Workholding: A Vital Piece of the Part Production Puzzle

“Machining a slab of steel or aluminum is easy. Workholding with standard or custom fixtures doesn’t seem like a complicated aspect of the production process.”

It’s this kind of mentality that starts manufacturers down the path of failed parts and wasted capital.

Workholding should ultimately reduce the costs inherent to part production and the requirements for skilled labor, while increasing conformity across a production run.

“I can have the best machine in the world, but if my workholding is not capable, I’m never going to have the part that I want at the end of the day,” said Wade Anderson, product specialist sales manager at Okuma. “We see a lot of customers who spend a lot of investment money into new capital equipment, but then they want to use their 1983 technology for workholding.”

Manufacturers can avoid making this mistake by taking a more thoughtful and deliberate approach to workholding.

Workholding with Fixtures

Workholding solutions can be categorized under jigs and fixtures. These terms are commonly and incorrectly used interchangeably.

The difference between the two lies in their physical relation to the cutting tool. As a jig holds and guides a cutting tool, a fixture holds the workpiece in place. Workholding is all about fixturing.

As fixtures are commonly used in applications requiring greater precision of the tool in relation to a workpiece, fixtures are commonly identified by the machine tools they are used with.

Common types of fixtures include:

• Milling fixtures
• Lathe fixtures
• Sawing fixtures
• Grinding fixtures
• Vises
• Clamps

 “The diversity of options that are available for workholding drive how to machine a part,” said Tim Krafton, sales engineer at Mitee-Bite Products. “The clamping can dictate the amount of operations required to machine a part, which in turn is directly connected to the machine type (VMC, HMC) it should be worked on to minimize the number of operations.”

With the right workholding solutions, manufacturers can utilize “high density workholding” to hold as many parts as possible on a single fixture.

“With high density workholding, a machine can run unattended for a long time,” said David Bishop, general manager at Mitee-Bite. “For this to be successful, a pallet changer must be used as well as another identical plate or a plate for the second operation if required. When the machine is running, the operator will unload and load a pallet, deburr or inspect parts and once the machine stops, they will remove the pallet and replace with a freshly loaded one and hit the go button.”

High density workholding can help reduce labor costs, reduce necessary tool changes and idle spindle time, as well as complete jobs faster.

INOVA’s Tale in High Density Workholding

In 2011, INOVA Geophysical Equipment began selling the G3i, a cable-based recording system for oil and gas exploration and for production companies and seismic contractors who are prospecting for reserves. INOVA managed to re-shore part production from China at a lower cost, along with achieving other benefits by working closely with their machining workholding partners.

Tom Mueller, a machining consultant for Tungaloy Canada Inc., was a machine shop supervisor for INOVA back when they decided to increase production for their G3i to meet increasing demand.

Mueller and his team intended to accomplish this without having to purchase a new machine.

“The 3½"×2½"×2½" (88.9mm × 63.5mm × 63.5mm) connector plates are made on two Haas VF3 vertical machining centers, each equipped with a two-pallet changer,” Mueller explained. “In our previous production process, each pallet used two double vises, each of which can hold two parts. The vises consumed too much room on a pallet, so we could only make four parts per pallet.

A single connector plate took 12 minutes to machine, running two 10-hour shifts over four days a week. Two operators were required to run both VMCs.

“With both running, we could produce 800 connector plates per week, but we needed at least 1,500 per week to keep up with demand,” Mueller added.

After delivery issues with their Chinese vendor, Mueller and his team began looking to make all of their connector plates in-house without increasing costs or adding machining capacity.

“We determined that better fixturing might accomplish this goal,” Mueller said. “We knew we had to get as many parts on a 3'×28" (0.9m × 711.2mm) pallet as possible. The more parts we could machine per tool change, the better.”

Mueller and INOVA’s director of technical services, Randy Cameron discovered if they could stagger parts by having one slightly higher and one slightly lower in each row, they could get 60 parts per pallet in four rows.

A GibbsCAM TMS (tombstone management system, paired with a Tung-Alu-Mill insert cutter made the job possible, but how to hold the parts reliably became a problem. INOVA turned to Mitee-Bite, a workholding solutions provider.

Efficient Workholding Solutions Helped Save Nearly $1 million

“We used two rows of Mitee-Bite locating rails on the bottom row of parts and a row of Mitee-Bite Uniforce clamps in the middle to securely hold two 2.5”x1.5”x36” (63.5mm x 38.1mm x 914.4mm) aluminum bars for roughing,” Mueller explained.

For the first operation, 15 parts were machined on each bar and separated during final machining. Each side of the pallet contained two bars, allowing for 60 machined parts on a single pallet.

“In the second operation, we used 30 Mitee-Bite ID Xpansion clamps,” Mueller continued. “Machining the clamps to exactly match multiple bore diameters greatly increased the clamping surface.”

Meuller and his team only had to remove the bars used in the first operation, flip them, and slide them onto the ID Xpansion clamps for machining on the back parts.

“When the connector plates were in place, the operator tightened a half inch bolt on the ID clamps for each part with a set torque wrench,” Mueller said. “Finishing machining of the bar in operation two separated the parts from each other and they were ready to be unbolted and readied for the molding department.”

