Forging vs. Casting: Which is better?

57 comments

by  on August 6, 2013

forging

This question, “Forging vs. Casting: Which is better?” is one that I have been asked many times. To properly explore the answer, let’s first consider the process of each.

Forging and casting are two very different manufacturing methods. When something is cast the material is heated above its melting temperature and poured into a mold where it solidifies. When something is forged it is physically forced into shape while remaining in a solid state – although it is frequently heated.

As an engineer, I have always known that forgings normally have less surface porosity, finer grain structure, higher tensile strength, better fatigue life/strength, and greater ductility than castings. In other words, forgings are generally better for shackles. The basics of why are pretty simple. When you melt metal to cast it, the grain size is free to expand. When it cools back to a solid, the grain structure is courser and more random, decreasing its strength.

But just how much better is a forging than a casting?

I  did some research on the internet and found an excellent research paper* written by members of the Industrial & Manufacturing Engineering Department at the University of Toledo, shared by the Forging Industry Association. This paper compares a single type of product made both ways. Read it here.

How’s this for hard numbers? No pun intended.

Based on this paper:

  • Forged parts had a 26% higher tensile strength than the cast parts. This means you can have stronger shackles at a lower part weight.
  • Forged parts have a 37% higher fatigue strength resulting in a factor of six longer fatigue life. This means that a forged shackle is going to last longer.
  • Cast iron only has 66% of the yield strength of forged steel. Yield strength is an indicator of what load a shackle will hold before starting to deform.
  • The forged parts had a 58% reduction in area when pulled to failure. The cast parts only had a 6% reduction in area. That means there would be much greater deformation before failure in a forged part.

To further illustrate the point, look at these photos from our in-house testing:

forging

These forged CM shackles show significant deformities before failure.

If you were hanging a load overhead from a shackle, wouldn’t you want that shackle to warn you before it failed? Or do you like surprises?

Fortunately, all of our CM shackles are forged;  and they’re forged right here in America at our Chattanooga, Tennessee Operations. Safer and made in America? I think that I will stick to forgings.  What will you do?

* The title of the research paper is “Fatigue Performance Comparison and Life Prediction of Forged Steel & Ductile Cast Iron Crankshafts” written by Jonathan Williams, Farzin Montazersadgh, and Ali Fatemi, Graduate Assistants and Professor, respectively, Mechanical, Industrial & Manufacturing Engineering Department, The University Of Toledo – Toledo, Ohio.

{ 56 comments… read them below or add one }

Troy Raines Troy Raines February 7, 2017 at 10:43 am

Hello Anu,
Glad that you found it to be helpful.
Troy

Troy Raines Troy Raines February 7, 2017 at 10:43 am

Jaya,
Thanks for your comment!
Troy

Troy Raines Troy Raines February 7, 2017 at 10:40 am

Hello Sunil,
I can certainly understand your train of thought. I’ll try to take a different approach to see if that helps the explanation.

Metals have crystalline structures. A piece of metal isn’t a single crystal but several smaller crystals commonly referred to as grains. The size, shape, and bonds of the metallic grains vary greatly with how the metal is processed.
Steels are the strongest when the grains are densest. Steel has a high thermal expansion rate. It gets bigger as heated. When metal melts the grains get even bigger and are free to move and expand more. Some of this expansion, or grain growth, remains after cooling. That’s a big factor in strength and ductility.

Another point is that steel is bigger as a liquid than it will be in its final cooled state. Remember that big thermal expansion factor? In a perfect world, the cooling would start from the center and progress outward. In that instance, the casting would be uniformly smaller than the cavity it was poured into. Things aren’t always perfect. The steel could cool quicker on the outside leaving a void in the center of the part. That is basically the casting process. The link below gives a more technical and in-depth explanation if you’re interested.

http://matse1.matse.illinois.edu/metals/prin.html

Thanks,
Troy

jaya February 2, 2017 at 8:14 am

Thanks for this stuff

Anu February 1, 2017 at 7:37 am

Thanks a`lot for this wonderful article

sunil January 30, 2017 at 2:45 am

Hi Troy ,
you covered all important detail regarding forged and cast iron but according to me cast is much stonger than forged because it is made by melting which means iron metal particles are compressed very well and have high strength than other one.
if i am wrong plz guide me .

