses. Cutting back on the copper percentage by a few points produces a brass suitable for rivets and screws. Cut back a bit more, add a little iron, and you’ve created Muntz metal, good for architectural trim and lining the bottoms of boats. Increase the copper content, toss in some manganese and a pinch of nickel, and you have the makings of Sacagawea one dollar coins. Brass is the ultimate switch hitter.

To a machinist, brass is as easy as it comes: coolant is optional, tool life exceptional, and feedrates quite high. Don’t let its easygoing nature fool you, however—brass is sturdy stuff, offering tensile strength rivaling that of mild steel. Ironically, copper is a far different story. Even though it’s the primary ingredient in brass, unalloyed copper’s machinability is roughly five times worse, and even the most patient of machinists avoid it due to copper’s tough, stringy nature. Chips are virtually impossible to break and, due to its high thermal conductivity, the material heats up very quickly during cutting.

Copper is only second to silver in electrical conductivity, a factor that makes it one of the most important metals in use today. Copper (and aluminum) wiring basically make electricity possible. Without it, lights would remain unlit, cars wouldn’t run and it would be impossible to blend a frozen margarita.

Copper is easy to braze but difficult to weld. Its extreme ductility makes it both strong and flexible, a rare occurrence among metals. Yet copper does far more than conducting the power needed to heat our grills. It’s used in semiconductor manufacturing as an element of high-temperature superconducting, in glass-to-metal seals such as those needed for vacuum tubes, and has even been approved by the United States EPA for use in hospitals and public places as an antimicrobial surface.

Because elemental copper exists in nature, people first started pounding it into coins and cutlery millennia ago. Today, it’s an ingredient in more than 570 different metallic alloys, of which cartridge brass is one. Tellurium copper, nickel copper, bronze, gunmetal, aluminum, and steel alloys—the list goes on. Copper can also be used for electrodes in electrical discharge machining (EDM), a technology often seen in injection molding and metal stamping. In the modern world, copper is indeed king.

Hard Metals: Steel, Stainless Steel, Inconel, Chrome, and Titanium

The world needs hard metals as well. Steel is used in everything from cars to cruise ships, cables to crescent wrenches. Regardless of alloy type, steel is mostly composed of iron. Iron smelting and limited steel manufacturing has been in use for thousands of years, but it wasn’t until the Bessemer steel process, invented in the mid-1800s, that mass production of high-quality steel was made possible. Thus began the industrial revolution.

As with the soft metals, a small quantity of alloying elements can have a dramatic effect on steel’s properties—the addition of less than 1 percent carbon and manganese, along with a little metallurgical legerdemain, is what makes brittle iron into tough 1018 steel. And 4140 alloy steel, suitable for aircraft use, is made by combining an equally small amount of chromium along with a dusting of molybdenum.

Carbon steels such as these can be hardened to one extent or another, and are easily welded. There’s just one problem: They rust, making plating or painting a requirement for most any application involving carbon steel.

The 300-series stainless steels offered by Protolabs carry at least 20 percent chromium along with a fair amount of nickel, making them more difficult to machine. Still, these popular materials are commonly used for medical instruments, vacuum and pressure vessels, and for food and beverage equipment. 300-series stainless is quite tough, but cannot be hardened like carbon steel. If hardness is a requirement for your application, consider kicking it up a notch with 17-4 PH.

This versatile but very tough material contains nickel, chromium, and copper. Although considered part of the stainless steel family, its machinability in the annealed state approaches superalloy status. When heat treated, it easily achieves hardness of 45 Rc and tensile strength of 150,000 psi or higher, three times that of carbon steel. It’s most commonly used in the medical, aerospace, and nuclear industries, or anywhere a combination of high strength and good corrosion resistance is needed.

Since rust never sleeps, metallurgists developed stainless steel. By increasing the amount of chromium to at least 10.5 percent, corrosion resistance is greatly enhanced. Stainless steel is widely used in the chemical industry, textile processing, and for marine applications. Many stainless steels are temperature resistant as well, and are able to withstand temperatures upwards of 2,700 degrees F, hot enough to turn aluminum, brass and copper into molten puddles. 316 stainless, for example, is excellent for heat exchangers, and sees regular use in steam turbines and exhaust manifolds.

If you’re looking for some truly robust alloys, look no further than cobalt chrome and Inconel. Protolabs doesn’t machine these materials, but its 3D printing service is happy to sinter them for you through a direct metal laser sintering (DMLS) process. Each material has unique, high-performance properties.

