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QUICK DIE CHANGE SYSTEMS AND UNIFORM DIE SETS

Ultimately the Stamper's objective is to maximize the profits that are generated by the metal forming process. A major factor affecting these bottom line profits is the Equipment Utilization factor (Equipment up time ).

The utilization factor indicates the amount of time that the equipment is actually producing acceptable parts. The utilization factor should be as high as possible with the norm between 60%-85%. One of the many factors that affect equipment utilization is the amount of time required to exchange die sets. Die exchange time can easily vary from 2 minutes for a full automatic system to 8 hours for a manual system.

Following are a few of the items that affect the die exchange process. Automating the die exchange process requires that special attention be paid to each of the items.

  • Press shut height requirements
  • Part pass line requirements
  • Bolster heights
  • Clamping methods
  • Press Stroke
  • Press tonnage
  • Press deflection characteristics
  • Control system
  • Counterbalance system
  • Management team objectives
  • Employee commitment

QDC Systems (Quick Die Change Systems)

Press die sets are massive precision components that must move quickly and accurately from presses to storage areas and back again. The system that performs these functions is called a QDC system, or Quick Die Change system. There are many QDC systems used, but the Rolling Bolster and Die Cart systems are the most common.

Rolling bolster systems:

There are three popular rolling bolster systems:

I. Single Bolster Operation:

The bolster moves laterally in a straight line into and out of the press. This may be done at either the front, rear, or sides of the press. In this type of system the die is placed onto the bolster in a preset position and manually clamped to the bolster. The bolster is then run into the press bed area and automatically clamped into position.


Advantages:

This system provides a means to easily install a die at a preset position, assure uniform clamping, and also insure uniform positioning in the press.


Disadvantages:

This type of system requires that the machine not be functioning during all phases of die exchange, therefore, not utilized.

II. Twin Bolster Operation:

Next on the list is the Twin Shuttle system that can be either a side to side shuttle or a front to back shuttle. In this system two bolsters are used, one on either side of the press. The side to side shuttle system is preferred. A twin shuttle system will provide faster die exchange time easily ranging within 15 minutes hit to hit.


Advantages:

The main advantage to this system is that the down time of the press is decreased. The placement, clamping, etc., required to install and remove the die sets from the bolsters may be accomplished with the machine operating, thus, the utilization of the machine is increased.


Disadvantages:

The major disadvantage to this system is that the bolster that is not in operation is located near the press usually interfering with movement of other equipment, namely the automation equipment. Also, this type of system is greatly dependent on the press design, although modifications to the press are frequently possible.

III. Tee Track Bolsters:

The other system that may be used, is the tee track bolster system. This bolster system has the capabilities to move on two separate track systems, normally at 90 degrees to one another.


Advantages:

The bolster may be moved completely from the press site and placed in a "storage" location until needed. Also, a twin tee track bolster system will simulate the twin shuttle system providing means to locate the unused bolster away from the traffic pattern.


Disadvantages:

This system requires more dedicated floor space and special power requirements to permit the press/bolster system to operate effectively and efficiently.

Bolster locating methods and die clamping methods:

I. Rolling Bolster Locators

There are two locating methods commonly employed with rolling bolsters. The first and probably most common is the use of special wedges located on the bed of the presses and on the bolsters. As the bolster is brought into position and lowered, the wedges force the bolster into a preset location. Using index pins on the top of the bolster and locators in the die also assure uniformity. Expected positioning tolerance is well within 1/32".

II. Clamping

Three assemblies require clamping; the upper shoe(s) to the slide(s), the lower shoe to the bolster, and the bolster to the press bed.

Bolster clamping:

Bolster clamping can be accomplished by manual means, a hydraulically operated swing clamp system, a t-slot clamp system, or a ledge clamp system. The type of clamping system used is mostly dependent on the type of press construction.


Upper die shoe clamping:

The upper shoes may be clamped either manually, by inserting hydraulic clamps in the tee slots, by swing clamps located in a fixed location, or by traveling clamps that will adjust automatically to the upper shoe size.


Lower die shoe clamping:

Normally, this is a manual operation performed when the dies are placed onto the bolster. Hydraulic clamps have been employed to reduce the number of skilled trades and tools required for die set.

Die Cart Systems

There are three popular die cart systems:

I. One die cart incorporating a single pull, i.e. install and replace die.

Advantages:

Normally this method would be less expensive than the rolling bolster system and will provide the same benefits as the single rolling bolster.


Disadvantages:

There are two major disadvantages to all die cart systems. To incorporate automatic capabilities, normally a common subplate must be provided for each die and provisions must be made for "rolling" these dies onto the bolster or bed of the press. This will increase the cost, depending on the amount of dies needed.

II. One cart per press with carts at both ends of press lines incorporating a "tandem pull" system.

Shown below is a typical system:



Advantages:

This system is usually considered to be very effective in reducing total die change time.

Disadvantages:

The disadvantages for this system include the disadvantages stated above and add a few more. The first is the inflexibility of the system. The system must be tailored to match the presses and the dies. The installation requirements of the press are more stringent, and there are many more interactive parts used.

Two carts per press offering very high flexibility and speed.

Advantages:

This system offers high speed die change and also offers high flexibility. Bolster heights are allowed to vary and the dies may alternately be exchanged.


Disadvantages:

Cost and floor space requirements are the major disadvantages.


Locating and clamping methods:

1. The locating method generally used for die carts are index pins mounted in the carts that extend into mating sockets in the floor.

2. Clamping of the lower shoe to the press is normally accomplished manually by tee slot hydraulic clamps or ledge clamps.

3. Hydraulic methods of clamping generally require that a common sub plate be utilized or dies be designed with common die clamping locations.

Summary:

To accomplish a completely automatic quick die change, it is necessary to provide automatic adjustments such as automatic shut height adjustment, automatic counterbalance control, etc., These automatic adjustments may either be controlled using die signatures or may be fully interactive with the system variables.

The most advantageous ADC system is one that integrates automatic die exchange with automatic tool exchange. Hit to hit times of two minutes or less can be obtained using a fully integrated system. Hit to hit times of ten minutes or less can be obtained by integrating manual activities with automatic functions.

A well designed and integrated ADC System will provide not only an increase in the overall Utilization of the equipment, but will also provide savings in maintenance, inventory costs, and tooling costs. Before investing in a die change system, it is important to develop a plan that will satisfy your overall objectives.