Troy Raines Troy Raines January 9, 2017 at 8:20 am

Hello Sunil,
Thank you for your kind feedback.
Troy

Troy Raines Troy Raines January 9, 2017 at 8:18 am

Hello Pooja,
We are glad that you found it helpful.Thank you!
Troy

pooja January 9, 2017 at 7:48 am

Thanks very much for this blog and information.

sunil January 6, 2017 at 6:09 am

very well differentiate

Troy Raines Troy Raines December 19, 2016 at 10:33 am

Hello Rahul,
The answer to your question is Yes and No.
Tensile strength and ductility of any heat treatable material can be changed a lot by quench and tempering (a.k.a. heat treating). This is true with cast or forged parts. I have seen a presentation on austempered ductile iron having three times the yield strength of the highest strength as-cast ductile iron.
Unfortunately, there is no heat treat method that can eliminate the possibility of voids in castings.
Troy

Rahul Soni December 12, 2016 at 8:26 am

Hello Mr. Raines,
I would like to ask you that Is it possible to change the characteristics of a casted part by heat treatment?

Troy Raines Troy Raines February 4, 2016 at 1:50 pm

Hello Santosh,

SS316L can be forged. I don’t have enough knowledge to comment much further than that without part prints and volumes.
You could send those to me for further general comments or contact our customer service department at cmcoleads@cmcoleads.com to get an actual quote on us forging it.

Thanks,
Troy

Santosh Kudar February 3, 2016 at 7:33 am

Hello Troy,

Thanks very much for this blog and information.

We are in manufacturing of Flow meters sizes from DN15 to around DN200.

We are having parts like middle body casting ID 15 mm and above by investment casting and flanges in forging. Both casting and forging material is stainless steel SS316L. Then we use to weld these casting and forging for our product flow meter.
Pls let us know, whether we can shift the mfg of middle body parts from investment casting to forging? What is pro and corns.

Thanks in advance for your answer.

Santosh Kudar.

Troy Raines Troy Raines January 12, 2016 at 9:29 am

Sudheer,
Raw material alone is seldom a determining factor. There are generally comparable materials for each process. Most materials that can be forged can be cast and vice versa. End product qualities and performance generally have more impact on process choice.

Troy

Troy Raines Troy Raines January 12, 2016 at 9:28 am

Sudheer,
To directly quote the attached link, “In this technology, high-speed filling of liquid melt and high-pressure forging of partially solidified melt were performed by using injection and forging systems of a double control forming device.”

While I have no direct personal experience with the technology, it seems to incorporate some of the best of both processes.

http://www.freepaperdownload.us/1753/Article6386656.htm

Thanks,
Troy

Troy Raines Troy Raines January 12, 2016 at 9:25 am

Hello Sudheer,
Of course not. Forging and casting are each a wonderfully useful process. They impact nearly every industry for the better. However there is no one process that can be used to manufacture any component. That’s just too broad of a statement. For instance you wouldn’t forge or cast a wooden coffee table.

Thanks,
Troy

sudheer January 6, 2016 at 7:40 am

hello troy
Can we use both the Casting and Forging process to manufacture any component?

sudheer January 5, 2016 at 6:20 am

Hello Troy,
Can you explain about double control forming process briefly?

sudheer January 5, 2016 at 4:46 am

Hi Troy,
How do you choose between forging and casting based on the raw materials?

Sainiflange December 14, 2015 at 6:39 am

Thanks for this article. Its’s very useful for us..

Troy Raines Troy Raines December 1, 2015 at 8:53 am

Hello Mohamed,

Each application is slightly different. The forged verses cast mechanical properties can vary. The method of forging or casting and the material used are influencing factors.

