When analyzing a hot stamping system and determining the best way to hot stamp a plastic part, die mounting is not usually viewed as a critical aspect. However, with increased options in the marketplace and companies, today, watching costs and product speeds closer than ever, die mounting has become a more integral part of the hot stamping process.
Die Bonding Tape
One of the oldest and most widely used processes for securing dies on the hot stamping chase is die bonding tape or heat tape. The tape works as a hot melt adhesive between the die and chase. The tape is applied to the back of the die and the heated head of the hot stamping press is lowered down onto the back of the die. The heat of the press and pressure melt the adhesive and bond the die to the chase.
This is an acceptable means of locking up dies for short runs using magnesium or silicone rubber dies. However, it is somewhat of an antiquated method. There is not an efficient way to register the die to the stamping image and it is difficult to mount the die flat and parallel to the stamping surface. Removing the die can sometimes be difficult and the adhesive can create a mess that is not easy to clean up.
Direct Attachment via Screws
Another traditional, and older, method for mounting dies to the die mounting plate is with screws. This method offers a positive way to locate dies with reliability and repeatability. Dies are provided with either mounting hole locations marked on the die or pre-drilled with countersunk mounting holes. Die riser blocks or spacers are recommended for most applications to prevent the incoming foil from being affected through contact with the heated platen adjacent to the die. Die risers are normally attached to the removable dovetail, or headslide plate. The hot stamping die is then attached to the face of the riser block with flat head machine screws.
The number one advantage of utilizing screws is that this method provides the most secure method of locking up the die. If the screws are secure, there is no feasible way for the die to move. It also provides a positive way of registering the die to the mounting plate, and because the die is mounted directly to the plate, it allows excellent heat transfer from the heated head to the die. Disadvantages of this method include the possibility of the heated screws binding when trying to remove the die. The pre-drilled and tapped holes in the mounting plate also can be susceptible to stripping. Lastly, removing the hot die can be somewhat cumbersome. Many times the die mounting plate must be completely removed from the hot stamping press to facilitate the changing of the die.
Camlocks or Toggles
A third procedure for locking up dies is to utilize a honeycomb style die mounting plate. The dies are held into the honeycomb plate with small camlocks or toggles that are tightened within the holes in the plate. One die might require four to eight camlocks to secure it in place. This is a common lock-up system in the graphics industry where multiple dies are attached to a large platen.
The advantage of this system is easy registration of the die to the die mounting plate. The camlocks also allow the operator to make easy adjustments in several directions when tight registration is involved. As with screws, the heated camlocks can bind when trying to remove them, and changing the dies can be cumbersome, requiring gloves or tools. In most cases, the die mounting plate must be totally removed from the press to change out the dies.
Magnetic Die Mounting Probably the fastest growing method of securing dies in recent years is the use of magnetic die lock-up systems. Several companies have developed magnetic mounting systems that are said to enable the operator to change out dies and position new dies in a matter of minutes. Bunting Magnetic Hot Stamping Bases are manufactured for both automatic and semi-automatic presses and are designed to lock into existing hot stamping presses and typically require a minimum of conventional quoins or furniture. Bi-metal dies are also available that combine a steel backing with commonly used hot stamping die materials.
Universal Engraving, Inc. has recently introduced the UniMagnetic® Die System for foil stamping plastic parts. The UniMagnetic® base can be permanently or temporarily mounted to the die mounting plate. What makes the UniMagnetic® system unique is the use of patented hot stamping dies that combine copper and steel. The copper provides the best metal to transfer heat evenly and will not smash like softer metals such as magnesium or zinc. The steel backing is molecularly bonded to the copper plate, ensuring the die will not delaminate from the steel. In addition, the dies are .070 thick versus standard .250 thick dies. This saves storage space for the dies and shipping costs.
United Silicone has also developed the Quick Change die technology that utilizes a magnetic die chase mounted into the hot stamping press. Using a pin registration system, the Quick Change solution improves repeatability from die to die by offering increased production and less downtime.
With magnetic die lock-up systems, the biggest advantage is certainly the ability to easily mount and adjust dies on press. It eliminates the messy clean up of die tape and provides optimum heat transfer from the die to the mounting plate. The disadvantage of a magnetic system is the initial cost of the magnetic base or chase. However, once this cost is absorbed, this can be an extremely effective and efficient way to lock-up dies.
Vacuum Mounting System
The last die lock-up system to discuss is a vacuum mounting system. Similar to a magnetic system, dies can be easily mounted and changed out, utilizing vacuumed air to hold the dies in place. The advantage of this type of system is that it provides positive location of the dies on the mounting plate and can drastically reduce downtime with die changeover. The disadvantage of a vacuum mounting system is the initial cost versus traditional die mounting plates. In addition, it is limited to lightweight magnesium and aluminum-backed silicone rubber dies. Heavier copper or brass dies would not hold properly with a vacuum system.
The number of changeovers, the speed the parts will run at, the type of die that will be used, and the size of the part are all important elements to consider before selecting the correct die-lockup system. It may seem like an insignificant portion of the entire process, but careful preplanning and implementation of a die-lockup system can make a remarkable difference in the final outcome of the hot stamped product.
Plastics Decorating would like to thank Dennis Cook of Kensol-Franklin (508) 528-2021 and Keith Hilstead of United Silicone (716) 681-8222 for their assistance with this article. Also, we would like to thank Bunting Magnetics (800) 835-2526 and Universal Engraving, Inc. (800) 221-9059 for providing information on their magnetic die mounting systems.