Mechanical Technology February 2015

Mechanical Technology — February 2015

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Local manufacturing and beneficiation

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The servo drives and controllers enable the slide motion curve for each part being formed to be individually

programmed to the speeds and forces required. These settings are automatically set when the die for a new

part is inserted.

Above:

The progression die process keeps

flat side strips of material attached to

the set of parts being formed. These strips

are used to advance the parts from die to die

through each successive pressing operation and

are cut off just before the finished parts leave the

press.

Right:

A test component used for machine com-

missioning, a steering wheel airbag housing and mounting

bracket pressed using a 2,8 m die.

before straightening it and draping a

buffer loop immediately in front of the

powerful main feeder.

Both transfer and progressive die

pressing processes can be accommo-

dated. Gunter explains the difference:

“When using the ‘prog die’ process,

flat strips of material remain attached

at either side to the set of parts being

formed. These strips are used to advance

the parts from die to die through each

successive pressing operation and are

cut off just before the finished parts leave

the press.

“The transfer die process involves cut-

ting the material to the size required as it

entered the press. Between each opera-

tion, the parts are systematically lifted

and placed in the subsequent position.

While the progressive process is much

faster − up to 60 strokes per minute −

the transfer process wastes much less

material. And since it can still achieve 30

strokes per minute, sometimes it can be

more cost effective,” he informs.

The servo press also offers very low

energy consumption – much less than

that drawn by traditional flywheel-based

machines. In a cavity below the new

Schuler press, Gunter points out the ca-

pacitor bank for energy recovery. “Instead

of using brakes to decelerate the press,

the power flow is switched to connect to

this capacitor bank instead of the mains

supply, changing the servo motor into

a generator and recovering some of the

electrical energy. When the press again

needs to accelerate, this stored energy

is the first to be used to power the servo

motors,” he explains. This system im-

proves the net energy efficiency of the

press and it can be used to reduce peak

demand from the grid.

To take full advantage of the speed

of this 630 t press, particularly in the

relatively low-volume South African

automotive market, changeover times

become a key productivity factor. “This is

a 15-minute system,” Gunter reveals.” It

has a quick die changing system, which

enables a die to be removed and replaced

within 15 minutes.” On changeover, the

die is closed in the press and the hydrau-

lic clamps for the dies and punch are

automatically released. The press comes

down to the ideal height for that particu-

lar die, and the support platform slides

forward on moving bolsters. The new die

is then loaded and, once the platform is

back inside the press, hydraulic clamps

automatically latch onto the two halves.

“Typically, we would change over every

four hours, although a long run might

take an entire shift to complete. We are

currently doing trial pressings of a steer-

ing wheel airbag housing and mounting

bracket using a 2,8 m die, but the

machine can accept a 4.0 m by

1.8 m die just as easily,” he adds.

In addition to metal press-

ings, the Schuler press also of-

fers value added fastening

options including: in die

tapping; nut welding; and

riveting of nuts and studs

into pressed parts, as well

as the ability to inspect parts

in cycle without significantly reducing

the cycle time of the press. “The fences,

doors and die and coil loading systems

make this press one of the safest in the

country. With its automatic lubrication

system and its hydraulic die release ram,

it is also well protected against common

incidents that might cause downtime.

“This is one of the most modern

transfer and progression die presses to

be installed in South Africa for many

years. It places us in an ideal position to

take advantage of the growing local and

export automotive market and the new

model releases that are due in the coming

years.” Gunter concludes.