Creating a pressroom preventive maintenance program
A step-by-step guide
A press maintenance program should be designed to minimize downtime, enhance machinery output, and establish a formal record keeping system for ongoing inspections.
Many fabricators rely on fire-house maintenance when a machine goes down, all available resources are marshaled to fix the problem. This approach works most of the time, but at a high cost.
To minimize this cost, stampers need to design a press maintenance program that decreases downtime, enhances machinery output, and establishes a formal recordkeeping system for ongoing inspections.
An effective pressroom maintenance program follows a specific step-by-step approach.
Step 1: Create a List
Compile a complete list of all the different machines that are used in a manufacturing workcell.
Step 2: Inspect All Equipment
Review each machine's manual and obtain a copy of an OEM preventive maintenance schedule for guidance. Look for abnormal wear of bushings, bearings, and wear surfaces. Check lubrication, electrical, pneumatic, hydraulic, and motors or drives. Note the items that normally cause downtime, and then record and evaluate the results.
Step 3: Keep the Program Manageable
Ideally, some items should be checked on a daily, weekly, monthly, or semiannual basis. It may seem like a great task, but remember the old saying: You can eat an elephant a bite at a time!
Many shops get to this point and the program stalls. The three most popular excuses are:
1. The cost is too high and it takes too much time.
2. We already have too much paperwork to fill out.
3. The paperwork sits on the shop manager's desk and the problems aren't corrected.
Excuse No. 1. This excuse stems from management's lack of commitment to follow through. Not enough homework was done. Stop right here, research the problems, and resell the concepts so all management levels are onboard with the effort.
Excuse No. 2. This reason stems from a lack of commitment and understanding on the part of those who actually perform the work. Again, stop here! Discuss the issues with those involved, and focus on changes that will make the preventive maintenance program easier and more effective for them. Resell the concept; without their help, the effort will fail.
Excuse No. 3. If middle managers do not follow through on the work that needs to be performed, workers' attitudes are justified, and the company is wasting its resources. Data must be organized and evaluated and work orders generated for the program to work.
It's important to remember that the purpose of any preventive maintenance program is to eliminate waste and maximize throughput.
Maintaining the Stamping Press: An Example
The focal point and workhorse of the manufacturing cell is the press. To maintain press integrity, press inspections must take place on a routine basis (see Figure 1). The following items normally are checked as part of an effective press inspection.
- Overall condition of the foundation is good.
- No cracks.
- Press is mounted securely to the foundation.
- No press movement during operation.
- No cracks.
- Tie rods are tight.
- Frame or bed is level.
- Brackets and components are secured to the frame.
Bushings and Vertical Lift Clearances
- Eccentric strap or upper connection clearance with eccentric gear or crankshaft is correct.
- Main pin or crankshaft clearance with frame is correct.
- Upper connection or eccentric strap to lower connection clearance is correct.
- Lower connection screw to housing/slide clearance is correct.
Main and Connection Bushings
- Tolerance for bushing clearances is at levels 0.001 per inch of diameter up to 12 in. and 0.0005 in. per each additional inch of diameter.
- Less clearance on large eccentric bushings is acceptable.
- Two times the optimal clearance is allowed if counterbalances are used.
Upper Connection to Lower Connection
- Upper connection to lower connection clearance is 0.006 in. overall, resulting in about 0.003-in. lift clearance (assuming connection head is 6 in.).
Lower Connection to Slide Clearance
- Clearance between the adjusting screw and nut and clearance between the adjusting nut and the housing are acceptable.
- Clearance is 0.010 in. to 0.014 in. on small presses.
- Clearance is 0.020 in. to 0.025 in. on large presses.
- Gear wear is even.
- Gear teeth are in good condition.
- Gear train is well-lubricated.
- No excessive gear noise.
- Gear backlash measured and recorded.
Drive Shaft Assembly
- No air leaks in the clutch or the brake.
- Lining thickness on the clutch and brake pads is optimal.
- No excessive lining dust caused by slippage between the plates and friction disks.
- Clutch and brake operating properly.
- Air pressure settings to both clutch and brake checked and recorded.
- Dual solenoid press safety valves and flywheel brake valves are functional.
- Fusable disconnect or circuit breaker is within easy access of the operator to remove power to the machine.
- Panel lights are functional.
- Antitiedown circuit is functional.
- Antirepeat circuit works.
- Press control selector switch is functional.
- Continuous circuit arming button must be pushed to set up continuous operation.
- Emergency-stop buttons are functional.
- Air pressure switches on the main air system can disable the press control if proper air pressure is not present.
- Pump is functional.
- No broken lines or fittings.
- Filter system in place.
- No signs of contamination in the oil or grease.
- No sign of lack of lubrication or excessive heat being generated.
- Dies are properly aligned.
- Surface condition of the bolster plate is good.
- Bolster plate is seated properly on the bed.
- Bolster plate is secured to the press frame.
A press is designed to provide one thing: a perfectly square, repeatable die space at the designed pressure for your tooling. The maximum allowable parallelism tolerance is 0.001 in. per foot of span in the bed area. Almost all press problems other than lubrication relate back to this square die space concept. If you want to obtain the most trouble-free production environment in your pressroom, always strive to maintain a square box for your tooling.
Making the Program Effective
Now that you've gathered the information, it's time to work with the press maintenance team to establish program goals, such as zero part defects and breakdowns during production hours.
Inspections are designed to provide a starting point. Next, it's important to generate work orders based on inspection reports. Analyze every process from a kaizen standpoint. Challenge your production and maintenance teams to recommend modifications or improvements for equipment or procedures. Create a list of items and prioritize what can be done quickly. From there, develop a timeline for medium-range and long-range items.
Recordkeeping is essential to make preventive maintenance program work. Shift reports should be generated, and press operators should record all downtime issues, possible causes, and solutions to avoid losing time for the next shift.
Remember, Inspection + Correction = Uptime Improvement and Increased Quality and Profitability.
Preventive maintenance is not a single event, but a long-term process.
A manager must have total responsibility and authority to administer all facets of the program to make it a success.
This article is adapted from Jeff Fredline's conference presented at FABTECH® Intl. /AWS Welding Show, Nov. 13-16, 2005, Chicago, © 2005 by the Fabricators & Manufacturers Association Intl.
STAMPING Journal is the only industrial publication dedicated solely to serving the needs of the metal stamping market. In 1987 the American Metal Stamping Association broadened its horizons and renamed itself and its publication, known then as Metal Stamping.