INOVA’s old setup had a cost of USD$19.29 per connector plate. The new setup reduced that cost down to only $4.96 (around 75 percent savings) and thanks to new lights-out machining capabilities, 450 parts could be made daily.

“By eliminating outsourcing, reducing machining time per unit and using the Mitee-Bite workholding, we saved $971,400 on the machining of 80,000 connector plates per year,” Mueller said. “My personal target was to make the connector plates cheaper than our Chinese supplier; the total cost of our part, including material, is $7.31, which is 70 cents cheaper than the parts purchased in China.”

Workholding with Automation and Advanced Manufacturing Technology

As automation becomes an increasingly popular, workholding has become capable of pairing up with sensor technology to achieve faster production times.

“Hydraulics and pneumatics can automatically actuate and feed parts in a fixture. Pressure sensors can tell you if the part is seeded in the fixture correctly. Sensors can even tell you if the part has accidently come out of the workholding,” said Anderson.

“More and more technology is becoming part of the fixture while also relying on integration with the machine tool, so you can then act on the signals and start the next part of the job.”

With their Partners in THINC, Anderson and his team at Okuma have been teaming up with partners across the US to advance the technology of workholding with other manufacturing technologies used today.

Anderson and his team employed workholding solutions with Okuma’s CNC machines, alongside robots mounted to rail systems to aid the production process in one application.

“We had two Multus machines and a MB-66V that were all tied together with a robot mounted to a rail system,” Anderson explained. “The Multus machines are tied to, what I refer to as an FMS system for workholding. FMS is like a giant racking system where you pre-stage all of your work going into the horizontals and the FMS is your automation cell that’s feeding into the machine.

“Instead of the racking system transporting pallets into a machine, they were transporting chucks into the Multus machine,” Anderson continued.

The chucks are then fed to the robot who changes the chucks in a quick-change chuck unit and from one part to the next, changes the entire workholding out. A double-action cylinder was required to support the chuck and the quick-exchange chuck top-in piece.

The solution was a collaboration between Okuma and partners including, Schunk, Gosiger and Kitagawa.

“What else we’ve done at Partners in THINC is take one Multus machine and tied in a smaller cell together with a drawer system that holds six chucks,” Anderson said. “It shows your small job shop for example, a lower entry point into the market with this automation, that is also scalable. If you wanted more than a system that has six chucks and a drawer cell, that could be scaled to 30 chucks and a racking system – the concept is the same.”

Custom vs. Standard Workholding Solutions

Manufacturers looking for the best workholding for their application will undoubtedly ask themselves, “Should I look for a custom solution, or go with standard parts?”

The answer has entirely to do with volume and part complexity.

Let’s assume that Manufacturer A is looking to prototype a part for a low volume run, while Manufacturer B is looking to produce a high volume of parts.

Manufacturer A will not find it economically feasible to invest the time and capital in a custom workholding solution for a low volume run. Vises, clamps and other common fixtures should be sufficient for prototyping.

Manufacturer A would only require a custom workholding solution if the part to be developed were to be particularly complex and this is not commonly the case.

Manufacturer B however, would require a custom workholding solution for his high volume run if he wanted to meet the deadlines for production. Manufacturer B may even require a series of uniquely designed fixtures to produce his parts.

“In automotive, they die-cast aluminum parts and every part is a different shape,” said Lee Johnston, applications engineer at Okuma. “You’re going to have different fixtures designed for each individual part, because you’re going to have to hold it in specific places to be able to machine it.”

Manufacturers can research existing part and workholding designs to help determine whether it’ll be necessary to seek out custom solutions.

Manufacturers can also experiment using CAD/CAM software. In a digital 3D space, parts can be measured and tested in a theoretical framework before any real-world resources can be put to the machine.

“At the end of the day, the part itself is going to drive how you hold it,” said Johnston. “People fall into the trap of not thinking back from the end result to the beginning of the process. They just throw the material into the house and start making it. To do it efficiently and effectively, you have to start with a finished product and work backward to form a plan about how you’re going to hold it each step of the way.”

Design software can also be used to thoroughly test the tooling design and especially workholding options, influencing every step of the design process and later of course, the production process.

In the end, workholding providers and their sales engineers are the ideal support group. A sales engineer can help a manufacturer generate ideas based upon their own experiences – they may have even solved a problem like yours before.

“We have manufacturer’s representatives and distributor salesmen that can visit customer’s facilities and make recommendations,” said Bishop. “We also have an ‘Ask an Engineer’ button on our website, where customer’s can submit CAD files for recommendations or have a go-to-meeting in SOLIDWORKS, allowing a customer to communicate directly with an engineer as they review clamping solutions on the computer screen.”

If possible, your workholding partner of choice can provide a turnkey solution – a one-stop-shop experience, where a manufacturer can generate everything from the design process to integration with as few partners and as little hassle as possible.

The key is looking for expert advice early.

“If you’re a manufacturer without the experience or know-how in-house on how to develop a certain part, remember that workholding companies know better than anyone what works best for workholding,” Johnston said.

To learn more about the other side of the coin, check out our 101 feature on toolholding, Top Tips for High Productivity Machining.