Fill up with high-density workholding

Metalworking professionals understand the importance of keeping machine tool spindles rotating as much as possible and overcoming labor shortages by enabling operators to run more than one machine or perform other duties while continuing to create chips. One way to achieve these goals is with high-density workholding, which calls for as many workpieces as reasonably possible to be placed in a machine work envelope, said David Bishop, general manager of Mitee-Bite Products LLC in Center Ossipee, New Hampshire.

“Compared to single part loading, it virtually removes the labor cost and reduces the cost per piece when factoring tool changes, etc.,” he said about high-density workholding and how one cutting tool can go rapidly from part to part rather than changing tools constantly. “I like to say it levels the playing field globally.”

An example of high-density workholding using a multiple-sided tombstone for a horizontal machining center in which labor cost is removed. Image courtesy of Mitee-Bite Products

Depending on the application, Mitee-Bite produces a variety of products to enable high-density workholding, such as the Uniforce clamp with a steel wedge that spreads the clamping force uniformly on both sides of the aluminum channel, and the low-profile, modular Pitbull clamps that exert a positive down force.

“The majority of our items can be used for high-density applications,” Bishop added, noting that the company’s engineers help determine how many parts can be held under or in front of the spindle and the options available to do so. “I hate being sold anything, so none of our guys sell. We provide options and let the customer make the decision.”

Many applications have straight-forward solutions, but Bishop said he prefers tackling ones that are more challenging. “It’s the main reason we have so many styles of fixturing clamps. It’s limited only by your imagination and creativity.”

Pack Them In

Advanced Machine & Engineering Co. is another source for devices that enable end users to take full advantage of a machine’s work envelope. “We can maximize that envelope based on the machine size and capacity,” said Kaleb Mertz, business development leader for the Rockford, Illinois-based company.

AME supplies Mitee-Bite products, but is “brand agnostic,” according to Mertz, and also offers workholders from Schunk, Triag International, 5th Axis and trunnion tables from Martin Manufacturing. “The benefit that we have is we’re very well known for our tombstones and grid plates.”

In addition to workholders, AME offers an array of machining products and performs contract manufacturing services.

One example of high-density workholding integrates Mitee-Bite Uniforce clamps onto an octagon tombstone, Mertz explained.

“It’s all about runtime,” added Nick Rupprecht, engineering manager at AME. “The more parts you can stack on the eight faces, the better the time in which the fixture is going to be staying in the machine.”

He noted that scenario is especially advantageous when a minimal number of machined features are required, such as drilling a hole in a part’s face and side. “Imagine if you had to change out that part every time it was completed.”

High-density workholding is essential to effectively satisfy high-production demands, according to Mertz. “If you’re a shop that runs three shifts and weekends, then you’re going to get a lot less out of loading one part at a time versus having a high-density fixture where you have a lot less door-open-and-close time.”

Mitee-Bite says its Pitbull clamps have an extremely low bite and exert a positive down force. In this example, each clamp produces 3,600 lbs. of pressure. Image courtesy of Mitee-Bite Products

High-density workholding is suitable even for job shops that typically see a high mix of parts, Mertz said. For that scenario, one approach is to incorporate modular workholders into a high-density design. For example, AME offers Amrok fixture plates with the
rail-based powerCLAMP 3D-modular workholding system from Triag and AME precision locating screws. Different types of mounting modules can be located anywhere on the rails, and the variety can include three-jaw chucks, collet chucks, miniature self-centering vises, magnetic clamps and vacuum clamps.

“You have a quick changeover and still have that density,” he said, conceding that programming considerations might limit how varied the part mix is.

Removing Idle Time

A pallet changer is not mandatory to enable high-density workholding, but it is if the goal is to maximize machine capability and eliminate as much idle spindle time as possible, Mitee-Bite’s Bishop said. “I’d rather see an operator waiting on a machine than a machine waiting on an operator.”

He noted that one manufacturer of electrical connectors was able to move production from China to the U.S. after experiencing quality and shipping delay issues by outfitting two Haas machines with Mitee-Bite automatic pallet changers set up with a carrier method. Uniforce clamps were also part of the arrangement. “They came out with finished parts, and they made them 70 cents cheaper than China — and they saved a million dollars a year.”

In addition to reducing the cost per part, an automatic pallet changer enables a part manufacturer to perform lights-out, or unattended, machining, Bishop said. “You could even load up two pallets before you go home, and you come in and it’s just finishing up. “So, you just got another day out of it, and you weren’t even there.”

Running unattended is especially beneficial on horizontal machining centers with pallet pool systems, he added. “Those are designed to run lights out and that’s really where we shine, because as expensive as those are the owner wants to make sure they’re getting the most efficiency or productivity out of that.”