Stamping Presses – Steps and Challenges of the Overhaul Process

In addition to regular maintenance, a complete overhaul or retrofit of stamping presses is sometimes necessary to:

• regain the press’ initial characteristics and thus gain in quality and reliability,

• improve productivity by implementing up-to-date technological standards.

The first step consists of an analysis and expertise phase to identify the press ‘weaknesses’ and define a quote or bill of specifications for the work that needs to be undertaken. This includes mechanical, automation and electrical aspects, and/or the technical obsolescence of certain parts, particularly any electronic parts.

In this article, Maurice Schauli, the director of Schuler France, has agreed to share his experience with us in terms of maintenance and overhauling stamping presses.
 

With regards to mechanical aspects, the inspection focuses on geometry, any “clearances”, and a visual observation of mechanical parts.

Maurice Schauli adds that “machine operators are our first ‘indicators’, with their eyes, sensations, etc. Vibrations, noises, or any other observations are valuable clues that need to be explored.”

Gears – an Essential Element
A gear reducer, at the heart of a mechanical press, transforms the motor’s rotational movement into a travelling motion of the slide(s), in order to power the process, via the slide on which the tool is fixed. The reducer is made up of gears, connecting rods, shafts with bearings, lots of bushes, etc.

When these parts become worn, the machine becomes less precise. Clearances can be measured during the inspection of a press, via two main operations:

• a visual inspection of the condition of parts,

• the gaps/clearances on the machine by means of analysis, such as the use of a jack. The latter makes it possible to simulate a force under the slide, as when the press is in operation. The movement of the slide represents the sum of the clearances and part of the deformation.

"If the clearances are different on either side of the kinematics, the geometry will never be perfect in the tool lab (i.e. under the press slides where the tool is inserted), which is problematic. The parallelism of the surfaces that accommodate the upper and lower tool must be good,” Maurice Schauli comments.

Wear is most frequently observed on the bushes. Parts that are not considered wear parts, such as gear teeth, can also cause stoppages. Maurice Schauli explains that “preventative inspection allows to limit the risks. It is therefore particularly interesting to provide for a general mechanical overhaul based on these inspections in order to replace any old parts that may lead to fatigue failure, i.e. a risk of breakage.”

If the press has been poorly maintained, or is in use for a long time, it is sometimes necessary to completely change the kinetics, i.e. all the transmission elements.

General Mechanical Overhaul
Equipment reliability is the first reason that justifies a general mechanical overhaul, in terms of both breakage and the quality of manufactured parts.

Productivity can also be increased, e.g. an increase in capacity, especially in terms of output and therefore the number of parts produced per minute, etc.

“These changes in capacity are nevertheless limited to the possibilities allowed by the structure of the press.”
 

The obsolescence of certain electrical and electronic system components means that the obsolete system or items must be replaced, for availability reasons. Indeed, if a part of the system has not been on the market for several years, it can be difficult to find spare parts in the event of a breakdown. Changes to safety norms and/or standards can also make it necessary to change certain parts.

Maurice Schauli adds that, "if the most complex parts, such as the electronic board of a PLC, cannot be found, then the durability of the installation is uncertain.”

One solution, is to keep a stock of the most important and/or complex parts.

Updating the electrical/electronic system does not directly increase the press’ productivity. However, such changes can lead to better control of the overall process with other line, or even factory, equipment, and therefore improve the overall productivity of the process. Adding functions, communication options, or optimising sequences, etc. will lead to productivity gains.
 

Over the past few years, the factory environment has considerably changed. Companies are now equipped with communication options via their company network.

Retrofitting a press can make the machines more connected, enabling them to make use of options provided by the so-called “Industry 4.0”.

The press can therefore be managed by a digital control tower. Below are examples of technical elements that can be controlled:

• temperature sensors,

• filters,

• force sensors,

• the protection of tools by camera (visual die protection)

• etc.

Maintenance thus becomes predictive and critical breakdowns are reduced.

Maurice Schauli shares an example of a predictive initiative: "Car manufacturer Porsche and Schuler have set up a joint venture ,“Smart Press Shop GmbH & Co”, with a brand new 4.0 factory set to open in 2021.”


In conclusion, it is also important to add that there is today possible to have ‘digital twin’ systems that perform the same operations as the press and provide an intelligent enough model to improve how the press works. The digital twin can thus carry out preventative, rather than curative, scheduled maintenance. Maurice Schauli believes that "the digital twin is a premise for the creation of a smart factory”. This technology has already been used for several years for process simulation purposes, such as for servo-driven press lines. Other possibilities include virtual start-up, faster ramp-up times, prior training of operators during machine assembly, etc.