A stamping press expert provides some guidance
November 2, 2012
From the perspective of a field service professional, the choice to repair, rebuild, or look for a new press isn't that hard of a decision. It's just a matter of clearly looking at the current shape of the press and what it will take to get it up to performance specs.
With the capacity utilization rate for the fabricated metal products sector hovering near 80 percent for most of this year, according to the Federal Reserve, you know that metal part manufacturers are busy folks. As a result, they need their stamping presses up and running to keep up with increased job orders.
Meanwhile, press repairs that have been postponed over the past several years are starting to become a real problem for metal forming operations struggling to balance downtime with production realities. Additionally, any lack of press maintenance becomes clearly evident as the press equipment, although built to last, begins to show its age as it is pushed beyond what can be expected of a neglected machine.
So when the stamping press stops running, the question has to be asked: Repair or rebuild? That depends on the circumstances and the amount of money that is set aside for the project.
Typically, many people involved in press repair and rebuild activities say that to rebuild a press costs about two-thirds of a new machine cost when the rebuild includes electrical updates. Truthfully, no one really knows the cost of a rebuild—or a repair that’s not visible to the naked eye—unless disassembly of the press occurs (see Figure 1). In some instances, the best advice is to scrap the press and look for a rebuilt used one or a new one.
For the record, this discussion is limited to making repairs and rebuilding to original OEM specs. Any change made to a stamping press, such as a new control system, is considered a press upgrade and is worthy of an entirely different debate for stamping shops looking to modernize equipment.
While no hard and fast rules exist to govern every situation where a stamping press may be out of commission, some basic guidelines can help you make the most cost-effective decision.
What if a few specific items on the stamping press are in need of fixing? Repair. That goes for what is evidently broken. Evaluate the rest for additional repairs or possible part replacement.
However, if repairs are required for more than five wearable major components on a stamping press, it might make sense for a rebuild (see Figure 2), because that will entail a detailed inspection and replacement of most wearable components. You’re talking about flywheel bearings, bull gear bearings, drive shaft bearings, bearings in the slide mechanisms, power transmission components in the slide mechanisms, clutch and brake components (see Figure 3), brake springs, brake anchor pins, anchor bushings, and all of the hardware. At that point, the additional work required to rebuild the press might cost more money, but the manufacturer can be confident that the press is ready to produce parts as it was originally designed to.
What if a problem arises, but maintenance records indicate that, outside of the problem area, wearable components of the press have been recently inspected and look good? Repair, but not before all of the machine operations have been inspected.
After all, there is a cause and a result for everything. If you do not locate and solve the issues causing the failure, you will just be fixing the results, and the possibility of those same issues coming back again are much greater (see Figure 4).
Additionally, make sure you trust your maintenance personnel. It’s not surprising to find a repair that a maintenance technician has made that only aggravates a deteriorating situation.
In one instance, a 125-ton stamping press that was experiencing excessive movement in the ram ball cup and pitman bushing was found with a faulty brake condition as well. The other service personnel had tinkered with the brake lining and OEM rivets and decided it would be okay to thread the holes in the brake strap and put in screws. Needless to say, the screws got loose (as well as the linings) and were wearing into the brake drum. Instead of just having to reline the brake and resurface the brake drum, the repair technician had to take the brake and drum off of the machine—which does not always happen without a good amount of disassembly—and machine those parts. Of course, that’s if the stamping shop is lucky; if the wearing gets to the point where machining won’t resolve the situation (because only a fraction of the drum surface can be removed without affecting braking performance), the stamper has to replace the whole drum. That can lead to more problems because, depending on machine make and model, a replacement drum might not be a stock item, requiring the stamper to wait for the new component and to endure significant downtime.
What if the machine’s ram is out of parallel? Repair or rebuild. It is going to depend on where the out-of-parallel concern is coming from.
The repair may be as simple as gib adjustments, with slightly worn gib strips being the problem, or it may not be so simple with out-of-parallel problems extending to the bottom of the ram, gib surface wear beyond adjustment, or major component wear. If the bottom of the ram is worn from years of hitting hard or gib wear is present, the ram needs to be removed to make the proper repairs. At that time, depending on the component age and running frequency, a rebuild might be required with new main bearings, brake/clutch components, and counterbalance kits (if needed), as well as all other wearable components, as these items are all much more accessible at this time.
What if a repair process requires that the press has to be totally disassembled? Rebuild.
Again, if a repair situation calls for completely disassembling a stamping press, the metal former has a piece of equipment that most likely has more than one simple problem wrong with it. It is likely more cost-effective to have the wearable components replaced at this time and all other remaining components looked at. That includes having the hard castings, the ram, flywheel and/or bull gear, shafts, and other parts that aren’t normal wearable items cleaned and inspected for unusable conditions, such as component cracks, wear, or out-of-concentric issues.
Keep in mind that an on-site repair or rebuild may be more expensive when compared to a job where the entire machine can be shipped back to a repair shop. Working on-site means that the repair technician is working out of the back of a service vehicle or a gang box of tools, making trips back and forth for tools and support equipment. Of course, very large presses are not easily transported from one place to another, so they typically require the on-site attention, which may entail removal of certain major components (such as ram or crown assemblies) and shipment back to a repair facility if necessary.
What if the machine has been neglected over the years? Start shopping? Maybe.
Sometimes if a machine has been abused for too many years because the shop ran the press consistently outside of OEM specifications or just failed to stay on top of any basic maintenance, the hard castings might be damaged. This type of damage includes cracks or too much wear that cannot be machined out. At that point, repairs will be costly. Those casted and machined components are not sitting around on a shelf somewhere in most cases; they have to be built, which is not cheap.
There is also the question if the repair technician wants to assume responsibility for trying to repair a casted component. He may not want to undertake the liability of trying to weld a damaged component back to an acceptable state.
In some cases, a used machine in great condition can be obtained for less than what it would cost to repair a machine with casting damage. However, the cost of bringing the used machine back to OEM specifications must be weighed against what it will take to have tooling reworked for the new press.
Actually, that debate has to take place with any decision related to repairing, rebuilding, or scrapping a stamping press. Anything can be fixed, but there always will be a cost to bear.
When the discussion turns to replacing a damaged stamping press, there are important factors beyond the purchase price of a new or used press. How long can the press be expected to last operating at full capacity? What kind of service is available for the press? Are replacement parts readily available for wearable items on the press? Knowing the answers to those questions can help a shop avoid weeks of possible downtime if a replacement stamping press goes down unexpectedly.
Repairs will always be a necessary part of stamping press use. However, three simple tips can help a stamper avoid complete rebuilds and most repairs:
1. Don’t forget to lubricate. Lubrication of all a machine’s moving surfaces is critical. Just like the blood in a human’s veins, a machine cannot survive without it. Proper lubrication should be checked at each point every day.
2. Avoid overloads. Ensure the machine is not getting pushed to its capacity every day. Overloads are one of the most common causes for component failure.
3. Tap the operator’s knowledge. The operator is a key factor in ensuring machine reliability. He or she should be completely familiar with all operational instructions and safety procedures for each piece of equipment. The operator should understand the importance of lubrication and remain aware of potential problems.