Sensors Bring More Than Just Die Protection

The best and most effective to implement a die-protection program revolves around a groundswell of support from all quarters of a metalforming shop to get the job done, coupled to the enthusiasm of a champion —an individual who mentors, drives and unwaveringly pioneers the program. Such is the case at Manufacturers Industrial Group (MIG), LLC, Athens, TN, a manufacturer of manual seat adjusters, welded assemblies, metal stampings, and fineblanked and wire-formed parts. Here we find sensor application specialist Carlos Tilley, a tool and die maker since 1990. Tilley brings to his position critical experiences with tool design, CNC and wire-EDM programming and operation. Over the years, his leadership skills have been honed as a shift leader and apprentice mentor.

Sensor application specialist Carlos Tilley feels right at home at his test bench, where he proves out all die-protection setups before bringing them onto the shop floor.

To best tap into Tilley’s varied experience, in August 2012 MIG promoted him to tool engineer, and in December 2012 he was tasked with launching, developing and managing the firm’s die-protection program.

Laying Out the Goals

Tilley has a healthy and positive outlook on his position and the goals of the die-protection program.

“All die protection must be proved out in the lab before it’s brought onto the shop floor,” he says. “Our goal is to reduce the amount of die crashes, increase press efficiency and reduce PPMs.”

MIG’s upper management advocates for Tilley’s sensor program, including general manager Robert Harrington and COO John Zardis. Says Zardis:

Fig. 1—This plunger mechanism uses two proximity sensors embedded in a block of steel to detect strip over- and underfeed.

“MIG intends to use die protection to create a competitive advantage, by allowing us to lower overhead costs associated with sorting, die repair and customer rejections, and by increasing press run rates. We also intend to use this technology to enhance our ability to perform more operations under the ram, such as projection welding and tapping, to further distinguish ourselves in the marketplace.”

As the saying goes, the proof is in the pudding, and the photographs illustrating this article illustrate MIG’s fusion of sensor development, implementation and utilization.

As I have described in earlier writings in this magazine, the type of pilots being used in the die determines the tolerance on such a feed. The pilots are meant to navigate (or fine-tune) the final position of the strip before the die fully closes, to perform the various forming, piercing, slitting and other operations. It is crucial that the feed meet the ability of the pilots to do so. So, for example, the feed length can be 10 in.—but plus or minus what? This tolerance can range from a few thousandths of an inch to 50 or more thousandths. Thus, the pitch and its tolerance should be clearly marked on the side of every die.

Fig. 2—Stripper sensors (one shown here) in each corner of a die will detect a poorly closed stripper, indicating foreign material laying on top of the strip or embedded in the stripper.

The first such image showcases Tilley’s approach to strip feed (Fig. 1). Within a robust block, he has located two inductive proximity sensors to monitor plunger motion. As the strip arrives at its final position, the plunger is pushed into position against a spring. The two sensors check to ensure that two carefully machined notches are in their respective proper locations, indicating a good feed.

Many stamping shops over- or underfeed strips on a regular basis on some of their tools, not realizing that such errors can easily lead to quality issues as holes are pierced incorrectly, forms are shaped poorly, etc. Scrap or slugs deposited on top of the strip or becoming embedded on the surface of a stripper can cause a phenomenal amount of die damage and quality issues. As the scrap or slug travels with the strip, punches can be sheared, features on the part altered and cosmetic issues developed that may not be caught until the part arrives at the customer’s facility. Likewise, a piece of scrap or a slug attached to the stripper can emboss patterns on parts that functionally or cosmetically become rejects with the customer.