A friction drag or brake is typically designed into tooling to help with blank control during the transfer cycle. In many cases it is a necessity, but it can also contribute to downtime.
According to Jerry L. Bupp, Director of Sales/Marketing at National Machinery LLC, Tiffin, OH, USA , high-speed cold forming machines are truly precision machines. Getting the most out of your equipment is important and in some cases the tooling setup over a long production run is often difficult, yet obtainable. One method to accomplish this is a tooling pin braking device or friction drag.
Blank Control During Transfer
A friction drag or brake is typically designed into tooling to help with blank control during the transfer cycle. In many cases it is a necessity, but it can also contribute to downtime. Machine cycle rates in the hundreds of parts per minute translate into blanks that are going from station to station as fast as five parts per second.
In the common tooling sequence, the forged part is held securely in a die cavity. As the ejector (or kickout) moves the part out of the die, the blank grippers or fingers must move instantaneously gain control. The part is then delivered to the next forming station and the grips must relinquish control back to the next station of tooling. The “pass off” of the part between fingers and dies is where the frictional drag system provides an important function.
Control of the blank is converted back to the tooling by either pushing the blank a short distance through the fingers into the die cavity, or the blank must be momentarily suspended in mid-air between the tool pin and die pin. Once suspended (Figure 1), the fingers can begin to open and clean the approaching tool. If the holding force of the braking system is not maintained, the blank can’t be held at its proper axial position. When this occurs, the blank will either fall free of the tooling or tilt down and be forged off center. Such partial hits will typically stop the machine via a fault to the load monitor. Damage to the transfer or tooling components can occur, causing production loss and higher tooling cost.
A Remedy to This Problem
Recent design advancements have made it possible to reduce the occurrence of this issue from a daily to only a monthly occurrence, and in some cases completely eliminate the problem.
In the past, various plastics or nylons have been used for friction drags. They have also been used as the spring component itself. The cold forming process as well as the frictional heat of the braking system pushes thermal conditions beyond the parameters of nylons and plastics. Once exposed to this elevated thermal environment, the material softens and loses strength, resulting in failure by loss of axial pressure.
Coil springs also introduce problems due to physical space limitations that require small springs lacking in force for the job. Operators are forced to over-tighten these delicate springs and compress them solid, which results in both damaged springs and unreliable setups with no adjustment range. And forming vibrations commonly cause tooling setscrews to back out and lose setting.
The new friction drag system (Figure 2) eliminates setscrew adjustment and gives needed pressure for proper blank control. Users report remarkably improved consistency, setup and reliability compared to old drag designs.
Previously, operators tended to set older brakes too hard, knowing they would lose pressure quickly. This aggravated tooling pickup or galling of the drag pin against the filler. Since the new friction drag design maintains pressure throughout its long life cycle, proper pressure can be applied, as opposed to excessive pressure. A simple cylindrical tungsten carbide puck maximizes contact area to reduce damaging pressure on the moving pin. This attribute, along with minor material and hardness changes, has eliminated the galling problem within the tooling components of the drag system. Assembly and adjustment of this system is simple. The filler is held in an ordinary bench vise or press. Axial load of the drag pin is adjusted by adding or subtracting disc washers or by altering their stacking sequence.
Also, some tooling setups require a drag in the punch and die sides of the same tooling station. Proper function needs one side to consistently yield to the other, and this bias is now easy and dependable with the new drag system.
The stability of the forming process is critical to optimizing machinery for the best production. This friction drag tooling breakthrough allows for consistency and reliability that matches the National cold former. For details, contact National Customer Support or Circle 201.
Fastener Technology International/ February 2005
Director of Sales & Marketing
National Machinery LLC
161 Greenfield St .
Tiffin , OH 44883