Not having more experience with your application, I can only answer in very general terms.
When choosing between forging and casting, mechanical properties are seldom the only decision factor. Forging generally has better mechanical properties.

Maybe someone else more familiar with centrifugal cast nickel aluminum bronze parts can share specifics on their experiences.

Troy

Troy Raines Troy Raines December 1, 2015 at 8:47 am

Hello Mayur,

I hope I understood your question. I believe you’re asking, “Why or when would a rigging equipment manufacturer choose to use the casting method over the forging method?” I’m happy to explain. Please be patient with me, as I use the word “mold” as a general reference to all tooling used in both the casting and forging processes.

The forging method is appropriate when a manufacturer is:
• (To a large extent) making solid parts. Forged parts can have open sides, through-cavities and pierced holes; however, certain design considerations, such as a draft angle for mold release, have to be taken into account.
• Producing high quantities of parts when an investment in tooling can be justified.
• Needing smaller, lighter parts. Parts can be smaller and lighter due to increased strength, toughness, and ductility.

The casting method is appropriate when a manufacturer is:
• Concerned about high tooling costs or a large mold inventory. Cast tooling is less expensive and disposable.
• Looking to eliminate draft angles. Draft angles are incorporated in the mold to allow the part to be removed from the mold. With casting, the mold can be considered disposable or sacrificial. So, because the mold will be destroyed, it eliminates the need for draft angles. Cast tooling is also cheaper, but it only makes one part before being sacrificed.
• Minimizing required secondary operations because casting allows manufacturers to start closer to the finished shape.

CONCLUSION
Forged parts are always better for rigging equipment because of their part size (same strength from a smaller part), weight, strength, toughness, and ductility properties. Cast parts are larger, heavier, weaker, more brittle and require more expensive inspection techniques due to the probability of internal defects. Unfortunately, many rigging manufacturers have resorted to cast rigging hardware because they have hammer size limitations. For years, Columbus McKinnon has limited the size of its rigging hardware because of its desire to only have its name on forged rigging products.

With our recent acquisition of Stahlhammer Bommern (STB), we are now able to forge some of the largest rigging hardware in the world. I’m very excited about the possibilities. In fact, I am so excited that I can’t keep from sharing some news. We will soon be launching a BIG expansion of our rigging hook product line. Not just anybody can make such high quality large hooks. Be sure to watch for it.

Troy

Mohamed Rizwan November 27, 2015 at 12:09 pm

Can anyone suggest me to how to compare the mechanical properties of forged parts to centrifugal cast parts (material is nickel aluminum bronze)

Mayur Kale November 18, 2015 at 8:20 pm

Any one component produced by using casting or forging , When we made any component by casting, Why or When we made any component by forging, Why

Troy Raines Troy Raines November 6, 2015 at 2:41 pm

Hello Harsh,
You raise some interesting questions. I am a little stronger on forgings than castings.
I recommend reaching out to the Casting Industry Suppliers Association for more information.
http://cisa.org/

Thanks,
Troy

harsh Khandelwal November 6, 2015 at 4:01 am

Hello Troy,
I have learnt a lot from your articles.
Which is the latest type of casting method developed or still under research?
I had a doubt. What are the benefits of semisolid casting over convetional casting and forging?
And can you please enlighten me about the difficulties faced by researchers during development of semisolid casting.

Troy Raines Troy Raines November 2, 2015 at 1:46 pm

Hello Sumit,
Thank you for your questions.
There are several different methods of both casting and forging. Some methods are capable of tighter tolerances than others.
Screw Press Forging is generally capable of tighter tolerances with less draft than Drop Forging. One of the major factors in forging tolerances is related to die wear. The same tool or die is generally used to make many parts. The die wears during use, so tolerance is directly related to how many parts are made before refreshing the tool.
Some methods of casting use a disposable tool or die for each part and don’t have tooling wear issues.

Forgings are generally better for high temperature applications. They both expand less and are slower to degrade.

