Hydroforming with a Spin

By Steve Paluszynski
Metalspun Products Co., Inc.

In metalspinning, flat metal disks, or pre-formed metal workpieces, are formed over the mandrel on a metalspinning lathe into conical, hemispherical, and cylindrical shapes. Though advances in CNC technology are making the process faster and more accurate, there is still a great deal of traditional handspinning. In this method, a mechanic uses a levered hand tool to force the blank to conform to the shape of the mandrel while the metal workpiece is spinning.

This cold-forming process is well suited to low volume production. As quantity requirements increase, stamping usually becomes more cost effective, especially if the stamping tool requirements are nominal.

Sometimes it appears metalspinning has been used to produce a part that was a candidate for the deep draw process. But the cost of deep draw tooling can be a deterrent to deep drawing parts in small lots. And the shape of a part can become too complex or too difficult to deep draw.

Metalspinning is a manual process. It needs a craftsman's skill to apply pressure to spinning metal. On the other hand, hydroforming automatically applies hydraulic pressure to non-spinning metal, seamlessly molding tight tolerance products of any shape up to 10 inches deep.

As in metalspinning, hydroforming also uses a mandrel with a metal blank over it. But unlike spinning, the mandrel is forced into a diaphragm of hydraulically pressurized rubber. The pressurized diaphragm encapsulates the mandrel and workpiece, making the metal blank conform top the shape of the mandrel.

Whereas spinning can thin the material in certain areas, hydroforming does not thin the material - thickness is uniform. Deep fry oil filters, soup kettles warming pots, and stainless steel floats are just a few of the applications for hydroforming.

The Combination
There is a unique combination of hydroforming and spinning that can often be a cost effective solution for some design challenges. The combines process can help maximize material usage, material integrity, and efficiency. Metalspun Products is the only spinning shop in Wisconsin that performs this process combination.

In this technique, the main body of a part is hydroformed into a cylinder, dome, or hemisphere. Then the spinning process is used to produce flanges, or reverse flanges, and to achieve the final shape.

A variation of the combination process involves hydroforming a preform shape and them finish-spinning the part to its exact shape. This method is commonly used when forming stainless steel because it saves on multiple breakdown and annealing costs.

Hydroforming, either alone or in combination with spinning, can maintain material thickness within the 0.005 inch tolerance range. One customer of Metalspun Products, which previously used only spinning to form parts, thought the company was using a heavier gauge material than the specifications required. The finished parts were much heavier and more durable than those of the previous spinning vendor.

But it wasn't heavier gauge. Metalspun hydroformed the body of the part and then spun the flange, producing noticeably less thin-out of the material.

Bowling Ball Spin
Metalspun was recently called upon to devise a more rounded approach to bowling ball molds. By using a combination of hydroforming and spinning, the company was able to make a 14 gauge, cold rolled steel mold for 8.8 inch diameter bowling balls. The mold produced uniform spherical shapes, close tolerances, and significant cost savings for the bowling ball manufacturer. The main body of the mold was hydroformed in halves. Then the two flanges were spun. The final mold looked as if it had been machined. The spherical part was excellent, the tolerance was tighter than before, and the entire part was precise and accurate.

Because the mold was so smooth and uniform, the bowling ball manufacturer had very little secondary finishing and polishing to do, which was a welcome saving for them.

Before approaching Metalspun, the manufacturer used molds that were spun by others. But they encountered problems with inconsistent sizes, balls that were out of round, and excessive machining to finish. Today, they are bringing repeat business to Metalspun.

Float Halves
In another example, a stainless steel float for pressure tanks recently challenged Metalspun's creative process. Spinning, as well as stamping, had failed to produce a float that would withstand 600 psi for the 10 minutes required to pass quality standards.

Several companies had tried, but were unable to hold the required material thickness. And the manufacturer was reluctant to invest in more tooling that would not produce acceptable results. Metalspun rose to the challenge, agreeing to front the cost of the initial tooling. If the samples passed muster, the customer would pay for the tooling, and the project would continue.

Instead of using the 18 gauge stainless the customer had specified, Metalspun was able to use the thinner 19 gauge. When the two float halves were hydroformed, they didn't thin out more than two thousandths all the way through the part. Then, when the float halves were put together, a step was spun on them to increase strength.

When the float samples were tested, they surpassed the high pressure test. Being able to use a thinner material without losing material thickness added to the savings on this project.

Metalspun was paid for the tooling, and another customer was satisfied.

New Equipment
Modern Technology and value added services have enhanced the art of metalspinning at Metalspun.

Metalspun recently established a new manufacturing cell consisting of two advanced spinning lathes, including one heavy duty model. Their fast, accurate 'playback' programming dramatically enhances productivity. It also makes lathes very cost effective for prototyping and one-of-a-kind work.

The two-lathe manufacturing cell will be used primarily to spin the company's usual array of custom parts, including lead parts for x-ray machines, aluminum light reflectors, stainless steel bowls, and a wide variety of other exotic metal components.

These machines can produce finishes so smooth, there are virtually no spinning lines. The lathes are three times more efficient than hand spinning, and can spin materials ranging from light gauge aluminum to 1/4 inch mild steel and 1/8 inch stainless steel. They provide an entirely new dimension in quality, consistency, and productivity.

This new equipment has led to a dramatic increase in both efficiency and productivity with thicker gauge materials. Hand spinning requires great physical strength on the part of the spinner, and is necessarily slower. Hand spinning cold formed metals up to 72 inches in diameter requires the craftsman to literally use his body weight to help form the piece being spun. Workers must be trained in the highly skilled and exacting art of hand spinning.

The new CNC lathes will also be used to fabricated some tooling. The CNC lathes are not only spinning centers, they are also full machining centers that can spin and machine in one operation, giving Metalspun a unique advantage in production capacity.

Metalspun Products Company, Inc. provides metal forming and fabricating services to a wide range of customers in the lighting, automotive, food equipment, dairy equipment, medical equipment, sanitation, and metal fabrication industries.

Supplementary services include hydroforming, stamping, welding, trimming, polishing, assembling, shearing, and inspecting.

Metalspun Products can spin aluminum, steel, stainless steel, copper, brass, Inconel, incoloy titanium, lead, and other exotic metals. Sink bowls, filters, and filter covers are often spun from stainless. Other finished products are made in a variety of shapes and sizes, including flanges, rolled rims, cups, cones, ball joints, venturis, diffusers, reflectors, and hemispheres.

The company is particularly proud of the four-foot light reflector covers, shaped like chocolate kisses, Metalspun manufactured for the city of Hershey, Pennsylvania. Over 30 years later, these remarkable aluminum street light components are still in use.

Efficiencies, accuracy, and overall productivity continue to improve at Metalspun through computer aided processes, such as coordinate measuring, and programmable automatic controls for both hydraulic and CNC spinning operations.

As printed in Job Shop Technology