Advantages and Disadvantages of Copper and Graphite ...

Figure 1: An example of a graphite electrode.

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Figure 6: Copper also can be used for photo engraving and acid etching.

Figure 2: Some new high-speed mills are specially designed to machine graphite - and can even cut square internal corners.

Figure 3: The finish on the graphite should be as good as you need in the mold.

Figure 5: Copper can be used for coining and forging.

Figure 4: Copper is useful in small cavities, where it is difficult to polish.

When it comes time to decide whether to use graphite or copper electrodes in your shop, it's important to look at the big picture. According to Stu Haley, regional manager of Belmont Technologies, Inc., a provider of EDM supplies, tooling, accessories and machines, "To say which electrode works best is very difficult, it is totally applications driven. So much depends on what you have to work with on your shop floor in the way of support equipment. Both copper and graphite provide approximately the same end result. The difference is time to EDM the work and electrode manufacturing time and cost."

Haley explains that choosing an electrode material is often a result of where you were born and what type of EDM equipment you use. "For example, graphite was basically developed in the United States back in the early s, so the American EDM equipment manufacturers in those days concentrated on the graphite circuitry when designing their equipment," he says. "Whereas, since the European and Asian EDM equipment manufacturers didn't have access to graphite, they developed copper circuitry.

"If you have newer equipment built after , the electrode material of choice in North America is graphite," he adds. "This is used in 90% of the applications. In Europe and Asia, graphite is becoming more popular as an electrode material because of availability, machinability and speed of cutting."

Following are some of the advantages and disadvantages of each material so that you can decide which is best for your application.

 

Graphite

Advantages and Benefits

Sold by grades, graphite cuts approximately three times faster than copper, according to Haley. "What makes a good grade or a poor grade is particle size," he explains. "Particle size gives you strength, machinability and greatly influences the metal removal rate, wear and the surface finish. Graphite is made up of carbon particles that are put through a graphitizing process to produce graphite. The smaller the particle size is, the better the graphite. Particle sizes in different grades of graphite can be ." for general-purpose use to ." for the extremely fine detail and superior surface finishes. Graphite can be purchased in big blocks, and then cut up to be machined; or it can be ordered precut or ground into the size you require.

"Graphite machines very easily &#; you can mill it, grind it, turn it, drill it, tap it, even file it to whatever shape you want," Haley continues. "Another advantage of graphite is that it doesn't burr. You can put it on a duplicating machine or a graphite high-speed mill and cut out complex shapes and forms, and once it's cut you are finished &#; with no deburring." (See Figure 1)

Additionally, graphite's high melting temperature results in less wear than other electrode materials, so a mold could be cut with one or two electrodes on a CNC EDM machine with very little wear, Haley adds. "A CNC sinker may need a third or forth electrode to finish the mold," he notes. "It depends on the age of the EDM machines."

Limitations

If your shop has older fabricating equipment, machining graphite electrodes will result in dust particles on the shop floor and in the nearby machines. However, the new high-speed mills that are sold today are specially designed to machine graphite. "They are totally enclosed and have a vacuum system to remove all of the dust," Haley points out, "and there are some machines that can even cut square internal corners." (See Figure 2)

Another important point to keep in mind is that the finish on any electrode is the finish that will be put in the mold. "So, if you have a lot of cutter or grinding marks on the electrode, you will reproduce that in your mold," Haley says. "Normally, the finish on the graphite should be as good as you need in the mold." (See Figure 3)

Copper

Advantages and Benefits

Haley notes that copper can be cut on wire EDM machines, but there are only certain graphites that can be cut on a wire machine &#; the particle size should be five microns or less. Copper also is a little more forgiving in a poor flush situation than graphite. "In EDM, if the flush doesn't remove the eroded particles or chips out of the cutting area, there's something that can occur where you get a non-pulsating, direct flow of current from the electrode to the workpiece," Haley explains. "The result of this is a pit in the workpiece. Copper is more forgiving in those applications &#; all metallic electrodes are &#; they won't arc out as fast. But some of the newer EDM power supplies have adaptive logic or fuzzy logic, which eliminates the problem altogether. Copper &#; when used at specific settings with the correct flushing techniques using a CNC machine or a machine with an orbiting system &#; can produce a mirror-like surface finish. This is useful in small cavities where it is difficult to polish." (See Figure 4)

When you add tungsten to copper (copper tungsten), the result is an electrode material that has extremely good wear characteristics but is very difficult to machine, Haley notes. "When EDM'ing carbide, this is the best metallic electrode material to use. The best graphite material would be copper graphite, which is graphite impregnated with copper," he says.

