In a successful operation, the nitrogen cylinders contact the tapping-head timing blocks at the same time that the stripper contacts the metal strip, allowing the strip and tapping head to move in unison. The total contact force for the nitrogen cylinder pushers should measure 2000 lb. for the 3100 tapping head and 3000 lb. for the 6100 tapping head, according to Hutchison, noting the force measurements for two models of HTS heads.
“The two most common questions people ask about in-die tapping are ‘What speeds can I run?’ and ‘How much press stroke do I need?’” Hutchison commented. An HTS in-die-tapping calculator is available on the firm’s website to help stampers determine speeds and press stroke.
What part-design features or other circumstances would negate the feasibility of an in-die operation? “Overwhelmingly, people will design a die from the start with the intent of in-die tapping rather than trying to retrofit,” Hutchison replied. “That’s not saying that an existing operation cannot be converted to in-die, but it’s not as common.”
In-die-tapping application. Chris and Tucker Martin shared their real-world experience with in-die tapping. Riverview Products leaned toward in-die tapping when Chris Martin replaced a customer’s spot-weld-nut operation in its plant with a pierce-nut operation. Then, seeking even more cost savings for his customer, he implemented in-die tapping. “Not only were we able to reduce labor, we got rid of the weld operation,” Chris said, adding, “there’s a learning curve, but it’s achievable.”
Chris said that he places even higher value on the tighter control achievable with in-die tapping than the cost and time savings. “It’s just managing where the parts are in the pipeline … basically production control, not moving the parts around,” he said. “That control is even more important to us than savings.”
The fabricator now produces 10 million parts/yr. using in-die tapping.” It’s been very successful for our operation,” Tucker concluded. “It’s a value add that we’re able to offer.”
In-Die Fastening, Clinching
In-die fastening involves automatically feeding, orienting and inserting fasteners into the part while it’s in the stamping die. This operation fully integrates with progressive or transfer dies. Clinch nuts and studs are installed automatically, precisely and with high repeatability, eliminating secondary operations such as welding.
Not only does the operation save time on material movement, but also ensures accuracy, Hess remarked. “You’re already guiding the strip using pilots and holding it in place. So, we’re able to then install the fasteners using guiding through the whole operation.”
The in-die process reaps time and labor savings. “Not having that secondary operation that comes with traditional fastening methods saves a lot of time,” Hess added.
How it works. Clinch heads are installed into the die stripper during the build process. These heads connect to a feed system using quick-change couplers. The press operator places the clinch fasteners into a hopper in the feed system, and they transport through a conveyor system into the slide-feeder hopper. The slide feeder orients each fastener and moves it to the distribution hub.
As the in-die clinch-head sensors call for more fasteners, an air solenoid fires compressed air into the shot tube, driving the fasteners through the system and into the clinch head. As the press cycles, the in-die clinch head installs the fastener into the part, creating a strong, permanent mechanical joint.
Clinch nuts are pressed into pre-punched holes in sheet metal. During installation, the force of the press causes material to flow into grooves, or undercuts in the nut, creating a strong mechanical bond—no welding or tapping required.
Clinch studs—externally threaded fasteners—are pressed into pre-punched holes in sheet metal. Similar to clinch nuts, the press forces displaced material to flow into the undercuts on the stud base. Unlike clinch nuts, the stud system feeds the fastener sideways through the shot tube and rotates it into the pneumatic fingers in the head. The fingers then advance over an anvil. As the anvil pushes the stud into the part, the fingers expand out of the way to perform an accurate installation.
Hess explained that clinching requires precise pre-pierced hole sizing and uses displaced material flow to create strong mechanical bonds. The process bonds the nuts and studs without heat distortion—a common problem with welding.
In-die-clinching application. Many stampings go into torque converters for combustion engine—those manufactured by Schaeffler Transmission Systems, for example. The manufacturer ships thousands of torque converters per day from its plant in Wooster, OH.
The company began implementing in-die clinching as part of its value-added customer interface, relayed David Stoll, tool design group leader for Schaeffler. In addition, it sought to remove bottlenecks. “Originally, we had secondary operations on the lines … always a bottleneck,” he offered. “We had operator variables, nut variables, all these different variables that we had to deal with down the line.”
The in-die process removed those bottlenecks, but its implementation was not without hiccups. Challenges originated in proper alignment of nuts in the feeder. Hess worked with Schaeffler to resolve that problem, as well as to ensure that the system developed adequate force to prevent the nuts from falling out.
The installation ultimately proved successful. “One of our lines has six clinch heads,” Stoll stated. “Every time the press cycles, it’s installing six fasteners.” Overall, the in-die clinch system has greatly increased the application’s speed. “Generally speaking, the stroke/min. has increased significantly over our older systems,” he added.
