May 13, 2008
Converting a current press to a transfer press requires altering the press, transfer dies, and the transfer system. Some presses are suitable for conversion, some are not. With a proper transfer retrofit, an old press can become a fully programmable state-of-the-art transfer press.
Does this sound familiar? You purchased a new press 20 years ago for a specific program that ended seven years after the installation. The press was paid for during those years because it always was at capacity. For the past 13 years your management team has been finding projects to fit the press, but has never come close to hitting past production numbers. Your sales department cannot bid on new transfer jobs with one of your biggest customers because quoting hand transfer no longer is competitive. Last year you could have landed some high-volume takeover transfer work from a Tier 1, but it went to your biggest competitor, which has a servo transfer press.
This scenario is common across North America. Some stampers are considering stamping components using transfer dies rather than in progressive dies for the following reasons:
1. As OEMs decrease the number of components in each new program launch, the resulting complexity of the new parts often indicates that they must be made in a transfer die.
2. Material savings can justify using transfer dies because blanks can be nested. Zigzag feeders are used in many applications to maximize the number of blanks coming off the coil, minimizing scrap.
3. Because a change can be done with one hit in a transfer station, as opposed to tearing out multiple stations in a progressive die, changes are simpler. This accommodates the possibility of engineering changes in the future.
4. Some flanging and cam operations can be performed more easily in a transfer die than a prog die. For example, the ability to rotate a part gives die designers creative freedom not possible in a progressive-die operation.
5. Today's servo transfer systems are more flexible, faster, and smoother than they used to be. The drive trains are modular and scalable and no longer should be the bottleneck in the stamping process. Some servo transfers are designed to retract up and out of the way for die changes or to run progressive dies (see Figure 1). With a proper transfer retrofit, an old press can become a fully programmable transfer press capable of running any part profile that can fit in that press and at rate.
6. Many old hand transfer or mechanical transfer systems run at 25 percent to 50 percent of the speed they would run in a servo transfer. The potential for higher speed provides the opportunity to pick up takeover jobs from these programs and run them efficiently and profitably in a servo transfer.
So, let's say you have decided to buy a transfer press. Before specifying a new press, look at your current presses to see whether you can modify any of them into a transfer press. Retrofitting a servo transfer system on the wrong press could be disastrous if not properly thought out. You should consider these factors when choosing a press for retrofitting:
1. Bed length and tonnage. Your sales department should know your current and potential target markets to help you assess desired bed length and tonnage. The current trend for the transfer retrofit market is for longer beds and higher tonnage so that additional stations can be added. Longer beds facilitate coil feeding and blanking in the first stations, which eliminates the need for offline blanking and the purchase of a destack feeder.
2. Press stroke. In a progressive-die press, the shorter the stroke, the faster the press runs. In a transfer press, this is not always the case. A transfer system runs more efficiently when a sufficient stroke window allows the transfer the time it needs to make its moves when the die is not engaged. Your transfer system vendor should look at the type of parts you plan to run and make recommendations on a press with a sufficient stroke. Drive-sizing software provides estimates on run rates if the following data is entered: lift, pitch, and grip per side; part weight; die engagement; and press stroke.
3. Press window. The press window has a direct relationship to the type of transfer system you select and how it is mounted to the press (see sidebar). When the servo retrofit market went into full swing in the mid-1990s, most of the automation suppliers were mounting their transfers through the press window. This design still is efficient and has some advantages, but front- and rear-mount systems also are an option.
4. Press control upgrades. Control upgrades may be required for safety or expansion purposes. Safety upgrades include guarding, such as light curtains or fencing. Upgrades also can expand press operation features and reliability depending on the press vintage. The older the press, the more the control system will require attention.
5. Mechanical upgrades. A modern transfer can physically mount on any press. The press design dictates the mounting location. Modifications to accommodate the transfer may include relocating piping or electrical services after you have determined the transfer's location.
6. Safety upgrades. After you have modified the press to accept a transfer, you need to upgrade the overall safety circuit to the latest standard. Local laws and safety authorities, such as the Occupational Safety and Health Administration (OSHA), dictate the extent of the modifications.
It is good business to maximize the use of older (paid for) capital equipment. Leasing companies treat servo transfers as capital equipment, which can free up initial cash requirements for financing the automation. Many stampers that have retrofitted their older presses into transfer presses have experienced a growth curve in their bottom lines and increased their customer's confidence in their capabilities.
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