Troy

sumit minj October 30, 2015 at 3:51 am

hello Mr. troy
I have a doubt regarding forging and casting
1. which of these have grater tolerance ? why?
2. as per temperature aspect is concerned(thermal expansion and contraction) which is best forging or casting and why?

Troy Raines Troy Raines September 28, 2015 at 10:15 pm

Hello Rahman,
Sorry, but I am not sure that I am qualified to answer such an industry specific question.
Are you referring to wheels for trolleys on overhead hoists or wheels for railroad trains?
Maybe someone else reading this blog has more specific product insight here.

Thanks
Troy

Troy Raines Troy Raines September 28, 2015 at 10:12 pm

Hello Shivam,

I have never made a weld neck flange. However according to Wikipedia https://en.wikipedia.org/wiki/Weld_neck_flange, they are normally machined from a forging. I can easily see how the neck extension could be forged by having extra material in the forging with adequate draft for the manufacturing process and machined to fit as a secondary operation. Does this make sense?

Thanks
Troy

Troy Raines Troy Raines September 28, 2015 at 10:09 pm

Hello Ashish,
Obviously I don’t know everything about your particular casting. However, most un-heat treated castings are pretty easy to machine with conventional methods.

Thanks
Troy

Rahman September 28, 2015 at 4:57 am

Pl. let me know for railway wheels which one is better- foged or casted steel.

Shivam Kodesia September 24, 2015 at 1:59 am

Dear Mr. Troy,

This blog has been very useful. Thank you for that.

I would like to know which process is widely used for the manufacturing of Weld Neck flanges. Is it forging or casting? If it is forging then how is the neck extension made? Please would you provide details.

Thank You,
Regards,
Shivam

Ashish September 23, 2015 at 2:24 pm

Dear Mr Troy
Can a long bush (made by casting) be cut by machining or hot work would be required for cutting. This is required to be undertaken in a congested area onboard a ship. Bush is about 2.2 m long, dia 538 mm and thickness 30mm. Pse advice. Hot work is undesirable view other issues.

Troy Raines Troy Raines September 8, 2015 at 2:50 pm

Hello Aditya,

Thank you for your question. A factor of safety is more of a design issue than a process issue. A product can be designed with almost any desired safety factor with either process. Using an extreme example to make a point: a bridge could be made from wood or steel and have the same capacity and safety factor. The wooden bridge would just need much larger pieces of wood than the steel bridge would need of steel. A casting might need to be larger and heavier to have the same safety factor as a machined or forged part. It can be done though.

Some good rules of thumb to consider when choosing between machining, casting, and forging as a manufacturing process for your design are:

Machining a component from a solid chunk of material takes the most machining time. Some angles or component features may not be producible by machining. The material grain will all be in one direction and might could be aligned for optimum part performance (if forces were linear). There is little to no risk of porosity or under fill of the part. It is usually most cost effective on low volume production runs.

A casting would require less machine time. It could have internal and external component features that might be difficult, if not impossible to machine (think of a hollow ball.) The grain size would be large and grain orientation would be random, causing possible strength issues. There is always the potential for porosity within the part. Castings are generally larger and heavier than forgings of the same strength. Usually more cost effective on high production quantities.

A forging would require less machine time. It could have external component features that might be difficult, if not impossible to machine. The grain size would be small and grain orientation would be controlled, providing optimum strength. There is no potential for porosity within the part. Usually more cost effective on high production quantities.

Thanks,
Troy

Aditya Anand K September 4, 2015 at 12:24 am

Dear Troy,
Could you please enlighten as which process will result in better ” FACTOR OF SAFETY” between Casting and Machining components? Moreover heating operation to be performed post casting process. Awaiting your responses and theories.
Thanks in Advance.
With Warmth,
Aditya Anand K
India.