According to Haley, there are alternative ways of machining copper &#; including coining (see Figure 5), forging, photo engraving/acid etching (see Figure 6) and stamping/forming. There are some shops that make a form and then copper plate it.

Limitations

"Copper is more difficult to machine," Haley says, "and when you mill it, it has the tendency to stick to the cutter. When you grind it, it can clog up the grinding wheel. It heats up quickly and has a tendency to grab the grinding wheel. You'll have burrs no matter how you machine it, so you have to deburr it. Size and weight also can be an issue. A 12" x 7" x 2 3/4" piece of copper weighs 75 pounds, whereas a piece of graphite the same size is 11 pounds.

"The bottom line is use what you think will work best in your shop with the equipment that you have available," Haley continues. "If some electrodes are beyond your machining ability, have someone make them for you. You have to base it on your own experience and the resources you have available. Ask for suggestions from the equipment manufacturer or from your electrode material supplier. Regardless of what electrode material or combination of materials you decide on, be sure that you know the speeds and feeds to machine the material safely. When in doubt, ask."

There are various characteristics that businesses look for in custom metal parts. Strength, size, material type, grain flow, and cost are some of the most important, and they are determined by the type of processing procedure used. 

Forging and casting are the most common.  

During the forging process, metal is pressed or hammered to give the desired shape, while in casting it is melted and then poured into a mold shaped in the desired form.

Both processes have particular advantages and disadvantages depending on the characteristics, cost, and service requirements that are needed.

The following sections will cover these key differences specifically in the areas of strength, types, sizes, alloy selection, additional processing, cost, and grain flow.

Strength or Structural Integrity

The stronger material is, the more likely it is to be able to maintain its structural integrity under various harsh conditions. This durability ensures functionality and safety.

Metals should be strong enough to maintain their structural integrity and perform at peak levels both under normal operational conditions and those that exceed them.

There are four ways in which the strength of metal can be measured.

Tensile strength refers to a material&#;s ability to withstand pressure or forces that would normally separate or pull a metal apart.

Compressive strength is the amount of pressure a material can tolerate without fracturing&#;in other words, the load it can bear. 

Shear strength denotes the capacity to withstand or resist shear, that is, the structural strain produced by pressure.

Torsional strength is the ability of a material to withstand twisting loads due to torque. 

Of the two processes we&#;ve mentioned in the previous section&#;forging and casting&#;forging produces a far stronger metal. This is because the process of forging alters the metal&#;s granular layout within and on top of the surface, making it more uniform. 

Forging also helps to eliminate holes (voids and gas pockets) that would normally decrease both the structural and chemical integrity of the material.  

On the other hand, the casting process tends to produce more porous holes since the metal shrinks from its thicker to its thinner sections during the process.

If you require strong material to maintain functional and structural integrity under normal and severe conditions such as is the case in the production of aerospace, railway, and ship components, then creating custom metal parts through forging is recommended. 

Product Type and Size

Not all products need to be strong and rigid. Some ought to be more pliable and flexible so they can be formed into complex and aesthetic designs. 

For those applications, casting is usually more appropriate, as it is more difficult to shape metals made through forging.

If you want to learn more, please visit our website Precision copper forging parts Supplier.

The casting process allows for more complex shapes to be formed since the metal is melted first, which means it can be easily poured into a pre-shaped mold or die. 

Moreover, since the metal is melted during the casting process, larger products can be created, even those measuring up to 400 to 4,000 tons. 

Therefore, the size of a particular product or application will also dictate which process should be used.