In-Die Vision Systems
Jenoptik’s Ekkehard Fluck highlighted the role of in-die vision systems in maintaining quality control at high production speeds.
“As more functions occur in the die, more technology is condensed in the die,” Fluck said. “Thus, it is very important to monitor the parts and check if the data is correct, especially when the operation speeds up and produces a high volume of parts.”
Jenoptik’s Otto Vision optical measuring and inspection system, integrated into the die, performs 100% part inspection, minimizing or in some cases eliminating the need for manual checks or external comparators.
How it works. In-die visual inspection uses camera technology to inspect parts in progressive dies, performing 100% part inspection at speeds to 2000 strokes/min. Inspection and sorting do not require a press stop or slow down; substandard parts are removed and sorted away from the good parts. Vision inspection of spot welds and surfaces also can be performed in-die.
“We want to set people free of the bondage of waiting for data results,” Fluck remarked.
Performing inspection before a part leaves the die results in significant time and cost reduction compared to inspection post-press-exit. “Otherwise, somebody’s always going with their parts back and forth to some kind of a comparator, then back to the press to make some adjustment,” Fluck said. “This led to the development of a totally new system. The goal: Have the press run all of the time and improve quality without stopping the process.”
“Also, we developed a solution to analyze every part on the strip, sort out the bad parts, laser cut to remove a defective section of strip while the press runs, and laser weld the strip back together,” Fluck said.
Fluck noted that while lubricants and reflective surfaces can pose challenges with vision inspection, advanced camera configurations and controlled lighting mitigate them.
In-die-visual-inspection applications. Bruderer’s Alois Rupp provided two applications for Jenoptik technology: inspection of automotive self-lubricating bearings in which the in-die vision system verified a coating’s integrity; and another involving a razor-blade manufacturer.
“Self-lubricating bearings are used in transmission lines, steering columns and other areas within the automobile,” Rupp reported before detailing the following application. “There are four modules in this particular die configuration. The first module is for stamping and forming. The next module for in-die dimensional inspection of the components; the third for surface inspection of the lubrication coating; and the fourth and final module basically is part clip-out-and-down stack. This application runs at about 400 strokes/min.
“The customer’s major challenge that prompted the need for the in-die vision system was that it had very little control over the coating process, with some areas on the strip missing the coating, or in some cases too much coating that caused trouble down the line,” Rupp relayed. “And, as Ekkehard showed previously, we were able to separate the bad parts from good parts so that the customer had only good parts. The customer’s big benefit from the in-die vision system was shipment only of parts with the absolute proper coating.”
In the razor-blade-manufacturing application, the in-die vision system inspected for dimensional accuracy and weld quality across 16 points. “This application is far more complex,” Rupp explained. “Our customer had a progressive die with six modules for stamping and forming, and an in-die cleaning module. The customer had an outside component supply that’s getting married to the stamped and formed strip. After that, a laser-welding system would weld the components together at 16 points, followed by a breakoff station and then the final inspection system. This tool ran at 500 strokes/min.
“The inspection system not only was checking the parts for dimensional accuracy but also verifying the integrity of the 16 welding points,” Rupp said. Visual inspection was the final step before the parts exited and went to the assembly machine, which guaranteed 100% good parts flowing downstream. “We’re using vision systems on the front end, in the die and at the back end—on the edge strip coming in to make sure it is properly orientated before it enters the press, checking the channel being stamped in the press, and then again in a final inspection post-cleaning to ensure perfect parts before they’re final-packaged for assembly,” he explained.
Rupp stated that the inspection works even at very high speeds. “We’re not limited by speed,” he said. “Normally, the dies or other production factors limit the speed, but not the vision system.” MF
Industry-Related Terms: Checks,
Die,
Edge,
Forming,
LASER,
Lines,
Run,
Stripper,
Stroke,
Surface,
Tapping,
Torque,
Transfer,
Forming,
Assembly,
Forming,
Stamping,
WeldingView Glossary of Metalforming Terms
See also: Bruderer Machinery, Inc., Hutchison Tool Sales Co., Jenoptik Automotive North America LLC
Technologies: In-Die Operations, Quality Control, Stamping Presses
In our recent MetalForming Live: In-Die Technologies That Eliminate Downstream Operations online session on June 24, Tom Hutchison, president, Hutchison Tool Sales (HTS); Ryan Hess, co-owner, Hess Industries; and Ekkehard Fluck, head of sales, optical inspection stamping, Jenoptik Optical Systems GmbH, described and demonstrated how their in-die-tapping, in-die-clinching and in-die-vision-inspection systems work, respectively. 
