Metal spinning and hydroforming are often thought of as specialized and narrowly focused metal forming processes. As a result, many engineers don’t understand the benefits these techniques offer.
What is Metal Spinning?
Metal spinning, or spin forming, is used for forming disks of metal using conceptually similar techniques to clay pottery sculpting. Typically used for short production runs, metal spinning can be done manually or with automation using CNC lathes.
Typically, metal spinning is used for producing parts like stainless steel bowls, satellite dishes, gas cylinders and brass instruments.
Metal spinning can be used to form any kind of ductile metal, such as:
- Stainless Steel
- Carbon Steel
Depending on the type of material being used, metal spinning can be considered both a cold and hot forming process.
When cold forming is not possible, technicians can hot form a part by heating it with a torch. The heated part can then be shaped or necked down to smaller diameters with less force and minimal work hardening.
“Some customers appreciate the work hardening phenomenon as a result of metal spinning, sometimes they want a harder part,” said Sam Ibrahim, president of Helander Metal Spinning Company. “They like the fact it comes in right off the machine with more ridged mechanical properties.”
As metal spinning technology and automation has improved in quality, parts can be spun today with a thickness in excess of 1 in (25 mm), while wasting considerably less material than other metal forming techniques.
“These days, with CNC technology, we’re able to spin a thicker material and machine the entire part contour, in one CNC setup, to give a uniform wall thickness.” Ibrahim said. “Typically, we would do some preforming operations to keep the material thicker at certain points.”
Diameters for metal spun parts can range from one inch up to eight feet.
Ibrahim says that machine shops are a common customer at Helander. A part such as a bearing ring/housing, can be spun out of sheet or plate stock and then machined, rather than machining the entire part out of solid block.
Other commonly spun components include satellite dished, pressure vessels, light fixtures and tank tops.
Metal spinning techniques can organically attain high quality production in tolerances ranging from +/-0.015” to +/-0.060” with surface finish quality typical of rough machining.
Spinning lines can be minimized or eliminated with proper roller geometry, burnishing or post-process polishing.
“We add geometry to rollers to do what’s similar to burnishing,” Ibrahim explained. “We call it the planishing angle and we put them on the roller’s back side in order to remove the lines of the front of the roller. If this is done properly and you have a conducive shape, you can sometimes get a mirror finish.”
Hydroforming as a Metal Spinning Alternative
As mentioned earlier in this article, metal spinning isn’t well understood by many in the manufacturing industry. As a result, Ibrahim and his team are occasionally met with customers who require an alternative to metal spinning to meet their needs.
“Sometimes a customer needs a part that is 0.020” thick with a uniform wall thickness, spinning that kind of part would be a bad option,” Ibrahim explained. “That’s why I always like to pitch sheet hydroforming to customers because it’s such a complement or sometimes a supplement to spinning and we do both in-house.”
Sheet hydroforming is a deep draw process, allowing machines to handle thinner materials more easily than metal spinning setups.
Using a punch press style, sheet hydroforming machines essentially force and fold a sheet of metal around a shape created by a female rubber diaphragm, which molds to the shape of the male punch, which is usually a solid steel mandrel.
Typical sheet hydroforming machines sport 15, 20 and 32 inch starting blank diameters, which are capable of very deep draws.
“The 15 can draw up to seven inches deep with a max part diameter of 12”, Ibrahim said. “The 20 inch can go 10” deep with a 15” diameter and the 32 inch can go 12” deep and get 25” diameter.”
In terms of diameter however, parts are not restricted to round shapes like with metal spinning. Hydroforming allows for square, rectangular and irregular shaped parts, like a sinks in an airplane lavatory, for example.
Like metal spinning, hydroforming is best utilized for annual volume runs up to fifty thousand units. In this range, the technique offers serious cost advantages versus high volume technology like triple action deep draw presses.
“I think a typical setup for a deep draw press would be anywhere from USD$25,000-150,000 and for hydroforming it would be like USD$2,500-10,000. USD$10,000 would be a lot of tooling for a hydroform,” Ibrahim pointed out. “Whenever the materials get thin or the precision needs to be higher, hydroforming is more precise all around than metal spinning.”
All the same materials that can be worked in metal spinning are also usable in hydroforming applications. However, the draw distances get much shorter before annealing is required when using titanium for example.
Unlike the rough machining results of metal spinning, hydroforming can maintain the original finish of starting materials, depending on the tooling, efficiency of design and proper lubrication of part.
Hydroforming is known widely among Tier 1’s and major OEMs for the techniques used in producing large parts. The technique finds heavy use in the aerospace and defense industries for development of housings and covers using specialty materials such as nickel.
“Nickel materials are very popular these days for their magnetic and radiation shielding properties,” Ibrahim said. “We can shield and cover many components that have a precise shape with thin and light material to protect the housed technology.”
Hydroforming is also widely used for magnetic pumps and specialty valves within the chemical process and refining industries.
“The best way to make many components is through hydroforming because the volume isn’t high enough to justify a stamping operation,” Ibrahim added. “These parts are three to four inches deep and that becomes a big deal when you’re looking at stamping.”
Metal Spinning and Sheet Metal Hydroforming with Helander
Ibrahim advises metal spinning and hydroforming are best utilized when paired with additional post-processing techniques to reach the highest possible tolerances.
The key considerations that all engineers and technical buyers to a plan for project volume, prototype phasing and pilot runs. An efficiently planned project could have lead times as short as four weeks.
“Know as much as you can about the forecast of a project,” Ibrahim recommended.
A significant amount of money can be wasted if volume is not properly planned for. No one wants a hundred-thousand-dollar die set to crack before meeting volume requirements.
“My biggest advice to buyers would be to make sure you realize all the post-processing involved,” Ibrahim continued. “I get a lot of people that say ‘How come this part is 500 dollars and all you’re doing is spinning the hemisphere?’ Well, because you asked me to polish the surface to a fine grit. That polishing can be 75 percent of the cost.”
It pays for customers to know the impact of secondary processing, which may make the part less about spinning and much more about the machining, polishing or welding.
Helander has taken on jobs including many of those mentioned above and more for companies such as Honeywell, Texaco and Steelcase.
To learn more about Helander and the processes behind metal spinning and sheet metal hydroforming, visit www.helandermetal.com.
Helander Metal Spinning Company has sponsored this post. They had no editorial input into this post. All opinions are mine. --Kagan Pittman