Gisela Clark Gisela Clark September 3, 2015 at 9:00 am

Hi Naresh,
We aren’t qualified to answer your question and we don’t have a specific supplier that we can recommend for this case. Sorry that we can’t be more helpful here.
Gisela

Naresh August 8, 2015 at 7:04 am

Hi, can anyone guide me regarding what machinery to install for manufacturing key blanks.
i am confused between forging and diecasting machine.i need to produce around 20000 key blanks everyday, using material like brass and some key blanks in zinc alloys.one key blank would just weigh around 15-20 gms.

nayan jain June 15, 2015 at 11:32 pm

Hello li and troy,
Thanks for your post. posts of li helped me in my research work .

Troy Raines Troy Raines June 1, 2015 at 9:24 am

Good day Jigar,
When processes are around as long as casting and forging have been, many different techniques are developed. Whole books could be, and have been written, about the different methods and equipment that can be used. Some day (when I have both more time and money) I hope to write my own. In the meantime, here are a couple of links that should help answer your questions:

https://www.forging.org/types-forging-processes
http://engineershandbook.com/MfgMethods/casting2.htm

Kind regards,
Troy

jigar May 26, 2015 at 4:41 pm

sir plz tell me…
1) what is defferent between simple casting and investment casting?
2) which different process is casting and forging?
3) how many types of forging and how many types of casting?
plz rply my mail id…

Troy Raines Troy Raines April 6, 2015 at 12:39 pm

Thanks Rupali. Many people agree with us that forgings are better in several ways and in some instances the only logical choice.
Troy

Rupali April 2, 2015 at 1:58 am

I read this types of blog regularly and also i have interest in forging process. I thing forging is better than casting from my point of view.

Troy Raines Troy Raines January 20, 2015 at 11:49 am

Hello and thanks for your comment.
I have seen a presentation from Applied Process Inc. http://www.appliedprocess.com/ on using austempering to greatly enhance the performance of castings. I also know that if the cast material has the right alloying elements in it, other heat treat methods can yield improvements. I have never tried it myself. To your other question, I see no financially desirable benefit to forging a part after it has been cast.

Thanks
Troy

M Saha Talukdar December 24, 2014 at 10:35 pm

I learn a lot from your article and i also have a question about forging and casting. Can the casting quality be improved by any heat-treatment process. Or, after casting the part can be forged (may be in a closed die). Thanks.

Troy Raines Troy Raines November 17, 2014 at 10:07 pm

Hi Henry,

So to your question, which is more cost effective – forging or casting?

That is a very difficult question to answer. There are just so many variables involved. Cost effectiveness is affected by how big the part is, surface finish requirement, quantity, tooling cost/life, secondary operations, required part strength, cost of defect, and cost of failure.
Some parts are so large that forging may not be the most cost effective option. This size range could have a low volume requirement that would further reduce the cost effectiveness of forging.

However other considerations might still make forging more cost effective. What would it cost if the finished part had a void in it? This could be very expensive if the part failed and caused damage or injury.

Would the application benefit from control of the grain alignment for better strength and wear? This could be important in a very large and critical bearing race supporting incredible loads for long periods. If the part wears out more often and there is associated downtime from the failure, it again becomes very expensive.

The number of secondary operations required to finish the part might be fewer with a casting. Holes could be cast in but not forged. That could decrease final part cost. However if secondary operations on a casting are required to achieve the specified part surface, that increases cost.

As much as I dislike wishy washy answers, I don’t feel there is a general answer to which process is most cost effective. Each application has its own unique requirements that make one method more cost effective than the other. A reputable manufacturer should be up front with you.

I do know which way I would prefer for my shackles to be made. Give me a forging every time.
Thanks
Troy

Gisela Clark Gisela Clark November 14, 2014 at 10:27 am

Good day Henry,
Thanks for your question. Troy has been in meetings these last couple of days and said that he will have an answer for you by Monday.
Gisela

Henry November 13, 2014 at 3:56 pm

Hello Troy’
From a manufacturing cost standpoint, which methodology is more cost effective for the customers: forging or casting? This is assuming everything else remain constant.

wayen li October 8, 2013 at 2:38 am

Thank you very much, Troy,
It’s useful for me.

