Mechanical Technology February 2015

Mechanical Technology — February 2015

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Local manufacturing and beneficiation

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lmost all presses currently

in use in South Africa are

mechanical presses that use

electrical motors and flywheels,

with the pressing stroke being driven by

a crank mechanism,” Gunter explains.

Simply put, a servo press is a press

driven by servo motors. The torque pro-

duced by the motors is converted via ball

screws and sliders into linear pressure,

which forms steel components from flat

sheet. This new servo press uses two

electric servo motors that provide some

15 000 Nm of torque – way more than

we had before,” he continues. While

the lack of a flywheel, clutch and brake

combination reduces the number of

wear parts and associated maintenance,

Gunter says that the real advantage lies

in the ability to “vary the stroke speed for

higher cycle times and better optimised

part pressing”.

He elaborates: “The limitation of the

During a visit to Port Elizabeth late last year,

Peter Middleton

visited Precision Press, a new G.U.D Holdings facility, where

Flip Gunter, PE plant manager, was commissioning the

company’s new Schuler 630 t servo press, part of a R70-

million investment that Gunter says could “change metal

pressing in the automotive sector”.

Precision Press’ new Schuler 630 t servo press in Port Elizabeth is part of a R70-million investment by

parent company G.U.D Holdings in the local automotive industry.

Flip Gunter, Precision Press’ PE plant manager, demonstrates the

HMI for the plc-based controller, which receives constant feed-

back signals though load cells and encoders embedded into both

the press and the dies.

PE’s new state-of-the-art servo press

slide mechanism on

a conventional fly-

wheel press is that it

is set to run at a fixed

speed. This directly

driven servo press

can be programmed

for the slide to run

at any speed. When pressing a part, the

upper forming die first moves down until

it is in contact with the metal sheet in the

lower die. From this point of contact with

the material, the press should, ideally,

slow down to a speed that optimises the

cold drawing process.

“Then, once the part is pressed and

the load is removed, the speed of the

press can again be increased. This is,

basically, the key advantage of this

modern press. A set of die tools that

can run at 10 strokes per minute on

a conventional press, can run at 20 or

more strokes per minute, simply by ac-

celerating and decelerating the stroke at

appropriate times. Actual pressing work

is only being done for 15 to 20 % of the

stroke. The remaining stroke movement is

for automation and clearance operations

for the advancement of the part to the

next pressing position. The servo motors,

therefore, allow the automation side to

run at high speed without impacting the

pressing operations,” he tells

MechTech

This speed control feature also allows

older dies to be used, because the actual

pressing speeds can be reduced to make

the die last longer, while the net cycle

times are significantly reduced.

The position and speeds of the slides

are very tightly controlled via a plc-based

controller, which receives constant feed-

back signals though load cells and encod-

ers embedded into both the press and

the dies. “Each die can be fitted with up

to 32 sensors to monitor and control the

process and to protect the tooling. The

slide motion curve for each part being

formed can be individually programmed

to the speeds and forces required, and

these settings will automatically be set

when the die for a new part is inserted,”

Gunter continues. “Another important

role of the control system and sensors is

the part transfer process, because you

need to know that a part has been suc-

cessfully picked up and properly placed

in the subsequent die cavity.”

Describing how the machine oper-

ates, he points to a sheet metal coil on

the left-hand side of the machine. This

press can accommodate a 7.0 t coil with

a width of up to 800 mm − enough for

7 000 1.0 kg components. An automatic

decoiler takes the material from the coil