However, casting is not solely delegated to only large-size applications. Since it adheres to very tight tolerances, it is very useful even in forming smaller products with complicated geometrical designs.

Additionally, casting is more cost-effective than other machining processes, including forging, because it promotes material efficiency&#;five times higher than standard machining&#;meaning that more parts can be made in less time. 

That is not to say that forging does not have its value, especially when strength and reliability are the primary concerns. It is just that casting is more useful when creating larger products with specific design requirements.

To get a better idea of which process is more useful for your specific project, take a look at the following list of products created through both methods.

Forged ProductsCasted ProductsAgricultural Machinery & EquipmentHeavy Construction EquipmentOil Field ApplicationsHeavy Farming EquipmentHand ToolsHeavy Mining EquipmentGeneral Industrial EquipmentMachining ToolsRailroad EquipmentChemical MachineryOff-Highway EquipmentPetroleum MachineryAerospace ComponentsDefense VehiclesValvesArtilleryFittingsMunitionsElectrical Machines (motors, pumps, generators, compressors)Household AppliancesGardening ToolsArt & Decorative Objects (sculptures, lamps, furniture)

To summarize, the forging process is ideal for parts and applications that need to be strong, tough, and resistant to various mechanical forces. 

On the other hand, casting is ideal for larger parts with detailed and complex shapes, patterns, and internal cavities.  

Alloy Selection

As forging and casting are different processes, they aren&#;t always used with the same types of alloys. 

Alloys are a combination of metals and non-metals, which are mixed and blended to enhance the desirable properties of a metal, such as corrosion resistance, tensile strength, and toughness.

It is important to choose the right alloy for your project because doing so will help reduce wear and tear, extend product life, and help increase overall performance. 

After the alloy is chosen, the process that best compliments the alloy must be selected. The selection process will primarily depend on whether forging or casting can shape and mold the alloy to exact specifications.  

Below is a list of alloy metals that are typically used in the forging process, and those that are more suited for casting.

Alloys Typically Used in ForgingAlloys Typically Used in CastingAlloy SteelNickel AlloysMicroalloy SteelCobalt AlloysStainless SteelAluminum AlloysCarbon SteelLead AlloysAluminumStainless SteelCopperCarbon SteelTitaniumIron (gray, white, ductile)MagnesiumSiliconNickelZincIronMagnesiumCobalt

As you can see in the chart, some alloys are equally suitable for both processes, so the choice of one instead of the other will depend on other factors listed in this guide. 

What is more, the above lists are not complete and there are many other combinations of metals and non-metals that can be used for both processes. 

In general, forging has a more limited selection when it comes to alloys, while casting can utilize almost any type of metal during its process.

Secondary Processing

Both forging and casting often rely on secondary operations to complement them. However, forging tends to require fewer of them. 

Secondary processes are additional manufacturing processes that are needed to enhance and refine the formed product in some way.

There are many types of those operations, but the most popular ones include:

• Punching
• Drilling
• Tapping
• Threading
• Bending
• Swaging
• Coining
• CNC machining
• Heat treating
• Plating/coating
• Metallurgical testing

They provide the following benefits:

• Improved product appearance
• Increased corrosion resistance
• Prolonged product life cycle
• Increased product value
• Additional product features
• Lower cost

The reason forging requires fewer secondary processes lies in the fact that forging methods can be utilized on their own to get as close as possible to the desired specifications.

Of the different forging methods, the most common ones are:

• Open die forging
• Rolled ring forging
• Impression die forging

And since these three forging methods pretty much ensure the main aims of forging&#;predictable strength and strong performance&#;not much is needed after they are implemented. 

However, some secondary actions are commonly used after the initial forging process is completed.

Punching, straightening, and trimming are often employed after forging to ensure and improve the dimensional accuracy of fittings.

Cleaning methods like blasting, tumbling, or picking may also be used to clean the forgings if needed.

Casting, on the other hand, has more secondary processing requirements that are essential in creating smoother finishes, optimal sizes, and increased protection against oxidation.

