Parallelism, off-center loading and slides in mechanical presses

1. What are the key press design elements that affect maintaining press parallelism under off-center loading conditions?

The two key press design elements that resist off-center loading throughout the stroke are the pressure points and the press guides. Both are critical to consistent part quality and tool life. They play a key role in maintaining parallelism not only at bottom dead center but throughout the entire working stroke.

2. How do the number and location of the press ram connection points affect parallelism?

The pressure point, or ram-rod connection point, is the most important point where the ram receives support against off-center loading. Presses are typically designed with one, two or four pressure points. In general, the design will increase the pressure point from one to two when the table length exceeds 1.5 m from left to right, and from two to four when it exceeds 2 m from front to back. Single-pressure point presses, especially C-type presses, are widely used in industry for smaller and less complex dies, while two- and four-pressure point presses allow the centering of off-center loads between the pressure points when pressing large progressive or transfer dies. This can reduce the negative effects of off-center loading. The distance between the connection points is very important; the greater the distance between them, the greater the resistance of the press to off-center loads. The wide connection gap places most of the load between the pressure points and prevents the pressure points from creating opposing reaction forces.

Kaçık yüklemelerde biyel kolları arasındaki mesafenin önemi ve pres paralelliği

3. What are the available guidance systems?

Guidance systems typically include four, six or eight surfaces of guidance. Historically, these guide slides were equipped with hydrodynamically lubricated linear bronze wedge liners. Recently, roller guide systems have been introduced, which eliminate the clearances and lubrication required in the bronze liner system. Die guide columns and bushings, while necessary during mold construction, maintenance and adjustment, do not have sufficient strength to be the primary guidance system for the stamping process, and a good press will soon be damaged if not supported by a suitable guidance system, both the die and the press slides.

Pres koçu kılavuz yapısı ve kılavuzlar arası boşluk

4. Besides the number of points in the slide guide, what other features of the guides affect parallelism?

Off-center loads tend to rotate the ram, thus applying increased pressure to the bottom of the guides on the high-load side and the top of the guides on the low-load side. To provide optimum resistance, it is important to have reduced or zero clearance in the slide system. Additionally, increasing the distance between the top and bottom of the slide guides increases torsional resistance to the loads.

5. What are some of the features and benefits of roller guide systems?

The benefits of a zero clearance system include resistance to off-center loads, improved part quality, and tool life. Roller guides also eliminate the need for press lubrication on the guide surfaces. This results in the elimination of cross-contamination of press and die lubricants. Eliminating cross-contamination can prevent significant press maintenance problems, including bearing and bushing failures. Eliminating lubrication used in sliding guide systems can also be beneficial when pressing stainless steel, brushed and polished aluminum, and pre-coated materials where contamination can cause costly scrap.

Parallelism in mechanical presses

Emrah Demirezen

Metal Forming Expert - Press Designer

emrahdmrzn@gmail.com