Forged parts are known for their structural strength, which is achieved through their high-pressure manufacturing process. Though forging lends strength to end-use parts, these structural differences require more consideration when machining forged parts compared to other types, such as castings.
Machining processes for forged parts include milling, turning, drilling, grinding — same as any other part. But what’s significant about machining some forged parts is that the first stage requires removing the scale from the entire part. The scale is a thin layer of material surrounding a forged part.
The material forms a tough, abrasive crust on the exterior of a forging, and it can be particularly hard on tooling. Once machinists get under the scale, they’ll have an easier time machining the rest of the part. But it’s important to know how to best approach machining forgings to effectively remove the scale and correctly machine the part.
Machining Forged Parts: First Operation Set-Up
When setting up the first operation (OP) on a machine, machinists should always think of the last OP. Where is the part going to finish?
“I want to make sure that the first OP sets me up for the finish,” says Mike Flowers, sales and service engineer at Greenleaf Corporation. “I've got to have everything done right up to the very last OP, because if you don't set up the first one just right, you could possibly fight the part all the way through the machining process.”
Without giving the first OP this extra attention, machinist risk a few things: you could start on the wrong side of the part, leaving yourself nothing to clamp to for finishing; or maybe it’s a thinner wall part, you’ve gone too far under the scale, and now it sprung out of shape? Now this part is scrap because there’s not enough stock to bring it back in tolerance. These are two totally different examples that probably happen daily when machining forgings.
To avoid some of this, machinist need to take the extra time studying the print and making sure they’ve located the best starting position for the entire process before taking their first cut. And once they are ready to go, they should have a plan in place from start to finish of how they are going to machine their part.
Flowers also recommends that machinists keep machine limitations and tooling choice in mind. Tool choice will mostly depend on what is being machined, and which type will work best with the machine.
“Machine limitations are a big part of my job; I’ve run into equipment that rapids slower than what we need to feed our Xsytin-1. In situations like that we have a lot of great carbide tools to choose from, capable of large depth of cuts and heavy feed rates. Generally speaking, with Phase Toughened or Whiskered Ceramics we look at each part and machine limits on a case-by-case basis. We choose tooling that best fits the application and the equipment,” explains Flowers.
Other information to know when setting up the machining process is the hardness of the material. Material hardness advises machinists on what surface footage they should be running so they can avoid the risk of burning inserts or shortening tool life.
This knowledge on properly setting up a machine when working with forged parts tends to come with experience, but it’s important for machinists to really pay attention to how they set up that first OP.
Expanding on this, Flowers adds: “Experience gains you that knowledge that tells you what's going to happen after you take that first cut. Where are you going to be after that second cut? What's this part going to look like when you pull it off the fixture? When you do the next operation or the semi-roughing pass, how's that part going to look?”
How to Effectively Machine Forged Parts
The focus on machine set-up is required to ensure everything is correct to get through the first operation of the machining process. Because the outcome of that stage is going to affect every machining stage that follows.
Once the machining process starts on a forged part, Flowers maintains that the first important element is removing the scale. If a machinist doesn’t get under the scale and stay under it, it can negatively affect the tool life. Some materials could also work harden, creating a whole new set of problems, while thinner forgings might bend or warp out of tolerance.
“Depending on the part, the first operation is going to be removing the scale,” explains Flowers. “A lot of forgings come in big chunks of material, and machinists have to remove all that stock quickly. Greenleaf Corporations Phased Toughened Ceramics are especially good at removing the scale fast, which is important when working with forged parts.”
Once the scale is off, a machinist can work on the actual part and form the required shape. During these stages of the machining process, Flowers says it’s important to pay attention and listen to what the tool is doing. If the tone starts to suddenly sound different or if it’s carrying sparks around it the tool should be pulled out and checked.
“This helps a machinist prolong tool life,” Flowers says. “When you hear a different pitch on the tool, it's tough trying to guess what it's doing. You’ve really got to look at it and visually see what’s happened.”
Let’s say the insert is flaked on top, that means you probably need to run a little faster surface footage. Or maybe the insert looks like it has grind marks on the flank edge, if that’s the case your feed rate is too slow and needs to speed up. These are two of the wear indicators of Phase Toughened Ceramics that will tell you what to do. Once you learn to understand the visual indicators and how to make the adjustments, your tool life and productivity will steadily improve.
Advice When Machining Forged Parts
Forged parts are prevalent in multiple industries, from aerospace and automotive to medical to oil and gas. The wide variety of forgings makes it likely machinists will work with these parts at some point during their careers. That’s why it’s important to know how to properly approach machining forged parts, especially in the first operation when the scale has to be removed.
“I recommend you build a database; keep extensive notes on the materials you run. There’s a wealth of knowledge to be gained from just writing information down, you’ll run into something similar down the road and be glad you did,” Flowers advises.
As machinists get more experience working with different types of parts and materials, knowledge of how to properly set up and run machines for those will come more naturally. Whether machining forged parts or any other type of part, machinists must pay close attention to the process and figure out how to yield the best results.
“Whenever you’re setting up a new part, don’t expect it to be plug and play. Just because it's the same material and has similar characteristics doesn't mean it's going to run the same as the last part,” adds Flowers. “While the other part may have run well at 600 SFM, this one seems to be running better at around 650 SFM, and it’s up to you to figure that out. How? Slight variations in the hardness could get you there. If you take the time to check.”
If you’re a manufacturer working with forged parts, explore Greenleaf Corporation’s tooling offerings to learn what might be a good fit for your machining operations. And if you want an up-close look at some of the latest machining technology, look into attending the Manufacturing Technology Series of events.
Biography
Mike Flowers
Sales and Service Engineer
Greenleaf Corporation
Mike has been with Greenleaf for 4 years and currently works as a Sales and Service Engineer. His 30-year resume includes CNC machining, programming, design and plant management.
As a Sales and Service Engineer, Flowers works with various types of manufacturers in his territory to find machining solutions for current and upcoming projects. He’s always eager to work with a newer machinist and mostly enjoys exchanging ideas on the shop floor.