Inconel contains 50 percent or more of nickel, giving it excellent strength at a range of temperatures. It’s used for extreme demands such as gas turbine blades, jet engine compressor discs, and even nuclear reactors and jet engine combustion chambers. The high nickel content makes Inconel one of the most difficult materials to a machine, requiring wear resistant coated carbide and a rigid machine tool. Sitting right next to nickel on the periodic table is cobalt, the main ingredient in cobalt chrome alloy. This material is known for superb wear resistance and human biocompatibility, making it ideal for dental implants, hip and knee replacements, and arterial stents.

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Finally, there’s titanium. This lightweight element is alloyed with aluminum and vanadium, providing a strong, corrosion-resistant material. Like cobalt chrome, titanium is biocompatible and is used extensively for bone screws, pins, and plates. Its tensile strength is roughly twice that of mild steel but weighs just half as much. This makes titanium appealing to the aerospace industry and high-performance vehicle manufacturers.

 

CNC Machining: The Foundation of Metal Manufacturing

Metallurgy—it’s a pretty cool subject, right? As we’ve seen, a dozen or so raw elements provide for hundreds of important, life-altering materials. None of these metals would be worth a wooden nickel without the means to shape them, however. Principal among these is machining, which evolved in lockstep with steel processing. Over the past 150 years, machine tools have grown from crude pulley and steam driven devices to the high-tech, ultra-precise computer numerical control (CNC) equipment of today.

Protolabs employs a veritable army of these machine tools, one that’s several hundred strong, standing ready to machine custom parts from most of the materials just discussed. Chief among these are machining centers, which work by rotating a cutting tool such as an end mill or drill to remove material. The workpiece is gripped in a vise or similar clamping device and moved in one or more axes against the cutter, thus creating complex geometries. Five-axis machining centers may use all axes simultaneously to generate the free-form shapes common in artificial knees and propellers, or indexed to machine multiple sides of the workpiece in one clamping.

CNC lathes use a chuck or collet to grip the workpiece and rotate it against a fixed cutting tool. Need to cut a set of candlestick holders or a fitting for a garden hose? Lathes make short work of these parts and more. Mill-turn machines, like Protolabs uses, take lathes one step further with the addition of rotating tools and secondary spindles, eliminating what were once secondary machining operations.

Casting and Molding: Adding Volume to Metal Fabrication

For large-volume production, machined parts are often transitioned to casting or molding processes. Metal injection molding, or MIM, is the process whereby metal powders such as nickel steel, 316 stainless, 17-4 PH or chrome-moly are mixed with a binder composed of wax and thermoplastic.

 

When it comes to creating mechanical assemblies, metal parts manufacturing plays a crucial role in almost any industry. These components are vital to ensuring that machines and tools perform as intended, and their demand continues to increase because of their durability and strength.

But just how do you manufacture metal parts? In this blog post, we’ll cover three key considerations involved in the process of fabricating metal components, including material selection, fabrication methods, and part requirements.

1. Selecting a Material Type

The first consideration in metal parts manufacturing is deciding on the material that will be used for the job. Various metals can be used to fabricate metal parts, and these metals can be categorized into two categories, hard and soft. Cost, weight, tensile strength, formability, machinability, and corrosion resistance are all important considerations when it comes to picking a metal for a part. Since different material types can affect a part’s performance, appearance, and cost, it’s essential to spend some time analyzing the characteristics of each option. By selecting the right material, manufacturers can ensure that the final product will meet the desired specifications and perform optimally.

Soft Metals:

Soft metals are prized for their malleability and lightweight properties. They are more comfortable to work with than hard metals and are ideal for creating parts with complex shapes and tight tolerances.

  • Aluminum: Since aluminum in element form is soft, it’s not ideal for mechanical purposes. That’s why it’s typically blended with other elements such as copper, magnesium, and zinc, then heat-treated to improve its properties. Automotive and aircraft parts are commonly made from aluminum.
  • Magnesium: Magnesium is a little more expensive than aluminum but offers some distinct advantages. Despite its lightweight, this material provides good strength and durability. It’s commonly alloyed with aluminum and zinc to make parts for household electronics like cell phone bodies and appliances.
  • Brass: The highly versatile brass is an ideal choice when corrosion resistance is important. For example, many plumbing parts – like valves – are made of brass. It’s also incredibly strong and, depending on the ratio of brass used can fabricate everything from marine parts to coins.
  • Copper: With its stringy structure, copper can be hard to machine. However, thanks to its electrical conductivity, copper is an extremely important metal for generating electricity and is often used in electrical wiring and tubing. Like other soft metals, it’s also commonly used as an element in many different metal alloys.