Troy Raines Troy Raines October 3, 2013 at 10:53 am

Wayen,
I’m not very familiar with ISO 15818. In the US there are DOT standards for securing equipment to trailers for transport. The DOT standards recognize that the WLL of the chain, hooks, binders, and etc. used to secure the equipment to a trailer, all have safety factors established by the equipment manufacturer. DOT doesn’t expect the end user to add another multiplier to increase the hardware safety factor.

For your reference, we have a safety webinar on Load Securement that might interest you. You can view it here:
http://owl.li/pt0xG

Thanks for your interest!
Troy

wayen li September 26, 2013 at 10:34 pm

Hello Troy,
Thanks for your time, actually for our product, we use different steel material for cast and weld parts , normally, the cast part is a little weaker than the weld structure, beacause the raw material’s strength for cast is lower than the metal base for weld.
a few days ago, my colleague ask me, if the material is same, which one is better for cast and weld, this question confused me, because as i said above, most of time, the material is different for our cast and weld structure, so it’s a little easy for us to judge which strength is bigger, but now they want me to calculate the different when the material is same, i think it’s difficult to calculate the difference in FEA software, because as you mentioned, there are a lot of internal defects for both the manufacturing process methods, and these defects are also uncertain. so i think the only method to find the difference is by lab test.
i have the second question, if you have time you can reply me. For our new machine, we must do the calculation for tie down, transportation constrains, we follow the ISO15818, now my question is when i calculated the lashing force or WLL, wheather i need to multiply another safety factor when i select rope or chain from our supplier? as you know, there is already some safety factor in ISO15818, if i multiply another factor, the load is enlarged many times.
Thank you,
Wayen

Troy Raines Troy Raines September 26, 2013 at 12:00 pm

Hello Wayen,
That would be a tough one to call. There are just so many variables involved. I’m sure there are many opinions out there on the subject. I’ll give you my standpoint and maybe it will generate some additional discussion.

As you pointed out, either welding or casting could have internal defects. There would probably be less volume of weld in a finished part than there would be cast metal in a cast part. So from a purely volume-driven stand point, you might assume there would be less chance of a defect in a weld. However, welding is heavily reliant on the skill of the welder and the robustness of the welding process being used. I’m certain that if it were a part that I had welded, you would be better off with a casting. However there are some great welders out there.

I would probably make my decision between welding and casting based on the economics of the part involved on a case by case basis. The two processes seldom compete for the same job. For instance you wouldn’t weld a small part together if you needed fifty million of them and they could be cast to the finished shape. But you couldn’t attempt to cast a sky scraper either.

Thanks,
Troy

wayen li September 25, 2013 at 9:37 pm

Thank you very much, Troy,
Wheather this difference can be calculated and compare the strength value. I’m not sure if there are weld structure in your productions, in my opinon, forging is better than casting and welding, how about welding, as you know there are also some flaws during welding, so for welding and casting, which one is better in your mind.
Thank you!
Wayen

Troy Raines Troy Raines September 25, 2013 at 10:16 am

Hello Wayen,
Even if the materials started out with the exact same chemistry and grain structure, the processes will still provide very different results. When metal is melted into a liquid form (as it is for casting) the individual grains that make up the steel are free to expand and float around. When the steel solidifies, the resultant large and random grain structure remains and makes a weaker more brittle part.
In forging, the material is not melted and the refined raw material grain structure is further compressed and aligned in the process, resulting in a stronger, tougher part from the same material.
Please let me know if you have any further questions. We appreciate your interest!
Thanks,
Troy

wayen li September 25, 2013 at 7:20 am

i learn a lot of things from your article, and i also have a question about forging and casting. i’m thinking if there is the case that the part is made by the same material but only the manufacturing process is different, for example, there are two part, the dimension and material is same, one is forged and another is casted, then how to compare these two parts, thank you, sir, you can send me email.

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