April 2008 Edition

WORKHOLDING

You' ve Got to Know When to Hold Them

A palleting system helped reduce setup time and saved a shop an estimated $75,000 by keeping zero at zero

Survival and growth in contract manufacturing isn't just a matter of getting more business. It's processing more business. In contract manufacturing facilities there are different levels of inefficiency, some considered acceptable. For example, changing a setup required significant machine down time to

• remove and clean the fixture and table;
• place the new fixture, vise, or other clamping method on the machine and find tools to mount it to the machine table;
• qualify the clamping method in the machine;
• load the part into the clamping method; and
• machine the part.

This process can take 30 to 60 minutes, which reduces spindle time, and adds to inefficiency - unless the machine has a pallet changer. On average, machine's spindles are running 60 percent of the time. The other 40 percent of the time is due to either setup or tear down, or if the machine is down for service.

Machine Specialties, Inc., Greensboro, NC, reduced its setup time, improved the flexibility of its shop, and maintained a level of accuracy, repeatability, and rigidity using the Unilock Zero Point pallet system from Schunk, Inc., Morrisville, NC. A Zero Point pallet system - also called a Program Zero - is a pallet system that establishes the qualified zero point of a pallet, so when the pallet is removed and placed back on the system on the same or a different machine the zero point remains the same. The part location remains the same, from machine to machine or operation to operation.

In pallet cost alone, Machine Specialties projected a savings of more than $75,000 in one year by using standard pallets instead of the special pallets

Bob Schumacher, CFO of Machine Specialties, said the company realized a need to improve its throughput. It had to find a way to change a fixture both on and off machines, between setups from one operation to the next, or from one machine to the next.

Replacing Pins and Bolts

Machine Specialties had used tooling plates with pins and bolts. Although a relatively quick method, Bob said he saw potential for even more time savings and improved ergonomics. When Machine Specialties first considered the Schunk Unilock system there were doubts about the benefits and cost justification. A key consideration in implementing a Zero Point locating system was the system's ability to be integrated into the company's current fixtures. Not only was Machine Specialties able to mount pins on the bottom of their fixtures, the pins could be added to the company's standard vises and other basic workholding devices. This made setting up a vise quick and painless. No more need to indicate the vise or fixture every time it was set in the machine.

Improved ergonomics is another reason Machine Specialties made the change. The Schunk Unilock system uses a clamping pin spring force of up to 16,800 lb, yet unclamps quickly with a boost of shop air. This eliminates repetitive tightening and loosening of bolts. The tapered pin design of the system lets the operator load a pallet at up to a 23° angle, unlike the tooling plate and dowel pin, where the pallet must be perpendicular in order to slide the pallet in place.

One machine - a Matsura MAM 72-25V - required a special pallet system, at a cost of more than $1,500 per pallet. By using the Schunk Unilock, Machine Specialties was able to add the Unilock pin to the back of its fixtures, saving $1,500 per pallet and reducing change-over time. In pallet cost alone, Machine Specialties projected a savings of more than $75,000 in one year by using standard pallets instead of the special pallets.

Machine Specialties started off with a few units. Because of the flexibility of the system, it increased use of the workholding systems with the goal of incorporating them shop-wide. The operators reported being pleased with the ease of use and rigidity of the set up.

Easy Math

Brian Sharpe, of Machine Specialties, said "changeover has gone from 45 minutes in a traditional setup to approximately two minutes with the Zero Point quick-change pallet system, with 0.0002" of repeatability. If a shop sets up twice a day, at the shop rate of $75 per hour in a shop that runs five days a week, 50 weeks a year, the total savings would be $28,125 per year."

"The math is easy; it pays back," Schumacher said.

Another reason the company chose the Zero Point pallet system was that as the availability of skilled workers for manufacturing decreases, shops can use their existing workforce more productively. Even when a machine has a pallet changer, setting up a clamping device on a machine takes time from these harder-to-find skilled workers.

The quick-change pallet system benefits more than the short- to medium-run production shops. Any shop that sets up machines on a regular basis can benefit from the system. The clamping pins can be used to clamp a standard 6" vise, a three-jaw chuck, a customized fixture, or even a pneumatic fixture.

Some shops avoid indicating a standard vise by not removing it from the end of the machine table. This method of setup reduction costs table space, subjects the vise to unnecessary chip build-up, and restricts the use of the vise.

Other instances where the Zero Point pallet system has benefited Machine Specialties is when a job is interrupted. A pallet can be removed and replaced with a more urgent job and changed back to the original job in the time it used to take to just tear down and setup. The pallet system has rescued the shop when a machine went down due to mechanical failure; a job was moved to another machine and zero was still zeroed with the Zero Point system.

The system also makes inspection easy. Both part and fixture can be moved to a CMM for an accurate measurement using the same pallet system. If additional modifications are needed the part can be returned to the machine and zero is still zero; no time lost re-indicating the part.

The Schunk Zero Point pallet system has helped Machine Specialties reduce its machine idle time, improve part throughput from operation-to-operation and machine-to-machine, as well as provide greater flexibility with machine job allocation, all accomplished without sacrificing accuracy, repeatability, and rigidity. Schunk, Inc.

Visit www.rsleads.com/804mn-203 for more information

What do you think?
Will the information in this article increase efficiency or save time, money, or effort? Let us know by e-mail from our website at www.ModernApplicationsNews.com or e-mail the editor at pnofel@nelsonpub.com.