Existing machining centers get a big boost in their output the more they remain in the cut. Reducing the number of tool changes, cutting vise changeover time, shortening spindle travel within the vise envelope, running at top machine speed -- all contribute to a shopowner's goal of maximum output per machine. In today's difficult economy, improving these processes can mean the difference between profit and loss, winning or losing a contract.
At Precise Products Corp, using a new high-density model vise from Kurt Mfg (HDM6AL manual model) not only improved output on an existing machining center, but also provided a new approach to other jobs requiring productivity improvement and cost reduction.
Employee-owned Precise Products specializes in precision machining for the aerospace, medical, military, and instrumentation industries, for customers such as Rockwell International, Woodward Governor, and Rosemount Aerospace. Employing 65 in a modern, 40,000 sq ft plant, the company provides a full range of precision services including boring, milling, drilling, turning, grinding, deburring, painting, silk screening, metal finishing, assembly, and testing.
HDM6AL the "Go To" Vise When There's Cost Pressure On a Part
The part in question is an aircraft sensor component machined from 410 stainless steel blanks with a series of slots, recessed surfaces, and contoured outer edges. Between 200 and 300 are delivered at 3-4 week intervals. The customary production method was to machine two parts, one at a time, on a Haas VF3 vertical machining center, using a conventional single-station Kurt D60 vise equipped with ductile iron jaws machined to hold two parts. With relatively small lot requirements and the need for individual part inspection, the process worked -- until the customer's delivery requirements increased.
"We looked at a lot of different alternatives, including switching to faster machining centers equipped with double station vises or cluster tower setups," reports Steve Gourley, manufacturing engineer for Precise Products. "We wanted to improve the process using existing equipment, so we focused on the workholding, the workholding setup time, tool change time, and operator attention needed while running the part. We heard about a new vise Kurt introduced for high-density applications called the HDM6AL Model, so we decided to check it out to see what we could get it to do to help us cut costs on this part."
Over the years, Precise Products has improved productivity using a vast array of Kurt workholding products. They use single station Kurt vises in 4, 5, and 6 in. capacities, often in multiple vise setups. They also use Kurt's double station vises in 4 and 6 in. capacities, and Kurt cluster towers with custom jaws for quick-change, high-density setups.
Gourley's first step was to compare the cycle time of the 2-part setup versus a 4-part setup in the HDM6AL vise. "After a little study, I could see potential for substantial cycle time reduction, particularly where one tool would machine all four parts before a tool change was made," Gourley said. "The travel distance part to part is small, so less machining time is lost when the cutting tool travels between parts. Setup time was more than cut in half machining 4 instead of 2 parts. Also, this new vise sets up much faster than the older, standard vises. Overall, we could see more free time for the operator between setups so he could check each finished part and still have time to tend to other nearby machines."
Holding Tight Tolerances On Part Slots, Notches, Contours
The 2-station Kurt HDM6AL easily accommodates 2 or more parts per clamping station. By machining 7075-T6 aluminum jaws to hold the outer contours of 4 parts per setup, Gourley's machine operators in effect created a custom fixture out of the standard vise. The beauty of this setup is that the parts "nest" inside the jaws so when the vise is clamped up, all outer surfaces are held tightly so there's no chance of part misalignment or chatter, even at the highest speeds. When the part run is completed, jaws can be replaced with others for different jobs. The jaws themselves relocate quickly and precisely without special alignment tools.
Precise Products started out with aluminum jaws and eventually plans to go to more permanent ductile iron jaws. The jaws can be machined on 2 sides for handling different-sized parts. The base of this new vise also enhances accuracy. Made of durable 60,000 psi ductile iron, the vise body provides rugged strength, rigidity, and long-term accuracy while absorbing machining vibration.
As for accuracy and speed, the process calls for a series of drilling, tapping, and milling operations with the slots held to .125 in. and the center slot to .050/.0585 in., verified offline with a touch probe. All operations are done at speeds between 4,000-7,500 rpm. The smallest tool used is a 3/32 carbide stub end mill, which turns at about 4,000 rpm.
Cycle time for the old setup was 30 minutes for 2 parts (15 minutes per part) compared to 45 minutes for 4 parts (11.25 minutes per part) with the new setup. The per-part saving is 3.75 minutes cycle time -- equal to a 25% reduction. Add to this setup-time savings over the old method, and the productivity improvement amounts to "a strong 50%," Gourley reports.
Several features of the HDM6AL vise design help expedite Gourley's process for reduced cycle time while maintaining quality. With a 13.75 in. length and 6 in. width, the vise is much more compact than predecessor models, so less spindle travel is required, part to part, to get into and around each part for machining. Clamping power is also important. This vise has clamping force of 5,556 lb with 70 ft lb of input torque, while providing repeatable accuracy to .001 in.
"Moving the vise on and off the machine for these shorter runs is also easier because the vise body weighs just 48 lb," reports Gourley. "Our HDM6AL requires just 2 bolts, versus 8 bolts for earlier vise models. It used to take 5 minutes to align a vise but with this new model, it takes just a minute. It's a cleaner vise to use, also. There's no problem with chips getting into the clamping mechanism because it's enclosed. The vise has a clean design, so it's easy to keep the area in and around the vise clear of chips and coolant with a quick blast with the air hose."
In the future, Gourley sees using HDM6AL vises for other jobs requiring cost reduction, particularly on repeat jobs of small- to medium-sized parts with smaller lot requirements.
"It definitely is the workholding we now look to when we have price pressures on a job. The HD vise gives us an extra measure of flexibility and process creativity with our existing machining centers that we didn't have before," he concludes.