Hard Metals:

Hard metals are important functional materials when it comes to metal parts manufacturing, providing greater strength and durability. Like their softer counterparts, hard metals also each have their own unique properties and benefits.

  • Steel: Steel is an iron alloy that contains about 1% carbon. Not only is steel a high-strength metal; but it also offers a lot of flexibility since it can be machined, stamped, roll-formed, welded, and more. This makes steel a universal material for metal parts.
  • Stainless Steel: Stainless steel has the advantages of steel plus the added benefit of corrosion resistance thanks to an increased amount of chromium – 10% or more by weight. Stainless steel parts are commonly seen in marine applications and in chemical plants.
  • Titanium: The biggest advantage of titanium is its strength. Yet it’s also lightweight, which accounts for its appeal and common use in aerospace, the medical industry, and the military. Because it’s also corrosion resistant, titanium is widely used in marine applications where metal parts will be exposed to water and rain.

2. Deciding Between Fabrication Methods

Once the material has been selected, the next step is to fabricate the metal part. Fabrication methods vary widely depending on the type of part that is being produced, and there are many factors to consider when choosing the right method for a given job. Various fabrication methods can produce different shapes and sizes to meet the desired specifications. Some common component fabrication methods include precision sheet metal fabrication, machining, joining, and welding. Understanding the pros and cons of each method is crucial in selecting which method will work best for their particular application.

Below are just a few examples. Since there are hundreds of methods to make metal parts, the requirements for each component will often dictate the best manufacturing process or combination of processes to use.

CNC Machining:

There are many types of CNC machines. Two of the most common are CNC mills, which are automated cutting machines, and CNC lathes which are used to turn round or bar parts. These machining technologies are commonly sought when manufacturing complex metal parts that require accuracy and detail since they are precise and repeatable. Since computer software controls a lot of the operation, costs can also be lower with CNC machines.

“Here at PEKO, our CNC Machine Shop and Sheet Metal Fabrication Shop provide the ability to manufacture the precision metal parts necessary in today’s high-tech machinery and equipment,” explained PEKO’s Manufacturing Engineering Manager, George Folwell.

Die Casting:

Die casting involves the use of a mold or die. It allows for the production of complex shapes with close tolerances. There’s little if any machining required and, since there aren’t separate parts fastened together, the piece can be stronger than parts made through other methods.

Injection Molding:

Metal injection molding is another fabrication method that requires little to no machining. With injection molding, a fine metal powder is mixed with a binder material and injected into a tool cavity. It can produce large quantities quickly and can also be cost-effective by eliminating manufacturing steps.

Sheet Metal Fabrication:

In sheet metal fabrication, thin sheets of metal are laser cut or bent to make custom parts. Less tooling time is required than with CNC machining yet sheet metal fabrication can also easily handle complex projects since the metal can be easily made into any shape.

Stamping:

Metal stamping uses both dies and stamping presses to fabricate sheet metal into the desired shape. Other metal forming techniques are also often involved like blanking and punching. Stamping is used in a variety of applications, especially those with three-dimensional designs or surface markings.

3. Understanding a Part’s Requirements

When it comes to manufacturing metal parts, some components are more difficult to produce than others. Simple parts can be made in a traditional machine shop, using standard equipment and tools. However, custom parts with specialized requirements may require more complex machinery and expertise. Besides specialized needs, custom parts might also require additional post-fabrication treatments such as surface finishing and heat treatment.

If a part has characteristics like difficult geometric tolerances, strict quality requirements, large overall dimensions, or tight process control, it’s best to work with a specialized metal fabricator who has experience in manufacturing complex components. Specialized metal fabricators, like PEKO, have the expertise and equipment to produce unique parts that meet the desired specifications, no matter how complex.

Metal parts manufacturing is a complex process that involves many different considerations. If you’re looking for a reliable and efficient way to manufacture metal parts, then you’ve come to the right place with PEKO. From selecting the best material for your part to the fabrication process itself, our team of experts takes the guesswork out of the complicated process of metal part fabrication—working closely with you every step along the way.

Whether it’s medical or aerospace grade components or just general components that require high-quality standards like complex geometric tolerances and strict quality requirements, PEKO is here to provide superior end results. Contact us today to get started!

Metal Fabrication: A Guide to Manufacturing Metal Parts

Metal Parts Manufacturing: 3 Key Considerations to Make When Manufacturing Metal Parts

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