How to Shim a Hydraulic Press Flat Sheet

Shimming refers to adding weight under certain sections of a bottom die to raise it during bending, an error-prone trial-and-error process.

Hydraulic presses consist of two primary cylinders connected by hydraulic lines. When oil or water is added to the smaller slave cylinder, pressure builds until exerted force can be felt on the larger master cylinder attached by clamps.

Bending

Bending is the process of deforming metal into an angular form by applying force exceeding its yield strength, plastically deforming it to produce plastic deformation and creating internal stresses which lead to cracking or weak spots within its structure.

To avoid this situation, many fabric shops employ a technique called "shimming". This involves placing small pieces of thin material beneath certain areas of a die, to raise them during bending without causing damage or costly repairs to machinery. Shimming provides stress relief without incurring costly repair expenses or harming machinery itself.

Designing a flat pattern requires also considering various forming methods, as this can drastically change its look. Bottom bending may produce large variations in angle while air forming offers greater consistency; conducting several test bends to determine the ideal form may help determine this. Changing this may also alter your inside bend radius so it is important to calculate this beforehand - doing this ensures your parts will always look consistent no matter which bending method is used.

Shimming

Shims are small washer-like discs designed to prevent axial movement between assembled components. Constructed from precise materials that meet precise tolerances, shims create an exact distance between two adjoining parts for alignment and precision purposes. Shims may be installed within bearing contact areas for alignment purposes as an added measure.

Slotted shims feature a narrow opening at their core and are used on machined parts for alignment and leveling purposes. Installed in place of washers, these allow tighter fitments with greater precision.

Modifying forming tonnage consistency will help alleviate crowning and twisting issues with older machines with worn or outdated bolsters, but correcting this with shims may prove challenging. An alternative would be a steel horseshoe shim or slotted motor shim which comes in various thicknesses for your consideration.

Crowning

Over time, coatings on materials, material tolerance variations and stickers or labels can lead to inaccuracies along bend lines. While form shimming may help at times, it may not always be effective and can result in uneven bending.

Crowning can provide an effective solution to this issue. Crowning is the practice of compensating for the natural flexing of Bed and Ram of press brakes when under strain due to tonnage being applied on sheet metal sheets.

Mechanical crowning provides compensation for deflection by continuously adjusting the wedge between ram and bed through real-time correction, using a motorized hydraulic cylinder to move up and down neutral plate. It's available on both X-Press Easy and LaserLine systems and features Gasparini crowning technology with proportional compensation that cancels out side frame deformation effects; standard on all X-Press machines.

Deflection

Hydraulic presses come equipped with many features to make your task simpler and more accurate, such as Finite Element Analysis - an analytical approach used in press design that predicts how real-world forces will impact it - and Gibs, adjustable mechanisms which regulate reciprocating motion of the ram for squareness and parallelism throughout its cycle.

Quick stroke depth control can reduce cycle times significantly. Ram speed can be adjusted to match material feed or other pressing needs, and set to reverse at distance or pressure specified by the operator. Blank holders and die cushions are available to provide uniform blank holding in deep drawing, and to easily strip finished parts from punches or dies after deep drawing has finished.

Other key press components include the frame, bolster and ram. The frame serves as the main structural support for carrying cylinders and work surfaces while the bed provides a level surface on which dies can be mounted on. Finally, the ram is the middle weldment that slides to apply pressure to tools or dies and should also include controls like stroke control, rapid approach speed and throat clearance (measurement from vertical centerline of ram to the frame member behind bed).