The following ones are used most frequently:

• Machining
• Sealing (paint, plating, powder-coating)
• Bluing
• Oil treating
• Assembling (if done on-site)

The above processes are particularly common in conjunction with casting, since the process itself only deals with the formation of a part, and not its assembly, protection, or final surface finish.

Many custom-metal part manufacturers offer all or most secondary processes that may be required after casting or forging is completed, so there is usually no need to go to a different provider.

Cost

When it comes to cost-effectiveness, there is no definitive answer as to which of the two processes is more expensive.

The price of forging or casting will depend on various factors surrounding the formation and completion of a product. 

Some of those factors include:

• Production volume
• Shape complexity
• Types of alloys used
• Required secondary operations
• Added specifications

As a general rule, however, forgings are less expensive when they are purchased in medium to large lot sizes and castings are less costly when smaller lot sizes are bought.

However, castings can also be cost-effective when purchased in medium to large lot sizes, depending on how many secondary options are needed after they have been acquired.

As far as the cost of raw materials goes, those required for casting are usually less expensive than those for forging. This is because casting requires fewer initial steps and therefore less machinery to complete.

Also, the preliminary process of turning ingots into billets is eliminated during the casting process. 

The price of tooling can also be eliminated for castings since it is usually not needed. 

However, keep in mind that some forging methods don&#;t require tooling either, making them cost-competitive with castings. For instance, such is the case with open die forgings (ODF).

The machining costs associated with casting and forging are almost identical. Nevertheless, since forged alloys like stainless steel tend to have finer grains, machining them is often easier and therefore less costly. 

Secondary operations will play a major role in the final cost of the manufacturing process. 

Since casting tends to require more of them, it can turn out to be more expensive than forging, even though, when no secondary processes are required, its general costs are often lower than those of forging.  

Therefore, the final costs depend on which casting method or forging method is chosen, as well as how many of the above-mentioned factors are involved in the overall manufacturing process of a particular application.  

This is precisely why it is always recommended to contact a metal manufacturer and ask which variables will most likely pertain to the casting or forging of your specific product. 

The information they supply you with will help you determine which one will be more economical for your project requirements. 

Grain Flow

Grain flows are fiber-shaped lines that appear on metal surfaces in the direction of metalworking (shaping) during the forging process.  

Grain flow can help strengthen metal surfaces, reduce fatigue, and increase mechanical properties. 

Casting, however, does not produce any grain flow and therefore does not provide its benefits to the formed product. 

What is more, because there is no grain flow, casting can result in metallurgical defects, such as:

• Hot tears
• Hot spots
• Cold shut
• Slag inclusions
• Gas porosity
• Shrinkage
• Mold

The directional strength (directional alignment or grain flow) produced during forging creates a refined microstructure on the surface of the metal. This gives it higher tensile strength, impact toughness, fracture toughness, fatigue strength, and ductility. 

Additional benefits that are derived from directional grain flows include:

• Low machinability variation
• Consistent finish levels
• Stable dimensional characteristics
• Reproducible heat treatment response

Applications such as surgical and dental instruments, hand tools and hardware, as well as aerospace and automotive components need the additional properties produced by grain flow.

It ensures their functionality under harsh conditions and increases their longevity of use. 

Unlike casting, which produces a random grain distribution that reduces impact strength, forging helps to produce longitudinal grain flow across metal surfaces.

This greatly increases their overall strength and resistance to impact.  

Therefore, if higher strength, toughness, and fatigue resistance are primary requirements, then forging would be the obvious choice.

The casting process will not be able to supply any grain flow and so none of the required attributes. 

Conclusion

Neither of the metal manufacturing processes is categorically better than the other. 

Instead, you can choose between casting or forging depending on the type, size, alloy composition, cost, and strength that your project requires.

You may need other secondary manufacturing processes apart from casting and forging to fulfill the demands of your project, which will also affect the time and the resources it takes to complete it.

Since there are so many variables affecting the formation of custom metal products and parts, it is best to consult a metal manufacturer to help you determine which process is best suited for your application and budget. 

For more information, please visit Rolled Ring Forging Inspection.