Archive for June, 2010

29
Jun
by Michael Riehn

Return on Position Control

Return on Position Control

Whether your process is stamping sheet metal or forming composite components, choosing the right press return for your application is crucial. Identifying the capability needs, up front, can eliminate additional costs and start up delays.

Hydraulic presses offer the capability of configuring the press stroke to meet your die or application needs. They also have the ability to adjust the overall travel of the ram and can be configured to return at a given position or a given force. This flexibility yields the greatest advantage for hydraulics for a wide variety of applications.

The most critical factor in selecting a hydraulic press, is to match the press capability to the needs of the application. There are three primary press capabilities available (though all can be combined depending on the required performance of the application).

Return on Pressure

Return on Pressure Control

Return on Pressure Control

The most common and economical performance capability for a hydraulic press is the ability to Return on Pressure. Because a hydraulic press can develop full tonnage anywhere in the stroke, this lends a great deal of inherent flexibility. Dies with integral stop blocks but multiple shut heights can be easily run on the same press with minimal set up.

In addition to flexibility and reduced set up time, dies and applications that are designed for this mode of operation gain absolute repeatability at very little cost. Even traditional punch tooling can be run under return on pressure mode by incorporating fixed stops into the tooling or press system. In this mode, the ram will lower and extend to a preset target force and then return to the up limit position.

Today, most dies are being designed with stop blocks either built into them or designed so that the die itself can be closed to “bottom out” and support the force of the ram. In this case, operators can set the target return force set point slightly above the necessary force

Return on Position
Return on Position is another commonly requested performance capability, but is also the most routinely misunderstood. Unlike a mechanical press, in which the ram always strokes to the same bottom position every cycle, a hydraulic press can be controlled to stop and return at any point in the stroke.

The repeatability and accuracy of this type of control varies widely and is dependent upon many variables such as; speed of the ram, the type of valving used, the type of work being performed, etc… The level of performance has an impact on the cost of the hydraulic and control systems.

Basic and simple systems yield somewhat loose performance capabilities due to the reliance on hard shift valves to control the direction of the ram. These systems achieve repeatability of perhaps ±0.020″ - ±0.025″. More sophisticated systems integrate open or closed loop control to significantly improve and tighten the level of performance for repeatability of ±0.001″.

Return on Pressure with Dwell

Return on Pressure and Position

Return on Pressure and Position

Return on Position is another commonly requested performance capability, but is also the most routinely misunderstood. Unlike a mechanical press, in which the ram always strokes to the same bottom position every cycle, a hydraulic press can be controlled to stop and return at any point in the stroke.

The repeatability and accuracy of this type of control varies widely and is dependent upon many variables such as; speed of the ram, the type of valving used, the type of work being performed, etc… The level of performance has an impact on the cost of the hydraulic and control systems.

Basic and simple systems yield somewhat loose performance capabilities due to the reliance on hard shift valves to control the direction of the ram. These systems achieve repeatability of perhaps ±0.020″ - ±0.025″. More sophisticated systems integrate open or closed loop control to significantly improve and tighten the level of performance for repeatability of ±0.001″.

Category : Blog | Hydraulic Press | Hydraulic Press Controls | Blog
25
Jun

Recently one my co-workers, who has never quoted a hydraulic press, asked me for a quote based solely upon the part number from an old machine. At this point, I began to ask him questions about the application, such as cycles per minute, stroke, etc., which he shrugged off and said the customer did not know the details, but just wanted a price based upon the P/N off of an old machine. I told him I could not possibly price a machine without this information, the old machines P.O. number or the serial number. At this point he went to our boss and asked the same question and was told ‘I can quote you a 30ton press for $20,000 or $200,000 based upon the customers requirements’ and was sent to get the details necessary to provide a proper quote.

This is not unique circumstance, I can remember selling filters and commonly someone would realize that the oil they were using in their hydraulic systems did not meet the oil cleanliness requirements of the hydraulic components on the system. Many customer’s would look at the filter they were using see that it was “rated” as a 10 micron media and then ask me and three other vendors to quote a 5 micron filter, buy the least expensive one and assume that it would clean the oil up. The problem here is that every filter, wire screen, piece of paper , up to and including my dirty socks are 100, 50, 20, 10 5, 3,and 2 micron filters all at the same time. They just happen to be much more efficient at removing certain particles than others. Just one of the details being over looked is the efficiency rating of the media, which has a large impact on the cleanliness. Then there is the fact that the new smaller pore size filter may not work at all in the application, because it has too large a pressure drop.

My point in all of this is that many times a customer calls in asking for a general quote with a very vague idea of what they need or want. It takes a knowledgeable individual to walk them through the process to dig for the details necessary to provide them with a quote that reflects what they are truly, needing. So, please be patient when someone is digging for information to get the details necessary to provide you with a proper quote. They would just as soon be playing solitaire, looking at the web, reading the daily news, as the next guy, but they know that if they make a mistake in the quote and it is not caught, they may have just sold you a $600,000 boat anchor which could get them or you fired. The devil is not in the details, but in the lack of them.

Category : Blog | Hydraulic Press | Blog
11
Jun

by Dan Michki
Electrical Engineer

Haifa, Israel

Haifa, Israel

My first opportunity to experience the country of Israel came from a Hydraulic Press Startup. The city that I visited was Haifa and it lies right on the coast of the Mediterranean.

My first thought was that this must be one of the best kept secrets in the world, since the beautiful beaches were completely void of people. I later found out that this is largely due to the fact that the entire population of Israel is under 10 million people.

The press is used for the extrusion of Aluminum in small laboratory batches, so that it can be analyzed.

The process begins by heating the stock material. It is then loaded into a heated container in the press. A dummy block is placed behind it where the ram then presses on the material to push it out of the die. Afterward the extrusion is stretched in order to straighten it.

The press uses a LabView based HMI PC for Data collection and Analysis and a Delta hydraulic controller for velocity/force controls. The operator can enter a velocity in MM per second and a “not to exceed force” in Kilograms.

The press is powered by a three phase 400VAC 50 Hz. circuit.  This is good to keep in mind as the current draw of a standard three phase 480VAC 60 Hz. Motor will be more, so the components need to be sized accordingly.

This was one of the best places that I have ever visited, due largely to the fact that 70% of the population there speak perfect English.

Category : Blog | Hydraulic Press | Hydraulic Press Controls | Blog