ARROW® Workholding Fixtures Cut Down on Cutting Time by 30%

Engineers from All World paired a custom heavyweight workholding fixture with a horizontal machining center to boost productivity. The 880-pound manual fixture saves time by reducing the number of operator interventions in the machining process, cutting two parts at a time, and enabling loading as part of the machine cycle.

“The fixture is much more productive than the previous method, not only because there are fewer steps, but also because the part is held much more rigidly. The machine can cut more aggressively,” said Steve Hagedorn, Project Manager at the time of the project and Sales Engineer at All World Machinery Supply.

A Need for Continuous Operation

A Chicago-based precision medical manufacturer sought assistance in manufacturing aluminum brackets used in a state-of-the-art surgical system in June of 2023. The projected annual volume was not going to be achievable using the current approach, so they reached out to All World.

Because the robotic surgical system uses a minimally invasive surgical approach, a secure monitor is a critical component of the system.

During the original machining process, it was necessary for the operator to interrupt the cycle for the manual addition and removal of various clamps, a procedure integral to that stage of production. This task demanded a repetitive sequence of four clamping and unclamping actions to produce a single finished component. Furthermore, the machinery was designed to accommodate only one part at a time, and the load/unload time was interrupting the machining cycle, resulting in reduced production.

“The moving of the clamps was cumbersome and prone to scrap,” Hagedorn added.

Overcoming Challenges

All World’s team of engineers promptly responded by devising a robust workholding fixture to firmly secure the brackets during the production process. They proposed the use of a horizontal machining center for this task, highlighting its advantage of continual operation even during loading and unloading phases. This approach would prevent the downtime typically experienced with the vertical machining center in the existing workflow. The customer also needed more flexibility and asked to integrate the fixture into a pallet pool which also gave them the option to run this part or other parts on the same machine.

During the design process, the part presented distinct complexities due to its length exceeding the machine's travel capacity. To address this, engineers implemented a two-stage cutting operation to create the features and ensure precise alignment. Accurate placement of the part in the second operation was imperative to maintain the specified tolerances for these features.

“We used spring loaded tapered pins to center up on the holes that we are drilling in the first operation. If we had used simpler and cheaper fixed pins, they wouldn’t have worked. We would never have been able to hold the finished part tolerances required,” Hagedorn said.

This project was also complicated when the end user—not the customer—redesigned the part in the middle of the process. This change necessitated the engineering team to juggle manufacturing two versions of the part, each with unique datum structures, using the same fixture. Despite these changes, it remained imperative that production for both the original and newly enhanced versions of the part continue uninterrupted.

“By closely collaborating with the customer and the end user, we were able to come up with a common locating scheme for both parts that improved the control of the machine features relative to the casting. It also helped improve the rigidity of the operation 10 clamp,” Hagedorn said. “This is why we maintain constant customer communication. It results in the right solution from the onset.”

Engineering Efficiency

The team designed a two-step process fixture to machine four parts—that holds two parts in operation (op) 10 and two parts in op 20. In op 10, the operator clamps the part against cast surfaces and cuts the part on three different sides. The operation includes five clamps and three work supports. The part is then transferred to op 20 where it gets located and clamped on machined surfaces to be cut from two sides. Op 20 includes 11 clamps and one work support. Because it was a large part and complicated to load, Arrow provided a detailed Powerpoint presentation to show the operators exactly how to properly clamp and unclamp the part.

Outstanding Outcomes

One significant benefit is the enhanced dimensional accuracy of the parts produced. With fewer operations required, the risk of tolerance stack-ups is minimized, leading to more consistent sizing and positioning of features from one part to the next. The increased rigidity of fixtures ensures that parts experience less movement during machining, further contributing to uniformity. Additionally, the reduced tool reach allows for the use of shorter, more rigid tools, enhancing precision even further.

The decision to outsource the fixtures paid for itself within the first year, thanks to the massive reductions in machine costs, labor, cutting tools, and materials. In addition to the overall process efficiency gains, the rigidity of the setup allowed an increase in cutting speeds that saved about 30% in cut time, and a similar increase in tool life as well. Production demands can now be met with a single horizontal machining center, eliminating the need for four vertical machining centers, each with its own fixtures.